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Title: Discoveries and Inventions of the Nineteenth Century

Author: Robert Routledge

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PLATE I.

THE GREAT WHEEL IN ACTION.

DISCOVERIES AND INVENTIONS
OF THE
NINETEENTH CENTURY
Who saw what ferns and palms were pressed
Under the tumbling mountain’s breast,
In the safe herbal of the coal?
But when the quarried means were piled,
All is waste and worthless, till
Arrives the wise selecting Will,
And, out of slime and chaos, Wit
Draws the threads of fair and fit.
Then temples rose, and towns, and marts,
The shop of toil, the hall of arts;
Then flew the sail across the seas
To feed the North from tropic trees;
The storm-wind wove, the torrent span,
Where they were bid the rivers ran;
New slaves fulfilled the poet’s dream,
Galvanic wire, strong-shouldered steam.
Emerson.

DISCOVERIES AND INVENTIONS
OF THE
NINETEENTH CENTURY

BY
ROBERT ROUTLEDGE, B.Sc.,
SOMETIME ASSISTANT EXAMINER IN CHEMISTRY AND IN NATURAL PHILOSOPHY TO THE UNIVERSITY OF LONDON
THIRTEENTH EDITION
Revised and Partly Re-written, with Additions
CONTAINING FOUR HUNDRED AND FIFTY-SIX ILLUSTRATIONS
LONDON
GEORGE ROUTLEDGE AND SONS, Limited
BROADWAY, LUDGATE HILL
1900
v

PREFACE.

In the following pages an attempt has been made to present a popular account of remarkable discoveries and inventions which distinguish the XIXth century. They distinguish it not merely in comparison with any previous century, but in comparison with all the centuries that have preceded, in regard to far-reaching intellectual acquisitions, and to material achievements, which together have profoundly affected our ways of thinking and our habits of life. In the latter, the enormously increased facilities of locomotion and international communication due to railways and steam navigation have wrought the greatest changes. These inventions depending primarily upon that of the steam engine, this first claims our notice, although properly assignable to a period preceding our era by a few years. Again, much of our material advancement is connected with improvements in the manufacture of iron and its applications in the form of steel, which have been especially the work of the last half of the century. So great has been the progress in this department, that for the present edition it has been found necessary to re-write altogether the article devoted to it. Our social conditions have also been greatly modified by the celerity of verbal intercourse afforded by the telegraph and the telephone, and these inventions have received appropriate notice in this work. In every branch of science also we have reason to be proud of the discoveries our era can claim, for they vastly excel in number and are not inferior in range to those of all the ages taken together. From so large a field, selection was of course necessary; and the instances selected have been those which appeared to some extent typical, or those which seemed to have the most direct bearing on the general advance of our time. The topics comprise chiefly those great applications of mechanical engineering and arts, and of physical and chemical science, in which every intelligent person feels concerned; while some articles are devoted to certain purely scientific discoveries that have excited general interest.

The author has aimed at giving a concise but clear description of the several subjects; and that without assuming on the part of the reader any knowledge not usually possessed by young persons of either sex who have received an ordinary education. The design has been to treat the visubjects as familiarly as might be consistent with a desire to impart real information; while the popular character of the book has not been considered a reason for regarding accuracy as unnecessary. On the contrary, pains have been taken to consult the best authorities; and it is only because the sources of information to which the author is under obligation are so many, that he cannot acknowledge them in detail.

The present edition has been revised throughout, and such changes have been made as were required to bring the matter into accordance with the progress that has taken place since this book was first published in 1876. But details given in the former editions have at the same time been retained where they served to indicate the successive stages of improvement. It would, for example, be impossible in a section on steam navigation, to omit some notice of the Great Eastern, and therefore the drawings and the account of the construction of that remarkable ship that appeared in the first edition, have been left with but slight alterations in the present volume, although the vessel has since been broken up. On the other hand, two sections are devoted to projects which the XIXth century has not seen realised; but the XXth century will in all probability shortly witness the completion of one or other of the great canal schemes; and if the first submarine tunnel is destined not to be one connecting England with the Continent, it will be one uniting Great Britain with her sister isle.

1899.


viiFor permission to make use of illustrations in this volume the author’s and publishers’ thanks are due to the several proprietors of The Graphic (for Plates I., XI., and XII.)—of The Engineer (for sketch design of the Great Wheel, map and views of the Tower Bridge)—of The Scientific American (map of North Sea Canal); also to Mr. Walter B. Basset (for Plate V.)—to “The Cassier Magazine Company” (for Edison’s Kinetographic Theatre and the Hotchkiss Gun)—to “The Century Company” (for portrait of M. Tesla, from a photograph by Sarony)—to “The Incandescent Gas Light Company” (for cuts of burners, etc.)—to The Engineering Magazine, and The Engineering News, both of New York—to the Remington Company—to Mr. W. W. Greener, of Birmingham (for cuts of rifles, etc., from his comprehensive book on “The Gun”)—to The Photogram, Limited—to the Proprietors of Nature—to the Linotype Company—and to Captains Hadcock and Lloyd (for illustrations of modern artillery from their great work on the subject).

ix

CONTENTS.

  PAGE
 
Introduction 1
 
Steam Engines 3
  THE LOCOMOTIVE 14
  PORTABLE ENGINES 24
  THE STEAM HAMMER 25
 
Iron 29
  IRON IN ARCHITECTURE 72
  BIG WHEELS 81
 
Tools 85
  THE BLANCHARD LATHE 96
  SAWING MACHINES 98
 
Railways 101
  THE METROPOLITAN RAILWAYS 114
  THE PACIFIC RAILWAY 116
  INCLINED RAILWAYS 125
 
Steam Navigation 129
  RIVER AND LAKE STEAMBOATS OF AMERICA 144
 
Ships of War 149
 
Fire-Arms 169
  THE MILITARY RIFLE 178
  RIFLED CANNON 190
  MACHINE GUNS 218
 
Torpedoes 227
 
Ship Canals 249
  THE SUEZ CANAL 251
  THE MANCHESTER SHIP CANAL 262
  THE NORTH SEA CANAL 271
  THE PANAMA AND NICARAGUA CANAL PROJECTS 272
 
Iron Bridges 276
  GIRDER BRIDGES 280
  SUSPENSION BRIDGES 284
  CANTILEVER BRIDGES 291
  THE TOWER BRIDGE, LONDON 297
  THE GREAT BROOKLYN BRIDGE 303
 
Printing Machines 305
  LETTERPRESS PRINTING 306
  PATTERN PRINTING 321
 
Hydraulic Power 324
 
Pneumatic Dispatch 340
 
Rock Boring 349
  THE MONT CENIS TUNNEL 351
  ROCK-DRILLING MACHINES 355
  THE CHANNEL TUNNEL 364
  THE ST. GOTHARD RAILWAY 371
 
Light 380
  SOME PHENOMENA OF LIGHT 382
x  VELOCITY OF LIGHT 384
  REFLECTION OF LIGHT 388
  REFRACTION 397
  DOUBLE REFRACTION AND POLARISATION 399
  CAUSE OF LIGHT AND COLOUR 408
 
The Spectroscope 416
  CELESTIAL CHEMISTRY AND PHYSICS 436
 
Roentgen’s X Rays 445
 
Sight 452
  THE EYE 454
  VISUAL IMPRESSIONS 468
 
Electricity 481
  ELEMENTARY PHENOMENA OF ELECTRICITY AND MAGNETISM 483
  THEORY OF ELECTRICITY 487
  ELECTRIC INDUCTION 488
  DYNAMICAL ELECTRICITY 490
  INDUCED CURRENTS 502
  MAGNETO-ELECTRICITY 507
  THE GRAMME MAGNETO-ELECTRIC MACHINE 511
  ELECTRIC LIGHTING AND ELECTRIC POWER 519
  THE NEW ELECTRICITY 538
 
The Electric Telegraph 547
  TELEGRAPHIC INSTRUMENTS 553
  TELEGRAPHIC LINES 572
  THE TELEPHONE 581
 
Lighthouses 593
 
Photography 607
  PHOTOGRAPHY IN COLOURS 630
 
Printing Processes 632
  STEREOTYPING 632
  LITHOGRAPHY 636
  OTHER PROCESSES 640
  THE LINOTYPE MACHINE 645
 
Recording Instruments 653
  THE PHONOGRAPH 665
 
Aquaria 675
  THE CRYSTAL PALACE AQUARIUM 677
  THE BRIGHTON AQUARIUM 682
 
Gold and Diamonds 687
  GOLD 687
  DIAMONDS 696
 
New Metals 714
 
India-Rubber and Gutta-Percha 724
  INDIA-RUBBER 724
  GUTTA-PERCHA 728
 
Anæsthetics 731
 
Explosives 740
 
Mineral Combustibles 751
  COAL 751
  PETROLEUM 757
  PARAFFIN 761
 
Coal-Gas 764
 
Coal-Tar Colours 781
 
The Greatest Discovery of the Age 801
 
Notes 811
 
Index 813
xi

LIST OF ILLUSTRATIONS.

FIG.   PAGE
 
  Heading—Rain, Steam, and Speed (after Turner) 1
 
1. Portrait of James Watt 3
 
2. Newcomen’s Steam Engine 4
 
3. Watt’s Double-action Steam Engine 5
 
4. Governor and Throttle-Valve 6
 
4a. Watt’s Parallel Motion 8
 
5. Slide Valve 9
 
6. Section of Gifford’s Injector 11
 
7. Bourdon’s Pressure Gauge 12
 
8. Steam Generator 13
 
9. Section of Locomotive 15
 
10. Stephenson’s Link Motion 17
 
10a. G. N. R. Express Passenger Locomotive 19
 
10b. Joy’s Valve Gear 20
 
11. Locomotive after Explosion 22
 
12. Hancock’s Steam Omnibus 22
 
13. Nasmyth’s Steam Hammer 27
 
14. Merryweather’s Steam Fire-Engine 28
 
15. A Foundry 29
 
16. Aerolite in the British Museum 31
 
17. Blast Furnace 41
 
18. Section and Plan of Blast Furnace (obsolete type) 42
 
19. Section of a Reverberatory Furnace 45
 
20. Fibrous Fracture of Wrought Iron 47
 
21. Cup and Cone 49
 
22. Section of Blast Furnace 51
 
23. Experiments at Baxter House 58
 
24. Bessemer Converter 63
 
25. Model of Bessemer Steel Apparatus 65
 
26. Section of Regenerative Stoves and Open Hearth 68
 
26a. Rolling Mill 71
 
26b. The Eiffel Tower in course of construction 73
 
26c. The Eiffel Tower 75
 
26d. St. Paul Building, N. Y. 77
 
26e. Manhattan Insurance Co.’s Building in course of erection 79
 
26f. Manhattan Insurance Co.’s Building nearly completed 80
 
26g. Original Design for the Great Wheel 82
 
27. Portrait of Sir Joseph Whitworth 85
 
28. Whitworth’s Screw Dies and Tap 86
 
29. Screw-cutting Lathe 87
 
30. Whitworth’s Measuring Machine 89
 
31. Whitworth’s Drilling Machine 91
 
32. Whitworth’s Planing Machine 93
 
33. Pair of Whitworth’s Planes or Surface Plates 94
 
34. Interior of Engineer’s Workshop 95
 
35. Blanchard Lathe 96
 
36. Vertical Saw 98
 
37. Circular Saw 99
 
38. Pit-Saw 100
 
39. Box Tunnel 101
 
40. Coal-pit, Salop 102
 
41. Sankey Viaduct 103
 
42. Rails and Cramp-gauge 104
 
43. Fish-plate 105
 
44. Section of Rails and Fish-plates 106
 
45. Conical Wheels 107
 
46. Centrifugal Force 107
 
47. Points 108
 
48. Signal Box on North London Railway 109
 
49. Post Office Railway Van 111
 
50. Gower Street Station, Metropolitan Railway 115
 
51. Map of the Route of Pacific Railway 117
 
52. Trestle Bridge 118
 
53. American Canyon 119
 
54. “Cape Horn” 121
 
55. Snow Plough 122
 
56. First Steam Railroad Train in America 123
 
57. Railway Embankment 124
 
57a. Train ascending the Rigi 126
 
57b. At the summit of the Rigi 127
 
58. The Great Eastern at Anchor 129
 
59. Casting Cylinder of a Marine Steam Engine 131
 
60. Screw Propeller 132
 
61. Section of Great Eastern Amidships 134
 
62. The Great Eastern in course of construction 135
 
63. The Great Eastern ready for launching 136
 
64. Comparative sizes of Steamships 137
 
65. The ss. City of Rome 138
 
66. The Castalia in Dover Harbour 140
 
67. The same—End View 141
 
68. Bessemer Steamer 142
 
68a. A Whaleback Steamer, No. 85, built at West Superior, Wisconsin 146
 
69. H.M.S. Devastation in Queenstown Harbour 149
 
70. Section of H.M.S. Hercules 151
 
71. Section of H.M.S. Inconstant 153
 
72. Section, Elevation and Plan of Turret of H.M.S. Captain 154
 
73. H.M.S. Captain 155
 
74. Diagram of H.M.S. Captain 158
 
75. Ditto 159
 
76. H.M.S. Glatton 162
 
77. H.M.S. Thunderer 163
 
78. The König Wilhelm 165
 
xii78a. The Victoria leaving Newcastle-on-Tyne 166
 
78b. Firing at Floating Battery 168
 
79. Krupp’s Works at Essen, Prussia 169
 
80. Trajectory of a Projectile 174
 
81. Diagram for Trajectory of a Projectile 176
 
82. Muzzle-loading Musket and Rifles (obsolete patterns) 179
 
83. The Minié Bullet 181
 
84. Greener’s Expanding Bullet 182
 
85. The Chassepot Rifle—Section of the Breech 183
 
86. Section of the Martini-Henry Lock 185
 
87. The Martini-Henry Rifle 186
 
88. The Mannlicher Magazine Rifle 188
 
89. The Magazine and Breech of the Mannlicher Rifle 189
 
90. 32–pounder, 1807 191
 
91. Whitworth Rifling and Projectile 193
 
92. 600–pounder Muzzle-loading Armstrong Gun 194
 
93. 35–ton Fraser Gun 195
 
94. Section of 9–in. Fraser Gun 196
 
95. Millwall Shield after being battered with Heavy Shot—Front View 200
 
96. Rear View of the Millwall Shield 200
 
97. Comparative Sizes of 35 and 81–ton Guns 201
 
98. Diagram of Velocities and Pressures 205
 
99. Elswick 4·7–in. Q. F. Gun on Pivot Mounting 207
 
100. The Moncrieff Gun raised and ready for firing 209
 
101. Moncrieff Gun lowered for loading 209
 
102. 68–ton Gun on Elswick Hydro-Pneumatic Mounting 211
 
103. Mallet’s Mortar 213
 
104. 32–pounder Krupp Siege Gun, with Breech-piece open 214
 
105. The Citadel of Strasburg after the Prussian Bombardment 215
 
105a. The Shrapnel and Segment Shells 217
 
105b. The Gatling Gun—Rear View 219
 
105c. The Gatling Gun—Front View 221
 
105d. The Montigny Mitrailleur 222
 
105e. A Hotchkiss Gun 224
 
106. Harvey’s Torpedo.—Working the Brakes 227
 
107. Submerged Torpedo 228
 
108. Mode of Firing Torpedo 230
 
109. Explosion of Whitehead’s Torpedo 231
 
110. Effect of the Explosion of Whitehead’s Torpedo 232
 
111. Experiment with a Torpedo charged with 10 lbs. Gun Cotton 233
 
112. Explosion of Torpedo containing 67 lbs. Gun Cotton 234
 
113. Explosion of 432 lbs. Gun Cotton in 37 ft. Water 235
 
114. The same in 27 ft. Water 235
 
115. Section of Priming Case and Exploding Bolt 236
 
116. Harvey’s Torpedo 237
 
117. The same 238
 
118. The same 239
 
119. Official Trial of “Harvey’s Sea Torpedo” 239
 
120. Model of Submarine Guns 240
 
121. The Warner Experiment off Brighton 241
 
122. Portrait of M. Lesseps 249
 
123. The Sand-Glass 253
 
124. A Group of Egyptian Fellahs and their Wives 254
 
125. Dredges and Elevators at Work 255
 
126. Map of the Suez Canal 256
 
127. Port Saïd, the Mediterranean Entrance to the Suez Canal 257
 
128. Bird’s-eye View of Port Saïd 258
 
129. One of the Breakwaters at Port Saïd 259
 
130. Lake Timsah and Ismaïlia 259
 
131. Railway Station at Ismaïlia 260
 
132. The Viceroy of Egypt cutting Embankment 261
 
133. Map of the Manchester Ship Canal, Western Portion 263
 
134. Map of the Manchester Ship Canal, Eastern Portion 263
 
135. A Cutting for the Manchester Ship Canal 265
 
136. Blasting Rocks for the Manchester Ship Canal 266
 
137. Manchester Ship Canal Works, Runcorn 267
 
137a. The French Steam Navvy 268
 
137b. The English Steam Navvy 269
 
137c. Sketch Map of the North Sea Canal 271
 
138. Britannia Bridge, Menai Straits 276
 
139. Diagram showing Strains 278
 
140. Ditto 279
 
141. Girder 279
 
142. Ditto 279
 
143. Ditto 280
 
144. Section of a Tube of the Britannia Bridge 281
 
145. Albert Bridge, Saltash 283
 
146. Clifton Suspension Bridge, near Bristol 285
 
147. Section of Shaft 286
 
147a. Clifton Suspension Bridge, Niagara 288
 
147b. Living Model of the Cantilever Principle 291
 
147c. Principal Dimensions of the Forth Bridge 294
 
147d. Map of the Tower Bridge and its Approaches 299
 
147e. The Tower Bridge 301
 
147f. Sketch 302
 
148. Newspaper Printing-Room 305
 
149. Inking Balls 306
 
150. Inking Roller 306
 
151. Diagram of Single Machine 308
 
152. Diagram of Perfecting Machine 309
 
153. Cowper’s Double Cylinder Machine 309
 
154. Tapes of Cowper’s Machine 310
 
155. Hopkinson and Cope’s Perfecting Machine 311
 
156. Section of Casting Apparatus 314
 
157. Diagram of the Walter Press 315
 
158. Hoe’s Type Revolving Cylinder Machine 317
 
159. Hoe’s “Railway” Machine 319
 
160. Napier’s Platen Machine 320
 
161. Roller for Printing Wall-Papers 322
 
162. Machine for Printing Paper-Hangings 323
 
163. Chain Testing Machine 324
 
164. Pascal’s Principle 325
 
165. Collar of Hydraulic Cylinder 326
 
166. Hydraulic Press 327
 
167. Section of Hydraulic Lift Graving Dock 331
 
168. Section of Column 332
 
169. Sir W. Armstrong’s Hydraulic Crane 335
 
170. Raising Tubes of Britannia Bridge 336
 
171. Press for Raising the Tubes 337
 
xiii172. Head of Link-Bars 338
 
173. Apparatus to Prove Transmission of Pressure 339
 
174. Pneumatic Tubes and Carriages 340
 
175. Diagram of Tubes, &c. 342
 
176. Sending and Receiving Apparatus 343
 
177. Section of Receiving Apparatus 344
 
178. Sommeiller Boring Machines 349
 
179. Transit by Diligence over Mont Cenis 353
 
180. Burleigh Rock Drill on Tripod 356
 
181. The same on Movable Column 358
 
182. The same Mounted on Carriage 359
 
183. Diamond Drill Crown 360
 
184. Diamond Drill Machinery 363
 
185. Chart of the Channel Tunnel 367
 
186. Section of the Channel Tunnel 368
 
187. View of Dover 369
 
187a. Map of the St. Gothard Railway 372
 
187b. The Uppermost Bridge over the Maïenreuss 375
 
187c. The Bridges over the Maïenreuss, near Wasen 377
 
187d. Windings of the Line near Wasen 378
 
188. Contrasts of Light 380
 
189. Rays 382
 
190. Diagram 383
 
191. Telescopic Appearance of Jupiter and Satellites 384
 
192. Diagram 386
 
193, 194, 195. Diagrams 388
 
196. Diagram 389
 
197. Polemoscope 390
 
198. Apparatus for Ghost Illusion 391
 
198a. The Ghost Illusion 393
 
199. Illusion produced by Mirrors 394
 
200. A Stage Illusion 395
 
201. View of Venice—Reflections 396
 
202. Refraction 397
 
203. Diagram 398
 
204, 205. Diagrams of Crystals 400
 
206. Diagram 401
 
207. Diagram 403
 
208. Diagram 404
 
209. Polariscope 406
 
210. Section showing Polarisation 407
 
211. Iceland Spar, showing Double Refraction 407
 
212. Diagram 408
 
213. Diagram 410
 
214. Diagram 412
 
215. Portrait of Professor Kirchhoff 416
 
216. Diagram 417
 
217. Newton’s Experiment 418
 
218. Bunsen’s Burner on Stand 421
 
219. Spectroscope with one Prism 423
 
220. Miniature Spectroscope 426
 
221. The Gassiot Spectroscope 427
 
222. Browning’s Automatic Adjustment of Prisms 429
 
223. Apparatus for Spark Spectra 430
 
224. The Sorby-Browning Micro-Spectroscope 433
 
225. Section of Micro-Spectroscope, with Micrometer 434
 
226. Diagram 435
 
227. Section of Micro-Spectroscope 436
 
228. Solar Eclipse, 1869 439
 
229. The Planet Saturn 441
 
230. Solar Prominences, No. 1 442
 
231. Ditto, No. 2 443
 
232. Section of Amateur Star Spectroscope 444
 
232a. X. Ray Photo of Living Hand, Exposure 4 minutes 446
 
232b. Skiagraph of a Hand by Dr. Roentgen 448
 
232c. Metal objects photographed through Calico and sheet of Aluminium 450
 
232d. Skiagraph of Layers of various substances 451
 
233. Portrait of Professor Helmholtz 452
 
234. Vertical Section of the Eye 454
 
235. Section of Retina 456
 
236. Diagram 457
 
237. Muscles of Eyes 459
 
238. Diagram 461
 
239. Diagram 464
 
240. Diagram 465
 
241. Ruete’s Ophthalmoscope 466
 
242. Diagram 467
 
243. Wheatstone’s Reflecting Stereoscope 469
 
244. Diagram 470
 
245. Diagram 471
 
246. The Telestereoscope 473
 
247. Lines 475
 
248, 249. Diagrams 476
 
250, 251. Diagrams 477
 
251a. Edison’s Kinetographic Theatre 479
 
252. Portrait of Sir W. Thomson 481
 
253. A simple Electroscope 485
 
254. The Gold-leaf Electroscope 489
 
255. The Leyden Jar 490
 
256. A Voltaic Element 491
 
257. Ampère’s Rule 492
 
258. Galvanometer 493
 
259. Daniell’s Cell and Battery 495
 
260. Grove’s Cell and Battery 495
 
261. Wire Ignited by Electricity 496
 
262. Duboscq’s Electric Lantern and Regulator 497
 
263. Decomposition of Water 498
 
264. Electro-plating 499
 
265. A Current producing a Magnet 500
 
266. An Electro-magnet 501
 
267. Ruhmkorff’s Coil 503
 
268. Discharge through Rarefied Air 504
 
268a. Large Induction Coil at the Old Polytechnic Institution, London 505
 
269. Appearance of Spark on Looking-glass 507
 
270. Magneto-electric Spark 508
 
271. A Magnet producing a Current 509
 
272. Clarke’s Magneto-electric Machine 509
 
273. Magneto-electric Light 510
 
274. Diagram 511
 
275. Gramme Machine 512
 
276. Insulated Coils 513
 
277. Hand Gramme Machine 513
 
278. Gramme Machine, with eight Vertical Electro-Magnets 516
 
279. Gramme Machine, with Horizontal Electro-magnets 517
 
280. Gramme Machine 519
 
280a. The Alliance Machine 520
 
280b. Wilde’s Machine 521
 
280c. Siemens’ Dynamo 522
 
280d. The Brush Dynamo 523
 
280e. Siemens’ Regulator 524
 
280f. Jablochkoff Candle 525
 
280g. Electric Lamp 526
 
280h. Incandescent Lamp 529
 
280i. Poles with Single Arms for Suburban Roads.—The Ontario Beach Railway, Rochester, N.Y. 533
 
xiv280j. The Glynde Telepherage Line, on the system of the late Fleeming Jenkin 534
 
280k. Diagrams 540
 
280l. The Tesla Oscillator 542
 
280m. M. Nikola Tesla 543
 
281. Portrait of Professor Morse 547
 
282. Double-Needle Instrument 554
 
283. Electro-magnetic Bells 555
 
284. Portable Single-Needle Instrument 556
 
285. Connections of Telegraph Line 558
 
286. Morse Recording Telegraph 559
 
287. Morse Transmitting Key 561
 
288. Morse Transmitting Plate 562
 
289. Step-by-step Movement 567
 
290. Froment’s Dials 567
 
291. Wheatstone’s Universal Dial Telegraph 568
 
292. Mirror Galvanometer 571
 
293. Telegraph Post and Insulators 573
 
294. Ditto 573
 
295. Wire Circuit 574
 
296. Wire and Earth Circuit 574
 
297. Submarine Cable 575
 
298. Making Wire for Atlantic Cable 577
 
299. Instrument Room at Valentia 578
 
300. Breaking of the Cable 579
 
301. Atlantic Telegraph Cable, 1866 580
 
302. Diagram 580
 
302a. Reiss’s Musical Telephone 584
 
302b. Bell’s Musical Telephone 585
 
302c. Superposition of Currents 587
 
302d. Bell’s Speaking Telephone 588
 
302e. Hughes’s Microphone 591
 
  Lighthouse (heading) 593
 
303. Eddystone Lighthouse 594
 
304. Eddystone in a Storm 595
 
305. Revolving Light Apparatus 601
 
306. Stephenson’s Holophotal Light 604
 
307. Camera 607
 
308. Camera and Slide 615
 
309. Folding Camera 616
 
310. Lenses 617
 
311. Bath 619
 
311a. The Roll-Slide 622
 
312. Portrait of Aloysius Senefelder 632
 
313. Press for Stereotyping by Clay Process 633
 
313a. The Linotype Machine 645
 
313b. A Matrix 646
 
313c. Diagram of Movements 647
 
313d. A Line of Matrices 648
 
313e. A finished Line entering galley 649
 
313f. The Melting Pot and Mould Wheel 650
 
313g. The Finished Line 651
 
313h. Lines assembled into a “Form” 651
 
313i. Matrices dropping into Magazine 652
 
314. Recording Anemometer 653
 
315. Registration of Height of Barometer and Thermometer 655
 
316. Electric Chronograph 657
 
317. Negretti’s Deep-Sea Thermometer 661
 
318. Ditto, General Arrangement 662
 
319. Atmospheric Recording Instrument 663
 
319a. Traces of Vibrations of a Tuning-Fork 667
 
319b. Phonautographic Tracings of Different Vowel Sounds 667
 
319c. Diagram 668
 
319d. Phases of Sound Waves 668
 
319e. Edison’s Original Phonograph 670
 
319f. Diagrammatic Section of Phonograph 671
 
319g. The Graphophone 672
 
319h. Edison’s Perfected Phonograph 674
 
320. Domestic Aquarium 675
 
321. The Opelet 679
 
322. Viviparous Blenny 680
 
323. The Lancelet 681
 
324. Sea-Horses 683
 
325. Proteus anguinus 684
 
326. Mud-Fish 685
 
327. The Axolotl 686
 
328. Sorting, Washing, and Digging at the South African Diamond Fields 687
 
329. Gold Miner’s Camp 689
 
330. Gold in Rocks 690
 
331. “Cradle” for Gold-washing 690
 
332. Pniel, from Jardine’s Hotel 702
 
333. Sifting at the “Dry Diggings” 703
 
334. Vaal River, from Spence Kopje 704
 
334a. Sketch Section of the Kimberley Diamond Mine 709
 
335. Portrait of Sir Humphrey Davy 714
 
336. Apparatus 717
 
337. Portrait of Mr. Thomas Hancock 724
 
338. Portrait of Sir James Young Simpson, M.D. 731
 
339. Railway Cutting 740
 
340. View on the Tyne 751
 
341. Fossil Trees in a Railway Cutting 752
 
342. Impression of Leaf in Coal Measures 753
 
343. Possible Aspect of the Forests of the Coal Age 754
 
344. The Fireside 756
 
345. View on Hyde and Egbert’s Farm, Oil Creek 761
 
346. View of City of London Gas-Works 764
 
347. Section of Gas-making Apparatus 765
 
348. The Retort 767
 
348a. Retort House of the Imperial Gas-Works 768
 
349. The Gas Governor 770
 
350. Bunsen’s Burner 772
 
351. Faraday’s Ventilating Gas-Burner 773
 
351a. Diagram 778
 
351b. Diagram 778
 
351c. Diagram 779
 
351d. Diagram 779
 
351e. Diagram 780
 
352. Apparatus for making Magenta 781
 
353. Iron Pots for making Nitro-Benzol 784
 
354. Section of Apparatus for making Nitro-Benzol 785
 
355. Apparatus for making Aniline 786
 
356. Section of Hollow Spindle 787
 
357. Portrait of J. Prescott Joule, F.R.S. 801
xv

LIST OF PLATES.

Plate I.
TO FACE
 
The Great Wheel in Action Title page
 
Plate II.
 
North-Eastern Railway Locomotive 18
 
Plate III.
 
The Great Steam Hammer, Royal Gun Factory, Woolwich 28
 
Plate IV.
 
The American Tract Society Building 76
 
Plate V.
 
General View of the Great Wheel at Earl’s Court 84
 
Plate VI.
 
Mount Washington Inclined Track 124
 
Plate VII.
 
Pike’s Peak Railroad, Rocky Mountains 128
 
Plate VIII.
 
The “Clermont” from a Contemporary Drawing 130
 
Plate IX.
 
The “Mary Powell” 144
 
Plate X.
 
The “New York” 148
 
Plate XI.
 
H.M.S. “The Terrible” 168
 
Plate XII.
 
The 110–Ton Armstrong Gun 202
 
Plate XIII.
 
The Forth Bridge 292
 
Plate XIV.
 
The Tower Bridge in course of Construction 298
 
Plate XV.
 
The Brooklyn Bridge 304
 
Plate XVI.
 
The North Mouth of the Great Tunnel, St. Gothard Railway 374
 
Plate XVII.
 
Spectra (Coloured Plate) 422

Wind, Steam, and Speed (after Turner).

1

INTRODUCTION.

Only by knowledge of Nature’s laws can man subjugate her powers and appropriate her materials for his own purposes. The whole history of arts and inventions is a continued comment on this text; and since the knowledge can be obtained only by observation of Nature, it follows that Science, which is the exact and orderly summing-up of the results of such observation, must powerfully contribute to the well-being and progress of mankind.

Some of the services which have been rendered by science in promoting human welfare are thus enumerated by an eloquent writer: “It has lengthened life; it has mitigated pain; it has extinguished diseases; it has increased the fertility of the soil; it has given new securities to the mariner; it has furnished new arms to the warrior; it has spanned great rivers and estuaries with bridges of form unknown to our fathers; it has guided the thunderbolt innocuously from heaven to earth; it has lighted up the night with the splendour of the day; it has extended the range of the human vision; it has multiplied the power of the human muscles; it has accelerated motion; it has annihilated distance; it has facilitated intercourse, correspondence, all friendly offices, all dispatch of business; it has enabled man to descend to the depths of the sea, to soar into the air, to penetrate securely into the noxious recesses of the earth, to traverse the land in cars which whirl along without horses, to cross the ocean in ships which run ten knots an hour against the wind. These are but a part of its fruits, and of its first-fruits; for it is a philosophy which never rests, which has never attained, which is never perfect. Its law is progress. A point which yesterday was invisible is its goal to-day, and will be its starting-point tomorrow.”—(Macaulay).

2Thus every new invention, every triumph of engineering skill, is the embodiment of some scientific idea; and experience has proved that discoveries in science, however remote from the interests of every-day life they may at first appear, ultimately confer unforeseen and incalculable benefits on mankind. There is also a reciprocal action between science and its application to the useful purposes of life; for while no advance is ever made in any branch of science which does not sooner or later give rise to a corresponding improvement in practical art, so on the other hand every advance made in practical art furnishes the best illustration of scientific principles.

The enormous material advantages which this age possesses, the cheapness of production that has placed comforts, elegancies, and refinements unknown to our fathers within the reach of the humblest, are traceable in a high degree to the arrangement called the “division of labour,” by which it is found more advantageous for each man to devote himself to one kind of work only; to the steam engine and its numerous applications; to increased knowledge of the properties of metals, and of the methods of extracting them from their ores; to the use of powerful and accurate tools; and to the modern plan of manufacturing articles by processes of copying, instead of fashioning everything anew by manual labour. Little more than a century ago everything was slowly and imperfectly made by the tedious toil of the workman’s hand; but now marvellously perfect results of ingenious manufacture are in every-day use, scattered far and wide, so that their very commonness almost prevents us from viewing them with the attention and admiration they deserve. Machinery, actuated by the forces of nature, now performs with ease and certainty work that was formerly the drudgery of thousands. Every natural agent has been pressed into man’s service: the winds, the waters, fire, gravity, electricity, light itself.

But so much have these things become in the present day matters of course, that it is difficult for one who has not witnessed the revolution produced by such applications of science to realize their full importance. Let the young reader who wishes to understand why the present epoch is worthy of admiration as a stage in the progress of mankind, address himself to some intelligent person old enough to remember the century in its teens; let him inquire what wonderful changes in the aspect of things have been comprised within the experience of a single lifetime, and let him ask what has brought about these changes. He will be told of the railway, and the steam-ship, and the telegraph, and the great guns, and the mighty ships of war—

“The armaments which thunderstrike the walls
Of rock-built cities, bidding nations quake,
And monarchs tremble in their capitals.”

He will be told of a machine more potent in shaping the destinies of our race than warlike engines—the steam printing-press. He may hear of a chemistry which effects endless and marvellous transformations; which from dirt and dross extracts fragrant essences and dyes of resplendent hue. He may hear something of a wonderful instrument which can make a faint beam of light, reaching us after a journey of a thousand years, unfold its tale and reveal the secrets of the stars. Of these and of other inventions and discoveries which distinguish the present age it is the purpose of this work to give some account.

3 JAMES WATT

STEAM ENGINES.

To track the steps which led up to the invention of the Steam Engine, and fully describe the improvements by which the genius of the illustrious Watt perfected it at least in principle, are not subjects falling within the province of this work, which deals only with the discoveries and inventions of the present century. But as it does enter into our province to describe some of the more recent developments of Watt’s invention, it may be desirable to give the reader an idea of his engine, of which all the more recent applications of steam are modifications, with improvements of detail rather than of principle.

Watt took up the engine in the condition in which it was left by Newcomen; and what that was may be seen in Fig. 2, which represents Newcomen’s atmospheric engine—the first practically useful engine in which a piston moving in a cylinder was employed. In the cut, the lower part of the cylinder, c, is removed, or supposed to be broken off, in order that the piston, h, and the openings of the pipes, d, e, f, connected with the cylinder, may be exhibited. The steam was admitted beneath the piston by the attendant turning the cock k, and as the elastic force of the steam was only equal to the pressure of the atmosphere, it was not employed to raise the piston, but merely filled the cylinder, the ascent of the piston being caused by the weight attached to the other side of the beam, which at the same time sent down the pump-rod, m; and when this was at its lowest position, the piston was nearly at the top of the cylinder, which was open. The attendant then cut off the communication with the boiler by closing the cock, k, at the same time opening another cock which allowed a jet 4of cold water from the cistern, g, to flow through the opening, d, into the cylinder. The steam which filled the cylinder was, by contact with the cold fluid, instantly condensed into water; and as the liquefied steam would take up little more than a two-thousandth part of the space it occupied in the gaseous state, it followed that a vacuum was produced within the cylinder; and the weight of the atmosphere acting on the top of the piston, having no longer the elastic force of the steam to counteract it, forced the piston down, and thus raised the pump-bucket attached to the rod, m. The water which entered the cylinder from the cistern, together with that produced by the condensation of the steam, flowed out of the cylinder by the opening, f, the pipe from which was conducted downwards, and terminated under water, the surface of which was at least 34 ft. below the level of the cylinder; for the atmospheric pressure would cause the cylinder to be filled with water had the height been less. The improvements which Watt, reasoning from scientific principles, was enabled to effect on the rude engine of Newcomen, are well expressed by himself in the specification of his patent of 1769. It will be observed that the machine was formerly called the “fire engine.”

Fig. 2.Newcomen’s Steam Engine.

Fig. 3.Watt’s Double-action Steam Engine.

“My method of lessening the consumption of steam, and consequently fuel, in fire engines, consists of the following principles:—First. That vessel in which the powers of steam are to be employed to work the engine (which is called the cylinder in common fire engines, and which I 5call the steam-vessel), must, during the whole time the engine is at work, be kept as hot as the steam that enters it; first, by enclosing it in a case of wood, or any other materials that transmit heat slowly; secondly, by surrounding it with steam or other heated bodies; and thirdly, by suffering neither water nor any other substance colder than the steam to enter or touch it during that time.—Secondly. In engines that are to be worked either wholly or partially by condensation of steam, the steam is to be condensed in vessels distinct from the steam-vessels or cylinders, although occasionally communicating with them,—these vessels I call condensers; and whilst the engines are working, these condensers ought to be kept at least as cold as the air in the neighbourhood of the engines by the application of water or other cold bodies.—Thirdly. Whatever air or other elastic vapour is not condensed by the cold of the condenser, and may impede the working of the engine, is to be drawn out of the steam-vessels or condensers by means of pumps, wrought by the engines themselves or 6otherwise.—Fourthly. I intend in many cases to employ the expansive force of steam to press on the pistons, or whatever may be used instead of them, in the same manner in which the pressure of the atmosphere is now employed in common fire engines. In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the air after it has done its office.—Lastly. Instead of using water to render the pistons and other parts of the engines air- and steam-tight, I employ oils, wax, resinous bodies, fat of animals, quicksilver, and other metals in their fluid state.”

Fig. 4.Governor and Throttle-Valve.

From the engraving we give of Watt’s double-action steam engine, Fig. 3, and the following description, the reader will realize the high degree of perfection to which the steam engine was brought by Watt. The steam is conveyed to the cylinder through a pipe, B, the supply being regulated by the throttle-valve, acted on by rods connected with the governor, D, which has a rotary motion. This apparatus is designed to regulate the admission of steam in such a manner that the speed of the engine shall be nearly uniform; and the mode in which this is accomplished may be seen in Fig. 4, where D D is a vertical axis carrying the pulley, d, which receives a rotary motion from the driving-shaft of the engine, by a band not shown in the figures. Near the top of the axis, at e, two bent rods work on a pin, crossing each other in the same manner as the blades of a pair of scissors. The two heavy balls are attached to the lower arms of these levers, which move in slits through the curved guides intended to keep them always in the same vertical plane as the axis, D D. The upper arms are jointed at f f to rods hinged at h h to a ring not attached to the axis, but allowing it to revolve freely within it. To this ring at F is fastened one end of the lever connected with the throttle-valve in a manner sufficiently obvious from 7the cut. The position represented is that assumed by the apparatus when the engine is in motion, the disc-valve, z, being partly open. If from any cause the velocity of the engine increases, the balls diverge from increased centrifugal force, and the effect is to draw down the ring at F, and, through the system of levers, to turn the disc in the direction of the arrows, and diminish the supply of steam. If, on the other hand, the speed of the engine is checked, the balls fall towards the axis, and the valve is opened wider, admitting steam more freely, and so restoring its former speed to the engine. On one side of the cylinder are two hollow boxes, E E, Fig. 3, communicating with the cylinder by an opening near the middle of the box. Each of these steam-chests is divided into three compartments by conical valves attached to rods connected with the lever, H. These valves are so arranged that when the upper part of the cylinder is in communication with the boiler, the lower part is open to the condenser, I, and vice versâ. The top of the cylinder is covered, and the piston-rod passes through an air and steam-tight hole in it; freedom of motion, with the necessary close fitting, being attained by making the piston-rod pass through a stuffing-box, where it is closely surrounded with greased tow. The piston is also packed, so that, while it can slide freely up and down in the cylinder, it divides the latter into two steam-tight chambers. In an engine of this kind, the elastic force of the steam acts alternately on the upper and lower surfaces of the piston; and the condenser, by removing the steam which has performed its office, leaves a nearly empty space before the piston, in which it advances with little or no resistance. On the rod which works the air-pump, two pins are placed, so as to move the lever, H, up and down through a certain space, when one pin is near its highest and the other near its lowest position, and thus the valves are opened and closed when the piston reaches the termination of its stroke. In the condenser, I, a stream of cold water is constantly playing, the flow being regulated by the handle, f. The steam, in condensing, heats the cold water, adding to its bulk, and at the same time the air, which is always contained in water, is disengaged, owing to the heat and the reduced pressure. Hence it is necessary to pump out both the air and the water by the pump, J, which is worked by the beam of the engine. In his engines Watt adopted the heavy fly-wheel, which tends to equalize the movement, and render insensible the effects of those variations in the driving power and in the resistance which always occur. In the action of the engine itself there are two positions of the piston, namely, where it is changing its direction, in which there is no force whatever communicated to the piston-rod by the steam. These positions are known as the “dead points,” and in a rotatory engine occur twice in each revolution. The resistance also is liable to great variations. Suppose, for example, that the engine is employed to move the shears by which thick plates of iron are cut. When a plate has been cut, the resistance is removed, and the speed of the engine increases; but this increase, instead of taking place by a sudden start, takes place gradually, the power of the engine being in the meantime absorbed in imparting increased velocity to the fly-wheel. When another plate is put between the shears, the power which the fly-wheel has gathered up is given out in the slight diminution of its speed occasioned by the increased resistance. But for the fly-wheel, such changes of velocity would take place with great suddenness, and the shocks and strains thereby caused would soon injure the machine. This expedient, in conjunction with that admirable contrivance, the “governor,” renders it possible to set the same engine at one moment to forge an 8anchor, and at the next to shape a needle. One of the most ingenious of Watt’s improvements is what is termed the “parallel motion,” consisting of a system of jointed rods connecting the head of the piston-rod, R, with the end of the oscillating beam. As, during the motion of the engine, the former moves in a straight line, while the latter describes a circle, it would be impossible to connect them directly. Watt accomplished this by hinging rods together in form of a parallelogram, in such a manner that, while three of the angles describe circles, the fourth moves in nearly a straight line. Watt was himself surprised at the regularity of the action. “When I saw it work for the first time, I felt truly all the pleasure of novelty, as if I was examining the invention of another man.”

A B is half the beam, A being the main centre; B E, the main links, connecting the piston-rod, F, with the end of the beam; G D, the air-pump links, from the centre of which the air-pump-rod is suspended; C D moves about the fixed centre, C, while D E is movable about the centre D, itself moving in an arc, of which C is the centre. The dotted lines show the position of the links and bars when the beam is at its highest position.

Fig. 4a.—Watt’s Parallel Motion.

Many improvements in the details and fittings of almost every part of the steam engine have been effected since Watt’s time. For example, the opening and closing of the passages for the steam to enter and leave the cylinder is commonly effected by means of the slide-valve (Fig. 5). The steam first enters a box, in which are three holes placed one above the other in the face of the box opposite to the pipe by which the steam enters. The uppermost hole is in communication with the upper part of the cylinder, and the lowest with the lower part. The middle opening leads to the condenser, or to the pipe by which the steam escapes into the air. A piece of metal, which may be compared to a box without a lid, slides over the three holes with its open side towards them, and its size is such that it can put the middle opening in communication with either the uppermost or the lowest opening, at the same time giving free passage for the steam into the cylinder by leaving the third opening uncovered. In A, Fig. 5, the valve is admitting steam below the piston, which is moving upwards, the steam which had before propelled it downwards now having free exit. When the piston has arrived at the top of the cylinder, the slide is pushed down by the rod connecting it with the eccentric into the position represented at B, and then the opposite movement takes place. The slide-valve is not moved, like the old pot-lid valves, against the pressure of the steam, and has other advantages, amongst which may be named the readiness with which a slight modification renders it available for using the steam “expansively.” This expansive working was one of Watt’s inventions, 9but has been more largely applied in recent times. In this plan, when the piston has performed a part of its stroke, the steam is shut off, and the piston is then urged on by the expansive force of the steam enclosed in the cylinder. Of course as the steam expands its pressure decreases; but as the same quantity of steam performs a much larger amount of work when used expansively, this plan of cutting off the steam is attended with great economy. It is usually effected by the modification of the slide-valve, shown at C, Fig. 5, where the faces of the slides are made of much greater width than the openings. This excess of width is called the “lap,” and by properly adjusting it, the opening into the cylinder may be kept closed during the interval required, so that the steam is not allowed to enter the cylinder after a certain length of the stroke has been performed. The slide-valve is moved by an arrangement termed the eccentric. A circular disc of metal is carried on the shaft of the engine, and revolves with it. The axis of the shaft does not, however, run through the centre of the disc, but towards one side. The disc is surrounded by a ring, to which it is not attached, but is capable of turning round within it. The ring forms part of a triangular frame to which is attached one arm of a lever that communicates the motion to the rod bearing the slide. Expansive working is often employed in conjunction with superheated steam, that is, steam heated out of contact with water, after it has been formed, so as to raise its temperature beyond that merely necessary to maintain it in the state of steam, and to confer upon it the properties of a perfect gas. Experience has proved that an increased efficiency is thus obtained.

Fig. 5.Slide Valve.

The actual power of a steam engine is ascertained by an instrument called the Indicator, which registers the amount of pressure exerted by the steam on the face of the piston in every part of its motion. The indicator consists simply of a very small cylinder, in which works a piston, very accurately made, so as to move up and down with very little friction. The piston is attached to a strong spiral spring, so that when the steam is admitted into the cylinder of the indicator the spring is compressed, and its elasticity resists the pressure of the steam, which tends to force the piston up. When the pressure of steam below the piston of the indicator 10is equal to that of the atmosphere, the spring is neither compressed nor extended; but when the steam-pressure falls below that of the atmosphere, as it does while the steam is being condensed, then the atmospheric pressure forces down the piston of the indicator until it is balanced by the tension of the now stretched spring. The extension or compression of the spring thus measures the difference between the pressure of the atmosphere and that of the steam in the cylinder of the engine, with which the cylinder of the indicator freely communicates.

From the piston-rod of the indicator a pencil projects horizontally, and its point presses against a sheet of paper wound on a drum, which moves about a vertical axis. This drum is made to move backwards and forwards through a part of a revolution, so that its motion may exactly correspond with that of the piston in the cylinder of the steam engine. Thus, if the piston of the indicator were to remain stationary, a level line would be traced on the paper by the movement of the drum; and if the latter did not move, but the steam were admitted to the indicator, the pencil would mark an upright straight line on the paper. The actual result is that a figure bounded by curved lines is traced on the paper, and the curve accurately represents the pressure of the steam at every point of the piston’s motion. The position of the point of the pencil which corresponds with each pound of pressure per square inch is found by trial by the maker of the instrument, who attaches a scale to show what pressures of steam are indicated.

If the pressure per square inch is known, it is plain that by multiplying that pressure by the number of square inches in the area of the piston of the engine, the total pressure on the piston can be found. The pressure does not rise instantly when the steam is first admitted, nor does it fall quite abruptly when the steam is cut off and communication opened with the condenser. When the steam is worked expansively, the pressure falls gradually from the time the steam is shut off. Now, the amount of work done by any force is reckoned by the pressure it exerts multiplied into the space through which that pressure is exerted. Therefore the work done by the steam is known by multiplying the pressure in pounds on the whole surface of the piston into the length in feet of the piston’s motion through which that pressure is exerted. The trace of the pencil on the paper—i.e., the indicator diagram—shows the pressures, and also the length of the piston’s path through which each pressure is exerted, and therefore it is not difficult to calculate the actual work which is done by the steam at every stroke of the engine. If this be multiplied by the number of strokes per minute, and the product divided by 33,000, we obtain what is termed the indicated horse-power of the engine. The work done per minute is divided by 33,000, because that number is taken to represent the work that a horse can do in a minute: that is, the average work done in one minute by a horse would be equal to the raising of the weight of 1,000 lbs. thirty-three feet high, or the raising of thirty-three pounds 1,000 feet high. The number, 33,000, as expressing the work that could be done by a horse in one minute, was fixed on by Watt, but more recent experiments have shown that he over-estimated the power of horses, and that we should have to reduce this number by about one-third if we desire to express the actual average working power of a horse. But the power of engines having come to be expressed by stating the horse-power on Watt’s standard, engineers have kept to the original number, which is, however, to be considered as a merely artificial unit or term of comparison between one engine and another; 11for the power of a horse to perform work will vary with the mode in which its strength is exerted. The source of the power which does the work in the steam engine is the combustion of the coal in the furnace under the boiler. The amount of work a steam engine will do depends not only on the quantity of steam which is generated in a given time, but also upon the pressure, and therefore the temperature at which the steam is formed.

Fig. 6.Section of Giffard’s Injector.

The water constantly evaporating in the boiler of a steam engine is usually renewed by forcing water into the boiler against the pressure of the steam by means of a small pump worked by the engine. In the engraving of Watt’s engine this pump is shown at M. But recently the feed-pump has been to a great extent superseded by a singular apparatus invented by M. Giffard, and known as Giffard’s Injector. In this a jet of steam from the boiler itself supplies the means of propelling a stream of water directly into the boiler. Fig. 6 is a section of this interesting apparatus through its centre, and it clearly shows the manner in which the current of steam is made to operate on the jet of water. The steam from the boiler passes through the pipe A and into the tube B through the holes. The nozzle of this tube is of a conical shape, and its centre is occupied by a rod pointed to fit into the conical nozzle, and provided with a screw at the other end, so that the opening can be regulated by turning the handle, C. At D the jet of steam comes in contact with the water which feeds the boiler, the arrangement being such that the steam is driven into the centre of the stream of water which enters by the pipe E, and is propelled by the steam jet through another cone, F, issuing with such force from the orifice of the latter that it is carried forward through the small opening at G into the chamber H. Here the water presses on the valve K, which it raises against the pressure of the steam and enters the boiler. The water issuing from the cone, F, actually traverses an open space which is exposed to the air, and where the fluid may be seen rushing into the boiler as a clear jet, except a few beads of steam which may be carried forward in the centre, the rest of the steam having been condensed by the cold 12water. The steam, of course, rushes from the cone, B D, with enormous velocity, which is partly communicated to the water. The pipe, L, is for the water which overflows in starting the apparatus, until the pressure in H becomes great enough to open the valve. The supplies of water and of steam have to be adjusted according to the conditions of pressure in the boiler, and according to the temperature of the feed-water. It is found that when the feed-water is at a temperature above 120° Fahrenheit, the injector will not work: the condensation of the steam is therefore necessary to the result. For, as the steam is continually condensed by the cold water, it rushes from D with the same velocity as into a vacuum, and the water is urged on by a momentum due to this velocity. We must observe, moreover, that the net result of the operation is a lessening of the pressure in the boiler; for the entrance of the feed-water produces a fall of temperature in the boiler, and the bulk of steam expended is fourteen times the bulk of the water injected: thus, although the apparatus before actual trial would not appear likely to produce the required result, the effect is no more paradoxical than in the case of the feed-pump. The injector has been greatly improved by Mr. Gresham, who has contrived to make some of the adjustments self-acting, and his form of the apparatus is now largely used in this country. The injector is applicable to stationary, locomotive, or marine engines.

Steam boilers are now always provided with one of Bourdon’s gauges, for indicating the pressure of the steam. The construction of the instrument will easily be understood by an examination of Fig. 7. The gauge is screwed into some part of the boiler, where it can always be seen by the person in charge. The stop-cock A communicates with the curved metallic tube C, which is the essential part of the contrivance. This tube is of the flattened form shown at D, having its greatest breadth perpendicular to the plane in which the tube is curved, and it is closed at the end E, where it is attached to the rod F, so that any movement of E causes the axle carrying the index-finger, F, to turn, and the index then moves along the graduated arc. The connection is sometimes made by wheelwork, instead of by the simple plan shown in the figure. The front plate is represented as partly broken away, in order to show the internal arrangement, which, of course, is not visible in the real instrument, where only the index-finger and graduated scale are seen, protected by a glass plate.

Fig. 7.Bourdon’s Pressure Gauge.

When a curved tube of the shape here described is subjected to a greater pressure on the inside than on the outside, it tends to become straighter, and the end E moves outward; but when the pressure is removed, the tube resumes its former shape. The graduations on the scale are made by marking the position of the index when known pressures are applied. The amounts of pressure, when the gauges are being graduated, are known by the compression produced in air contained in another apparatus. Gauges constructed on Bourdon’s principle are applied to other purposes, and can be made strong enough to measure very great pressures, such as several 13thousand pounds on the square inch; they may also be made so delicate as to measure variations of pressure below that of the atmosphere. The simplicity and small size of these gauges, and the readiness with which they can be attached, render them most convenient instruments wherever the pressure of a gas or liquid is required to be known.

Fig. 8.Steam Generator.

A point to which great attention has been directed of late years is the construction of a boiler which shall secure the greatest possible economy in fuel. Of the total heat which the fuel placed in the furnace is capable of supplying by its combustion, part may be wasted by an incomplete burning of the fuel, producing cinders or smoke or unburnt gases, another part is always lost by radiation and conduction, and a third portion is carried off by the hot gases that escape from the boiler-flues. Many contrivances have been adopted to diminish as much as possible this waste of heat, and so obtain the greatest possible proportion of available steam power from a given weight of fuel. Boilers wholly or partially formed of tubes have recently been much in favour. An arrangement for quickly 14generating and superheating steam is shown in Fig. 8, in connection with a high-pressure engine.

Steam engines are constructed in a great variety of forms, adapted to the purposes for which they are intended. Distinctions are made according as the engine is fitted with a condenser or not. When steam of a low pressure is employed, the engine always has a condenser, and as in this way a larger quantity of work is obtainable for a given weight of fuel, all marine engines—and all stationary engines, where there is an abundant supply of water and the size is not objectionable—are provided with condensers. High-pressure steam may be used with condensing engines, but is generally employed in non-condensing engines only, as in locomotives and agricultural engines, the steam being allowed to escape into the air when it has driven the piston to the end of the stroke. In such engines the beam is commonly dispensed with, the head of the piston-rod moving between guides and driving the crank directly by means of a connecting-rod. The axis of the cylinder may be either vertical, horizontal, or inclined. A plan often adopted in marine engines, by which space is saved, consists in jointing the piston-rod directly to the crank, and suspending the cylinder on trunnions near the middle of its length. The trunnions are hollow, and are connected by steam-tight joints, one with the steam-pipe from the boiler, and the other with the eduction-pipe. Such engines have fewer parts than any others; they are lighter for the same strength, and are easily repaired. The trunnion joints are easily packed, so that no leakage takes place, and yet there is so little friction that a man can with one hand move a very large cylinder, whereas in another form of marine engine, known as the side-lever engine, constructed with oscillating beams, the friction is often very great.

THE LOCOMOTIVE.

The first locomotive came into practical use in 1804. Twenty years before, Watt had patented—but had not constructed—a locomotive engine, the application of steam to drive carriages having first been suggested by Robinson in 1759. The first locomotives were very imperfect, and could draw loads only by means of toothed driving-wheels, which engaged teeth in rack-work rails. The teeth were very liable to break off, and the rails to be torn up by the pull of the engine. In 1813, the important discovery was made that such aids are unnecessary, for it was found that the “bite” of a smooth wheel upon a smooth rail was sufficient for all ordinary purposes of traction. But for this discovery, the locomotive might never have emerged from the humble duty of slowly dragging coal-laden waggons along the tramways of obscure collieries. The progress of the locomotive in the path of improvement was, however, slow, until about 1825, when George Stephenson applied the blast-pipe, and a few years later adopted the tubular boiler. These are the capital improvements which, at the famous trial of locomotives, on the 6th of October, 1829, enabled Stephenson’s “Rocket” to win the prize offered by the directors of the Liverpool and Manchester Railway. The “Rocket” weighed 4½ tons, and at the trial drew a load of tenders and carriages weighing 12¾ tons. Its average speed was 14 miles an hour, and its greatest, 29 miles 15an hour. This engine, the parent of the powerful locomotives of the present day, may now be seen in the Patent Museum at South Kensington. Since 1829, numberless variations and improvements have been made in 16the details of the locomotive. In weight, dimensions, tractive power and speed, the later locomotives vastly surpass the earlier types.

Fig. 9.Section of Locomotive (A.D. 1837).

Fig. 9 represents the section of a locomotive constructed c. 1837. The boiler is cylindrical; and at one end is placed the fire-box, partly enclosed in the cylindrical boiler, and surrounded on all sides by the water, except where the furnace door is placed, and at the bottom, where the fuel is heaped up on bars which permit the cinders to drop out. At the other end of the boiler, a space beneath the chimney called the smoke-box is connected with the fire-box by a great number of brass pipes, open at both ends, firmly fixed in the end plates of the boiler. These tubes are from 1¼ in. to 2 in. in diameter, and are very numerous—usually about one hundred and eighty, but sometimes nearly double that number. They therefore present a large heating surface to the water, which stands at a level high enough to cover them all and the top of the fire-box. The boiler of the locomotive is not exposed to the air, which would, if allowed to come in contact with it, carry off a large amount of heat. The outer surface is therefore protected from this cooling effect by covering it with a substance which does not permit the heat to readily pass through it. Nothing is found to answer better than felt; and the boiler is accordingly covered with a thick layer of this substance, over which is placed a layer of strips of wood ¾ in. thick, and the whole is surrounded with thin sheet iron. It is this sheet iron alone that is visible on the outside. The level of the water in the boiler is indicated by a gauge, which is merely a very strong glass tube; and the water carried in the tender is forced in as required, by a pump (not shown in the Fig.). The steam leaves the boiler from the upper part of the steam-dome, A, where it enters the pipe, B; the object being to prevent water from passing over with the steam into the pipe. The steam passes through the regulator, C, which can be closed or opened to any extent required by the handle, D, and rushes along the pipe, E, which is wholly within the boiler, but divides into two branches when it reaches the smoke-box, in order to conduct the steam to the cylinders. Of these there are two, one on each side, each having a slide-valve, by means of which the steam is admitted before and behind the pistons alternately, and escapes through the blast-pipe, F, up the chimney, G, increasing the draught of the fire by drawing the flame through the longitudinal tubes in proportion to the rush of steam; and thus the rate of consumption of fuel adjusts itself to the work the engine is performing, even when the loads and speeds are very different. Though the plane of section passing through the centre of boiler would not cut the cylinders, one of them is shown in section. H is the piston; K the connecting-rod jointed to the crank, L, the latter being formed by forging the axle with four rectangular angles, thus, ; and the crank bendings for the two cylinders are placed in planes at right angles to each other, so that when one is at the “dead point,” the other is in a position to receive the full power of the piston. There are two safety valves, one at M, the other at N; the latter being shut up so that it cannot be tampered with.

Locomotives are fitted with an ingenious apparatus for reversing the engines, which was first adopted by the younger Stephenson, and is known as the “link motion.” The same arrangement is employed in other engines in which the direction of rotation has to be changed; and it serves another important purpose, namely, to provide a means by which steam may be employed expansively at pleasure. The link motion is represented in Fig. 10, where A, B, are two eccentrics oppositely placed on the driving-shaft, 17and their rods joined to the ends of the curved bar or link, C D. A slit extends nearly the whole length of this bar, and in it works the stud E, forming part of the lever, F, G, movable about the fixed joint, G, and having its extremity, F, jointed to the rod H, that moves the slide-valve. The weight of the link and the eccentric rods is counterpoised with a weight, K, attached to the lever, I K, which turns on the fixed centre, L. This lever forms one piece with another lever, L M, with which it may be turned by pulling the handle of O P, connected with it through the system of jointed rods. When the link is lowered, as shown in the figure, the slide-valve rod will follow the movement of the eccentric, B, while the backward and forward movement of the other eccentric will only be communicated to the end of C, and will scarcely affect the position of the stud E at all. By drawing the link up to its highest position, the motion due to eccentric A only will be communicated to the slide-valve rod, which will therefore be drawn back at the part of the revolution where before it was pushed forward, and vice versâ; hence the engine will be reversed. When the link is so placed that the stud is exactly in the centre, the slide-valve will receive no motion, and remain in its middle position, consequently the engine is stopped. By keeping the link nearer or farther from its central position, the throw of the slide-valve will be shorter or longer, and the steam will be shut off from entering the cylinder when a smaller or larger portion of the stroke has been performed.

Fig. 10.Stephenson’s Link Motion.

18Although Fig. 9 represents with sufficient clearness all the essential parts of a locomotive, it should be observed that as actually constructed for use on the different lines of railway the machine is greatly modified in the arrangement and proportions of its parts. A greater number of adjuncts and subsidiary appliances are also provided for the more effective and convenient working of the engine, and for giving control over the movement of the train, and these, in fact, conduce much to the greater economy and safety with which trains are now run. As the circumstances and conditions under which railways are worked vary much in different parts of the world, the locomotive has to be designed to meet the requirements of each case, and its general appearance, details and dimensions are accordingly much diversified. From among the many types of recent locomotives we select for illustration and a short description the form of express passenger engine that has lately been designed by Mr. T. W. Worsdell, the engineer of the North Eastern Railway, and this will give the opportunity of noticing some of the newest improvements, which are embodied in this engine. See Plate II.

The plan of causing the steam to work expansively has already been mentioned on pages 8 and 9, as used by cutting off the steam when part of the stroke of the piston has been made. Another mode by which the expansive principle has long been made use of in stationary and marine engines is to allow the steam from the boiler to enter first a smaller cylinder and from that, at the end of the stroke, to pass into a larger one in which, as it expands, it exercises a diminished pressure. This arrangement has been called the compound or double-cylinder engine, and was known to possess certain advantages where high pressure steam was made use of. Indeed, in marine engines the principle of “triple expansion” is now quite commonly adopted—that is, the steam passes successively into three cylinders of successively greater diameter. Mr. Webb, the locomotive engineer of the London and North Western Railway, appears to have been the first to make the “compounding” system a practical success as applied to the locomotive. In Mr. Webb’s arrangement there are three cylinders, two smaller ones for the high-pressure steam from the boiler, and between these a single large low-pressure cylinder which receives the steam that has done its work from both the smaller cylinders. In Mr. Worsdell’s engine the original and simpler locomotive construction of two cylinders has been adhered to, and thus the general plan of the engine is unchanged except in the larger size of the low-pressure cylinder. In the present engine the stroke is 24 in.; the high-pressure cylinder has its internal diameter 20 in. and the low-pressure cylinder a diameter of 28 in. The boiler-shell is made of steel, the fire-box is of copper, and there are 203 brass tubes, 1¾ in. diameter and 10 ft. 11 in. long, connecting the fire-box with the smoke-box. The frame, and indeed most parts of the engine, are also made of steel. The driving-wheels, which here are a single pair, have a diameter of 7 ft. 7¼ in. The total “wheel-base” is nearly 21 ft., and it will be observed that the forepart of the engine is supported on a four-wheeled bogie. The bogie is capable of a certain amount of horizontal motion by turning round a swivel, but this movement is controlled by springs, so that, notwithstanding the length of the frame, the engine is enabled to take curves with great facility, while its motion is perfectly steady even at the highest speeds. The working pressure of the steam in the boiler is 170 lbs. on the square inch. The steam which leaves the high-pressure cylinder is conveyed to 19the low-pressure cylinder by a pipe that is led round the inside of the smoke-box, and thus enters the larger cylinder after taking up heat that would otherwise be wasted, so that its elastic force is fully maintained. This circumstance, no doubt, contributes to the very marked economy of fuel that has been effected by the compound engines. How great the economy is found in the working will be seen by the following results, which are taken from the actual records. The same train was taken over the same rails in ordinary quick passenger traffic for several journeys which, as performed in the same time by the compound engine and by another otherwise similar non-compound engine, required for the compound, 25,254 lbs. of coal; for the non-compound, 32,104 lbs.; or, the consumption of coal by the former was 28 lbs. per mile; by the latter, 36 lbs. per mile. This represents a saving of about 21 per cent. of the fuel. As the steam enters the high-pressure cylinder first, it would not be possible to start the engine if it had stopped at one of the “dead-points” on that side, without a special arrangement for admitting the steam directly to the other cylinder in such cases. This, of course, is required only for the first stroke, and Mr. Worsdell and M. von Borries have contrived for this purpose an ingenious valve, brought into operation when required by a touch from the engineer, and then immediately adjusting itself automatically, so as to restore the steam connections to their normal condition.

PLATE II.

NORTH EASTERN RAILWAY LOCOMOTIVE.

Fig. 10a.—G.N.R. Express Passenger Locomotive.

Another type of the high-speed passenger engines used for express trains on several of the great English railways is well represented by one of the Great Northern Company’s locomotives, as depicted in Fig. 10a. In this there are a single pair of driving wheels of very large diameter, namely, 8 ft. 2 in., so that each complete movement of the pistons will carry the engine forwards a length of nearly 26 ft. There are outside cylinders, and therefore the driving axle is straight, and the leading wheels are in two pairs, mounted on a bogie which is capable of a certain amount of independent horizontal rotation.

The Stephenson’s link motion, described on page 17, has lately been often supplanted by another arrangement known as Joy’s valve gear, which leaves the crank axle unencumbered with eccentrics, and, as taking up less space, is generally now preferred for locomotives and also for marine engines. Its principle is very simple, and will be readily understood from the diagram in Fig. 10b, where c is the spindle of the slide-valves 20as in Fig. 5, but capable, we shall now suppose, of a horizontal movement only. Jointed to it at D is a rod D E attached to a block at E, which can move only within a slot in the strong bar E F in a circular segment, the centre of which is at D. The bar we suppose for the moment to be immovable, and disposed symmetrically to C D. Now let an alternate up and down motion along the circular segment be given to block E, and the effect will be to leave the centre, D, unchanged in position, and, therefore, in that case the valve will not be moved at all. Now this reciprocating movement is given to the block E by a system of levers (not here shown), jointed to the connecting-rod (K, Fig. 9) in such a manner that the rod D E is compelled to follow the movement of the connecting-rod, but the end E must always travel in the circular segment. We have hitherto supposed this segmental piece to be fixed, but the engineer has the power of so turning it as to tilt either the upper or lower part towards D. If, for instance, the guiding segment is fixed as at II, the block in rising will push in the valve-spindle, and in descending draw it out, as the length of the rod D E is invariable. But if the guides be turned over so as to bring F nearer D than E, the same movement of the block will give the reverse motions to the valve-spindle.

Fig. 10b.—Joy’s Valve Gear.

From the great rapidity with which the machinery of the locomotive moves, the different parts require to be carefully balanced in order to prevent dangerous oscillations. For example, the centrifugal force of the massive cranks, etc., is balanced by inserting between the spokes of the driving wheels certain counterpoises, the weights and positions of which are finally adjusted by trial. The engine is suspended by chains and set in motion, and a pencil attached to one corner of the frame marks on a horizontal card the form of the oscillation, usually by an oval figure. When the diameter of this figure is reduced to about 1
16
inch, the adjustment is considered complete.

21The power of a locomotive, of course, depends on the pressure of the steam and the size of the cylinder, &c.; but a very much lower limit than is imposed by these conditions is set to the power of the engine to draw loads by the adhesion between the driving wheels and the rails. By the term “adhesion,” which is commonly used in this case, nothing more is really meant than the friction between surfaces of iron. When the resistance of the load drawn is greater than this friction, the wheels turn round and slip on the rails without advancing. The adhesion depends upon the pressure between the surfaces, and upon their condition. It is greater in proportion as the weight supported by the driving-wheels is greater, and when the rails are clean and dry it is equal to from 15 to 20 per cent. of that part of the weight of the engine which rests on the driving-wheels; but when the rails are moist, or, as it is called, “greasy,” the tractive power may be only 5 per cent. of the weight; about one-tenth may be taken as an average. Suppose that 30 tons of the weight of a locomotive are supported by the driving-wheels, that locomotive could not be employed to drag a train of which the resistance would cause a greater pull upon the coupling-links of the tender than they would be subject to if they were used to suspend a weight of 3 tons. The number of pairs of wheels in a locomotive varies from two to five; most commonly there are three pairs; and one, two, or all, are driven by the engine, the wheels being coupled accordingly; very often two pairs are coupled.

The pressure at which the steam is used in the locomotive is sometimes very considerable. A pressure equal to 180 lbs. on each square inch of the surface of the boiler is quite usual. The greater economy obtained by the employment of high-pressure steam acting expansively in the cylinder, points to the probability of much higher pressures being adopted. There is practically no limit but the power of the materials to resist enormous strains, and there is no reason, in the nature of things, why steam of even 500 lbs. per square inch should not be employed, if it were found otherwise desirable. It need hardly be said that locomotives are invariably constructed of the very best materials, and with workmanship of the most perfect kind. The boilers are always tested, by hydraulic pressure, to several times the amount of the highest pressure the steam is required to have, and great care is bestowed upon the construction of the safety-valves, so that the steam may blow off when the due amount of pressure is exceeded. The explosion of a locomotive is, considering the number of engines in constant use, a very rare occurrence, and is probably in all cases owing to the sudden generation of a large quantity of steam, and not to an excessive pressure produced gradually. Among the causes capable of producing explosive generation of steam may be mentioned the deposition of a hard crust of stony matter, derived from the water; this crust allows the boiler to be over-heated, and if water should then find its way into contact with the heated metal, a large quantity of steam will be abruptly generated. Or should the water in the boiler become too low, parts of the boiler may become so heated that on the admission of fresh water it would be suddenly converted into steam. When an explosion does take place, the enormous force of the agent we are dealing with when we bottle up steam in an iron vessel, is shown by the effects produced. Fig. 11 is from a photograph taken from an exploded locomotive, where we may see how the thick plates of iron have been torn like paper, and the tubes, rods, and levers of the engine twisted in inextricable confusion.

Fig. 11.Locomotive after Explosion.

Fig. 12.Hancock’s Steam Omnibus.

Locomotive engines for propelling carriages on common roads were 22invented many years ago, by Gurney, Anderson, Scott Russell, Hancock, and others. One designed by Hancock is represented in Fig. 12. Such engines do not appear to have found much favour, though the idea has been successfully realized in the traction engines lately introduced. Probably the application of steam power to the propulsion of vehicles along common roads fell into neglect on account of the superior advantages of railways, but the common road locomotive is at present receiving some attention. In the tramways which are now laid along the main roads in most large cities we see one-half of the problem solved. It is not so much mechanical difficulties that stand in the way of this economical system of 23locomotion, as the prejudices and interests which have always to be overcome before the world can profit by new inventions. The engines can be made noiseless, emitting no visible steam or smoke, and they are under more perfect control than horses. But vestries and parochial authorities offer such objections as that horses would be frightened in the streets, if the engine made a noise; and if it did not, people would be liable to be run over, and the horses be as much startled as in the other case. But horses would soon become accustomed to the sight of a carriage moving without equine aid, however startling the matter might appear to them at first; and the objection urged against the noiseless engines might be alleged against wooden pavements, india-rubber tires, and many other improvements. It is highly probable that in the course of a few years the general adoption of steam-propelled vehicles will displace horses, at least upon tramways. The slowness with which inventions of undeniable utility and of proved advantage come into general use may be illustrated by the fact of some great English towns and centres of engineering industry not having made a single tramway until, in all the populous cities of the United States, and in almost every European capital, tramways had been in successful operation for many years. [1890.]

Some time has elapsed since the foregoing paragraph was written for an earlier edition of this work, and during that period there has been an advance in both practice and opinion; so that now it has become highly probable that before the century ends a great change may be witnessed in our modes of locomotion, even on ordinary roads. Already every town of importance throughout the United Kingdom has been provided with excellent tramways, along which, in not a few instances, horseless vehicles roll smoothly, to the great convenience of the general public, while not one of the difficulties and dangers to general street traffic has been experienced that were so confidently predicted by those who were unable to perceive that an innovation might be an improvement. The now universally-popular bicycle has been continually receiving improvements, of which there appears to be no end, and as the machine and all the contrivances connected with it are so familiar to everyone, there is no need here to do more than to refer to them, because they have led the way to great improvements in ordinary carriages.

The steam-propelled vehicle for common roads has just been mentioned as an invention belonging to the first half of the century, and the reasons it did not find favour have been alluded to. There exists in the United Kingdom a law concerning horseless carriages travelling on highways, which was passed to apply to traction engines, and enacts that other than horse vehicles are not to go along a road at a greater speed than four miles an hour, and only two miles an hour through a town, and moreover they are to be preceded by a man bearing a red flag, etc. But a bill has been introduced (1895) into the legislature to amend this law, and permit the British people to use on their common roads such light self-propelled carriages as are becoming popular in France, as may be seen from the following account:—

On Tuesday, 11th June, 1895, a race was started from Versailles to Bordeaux and back, a distance of 727 miles or more for the double journey. The first prize was the substantial sum of 40,000 francs (£1,600), to which was attached the condition of the carriage seating four persons, and other prizes were also to be awarded to various kinds of automatic vehicles. No fewer than sixty-six vehicles were entered for competition, 24and these were variously supplied with motive power from steam, electricity, or petroleum spirit. The starting place was Versailles at 12·9 p.m., and at 10·32 on Wednesday morning MM. Panhard & Levassor’s petroleum carriage arrived at Bordeaux, whence, after a stop of only four minutes, the return journey was begun, but shortly afterward an accident caused a delay of one hour, but the carriage made the whole distance at the average of 14·9 miles per hour. In this and three other carriages belonging to the same firm, the propeller was the Daimler motor. Though this carriage was the first to accomplish the trip it received only the second prize, the condition of seating four persons not having been complied with. The first prize fell to a four-seated vehicle by Les Fils de Peugeot Frères, a firm who carried off besides the third and fourth prizes. These carriages were also driven by so-called petroleum motors. These motors are really gas engines on the principle to be presently mentioned, but the gas is produced by the vapourisation of a volatile constituent of petroleum (benzoline). The Daimler motor is a compact combination of two cylinders connected with a chamber containing the explosive mixture of gas and air. The pistons perform their in and out strokes simultaneously, but their working strokes alternately.

PORTABLE ENGINES.

The application of steam power to agricultural operations has led to the construction of engines specially adapted by their simplicity and portability for the end in view. The movable agricultural engines have, like the locomotives, a fire-box nearly surrounded by the water, and horizontal tubes, and are set on wheels, so that they may be drawn by horses from place to place. There is usually one cylinder placed horizontally on the top of the boiler; and the piston-rod, working in guides, is, as in the old locomotive, attached by a connecting-rod to the crank of a shaft, which carries a fly-wheel, eccentrics, and pulleys for belts to communicate the motion to the machines. Engines of this kind are also much used by contractors, for hoisting stones, mixing mortar, &c. These engines are made with endless diversities of details, though in most such simplicity of arrangement is secured, that a labourer of ordinary intelligence may, after a little instruction, be trusted with the charge of the engine; while their economy of fuel, efficiency, and cheapness are not exceeded in any other class of steam engine.

Besides the steam engines already described or alluded to, there are many interesting forms of the direct application of steam power. There are, for example, the steam roller and the steam fire-engine. The former is a kind of heavy locomotive, moving on ponderous rollers, which support the greater part of the weight of the engine. When this machine is made to pass slowly over roads newly laid with broken stones, a few repetitions of the process suffice to crush down the stones and consolidate the materials, so as at once to form a smooth road. Steam power is applied to the fire engine, not to propel it through the streets, but to work the pumps which force up the water. The boilers of these engines are so arranged that in a few minutes a pressure of steam can be obtained sufficient to throw an effective jet of water. The cut at the end of this chapter represents 25a very efficient engine of this kind, which will throw a jet 200 feet high, delivering 1,100 gallons of water per minute. It has two steam cylinders and two pumps, each making a stroke of two feet. These are placed horizontally, the pumps and the air reservoir occupying the front part of the engine, while the vertical boiler is placed behind. The steam cylinders, which are partly hid in the cut by the iron frame of the engine, are not attached to the boiler, which by this arrangement is saved from injurious strains produced by the action of the moving parts of the mechanism. There are seats for eight firemen, underneath which is a space where the hose is carried. A first-class steam fire-engine of this kind, completely fitted, costs upwards of £1,300.

A cheap and very convenient prime mover has lately come into use, which has certain advantages over even the steam engine. Where a moderate or a very small power is required, especially where it is used only at intervals, the gas engine is found to be more convenient. It is small and compact, no boiler or furnace is required, and it can be started at any moment. As now made, it works smoothly and without noise. The piston is impelled, not by the expansive force of steam, but by that of heated air, the heat being generated by the explosion of a mixture of common coal gas and air within the cylinder itself. Thus a series of small explosions has the same effect as the admissions of steam through a valve. A due quantity of gas and air is introduced into the cylinder, and is ignited by the momentary opening of a communication with a lighted gas jet outside. But the machine is provided with a regulator or governor, which so acts on the valve mechanism that this communication is made at each stroke only when the speed of rotation falls below a certain assigned limit, and thus the number of the explosions is less than the number of strokes, unless its work absorbs the machine’s whole energy, which, according to the size of the engine, may be from that of a child up to 30–horse power.

THE STEAM HAMMER.

Before the invention of the steam hammer, large forge hammers had been in use actuated by steam, but in an indirect manner, the hammer having been lifted by cams and other expedients, which rendered the apparatus cumbersome, costly, and very wasteful of power, on account of the indirect way in which the original source of the force, namely, the pressure of the steam, had to reach its point of application by giving the blow to the hammer. Not only did the necessary mechanism for communicating the force in this roundabout manner interfere with the space necessary for the proper handling of the article to be forged, but the range of the fall of the hammer being only about 18 in., caused a very rapid decrease in the energy of the blow when only a very moderate-sized piece of iron was introduced. For example, a piece of iron 9 in. in diameter reduced the fall of the mass forming the hammer to one-half, and the work it could accomplish was diminished in like proportion. Besides, as the hammer was attached to a lever working on a centre, the striking face of the hammer was parallel to the anvil only at one particular point of its fall; and again, as the hammer was always necessarily raised to the same height at each stroke, there was absolutely no means of controlling 26the force of the blow. When we reflect on the fact that the rectilinear motion of the piston in the cylinder of the engine had first to be converted into a rotary one, by beams, connecting-rod, crank, &c., and then this rotary movement transformed into a lifting one by the intervention of wheels, shafts, cams, &c., while all that is required in the hammer is a straight up-and-down movement, the wonder is that such an indirect and cumbersome application of power should have for so many years been contentedly used. But in November, 1839, Mr. Nasmyth, an eminent engineer of Manchester, received a letter from a correspondent, informing him of the difficulty he had found in carrying out an order received for the forging of a shaft for the paddle-wheels of a steamer, which shaft was required to be 3 ft. in diameter. There was in all England no forge hammer capable of executing such a piece of work. This caused Mr. Nasmyth to reflect on the construction of forge hammers, and in a few minutes he had formed the conception of the steam hammer. He immediately sketched the design, and soon afterward the steam hammer was a fait accompli, for Mr. Nasmyth had one at once executed and erected at his works, where he invited all concerned to come and witness its performances. Will it be believed that four years elapsed before this admirable application of steam power found employment outside the walls of Mr. Nasmyth’s workshops? After a time he succeeded in making those best able to profit by such an invention aware of the new power—for such it has practically proved itself, having done more to revolutionize the manufacture of iron than any other inventions that can be named, except, perhaps, those of Cort and Bessemer. The usual prejudice attending the introduction of any new machine, however obvious its advantages are afterward admitted to be, at length cleared away, and the steam hammer is from henceforth an absolute necessity in every engineering workshop, and scarcely less so for some of the early stages of the process of manufacturing crude wrought iron. Whether blows of enormous energy or gentle taps are required, or strokes of every gradation and in any order, the steam hammer is ready to supply them.

Fig. 13.Nasmyth’s Steam Hammer.

A steam hammer of the smaller kind is represented in Fig. 13. The general mode of action will easily be understood. The steam is admitted below the piston, which is thus raised to any required height within the limits of the stroke. When the communication with the boiler is shut off and the steam below the piston is allowed to escape, the piston, with the mass of iron forming the hammer attached to the piston-rod, falls by its own weight. This weight, in the large steam hammers, amounts to several tons; and the force of the blow will depend jointly upon the weight of the hammer, and upon the height from which it is allowed to fall. The steam is admitted and allowed to escape by valves, moved by a lever under the control of a workman. By allowing the hammer to be raised to a greater or less height, and by regulating the escape of the steam from beneath the piston, the operator has it in his power to vary the force of the blow. Men who are accustomed to work the valves can do this with great nicety. They sometimes exhibit their perfect control over the machine by cracking a nut on the anvil of a huge hammer; or a watch having been placed—face upwards—upon the anvil, and a moistened wafer laid on the glass, a practised operator will bring down the ponderous mass with such exactitude and delicacy that it will pick up the wafer, and the watch-glass will not even be cracked. The steam hammer has recently been improved in several ways, and its power has been more than doubled, by causing the steam, 27during the descent, to enter above the piston and add its pressure to the force of gravity. Probably one of the most powerful steam hammers ever constructed is that recently erected at the Royal Gun Factory at Woolwich, for the purpose of forging great guns for the British Navy. It has been made by Nasmyth & Co., and is in shape similar to their other steam hammers. Its height is upwards of 50 ft., and it is surrounded with furnaces and powerful cranes, carrying the huge iron tongs that are to grasp the glowing masses. The hammer descends not merely with its own weight of 30 tons; steam is injected behind the falling piston, which is thus driven down with vastly enhanced rapidity and impulse. Of the lower portion of this stupendous forge, nothing is visible but a flat table of iron—the anvil—level with the floor of the foundry. But more wonderful, perhaps, than anything seen aboveground, is the extraordinarily solid foundation beneath. Huge tablets of foot-thick castings alternate with concrete and enormous baulks of timber, and, lower down, beds of concrete, and piles driven deep into the solid earth, form a support for the uppermost plate, upon which the giant delivers his terrible stroke. Less than this would render it unsafe to work the hammer to its full power. As the monster works—soberly 28and obediently though he does it—the solid soil trembles, and everything movable shivers, far and near, as, with a scream of the steam, our ‘hammer of Thor’ came thundering down, mashing the hot iron into shape as easily as if it were crimson dough, squirting jets of scarlet and yellow yeast. The head of the hammer, which of course works vertically, is detachable, so that if the monster breaks his steel fist upon coil or anvil, another can be quickly supplied. These huge heads alone are as big as a sugar-hogshead, and come down upon the hot iron with an energy of more than a thousand foot-tons. By the courteous permission of Major E. Maitland, Superintendent of the Royal Gun Factories, we are enabled to present our readers with the view of the monster hammer which forms the Plate III.

Mr. Condie, in his form of steam hammer, utilizes the mass of the cylinder itself to serve as the hammer. The piston-rod is hollow, and forms a pipe, through which the steam is admitted and discharged, and the piston is stationary, the cylinder moving instead—between vertical guides. A hammer face is attached to the bottom of the cylinder by a kind of dovetail socket, so that if the striking surface becomes injured in any way, another can easily be substituted. The massive framework which supports the moving parts of Condie’s hammer has its supports placed very far apart, so as to leave ample space for the handling of large forgings.

Fig. 14.Merryweather’s Steam Fire-Engine.

PLATE III.

THE GREAT STEAM HAMMER, ROYAL GUN FACTORY, WOOLWICH.

29

Fig. 15.A Foundry.

IRON.

“Iron and coal,” it has been well said, “are kings of the earth”; and this is true to such an extent that there is scarcely an invention claiming the reader’s attention in this book but what involves the indispensable use of these materials. Again, in their production on the large scale it will be seen that there is a mutual dependence, and that this is made possible only by means of the invention we have begun with; for without the steam engine the deep coal mines could not have the water pumped out of them,—it was indeed for this very purpose that the steam engine was originally contrived,—nor could the coal be efficiently raised without steam power. Before the steam engine came into use iron could not be produced or worked to anything like the extent attained even in the middle of the nineteenth century, for only by steam power could the blast be made effective and the rolling mill do its work. On the other hand, the steam engine required iron for its own construction, and this at once caused a notable increase in the demand for the metal. Once more, the engine itself supplies no force; for without the fuel which raises steam from the water in the boiler it is motionless and powerless, and that fuel is practically coal. In consequence of thus providing power, and also of supplying a requisite for the production of iron, coal has acquired supreme industrial importance, so that all our great trades and places of 30densest population are situated in or near coal-fields. But what we have further to say about coal may be conveniently deferred to a subsequent article, while we proceed to treat of iron, and of the contrivances in which it plays an essential part.

Iron has also been called “the mainspring of civilization,” and the significance of the phrase is obvious enough when we consider the enormous number and infinite variety of the things that are made of it: the sword and the ploughshare; all our weapons of war and all our implements of peace; the slender needle and the girders that span wide rivers; the delicate hair-spring of the tiny watch and the most tenacious of cables; the common utensils of domestic life and the huge battle-ships of our fleets; the smoothest roads, the loftiest towers, the most spacious pleasure palaces. Such extensive applications of iron for purposes so diverse have been rendered possible only by the greater facility and cheapness of production, together with the better knowledge of the properties of the substance and increased skill in its treatment, that have particularly distinguished our century. Apart again from the constructive uses of iron, it enters essentially into another class of inventions of which the age is justly proud, namely, those which utilize electricity in the production of light, mechanical power, and chemical action; for it is on a quality possessed by iron, and by iron alone, that the generation of current by the electric dynamo ultimately depends. This peculiar property of iron, which was first announced by Arago in 1820, and has since proved so fertile in practical applications, is that a bar of the metal can, under suitable conditions, be instantly converted into the most powerful of magnets, and as quickly demagnetized. What these conditions are will be explained when we come to treat of electricity.

Fig. 16.Aerolite in the British Museum.

Besides the unique property of iron just referred to, and its superlative utility in arts and industries, there are other circumstances that give a peculiar interest to this metal. It is the chief constituent of many minerals, and traces or small quantities are found in most of the materials that make up the crust of the earth; it is present also in the organic kingdoms, being especially notable in the blood of vertebrate (back-boned) animals, of which it is an essential component. Notwithstanding its wide diffusion, iron is not found native, that is, as metal, but has to be extracted from its ores, which are usually dull stony-looking substances, as unlike the metal as can be conceived. In this respect it differs from gold, which is not met in any other than the metallic state, in the form of nuggets, minute crystals or branching filaments, and from metals such as silver, copper, and a few others which also are occasionally found native. It is true that rarely small quantities of metallic iron have been met with in the form of minute grains disseminated in volcanic rocks; but in contrast with the practical absence of metallic iron from terrestrial accessible materials is the fact that masses of iron, sometimes of nearly pure metal, occasionally descend upon the earth from interplanetary space. These are aerolites, of which there are several varieties, some consisting only of crystalline minerals without any metallic iron, others of a mixture of minerals and metals, but the most common are of iron, always alloyed with a small quantity of nickel, and usually containing also traces more or less of a few other metals and known chemical elements. The iron in some specimens has been found to amount to 93 per cent. of the whole. These aerolites, or meteorites, as they are also 31called, are of irregular shape and vary greatly in size, which however is sometimes very considerable: one found in South America was calculated to weigh 14 tons, another discovered in Mexico, 20 tons. There is in the British Museum a good specimen of an iron meteorite, which is represented in Fig. 16, where it will be observed that a portion has been cut off to form a plane surface, which when polished and etched by an acid, reveals a crystalline structure quite peculiar and distinctive, so that such meteorites can be recognized with certainty, even if they did not possess surface characters which are easily observed and identified when once a specimen has been examined. The fall of meteorites to the surface of the earth is comparatively rare, but it has been witnessed by even scientific observers; as when Gassendi, the French astronomer, saw in Provence the fall of a meteorite weighing 59 lbs. In the Transactions of the Royal Society for 1802 may be found a detailed account of an instance in England of the fall which took place in Yorkshire, on the 13th December 1795, of a stone 56 lbs. in weight. Aerolites become ignited or incandescent by reason of the great velocity with which they 32pass through the atmosphere, whereby the air in front of them is condensed and heated, the heat often being sufficient to liquefy or even vaporize the solid matter. The so-called shooting stars are with good reason believed to be nothing but such incandescent aerolites, and the aerolites themselves are regarded as small asteroids, or scattered planetary dust, portions of which occasionally coming within the sphere of the earth’s attraction are drawn to its surface. Meteoric iron is too rare to be of any value as a source of iron, but certain specimens have been found in which the metal was malleable and of excellent quality. From such meteorites the natives of India and other places have, it is said, sometimes forged weapons of wonderful temper and keenness, and we may well imagine that when such weapons have been made from iron that had actually been observed to fall from the sky, they would be regarded as endowed with magical powers, so that we may perhaps ascribe to such circumstances the origin of some of the legends about enchanted swords, etc. It is significant also that in some Egyptian inscriptions of the very highest antiquity, the word indicating iron has for its literal meaning stone of the sky.

But as nature has hardly provided man with the metal iron, he has been obliged to find the art of extracting it from substances which are utterly unlike the metal itself. In this case, as in many others, the art has been discovered and practised ages before any scientific knowledge of the nature of the processes employed had been acquired. The idea prevails that there are such difficulties in extracting this metal; that elaborate and complex appliances, not unlike those in use in modern times, were requisite for the purpose; and therefore that the use of iron is compatible only with a somewhat late period in man’s history, and implies a comparatively advanced stage of civilization. Now there undoubtedly are facts which tend to confirm this view; for instance, the Spaniards who first colonized North America found the natives perfectly familiar with the use of copper, but without any acquaintance with iron, although the region abounded with the finest ferruginous minerals; and, again, the archæologists who have examined the relics of ancient civilizations and of pre-historic peoples about the shores of the Mediterranean, find in the earliest of these relics weapons and implements of rudely chipped stones, followed later by the use of better-shaped and polished stones; hence the periods represented by these, they have respectively designated by the terms palæolithic and neolithic—the old and the new stone ages. At some later time the stone of these implements was gradually replaced by bronze, which is a mixture of copper and tin, while as yet iron does not occur in any form among the remains. In the latest layers, however, articles of iron are found, and it is inferred that this metal came into use only after bronze had been known for an indefinite period; hence these later pre-historic periods have come to be respectively called the bronze age and the iron age. No doubt this succession really occurred in the localities where the observations were made, but it would not be justifiable to assume that the same was the case in every part of the world, for much would depend on such circumstances as the presence or absence of the essential minerals. We may also set against the supposed difficulty of obtaining iron from the ores, the still greater complexity of the methods required for the production of copper and of tin. Besides this is the fact that the ores of tin are found but in very few places in the world, and of these only the Cornwall mines, so well known 33in ancient times, would be likely to furnish a supply to the places where pre-historic bronzes are found; this implies that navigation and commerce must have already made considerable progress. On the other hand, iron has been produced and worked for untold ages by the negro races all over Central Africa, and the method of treating the ore has no doubt been that which is there still practised by certain scarcely civilized tribes, and it is as simple as any metallurgical operation can possibly be, requiring merely a hole dug in a clay bank, wherein the fuel and minerals are piled up, and the mere wind supplies sufficient blast to urge the fire to the needful temperature, or air is blown in from rude bellows made of a pair of skins alternately raised and compressed. These very primitive furnaces have in some places developed into permanent clay structures, seven or eight feet in height. The natives of Central Africa have therefore long known the method of extracting iron, as well as of forging and casting it.

The nature and value of what has been done during the century in the treatment of iron would not be intelligible without some description of the ordinary processes of extracting the metal from the ores; and a scientific understanding of these implies some acquaintance with chemistry. Not because metallurgy has been developed from chemistry, for the fact is rather the reverse; indeed, as we have seen, the art of extracting iron from its ores was practised ages before chemistry as a science was dreamt of. Although we may assume that many of our readers have sufficient knowledge of chemistry to attach distinct ideas to such few chemical terms as we shall have occasion to use, yet it may be of advantage to others to have some preliminary notes of the character of the chemical actions, and of some properties of the substances that will have to be referred to. It is certainly the case that people in general, and even people very well informed in other subjects, have but the vaguest notions of the nature of chemical actions, and of the meaning of the terms belonging to that science. For example, one of our most popular and justly esteemed writers, treating of the very subject of iron extraction, calls the ore a matrix, thereby implying that the iron as metal is disseminated in detached fragments throughout the mass, which is a conception inconsistent with the facts. The reader will be in a more advantageous position for understanding the relation of the ores of iron to the metal, if he will follow in imagination, or still better in reality, a few observations and experiments like the following—of which, however, he is recommended not to attempt the chemical part unless he is himself practically familiar with the performance of chemical operations, or can obtain the personal assistance of someone who is. Taking, say, a few common iron nails, let him note some obvious properties they possess: they have weight—are hard and tough so that they cannot be crushed in a mortar—are opaque to light—if a smooth surface be produced on any part, it will show that peculiar shiny appearance which is called metallic lustre, in this case without any decided colour—they are not dissolved by water as sugar or salt is—and are attracted by a magnet. If several of the nails be heated to bright redness they may be hammered on an anvil into one mass, and this may be flattened out into a thin plate, or it may be shaped into a slender rod and then drawn out into wire; or otherwise the nails may be converted into the small fragments called iron filings. In these several forms the nails, as nails, will have ceased to exist; but the material of which they were formed will remain 34unchanged, and each and every part of it however large or small will continue to exhibit all the properties noted above as belonging to the substance of the nails, which in the cases supposed has undergone merely physical change of shape. Treating our nails in yet another way, we may proceed to subject them to a chemical change, by an experiment very simple in itself, but involving certain precautions, by neglect of which the tyro in chemical operations would incur some personal risks; these might however be obviated by using only very small quantities of the materials (a mere pinch of iron filings and a few drops of sulphuric acid), when the results would still be sufficiently observable. A few of the iron nails having been placed in a flask of thin glass, we pour upon them a mixture of oil of vitriol (sulphuric acid) and water, which has previously been prepared by gradually adding 1 measure of the acid to 5 measures of water. The action that takes place is greatly accelerated by heat, and indeed the contents should be heated to boiling by standing the flask on a layer of fine sand spread on an iron plate and gently heated from below. The nails will soon disappear, being completely dissolved by the acid liquid, and the turbid solution should be filtered through filtering paper as rapidly as possible and while still hot. This turbid and dirty looking condition is due to foreign matters in the nails, for these never consist of pure iron. The filtered liquid is set aside to cool in a closed vessel, in which after a time will be found a deposit of crystals of a pale bluish-green colour. The liquor above these having been poured off, the crystals are to be rinsed with a very small quantity of cold water, and then dried between folds of blotting-paper, after which they are ready for examination. The quantity of the diluted acid put into the flask should have a certain proportion to the weight of the nails; about 5 fluid ounces to 1 ounce of iron will be found convenient, for if less is used the nails will not be entirely dissolved, and an excess will tend to keep the crystals in solution instead of depositing them when cold. The nails—as such—will now have passed out of existence: can we say that the iron that formed them exists in the crystals? Certainly not as the metal iron, for every property of the metal will have disappeared. The crystals are brittle, can be crushed in a mortar—they are translucent—they show no metallic lustre, but only glassy surfaces—they are readily dissolved by water—they are not attracted by a magnet. The most powerful lens will fail to show the least particle of iron in them; they have in their properties no assignable relation to the metal of the nails, but are matter of quite another sort; and be it noted that this entire otherness is the special and characteristic sign of chemical change. So complete is the transformation in the case we have been considering that it would never have been said that iron was contained in these crystals, but rather that the metal had for ever passed out of existence, but for one circumstance; and that is, that by subjecting the crystals to certain processes of chemical analysis we can again obtain from them the iron in metallic state. Nay more, we should find the weight of metal so obtained to be exactly equal to that of the pure iron dissolved from the original nails, supposing of course that we operated upon the whole of the crystalline matter so produced. The inference therefore is that although every property of the iron appeared to be absent from the crystals, the iron entering in them retained there its original weight, and the correct statement of the change would be, that in the crystals the iron had lost all its original properties SAVE ONE, namely, its weight, or gravitating force, if we choose to call it 35so, a property belonging to it in common with every material substance. Chemical analysis can also separate from the crystals their other constituents and weigh them apart—so much water and so much sulphuric acid—and when to these weights that of the iron is added, the sum exactly makes up the weight of the crystals.

A still simpler experiment, which may be performed by anyone with the greatest ease, may serve as a further illustration of the profound nature of the change in the properties of bodies brought about by chemical combination, and it will also serve as the occasion of directing attention to a remarkable circumstance that invariably characterizes such changes, and one that should always be present in our minds when we are considering them. A yard of flat magnesium wire can be bought for a few pence, and after its metallic character has been observed in the silvery lustre disclosed by scraping the dull white surface, a few inches is to be held vertically by a pair of tongs, or by inserting one extremity in a cleft at the end of a stick, then the lower part is brought into contact with a candle or gas flame. The metal will instantly burn with a dazzlingly brilliant light, and some white smoke (really fine white solid particles) will float into the air; but if a plate be held under the burning metal, some of the smoke will settle upon it, together with white fragments that have preserved some shape of the metallic ribbon, but which a touch will reduce into a fine white powder, identical with the well-known domestic medicine called “calcined magnesia”—a substance totally different from the metal magnesium. The reader will scarcely require to be told that in this burning the metal is entering into combination with the oxygen of the air—by which that invisible gas somehow becomes fixed in these solid white particles, so entirely unlike itself. But this experiment might be so arranged that the quantities of magnesium and oxygen entering into the magnesia could be weighed. For this purpose special appliances would be required in order to ensure complete combustion of the metal, for in the experiment as just described some small particles are liable to be shielded from the oxygen by a covering of magnesia, and the arrangement would have to be such that the whole of the white powder could be gathered up and weighed. In the absence of such appliances, and of a delicate balance, together with the skill requisite for their use, the reader must for the time be contented to take our word for what would be the result. In every experiment the magnesia would be found heavier than the metal burned in the proportion of 5 to 3; in other words, magnesia always contains (so the phrase runs) 3 parts of magnesium combined with 2 of oxygen: never more nor less. A definite proportion between the weights of the constituent substances characterizes every chemical combination, and when this is once determined in a single sample of the compound, it is determined for every portion of the same, wherever found or however produced. But each compound has its own particular proportion, that is, the quantitative relations are different for each. For example, the two constituents of water, hydrogen and oxygen, are combined in the ratio of 1 to 8, etc.; and oxygen combines with metals in a ratio different in each case. Then occasionally the same ratio of constituents occurs in compounds of different composition. The elementary student is apt to suppose that this is because of the law which he finds stated, probably in almost the first page of his text-book: “Every compound contains its elements in definite and invariable proportions”; and even well-educated people entertain 36the idea of the fact being “governed by” or “obeying” the law just quoted,—a misconception arising from the other use of the word “law,” as signifying an enactment. The real case however is the converse; namely, that a multitude of facts like that above stated have governed the law, and caused it to be what it is—the general statement of many observed facts.

We have assumed that the reader’s chemical knowledge had already made him aware that in every case of ordinary combustion the oxygen of the atmosphere is in the act of entering into combination with the burning body: as with the magnesium, so with a coal fire, a gas flame, or a burning candle; only in these last cases the products of the combustion pass away invisibly. The candle by burning disappears from sight, but its matter is not lost, and as in the case of magnesium, the compounds it forms weigh more than the unburnt candle. The experiment is commonly shown in courses of elementary lectures on chemistry, of so burning a candle that the invisible products are retained in the apparatus, instead of being dissipated in the atmosphere, and the increase of weight of the burnt candle over the original one is demonstrated by the balance. Important as is the part played by oxygen in all chemical actions on the earth, the composition of the atmosphere was not understood until the end of the eighteenth century, and it was well on into the nineteenth before the quantities of its constituents were accurately determined. Now everyone knows that air is mainly made up of a mixture of the two gases oxygen and nitrogen. A mixture of two or more things is very different from a chemical combination of them; for in the former each ingredient retains its own properties. (See Air in Index.) Nitrogen being an inert gas that takes no part in combustion, or in the ordinary chemical actions of the air, acts therein simply as a diluent of the oxygen. It is necessary in relation to our present subject to bear this in mind, as well as the relative quantities of the two gases in air. For our immediate purpose we may neglect the minor constituents of air—such as watery vapour, carbonic acid, etc., of which the total weight does not exceed one hundredth part of the whole—and consider air as a mixture of 23 parts by weight of oxygen with 77 of nitrogen, or calculated in volumes, 21 measures of oxygen with 79 of nitrogen. Compounds of oxygen with nearly every one of the other seventy or more chemical elements are known, and these compounds, which are called oxides, are arranged by chemists under five or six classes, forming as they do basic radicles, acid radicles, saline oxides, etc. With some of these compounds belonging to different classes, we must make acquaintance after noticing the elementary substance with which the oxygen is united.

We begin with carbon, which forms the chief constituent of all our combustibles. Some specimens of graphite, plumbago, or “blacklead” consist of almost pure carbon (98 per cent.), and some varieties of wood charcoal exceptionally contain 96 per cent.; but in ordinary charcoal the percentage is much less. Coal, the most familiar of our solid fuels, varies greatly in composition, carbon being the predominating constituent, in amount from 57 to 93 per cent. Coke, another fuel much used in metallurgical operations, is made by heating coal without access of air, when a large quantity of gaseous substances is expelled. Coke burns with an intense and steady heat without emitting any visible smoke, but it does not ignite as readily as coal. Carbon forms two different compounds with oxygen: both are invisible gases, but they differ in the proportions of the constituents, 37and present different properties. When carbon (coal, coke, or charcoal) is completely burnt, that is, with an abundant supply of air, the product is carbonic acid gas, in which 3 parts of carbon are combined with 8 of oxygen: when, on the other hand, the carbon is burnt with a sufficiently restricted access of air, the result is carbonic oxide gas, in which 3 parts of carbon are united with only 4 of oxygen. The reader will here observe that the former contains just twice as much oxygen as the latter for the same quantity of carbon. This fact and numberless others like it are expressed or summed up by another law of chemical combination which states that when two elements combine in several different proportions these are invariably such that the ratios in the several compounds will be found to have exact and simple numerical relations; that is, such as may, when reduced to their lowest terms, be expressed by the simple integers 1, 2, 3, etc., as 1 : 2, 3 : 2; ... 8 : 9, etc. It comes to the same thing if we compare together the weights A and A´ which are united in each compound with any one identical weight of B, giving of course the ratio A : B ÷ A´ : B. For instance, in the case just given, of carbon and oxygen, 3 : 4 ÷ 3 : 8 = 2 : 1. This, which is simply stating the facts, is called the law of multiple proportions. On a later page will be found another illustration (see Index, Nitrogen and Oxygen Compounds), and its expression in terms of the atomic theory, which goes behind the facts (so to speak), but is extremely useful by comprehending many other groups of facts in chemistry and in other sciences. Carbonic acid gas is of course incombustible, but carbonic oxide gas burns by uniting with the additional proportion of oxygen and becoming carbonic acid. On the other hand, carbonic acid gas passing over red-hot coals takes up from them the additional proportion of carbon, and is, we may say, unburnt into carbonic oxide. When we see a pale blue flame flickering over the bright embers in a fire grate, it is carbonic oxide burning back again by taking more oxygen from the air above the coals. Carbonic oxide combines directly with two or three of the metals, as, for instance, it forms a volatile compound with nickel, at a certain temperature, and this is decomposed again at a higher temperature. The like takes place with iron, although in very small quantities, but the observation throws some light on the processes of reduction. Carbonic oxide is neither acid nor basic, but carbonic acid is an acid oxide, and as such unites with oxides of the basic class to form another range of compounds. Thus, for example, the oxide of the metal calcium is quicklime, which is strongly basic, and this directly combines with carbonic acid, forming a neutral substance called in systematic chemistry calcium carbonate, or more commonly but less correctly, carbonate of lime, familiar to everyone in the compact state as limestone, and marble, and in a more or less pulverent condition as chalk. When any of these is heated to redness, carbonic acid is expelled and quicklime remains. Like most oxides, quicklime forms a compound with water, the combination being attended with the extrication of much heat, the compact quicklime swelling and crumbling into slaked lime. The chemist’s term for a compound of a basic oxide with water is hydrate, while that of an acid oxide with water is for him properly an acid, or in order to particularly distinguish this class, an oxy-acid. It was however the older practice to give the name of acid to the oxide alone, and this naming having found its way into popular language is much more familiar to the non-scientific reader. The systematic names of the two compounds of carbon and oxygen are 38carbon monoxide and carbon dioxide, but we shall use here the more familiar terms carbonic oxide and carbonic acid.

We have now to call attention to a substance which contributes by far the largest part to the solid crust of our globe. It is called silica, from silic-, the Latin word for flint (without case suffix): it is seen in flint, and very pure in rock crystal, quartz, agate, and calcedony. It forms the essential part of every kind of sand and sandstone, and is the principal ingredient of clay, granite, slate, basalt, and many other minerals. Silica is the oxide of a quasi-metal called silicon, which can be obtained from silica with difficulty, and only by roundabout processes, presenting itself in different conditions according to the process used. Silica is an acid oxide, and it readily unites with most of the basic oxides when heated with them, forming a class of compounds of different properties which are much modified in admixtures containing two or more. Very few of these silicates are soluble in water, most of them are not: they are all fusible at various temperatures, except silicate of alumina, of which fire-clay is chiefly constituted. Alumina, it should be stated, is the oxide of the metal aluminium. The silicates of lime and of magnesia fuse only with great difficulty; but the silicates of iron and of manganese are easily fused, and silicate of lead still more so. Glass is a mixture of silicates, often of lime, soda, and alumina; sometimes of lead and potash mainly; porcelain and pottery consist chiefly of silicate of alumina with varying proportions of silicates of iron, of lime, etc.

It now remains only to mention two non-metallic elements that are nearly always present in crude iron, but which the metallurgist strives to eliminate, as they are in general very injurious to the quality of the material even when their amount is very small. The first is sulphur, well known as brimstone, also as flowers of sulphur, a yellow coloured solid, which burns in the air. The product of the combustion is an invisible gas of a readily recognized pungent odour: this is an acid-forming oxide containing equal weights of sulphur and oxygen. There is another oxide in which the weight of oxygen is one and a half times that of the sulphur, and this is the radicle of the very active sulphuric acid or oil of vitriol. Sulphur, like oxygen, unites with most of the other elements, forming compounds called sulphides. Of these the iron compound called pyrites is the best known, and its occurrence in coal prevents the use of that material as fuel in contact with iron or other metals. Phosphorus is an element that occurs naturally only in combination; in its separated state it is a very inflammable solid. It combines directly with other substances and is taken up by some fused metals in large quantities. In many cases a very small proportion of it existing in a metal greatly modifies the properties of that metal. Phosphorus forms several oxides, and these are radicles of powerful acids, among which is phosphoric acid that combines with basic oxides to form phosphates.

We have now, in the few last paragraphs, set before the reader the minimum of chemical knowledge that will enable him to follow the rationale of such processes of the modern treatment of iron and its ores as we can here give an outline of. Although there are numberless minerals from which some iron can be extracted, the name of iron ore is confined to such as contain a sufficient amount to make the extraction commercially profitable, and this requires that the mineral should be capable of yielding at least one-fifth of its weight. The ores are very abundant in many parts of the world, and they consist mainly of oxides and their hydrates, 39or of carbonate, or of carbonate mixed with clay and silicates, sometimes also with coaly matters in addition. The carbonate iron ores are often mixed with oxides. Each class of ore is liable to be contaminated with phosphates and with sulphur. The richest ore is the magnetic iron ore, which is found in enormous masses in Sweden, Russia, and North America. It is an oxide containing 72·41 per cent. of iron. Red hæmatite and specular ore are varieties of another oxide with 70 per cent. of iron: the former is a very pure ore when compact. It is found in Lancashire, Cumberland, and South Wales, and much has been imported from Spain, while America has abundant supplies near Lake Superior. Specular iron ore forms brilliant steel-like crystals which show the red colour of hæmatite only when scratched or powdered. Elba was famous for this ore, which occurs also in Russia and Sweden, and large deposits are met with in both North and South America. Brown hæmatite is a hydrate of the former, containing 60 per cent. of iron; it abounds in France and Spain, where some kinds are associated with a noteworthy quantity of phosphate of iron. Spathic or sparry iron ore is, when pure, a collection of nearly colourless transparent crystals, consisting of carbonate of iron; it contains about 48 per cent. of iron, and also some of the metal manganese, which last circumstance makes it, as we shall see, particularly suitable for producing certain kinds of steel—indeed it is sometimes called steel ore. Large beds of it occur in Styria and Carinthia. Clay iron stone, or clay-band, has been extensively mined in Britain. It is found abundantly in Staffordshire, Yorkshire, Derbyshire, and South Wales. It consists of carbonate of iron intimately mixed with clay. The quantity of iron in some samples falls as low as 17 per cent., but it rises with variations to as much as 50 per cent. Much of its importance arises from the fact of its occurring in beds alternating with layers of coal, limestone, and clay, so that the same pit is sometimes able to supply firebricks for building the furnace, fuel for the smelting, and limestone for the flux,—a combination of advantages that for long enabled iron to be produced in England cheaper than elsewhere. The like is true of the blackband ore, which, in addition to the same ferruginous composition as the last, contains also so much combustible or bituminous material that it can be calcined (roasted) without additional fuel. The deposits of blackband in Lanarkshire and Ayrshire, which were discovered only in 1801, have given great industrial importance to the district. Yet another British ore must be noticed, namely, the Cleveland ironstone of the North Riding of Yorkshire. This is a carbonate of a grey or bluish colour caused by the presence of a little iron silicate. It contains also a considerable amount of phosphorus.

How simple is the operation of obtaining iron from the ore has already been stated—that it is necessary only to surround lumps of ore by fuel in a fire urged by a natural or artificial blast, and then to hammer the mass extracted from the furnace so as to weld together the scattered particles of the metal, and at the same time squeeze out the associated slag and cinders, in order to obtain a coherent malleable piece, which can be reheated in a smith’s fire, and forged into any required form. It is no wonder therefore that iron was so produced by the ancient Britons; at any rate Cæsar found them well provided with iron implements and weapons. No doubt the Romans brought their more advanced skill to the working of the metal; but in the matter of treating the original ore, the methods they pursued on an extensive scale in Britain were of the 40rude kind already described. Indeed in localities where the Romans were known to have carried on their operations, the remains of their workings are almost always found on high ground, so that it may be inferred that they relied upon the winds to fan their fires, and their operations were incomplete and wasteful. The most extensive of them appear to have been in Sussex and Monmouthshire, in which last county there are places where the ground is in large areas covered by their cinders and refuse, and in this about 30 or 40 per cent. of iron occurs, so that for some centuries this material was found capable of being profitably reworked as a source of the metal. Iron continued to be produced in England during the middle ages with charcoal for fuel, but its export was forbidden, and whatever steel was required had to be imported from abroad. Afterwards German artisans were brought over for making steel, and soon afterwards the importation of shears, knives, locks, and other articles was prohibited. The native production of iron continued, and this consumed the forests so rapidly for the supply of charcoal, that various Acts were passed to restrain the iron-makers, in order to preserve the timber. In spite of these, the arts of smelting and working iron advanced apace: bellows were used for the blast, and then the works were brought down into the valleys, where water power could be employed to work them. The scarcity of charcoal fuel caused many attempts to supply its place with pit coal, but these met with small success, partly on account of the coal containing so much sulphur, and partly from the difficulty of obtaining with it a sufficiently high temperature, especially as the blowing apparatus was as yet very imperfect. At length, in the first half of the seventeenth century, the problem was solved by Dud Dudley, whose process was kept secret, but is believed to have consisted in supplying coal at the top of a higher furnace, in such a manner that the coal was converted into coke by the heat of the escaping gases before it reached the reducing zone of the furnace. This innovation was violently opposed by the charcoal smelters, who persecuted the inventor in every way, until their resistance was successful. But before the middle of the next century coke was regularly used in iron smelting, the process having been made successful by Darby at Coalbrookdale, and then many new applications of cast iron came into vogue. Coke being a substance burning less freely than charcoal, bellows were found inadequate to give the necessary blast, and were displaced by blowing cylinders, actuated at first by water wheels, but this uncertain and comparatively feeble source of power was soon superseded by the steam engine, the “fire engine,” for which, as we have seen, Watt obtained his patent in 1769. The furnaces were not then all engaged in producing the fusible metal now called cast or pig iron as are the huge blast furnaces we see at the present time. Indeed it was much to the disgust of the old iron smelter that occasionally his product turned out to be of the fusible kind, unworkable by the hammer, which therefore he regarded as worthless. At what date cast iron was first used is uncertain; but probably it was not long before the fourteenth century. The furnaces in use up to that time were small square walled-in structures only 3 or 4 feet high, and their effect would not greatly exceed that of a smith’s forge: but as improved blowing apparatus gave more power, they soon became enlarged into oval or round brick towers from 10 to 15 feet high, and they, like the small furnaces, could be made to yield either smith iron or steel by modifying the charge and the manner of applying the blast; while furnaces of dimensions exceeding a certain limit could no longer be trusted 41to turn out malleable metal, but they produced instead the cruder substance we call white pig iron, and this requires much subsequent treatment before it is converted into malleable or “merchant iron.” Nevertheless the demand for cast iron as such, and more particularly the adoption of improved methods of deriving malleable iron from it, caused further increase in the size and numbers of blast furnaces, until in the early part of our century 30 feet was not an unusual height, the highest one in England in 1830 attaining 40 feet. The total make of pig iron in England was in that year nearly 700,000 tons, perhaps about fifty times as much as it was a century before, and thirty years later (1860) it had risen to nearly 4,000,000 tons. These figures show the extraordinary expansion of the British iron manufacture in the earlier part of the century; and the still more extensive applications of iron during the next twenty years had the effect of almost doubling the produce in 1880, and of 42increasing also three-fold the amount of foreign metal imported, raising it to 2,500,000 tons. The reader will now, it is hoped, be prepared to follow with some interest a brief account of the principal inventions which have brought about results of such importance.

Fig. 17.Blast Furnace (Obsolete Type).

Fig. 18.Section and Plan of Blast Furnace (Obsolete Type).

Deferring for the moment any description of the latest blast furnaces, we invite his attention to Fig. 17, which represents the furnace used in the first half of our century, but which now is of an obsolete type, Fig. 18 being the section and plan of the same. The lower part of Fig. 17 shows 43where the molten metal has been allowed to run out of the furnace into channels made in dry sand; first a main stream, then branches to right and left, each of these with smaller offsets on each side of it. These smaller channels are the moulds for the pigs, so called because of the fancied resemblance of their position with regard to the branch that supplied them, to the litter of a sow. They are easily broken off from the larger mass, and then form pieces about 3 ft. long with a -shaped section, 4 in. wide, the weight being from 60 to 80 lbs. This is iron of the crudest kind, and though it is often referred to as “cast iron,” it is, as a matter of fact, not used in this state for any castings, except those of the very roughest and largest kind: a certain amount of purification is requisite in most cases. This is given by fusing the metal—along with some form of oxide and often other matters—in a cupola furnace, which is like a small blast furnace, being from 8 ft. to 20 ft. high and uses coke for fuel with a cold blast.

So far from being simply iron, pig contains a large and variable proportion of other matters amounting often to 10 or 12 per cent.; and these confer upon it its fusibility. The principal one is carbon, which is found in the metal partly in the state of chemical combination with it, and partly in the form of small crystals similar to those of graphite or plumbago, disseminated through the mass. When there is a comparatively small proportion of the carbon combined with the iron, the substance is grey, and it can be filed or drilled or turned in a lathe. In white cast iron the combined carbon predominates, or is sometimes accompanied by scarcely any graphitic carbon; it is brittle and so very hard that a file makes no impression. It fuses at a lower temperature than the other varieties. A third kind is the mottled cast iron, which shows a large coarse grain when broken, and distinct points of separate graphite particles; it is tougher than the others, and therefore when cannon were made of cast iron this variety was preferred. The following table giving the percentage composition of four samples of crude cast iron will show their diversities.

  White. White. Mottled. Grey.
Iron 88·81 89·304 93·29 90·376
Combined carbon 4·94 2·457 2·78 1·021
Graphite, or uncombined carbon ... 0·871 1·99 2·641
Silicon 0·75 1·124 0·71 3·061
Sulphur trace 2·516 trace 1·139
Phosphorus 0·12 0·913 1·23 0·928
Manganese 5·38 2·815 trace 0·834

The reader will observe that the last item in the table above is a substance that he has not yet made the acquaintance of, namely, manganese. This is a metal which in many of its chemical relations much resembles iron, and ferruginous ores usually contain a greater or less proportion of it. Manganese is of great importance in the manufacture of steel, as we shall presently see; but as a separate metal it has no application, and is obtainable in the metallic state with much difficulty. One of its oxides has however very extensive applications in the chemical arts, and others 44form acid radicles, which in combination with potash or soda give rise to useful products. The well-known “Condy’s fluid” is a solution of one of these.

We have seen how malleable iron or steely iron may be directly obtained from the ores, but it has been found that on the large scale it is necessary and more economical to operate on the pig iron produced by the blast furnaces in such a manner as to remove the greater part of the foreign substances.

Fig. 19.Section of a Reverberatory Furnace.

The first step in the conversion of the pig iron usually taken has been, and to a certain extent even is still, to remelt the metal in what is termed a finery furnace, a kind of forge in which a charcoal fire is urged by a cold blast, and so regulated that an excess of oxygen is supplied, or rather more than would suffice to convert all the carbon of the fuel into carbonic acid; although this is perhaps not absolutely necessary, as carbonic acid would itself supply oxygen by suffering reduction to carbonic oxide. At any rate the melted metal is exposed to an oxidizing atmosphere and constantly stirred. Many different arrangements of the furnace and details of the process have been used. For instance, where the finest quality of malleable iron was not aimed at, coke has been the fuel employed, and many shapes of furnaces, etc., have been contrived, and various additions of ores, oxides, etc., made to the charge, according to local practice and the nature of the crude iron. One marked effect of the operation is the final removal of nearly all the silicon, which is burnt or oxidized into silica, and this at once unites with oxide of iron, which is also formed, to produce a readily fusible slag of silicate of iron, and in the production of this silicate any sand attached to the pig will also take part. Much of the carbon, amounting sometimes to more than half, is also eliminated as carbonic oxide, and of what is left but little remains in the graphitic state. The action on the phosphorus is usually less marked, but there is always a notable reduction of the quantity. The sulphur is also lessened in some degree, although when coke is used, the fuel has the disadvantage of itself containing sulphur, phosphates, and other deleterious matters. Sometimes a little lime is added to the charge to take up the sulphur from the coke. The operation lasts some hours, the fused metal being frequently stirred with an iron rod, until it assumes a pasty granular condition, when the workman gradually collects it upon the end of the rod into a ball of about three-quarters of a cwt. in weight. These balls, or blooms as they are called, are removed from the furnace while still intensely hot, and at once submitted to powerful pressure by means of some suitable mechanical arrangement, the effect being to squeeze out the liquid slag and force the particles of metal together by which the whole becomes partially welded into a more compact mass. Then this mass is, while still hot, either hammered with gradually increased force of the strokes, or in the more modern practice, passed between iron rollers (these we shall presently describe), by which it is shaped into a bar. The bars are afterwards cut into lengths, reheated without contact of fuel, again hammered or re-rolled; and this process is several times repeated when the best product is required. During the first treatment of the blooms, and also in the subsequent hammering or rolling, the oxygen of the atmosphere acts on the surface of the glowing metal, so as to cover it with thin scales of oxide, and these, carried into the interior of the mass, will give up their oxygen to any residual silicon, carbon, etc., producing a little more slag, carbonic oxide, phosphate of 45iron, etc., which by the pressure of the hammers or rolls are ultimately forced out of the metal. It will be observed that in producing the pig iron the chemical action is the separation of oxygen from the metal, while conversely an oxidizing action is set up in the finery and subsequent treatment, in order to burn off the foreign ingredients. But this cannot be done without at the same time re-oxidizing some of the iron itself, of which therefore there is always a considerable loss, by its formation into slag (silicate), cinder, foundry scale (oxide), etc. The quantity of iron lost depends of course on many conditions, such as the care exercised in the operations, but it occurs in all the processes that have been devised for the conversion in question, even in the most modern: its amount may be taken to range between 10 and 20 per cent. The reader is requested to bear in mind the nature of the chemical actions that have just been described, for in even the most recently invented processes the principle is the same in nature and effect. So completely can the foreign elements be eliminated by this, or some analogous process, such as we shall presently mention, that the finest Swedish bar iron contains more than 99½ per cent. of the metal, and in some cases only a very little carbon and a mere trace of phosphorus remain, amounting together to less than 1 part in 2000. Such metal is made from very pure ore, containing no sulphur and scarcely any phosphorus, while charcoal is the fuel used in all the operations. As already mentioned, the objection to the use of coke is the sulphur, phosphates, and siliceous matters it contains. Toward the close of the eighteenth century an invention came into use which obviated the disadvantages of the cheaper fuel for converting crude iron. This was the puddling furnace, brought into use after much experimenting by Henry Cort in 1784. In it the pig iron is fused in a reverberatory furnace, the form of which will be understood from Fig. 19, which is a diagram showing such a furnace in section, where f is the fire, a an aperture at which the fuel is introduced, p the ash pit, b is a low 46wall of refractory material called the “bridge,” over which the flame passes, and is by the low arched roof reflected or reverberated downwards upon the charge, c, which is laid on a hearth, or iron floor, having spaces below it where air circulates in order to prevent it becoming too hot. In Cort’s original arrangement the bed of the hearth was formed of sand, which gave rise to much inconvenience by producing a quantity of the very fusible silicate of iron, that speedily attacked the masonry of the furnace, and therefore a very important improvement was devised some years later by S. B. Rogers, who made the bed of his furnace of a layer of oxide of iron, spread on a cast iron plate 1½ inches thick. In later times it has become usual to cover the iron hearth with certain other refractory mixtures varied according to circumstances, of oxide, ore, cinder, lime, etc. There is one of these mixtures significantly designated “bull-dog” by the workmen. We may mention here that it has, in more recent times, when very high temperatures are obtainable, been found unnecessary to cause even the flame to come into contact with the substances on the hearth, inasmuch as the heat radiated from the flame and the intensely heated roof of the furnace suffices, so that in consequence of this the roofs are now constructed nearly flat. In the puddling furnace the melted metal is constantly stirred, and no little skill is required to regulate the fire by the damper on the chimney, and to admit the proper amount of air to mix with the flame. The pig iron softens and melts gradually, until at length it becomes perfectly liquid, at which stage it swells up and appears to boil owing to the escape of carbonic oxide in numerous jets, which burn with the characteristic pale blue flame. The puddler then briskly stirs the mass to cause more complete oxidation of the carbon, silicon, etc., by bringing the superficially formed oxide of iron into the interior. As the iron loses its carbon, it assumes much the texture of porridge, consisting of pasty lumps of malleable iron implexed with the liquid slag (silicate of iron, etc.) which drips from the spongy balls as the puddler collects them at the end of his stirring rod, as in the finery operation. The next thing is to run the mass immediately between powerful rolls (puddling rolls) by which the slag is squeezed out, as before, and finally through the finishing rolls that shape it into bars or plates.

When a comparatively impure pig iron is used or when a better quality of malleable metal is desired, the crude iron is submitted to a preliminary treatment before puddling. This treatment, by a technical distinction, called refinery, is practically identical with the finery process already described, except that instead of being collected into blooms, the fluid metal is run out to form a layer 2 or 3 inches thick, and this, before becoming quite solid, is suddenly cooled by having water thrown over it, the result being a white, hard, brittle mass, which broken into pieces is ready for the puddling furnace.

The operation that has been described is known as hand puddling, in contradistinction to later methods in which it has been sought to substitute some form of machine that will produce the same result automatically, such as revolving furnaces, etc. It has been found difficult to maintain these in good working order, and in England at least mechanical puddling has never found much favour, but in the great iron works of Creusot, in France, large revolving furnaces were in use about 1880, which could turn out 20 tons of converted iron in 24 hours, whereas the old hand puddling furnaces could in the same period produce only 2½ or 3 47tons, with two sets of men, the puddler and one assistant. Of these mechanical furnaces it is unnecessary to give any account, especially as the puddling process itself has nearly gone out of use, having been superseded by more economical methods.

The use of rolls for treating the product of the puddling furnace, and for making it into bars, was also an invention of Henry Cort’s, for which he obtained a patent in 1783. This was in many respects an immense improvement on the older system of hammering; it is still practised, and by it shapes can be given to the metal scarcely possible on the older system, while the tenacity of the metal is increased by the uniformity given to the grain. The difference of chemical composition between cast and wrought iron the reader has already been made acquainted with, and there is quite as great a difference in their textures. The former, when broken across, shows a distinctly crystalline structure, which we may compare to that of loaf-sugar, while the latter exhibits grain, not unlike that of a piece of wood. This fibrous structure depends upon the mechanical treatment of the iron, and in rolled bars the fibres always arrange themselves parallel to the length of the bar. Fig. 20 shows this fibrous structure in a piece of iron where a portion has been wrenched off. Like wood, wrought iron has much greater tenacity along the fibres than across them; that is, a much less force is required to tear the fibres asunder than to break them transversely. Consequently, to obtain the greatest advantage from the strength of wrought iron, the metal must be so applied that the chief force may act upon it in the direction of the fibres. Near the beginning of our article on Iron Bridges (q.v.) the reader will find some illustrations of the very different resisting powers of cast and wrought iron.

Fig. 20.Fibrous Fracture of Wrought Iron.

Nothing in the way of inventions can be compared to those of Cort’s as to the effect they have had in promoting the iron industry, until we reach a period some years after the middle of our century; but we must not neglect to recognize the scarcely inferior importance of Rogers’ improvement. 48Singularly enough, neither of these men reaped any benefit from his inventions. Cort died in the last year of the eighteenth century, quite a poor man, having been supported only by a niggardly pension of some £160 from the Government, and leaving his family in indigent circumstances. Yet a most eminent authority on iron questions (Sir W. Fairbairn) estimated—some time about the middle of our era—that the two inventions of Cort’s alone, the rolling-mill and the reverberatory puddling furnace, had by that time added to the wealth of Great Britain by an amount equivalent to six hundred million pounds sterling. For many iron-masters had profited by these inventions, amassing very great fortunes, in some instances also acquiring titles of honour. Clearly to Cort and Rogers may be applied the sic vos non vobis saying.

We shall now turn to the improvements that have been effected in the blast furnace, and of these none perhaps has been more marked than that made by Neilson, when in 1828 he substituted heated air for the ordinary cold air that had before always supplied the blast. It will be remembered that the heat is due to the combination of only the oxygen of the air with the carbon of the coke, but the greater part of the air—the four-fifths of nitrogen—take no part in the action, beyond abstracting a large proportion of the heat; but when the air is heated to a high temperature before entering the furnace, the cooling effect of the nitrogen is greatly obviated, and consequently a much higher temperature is obtained at the place of combustion, and the requisite intensity of heat is at once produced, which is most effective in completing the fusion and separation from each other of the slags and iron, and also in accomplishing the reduction of the oxide. But Neilson found that the net result of burning some fuel to heat the air before entering the furnace was a great economy of the total fuel required for smelting the ore. He had to encounter many difficulties in carrying his invention into practice; the iron ovens first used for heating the air were rapidly oxidized; and when thick cast iron pipes were substituted, these were liable to leak at the joints on account of the expansions and contractions caused by changes of temperature. Then the new invention had as usual to contend with established prejudices and misconceptions; but it soon came into use in Scotland, where it effected a great saving; inasmuch as it was found possible to use with the hot blast raw coal of a certain kind, plentiful in Scotland, because the heat retained by the ascending gases sufficed to convert the coal at the top of the charge into coke.

It will be remembered that the active agent in the reduction of the ore is the carbonic oxide gas formed by the incomplete combustion of the carbon of the fuel; or what comes to the same thing, the absorption by carbonic acid first produced of another proportion of carbon. The carbon oxide robs the iron oxide of its oxygen to become itself changed into carbonic acid. In reality however the action is more complex than this in its chemical relations; for instance, metallic iron will under certain circumstances act conversely on carbonic acid, and rob it of half its oxygen. The net result of the reactions between carbon, iron, iron oxide, and these gases depends mainly upon the temperature and pressure and upon the relative quantities of each substance present. In the gases escaping from the blast furnace there is always a large quantity (nearly one-third) of carbonic oxide. At the blast furnaces in work during the first half of our century the combustible gases were allowed to burn to waste as they issued from the top of the furnace, in the manner shown in 49Fig. 17, and at night the flames used to form a weird and striking feature in the prospect of an iron-smelting region.

Instead of allowing the escaping gases to burn to waste, it became the practice about 1860, and so continues, to draw them off and burn them under steam boilers or use their flames for heating the blast. An effective method of withdrawing the gases is shown in Fig. 21, which is a section through the upper part of a smelting furnace, with the “cup and cone” arrangement. The mouth of the furnace is covered by a shallow iron cone a, open at the bottom, into which fits another cone b, attached to a chain c, sustained by an arm of the lever d, which is firmly held in position by the chain e, and is also provided with a counterpoise f. When the mouth of the furnace is thus closed, the gases find an exit by the opening g, seen behind the cones, and leading into a downward passage, through which they are drawn by the draught of a tall chimney to the place where they are burnt. The charge for the furnace is filled into the hopper a, and at the proper time the chain, e, is slackened when the weight of the material resting on the suspended cone overcomes that of the counterpoise, and the charge slides down over the surface of the cone b, which is immediately drawn up again by the counterpoise, so that the opening into the air is at once closed.

Fig. 21.Cup and Cone.

The march of improvement in the blast furnace has been characterized particularly in Britain and the United States by a great increase of dimensions, which is found to promote economy in fuel, etc. In the former country the furnace of the latter part of our century is commonly from 70 to 80 feet high, and some have even been built with a height of more than 100 feet, while in the States the tendency to build very high furnaces is still more marked. A single large furnace may turn out as much as 1,500 tons of pig iron in a week, and some in America, it is said, actually produce as much as 2,500 tons. The more usual output of a blast furnace is however much less than these amounts; but if we say only one-half, or even one-third of these quantities, a state of things is indicated very different from what obtained about 1837, when the best Welsh furnaces produced only 200 tons a week. If we go back to the beginning of the century, the difference is much more marked, for the 50blast furnaces of that period could turn out only about 30 tons in a week.

The proportions of fuel, ore, and limestone charged into the furnace vary greatly according to the composition of the ore, the quality of iron aimed at, and the practice of each manufacturer. It is usual previously to calcine the carbonate ores and others also, in order to expel the carbonic acid and the moisture, of which last all contain a considerable amount: and sometimes the limestone is mixed with the ore to undergo this preliminary process. The charge being conveyed from the roasting kilns to the blast furnace while still hot effects an obvious economy of fuel in the latter. In the case of hæmatite ore the quantities of materials in one charge may be something like 54 cwt. of ore, 9 cwt. of limestone, and 33 cwt. of coke. It is quite common to use mixtures of different kinds of ore, so as to modify the quality of the product according to particular requirements. The use of the limestone is to take up silica, and the slag is found to consist mainly of silicates of lime and alumina. The amount flowing from a blast furnace of course varies much according to the conditions, and is larger than would commonly be supposed; for the production of one ton of pig iron involves the production of from ½ to 1½ tons of slag.

Fig. 22 represents in section the later type of blast furnace, which of course is circular in plan. Its height may be taken as 80 feet, and the diameter at the widest part of the interior as 22½ feet, narrowed to 20 feet near the top. The lowest portion, C, is called the crucible, the bottom of which is the hearth, both formed of the most refractory materials obtainable. The conical widening, B, above the crucible is the boshes, and at the top is seen the “cup and cone” apparatus already described, A, surmounted by the short cylindrical iron mouth, through apertures in which the charges are tipped from the gallery, D, these having been raised there in small trucks by hydraulic or other elevators. The escaping gases leave the furnace by the exit, E, which leads into the “down-come,” G, and they are conducted from it to the “regenerative stoves” and dealt with as presently to be described. Our section represents the masonry of the furnace as sustained by pillars, P, at the outside of the lower part; these pillars support a strong ring of iron plates upon which the wall rests. This arrangement has the advantage of allowing the workmen the greatest freedom of access to parts about the crucible, which require much attention. Here, at the lowest part, is an aperture from which the liquid iron is allowed to run out every five or six hours, it being plugged in the meantime by clay and sand. The slag being much lighter than the iron, floats above it, and runs off at a higher level over the tympstone. Opening into the hearth are several orifices to admit the hot blast from the nozzles of the tuyères, which of course do not project into the furnace itself; but they are so near to the region of intensest heat that they would be rapidly destroyed unless they were surrounded by a casing through which a current of water is constantly running. The tuyères, of which there may be 3 or 5, are supplied from the pipe seen at K. The earlier plans of heating the air did not permit of a very high temperature being given to the hot blast, about 600° F. being the limit; but the “regenerative” stoves can supply a blast of more than 1,600° F., or not far below the melting point of silver. Another great increase has been in the pressure of the blast; 2 or 3 lbs. per square inch sufficed in the earlier practice; but the lofty 51modern furnaces have to be supplied with the blast at a pressure of 10 lbs. per square inch, and over. Even when comparatively low pressures were the rule, a large ironworks required much blowing power. The works formerly at Dowlais, in South Wales, for instance, had an engine of 650 horse-power for the blowing engine, in which a piston of 12 feet diameter moved in a cylinder 12 feet in length. The quantity of air that passes into a blast furnace amounts to thousands of tons per week, its weight being much greater than that of all the ore, coke, and limestone put together.

Fig. 22.Section of Blast Furnace.

It need scarcely be said that great care and expense are bestowed on the construction of these furnaces. Only the best and most refractory materials, such as firebricks, are used for the lining, and the exterior is a casing of solid masonry, strengthened with iron bands. When a new furnace is finished it takes a month or six weeks to put it into operation; but when this is done it will remain in action night and day continuously 52for a long period—perhaps for eight or ten years—before the necessity for repairs requires a “blow out.” And the blow out and restarting, without the cost of repairs, entail an outlay of several hundred pounds.

The gases leaving the throat of the furnace consist mainly of nitrogen and a little carbonic acid, together with about one-third of their volume of the combustible gases, carbonic oxide, and some hydrogen; but these last do not leave the furnace in an ignited state, because the oxygen there has already been consumed. They are conducted by the “down-come” pipe, G, Fig. 22, to a point at which, by means of a valve, they can be directed to one or other of two circular towers entirely filled with firebricks, arranged chequerwise, so as to form innumerable passages between them. The furnace gases are admitted at the bottom of the Cowper tower, or “regenerative stove,” into a flue to which a regulated quantity of air has access, and there they are fired: the flame ascending the flue to the upper part of the tower, thence descends, communicating its heat to the firebricks, which soon acquire a very high temperature, especially where the flame first enters, and the burnt gases leave the tower for a tall chimney, leaving most of their heat in the firebricks. When this action has continued for a sufficient time, the connection of the regenerator with the throat of the furnace is cut off, and the escaping gases are directed into the other regenerator, and at the same time the blast from the blowing engine is made to ascend among the firebricks of the first, where gaining increasing temperature as it ascends—the stove being hottest at the top—the air leaves the tower to be conducted to the tuyères at such high temperature as already mentioned. While the one regenerator is thus heating the blast, the other is in its turn accumulating heat from the flames of the escaping gases; and thus they are worked alternately, the action being constantly reversed after suitable intervals.

When iron is combined with a much smaller proportion of carbon than in cast iron, and contains little or no graphitic or uncombined carbon, we have the very useful compound known as steel. In the earlier half of the century it was customary to distinguish steel from malleable iron on the one hand, and cast iron on the other. If the compound contained from 0·5 to 1·5 per cent. of carbon, it was called steel by some authorities, while others extended these limits a little on either side. Later it was found that the presence of elements other than carbon can confer steely properties on iron, and indeed it is possible to have a metal containing no carbon, but possessing the characteristic properties of steel. Sir Joseph Whitworth proposed to classify a piece of metal according to its tensile strength, without any regard to either its chemical composition or its mode of manufacture: if it could not bear more than 30 tons per square inch it should be considered iron, but if it had a higher tensile strength, it should then be regarded as steel. To estimate the engineering value a figure depending upon the elongation or stretching of the specimen before breaking was to be added to the number of tons of the breaking load. This stretching power of steel is in some cases of as much importance as the tensile strength: the ordnance maker, for instance, considers a steel with a breaking strength of 53 tons under an elongation of 5 per cent. as for his purposes to be rejected: while a specimen showing a breaking strain of only 30 tons along with an elongation of 35 per cent., on 2 inches of length, he will regard as good. The tensile strength of steel depends in part on its composition, in part on the mode of manufacture, 53and in part on the subsequent treatment. The average tensile strength of a wrought iron bar per square inch of section is about 25 tons (30 is the maximum); while the like average for steel is 43 tons, and some kinds of cast steel will bear nearly 60 tons. Steel bars of a certain temper subjected by Sir Joseph Whitworth to a process of hardening in oil showed a tensile strength of even 90 tons per square inch. These figures will suffice to show the great utility of steel in structures and machines. But steel has besides a characteristic property which makes it extremely valuable in a great variety of applications, namely, its capability of being tempered. If a piece of steel is heated to dull redness and suddenly cooled by plunging it into cold water, it becomes so extremely hard that it cannot be acted on by a file; nay, its hardness may be made to rival that of the diamond, which is the hardest substance known. Now by a second operation this hardness can be reduced to any required degree: this is done by re-heating the metal to a certain moderate degree between 430° F. and 630° F. and again cooling it by immersion in some cooling medium. In this “letting down” process, it is the highest temperature that produces the greatest softening, and the properties of the tempered steel will depend upon the precise degree to which the metal has been reheated. For example, if the product be required for making into sword blades, or watch-springs, and to possess much elasticity, the proper temperature is between 550° F. and 570° F.; but if the steel is to be suitable for saws the temperature must range within a few degrees of 600° F., according to the fineness of the tool intended; a lower temperature would give a metal too hard for them to be sharpened with a file. On the other hand, sharp cutting instruments and tools for working metals are obtained hard by tempering at lower degrees than springs. In practice the index of the temperature is taken from the colour of the film of oxide that gradually forms on a polished surface of the metal as the heat is raised, and begins by a very pale yellow (at 430° F.), passing through deeper shades into brown, then through purple into deep blue (at 570° F.), etc. The reader will now see why watch and clock springs have their deep blue colour, and he can observe for himself the whole series of colours by very gradually heating a piece of polished steel over a small flame.

If we compare the chemical composition of wrought iron and of cast iron with that of steel as regards the content of carbon, we see at once that steel holds an intermediate position, so that if in the puddling furnace we could arrest the decarbonization at a certain point we should obtain steel; or if, on the other hand, we could put back into chemical combination with the decarbonized wrought iron a due percentage of carbon we should in that way also obtain steel. And it will be observed that the oldest primitive furnaces could not have failed sometimes to have produced steel as the net or final result of such actions. In fact, steel always has been and still is produced on one or other of these two principles, applied in divers ways, but severally and distinctly directed to that end. Of the many more or less modified processes of steel-making that have been in use, we need here but briefly mention a few which were the processes of the first sixty years of our century, and are to a considerable extent still in operation, although eclipsed in importance by two other processes that, since the date referred to, have been supplying the metal in enormously increased quantities, and which will have to be particularly described.

54The most usual of the older processes of steel-making, still carried on at Sheffield and elsewhere, is known as the cementation process: it consists in heating bars of the best wrought iron in contact with charcoal, at a high temperature, for three or four weeks. At Sheffield the iron bars and charcoal are packed in alternate layers into troughs 14 ft. long by 3½ ft. deep and wide, constructed of slabs of siliceous sandstone 6 in. thick. The last layer of charcoal at the top is covered to a certain depth with a layer of refractory matter, and the flames from a furnace beneath are made to envelop the stone troughs or pots, as they are technically called, for a period of a week or more according to the thickness of the bars operated upon. These are generally 3 in. broad and from five- to six-eighths of an inch thick. When it is found by withdrawing a test bar for examination that the operation is complete, the fire is gradually diminished and the whole allowed to cool slowly, which requires about a fortnight. Instead of only charcoal, a mixture of powdered charcoal or soot with a little salt has been used by some makers—which mixture, technically called cement powder, has given its name to the process. In some works 16 tons or more of iron are treated in one operation. The bars are found unchanged in form, but increased in weight by perhaps 27 lbs. per ton, for carbon has combined with the iron, being apparently transferred in the iron from one particle to another. The surface of the bars becomes rough and uneven from a multitude of blebs or blisters, and hence they are called blister bars, and the steel of which they now consist is named blister steel. In this conversion we may suppose that the iron at its outer surface first enters into combination with carbon taken from the carbonic oxide gas, which would be produced by combustion of the charcoal with the limited quantity of air in its interstices, and the oxygen thus set free would immediately seize again on the surrounding charcoal, and by repeated changes of this kind in which the oxygen acts as a carrier of carbon to the iron, in which it is transferred inwards from particle to particle. The cause of the blisters has been much discussed: probably the cause is the formation and escape of a volatile compound of carbon and sulphur at the surface of the soft metal; for it is known that nearly the whole of the little sulphur in the wrought iron disappears in the cementation process. Blister steel is never homogeneous, for near the surface it always contains more carbon than within; the bars are therefore broken up into short lengths which are carefully assorted, bound together with wire, heated, welded together under a hammer or by rolling, and finally formed into a bar, which is stamped with the outline of a pair of shears, and is then known as shear steel, because this product was generally found the most suitable for making the shears used in dressing cloth.

Another method of dealing with the blister steel is to charge crucibles or pots having covers with 50 or 100 lbs. weight of the broken-up bars, and subject the crucibles to a strong heat in a reverberatory furnace, when the metal melts, and at the proper moment the contents of a great number of pots are almost simultaneously poured into a mould to form an ingot. The result is a very uniform steel of the finest texture, known and highly esteemed as cast steel or crucible steel. This steel is much more fusible than iron, but less so than cast iron.

The production of steel by arresting at a certain stage the decarbonizing of cast iron in the puddling furnace requires much experience on the part of the workman, who has to learn when the desired point has 55been reached by certain indications, such as the appearance of the flame, or by the examination of a small sample of the fluid metal withdrawn and rapidly cooled. Various additions to the charge in definite proportions are generally made, such as scales of iron oxide, or a quantity of an oxide ore (hæmatite, etc.) or other materials, the most essential for a good product consisting of a little manganese in some form. The result is puddled steel; and this, like blister steel, can be converted into cast steel by fusion in crucibles, running into ingot moulds, and subsequent treatment by hammering, pressing, rolling, etc. In 1864 puddled steel was described as an article of great commercial importance, but this it soon lost by the introduction of simpler, cheaper, and more reliable processes. The methods and improvements proposed for the production of steel have been exceedingly numerous, as is shown by the records of the English Patent Office alone, which contain up to the end of 1856 specifications of ninety-two patents for different steel-manufacturing processes, while from 1857 to 1865, the epoch-marking period of steel making, seventy-four more patents were obtained for this purpose. It would be quite beyond our limits to make special reference to these, and to the numerous patents which have since been granted, but there is one of great importance in steel-making which must be mentioned, and that is the patent for the employment in the cementation process of carbide of manganese, taken out by J. M. Heath in 1839. This made England almost independent of the former large importations of Swedish and Russian iron, and it caused an immediate reduction of £40 in the price per ton of good steel, effecting a saving which up to 1855 is calculated at not less than £2,000,000. Heath was one of those who fail to benefit by their inventions, for his was boldly appropriated by another person who took advantage of a verbal flaw in the specification, and Heath did not obtain any redress from the law courts until, after ten years’ litigation, a majority of Exchequer judges reversed all the previous decisions against him (1853). In the meantime the man had died, but as the patent was about to expire his widow was on petition granted an extension of it for seven years. The nature of the influence of manganese on steel-making has not been fully explained, and there is some diversity of opinion on the subject, as it is said—on the one hand, merely to remove or counteract the injurious effects of sulphur or phosphorus; on the other, to impart to the steel greater ductility, strength, and power of welding, tempering, etc.

The manufacture of crucible or cast steel has been carried on at Essen in Prussia by the firm of A. Krupp & Co., on a scale surpassing anything attempted elsewhere,—theirs being the largest steel-works in the world, and remarkable for the variety and excellence of its products. It began in so small a way that it is said only a single workman was employed. To the Great Exhibition of 1851, at London, Krupp’s firm sent a block of crucible cast steel weighing 2¼ tons, a larger mass of the metal than had ever been shown before, and looked upon with no little astonishment, for at that time steel was a precious commodity, the price of refined steel ranging from £45 to £60 per ton. At the next London Exhibition, in 1862, the Essen Works showed a block of cast steel 20 tons in weight, and at the Vienna Exhibition of 1873, one of 52 tons. This casting, which was first made of a cylindrical shape, was forged into an octagonal form under an immense steam-hammer, larger than the Woolwich hammer described on a previous page, for the weight of the moving part is no less than 50 tons. This huge mass of cast steel was of the finest quality; the 56forging into the prismatic form was to show its malleability, for it was intended for the body of a gun to have a bore of 14 inches. Since the period referred to, ingots of more than 100 tons have been cast. That shown at Vienna was the product of some 1,800 crucibles, each containing 65 lbs. of melted steel, which had to be poured into the mould in a regular and continuous stream, so that the metal might solidify into a perfectly uniform mass. Such work can be done only by trained men, who act in regular ranks with military precision, and in pairs emptying their crucibles into channels previously assigned, then filing off to the other end of the rank to receive another crucible, while the pair of men who were behind are pouring out theirs, and so on in succession. The crucibles are emptied into a number of channels formed of iron lined with fire-clay, and leading down into the mould. Many precautions have to be taken to ensure the regular progress of the operations, and all the time required to fill the huge moulds may be counted by minutes.

The headpiece to our chapter on Fire-Arms gives but a very inadequate idea of the magnitude of the Essen Works about 1870. A better notion will be obtained from a few figures which we select from a list giving some of the contents of the Essen Works in 1876. There were 1,109 furnaces of various kinds, of which 250 were for smelting; 77 steam hammers, 294 steam engines, 18 rolling mills, 365 turning lathes, and 700 other machine tools; 24 miles of ordinary gauge railway for traffic within the works; together with 10 miles of narrow gauge railway; 38 miles of telegraph lines, with 45 Morse apparatus, etc. (J. S. Jeans’ Steel: its History, etc., 1880). These figures belong, be it observed, to the state of things in 1876; but we learn from a later authority that in 1894 these works employed 15,000 men, and we must suppose that the plant has been proportionately increased since the earlier period, when 10,000 men were employed.

In the year 1854 a regular system of records began to be kept of the amounts of coal and ores raised in Great Britain, and also of the quantities of the various metals produced. These show that in 1894 very nearly three times as much coal was raised as in 1854, and that in the same period the quantity of British pig iron smelted annually had increased four-fold; these increases look small when compared with the expansion of the steel production in Britain within the same period of forty years, for this had enlarged thirty-fold. This extraordinary development is attributable to the introduction of two processes by either of which various steels of excellent quality, and adapted to a great range of applications, can be produced cheaply and with certainty. These processes are respectively known as the Bessemer and the Open Hearth, and the reader should observe that with the main principles involved in these he has already been made acquainted.

Henry Bessemer, who first saw the light in England in 1813, may be said to have been born an inventor, for his father was one before him—a Frenchman employed in the royal mint at Paris, afterwards appointed by the Revolutionary authorities to superintend a public bakery; on an accusation of giving short weight, thrown into prison, from which, and probably from the guillotine, he escaped, and found employment in the English mint. Subsequently he devised some notable improvements in the art of producing letterpress type, and for many years carried on a prosperous business as a typefounder. The son developed inventive faculties at a very early age: in lathe engraving, dies, dating stamps, 57etc. His name became familiar to everyone by his production of the metallic powder long known as “Bessemer’s Gold Paint.” It became known to Bessemer that the raw material of this substance, which was then sold at £5, 10s. per lb., really cost only about one shilling per lb., and he set himself to discover its composition and mode of manufacture. He succeeded in this so well that he could produce the article at the insignificant cost of four shillings a pound, and his first order for a supply of it was at the rate of £4 per lb., and the business was continued, realising profits of something like 1,000 per cent. at first. For this article no patent was taken out, but Bessemer himself, assisted by two trustworthy workmen, carried on the manufacture in secret, and he some time afterwards rewarded the fidelity of his men by handing over the business to them as a free gift. Then he took out patents for improvements in the manufacture of oils, varnishes, sugar, plate glass, etc. Several of his machines for these purposes were shown at the London Exhibition of 1851. Bessemer is said to have obtained altogether some 150 patents, including those granted for inventions connected with our subject. He may be regarded as the type of the very fortunate inventor, since on the patents of the one process we are going to describe he ultimately obtained royalties to the value of more than £1,057,000, and this irrespective of profits derived from commercially working it himself.

At the time of the Crimean War, Bessemer had some experiments made at Vincennes with cylindrical projectiles he had devised for firing from smooth-bore guns, yet so as to impart to the projectile at the same time rotation about its axis. The experiments were successful, but it was pointed out that the guns of cast iron then in use would not bear heavy projectiles, and he was induced, at the suggestion of the Emperor Napoleon III., to undertake some researches with the view of finding metal more suitable for artillery. Bessemer, having then little knowledge of the metallurgy of iron, applied himself on his return to England to the study of the best books on the subject, visited the principal iron-working districts, and began a series of experiments at a small experimental installation he set up in London. There, after repeated failures, he did at length succeed in producing a metal much tougher than the cast iron then used, and a small model gun was submitted to the Emperor, who encouraged Bessemer to persevere with his experiments; which he did, though the expense was a great tax on his capital, continued as the experiments were for two years and a half. But by this time he had acquired a knowledge of many important facts, and these gradually led him to the experimental realization of the idea he had conceived, but only after many trials in which several thousand pounds were expended. At length the agenda of the British Association for the Cheltenham meeting of 1856 announced that a paper would be read by H. Bessemer, entitled “The Manufacture of Iron and Steel without Fuel.” It will be easily understood that a title in such terms would give rise to much derisive incredulity; and we may imagine the iron-masters on that occasion crowding into Section G, while asking each other in the spirit of certain philosophers of old, “What will this babbler say?” Some of what he did say may here be quoted, as at once explanatory and historically memorable.

“I set out with the assumption that crude iron contains about 5 per cent. of carbon; that carbon cannot exist at a white heat in the presence 58of oxygen without uniting therewith and producing combustion; that such combustion would proceed with a rapidity dependent on the amount of surface of carbon exposed; and lastly, that the temperature which the metal would acquire would be also dependent on the rapidity with which the oxygen and carbon were made to combine; and consequently, that it was only necessary to bring the oxygen and carbon together in such a manner that a vast surface should be exposed to their mutual action, in order to produce a temperature hitherto unattainable in our largest furnaces.

Fig. 23.Experiments at Baxter House.

“With a view of testing practically this theory, I constructed a cylindrical vessel of 3 ft. in diameter and 5 ft. in height, somewhat like an ordinary cupola furnace (see Fig. 23). The interior is lined with firebricks, and at about 2 in. from the bottom of it I inserted five tuyère pipes, the nozzles of which are formed of well-burned fire-clay, the orifice of each tuyère being about three-eighths of an inch in diameter; they are so put into the brick lining (from the outer side) as to admit of their removal and renewal in a few minutes, when they are worn out. At one side of the vessel, about half-way up from the bottom, there is a hole made for running-in the crude metal, and on the opposite side there is a tap-hole, stopped with loam, by means of which the iron is run out at the end of the process. In practice this converting vessel may be made of any convenient size, but I prefer that it should not hold less than one nor more than five tons of fluid iron at each charge; the vessel should 59be placed so near to the discharge hole of the blast furnace as to allow the iron to flow along a gutter into it. A small blast cylinder is required capable of compressing air to about 8 lbs. or 10 lbs. to the square inch. A communication having been made between it and the tuyères before named, the converting vessel will be in a condition to commence work; it will however on the occasion of its first being used after re-lining with firebricks be necessary to make a fire in the interior with a few baskets of coke, so as to dry the brickwork and heat up the vessel for the first operation, after which the fire is to be all carefully raked out at the tapping-hole, which is again to be made good with loam: the vessel will then be in readiness to commence work, and may be so continued without any use of fuel until the brick lining, in the course of time, becomes worn away, and a new lining is required. I have before mentioned that the tuyères are situated nearly close to the bottom of the vessel, the fluid metal will therefore rise some 18 in. or 2 ft. above them; it is therefore necessary, in order to prevent the metal from entering the tuyère holes, to turn on the blast before allowing the fluid crude iron to run into the vessel from the blast furnace. This having been done, and the metal run in, a rapid boiling up of the metal will be heard going on within the vessel, the metal being tossed violently about and dashed from side to side, shaking the vessel by the force with which it moves; from the throat of the converting vessel flame will immediately issue, accompanied by a few bright sparks such as are always seen rising from the metal when running into the pig-beds. This state of things will continue for about fifteen minutes, during which time the oxygen in the atmospheric air combines with the carbon contained in the iron, producing carbonic oxide, or carbonic acid gas, and at the same time evolving a powerful heat. Now, as this heat is generated in the interior of, and is diffused in innumerable fiery bubbles through, the whole fluid mass, the metal absorbs the greater part of it, and its temperature becomes immensely increased, and by the expiration of the fifteen minutes before named that part of the carbon which appears mechanically mixed and diffused throughout the crude iron has been entirely consumed: the temperature however is so high that the chemically combined carbon now begins to separate from the metal, as is at once indicated by an immense increase in the volume of flame rushing out of the throat of the vessel. The metal in the vessel now rises several inches above its natural level, and a light frothy slag makes its appearance and is thrown out in large foam-like masses. This violent eruption of cinder generally lasts about five or six minutes, when all further appearance of it ceases, a steady and powerful flame replacing the shower of sparks and cinder which always accompanies the boil. The rapid union of carbon and oxygen which thus takes place adds still further to the temperature of the metal, while the diminished quantity of carbon present allows a part of the oxygen to combine with the iron, which undergoes combustion and is converted into an oxide. At the excessive temperature that the metal has now acquired, the oxide as soon as formed undergoes fusion, and forms a powerful solvent of those earthy bases that are associated with the iron; the violent ebullition which is going on mixes most intimately the scoria and metal, every part of which is thus brought in contact with the fluid oxide, which will thus wash and cleanse the metal most thoroughly from the silicon and other earthy bases which are combined with the crude iron, while the sulphur and other volatile matters which cling so tenaciously to iron at ordinary 60temperatures are driven off, the sulphur combining with the oxygen and forming sulphurous acid gas.

“The loss in weight of crude iron during its conversion into an ingot of malleable iron was found, on a mean of four experiments, to be 12½ per cent., to which will have to be added the loss of metal in the finishing rolls. This will make the entire loss probably not less than 18 per cent. instead of about 28 per cent., which is the loss on the present system. A large portion of this metal is however recoverable by heating with carbonaceous gases the rich oxides thrown out of the furnace during the boil. These slags are found to contain innumerable small grains of metallic iron, which are mechanically held in suspension in the slags and may be easily recovered.

“I have before mentioned that after the boil has taken place a steady and powerful flame succeeds, which continues without any change for about ten or twelve minutes, when it rapidly falls off. As soon as this diminution of flame is apparent the workman will know that the process is completed, and that the crude iron has been converted into pure malleable iron, which he will form into ingots of any suitable size and shape by simply opening the tap-hole of the converting vessel and allowing the fluid malleable iron to flow into the iron ingot moulds placed there to receive it. The masses of iron thus formed will be free from any admixture of cinder, oxide, or other extraneous matters, and will be far more pure and in a forwarder state of manufacture than a pile formed of ordinary puddle bars. And thus it will be seen that by a single process, requiring no manipulation or particular skill, and with only one workman, from three to five tons of crude iron pass into the condition of several piles of malleable iron in from thirty to thirty-five minutes, with the expenditure of about a third part the blast now used in a finery furnace, with an equal charge of iron, and with the consumption of no other fuel than is contained in the crude iron.

“To those who are best acquainted with the nature of fluid iron, it may be a matter of surprise that a blast of cold air forced into melted crude iron is capable of raising its temperature to such a degree as to retain it in a perfect state of fluidity after it has lost all its carbon and is in the condition of malleable iron, which, in the highest heat of our forges, only becomes softened into a pasty mass. But such is the excessive temperature that I am enabled to arrive at with a properly shaped converting vessel and a judicious distribution of the blast, that I am enabled not only to retain the fluidity of the metal, but to create so much surplus heat as to remelt all the crop-ends, ingot-runners, and other scrap that is made throughout the process, and thus bring them, without labour or fuel, into ingots of a quality equal to the rest of the charge of new metal....

“To persons conversant with the manufacture of iron, it will be at once apparent that the ingots of the malleable metal which I have described will have no hard or steely parts, such as are found in puddled iron, requiring a great amount of rolling to blend them with the general mass, nor will such ingots require an excess of rolling to expel cinder from the interior of the mass, since none can exist in the ingot, which is pure and perfectly homogeneous throughout, and hence requires only as much rolling as is necessary for the development of fibre; it therefore follows that, instead of forming a merchant bar, or rail, by the union of a number of separate pieces welded together, it will be far more simple and less 61expensive to make several bars or rails from a single ingot. Doubtless this would have been done long ago had not the whole process been limited by the size of the ball which the puddler could make.

“The facility which the new process affords of making large masses will enable the manufacturer to produce bars that, in the old mode of working, it was impossible to obtain; while at the same time it admits of the use of more powerful machinery, whereby a great deal of labour will be saved and the process be greatly expedited.... I wish to call the attention of the meeting to some of the peculiarities which distinguish cast steel from all other forms of iron, viz., the perfectly homogeneous character of the metal, the entire absence of sand-cracks or flaws, and its greater cohesive force and elasticity, as compared with the blister steel from which it is made,—qualities which it derives solely from its fusion and formation into ingots, all of which properties malleable iron acquires in like manner by its fusion and formation into ingots in the new process; nor must it be forgotten that no amount of rolling will give the blister steel, although formed of rolled bars, the same homogeneous character that cast steel acquires by a mere extension of the ingot to some ten or twelve times its original length....

“I beg to call your attention to an important fact connected with the new process which affords peculiar facilities for the manufacture of cast steel. At that stage of the process immediately following the boil the whole of the crude iron has passed into the condition of cast steel of ordinary quality. By the continuation of the process the steel so produced gradually loses its small remaining portion of carbon, and passes successively from hard to soft steel, and from soft steel to steely iron, and eventually to very soft iron; hence, at a certain period of the process, any quality of metal may be obtained. There is one in particular which by way of distinction I call semi-steel, being in hardness about midway between ordinary cast steel and soft malleable iron. This metal possesses the advantage of much greater tensile strength than soft iron; it is also more elastic, and does not readily take a permanent set, while it is much harder and is not worn or indented so easily as soft iron; at the same time it is not so brittle or hard to work as ordinary cast steel. These qualities render it eminently well adapted to purposes where lightness and strength are specially required, or where there is much wear, as in the case of railway bars, which from their softness and lamellar texture soon become destroyed. The cost of semi-steel will be a fraction less than iron, because the loss of metal that takes place by oxidation in the converting vessel is about 2½ per cent. less than it is with iron; but as it is a little more difficult to roll, its cost per ton may fairly be considered to be the same as iron; but as its tensile strength is some 30 or 40 per cent. greater than bar iron, it follows that for most purposes a much less weight of metal may be used than that so taken. The semi-steel will form a much cheaper metal than any we are at present acquainted with. These facts have not been elicited from mere laboratory experiments, but have been the result of working on a scale nearly twice as great as is pursued in our largest iron works, the experimental apparatus doing 7 cwt. in thirty minutes, while the ordinary puddling furnace makes only 4½ cwt. in two hours, which is made into six separate balls, while the ingots or blooms are smooth, even prisms, 10 in. square by 30 in. in length, weighing about equal to ten ordinary puddle balls.”

The startling novelty of the methods and results described in this 62paper had the effect of paralyzing discussion at the time. But soon the voice of detraction was heard; many iron-masters ridiculed the idea of producing iron and steel without fuel, and indeed it may have been observed, the title of the paper notwithstanding, that first the silicon and carbon, and then the iron itself, really supplied the fuel. And we must remember that malleable iron in a molten state was then deemed an impossibility, for the hottest furnaces then known could not effect the fusion, however prolonged their action might be, yet Bessemer was to obtain five tons in this condition in the short space of half an hour with no other aid than cold air. Then it was said that Bessemer’s process of forcing air into melted cast iron had no claim of novelty, for it had been tried before and found valueless. Some iron-masters on trying experiments on a small scale and with imperfect appliances met with failures, and discredited the process at once; but five large establishments paid for licences sums amounting to £26,500 within three weeks of the reading of the paper. At the works of the Dowlais Iron Co., in South Wales, who were the first licensees, the first converter was set up under Bessemer’s personal superintendence, and at the first operation five tons of iron were produced direct from the blast furnace pig. This apparently satisfactory result proved quite otherwise when this iron came to be practically tested; for it was found quite useless! It was both “cold-short” and “red-short,” to use the technical terms,—the former of which means that although the sample may be welded, it is when cold brittle and rotten; the latter means that at a low red heat it breaks and crumbles under the hammer. Further trials were made, new experiments instituted, but the success that attended Bessemer’s early experiments could not be repeated, and as yet no one knew the reason why. Now it so happened that in the preliminary experiments an exceptionally pure pig iron had been made use of containing little or no phosphorus or sulphur, substances very deleterious in iron, and still more so in steel. With the capital obtained by the sale of his licences Bessemer quietly set to work to investigate the cause of his non-success, making daily experiments with a ton or two of metal at a time. These experiments extended over a period of two and a half years, and upon them Bessemer and his partner spent about £16,000, besides the £4,000 the preliminary researches had cost. But all difficulties were at length overcome, and the process was now found capable of turning out pure iron and steel when the pure pig iron of Sweden was used in the converter. In the meantime the licensees had made no attempts practically to carry out the process, which began to be denounced as visionary: it was “a mare’s nest”; it was “a meteor that had passed through the metallurgical world, but had gone out with all its sparks.” When Bessemer again brought the subject before the public, he found that no one believed in it; everyone said, “Oh, this is the thing that made such a blaze two or three years ago, and which was a failure.” Neither iron-makers nor steel-makers would now take it up. Bessemer and his partner thereupon joined with three other gentlemen to establish at Sheffield a steel-works of their own, where the invention should be carried into full practice. In due time works were erected, and they commenced to sell steel, receiving at first very paltry orders, for such quantities as 28 lbs. or 56 lbs.; but the orders soon became larger, and afterwards very much larger, for they were underselling the Sheffield manufacturers by £20 a ton, and their steel was undistinguishable from 63the higher priced article. Bessemer had now bought his licences back again, and in the course of his second set of experiments had patented each improvement as it occurred to him, finally bringing the mechanical apparatus to the degree of efficiency requisite for practical working, without which his primary idea would have been valueless. Before directing the reader’s attention to the form the apparatus had assumed, we may transcribe what Mr. Jeans, in the work above referred to, has told about the commercial success of the Bessemer steel-making firm:—

“On the expiration of the fourteen years’ term of partnership of this firm the works, which had been greatly increased from time to time out of revenues, were sold by private contract for exactly twenty-four times the amount of the whole subscribed capital, notwithstanding that the firm had divided in profits during the partnership a sum equal to fifty-seven times the gross capital, so that by the mere commercial working of the process, apart from the patent, each of the five partners retired after fourteen years from the Sheffield works with eighty-one times the amount of his subscribed capital, or an average of nearly cent. per cent., every two months,—a result probably unprecedented in the annals of commerce.”

Fig. 24.Bessemer Converter.

A, Front view, showing the mouth, c; B, Section.

The form of the Bessemer apparatus as it finally left the inventor’s hands may now be considered: but in certain details and arrangements some modifications, dictated by the experience and requirements of individual establishments, have been made, leaving the principles of the apparatus unchanged. Thus instead of making the converting vessel turn on trunnions, it is sometimes constructed fixed, the fluid metal after conversion being let out at a tap-hole; the number and size of the tuyères are varied; and so with the disposition of the air chamber or tuyère box, the pressure of the blast, the capacity of the converter itself, etc. In capacity converters vary between 2½ tons and 10 tons; one of medium size is shown in elevation and section in Fig. 24, and may 64be described as an egg-shaped vessel about 15 ft. high and 6 ft. diameter inside. It is strongly made of wrought iron in two parts bolted together, and is lined inside with some thick infusible coating, of which more is to be said presently. The converter swings on trunnions, one of which is hollow, and admits the blast by the pipe b to the base of the vessel, whence it passes through the passages shown at e. The thickness of the lining at e may perhaps be 20 in., and passages for the air are perforated in fire-clay tuyères, of which there may be seven, each with seven perforations of half an inch diameter. To the other trunnion is attached a toothed wheel which engages the teeth of a rack receiving motion from hydraulic pressure. The iron for the operation is melted in a furnace having its hearth above the level of the converter; and to receive its charge the latter is turned so that the molten cast iron may be poured in from a trough until its surface is nearly on a level with the lowest of the tuyères. The blast having been turned on, the hydraulic power is set to work and the converter is slowly brought to an upright position. The pressure of the current of air prevents any of the fluid metal from entering the blow-holes. The blast of cold air is continued until all the silicon and carbon have been removed by oxidation. If the production is to be steel, there is then added to the contents of the converter, placed in position to receive it, a certain weight of melted cast iron of a special constitution, and the blow is resumed for a few minutes; or in more recent practice this special metal is added to the fluid metal run out of the converter into a spacious ladle in known quantity. On this addition an intense action takes place, attended by an extremely brilliant flame and a throwing out of cinder or slag. The metal thus added to the decarbonized iron is a carbonized alloy of iron and manganese obtained from an ore naturally containing the latter metal, and scarcely any phosphorus or sulphur. The charcoal pig from this ore is called spiegeleisen (German = mirror-iron) from its brilliant reflecting facets; it contains from 12 to 20 per cent. of manganese, with about 5 per cent. of carbon, and a considerable proportion of silicon. An exact chemical analysis of the particular spiegeleisen having been previously made, it is known what proportion of it is to be added to the decarbonized iron in order to convert this into a steel with any required content of carbon. The manganese probably acts by combining with oxide of iron diffused through the mass, and together with the silicon forming the very easily separated slag which is ejected.

The whole series of operations connected with the Bessemer process may be easily followed by the help of Fig. 25, which is taken from a beautiful model in the Museum of Practical Geology. This model, which was presented to the museum by Mr. Bessemer himself, represents every part of the machinery and appliances of the true relative sizes. C is the trough, lined with infusible clay, by which the liquid pig iron is conveyed to the converters, A. The hydraulic apparatus by which the vessels are turned over is here below the pavement, but the rack which turns the pinion on the axis of the converter is shown at B. The vessel into which the molten steel is poured from the converter is marked E, and this vessel is swung round on a crane, D, so as to bring it exactly over the moulds, placed in a circle ready to receive the liquid steel, which on cooling is turned out in the form of solid ingots. The valves which control the blast, and those which regulate the movements of the converter through the hydraulic apparatus, are worked by the handle seen at H. The 66crane, or revolving table, D, is also under perfect control, so that the crude pig iron is converted into steel, and the moulds are filled with a rapidity and ease that are positively marvellous to a spectator.

Fig. 25.Model of Bessemer Steel Apparatus.

The development of the Bessemer process soon had the effect of so reducing the price of steel that this material came into use for almost every purpose for which iron had previously been employed, such as railway bars, girders, etc., for bridges, boiler plates, etc., for all which “steely iron” containing only 0·12 to 0·40 per cent. carbon proved admirably adapted. The practical success of the Bessemer process had not long been demonstrated commercially by the inventor and his partners at Sheffield before other firms began the manufacture: so that in 1878 there were in Great Britain alone twenty-seven establishments making Bessemer steel and using 111 converters. It may give an idea of the magnitude the Bessemer steel manufacture had attained even at that time if we quote the cost of erecting a complete plant for two 5–ton converters: it was £44,400, as given in a detailed estimate. In all these cases pig iron from ores free from phosphorus and sulphur had to be used, for as we have seen the converter failed to eliminate these vitiating elements. Imported pig ores had in general to be used, or pig from the limited supply of British hæmatite ores in West Cumberland. The Barrow Hæmatite Steel Company engaged in the production of Bessemer steel on a very large scale, having by 1878 erected no fewer than sixteen converters of the capacity of 6 tons each. In the meanwhile many efforts were made to discover some method of eliminating phosphorus, so that the ordinary qualities of British pig iron, and iron derived in any part of the world from the coarse phosphorized ores, might be available for the converter. Many of the methods then devised proved correct in principle and feasible in practice; but as, for sundry reasons, none of them came extensively into use, we need not here allude to them further.

The solution of the problem was announced in 1879. Some years before, G. J. Snelus had come to the conclusion that with a siliceous lining it would be impossible to eliminate phosphorus in the Bessemer converter, and that some refractory substance of a basic character must be sought for in order that the slag produced should be in a condition to absorb the phosphoric acid as fast as it is produced. He patented in 1872 the use of magnesian limestone as a material for the lining; as that substance when intensely heated became very hard and stony, being in that condition quite unaffected by water. Two young chemists, Messrs. Thomas and Gilchrist, apparently without being aware of Mr. Snelus’s conclusions, had also convinced themselves that the chief deficiency in the Bessemer process was due to the excess of silica in the slag, and in 1874 they began to try the effect of basic linings, and also of basic additions, such as lime, etc., to the charge in the converter, so that the lining itself should not be worn out by entering into the slag. Their results proved that phosphorus could be eliminated when the slag contained excess of a strong base. An example of an operation at Bolckow, Vaughan, & Company’s Eston works with the highly phosphorized Cleveland pig iron may be quoted. The basic-lined converter received first 9 cwt. of lime, then 6 tons of metal. When the blast at 25 lbs. pressure was turned on, the silicon began at once to burn; for three minutes the carbon was not affected, but for fourteen minutes longer it regularly diminished, the silicon keeping pace with it. After 67the blow had been continued for thirteen minutes from the commencement, the converter was turned down to allow of the further introduction of 19½ cwt. of a mixture of two parts of lime with one of oxide of iron. So long as 1·5 per cent. of carbon remained in the metal the phosphorus was untouched, and at the end of the blow, i.e. when the flame dropped, only one-third of it had been eliminated; it still formed 1 per cent. of the metal. The blast continued for another two minutes brought it down to ¼ per cent., and in one more minute only a trace was left. Most of the sulphur was got rid of at the same time. From Cleveland pig, thus de-phosphorized in the Bessemer converter, large quantities of steel rails were rolled for the North Eastern Railway Company, and were found entirely satisfactory, being as good as those made from the Cumberland hæmatite steel. This de-phosphorized process has been brought into operation wherever phosphoric ores are dealt with, and it has been applied with equal success in the “open hearth” furnaces, of which we have now to speak.

All discoveries and all inventions may be traced back to preceding discoveries and inventions in an endless series, and it is only by its precursors that each in its turn has been made possible. If we take one of the greatest marvels brought into existence at nearly the close of our epoch, namely, “wireless telegraphy,” we may follow up links of a chain connecting it with the recorded observations of an ancient Greek (Thales) who flourished seven centuries before our era, and even these may not have been original discoveries of his. And it will have been gathered from what has already been said that steel must have been produced, however unwittingly, at the earliest period at which man began to reduce iron from its ores. So the very latest, and for many purposes the most extensively practised, process of modern steel-making, brought indeed to working perfection mainly by the perseverance and scientific insight of two individuals, is the result of the observation and the accumulated experience of former generations. The observations and experience here alluded to are chiefly those that follow two lines: one concerning the properties of the metal itself, the other relating to the means of commanding very high temperatures on a great scale. On this occasion we are able almost to lay a finger on some proximate links of the chain. Réaumur, the French naturalist, made steel in the early part of the eighteenth century by melting cast iron in a crucible, and in this liquid metal he dissolved wrought iron, the product being, as the reader will now easily understand, the intermediate substance, steel; and this was obtained of course at a temperature which was incapable of fusing wrought iron by itself. He published in 1722 a treatise on “The Art of converting Iron into Steel, and of softening Cast Iron.” For this, and certain other metallurgical discoveries, Réaumur received a life-pension equivalent to about £500 per annum,—a treatment very different from that dealt out by the British to Henry Cort. The action in Réaumur’s crucible is precisely that used on the large scale in Siemens’ open hearth. But this last became possible only when Siemens had worked out his “regenerative stove” or heat accumulator, the development of an idea suggested by a Dundee clergyman in 1817.

A general notion of the Siemens’ regenerative stove will have been already gained from the account given before of its application to the modern type of blast furnace. Of the inventor himself, C. William Siemens, it may be observed that he was one of a family of brothers, all 68remarkable for their scientific attainments, and in many of his researches and processes he was aided by his brothers Frederick and Otto. In our article on “Electric Power and Lighting” there will be found some notice of a few of Siemens’ inventions pertaining to those subjects. A still more admirable invention of his is the electric pyrometer, an instrument of the utmost utility for measuring, with an accuracy previously unapproachable, the high temperature of furnaces, etc. Indeed there are few departments of science, pure or applied, which have not been enriched by the researches and contrivances of this distinguished man, whose merits were acknowledged by the bestowal upon him of the highest scientific and academical honours, and also of a title, for he became Sir William Siemens.

Fig. 26.Section of Regenerative Stoves and Open Hearth.

Siemens was much engaged from 1846 in conjunction with his brother Frederick in experimental attempts, continued over a period of ten years, at the construction of the regenerative gas furnace. At length, in 1861, he proposed the application of his furnace to an “open hearth,” and during the next few years some partial attempts to carry out his process were made, and he himself had established experimental works at Birmingham in order to mature his processes, while Messrs. Martin of Sireuil, in France, having obtained licences under Siemens’ patents, gave their attention to a modification of his process, by which they succeeded in producing excellent steel. Siemens having in 1868 proved the practicability of his plans by converting at his Birmingham works some old phosphorized iron rails into serviceable steel, a company was formed, and in 1869 the Landore Siemens’ Steel Works were established at Landore in Glamorganshire, and a few years after, these had sixteen Siemens 69open hearth melting furnaces at work, giving a total output of 1,200 tons of steel per week. The number of furnaces was subsequently increased. Extensive works specially designed for carrying out the Siemens and the Siemens-Martin process were shortly afterwards erected at other places, as at Newtown, near Glasgow, Panteg in Wales, etc. In Great Britain the open hearth process gradually gained upon the Bessemer, until in 1893, when the total output of both kinds amounted to nearly 3,000,000 tons, this was almost equally divided between them, and since that period the steel made by the former has greatly surpassed in amount that made by the latter.

How the regenerative stove, or heat accumulator, works, and how it is applied in the open hearth process, the reader may learn by aid of the diagram Fig. 26, in which however no representation of the disposition of the parts in any actual furnace is given, nor any details of construction beyond what is necessary to make the principle clear. On the right and on the left of the diagram will be seen a pair of similar chambers which are shown as partly below the level of the ground S , such being a usual disposition. The outer walls of these chambers are thick and the interior is entirely lined with the most refractory fire-bricks, of which also is formed the partition in between each pair of compartments, as well as the passages from the top of each opening on the furnace H. Each chamber or compartment is filled with rows of fire-bricks, laid chequerwise so as to leave a multitude of channels between. At the bottom of the chamber on the left let us suppose atmospheric air to be admitted by the channels A, A, A, and a combustible gas which we may take to be a mixture of carbonic oxide with some hydrogen is admitted in the same way to the second compartment on the left through the passages G, G, G. Supposing the apparatus quite cold in the first instance, the gas would ascend into the furnace H as shown by the arrows, because it might be drawn by an up-draught in a chimney connected with the six chambers shown at the bottom of the right, and it would also tend to rise up into the space H by its lighter specific gravity, and there it could be set on fire, when a volume of flame would pass across to the right, a plentiful supply of air rushing in through the air chamber from A, A, A, and the products of the combustion, mainly hot carbonic acid gas and hot nitrogen gas, in passing through the right-hand chambers, would make the bricks in both compartments very hot after a time, for the current would divide itself between the two passages, as indicated by the divided arrow. We have not shown the valves by which the workman is able, by merely pulling a lever, to shut off the air supply from A, A, A, and of gas from G, G, G, and put these channels into direct communication with the up-draught chimney, at the same time supplying gas at , , , and air at , , . These rise up among the now heated bricks each in its own compartment, but mix where they enter the furnace H, now hot enough to set them on fire, and the gaseous products of combustion, hotter now than before, descend among the fire-bricks of the left-hand compartments, heating them in turn. After another period, say half an hour, the valves are again reversed, and again gas and air both heated burn in the space H, and their products supply still more heat to the right-hand compartments. And so the action may be continued with a great temperature each time produced by the combustion of the combining bodies at increasingly higher temperatures. Thus, if cold gas and air by combination give rise to 500° of heat, when the same combine, at say the initial temperature of 70400°, the result would be a temperature of 900°; if burnt at this latter degree, then 900° + 500° would be reached, and so on. It would seem as if there were no limit to the temperatures obtainable in this way. But the nature of the materials of which the furnace is constructed imposes a limit, for even the most refractory matters yield at length, and the working would come to an end by the fusing of the brickwork. The diagram is a section through the length of the hearth (for it is usually oblong in plan), and the low arch above H being exposed to the fiercest heat, is formed of the most refractory “silica bricks,” that is, bricks made of coarsely ground silica held together with a little lime; yet this extremely resisting material is acted upon, and the arch has to be renewed every few months or sometimes weeks. The hearth itself is supported by massive iron plates, shown in the diagram by the thick lines, above which is laid a deep bed L, of quartz sand or ganister, or where required a basic lining, beaten hard down, and forming a kind of basin with sides sloping down in all directions to a point immediately below the centre of the fire-brick door D, where is the aperture for tapping, stopped by a mixture of sand and clay until the metal is ready for drawing off, when it runs outside into an iron spout lined with sand and is received into the ingot moulds. B in the figure represents the “bath,” as it is called, of molten metal, which, in the larger furnaces, where 20 tons of metal is operated on at once, may occupy an area of 150 square ft.

It need hardly be mentioned that there has to be a certain adjustment between the volumes of air and of gas that pass into the regenerative stoves, in order that the best effect may be obtained. Besides the limit of temperature occasioned by the nature of the materials, there is a chemical reason why the regenerative stoves cannot increase the temperature indefinitely. It is noticed that when the temperature of the furnace has become very high indeed, the flame over the hearth assumes a peculiar appearance, being interrupted by dark spaces. These are attributable to what is called in chemistry “dissociation,”—in this case the dissociation of carbonic acid gas, which by the heat alone separates into carbonic oxide and oxygen gases. In the same way these gases refuse to combine if brought together heated beyond a certain temperature. This phenomenon of dissociation is a general one, for it is found that for any pair of substances there is a characteristic range of temperature above or below which they refuse to combine. The gas used in these stoves is either unpurified coal gas, or that produced by passing steam over red-hot coal or coke.

We have spoken of the Siemens and the Siemens-Martin open hearth processes. In the latter a charge of pig iron, say 1½ tons, is first melted on the hearth, then about 2 tons of wrought iron is added in successive portions, and in like manner nearly as much scrap steel (i.e. turnings, etc.), the final addition being half a ton of spiegeleisen containing 12 per cent. of manganese. A furnace of corresponding dimensions will allow of three charges every twenty-four hours. In the Siemens process it is not wrought iron or steel scrap that is mainly used to decarbonize the pig, but a pure oxide ore. This is thrown into the bath of molten metal in quantities of a few cwts. at a time, when a violent ebullition occurs. When samples of the metal and of the slag are found to be satisfactory, spiegeleisen or ferro-manganese is added, and the charge is cast. This process takes a rather longer time than the former, but gives steel of 71more uniform character. In both processes, phosphorus is oxidized at the high temperature attained and passes into the slag, which last floats of course on the molten metal and is from time to time tapped off as the action proceeds.

Fig. 26a.—Rolling Mill.

Fig. 26a shows a rolling mill with what is called a “two-high” train for finishing bars by passing them between the grooves cut in the rolls to give the required section. The rolls in the illustration turn in one direction only, and therefore the bars after emerging from the larger grooves have to be drawn back over the machine and set into a smaller pair from the same side. This inconvenience is avoided in the “three-high train,” on which three rolls revolve, and the bars can be passed through them from one side to the other alternately. The celerity with which a glowing steel ingot is without re-heating converted into a straight steel rail 60 or 100 feet long, by passing a few times backwards and forwards between the rolls, is very striking. These rolls are made of solid steel, and in some cases have a diameter of 26 inches or more.

72

IRON IN ARCHITECTURE.

Everyone knows how much iron is used in those great engineering structures that mark the present age, and of which a few examples will be described in succeeding articles. One other feature of the nineteenth century is the use of iron in architecture. Some have, indeed, protested against the use of iron for this purpose, and would even deny the name of architecture to any structure obviously or chiefly formed of that material. Stone and wood, they say, are the only proper materials, because each part must be wrought by hand, and cannot be cast or moulded; and further, iron being liable to rust, suggests decay and want of permanence, and these are characters incompatible with noble building. All this can rest only on a relative degree of truth—as, for instance, machinery is used to dress and shape both wood and stone, and the permanence of even the latter is as much dependent on conditions as that of iron. Iron used in architecture is hideous when applied in shapes appropriate only to stone; but when it is disposed in the way suggested by its own properties, and receives ornament suitable to its own nature, the result is harmonious and graceful, and the structure may display beauties that could be attained by no other materials. Be that as it may, the great and lofty covered spaces that are required for our railway stations and for other purposes could have been obtained only by the free use of iron, and everyone can recall to mind instances of such structure not devoid of elegance, in spite of the absence—the proper absence—of the Classic “orders” or Gothic “styles.” The first notable instance of the application of iron on a large scale was the erection of the “Crystal Palace,” in Hyde Park, for the great Exhibition of 1851. It was taken down and re-erected at Sydenham, and there it has become so well known to everyone that any description of it is quite unnecessary in this place.

As another conspicuous example of what may be done with iron, the Eiffel Tower at Paris may be briefly described.

The idea of erecting a tower 1,000 feet high was not of itself new. It had been entertained in England as early as 1833, in America in 1874, and in Paris itself in 1881. It has been reserved for M. Gustave Eiffel, a native of Dijon, who commenced to practise as an engineer in 1855, to realize this ambitious project. He has long been occupied in the construction of great railway bridges and viaducts, and in these he has adopted a system peculiar to himself of braced wrought-iron piers without masonry or cast-iron columns. He also was the first French engineer to erect bridges of great span without scaffolding. In the Garabit viaduct he planned an arch of 541 feet, crossing the Truyère at a height of nearly 400 feet above it. One result of M. Eiffel’s studies in connection with these lofty piers was his proposal to erect the tower for the Paris Exhibition of 1889. This proposal met with great opposition on the part of many influential people in Paris—authors, painters, architects, and others protesting with great energy against the modern Tower of Babel, which was, as they said, to disfigure and profane the noble stone buildings of Paris by the monstrosities of a machine maker, etc. etc. The Eiffel Tower is now constructed, and no one has heard that it has dishonoured the monuments of Paris, for it has been instead a triumph of French skill, the glory of its designer, and the wonder of the Exhibition.

73

Fig. 26b.—The Eiffel Tower in course of construction.

The tower rests on four independent foundations, each at the angle of a square of about 330 feet in the side, and it may be noted that the two foundations near the Seine had to be differently treated from the other two, where a bed of gravel 18 feet thick was found at 23 feet below the 74surface, and where a bed of concrete, 7 feet thick, gave a good foundation. The foundations next the river had to be sunk 50 feet below the surface to obtain perfectly good foundations. Underlying the whole is a deep stratum of clay; but this is separated from the foundations by a layer of gravel of sufficient thickness. Above this are beds of concrete, covering an area of 60 square metres, and on the concrete rests a pile of masonry. Each of the four piles is bound together by two great iron bars, 25 feet long and 4 inches diameter, uniting the masonry by means of iron cramps, and anchoring the support of the structure, although its stability is already secured by its mere weight. The tower is of curved pyramidal form, so designed that it shall be capable of resisting wind pressure, without requiring the four corner structures to be connected by diagonal bracing. The four curved supports are, in fact, connected with each other only by girders at the platforms on the several stages, until at a considerable length they are sufficiently near to each other to admit the use of the ordinary diagonals. The work was begun at the end of January, 1887, and M. Eiffel notes how the imagination of the workmen was impressed by the notion of the vast height of the intended structure. Not steel, but iron is the material used throughout, and the weight of it is about 7,300 tons, without reckoning what is used in the foundations, and in the machinery connected with the lifts, etc. It has long ago been found that stone would be an unsuitable material for a structure of this kind, and it is obvious that only iron could possibly have been used to build a tower of so vast a height and within so short a space of time, for it was completed in April, 1889. A comparison of heights with the loftiest stone edifices may not be without interest. The highest building in Paris is the dome of the Invalides, 344 feet; Strasburg Cathedral rises to 466 feet; the Great Pyramid to 479 feet; the apex of the spire in the recently completed Cathedral at Cologne to 522 feet. These are overtopped by the lofty stone obelisk the Americans have erected at Washington, which attains a height of more than 550 feet. Such spires and towers have been erected only at the cost of immense labour. But iron, which can be so readily joined by riveting, lends itself invitingly to the skill of the constructor, more particularly by reason of the wonderful tensile strength it possesses. It is scarcely possible to convey any adequate idea of the great complicated network of bracings by which in the Eiffel Tower each standard of the columns is united to the rest to form one rigid pile. The horizontal girders unite the four piers in forming the supports of the first storey some 170 feet above the base. The arches which spring from the ground and rise nearly to the level of these girders are not so much intended to add to the strength of the structure as to increase its architectural effect. The first storey stands about 180 feet above the ground, and is provided with arcades, from which fine views of Paris may be obtained. Here there are spacious restaurants of four different nationalities. And in the centre of the second storey (380 feet high) is a station where passengers change from the inclined lifts to enter other elevators that ascend vertically to the higher stages of the tower. On the third storey, 900 feet above the ground, there is a saloon more than 50 feet square, completely shut in by glass, whence a vast panorama may be contemplated. Above this again are laboratories and scientific observatories, and, crowning all, is the lighthouse, provided with a system of optical apparatus for projecting the rays from a powerful electric light. This 76light has been seen from the Cathedral at Orléans, a distance of about 70 miles.

Fig. 26c.—The Eiffel Tower.

The buildings of the Paris Exhibition of 1889 are themselves splendid examples, not only of engineering skill, but of good taste and elegant design in iron structures and their decorations. The vast Salle des Machines (machinery hall) exceeds in dimensions anything of the kind in existence, for it is nearly a quarter of a mile long, and its roof covers at one span its width of 380 feet, rising to a height of 150 feet in the centre. This great hall is to remain permanently, as well as the other principal galleries with their graceful domes.

The Eiffel Tower having proved one of the most striking features of the great Paris Exhibition, and of itself a novelty sufficient to attract visitors to the spot, and having, long before the Exhibition closed, completely defrayed the expense of its construction, with a handsome profit besides, its success has naturally provoked similar enterprises,—as, for instance, at Blackpool, a seaside resort in Lancashire, there has been erected an openwork metal tower, resembling the Paris structure, but of far less altitude.

Tall Buildings in American Cities.

In several of the great cities of the United States, the last few years have witnessed a novel and characteristic development of the use of iron in architecture. In many structures on the older continent, this material has been frankly and effectively employed, forming the obvious framework of the erection, even when the leading motive was quite other than a display of engineering skill. The Crystal Palace at Sydenham and other erections have been referred to, in which iron has taken its place as the main component of structures designed more or less to fulfil æsthetic requirements: the guiding principle in “tall office buildings” in the cities of the Western continent is, on the contrary, avowedly utilitarian. Iron has, of course, long been used in the form of pillars, beams, etc., in ordinary buildings, and it is only the extraordinary extension of this employment of it, after the lift or elevator had been perfected, and the ground-space in great commercial centres was daily becoming more valuable, that has led to the erection of structures of the “sky-scraper” class in American cities. For a given plot at a stated rent, a building of many stories, let throughout as offices, will obviously bring to its owner a greater return than one of few stories. The elevators now make a tenth story practically as accessible as a third storey, and the tall building readily fills with tenants. No claim for artistic beauty has been advanced for these structures, which aim simply at being places of business, and if provision be made for sufficient floor-space and daylight, and for artificial lighting, heating, and ventilation, together with the ordinary conveniences of modern life, and ready elevator service, nothing more is required by the utilitarian spirit, that seeks only facilities for money-getting. These tall buildings are usually erected on plots disproportionately small, and the architectural effect is apt to be bizarre and incongruous, especially when the structure shoots up skyward in some comparatively narrow street amid more modest surroundings. They are really engineering structures, but invested with features belonging to edifices of quite another order of construction. If they are necessities of the place and period, and are “come to stay,” it cannot be doubted but that decoration of an appropriate 78and harmonious character will, in course of time, be evolved along with them, when the conventionality that clings to architecture shall be broken through, and a new style appear, as consistent, and therefore as beautiful, in relation to the “tall office building,” as were those of the Greek temple and the Gothic minster in their free and natural adaptation.

PLATE IV.

THE AMERICAN TRACT SOCIETY BUILDING.

Fig. 26d.—St. Paul Building, N. Y.

Here, apparently, is the opportunity for the advent of a new and characteristic style. There is great ingenuity displayed in the arrangement and internal finish of these buildings. But besides the somewhat novel application of iron, the most notable circumstances regarding them are the tendency to make them of greater and greater height, and the wonderfully short time in which, upon occasion, they can be run up. Chicago has recently been noted for its tall edifices, among which may be named The Reliance Building, erected upon a site only 55 feet in breadth, but rising in fourteen stories to the height of 200 feet, and presenting the appearance of a tower. There are no cast iron pillars, but the whole metal framework is of rolled steel, the columns consisting of eight angle-sections, bolted together in two-story lengths, adjoining columns breaking joint at each floor, and braced together with plate girders, 24 inches deep, bolted to the face of the columns, with which they form a rigid connection. Externally, the edifice shows nothing but white enamelled terra-cotta and plate glass. This building was originally a strongly-built structure of five stories, the lower one being occupied as a bank. The foundations and the first story were taken out, and prepared for the lofty edifice, the superstructure being the while supported on screws. Then the three upper stories were taken down, and the building was continued from the second story, which was filled with tenants while the building was in course of erection above.

Fig. 26e.—Manhattan Insurance Co.’s Building, in course of erection.

Still more lofty edifices have been going skyward in other places. Already in New York there are a great number of lofty piles due to the introduction of the lifts or elevators, by which an office on the tenth floor is made as convenient as one on the second. These buildings usually receive the name of the owners of the structure, who occupy, perhaps, only one floor. To mention only a few. There is the American Tract Society building, with its twenty-three stories, 285 feet high, which is one of the latest and handsomest of these tall piles in the city. See Plate IV. Still loftier is the St. Paul building, fronting the New York Post-Office at the junction of Park Row and Broadway. This structure is splayed at the angle between Ann Street and Broadway, where its width is 39½ feet, while its loftiest part has frontages of about 30 feet along each of these thoroughfares. The height is no less than 313 feet above the pavement, and the number of stories is twenty-five. This building is faced with light yellow limestone, and although it was commenced only in the summer of 1895, it was expected to be ready for occupation by the autumn of 1896. Even this great height is overtopped by the Manhattan Life Insurance Company’s building, rising 330 feet, and remarkable as perhaps beyond previous record of quickness in building a gigantic structure. Obviously, the foundations of such a building must be most seriously considered, prepared and tested, before the great bulk of the building is begun, and in the New York Engineering Magazine one of the architects has given a full account, with complete illustrations, of all the works, from the rock foundation to the completed edifice. A description of the foundation work, though most interesting for the professional engineer, would probably have little attraction for the general reader; 79but its importance may be inferred from the fact of its having taken nearly six months for its completion, while the huge superstructure required only eight months. The eighteenth tier of beams was reached in “three months from the time the foundations were ready on which to set the first piece of steel, composing the bolsters that support the cantilever system.... The substructure, which starts in bed-rock and continues to the cellar-floor, consists of fifteen piers, varying in size from 9 feet in diameter, to 21 feet 6 inches by 25 feet square.... The number of bricks used in the piers amounted to 1,500,000. From this it may be seen that a good-sized building was sunk out of sight before any part of the superstructure could be begun.” An open court within the main structure, special framing for the arrangements of the company’s offices on the sixth floor, the great height and weight of the tower, and the requisite provision for wind-bracing, delayed in some degree a regular advance of the stories; 80but within three months no less than 5,800 tons were placed in position. There were girders weighing 40 tons, many columns of 10 and 12 tons, and cantilevers of 80 tons weight and 67 feet long. Strange to say, that in a building of this magnitude, where such masses had to be raised 300 feet into the air, there was not a single accident involving loss of life. When four stories of the steel framework had been put up, the bricklayers were set to work, and they followed the frame-setters throughout. After the masons came the pipe-layers, with their ten miles of pipes, followed by electricians, fixing their thirty-five miles of communicating wires. Thirty thousand cubic feet of stone was cut and set on the Broadway front in eighty days. Then craftsmen of the different trades followed each other, or worked in harmony together, story after story upwards: the engineers for boilers, heating, and elevators, the plumbers, the decorators, the carpenters and cabinet-makers, the plasterers, the marble and tile workers, 81the gasmen, etc. In fine, every story was completely finished and ready for occupation in eight months after the start from the foundations.

Fig. 26f.—Manhattan Insurance Co.’s Buildings nearly completed.

The shortness of the time in which these lofty buildings were run up is not less remarkable than the completeness of their fittings, which comprise everything requisite for communication within the premises and in connection with the outer world. The elevators or lifts are the perfection of mechanism in their way, and act with wonderful smoothness and regularity; of these are usually two at least, as well as an ample staircase. Notwithstanding all these appliances, some disastrous and fatal conflagrations have occurred at buildings erected on the “tall” principle; and as “business premises” of even 380 feet high are projected, the authorities have been considering the desirability of restricting the heights. It has been proposed that offices should not exceed in height 200 feet; hotels, 150 feet; and private houses, 75 feet.

BIG WHEELS.

The Paris example of an engineering feat upon an unprecedented scale having proved sufficiently captivating for the general public to ensure for itself a great commercial success, even amid the attractions of an International Exhibition, was not lost upon the enterprising people of the States when the “World’s Fair” at Chicago was in preparation in 1893. It was then that Mr. G. W. G. Ferris, the head of a firm of bridge constructors at Pittsburg, conceived the idea of applying his engineering skill to the erection of a huge wheel, revolving in a vertical plane, with cars for persons to sit in, constituting, in fact, an enormous “merry-go-round,” as the machine once so common at country fairs was called. The novelty of the Chicago erection was, therefore, not the general idea, but the magnitude of the scale, which, for that reason, involved the application of the highest engineering skill, and the solution of hitherto unattempted practical problems. Several thousand pounds were, in fact, expended on merely preliminary plans and designs. The great wheel at Chicago was 250 feet in diameter, and to its periphery were hung thirty-six carriages, each seating forty persons. At each revolution, therefore, 1,440 people would be raised in the air to the height of 250 feet, and from that elevation afforded a splendid prospect, besides an experience of the peculiar sensation like that of being in a balloon, when the spectator has no perception of his own motion, but the objects beneath appear to have the contrary movement, that is to say, they seem to be sinking when he is rising, and vice versâ. The axle of the Chicago wheel was a solid cylinder, 32 inches in diameter and 45 feet long; on this were two hubs, 16 feet in diameter, to which were attached spoke rods, 2½ inches in diameter, passing in pairs to an inner crown, which was concentric with the outer rim, but 40 feet within it. The inner and outer crowns were connected together, and the former joined to the crown of the twin wheel by an elaborate system of trusses and ties, which, however, left an open space between the rims of 20 feet from the outside. These last were formed of curved riveted hollow beams, in section 25½ inches by 19 inches, and between them, slung upon iron axles through the roofs, were suspended, at equal intervals, the thirty-six carriages, each 27 feet long, and weighing 13 tons without its passengers, who added 3 tons more to the weight. The wheel with its passengers was calculated to weigh about 831,200 tons, and it rested on two pyramidal skeleton towers of ironwork 140 feet high, having bases 50 feet by 60 feet. The wheel was moved by power applied at the lowest point, the peripheries of both the rims having great cogs 6 inches deep and 18 inches apart, which engaged a pair of large cog-wheels, carried on a shaft 12 inches in diameter.

Fig. 26g.—Original Design for the Great Wheel.

This curious structure was not begun until March, 1893, yet it was set in motion three months afterwards, having cost about £62,500. The Company had to hand over to the Exhibition one half of the receipts after the big wheel had paid for its construction, but even then they realised a handsome profit, and at the close of the World’s Fair, they sold the machine for four-thirds of its cost, in order that it might be re-erected at Coney Island.

No sooner had the great Ferris wheel at Chicago proved a financial success than an American gentleman, Lieutenant Graydon, secured a patent for a like machine in the United Kingdom; and as it has now become almost a matter of course that some iron or steel structure, surpassing everything before attempted, should form a part of each great exhibition, a Company was at once formed in London, under the title of “The Gigantic Wheel and Recreation Towers Co., Limited,” to construct and work at the Earl’s Court Oriental Exhibition of 1895, a great wheel, similar in general form to that of Chicago. But the design of the London wheel had some new features, as will be seen from the sketches, Fig. 26c (from The Engineer of 20th April, 1894), and, moreover, having been planned of larger dimensions than its American prototype, presented additional engineering problems of no small complexity. After due deliberation the scheme of the work was entrusted to Mr. Walter B. Basset, a talented young engineer, connected with the firm of Messrs. Maudslay, Sons, & Field, and already experienced in designing iron structures. Under this gentleman, with the assistance of Mr. J. J. Webster in carrying out some of the details, the work has been so successfully accomplished that the “Great Wheel” of 1895 may be cited as one of the crowning mechanical triumphs of the nineteenth century. The original design has not been followed so far as regards the lower platforms for refreshment rooms, &c. Plate V., for which we are indebted to Mr. Basset, is a photographic representation of the actual structure.

The wheel at Earl’s Court exceeds the Ferris wheel in diameter by 50 feet, being 300 feet across. It is supported on two towers, 175 feet high, each formed by four columns 4 feet square, built of steel plates with internal diaphragms, and surmounted by balconies that may be ascended in elevators raised by a weight of water, which, after having been discharged into a reservoir under the ground level, is again pumped up to the top of the towers. Between the balconies on each tower there is also a communication through the axle of the wheel, which, instead of being solid as at Chicago, is a tube of 7 feet diameter, and 35 feet long, made in sections, riveted together, of steel 1 inch thick, and weighing no less than 58 tons. The raising and fixing in its high place of such a mass of metal required specially ingenious devices, which have been greatly appreciated by professional engineers. But for these devices, the erection of scaffolding in the ordinary way of proceeding would have entailed an outlay simply enormous. The axle is stiffened by projecting rings, and, between pairs of these, the spoke rods are attached by pins 3 inches in diameter. The axle was the production of Messrs. Maudslay, Field & Co.; all the rest of the metal work was made at the Arrol Works at 84Glasgow, and the carriages were constructed by Brown, Marshall & Co., of Birmingham. The Earl’s Court wheel is turned by a mechanism different from that of the Chicago wheel, for whereas the latter was provided with cogs, the former has two chains, each 1,000 feet long and 8 tons weight, surrounding the periphery of the wheel on either side. The chains go over drums in the engine-shed, from which they pass underground to guide-pulleys, and as they unwind from the Great Wheel, they again go over guide-pulleys to lead them back to the drums. These chains are firmly held throughout in the jaws of V-shaped grooves, and there are arrangements for taking up the slack. The drums are actuated by wheel gearing, connected with two horizontal Robey steam engines, each of 50 horse-power, one on either side, capable of being worked singly or together. It is, however, found sufficient to use the engine of one side only, and even then to work it at but 16 horse-power, and the operation can be controlled by one man, who has also the command of a brake. Both starting and stopping are accomplished with the greatest smoothness and absence of strain or jar. There are forty carriages, each 25 feet long, 9 feet wide, and 10 feet high. Each will accommodate forty passengers, and these enter at the ends from eight platforms at different heights from the ground, so arranged as to be on the level of the eight lowest carriages while the wheel is stationary. The passengers who have had their ride leave at the other end of the carriages by eight similar platforms on the other side of the wheel. After the change of passengers in one set of eight carriages, the wheel is turned through exactly one-fifth of a revolution, which has the effect of bringing the next eight carriages to the level of the platforms, and it is again brought to a standstill whilst the change of passengers is taking place; and so on, until the whole freight of say 1,600 persons has been changed during the five stoppages in one revolution, for which about thirty-five minutes are required, and the process of emptying and filling eight carriages at once is repeated. There are first and second class carriages, the charge for the former being two shillings, and for the latter one shilling; so that, reckoning 800 passengers of each class, one turn would bring to the treasury the handsome sum of £120.

The sensations experienced in a journey on the Great Wheel are, as already mentioned, comparable to those enjoyed by the aërial voyagers in a balloon, where all perception of proper motion is lost, and it is the world beneath that seems to recede and float away, presenting the while a strangely changing panorama. Many people who have never made a balloon ascent yet know the calm delight of floating in a boat without effort down some placid stream, unconscious of any motion beyond that vaguely inferred from the silent apparent gliding by of the banks. Very similar are, in part, the feelings of the passenger who is almost imperceptibly carried up into the air in a carriage of the Great Wheel, but the vertical direction of the movement, and the gradual expansion of the horizon as the vertex is approached, lend an unwonted novelty to the situation. From the Earl’s Court Wheel the view is both interesting and extensive, for on a clear day the prospect stretches as far as the Royal Castle of Windsor.

The “Gigantic Wheel” at Earl’s Court was inaugurated on the 11th July, 1895, in the presence of an assemblage of 5,000 people, including many distinguished personages, who were all treated to a ride. Plate I. shows a portion of the wheel and carriages as in motion.

PLATE V.

GENERAL VIEW OF THE GREAT WHEEL AT EARL’S COURT.

85

Fig. 27.Sir Joseph Whitworth.

TOOLS.

Of the immense variety of tools and mechanical contrivances employed in modern times, by far the greatest number are designed to impart to certain materials some definite shape. The brickmaker’s mould, the joiner’s plane, the stonemason’s chisel, the potter’s wheel, are examples of simple tools. More elaborate are the coining press, the machine for planing iron, the drilling machine, the turning lathe, the rolling mill, the Jacquard loom. But all such tools and machines have one principle in common—a principle which casual observers may easily overlook, but one which is of the highest importance, as its application constitutes the very essence of the modern process of manufacture as distinguished from the slow and laborious mode of making things by hand. The principle will be easily understood by a single example. Let it be required to draw straight lines across a sheet of paper. Few persons can take a pen or pencil, and do this with even an approach to accuracy, and at best they can do it but slowly and imperfectly. But with the aid of a ruler any number of straight lines may be drawn rapidly and surely. The former case is an instance of making by hand, the latter represents manufacturing, the ruler being the tool or machine. Let it be observed that the ruler has in itself the kind of form required—that is to say, straightness—and that in using it we copy or transfer this straightness to the mark made on the paper. This is a 86simple example of the copying principle, which is so widely applied in machines for manufacturing; for, in all of these, materials are shaped or moulded by various contrivances, so as to reproduce certain definite forms, which are in some way contained within the machine itself. This will be distinctly seen in the tools which are about to be described.

Fig. 28.Whitworth’s Screw Dies and Tap.

Probably no one mechanical contrivance is so much and so variously applied as the Screw. The common screw-nail, which is so often used by carpenters for fastening pieces of metal on wood, or one piece of wood to another, is a specimen of the screw with which everybody is familiar. The projection which winds spirally round the nail is termed the thread of the screw, and the distance that the thread advances parallel to the axis in one turn is called the pitch. It is obvious that for each turn the screw makes it is advanced into the wood a depth equal to the pitch, and that there is formed in the wood a hollow screw with corresponding grooves and projections. Screws are formed on the ends of the bolts, by which various parts are fastened together, and the hollow screws which turn on the ends of the bolts are termed nuts. The screws on bolts and nuts, and other parts of machines, were formerly made with so many different pitches that, when a machine constructed by one maker had to be repaired by another, great inconvenience was found, on account of the want of uniformity in the shape and pitch of the threads. A uniform system was many years ago proposed by Sir Joseph Whitworth, and adopted by the majority of mechanical engineers, who agreed to use only a certain defined series of pitches. The same engineer also contrived a hand tool for cutting screws with greater accuracy than had formerly been attained in that process. A mechanic often finds it necessary to form a screw-thread on a bolt, and also to produce in metal a hollow screw. The reader may have observed gas-fitters and other workmen performing the first operation by an instrument having the same general appearance as Fig. 28. This contains hard steel dies, which are made to press on the bolt or pipe, so that when the guide-stock is turned by the handles, the required grooves are cut out. 87The arrangement of these dies in Sir Joseph Whitworth’s instrument is shown in Fig. 28, which represents the central part of the guide-stock; A, B, C are the steel dies retained in their places, when the instrument is in use, by a plate which can be removed when it is necessary to replace one set of dies by another, according to the pitch of thread required. The figure also shows the set of dies, A, B, C, removed from the guide-stock. D is the work, pressed up against the fixed die, A, by B and C, the pressure being applied to these last as required by turning the nut, thus drawing up the key, E, so that the inclined planes, f, g, press against similar surfaces forming the ends of the dies. For producing the hollow screws, taps are provided, which are merely well-formed screws, made of hard steel and having the threads cut into detached pieces by several longitudinal grooves, as represented in the lower part of Fig. 28.

Fig. 29.Screw-cutting Lathe.

The method of forming screws by dies and taps is, however, applicable only to those of small dimensions, and even for these it is not employed where great accuracy is required. Perfect screws can only be cut with a lathe, such as that represented in Fig. 29. In this we must first call the reader’s attention to the portion of the apparatus marked A, which receives the name of the slide-rest. The invention of this contrivance by Maudsley had the effect of almost revolutionizing mechanical art, for by its aid it became possible to produce true surfaces in the lathe. Before the slide-rest was introduced, the instrument which cut the wood or metal was held in the workman’s hand, and whatever might be his skill and strength, the steadiness and precision thus obtainable were far inferior to those which could be reached by the grip of an iron hand, guided by unswerving bars. The slide-rest was contrived by Maudsley in the first instance for cutting screws, but its principle has been applied for other purposes. This principle consists in attaching the cutting tool to a slide which is incapable of any motion, except in the one direction required. Thus the slide, A, represented in Fig. 29, moves along the bed of the lathe, B, carrying the cutter with perfect steadiness in a straight line parallel to the axis of the lathe. There are also two other slides for adjusting the position of the cutter; the handle, a, turns a screw, which imparts a transverse motion to the piece, b, and the tool receives another longitudinal movement from the 88handle, c. The pieces are so arranged that these movements take place in straight lines in precisely the required direction, and without permitting the tool to be unsteady, or capable of any rocking motion. In Whitworth’s lathe, between the two sides of the bed, and therefore not visible in the figure, is a shaft placed perfectly parallel to the axis of the lathe. One end of this shaft is seen carrying the wheel, C, which is connected with a train of wheels, D, and is thus made to revolve at a speed which can be made to bear any required proportion to that of the mandril, E, of the lathe, by properly arranging the numbers of the teeth in the wheels; and the machine is provided with several sets of wheels, which can be substituted for each other. The greater part of the length of this shaft is formed with great care into an exceedingly accurate screw, which works in a nut forming part of the slide-rest. The effect, therefore, of the rotation of the screw is to cause the slide-rest to travel along the bed of the lathe, advancing with each revolution of the screw through a space equal to its pitch distance. There is an arrangement for releasing the nut from the guiding-screw, by moving a lever, and then by turning the winch the slide-rest is moved along by a wheel engaging the teeth of a rack at the back of the lathe. Now, if the train of wheels, C D, be so arranged that the screw makes one revolution for each turn of the mandril, it follows that the cutting tool will move longitudinally a distance equal to the pitch of the guiding-screw while the bar placed in the lathe makes one turn. Thus the point of the cutter will form on the bar a screw having the same pitch as the guiding-screw of the lathe.

Here we have a striking illustration of the copying principle, for the lathe thus produces an exact copy of the screw which it contains. The screw-thread is traced out on the cylindrical bar, which is operated upon by the combination of the circular motion of the mandril with the longitudinal movement of the slide-rest. By modifying the relative amounts of these movements, screw-threads of any desired pitch can be made, and it is for this purpose that the change wheels are provided. If the thread of the guiding-screw makes two turns in one inch, one revolution of the wheel C will advance the cutter half an inch along the length of the bar. If the numbers of teeth in the wheels be such that the wheel D makes ten revolutions while C is making one, then in the length of half an inch the thread of the screw produced by the cutter will go round the core ten times, or, in technical language, the screw will be of 1
20
inch pitch.

Fig. 30.Whitworth’s Measuring Machine.

Since a screw turning in a nut advances only its pitch distance at each revolution, a finely-cut screw furnishes an instrument well adapted to impart a slow motion, or to measure minute spaces. Suppose a screw is cut so as to have fifty threads in an inch, then each turn will advance it 1
50
in.; half a turn 1
100
in.; a quarter of a turn, 1
200
, and so on. It is quite easy to attach a graduated circle to the head of the screw, so that, by a fixed pointer at the circumference, any required fraction of a revolution may be read off. Thus if the circle had two hundred equal parts, we could, by turning the screw so that one division passed the index, cause the screw to advance through 1
200
of 1
50
inch, or 1
10000
part of an inch. This is the method adopted for moving the cross-wires of the instruments for measuring very small spaces under the microscope. Sir Joseph Whitworth, who has done so many great things in mechanical art, was the first mechanician to perceive the importance of extreme accuracy of workmanship, and he invented many beautiful instruments and processes by which this accuracy might be attained. Fig. 30 represents one of his measuring machines, 89intended for practical use in the workshop, to test the dimensions of pieces of metal where great precision is required. The base of the machine is constructed of a rigid cast iron bed bearing a fixed headstock, A, and a movable one, B, the latter sliding along the bed, C, with a slow movement, when the handle, D, is turned. This slow motion is produced by a screw on the axis, a, working in the lower part of the headstock, just as the slide-rest is moved along the bed of the lathe. The movable headstock, when it has been moved into the position required, is firmly clamped by a thumbscrew. The face of the bed is graduated into inches and their subdivisions. Here it should be explained that the machine is not intended to be used for ascertaining the absolute dimensions of objects, but for showing by what fraction of an inch the size of the work measured differs from a certain standard piece. Each headstock carries a screw of 1
20
inch pitch, made with the greatest possible care and accuracy. To the head of the screw in the movable headstock is attached the wheel, b, having its circumference divided into 250 equal parts, and a fixed index, c, from which its graduations may be counted. An exactly similar arrangement is presented in connection with the screw turning in the fixed headstock, but the wheel is much larger, and its circumference is divided in 500 equal parts. It follows, therefore, that if the large wheel be turned so that one division passes the index, the bar moves in a straight line 1
500
of the 1
20
of an inch, that is, 1
10000
an inch. The ends of the bars, d and e, are formed with perfectly plane and parallel surfaces, and an ingenious method is adopted of securing equality of pressure when comparisons are made. A plate of steel, with perfectly parallel faces, called a gravity-piece, or feeler, is placed between the flat end of the bar and the standard-piece, and the pressure when the screw-reading is taken must be just sufficient to prevent this piece of steel from slipping down, and that is the case when the steel remains suspended and can nevertheless be easily made to slide about by a touch of the finger. Thus any piece which, 90with the same screw-readings, sustains the gravity-piece in the same manner as the standard, will be of exactly the same length; or the number of divisions through which the large wheel must be turned to enable it to do so tells the difference of the dimensions in ten-thousandth parts of an inch. By this instrument, therefore, gauges, patterns, &c., can be verified with the greatest precision, and pieces can be reproduced perfectly agreeing in their dimensions with a standard piece. Thus, for example, the diameters of shafting can be brought with the greatest precision to the exact size required to best fit their bearings.

In another measuring machine on the same principle the delicacy of the measurement has been carried still farther, by substituting for the large divided wheel one having 200 teeth, which engage an endless screw or worm. This will easily be understood by reference to Fig. 31, where a similar arrangement is applied to another purpose. Imagine that a wheel like P, Fig. 31, but with 200 teeth, has taken the place of E in Fig. 30, and that the wheel, T, on the axis of the endless screw is shaped like E, Fig. 30. One turn of the axis carrying the endless screw, therefore, turns the wheel through 1
200
of a revolution, and as this axis bears a graduated head, having 250 divisions, the screw having 20 threads to the inch, is, when one division passes the index, advanced through a space equal to 1
250
× 1
200
× 1
20
, or 1
1000000
an inch; that is, the one-millionth part of an inch. This is an interval so small that ten times its length would hardly be appreciated with the highest powers of the microscope, and the machine is far too delicate for any practical requirements of the present day. It will indicate the expansion caused by heat in an iron bar which has merely been touched with the finger for an instant, and even the difference of length produced by the heat radiated from the person using it. A movement of 1
1000000
of an inch is shown by the gravity-piece remaining suspended instead of falling, and the piece falls again when the tangent-screw is turned back through 1
250
of a revolution, a difference of reading representing a possible movement of the measuring surface through only 2
1000000
an inch. This proves the marvellous perfection of the workmanship, for it shows that the amount of play in the bearings of the screws does not exceed one-millionth of an inch.

A good example of a machine-tool is the Drilling Machine, which is used for drilling holes in metal. Such a machine is represented in Fig. 31, where A is the strong framing, which is cast in a single piece, in order to render it as rigid as possible. The power is applied by means of a strap round the speed pulley, B, by which a regulated speed is communicated to the bevel wheel, C, which drives D, and thus causes the rotation of the hollow shaft, E. In the lower part of the latter is the spindle which carries the drilling tool, F, and upon this spindle is a longitudinal groove, into which fits a projection on the inside of E. The spindle is thus forced to rotate, and is at the same time capable of moving up and down. The top of the spindle is attached to the lower end of the rack, G, by a joint which allows the spindle to rotate freely without being followed in its rotation by the rack, although the latter communicates all its vertical movements to the spindle, as if the two formed one piece. The teeth of the rack are engaged by a pinion, which carries on its axis the wheel H, turned by an endless screw on the shaft, I, which derives its motion by means of another wheel and endless screw from the shaft, K. The latter is driven by a strap passing over the speed pulleys, L and M, and thus the speed of the shaft K can be modified as required by passing the strap from one pair of pulleys to 91another. The result is that the rack is depressed by a slow movement, which advances the drill in the work, or, as it is technically termed, gives the feed to the drill. By a simple piece of mechanism at N the connection of the shafts K and I can be broken, and the handle O made to communicate a more rapid movement to I, so as to raise up the drill in a position to begin its work again, or to bring it quickly down to the work, and then the arrangement for the self-acting feed is again brought into play. By turning the wheel, P, the table, Q, on which the work is fastened, is capable of being raised or lowered, by means of a rack within the piece R, acted on by a pinion carried on the axle, P. The table also admits of a horizontal motion by the slide S, and may besides be swung round when required.

Fig. 31.Whitworth’s Drilling Machine.

The visitor to an engineer’s workshop cannot fail to be struck with the 92operation of the powerful Lathes and Planing Machines, by which long thick flakes or shavings of iron are removed from pieces of metal with the same apparent ease as if the machine were paring cheese. The figure on the opposite page represents one of the larger forms of the planing machine, as constructed by Sir J. Whitworth. The piece of work to be planed is firmly bolted down to the table, A, which moves upon the -shaped surfaces, running its whole length, and accurately fitting into corresponding grooves in a massive cast iron bed. The bevel wheel, of which a portion is seen at B, is keyed on a screw, which extends longitudinally from end to end of the bed. This screw works in nuts forming part of the table, and as it turns in sockets at the ends of the bed, it does not itself move forward, but imparts a progressive movement to the table, and therefore to the piece of metal to be planed. As this table must move backwards and forwards, there must be some contrivance for reversing the direction of the screw’s rotation, and this is accomplished in a beautifully simple manner by an arrangement which a little consideration will enable any one to understand. It will be observed that there are three drum-pulleys at C. Let the reader confine, for the present, his attention to the nearest one, and picture to himself that the shaft to which it is attached is placed in the same horizontal plane as the axis of the screw and at right angles to it, passing in front of bevel wheel B. A small bevel wheel turning with this shaft, and engaging the teeth of the wheel B, may, it is plain, communicate motion to the screw. Now let the reader consider what will be the effect on the direction of the rotation of B of applying the bevelled pinion to the nearer or to the farther part of its circumference, supposing the direction of the rotation of this pinion to be always the same. He will perceive that the direction in one case will be the reverse of that in the other. The shaft to which the nearest pulley is attached carries a pinion engaging the wheel at its farther edge, and therefore the rotation of this pulley in the same direction as the hands of a watch causes the wheel B to rotate so that its upper part moves towards the spectator. The farthest pulley, a, turns with a hollow shaft, through which the shaft of the nearest pulley simply passes, without any connection between them, and this hollow shaft carries a pinion, which engages the teeth of B at the nearer edge, and, in consequence, the rotation of the farther pulley, a, in the direction of the hands of a watch, would cause the upper part of B to be moving from the spectator. The middle pulley, b, runs loosely on the shaft, and the driving-strap passes through the guide, c, and it is only necessary to move this, so as to shift the strap from one drum to another, in order to reverse the direction of the screw and the motion. This shifting of the strap is done by a movement derived from the table itself, on which are two adjustable stops, D and E, acting on an arrangement at the base of the upright frame when they are brought up to it by the movement of the table, so as not only to shift the strap, but also to impart a certain amount of rotation to upright shaft, F, in each direction alternately. The piece which carries the tools, G and H, is placed horizontally, and can be moved vertically by turning the axis, I, thus causing an equal rotation of two upright screws of equal pitch, which are contained within the uprights and work in nuts, forming part of the tool-box. The pieces carrying the tools are moved horizontally by the screws which are seen to pass along the tool-box, and these screws receive a certain regulated amount of motion at each reversal of the movement of the table from the mechanism shown at K. The band-pulley, L, receives a certain amount of rotation from the same shaft, and the catgut band passing round the tops 94of the cylinders which carry the cutters is drawn in alternate directions at the end of each stroke, the effect being to turn the cutters half round, so as always to present their cutting edges to the work. There are also contrivances for maintaining the requisite steadiness in the tools and for adjusting the depth of the cut. The cutting edge of the tools is usually of a -shape, with the angle slightly rounded, and the result of the process is not the production of a plane, but a grooved surface. But by diminishing the amount of horizontal feed given to the cutters, the grooves may be made finer and finer, until at length they disappear, and the surface is practically a plane. Planing machines are sometimes of a very large size. Sir J. Whitworth has one the table of which is 50 ft. in length, and the machine is capable of making a straight cut 40 ft. long in any article not exceeding 10 ft. 6 in. high or 10 ft. wide.

Fig. 32.Whitworth’s Planing Machine.

Fig. 33.Pair of Whitworth’s Planes, or Surface Plates.

The copying principle is evident in this machine; for the plane surface results from the combination of the straightness of the bed with the straightness of the transverse slide along which the tools are moved. It should, moreover, be observed that it is precisely this machine which would be employed for preparing the straight sliding surfaces required in the construction of planing and other machines, and thus one of these engines becomes the parent, as it were, of many others having the same family likeness, and so on ad infinitum. Thus, having once obtained perfectly true surfaces, we can easily reproduce similar surfaces. But the reader may wish to know how such forms have been obtained in the first instance; how, for example, could a perfectly plane surface be fashioned without any standard for comparison? This was first perfectly done by Sir J. Whitworth, forty-five years ago. Three pieces of iron have each a face wrought into comparatively plane surfaces; they are compared together, and the parts which are prominent are reduced first by filing, but afterwards, as the process approaches completion, by scraping, until the three perfectly coincide. The parts where the plates come in contact with each other are ascertained by smearing one of them with a little oil coloured with red ochre: when another is pressed against it, the surfaces of contact are shown by the transference of the red colour. Three plates are required, for it is possible for the prominences of No. 1 exactly to fit into the hollows of No. 2, but in that case both could not possibly exactly coincide with the surface of No. 3; for if one of them did (say No. 1), then No. 3 must be exactly similar to No. 2, and consequently when No. 2 was applied to No. 3, hollow would be opposed to 95hollow and prominence to prominence. A little reflection will show that only when the three surfaces are truly plane will they exactly and entirely coincide with each other. The planes, when thus carefully prepared, approach to the perfection of the ideal mathematical form, and they are used in the workshop for testing the correctness of surfaces, by observing the uniformity or otherwise of the impression they give to the surface when brought into contact with it, after being covered by a very thin layer of oil coloured by finely-ground red ochre.

Fig. 33 represents a small pair of Whitworth’s planes. When one of these is placed horizontally upon the other, it does not appear to actually come in contact with it, for the surfaces are so true that the air does not easily escape, but a thin film supports the upper plate, which glides upon it with remarkable readiness (A). When, however, one plate is made to slide over the other, so as to exclude the air, they may both be lifted by raising the upper one (B). This effect has, by several philosophers, been attributed to the mere pressure of the atmosphere; but recent experiments of Professor Tyndall’s show that the plates adhere even in a vacuum. The adhesion appears therefore to be due to some force acting between the substances of the plates, and perhaps identical in kind with that which binds together the particles of the iron itself.

Fig. 34.Interior of Engineer’s Workshop.

96

Fig. 35.The Blanchard Lathe.

THE BLANCHARD LATHE.

This machine affords a striking example of the application of the copying principle which is the fundamental feature of modern manufacturing processes. It would hardly be supposed possible, until the method had been explained, that articles in shape so unlike geometrical forms as gun-stocks, shoemakers’ lasts, &c., could be turned in a lathe. The mode in which this is accomplished is, however, very simple in idea, though in carrying that idea into practice much ingenious contrivance was required. The illustration, Fig. 35, represents a Blanchard’s lathe, very elegantly constructed by Messrs. Greenwood and Batley, of Leeds. The first obvious difference between an ordinary lathe and Blanchard’s invention is that in the former the work revolves rapidly and the cutting-tool is stationary, or only slowly shifts its position in order to act on fresh portions of the work, while in the latter the work is slowly rotated and the cutting-tools are made to revolve with very great velocity. Again, it will be observed that the headstock of the Blanchard lathe, instead of one, bears two mandrels, having their axes parallel to each other. One of these carries the pattern, C, which in the figure has the exact shape of a gun-stock that is to be cut in the piece of wood mounted on the nearer spindle. One essential condition in the arrangement of the apparatus is that the pattern and the work having been fixed in similar and parallel positions, shall always continue so at every point of their revolutions. This is easily accomplished by placing exactly similar toothed wheels on the two axles, and causing these to be turned by one and the same smaller toothed wheel or pinion. The two axles must thus always turn round in the same direction and with exactly the same speed, so that the work which is attached to one, and the pattern which is fixed on the other, will always be in the same phase of their revolutions. If, for example, the part of the wood which is to form the upper part of the gun-stock is at the 97bottom, the corresponding part of the pattern will also be at the bottom, as in the figure, and both will turn round together, so that every part of each will be at every instant in a precisely similar position. The wood to be operated upon is, it must be understood, roughly shaped before it is put into the lathe. The toothed wheels and the pinion which drives them are in the figure hid from view by the casing, h, which covers them. The pinion receives the power from a strap passing over f. The cutters are shown at e; they are placed radially, like the spokes of a wheel, and have all their cutting edges at precisely one certain distance from the axis on which they revolve, so that they all travel through the same circle. These cutting-edges, it may be observed, are very narrow, almost pointed. The shaft carrying the cutters is driven at a very high speed, by means of a strap passing over k and i. The number of revolutions made by the cutters in one second is usually more than thirty. The great peculiarity of the lathe consists in the manner in which the position of the cutters is made to vary. The axle which carries them rotates in a kind of frame, which can move backwards and forwards, so that the cutters may be readily put at any desired distance from the axis of the work. Their position is, however, always dependent on the pattern, for, fixed in a similar frame, b, which is connected with the former, is a small disc wheel, a, having precisely the same radius as that of the circle traced out by the cutters, and this disc is made by a strong spring to press against the pattern. The cutters, being fixed in the same rocking-frame which carries this guiding-wheel, must partake of all its backward and forward motions, and as the cutting-wheel and the guide-wheel are so arranged as to have always the same relative positions to the axes of the two headstocks, it follows that the edges of the cutters will trace out identically the same form as the circumference of the guiding-disc. The latter is, of course, not driven round, but simply turns slowly with the pattern by friction, for it is pressed firmly against the pattern by a spring or weight acting on the frame, in order that the cutters may be steadily maintained in their true, but ever-varying, position. The rocking-frame receives a slow longitudinal motion by means of the screw, n, so that the cutters are carried along the work, and the guide along the pattern.

The whole arrangement is self-acting, so that when once the pattern and the rough block of wood have been fixed in their positions, the machine completes the work, and produces an exact repetition of the shape of the pattern. It is plain that any kind of forms can be easily cut by this lathe, the only condition being that the surface of the pattern must not present any re-entering portions which the edge of the guide-wheel cannot follow. The machine is largely used for the purposes named above, and also for the manufacture of the spokes of carriage-wheels. The limits of this article will not permit of a description of the beautiful adjustments given to the mechanism in the example before us, particularly in the arrangement for driving the cutters in a framework combining lateral and longitudinal motions; but the intelligent reader may gather some hints of these by a careful inspection of the figure. The machine is sometimes made with the frame carrying the guide-wheel and cutters, not rocking but sliding in a direction transverse to the axes of the headstocks. It is extremely interesting to see the Blanchard lathe at work, and observe how perfectly and rapidly the curves and form of the patterns seem to grow, as it were, out of the rudely-shaped piece of wood, which, of course, contains a large excess of material, or, in the picturesque and expressive phrase of the workmen, always gives the machine something to eat.

98

Fig. 36.Vertical Saw.

SAWING MACHINES.

With the exception of the last, all the machines hitherto described in the present article are distinguished by this—they are tools which are used to produce other machines of every kind. Without such implements it would be impossible to fashion the machines which are made to serve so many different ends. Another peculiarity of these tools has also been referred to, namely, that they are especially serviceable, and indeed essential, for the reproduction of others of the same class. Thus, the accurate leading-screw of the lathe is the means used to cut other accurate screws, which shall in their turn become the leading-screws of other lathes, and a lathe which forms a truly circular figure is a necessary implement for the construction of another lathe which shall also produce truly circular figures. In these tools, therefore, we find the copying principle, to which allusion has been already made, as the great feature of all machines; but in order to bring this principle still more clearly before the reader, we have described in the Blanchard Lathe a machine of a somewhat different class, because it embodied a very striking illustration of the principle in question. We are far from having described all the implements of the mechanical engineer, or even all the more interesting ones; for example, we have given no account of the powerful lathes in which great masses of iron are turned, or of the analogous machines, which, with so much accuracy, shape the internal surfaces of the cylinders of steam engines, of cannons, &c. The 99history of the steam engine tells us of the difficulties which Watt had to contend with in the construction of his cylinders, for no machine at that time existed capable of boring them with an approach to the precision which is now obtained.

Fig. 37.Circular Saw.

The kind of general interest which attaches to the tools we have already described is not wanting in yet another class of machine-tools, namely, those employed in converting timber into the forms required to adapt it for the uses to which it is so extensively applied. And for popular illustration, this class of tools presents the special advantage of being readily understood as regards their purpose and mode of action, while their simplicity in these respects does not prevent them from showing the advantages of machine over hand labour. Everybody is familiar with the up-and-down movement of a common saw, and in the machine for sawing balks of timber into planks, represented in Fig. 36, this reciprocating motion is retained, but there are a number of saws fixed parallel to each other in a strong frame, at a distance corresponding to the thickness of the planks. The saws are not placed with their cutting edges quite upright, but these are a little more forward at the top, so that as they descend they cut into the wood, but move upwards without cutting, for the teeth then recede from the line of the previous cut, while in the meantime the balk is pushed forward ready for the next descent of the saw-frame. This pushing forward, or feeding, of the timber is accomplished by means of ratchet-wheels, which are made to revolve through a certain space after each descent of the saw-frame, and, by turning certain pinions, move forward the carriage on which the piece of timber is firmly fixed, so that when the blades 100of the saws are beginning the next descent they are already in contact with the edge of the former cut. To prevent the blades from moving with injurious friction in the saw-cuts, these last are made of somewhat greater width than the thickness of the blades, by the simple plan of bending the teeth a little on one side and on the other alternately. The rapidity with which the machine works, depends of course on the kind of wood operated upon, but it is not unusual for such a machine to make more than a hundred cuts in the minute. The figure shows the machine as deriving its motion by means of a strap passing over a drum, from shafting driven by a steam engine. This is the usual plan, but sometimes the steam power is applied directly, by fixing the piston-rod of a steam cylinder to the top of the saw-frame, and equalizing the motion by a fly-wheel on a shaft, turned by a crank and connecting-rod.

A very effective machine for cutting pieces of wood of moderate dimensions is the Circular Saw, represented in Fig. 37. Here there is a steel disc, having its rim formed into teeth; and the disc is made to revolve with very great speed, in some cases making as many as five hundred turns in a minute, or more than eight in a second. On the bench is an adjustable straight guide, or fence, and when this has been fixed, the workman has only to press the piece of wood against it, and push the wood at the same time towards the saw, which cuts it at a very rapid rate. Sometimes the circular saw is provided with apparatus by which the machine itself pushes the wood forwards, and the only attention required from the workman is the fixing of the wood upon the bench, and the setting of the machine in gear with the driving-shaft. Similar saws are used for squaring the ends of the iron rails for railways, two circular saws being fixed upon one axle at a distance apart equal to the length of the rails. The axle is driven at the rate of about 900 turns per minute, and the iron rail is brought up parallel to the axle, being mounted on a carriage, and still red hot, when the two ends are cut at the same time by the circular saws, the lower parts of which dip into troughs of water to keep them cool.

Fig. 38.Pit-Saw.

101

Fig. 39.Box Tunnel.

RAILWAYS.

Fig. 40.Coal-pit, Salop.

Towards the end of last century, tramways formed by laying down narrow plates of iron, were in use at mines and collieries in several parts of England. These plates had usually a projection or flange on the inner edge, thus—L, in order to keep the waggons on the track, for the wheels themselves had no flange, but were of the kind used on ordinary roads. These flat tramways were found liable to become covered up with dirt and gravel, so that the benefit which ought to have been obtained from their smoothness was in a great measure lost. Edge rails were, therefore, substituted, and the wheels were kept on the rails by having a flange cast on the inner edge of the rim. The rails were then always made of cast iron, for, although they were very liable to break, the great cost of making them of wrought iron prevented that material from being used until 1820, when the method of forming rails of malleable iron by rolling came into use. The first time a tramway was used for the conveyance of passengers was in 1825, when the Stockton and Darlington Railway was opened—a length of thirty-seven miles. It appears that the carriages were at first drawn by horses, although locomotives were used on this and other colliery lines for dragging, at a slow rate, trains of mineral waggons. At that time engineers were exercising their ingenuity in overcoming a difficulty which never existed by devising plans for giving tractive power to the locomotive through the instrumentality of rack-work rails. It never occurred to them to first try whether the adhesion of the smooth wheel to the smooth rail was not sufficient for the purpose. During the first quarter of the present 102century the greater part of the goods and much passenger traffic was monopolized by the canals. It is quoted, as a proof of the careless manner in which this service was performed, that the transport of bales of cotton from Liverpool to Manchester sometimes occupied twice the length of time required in their voyage across the Atlantic. When an Act of Parliament authorizing the construction of a railway between Liverpool and Manchester was applied for, the canal companies succeeded in retarding, by their influence, the passing of that Act for two years. It was passed, however, in 1828, and the construction of the line was proceeded with. This line was at first intended only for the conveyance of goods, especially of cotton and cotton manufactures, and the waggons were to be drawn by horses. When the line was nearly finished the idea of employing horses was, at the instigation of Mr. George Stephenson, abandoned in favour of steam power. The directors were divided in opinion as to whether the carriage should be dragged by ropes wound on large drums by stationary engines, or whether locomotives should be employed. Finally, the latter plan was adopted, and it was also suggested that passengers might be carried. The directors offered a prize for the best locomotive, and the result has been already mentioned. In the light of our experience since that time, it is curious to read of the doubts then entertained by skilful engineers about the success of the locomotive. In a serious treatise on the subject, one eminent authority hoped “that he might not be confounded with those hot-brained enthusiasts who maintained the possibility of carriages being driven by a steam engine on a railway at such a speed as twelve miles an hour.” When the “Rocket” had accomplished the unprecedented velocity of twenty-nine miles an hour, and the railway was opened for passengers as well as goods, the thirty stage coaches daily plying between Liverpool 103and Manchester found their occupation gone, and all ceased to run except one, which had to depend on the roadside towns only, while the daily number of passengers between the two cities rose at once from 500 to 1,600. In that delightful book, Smiles’s “Life of George Stephenson,” may be found most interesting details of the difficulties attending the introduction of railways, especially with regard to the construction of this first important line. Mr. Smiles relates how the promoters of the scheme struggled against “vested interests;” how the canal proprietors, confident at first of a secure and continuous enjoyment of their monopoly, ridiculed the proposed railway, and continued their exorbitant charges and tardy conveyance, pocketing in profits the prime cost of their canal about every three years; how, roused into active opposition, they did all in their power to thwart the new scheme; how the Lord Derby and the Lord Sefton of that day, and other landowners, offered every resistance to the surveyors; how the Duke of Bridgewater’s farmers would not allow them to enter their fields, and the Duke’s gamekeepers had orders to shoot them; how even a clergyman threatened them with personal violence, and they had to do their work by stealth, while the reverend gentleman was conducting the services in his church; how newspaper and other writers declared that the locomotives would kill the birds, prevent cows from grazing and hens from laying, burn houses, and cause the extinction of the race of horses. All the civil engineers scouted the idea of a locomotive railway, and Stephenson was held up to derision as an ignoramus and a maniac by the “most eminent lawyers,” and the most advanced and “respectable” professional C.E.s of the time. An article appeared in the “Quarterly Review,” very favourable to the construction of railways, but remarking in reference to a proposed line between London and Woolwich: “What can be more palpably absurd and ridiculous than the prospect held out of locomotives travelling twice as fast as stage coaches! We should as soon expect the people of Woolwich to suffer themselves to be fired off upon one of Congreve’s ricochet rockets 104as trust themselves to the mercy of a machine going at such a rate. We will back old Father Thames against the Woolwich Railway for any sum. We trust that Parliament will, in all railways it may sanction, limit the speed to eight or nine miles an hour, which we entirely agree with Mr. Sylvester is as great as can be ventured on with safety.” This passage, which reads so strangely now, may be seen in the “Quarterly Review” for March, 1825. But still more curious appear now the reports of the debates in Parliament, and of the evidence taken before the Parliamentary Committee, in which we find the opinions and fears of the best informed men of that period, and trace the frantic efforts of the holders of the “vested interests” to retain them, however obstructive of the public good.

Fig. 41.Sankey Viaduct.

Fig. 42.Rails and Cramp-gauge.

When it has been decided to construct a railway between two places, the laying-out of the line is a subject requiring great consideration and the highest engineering skill—for the matter is, on account of the great cost, much more important than the setting-out of a common road. The idea of a perfect railroad is that of a straight and level line from one terminus to another; but there are many circumstances which prevent such an idea from being ever carried into practice. First, it is desirable that the line should pass through important towns situated near the route; and then the cost of making the roadway straight and level, in spite of natural obstacles, would be often so great, that to avoid it detours and inclines must be submitted to—the inconvenience and the increased length of road being balanced by the saving in the cost of construction. It is the business of the engineer who lays out the line to take all these circumstances into consideration, after he has made a careful survey of the country through which the line is to pass. The cost of making railways varies, of course, very much according to the number and extent of the tunnels, cuttings, embankments, or other works required. The average cost of each mile of railway in Great Britain may be stated as about £35,000. The road itself when the rails are laid down is called the permanent way, perhaps originally in distinction to the temporary tramways laid down by the contractors during the progress of the works. The permanent way is formed first of 105ballast, which is a layer of gravel, stone, or other carefully chosen material, about 2 ft. deep, spread over the roadway. Above the ballast and partly embedded in it are placed the sleepers, which is the name given to the pieces of timber on which the rails rest. These timbers are usually placed transversely—that is, across the direction of the rails, in the manner shown in Fig. 42. This figure also represents the form of rails most commonly adopted, and exhibits the mode in which they are fastened down to the sleepers by means of the iron chairs, b c, the rail being firmly held in its place by an oak wedge, d. These wedges are driven in while the rails are maintained at precisely the required distance apart by the implement, e f, called a cramp gauge, the chairs having previously been securely attached to the sleepers by bolts or nails. The double form of rail has several important advantages, such as its capability of being reversed when the upper surface is worn out, and the readiness with which the ends of the rails can be joined by means of fish-plates. These are shown in Fig. 43, where in a we are supposed to be looking down on the rails, and in B to be looking at them sideways. In Fig. 44 we have the rail and fish-plates in section. The holes in the rails through which the bolts pass are not round but oval, so that a certain amount of play is permitted to the ends of the rails.

Fig. 43.Fish-plate.

It may easily be seen on looking at a line of rails that they are not laid with the ends quite touching each other, or, at least, they are not usually in contact. The reason of this is that space must be allowed for the expansion which takes place when a rise in the temperature occurs. If the rails are laid down when at the greatest temperature they are likely to be subject to, they may then be placed in actual contact; but in cold weather a space will be left by their contraction. For this reason it is usual when rails are laid to allow a certain interval; thus rails 20 ft. long laid when the temperature is 70°, are placed with their ends 1
20
th of an inch apart, at 30° 1
10
th of an inch apart, and so on. The neglect of this precaution has sometimes led to damage and accidents. A certain railway was opened in June, and after an excursion train had in the morning passed over it, the midday 106heat so expanded the iron, that the rails became in some places elevated 2 ft. above the level, and the sleepers were torn up; so that, in order to admit of the return of the train, the rails had to be hastily relaid in a kind of zigzag. In June, 1856, a train was thrown off the metals of the North-Eastern Railway, in consequence of the rails rising up through expansion.

Fig. 44.Section of Rails and Fish-plates.

The distance between the rails in Great Britain is 4 ft. 8½ in., that width having been adopted by George Stephenson in the construction of the earlier lines. Brunel, the engineer of the Great Western, adopted, however, in the construction of that railway, a gauge of 7 ft., with a view of obtaining greater speed and power in the engines, steadiness in the carriages, and increased size of carriages for bulky goods. The proposal to adopt this gauge gave rise to a memorable dispute among engineers, often called “The Battle of the Gauges.” It was stated that any advantages of the broad gauge were more than compensated by its disadvantages. The want of uniformity in the gauges was soon felt to be an inconvenience to the public, and a Parliamentary Committee was appointed to consider the subject. They reported that either gauge supplied all public requirements, but that the broad gauge involved a great additional outlay in its construction without any compensating advantages of economy in working; and, as at that time 2,000 miles of railway had been constructed on the narrow gauge, whereas only 270 miles were in existence on the broad gauge, they recommended that future railways should be made the prevailing width of 56½ in. The Great Western line had engines, bridges, tunnels, viaducts, &c., on a larger scale than any other railway in Britain. The difference of gauge was after a time felt to involve so much inconvenience that lines which adopted the 7–ft. gauge have since relaid the tracks at the more common width. At the present day we find the Great Western Railway completely reconstructed on the narrow gauge system, in order that trains may run without interruption in connection with other lines.

Fig. 45.Conical Wheels.

Fig. 46.Centrifugal Force.

The wheels of railway carriages and engines differ from those of ordinary 107carriages in being fastened in pairs upon the axles, with which they revolve (see Fig. 45). The tire of the wheel is conical, the slope being about 1 in 20; that is, in a wheel 5 in. broad the radius of the outer edge is ¼ in. less than that of the inner; and the rails are placed sloping a little inwards. The effect of this conical figure is to counteract any tendency to roll off the rails; for if a pair of wheels were shifted a little to one side, the parts of the tires rolling upon the rails being then of unequal circumference, would cause the wheels to roll towards the other side. The conical shape produces this kind of adjustment so well that the flanges do not in general touch the rails. They act, however, as safeguards in passing over curves and junctions. In curves the outer line of rails is laid higher than the inner, so that in passing over them the train leans slightly inwards, in order to counteract what is called the centrifugal force, to which any body moving in a curve is subject. This so-called force is merely the result of that tendency which every moving body has to continue its motion in a straight line. A very good example of the effect of this may be seen when a circus horse is going rapidly round the ring. The inclination inwards is still more perceptible when a rider is standing on the horse’s back, as shown in Fig. 46. The earth’s attraction of gravity is pulling the performer straight down, and the centrifugal force would of itself throw her outwards horizontally. The resultant or combined effect of both acts is seen in the exact direction in which she is leaning, and it presses her feet on the horse’s back, the animal itself being under similar conditions. It is obvious that the amount of centrifugal force, and therefore of inward slope, will increase with the speed and sharpness of the curve, and on the railways the rails 108are placed so that the slope counteracts the centrifugal force when the train travels at about the rate of twenty miles per hour.

Fig. 47.Points.

A very important part of the mechanism of a railway is the mode of passing trains from one line of rails to another. Engines and single carriages are sometimes transferred by means of turn-tables, but the more general plan is by switches, which are commonly constructed as shown in Fig. 47. There are two rails, A and B, tapering to a point and fixed at the other end, so that they have sufficient freedom to turn horizontally. A train passing in the direction shown by the arrow would continue on the main line, if the points are placed as represented; but if they be moved so that the long tongue is brought into contact with the rail of the main line, then the train would run on to the side rails. These points are worked by means of a lever attached to the rod, C, the lever being either placed near the rails, or in a signal-box, where a man is stationed, whose sole duty it is to attend to the points and to the signals. The interior of a signal-box near an important junction or station is shown in Fig. 48, and we see here the numerous levers for working the points and the signals, each of these having a connection, by rods or wires, with the corresponding point or signal-post. The electric telegraph is now an important agent in railway signalling, and in a signal-box we may see the bells and instruments which inform the pointsman whether a certain section of the line is “blocked” or “clear.” The signals now generally used on British railways are made by the semaphore, which is simply a post from which an arm can be made to project. When the driver of the train sees the arm projecting from the left-hand side of the post, it is an intimation to him that he must stop his train; when the arm is dropped half-way, so as to project 45° from the post, it is meant that he must proceed cautiously; when the arm is down the line is clear. These signals, of course, are not capable of being seen at night, when their place is supplied with lamps, provided with coloured glasses—red and green—and also with an uncoloured glass. The lamp may have the different glasses on three different sides, and be turned round so as to present the required colour; or it may be made to do so without turning, if provided with a frame having red and green glasses, which can be moved 109like spectacles in front of it. The meanings of the various coloured lights and the corresponding semaphore signals are these:

White All right Go on.
Green Caution Proceed slowly.
Red Danger Stop.

Fig. 48.Signal-box on the North London Railway.

A very clear account of the mode of working railway signals on what is now called the block system, together with a graphic description of a signal-box, was given in a paper which appeared some years ago in “The Popular Science Review,” from the pen of Mr. Charles V. Walker, F.R.S., the telegraph engineer to the South-Eastern Railway Company, who was the first to organize an efficient system of electric signalling for railways. We may remark that the signalling instruments on the South-Eastern line, and indeed on all the lines at the present day, address themselves both to the ear and to the eye, for they consist of—first, bells, on which one, two, or more blows are struck, each series of blows having its own particular meaning; and, second, of a kind of miniature signal-post, with arms capable of being moved by electric currents into positions similar to those of the arm of an actual signal-post, so that the position of the arms is made always to indicate the state of the line. One arm of the little signal-post—the left—is red, and it has reference to receding trains; the other—viz., the right—arm is white, and relates to approaching trains. Mr. Walker thus describes the signalling:

110“The ordinary position of the arms of the electro-magnetic telegraph semaphores will be down; that is to say, when the line is clear of all trains, and business begins, say in early morning, all the arms will be down, indicating that no train is moving. When the first train is ready to start, say from Charing Cross, the signalman will give the proper bell-signal to Belvidere—two, three, or four blows, according as the train is for Greenwich, for North Kent, or Mid-Kent, or for the main line; and the Belvidere man will acknowledge this by one blow on the bell in reply, and without raising the Charing Cross red or left arm. This is the signal that the train may go on; and when the train has passed, so that the Charing Cross man can see the tail lights, he gives the out signal a second time, which the Belvidere man acknowledges, at the same time raising the red arm at Charing Cross, behind the train, and so protecting it until it has passed him at Belvidere, when he signals to that effect to Charing Cross, at the same time putting down the red arm there, as an indication that the line is again clear. While these operations are going on for down trains, others precisely similar, but in the reverse direction, are going on for up trains.... One and the same pressure on the key sends a bell signal and raises or depresses the semaphore arm as the case may require, a single telegraph wire only being required for the combined system, as for the more simple bell system.” In one of the signal-boxes on the South-Eastern line, Mr. Walker states, on a certain day 650 trains or engines were signalled and all particulars accurately entered in a book, the entries requiring the writing down of nearly 8,000 figures: an illustration of the amount of work quietly carried on in a signal-box for the advantage and security of the travelling public.

Mr. Walker also gives us a peep into the inside of one of the signal-boxes, thus: “The interior of a large signal-box exhibits a very animated scene, in which there are but two actors, a man and a boy, both as busy as bees, but with no hurry or bustle. The ruling genius of the place is the strong, active, intelligent signalman, standing at one end of the apartment, the monarch for the time being of all he surveys. Immediately before him in one long line, extending from side to side, is a goodly array of levers, bright and clean from constant use and careful tending, each one labelled for its respective duty. Before him to the right and left are the various electro-magnetic semaphores, each one in full view and adjusted in position to the pair of roads to which it is appropriated, and all furnished with porcelain labels. Directly in front of him is a screen, along which are arranged the various semaphore keys; and on brackets, discreetly distributed, are the bells and gongs, the twin companions each of its own semaphore. Before the screen are the writing-desk and books, and here stands the youngster, the ministering spirit, all on the alert to take or to send electric signals and to record them, his time and attention being devoted alternately to his semaphore keys and to his books, being immediately under the eye and control of the signalman. This is no place for visitors, and the scenes enacted here have little chance of meeting the public gaze; indeed, the officers whose duties take them hither occasionally are only too glad to look on, and say as little as may be, and not interrupt the active pair, between whom there is evidently a good understanding in the discharge of duties upon the accurate performance of which so much depends. Looking on, the man will be seen in command of his rank and file: signals come, are heard and seen by both man and boy; levers are drawn and withdrawn, one, two, three, or more; the arms and the lamps on the gigantic masts outside, of which there are three, well laden, are displayed as required, 111distant signals are moved, points are shifted and roads made ready; telegraph signals are acknowledged; and on looking out—for the box is glazed throughout—trains are seen moving in accordance with the signals made; and on the signal-posts at the boxes, right and left—for here they are within easy reach of each other—arms are seen up and down in sympathy with those on the spot, and with the telegraph signals that have been interchanged. There is no cessation to this work, and there is no confusion in it; one head and hand directs the whole, so that there are no conflicting interests and no misunderstandings; all is done in perfect tranquillity, and the great secret is that one thing is done at a time. All this, which is so simple and so full of meaning to the expert, is to the uninitiated intricate and vague; and though he cannot at first even follow the description of the several processes, so rapidly are they begun and ended, yet, as the cloud becomes thin, and his ideas become clearer, he cannot fail to be gratified, and to be filled with admiration at the great results that are brought about by means so simple.”

Fig. 49.Post Office Railway Van.

Most of the carriages used on railways are so familiar to everyone that it is unnecessary to give any description of them. We give a figure of one which, though of early type, has special features of interest, being the well-designed Travelling Post Office, Fig. 49. In such vans as that here represented letters are sorted during the journey, and for this purpose the interior is provided with a counter and with pigeon-holes from end to end. When the train stops bags may, of course, be removed from or received into the van in the ordinary manner; but by a simple mechanism bags may be delivered at a station and others taken up while the train continues its journey at full speed. A bar can be made to project from the side of the carriage, and on this the bag is hung by hooks, which are so contrived that they release the bag when a rod, projecting from the receiving apparatus, strikes a certain catch on the van. The bag then drops into a netting, which is spread for its reception; and in order to receive the bags taken up, a similar netting is stretched on an iron frame attached to the van 112This frame is made to fold up against the side of the carriage when not in use. When the train is approaching the station where the bag is to be taken up, this frame is let down, and a projecting portion detaches the bags, so that they drop into the net, from which they are removed into the interior of the vehicle. These travelling post offices are lighted with gas, and are padded at the ends, so that the clerks may not be liable to injury by concussions of the carriages.

England has had to borrow from the United States not a few hints for such adaptations and appliances as tend to promote the comfort and convenience of travellers by rail, especially on what we insularly call long journeys. Some of these vehicles on the American railways are luxurious hotels upon wheels; they contain accommodation for forty persons, having a kitchen, hot and cold water, wine, china and linen closets, and more than a hundred different articles of food, besides an ample supply of tablecloths, table napkins, towels, sheets, pillowcases, &c. Then there are other Pullman inventions, such as the “palace” and the “sleeping” cars, in which the traveller who is performing a long journey makes himself at home for days, or perhaps for a week, as, for instance, while he is being carried across the American continent from ocean to ocean at the easy rate of twenty miles an hour on the Pacific and other connecting lines. Mr. C. Nordhoff, an American writer, giving an account of his journey to the Western States, writes thus: “Having unpacked your books and unstrapped your wraps in your Pullman or Central Pacific palace car, you may pursue all the sedentary avocations and amusements of a parlour at home; and as your housekeeping is done—and admirably done—for you by alert and experienced servants; as you may lie down at full length, or sit up, sleep, or wake at your choice; as your dinner is sure to be abundant, very tolerably cooked, and not hurried; as you are pretty certain to make acquaintances in the car; and as the country through which you pass is strange and abounds in curious and interesting sights, and the air is fresh and exhilarating—you soon fall into the ways of the voyage; and if you are a tired business man or a wearied housekeeper, your careless ease will be such a rest as certainly most busy and overworked Americans know how to enjoy. You write comfortably at a table in a little room called a ‘drawing-room,’ entirely closed off, if you wish it, from the remainder of the car, which room contains two large and comfortable armchairs and a sofa, two broad clean plate-glass windows on each side (which may be doubled if the weather is cold), hooks in abundance for shawls, hats, &c., and mirrors at every corner. Books and photographs lie on the table. Your wife sits at the window sewing and looking out on long ranges of snow-clad mountains or on boundless ocean-like plains. Children play on the floor or watch at the windows for the comical prairie dogs sitting near their holes, and turning laughable somersaults as the car sweeps by. The porter calls you at any hour you appoint in the morning; he gives half an hour’s notice of breakfast, dinner, or supper; and while you are at breakfast, your beds are made up and your room or your section aired. About eight o’clock in the evening—for, as at sea, you keep good hours—the porter, in a clean grey uniform, comes in to make up the beds. The two easy-chairs are turned into a berth; the sofa undergoes a similar transformation; the table, having its legs pulled together, disappears in a corner, and two shelves being let down furnish two other berths. The freshest and whitest of linen and brightly-coloured blankets complete the outfit; and you undress and go to bed as you would at home.”

113An important general truth may find a familiar illustration in the subject now under notice. The truth in question may be expressed by saying that, in all human affairs, as well as in the operations of nature, the state of things at any one time is the result, by a sort of growth, of a preceding state of things. And in this way it is certainly true of inventions, that they never make their appearance suddenly in a complete and finished state—like Minerva, who is fabled to have sprung from the brain of Jupiter fully grown and completely armed; but rather their history resembles the slow and progressive process by which ordinary mortals attain to their full stature. We have already seen that railways had their origin in the tramways of collieries; and, in like manner, the railway carriage grew out of the colliery truck and the stage coach; for when railway carriages to convey passengers were first made, it did not occur to their designers that anything better could be done than to place coach bodies on the frame of the truck; and accordingly the early railway carriages were formed by mounting the body of a stage coach, or two or three such bodies side by side, on the timber framework which was supported by the flanged wheels. The cut, Fig. 56, is from a painting in the possession of the Connecticut Historical Society, and it represents the first railway train in America on its trial trip (1831), in which sixteen persons took part, who were then thought not a little courageous. Here we see that the carriages were regular stage coaches, and the same was the case in England. But it is very significant that, to this day, the stage coach bodies are traceable in many of the carriages now running on English lines, especially in the first-class carriages, where, in the curved lines of the mouldings which are supposed to ornament the outside, one may easily recognize the forms of the curved bodies of the stage coaches, although there is nothing whatever, in the real framing of the timbers of the railway carriage, which has the most distant relation to these curves. Then again, almost universally on English lines, the old stage coach door-handles are still retained on the first-class carriages, in the awkward flat oval plates of brass which fold down with a hinge. Many other points might be named which would show the persistence of the stage coach type on the English railways. The cut, Fig. 56, proves that the Americans set out with the same style of carriages; but North America, as compared with the Old World, is par excellence the country of rapid developments, and there carriages, or cars, as our Transatlantic cousins call them, have for a long time been made with numerous improvements, and in forms more in harmony with the railway system, than the conservatism of English ideas, still cleaving to the stage coach type, permitted to be attempted in this country.

Railway travellers in the United States had long enjoyed the benefit of comforts and convenience in the appointments of their carriages long before any change had been effected in the general arrangements of the vehicles provided by the railway companies in England. It is now indeed a considerable number of years since this state of things has been altered in the older country; as all the great lines, following the example of the Midland Company, who first adopted the Pullman cars, have constructed luxurious vehicles in which every elegance and comfort are placed within the reach of the English traveller, and these improvements are highly appreciated by all who have long journeys to make by day or night.

The elegance and comfort of the arrangements are almost too obvious to require description. We see the luxuriously padded chairs, which, by turning on swivels, permit the traveller to adjust his position according to his individual wishes, so that he can, with ease, place his seat either to gaze 114directly on the passing landscape, or turn his face towards his fellow-travellers opposite or on either side. The chairs are also provided with an arrangement for placing the backs at any required inclination, and the light and refined character of the decorations of the carriage should not escape the reader’s notice. Pullman Cars of another kind, providing sleeping accommodation for night journeys, are also in use on the Midland line, and they are fitted up with the same thoughtful regard to comfort as the Parlour Car.

The great engineering feats which have been accomplished in the construction of railways are numerous enough to fill volumes. We give, therefore, only a short notice of one or two recently constructed lines which have features of special interest, concluding with a brief account of such remarkable constructions as the railway by which the traveller may now go up the Rigi, and the railways which ascend Vesuvius and Mt. Pilatus.

THE METROPOLITAN RAILWAYS.

When the traffic in the streets of London became so great that the ordinary thoroughfares were unable to meet public requirements, the bold project was conceived of making a railway under the streets. The construction of a line of railway beneath the streets of a populous city, amidst a labyrinth of gas-pipes, water-mains, sewers, &c., is obviously an undertaking presenting features so remarkable that the London Underground Railway cannot here be passed over without a short notice. Its construction occupied about three years, and it was opened for traffic in 1863. The line commencing at Paddington, and passing beneath Edgware Road at right angles, reaches Marylebone Road, under the centre of which it proceeds, and passing beneath the houses at one end of Park Crescent, Portland Place, it follows the centre of Euston Road to King’s Cross, where connection with the Great Northern and Midland system is effected. Here the line bends sharply southwards, and proceeds to Farringdon Street Station, the original terminus. A subsequent extension takes an easterly direction and reaches Aldgate Station, the nominal terminus. The crown of the arch which covers the line is in some places only a few inches beneath the level of the streets; in other places it is several feet below the surface, and, in fact, beneath the foundations of the houses and other buildings. The steepest gradient on the line is 1 in 100, and the sharpest curve has a radius of 200 yards. The line is nearly all curved, there not being in all its length three-quarters of a mile of straight rails. The difficulties besetting an undertaking of this kind would be tedious to describe, but may readily be imagined. The line traverses every kind of soil—clay, gravel, sand, rubbish, all loosened by previous excavations for drains, pipes, foundations, &c.; and the arrangements of these drains, water and gas-pipes, had to be reconciled with the progress of the railway works, without their uses being interfered with even for a time. Of the stations the majority have roofs of the ordinary kind, open to the sky; but two of them, namely, Baker Street and Gower Street, are completely underground stations, and their roofs are formed by the arches of brickwork immediately below the streets. The arrangements at these stations show great boldness and 115inventiveness of design. The booking offices for the up line are on one side of the road, and those for the down line on the other. Fig. 50 represents the interior of the Gower Street Station, and the other is very similar. In each the platforms are 325 ft. long and 10 ft. broad, and the stations are lighted by lateral openings through the springing of the arch which forms the roof. This arch is a portion of a circle of 32 ft. radius, with a span of 45 ft. and a rise of 9 ft. at the crown. The lateral openings are arched at the top and bottom, but the sides are flat. The width of each is 4 ft. 9 in., and the height outside 6 ft., increasing to 10 ft. at the ends opening on the platform. The openings are entirely lined with white glazed tiles, and the outward ends open into an area, the back of which is inclined at an angle of 45°, and the whole also lined with white glazed tiles, and covered with glass, except where some iron gratings are provided for ventilation. The tiles reflect the daylight so powerfully that but little gas is required for the illumination of the station in the day-time. The arched roofs of these stations are supported by piers of brickwork, 10 ft. apart, 5 ft. 6 in. deep, and 3 ft. 9 in. wide. In the spaces between the piers vertical arches, like parts of the brick lining of a well, are wedged in, to resist the thrust of the earth, and a straight wall is built inside of this between the piers, to form the platform wall of the station. The tops of the piers are connected by arches, and are thus made to bear the weight of the arched roof, which has 2 ft. 3 in. thickness of brickwork at the crown, and a much greater thickness towards the haunches.

Fig. 50.Gower Street Station, Metropolitan Railway.

The benefit derived by the public from the completion of the Metropolitan Railway was greatly increased by the subsequent construction of another railway—“The Metropolitan District,” which, joining the Metropolitan at Paddington, makes a circuit about the west-end of Hyde Park, and passing close to the Victoria Terminus of the London, Chatham, and Dover and the Brighton and South Coast Railways, reaches Westminster Bridge, and then follows the Thames Embankment to Blackfriars Bridge, where it 116leaves the bank of the river for the Mansion House, Mark Lane and Aldgate stations. This line, taken in conjunction with the Metropolitan, forms the “inner circle” of the railway communication in London. The circuit was for a long time incomplete at the east by the want of connection between the Mansion House Station and that of Moorgate Street, although these stations are but little more than half a mile apart. A line connecting these two points has lately been constructed at great cost, and the public now possess a complete circle of communication. The number of trains each day entering and leaving some of the stations on the Metropolitan system is very great. Moorgate Street Station—a terminus into which several companies run—may have about 800 trains arriving or departing in the course of a day.

THE PACIFIC RAILWAY.

The remarkable development of railways which has taken place in the United States has its most striking illustration in the great system of lines by which the whole continent can be traversed from shore to shore. The distance by rail from New York to San Francisco is 3,215 miles, and the journey occupies about a week, the trains travelling night and day. The traveller proceeding from the Eastern States to the far west has the choice of many routes, but these all converge to Omaha. From this point the Pacific Railroad will convey him towards the land of the setting sun. The map, Fig. 51, shows the course of this railway, which is the longest in the world. It traverses broader plains and crosses higher mountains than any other. Engineering skill of the most admirable kind has been displayed in the laying-out and in the construction of the line, with its innumerable cuttings, bridges, tunnels, and snow-sheds.

Fig. 51.Map of the Route of the Pacific Railway.

The road from Omaha to Ogden, near the Great Salt Lake—a distance of 1,032 miles—is owned by the Union Pacific Company, and the Central Pacific joins the former at Ogden and completes the communication to San Francisco, a further length of 889 miles—the whole distance from Omaha to San Francisco being 1,911 miles. The Union Pacific was commenced in November, 1865, and completed in May, 1869. There are at Omaha extensive workshops provided with all the appliances for constructing and repairing locomotives and carriages, and these works cover 30 acres of ground, and give employment to several thousand men. The population of Omaha rose during the making of the railway from under 3,000 in 1864 to more than 16,000 in 1870, and it is now a flourishing town. A little distance from Omaha the line approaches the Platte River, and the valley of this river and one of its tributaries is ascended to Cheyenne, 516 miles from Omaha, the line being nowhere very far from the river’s course. Cheyenne is 5,075 ft. higher above the sea than Omaha, the elevation of which is 966 ft. The Platte River is a broad but very shallow stream, with a channel continually shifting, owing to the vast quantity of sand which its muddy waters carry down. This portion of the line passing through a district where leagues upon leagues of fertile land await the hand of the tiller, has opened up vast tracts of land—hedgeless, gateless green fields, free to all, and capable of receiving and supporting millions of human inhabitants. 117Cheyenne, a town of 3,000 inhabitants, is entirely the creation of the railways, for southward from Cheyenne a railway passes to Denver, a distance of 106 miles, through rich farming and grazing districts. Seven miles beyond Cheyenne the line begins to ascend the Black Hills by steep gradients, and at Granite Canyon, for example, the rise in five miles is 574 ft., or about 121 ft. per mile. Many lime-kilns have been erected in this neighbourhood, where limestone is very abundant. A little beyond this point the road is in many places protected by snow-sheds, fences of timber, and rude stonework. At Sherman, 549 miles from Omaha, the line attains the summit of its track over the Black Hills, and the highest point on any railway in the world, being 8,242 ft. above the level of the sea. Wild and desolate scenery characterizes the district round Sherman, and the hills, in places covered with a dense growth of wood, will furnish an immense supply of timber for years to come. The timber-sheds erected over the line, and the fences beside it are not so much on account of the depth of snow that falls, but to prevent it from blocking the line by being drifted into the cuts by the high wind. A few miles beyond Dale Creek at Sherman is the largest bridge on the line. It is a trestle bridge, 650 ft. long and 126 ft. high, and has a very light appearance—indeed, to an English eye unaccustomed to these impromptu timber structures, it looks unpleasantly light. From Sherman the line descends to Laramie, which is 7,123 ft. above the sea level and 24 miles from Sherman, and here the railway has a workshop, for good coal is found within a few miles. A fine tract of grazing land, 60 miles long and 20 miles broad, stretches around this station, and it is said that nowhere in the whole North American continent can cattle be reared and fattened more cheaply. The line, now descending the Black Hills, crosses for many miles a long stretch of rolling prairie, covered in great part with sage-bush, and forming a tableland lying between 118the western base of the Black Hills and the eastern base of the snowy range of the Rocky Mountains, which latter reach an elevation of from 10,000 to 17,000 ft. above the sea level and are perpetually covered with snow. Such tablelands are termed in America “parks.” Before the line reaches the summit of the pass by which it crosses the range of the snowy mountains, it traverses some rough country among the spurs of the hills—through deep cuts and under snow-sheds, across ravines and rivers, and through tunnels. At Percy, 669 miles, is a station named after Colonel Percy, who was killed here by the Indians when surveying for the line. He was surprised by a party of the red men, and retreated to a cabin, where he withstood the attack of his assailants for three days, killing several of them; but at length they set fire to the cabin, and the unfortunate Colonel rushing out, fell a victim to their ferocity. Near Creston, 737 miles from Omaha, the highest point of the chief range is reached, though at an elevation lower by 1,212 ft. than the summit of the pass where the line crosses the Black Hills, which are the advanced guard of the Rocky Mountains. Here is the water-shed of the continent, for all streams rising to the east of this flow ultimately into the Atlantic,—while these, having their sources in the west, fall into the Pacific. Before reaching Ogden the line passes through some grand gorges, which open a way for the iron 119horse through the very hearts of the mountains, as if Nature had foreseen railways and providently formed gigantic cuttings—such as the Echo and Weber Canyons, which enable the line to traverse the Wahsatch Mountains.

Fig. 52.Trestle Bridge.

Echo Canyon is a ravine 7 miles long, about half a mile broad, flanked by precipitous cliffs, from 300 to 800 ft. high, and presenting a succession of wild and grand scenery. In Weber Canyon the river foams and rushes along between the mountains, which rise in massive grandeur on either side, plunging and eddying among the huge masses of rock fallen from the cliffs above. Along a part of the chasm the railway is cut in the side of the steep mountain, descending directly to the bed of the stream. Where the road could not be carried round or over the spurs of the mountains it passes through tunnels, often cut through solid stone. A few miles farther the line reaches the city of Ogden, in the state of Utah, the territory of the Mormons. This territory contains upwards of 65,000 square miles, and though the land is not naturally productive, it has, by irrigation, been brought into a high state of cultivation, and it abounds in valuable minerals, so that it now supports a population of 80,000 persons.

Fig. 53.American Canyon.

We have now arrived at Ogden, where the western portion of the great railway line connecting the two oceans unites to the Union Pacific we have just described. This western portion is known as the Central Pacific Railroad, and it stretches from Ogden to San Francisco, a distance of 882 miles.

The portion of the line which unites Sacramento to Ogden, 743 miles, was commenced in 1863 and finished in 1869, but nearly half of the entire length was constructed in 1868, and about 50 miles west of Ogden, the remarkable engineering feat of laying 10 miles of railway in one day was performed. It was thus accomplished: when the waggon loaded with the 120rails arrived at the end of the track, the two outer rails were seized, hauled forward off the car, and laid upon the sleepers by four men, who attended to this duty only. The waggon was pushed forwards over these rails, and the process of putting down the rails was repeated, while behind the waggon came a little army of men, who drove in the spikes and screwed on the fish-plates, and, lastly, a large number of Chinese workmen, with pickaxes and spades, who ballasted the line. The average rate at which these operations proceeded was about 240 ft. of track in 77½ seconds, and in these 10 miles of railway there were 2,585,000 cross-ties, 3,520 iron rails, 55,000 spikes, 7,040 fish-plates, and 14,080 bolts with screws, the whole weighing 4,362,000 lbs.! Four thousand men and hundreds of waggons were required, but in the 10 miles all the rails were laid by the same eight men, each of whom is said to have that day walked 10 miles and lifted 1,000 tons of iron rails. Nothing but the practice acquired during the four previous years and the most excellent arrangement and discipline could have made the performance of such a feat possible as the laying of eight miles of the track in six hours, which was the victory achieved by these stalwart navvies before dinner.

The line crosses the great American desert, distinguished for its desolate aspect and barren soil, and so thickly strewn with alkaline dust that it appears almost like a snow-covered plain. The alkali is caustic, and where it abounds no vegetation can exist, most of the surface of this waste being fine, hard grey sand, mixed with the fragments of marine shells and beds of alkali.

The third great mountain range of the North American continent is crossed by this line, at an elevation of 7,043 ft. above the sea level. The Sierra Nevada, as the name implies, is a range of rugged wild broken mountain-tops, always covered with snow. The more exposed portions of the road are covered with snow-sheds, solidly constructed of pine wood posts, 16 in. or 20 in. across: the total length of snow-sheds on the Sierra Nevada may equal 50 miles. These sheds sometimes take fire; but the company have a locomotive at the Summit Station, ready to start at a moment’s notice with cars carrying tanks of water. The snow falls there sometimes to a depth of 20 ft. in one winter; and in spring, when it falls into the valleys in avalanches, sweeping down the mountain-sides, they pass harmlessly over the sloping roofs of the snow-sheds. Where the line passes along the steep flank of a mountain, the roofs of these snow-sheds abut against the mountain-side, so that the masses of snow, gliding down from its heights, continue their slide without injury to line, or sheds, or trains. Where, however, the line lies on level ground, or in a ridge, the snow-sheds are built with a strong roof of double slope, in order to support or throw off the snow. From Summit (7,017 ft.) the line descends continuously to Sacramento, which is only 30 ft. above the sea level, and 104 miles from Summit. About 36 miles from Summit, the great American Canyon, one of the wildest gorges in the Sierra Nevada range, is passed. Here the American River is confined for a length of two miles between precipitous walls of rock, 2,000 ft. in height, and so steep that no human foot has ever yet followed the stream through this tremendous gorge (Fig. 53). A few miles beyond this the line is carried, by a daring feat of engineering, along the side of a mountain, overhanging a stream 2,500 ft. below. This mountain is known as “Cape Horn,” and is a place to try the nerves of timid people. When this portion of the line was commenced, the workmen were lowered and held by ropes, until they had hewn out a standing-place on 121the shelving sides of the precipice, along whose dizzy height, where even the agile Indian was unable to plant his foot, the science of the white man thus made for his iron horse a secure and direct road. (Fig. 54.)

Fig. 54.—“Cape Horn.

Fig. 55.Snow Plough.

These lines of railway, connecting Omaha with Sacramento, are remarkable evidences of the energy and spirit which characterize the Anglo-Saxon race in America. The men who conceived the design of the Central Pacific Railroad, and actually carried it into effect, were not persons experienced in railway construction; but five middle-aged traders of Sacramento, two of whom where drapers, one a wholesale grocer, and the others ironmongers, believing that such a railway should be made, and finding no one ready to undertake it, united together, projected the railway, got it completed, and now manage it. These gentlemen were associated with an engineer 122named Judah, who was a sanguine advocate of the scheme, and made the preliminary surveys, if he did not plan the line. The line is considered one of the best appointed and best managed in the States; yet the project was at first ridiculed and pronounced impracticable by engineers of high repute, opposed by capitalists, and denounced by politicians. An eminent banker, who personally regarded the scheme with hopefulness, would not venture, however, to take any stock, lest the credit of his bank should be shaken, were he known to be connected with so wild a scheme. And, indeed, the difficulties appeared great. Except wood, all the materials required, the iron rails, the pickaxes and spades, the waggons, the locomotives, and the machinery had to be sent by sea from New York, round Cape Horn, a long and perilous voyage of nine months duration, and transhipped at San Francisco for another voyage of 120 miles before they could reach Sacramento. Add to this that workmen were so scarce in California, and wages so high, that to carry on the work it was necessary to obtain men from New York; and during its progress 10,000 Chinamen were brought across the Pacific, to work as labourers. Subscriptions came in very slowly, and before 30 miles of the line had been constructed, the price of iron rose in a very short time to nearly three times its former amount. At this critical juncture, the five merchants decided to defray, out of their own private fortunes, the cost of keeping 800 men at work on the line for a whole year. We cannot but admire the unswerving confidence in their enterprise displayed by these five country merchants, unskilled in 123railway making, unaided by public support, and even discouraged in their project by their own friends. The financial and legal obstacles they successfully surmounted were not the only difficulties to be overcome. They had the engineering difficulties of carrying their line over the steep Sierra, a work of four years; long tunnels had to be bored; one spring when snow 60 ft. in depth covered the track, it had to be removed by the shovel for 7 miles along the road; saw-mills had to be erected in the mountains, to prepare the sleepers and other timber work; wood and water had to be carried 40 miles across alkali plains, and locomotives and rails dragged over the mountains by teams of oxen. The chief engineer, who organized the force of labourers, laid out the road, designed the necessary structures, and successfully grappled with the novel problem of running trains over such a line in all seasons, was Mr. S. S. Montague. The requirements of the traffic necessitate not only solidly constructed iron-covered snow-sheds, but massive snow-ploughs to throw off the track the deep snow which could in no other way be prevented from interrupting the working of the line. These snow-ploughs are sometimes urged forward with the united power of eight heavy locomotives. Fig. 55 represents one of these ploughs cleaning the line, by throwing off the snow on to the sides of the track. The cutting apparatus varies in its arrangements, some forms being designed to push the snow off on one side, some on the other, and to fling it down the precipices; and others, like the one represented, are intended merely to throw it off the track.

Fig. 56.The first Steam Railroad Train in America.

Sacramento is 1,775 miles from Omaha, and is connected with San Francisco by a line 139 miles long. At San Francisco, or rather at Oakland, 1,911 miles from Omaha and 3,212 miles from New York, is the terminus of the great system of lines connecting the opposite shores of the vast North American continent. San Francisco, situated on the western shore of a bay, is connected with Oakland by a ferry; but the railway company have recently constructed a pier, which carries the trains out into the bay for 2¼ miles. This pier is strongly built, and is provided with a double set of rails and a carriage-road, and with slips at which ships land and embark passengers, so that ships trading to China, Japan, and Australia can load and unload directly into the trains, which may pass without change from the shores of the Pacific to those of the Atlantic Ocean. San Francisco is a marvellous example of rapid increase, for the population now numbers 170,000, yet a quarter of a century ago 500 white settlers could not be found in as many miles around its site. The first house was erected in 1846, and in 1847 not a ship visited the bay, but now forty large steamships ply regularly, carrying mails to China, Japan, Panama, South America, Australia, &c., and there are, of course, hundreds of other steamers and ships.

124The descriptions we have given of only two lines of railway may suffice to show that the modern engineer is deterred by no obstacles, but boldly drives his lines through places apparently the most impracticable. He shrinks from no operations however difficult, nor hesitates to undertake works the mere magnitude of which would have made our forefathers stand aghast. Not in England or America alone, but in almost every part of the world, the railways have extended with wonderful rapidity; the continent of Europe is embraced by a network of lines; the distant colonies of Australia and New Zealand have thousands of miles of lines laid down, and many more in progress; the map of India shows that peninsula traversed in all directions by the iron roads; and in the far distant East we hear of Japan having several lines in successful operation, and the design of laying down more. In connection with such works, at home and abroad, many constructions of great size and daring have been designed and erected; many navigable rivers have been bridged, and not seldom has an arm of the sea itself been spanned; hundreds of miles of embankments and viaducts have been raised; hills have been pierced with innumerable cuttings and tunnels, and all these great works have been accomplished within the experience of a single generation of men, and have sprung from one single successful achievement of Stephenson’s—the Liverpool and Manchester Railway, completed and opened in 1830. We in England should also have pride in remembering that the growth of the railways here is due to the enterprise, industry, and energy of private persons; for the State has furnished no funds, but individuals, by combining their own resources, have executed the works, and manage the lines for their common interest and the public good. It is said that the amount of money which has been spent on railways in Great Britain is not far short of 500 millions of pounds sterling. The greatest railway company in the United Kingdom is the London and North-Western, which draws in annual receipts about seven millions of pounds; and the total receipts of all the railway companies would nearly equal half the revenue of the State.

Fig. 57.Railway Embankment near Bath.

PLATE VI.

MOUNT WASHINGTON INCLINED TRACK.

125

INCLINED RAILWAYS.

The construction of railways over lofty ranges of mountains will be found illustrated by the brief notices in other pages of the Union Pacific line in the United States, and of the St. Gothard railway over the Alps. In such cases, the track has been to a great extent carried over the spurs or along the sides of the mountains, so that such inclines might be obtained as the ordinary locomotive was capable of ascending. The expensive operation of tunnelling was resorted to only where sinuous deviations from the more direct route involved a still greater expenditure of initial cost, or a continual waste of time and energy in the actual working of the line. Sometimes winding tracks, almost returning by snake-like loops on their own route, as projected on the map, were required in order that the ascent could be made with an incline practicable for the ordinary locomotive. In the earlier development of railways, there were to be met with cable inclines, where the traction of the locomotive had to be superseded or supplemented by that of a rope or chain wound round a drum actuated by a stationary steam-engine. The more powerful locomotives of the present day are able to mount grades of such inclination that the employment of cable traction is no longer requisite, except in but a few cases. Railways had carried passengers about in all parts of the world for many years before the engineer addressed himself to the problem of easily and quickly taking people up heights of steep and toilsome ascent, sought generally for the sake of the prospect, etc. Such, at least, has been the object of most of the inclined railways already constructed, but to this their utility is by no means limited, and as their safety and stability has been proved by many years of use, they may find wider applications than the gratification of the tourist and pleasure-seeker.

The toothed rail or rack which was formerly supposed necessary to obtain power of traction on rails has been already mentioned (p. 101), and as early as 1812 such a contrivance appears to have been in use in England, near Leeds, the invention of a Mr. Blenkinsop. This mode of traction received no development or improvement worthy of notice until Mr. S. Marsh constructed, in 1866, a railway ladder—for so it may be called—for the ascent of Mount Washington in the United States. In this case there was a centre rail formed of iron, angle iron laid between and parallel to the metals on which ran the wheels of the carriages. In this centre rail angle irons were connected by round bars of wrought iron, which the teeth of a pinion of the locomotive engaged, so that a climbing action, resembling somewhat that of a wheel entering on the successive rounds of a ladder, was produced, and in this way an ascensive power was obtained sufficient to overcome gravity, the gradient not much exceeding a rise of one foot in three at any point (12 vertical to 32 horizontal). This railway was completed in 1869, and for more than a quarter of a century it has carried thousands of tourists to the summit of Mount Washington without a single fatal accident. This system of ascending mountains was soon adopted in Europe with certain improvements, for in 1870 an inclined railway was constructed to the summit of the Rigi, in which a system of involute gearing was substituted for the ladder-like rounds of Mr. Marsh. A certain vibratory action, due to the successive engagements of the teeth in the central rack, which was somewhat 126disagreeable for passengers, was soon afterwards obviated in the Abt system, in which two racks are used, with the teeth of one opposite the spaces of the other, and a double pinion provided, so that greater uniformity in the acting power is obtained. With certain modifications in detail, such as horizontal instead of vertical pinions, this system has been largely adopted wherever cables have been dispensed with. In the inclined railway by which Mount Pilatus, near Lucerne, is now ascended, horizontal teeth project from both sides of a centre rail, and these are engaged by horizontal pinions. The incline here is very steep, being in places nearly 30 degrees; teeth perpendicular to the plane of the incline would have offered a less margin of safety than those on the plan actually adopted. In some places, as among the Alps, and more particularly in South America, there are railways in which the ordinary mode of traction and that with the rack are combined; that is, where the gradient exceeds the ordinary limit, a central rack-rail is laid down, on approaching which the engineer slackens his speed, and allows pinions, moved by the locomotive, to become engaged in the double rack, by which he slowly climbs the steep ascent until a level tract is reached which permits of the ordinary traction being resumed.

Fig. 57a.—Train Ascending the Rigi.

Instead of climbing the inclines by rack-work rails, there is another system which offers great advantages for economy in working, and one generally resorted to where the incline can be made in one vertical plane. This is the balanced cable, in which the gravitation force of a descending car or train is utilised to draw up, or assist to draw up, the ascending car or train. These cars are attached to the ends of a cable which passes round a drum at the top of the incline, and means are provided, according to circumstances, so that the drum may be turned, or its revolutions 127controlled by brakes. When there is a water supply at the upper end of the incline, a simple and economical mode of working the cable is available; for all that is necessary is to provide each car with a water-tank capable of being rapidly filled and emptied. The upper car is made the heavier when required, by filling its tank with water, when it raises the lower car, and on itself arriving at the bottom, the water is discharged before the load to be taken up is received.

Fig. 57b.—At the Summit of the Rigi.

Many inclined railways are now in operation in various parts of the world, as at Mount Vesuvius, where two of the slopes have a combined length of 10,500 feet; at Mount Supurga and at Mount San Salvatore there are others. At Burgen-stock in Switzerland there is one having a slope 57 feet vertical to 100 feet horizontal. These are cable inclines; but a rack is also used with a pinion regulated by a friction-brake to avoid accident, in case of the cable parting. The largest inclined railway in America is at the Catskill Mountains, where an ascent of 1,600 feet is made in a horizontal distance of 6,780 feet. In this a novel plan has been adopted for compensating the varying weight that has to be moved, for it is obvious that at the commencement the load at the top of the incline has to raise not only that at the bottom, but the whole weight of the cable 128also, equal to 35,000 pounds of wire rope, and again after the middle point has been passed, the descending power is constantly increasing, while the load being raised is diminishing. Now, in order that the engine may work with more uniform effect, the engineer has not made the incline a straight line, but with the slope lightest at the bottom and gradually increased towards the top, so that the line is really a curve in the vertical plane, and has at every point just the inclination required for balancing the weight of the wire cable, as this shifts from the one track to the other. Instead of a rack pinion and brake to control a too rapid descent from any accident, the cars are provided with clutches, which are automatically thrown out on wooden guard-rails, when a safe speed is exceeded. Inclined railways have also been constructed to the summit of Snowdon, in North Wales, and to that of the Jungfrau, in Switzerland.

PLATE VII.

PIKE’S PEAK RAILWAY, ROCKY MOUNTAINS.

129

Fig. 58.The Great Eastern at Anchor.

STEAM NAVIGATION.

The first practically successful steamboat was constructed by Symington, and used on the Forth and Clyde Canal in 1802. A few years afterwards Fulton established steam navigation in American waters, where a number of steamboats plied regularly for some years before the invention had received a corresponding development in England, for it was not until 1814 that a steam-packet ran for hire in the Thames. From that time, however, the principle was quickly and extensively applied, and steamers made their appearance on the chief rivers of Great Britain, and soon began also to make regular passages from one sea-port to another, until at length, in 1819, a steamer made the voyage from New York to Liverpool. It does not appear, however, that such ocean steam voyages became at once common, for we read that in 1825 the captain of the first steam-ship which made the voyage to India was rewarded by a large sum of money. It was not until 1838 that regular steam communication with America was commenced by the dispatch of the Great Western from Bristol. Other large steamers were soon built expressly for the passage of the Atlantic, and a new era in steam navigation was reached when, in 1845, the Great Britain made her first voyage to New York in fourteen days. This ship was of immense size, compared with her predecessors, her length being 320 ft., and she was 130moreover made of iron, while instead of paddles, she was provided with a screw-propeller, both circumstances at that time novelties in passenger ships. Fulton appears to have made trial in America of various forms of mechanism for propelling ships through the water. Among other plans he tried the screw, but finally decided in favour of paddle-wheels, and for a long time these were universally adopted. Many ships of war were built with paddle-wheels, but the advantages of the screw-propeller were at length perceived. The paddle-wheels could easily be disabled by an enemy’s shot, and the large paddle-boxes encumbered the decks and obstructed the operations of naval warfare. Another circumstance perhaps had a greater share in the general adoption of the screw, which had long before been proposed as a means of applying steam power to the propulsion of vessels. This was the introduction of a new method of placing the screw, so that its powers were used to greater advantage. Mr. J. P. Smith obtained a patent in 1836 for placing the propeller in that part of the vessel technically called the dead-wood, which is above the keel and immediately in front of the rudder. When the means of propulsion in a ship of war is so placed, this vital part is secure from injury by hostile projectiles, and the decks are clear for training guns and other operations. Thus placed, the screw has been proved to possess many advantages over paddle-wheels, so that at the present time it has largely superseded paddle-wheels in vessels of every class, except perhaps in those intended to ply on rivers and lakes. Many fine paddle-wheel vessels are still afloat, but sea-going steamers are nearly always now built with screw-propellers. In the application of the steam engine to navigation the machine has received many modifications in the form and arrangement of the parts, but in principle the marine engine is identical with the condensing engine already described. The engines in steam-ships are often remarkable for the great diameter given to the cylinders, which may be 8 ft. or 9 ft. or more. Of course other parts of the machinery are of corresponding dimensions. Such large cylinders require the exercise of great skill in their construction, for they must be cast in one piece and without flaws. The engraving, Fig. 59, depicts the scene presented at the works of Messrs. Penn during the casting of one of these large cylinders, the weight of which may amount to perhaps 30 tons. Only the top of the mould is visible, and the molten iron is being poured in from huge ladles, moved by powerful cranes. In paddle vessels the great wrought iron shaft which carries the paddle-wheels crosses the vessel from side to side. This shaft has two cranks, placed at right angles to each, and each one is turned by an engine, which is very commonly of the kind known as the side-lever engine. In this engine, instead of a beam being placed above the cylinder, two beams are used, one being set on each side of the cylinder, as low down as possible. The top of the piston-rod is attached to a crosshead, from each end of which hangs a great rod, which is hinged to the end of the side-beam. The other ends of the two beams are united by a cross-bar, to which is attached the connecting-rod that gives motion to the crank. Another favourite form of engine for steam-ships is that with oscillating cylinders. The paddle-wheels are constructed with an iron framework, to which flat boards, or floats, are attached, placed usually in a radial direction. But when thus fixed, each float enters the water obliquely, and in fact its surface is perpendicular to the direction of the vessel’s course only at the instant the float is vertically under the axis of the wheel. In order to avoid the loss of power consequent upon this oblique movement of the floats, they are sometimes hung upon centres, and are so moved by suitable 131mechanism that they are always in a nearly vertical position when passing through the water. Paddle-wheels constructed in this manner are termed feathering wheels. They do not appear, however, to possess any great advantage over those of the ordinary construction, except when the paddles are deeply immersed in the water, and this result may be better understood when we reflect that the actual path of the floats through the water is not circular, as it would be if the vessel itself did not move; for all points of the wheel describe peculiar curves called cycloids, which result from the combination of the circular with the onward movement.

PLATE VIII.

THE “CLERMONT,” FROM A CONTEMPORARY DRAWING.

Fig. 59.Casting Cylinder of a Marine Steam Engine.

The next figure, 60, exhibits a very common form of the screw propeller, and shows the position which it occupies in the ship. The reader may not at once understand how a comparatively small two-armed wheel revolving in a plane perpendicular to the direction of the vessel’s motion is able to propel the vessel forward. In order to understand the action of the propeller, he should recall to mind the manner in which a screw-nail in a piece of wood advances by a distance equal to its pitch at every turn. If he will conceive a gigantic screw-nail to be attached to the vessel extending along the keel,—and suppose for a moment that the water surrounding this screw is not able to flow away from it, but that the screw works through the water as the nail does in the wood,—he will have no difficulty in understanding that, under such circumstances, if the screw were made to revolve, it would advance and carry the vessel with it. The reader may now form an accurate notion of the actual propeller by supposing the imaginary screw-nail to have the thread so deeply cut that but little solid core is left in the centre, 132and supposing also that only a very short piece of the screw is used—say the length of one revolution—and that this is placed in the dead-wood. Such was the construction of the earlier screw-propellers, but now a still shorter portion of the screw is used; for instead of a complete turn of the thread, less than one-sixth is now the common construction. Such a strip or segment of the screw-thread forms a blade, and two, three, four, or more blades are attached radially to one common axis. The blades spring when there are two from opposite points in the axis, and in other cases from points on the same circle. The blades of the propeller are cut and carved into every variety of shape according to the ideas of the designer, but the fundamental principle is the same in all the forms. It need hardly be said that the particles of the water are by no means fixed like those of the wood in which a screw advances. But as the water is not put in motion by the screw without offering some resistance by reason of its inertia, this resistance reacting on the screw operates in the same manner, but not to the same extent, as the wood in the other case. When we know the pitch of the screw, we can calculate what distance the screw would be moved forward in a given number of revolutions if it were working through a solid. This distance is usually greater than the actual distance the ship is propelled, but in some cases the vessel is urged through the water with a greater velocity than if the screw were working in a solid nut. The shaft which carries the screw extends from the stem to the centre of the ship where the engines are placed, and it passes outward through a bearing lined with wood, of which lignum vitæ is found to be the best kind, the lubricant for this bearing being not oil but water. The screw would not have met with the success it has attained but for this simple contrivance; for it was found that with brass bearings a violent thumping action was soon produced by the rapid rotation of the screw. The wearing action between the wood and the iron is very slight, whereas brass bearings in this position quickly wear and their adjustments become impaired. The screw-shaft is very massive and is made in several lengths, which are supported in appropriate bearings; there is also a special arrangement for receiving the thrust of the shaft, for it is by this thrust received from the screw that the vessel is propelled, and the strain must be distributed to some strong part of the ship’s frame. There is usually also an arrangement by which the screw-shaft can, when required, be disconnected from the engine, in order to allow the screw to turn freely by the action of the water when the vessel is under sail alone.

Fig. 60.Screw Propeller.

A screw-propeller has one important advantage over paddle-wheels in the following particular: whereas the paddle-wheels act with the best effect when the wheel is immersed in the water to the depth of the lowest 133float, the efficiency of the screw when properly placed is not practically altered by the depth of immersion. As the coals with which a steamer starts for a long voyage are consumed, the immersion is decreased—hence the paddle-wheels of such a steamer can never be immersed to the proper extent throughout the voyage; they will be acting at a disadvantage during the greater part of the voyage. Again, even when the immersion of the vessel is such as to give the best advantage to the paddle-wheels, that advantage is lost whenever a side-wind inclines the ship to one side, or whenever by the action of the waves the immersion of the paddles is changed by excess or defect. From all such causes of inefficiency arising from the position of the vessel the screw-propeller is free. The reader will now understand why paddle-wheel steamers are at the present day constructed for inland waters only.

A great impulse was given to steam navigation, by the substitution of iron for wood in the construction of ships. The weight of an iron ship is only two-thirds that of a wooden ship of the same size. It must be remembered that, though iron is many times heavier than wood, bulk for bulk, the required strength is obtained by a much less quantity of the former. A young reader might, perhaps, think that a wooden ship must float better than an iron one; but the law of floating bodies is, that the part of the floating body which is below the level of the water, takes up the space of exactly so much water as would have the same weight as the floating body, or in fewer words, a floating body displaces its own weight of water. Thus we see that an iron ship, being lighter than a wooden one, must have more buoyancy. The use of iron in ship-building was strenuously advocated by the late Sir W. Fairbairn, and his practical knowledge of the material gave great authority to his opinion. He pointed out that the strains to which ships are exposed are of such a nature, that vessels should be made on much the same principles as the built-up iron beams or girders of railway bridges. How successfully these principles have been applied will be noticed in the case of the Great Eastern. This ship, by far the largest vessel ever built, was designed by Mr. Brunel, and was intended to carry mails and passengers to India by the long sea route. The expectations of the promoters were disappointed in regard to the speed of the vessel, which did not exceed 15 miles an hour; and no sooner had she gone to sea than she met with a series of accidents, which appear, for a time, to have destroyed public confidence in the vessel as a sea-going passenger ship. Some damage and much consternation were produced on board by the explosion of a steam jacket a few days after the launch. Then the huge ship encountered a strong gale in Holyhead Harbour, and afterwards was disabled by a hurricane in the Atlantic, in which her rudder and paddles were so damaged, that she rolled about for several days at the mercy of the waves. At New York she ran upon a rock, and the outer iron plates were stripped off the bottom of the ship for a length of 80 ft. She was repaired and came home safely; but the companies which owned her found themselves in financial difficulties, and the big ship, which had cost half a million sterling, was sold for only £25,000, or only about one-third of her value as old materials.

The misfortunes of the Great Eastern, and its failure as a commercial speculation in the hands of its first proprietors, have been quoted as an illustration of the ill luck, if it might be so called, which seems to have attended several of the great works designed by the Brunels—for the Thames Tunnel was, commercially, a failure; the Great Western Railway, with its magnificent embankments, cuttings, and tunnels, has reverted to 134the narrow gauge, and therefore the extra expense of the large scale has been financially thrown away; the Box Tunnel, a more timid engineer would have avoided; and then there is the Great Eastern. It is, however, equally remarkable that all these have been glorious and successful achievements as engineering works, and the scientific merit of their designers remains unimpaired by the merely accidental circumstance of their not bringing large dividends to their shareholders. Nor is their value to the world diminished by this circumstance, for the Brunels showed mankind the way to accomplish designs which, perhaps, less gifted engineers would never have had the boldness to propose. The Box Tunnel led the way to other longer and longer tunnels, culminating in that of Mont Cenis; but for the Thames Tunnel—once ranked as the eighth wonder of the world—we should probably not have heard of the English Channel Tunnel—a scheme which appears less audacious now than the other did then; if no Great Eastern had existed, we should not now have had an Atlantic Telegraph. Possibly this huge ship is but the precursor of others still larger, and it is undoubtedly true that since its construction the ideas of naval architects have been greatly enlarged, and the tendency is towards increased size and speed in our steam-ships, whether for peace or war.

Fig. 61.Section of Great Eastern Amidships.

Fig. 62.The Great Eastern in course of Construction.

The accidents which had happened to the ship had not, however, materially damaged either the hull or the machinery; and the Great Eastern was refitted, and afterwards employed in a service for which she had not been designed, but which no other vessel could have attempted. This was the work of carrying and laying the whole length of the Atlantic Telegraph Cable of 1865, of which 2,600 miles were shipped on board in enormous tanks, that with the contents weighed upwards of 5,000 tons. The ship has since been constantly engaged in similar operations.[1] The Great Eastern is six times the size of our largest line-of-battle ships, and about seven times as large as the splendid steamers of the Cunard line, which run between Liverpool and New York. She has three times the steam power of the largest of these Atlantic steamers, and could carry twenty times as 135many passengers, with coal for forty days’ consumption instead of fifteen. Her length is 692 ft.; width, 83 ft.; depth, 60 ft.; tonnage, 24,000 tons; draught of water when unloaded, 20 ft.; when loaded, 30 ft.; and a promenade round her decks would be a walk of more than a quarter of a mile. The vessel is built on the cellular plan to 3 ft. above the water-line; that is, there is an inner and an outer hull, each of iron plates ¾ in. thick, placed 2 ft. 10 in. apart, with ribs every 6 ft., and united by transverse plates, so that in place of the ribs of wooden ships, the hull is, as it were, built up of curved cellular beams of wrought iron. The ship is divided longitudinally by two vertical partitions or bulkheads of wrought iron, ½ in. thick. These are 350 ft. long and 60 ft. high, and are crossed at intervals by transverse bulkheads, in such a manner that the ship is divided into nineteen compartments, of which twelve are completely water-tight, and the rest nearly so. The diagram (Fig. 61) represents a transverse section, and shows the cellular construction below the water-line. The strength and safety of the vessel are thus amply provided for. The latter quality was proved in the accident to the ship at New York; and the former was shown at the launch, for when the vessel stuck, and for two months could not be moved, it was found that, although one-quarter of the ship’s length was unsupported, it exhibited no deflection, or rather the amount of deflection was imperceptible. Fig. 62 is from a photograph taken during the building of the ship, and Fig. 63 shows the hull when completed and nearly ready for launching, while the vignette at the head of the chapter exhibits the big ship at anchor when completely equipped. The paddle-wheels are 56 ft. in diameter, and are 136turned by four steam engines, each having a cylinder 6 ft. 2 in. in diameter, and 14 ft. in length. The vessel is also provided with a four-bladed screw-propeller of 24 ft. diameter, driven by another engine having four cylinders, six boilers, and seventy-two furnaces. The total actual power of the engines is more than that of 8,000 horses, and the vessel could carry coals enough to take her round the world—a capability which was the object of her enormous size. The vessel as originally constructed contained accommodation for 800 first-class passengers, 2,000 second class, and 1,200 third class—that is, for 4,000 passengers in all. The principal saloon was 100 ft. long, 36 ft. wide, and 13 ft. high. Each of her ten boilers weighs 50 tons, and when all are in action, 12 tons of coal are burnt every hour, and the total displacement of the vessel laden with coal is 22,500 tons.

1.  She was broken up for old iron, 1889.

Fig. 63.The Great Eastern ready for Launching.

The use of steam power in navigation has increased at an amazing rate. Between 1850 and 1860 the tonnage of the steam shipping entering the port of London increased three-fold, and every reader knows that there are many fleets of fine steamers plying to ports of the United Kingdom. There are, for example, the splendid Atlantic steamers, some of which almost daily enter or leave Liverpool, and the well-appointed ships belonging to the Peninsular and Oriental Company. The steamers on the Holyhead and Kingston line may be taken as good examples of first-class passenger ships. These are paddle-wheel boats, and are constructed entirely of iron, with the exception of the deck and cabin fittings. Taking one of these as a type of the rest, we may note the following particulars: the vessel is 334 ft. long, the diameter of the paddle-wheels is 31 ft., and each has fourteen floats, which are 12 ft. long and 4 ft. 4 in. wide. The cylinders of the engines are 8 ft. 2 in. in diameter, and 6 ft. 6 in. long. The ship cost 137about £75,000. The average passage between the two ports—a distance of 65½ miles—occupies 3 hours 52 minutes, and at the measured mile the vessel attained the speed of 20·811 miles per hour. As an example of the magnificent vessels owned by the Cunard Company, we shall give now a few figures relating to one of their largest steam-ships, the Persia, launched in 1858, and built by Mr. N. Napier, of Glasgow, for the company, to carry mails and passengers between Liverpool and New York. Her length is 389 ft., and her breadth 45 ft. She is a paddle-wheel steamer, with engines of 850 horse-power, having cylinders 100 in. in diameter with a stroke of 10 ft. The paddle-wheels are 38 ft. 6 in. in diameter, and each has twenty-eight floats, 10 ft. 8 in. long and 2 ft. wide. The Persia carries 1,200 tons of coal, and displaces about 5,400 tons of water.

Fig. 64.Comparative Sizes of Steamships.

1838, Great Western; 1844, Great Britain; 1856, Persia; 1858, Great Eastern.

A, Section amidships of Great Eastern; B, The same of Great Western. Both on the same scale, but on a larger one than their profiles.

A velocity of twenty-six miles per hour appears to be about the highest yet attained by a steamer.[2] This is probably near the limit beyond which the speed cannot be increased to any useful purpose. The resistance offered by water to a vessel moving through it increases more rapidly than the velocity. Thus, if a vessel were made to move through the water by being pulled with a rope, there would be a certain strain upon the rope when the vessel was dragged, say, at the rate of five miles an hour. If we desired the vessel to move at double the speed, the strain on the rope must be increased four-fold. To increase the velocity to fifteen miles per hour, we should have to pull the vessel with nine times the original force. This is expressed by saying that the resistance varies as the square of the velocity. Hence, to double the speed, the impelling force must be quadrupled, and as that force is exerted through twice the distance in the same time, an engine would be required of eight times the power—or, in other words, the power 138of the engine must be increased in proportion to the cube of the velocity; so that to propel a boat at the rate of 15 miles an hour would require engines twenty-seven times more powerful than those which would suffice to propel it at the rate of five miles an hour.

2.  This has now (1895) been far surpassed.—Vide infra.

The actual speed attained by steam-ships with engines of a given power and a given section amidships will depend greatly upon the shape of the vessel. When the bow is sharp, the water displaced is more gradually and slowly moved aside, and therefore does not offer nearly so much resistance as in the opposite case; but the greater part of the power required to urge the vessel forward is employed in overcoming a resistance which in some degree resembles friction between the bottom of the vessel and the water.

The wonderful progress which has, in a comparatively short time, taken place in the power and size of steam-vessels, cannot be better brought home to the reader than by a glance at Fig. 64, which gives the profiles of four steamships, drawn on one and the same scale, thus showing the relative lengths and depths of those vessels, each of which was the largest ship afloat at the date which is marked below it, and the whole period includes only the brief space of twenty years!—for this, surely, is a brief space in the history of such an art as navigation. All these ships have been named in the course of this article, but in the following table a few particulars concerning each are brought together for the sake of comparing the figures:

Date. Name. Propulsion. Length. Breadth.
1838 Great Western Paddles 236 ft. 36 ft.
1844 Great Britain Screw 322 ft. 51 ft.
1856 Persia Paddles 390 ft. 45 ft.
1858 Great Eastern Screw and paddles 690 ft. 83 ft.

Fig. 65.The s.s. City of Rome.

Several passenger ocean-going steamships have been built since the Persia, of still greater dimensions, and of higher engine power. These 139have generally been surpassed in late years by some splendid Atlantic liners, such as the sister vessels owned by the International Navigation Co., and now named respectively the New York and the Paris. The City of Rome, launched in 1881 by the Barrow Steamship Co., is little inferior in length to the Great Eastern, although the tonnage is only about one-third. The City of Rome is 560 ft. long, 52 ft. wide, and 37 ft. deep. Her engines are capable of working up to 10,000 indicated horse-power. Fig. 65 is a sketch of this ship, and shows that she carries four masts and three funnels. The main shaft measures more than 2 ft. across, and the screw-propeller is 24 ft. in diameter. She has accommodation for 1,500 passengers, and is fitted with all the conveniences and luxuries of a well-appointed hotel. The International Navigation Co.’s ship Paris, has made the passage across the Atlantic in less than six days, and appears to be the fastest vessel in the transatlantic service. In August, 1889, she made the run from shore to shore in 5 days, 22 hours, 38 minutes.

The extraordinary increase in the speed of steamships that has been effected within the last few years depends mainly upon the improvements that have latterly been made in the marine engine—a machine of which we have been unable to give an account, because its details are too numerous and complicated to be followed out by the general reader. Suffice it to say, that the use of higher steam pressures with compound expansion (p. 18), condensers which admit of the same fresh water being used in the boilers over and over again, and better furnace arrangements, are among the more important of these improvements. But not only have the limits of practicable speed been enlarged, but a greater economy of fuel for the work done has been attained; the result being that ocean carriage is now cheaper than ever. The outcome of this will not cease with simply a greatly extended steam navigation, but appears destined ultimately to produce effects on the world at large comparable in range and magnitude with those that may be traced to the use of the steam engine itself since its first invention.

Among the curiosities of steamboat construction may be mentioned a remarkable ship which was built a few years ago for carrying passengers across the English Channel without the unpleasant rolling experienced in the ordinary steamboats. The vessel, which received the name of the Castalia, was designed by Captain Dicey, who formerly held an official position at the Port of Calcutta. His Indian experience furnished him with the first suggestion of the new ship in the device which is adopted there for steadying boats in the heavy surf. The plan is to attach a log of timber to the ends of two outriggers, which project some distance from the side of the vessel; or sometimes two canoes, a certain distance apart, are connected together. Some of these Indian boats will ride steadily in a swell that will cause large steamers to roll heavily. Improving on this hint, Captain Dicey built a vessel with two hulls, each of which acted as an outrigger to the other. Or, perhaps, the Castalia may be described as a flat-bottomed vessel with the middle part of the bottom raised out of the water throughout the entire length, so that the section amidships had a form like this—

The two hulls were connected by what we may term “girders,” which extended completely across their sections, forming transverse partitions or bulkheads, and these girders were strongly framed together, so as to form rigid triangles. These united the two hulls so completely, that 140there was not any danger of the vessel being strained in a sea-way. The decks were also formed of iron, although covered with wood, so that the whole vessel really formed a box girder of enormous section.

Fig. 66.The Castalia in Dover Harbour.

The reason why the steamers which until lately ran between Dover and Calais, Folkestone and Boulogne, and other Channel ports, were so small, was because the harbours on either side could not receive vessels with such a draught as the fine steamers, for example, which run on the Holyhead and Kingston line. Now, the Castalia drew only 6 ft. of water, or 1 ft. 6 in. less than the small Channel steamers, and would, therefore, be able to enter the French ports at all states of the tide. Yet the extent of the deck space was equalled in few passenger ships afloat, except the Great Eastern and some of the Atlantic steamers. The vessel was 290 ft. in length, with an extreme breadth of 60 ft. The four spacious and elegantly-fitted saloons—two of which were 60 ft. by 36 ft., and two 28 ft. by 26 ft.—and the roomy cabins, retiring rooms, and lavatories, were the greatest possible contrast to the “cribbed, cabined, and confined” accommodation of the ordinary Channel steamers. There were also a kitchen and all requisites for supplying dinners, luncheons, etc., on board. But besides the above-named saloons and cabins, there was a grand saloon, which was 160 ft. long and 60 ft. wide; and the roof of this formed a magnificent promenade 14 ft. above the level of the sea. There was comfortable accommodation in the vessel for more than 1,000 passengers.

The inner sides of the hulls were not curved like the outside, but were straight, with a space between them of 35 ft. wide, and the hulls were each 20 ft. in breadth, and somewhat more in depth. There were two paddle-wheels, 141placed abreast of each other in the water-way between the two hulls, and each of these contained boilers and powerful engines. The designers of this vessel calculated that she would attain a speed of 14¾ knots per hour, but this result failed to be realized. Probably there were no data for the effect of paddles working in a confined water-space. The position of the paddles is otherwise an advantage, as it leaves the sides of the vessel free and unobstructed. The ship had the same form at each end, so it could move equally well in either direction. There were rudders at both ends, and the steering qualities of the ship were good. Although the speed of the Castalia was below that intended, the vessel was a success as regards steadiness, for the rolling and pitching were very greatly reduced, and the miseries and inconveniences of the Channel passage obviated.

Fig. 67.The Castalia in Dover Harbour—End View.

The Castalia is represented in Figs. 66 and 67. She was constructed by the Thames Iron Shipbuilding Co., and launched in June, 1874, but after she had been tried at sea, it was found necessary to fit her with improved boilers, and this caused a delay in placing the vessel on her station.

The Castalia proved a failure in point of speed, and she was soon replaced by another and more powerful vessel constructed on the same general plan, and named the Calais-Douvres. But this twin-ship again failed to answer expectations, and as the harbour on the French shore was meanwhile deepened and improved, new and very fine paddle-wheel 142boats, named the Invicta, Victoria, and Empress have been placed on the service. As the latter boat, at least, has steamed from Dover to Calais, nearly twenty-six miles, under the hour, there is nothing more to be desired in point of speed. A fourth vessel is to take the place of the twin-ship, Calais-Douvres, and will receive the same name.

Fig. 68.Bessemer Steamer.

Another very novel and curious invention connected with steam navigation was the steamer which Mr. Bessemer built at Hull in 1874. This invention also was to abolish all the unpleasant sensations which landsmen are apt to experience in a sea voyage, by effectually removing the cause of the distressing mal de mer. The ship was built for plying between the shores of France and England, and the method by which he purposed to carry passengers over the restless sea which separates us from our Gallic neighbours was bold and ingenious. He designed a spacious saloon, which, instead of partaking of the rolling and tossing of the ship, was to be maintained in an absolutely level position. The saloon was suspended on pivots, much in the same way as a mariner’s compass is suspended; and by an application of hydraulic power it was intended to counteract the motion of the ship and maintain the swinging saloon perfectly horizontal. It was originally proposed that the movements should be regulated by a man stationed for that purpose, where he could work the levers for bringing the machinery into action, so as to preserve the saloon in the required position. This plan was, however, improved upon, and the adjustments made automatic. It may be well to mention that it is a mistake to suppose that anything freely suspended, like a pendulum, on board a ship rolling with the waves, will hang vertically. If, however, 143we cause a heavy disc to spin very rapidly, say in a horizontal plane, the disc cannot be moved out of the horizontal plane without the application of some force. A very well-made disc may be made to rotate for hours, and would, by preserving its original plane of rotation, even show the effect of the earth’s diurnal motion. Mr. Bessemer designed such a gyroscope to move the valves of his hydraulic apparatus, and so to keep his swinging saloon as persistently horizontal as the gyroscope itself. Mr. Bessemer’s ship was 350 ft. long, and each end, for a distance of 48 ft., was only about 4 ft. from the line of floating. Above the low ends a breastwork was raised, about 8 ft. high, and 254 ft. long. In the centre, and occupying the space of 90 ft., was the swinging saloon intended for first-class passengers. At either end of this apartment were the engines and boilers. The engines were oscillating and expansive, working up to 4,600 horse-power, which could be increased to 5,000. There were two pairs of engines, one set at either end of the ship, and each having two cylinders of 80 in. in diameter, and a stroke of 5 ft., working with steam of 30 lbs. pressure per square inch, supplied from four box-shaped boilers, each boiler having four large furnaces. The paddle-wheels, of which there were a pair on either side of the vessel, were 27 ft. 10 in. in diameter outside the outer ring, and each wheel has twelve feathering floats. The leading pair of wheels, when working at full speed, were to make thirty-two revolutions per minute, and the following pair of wheels move faster.

Entrance into the Bessemer saloon was gained by two broad staircases leading to one landing, and a flexible passage from this point to the saloon. The saloon rested on four steel gudgeons, one at each end, and two close together near the middle. These were not only to support the saloon, but also to convey the water to the hydraulic engines, by which the saloon was to be kept steady. For this purpose the after one was made hollow, and connected with the water mains from powerful engines, and also with a supply-pipe leading to a central valve-box, by means of which the two hydraulic cylinders on either side were supplied with water. Between the two middle gudgeons, a gyroscope, worked by a small turbine, filled with water from one of the gudgeons, enabled Mr. Bessemer to dispense with the services of a man, and thus completed his scheme of a steady saloon, by making the machinery completely automatic. The saloon was 70 ft. long, 35 ft. wide, and 20 ft. high. The Bessemer ship proved to be a total failure, and never went to sea as a passenger boat.

On board of some modern war-ships where speed is essential, and where the engines are driven at a very great number of revolutions per minute, as in the case of torpedo-boat catchers, the vibration throughout the whole of the vessel becomes extremely trying, not only for the nerves of the crew, but for the security of the structure itself. The cause of this vibration and consequent strain and loss of power is not far to seek. The cylinders of marine engines are always of a large diameter, 6 feet, 8 feet, or even more sometimes, and the pistons and piston-rods are necessarily of great strength and corresponding weight. Now, at every half revolution of the engines, this heavy mass of piston and piston-rod, though moving at an exceedingly high speed in the middle of the stroke, has to be brought to a standstill, and an equal velocity in the opposite direction imparted to it. A large portion of the power is therefore uselessly expended in stopping a great moving mass, and reversing its motion. All the force required to do this reacts on the vessel’s frame. Many attempts have been made to construct rotatory steam-engines, and some hundreds 144of patents taken out for such inventions, which in general have a piston revolving about a shaft; but the great friction, and consequent liability to wear out, have prevented their practical use.

Lately, a method of using steam on the principle embodied in the water turbine has been developed, and within the last six or seven years has found successful application in propelling electro-dynamos at very high speeds. In the steam turbine there are no pistons, piston-rods, or other reciprocating parts, the effect depending on the same kind of reaction that is taken advantage of in the water turbine (which has a high efficiency in giving out a large proportion of energy), and the power is applied with smoothness and an entire absence of the oscillations that would shake to pieces any vessel that an ordinary steam-engine could propel at the same rate.

The advantages of the steam turbine have been proved by the performances of a small experimental vessel lately built at Newcastle, and appropriately named the Turbinia. She is only 100 feet in length, and 9 feet in breadth, with a displacement of some 44 tons. Now the highest record speed for any vessel of that size is 24 knots per hour; but the Turbinia, in a heavy sea, showed, at a measured mile, the speed of 32¾ knots, which is believed to be greater than that of any craft now afloat, being nearly 37¾ miles an hour, or equal to that of an ordinary railway train. Besides that, it has been found by experiment, that an arrangement of the blades of the screw propeller more suitable to high velocities will enable a still greater speed to be obtained. The weight of the turbine engines of this vessel is only 3 tons, 13 cwts., and the whole weight of the machinery, including boilers and condensers, is only 22 tons, with an indicated H.P. of 1576, and a steam consumption of but 16 lbs. per hour. The weight of the turbine is only one-fifth of that of marine engines of equal power; the space occupied is smaller; the initial cost is less; not so much superintendence is required; the charges of maintenance are diminished; reduced dimensions of propeller and shaft suffice; vibration is eliminated; speed is increased; and greater economy of fuel is secured.

THE RIVER AND LAKE STEAM-BOATS OF AMERICA.

The chapter on “Steam Navigation,” in the foregoing pages, has dealt mainly with the progress of the ocean-going steam-ship, from the establishment of regular transatlantic services down to the building of the splendid liners, the New York and the Paris, and we have recorded, in addition, the performances of the pair of hitherto unsurpassed sister ships, the Campania and the Lucania. The importance and interest attaching to steam navigation is, however, by no means confined to ocean-going vessels, and the chapter demands a supplementary notice of the great developments of the steam-ship in other parts of the world than Britain, more particularly where great rivers, navigable for hundreds of miles, and lakes, spreading their waters over vast areas, present conditions of traffic and opportunities for adaptation to an extent that could not be required within the range of Britain or British oceanic lines.

PLATE IX.

THE “MARY POWELL.”

145If the reader will cast his eye on the map of the United States, he will see towards the northern boundary a great fresh-water system, comprising five enormous lakes, the least of which is nearly two hundred, and the largest nearly three hundred miles in length, in all presenting a total area greater by far than that of England and Scotland together thrice told. This lake system has a line of coast to be reckoned only by thousands of miles, and for a long time an enormous traffic has been carried across its waters by sailing vessels of all kinds, two- or three-masted schooners, brigs, and other craft, carrying wood, stone, lime, and other commodities. On the map, the position of the Detroit River, which leads from the southern extremity of Lake Huron to Lake Erie, will readily be recognised, and this strait, which is in the only line of transport from the three great upper lakes, formerly presented all the picturesqueness that crowds of boats of every build could impart. Especially was this the case at Amherstburg, its southern extremity, where sometimes a northern wind would make the passage impracticable for several days in succession, and a fleet of a hundred or two hundred sailing vessels would collect to await the opportunity of a favouring breeze in order to carry them against the current to Port Huron. Then, taking advantage of the right moment, they would set their sails, and in a compact body move slowly up the strait. This was not quick enough to meet the traffic, and, before long, larger vessels were built, which were towed up and down the Detroit by steam-tugs. The next step of replacing sailing ships by steam-vessels was not long in following, and though there still exist fine specimens of sailing craft on the lakes, their day may be said to be over. The navigation of these lakes, before the extensive development of the railway systems near their shores, comprised a large passenger traffic, which was carried on by big paddle-wheel steamers, and at the time of the great westward set of emigration to Michigan, Wisconsin, and Minnesota, these steamers were crowded to their utmost capacity. The great improvement which in recent years has become possible for passenger steamers in speed, cabin accommodation, and other particulars, above all, the growth of great cities on the shores, the progress of the territories adjoining the lake system, and other circumstances, are now combining to renew the passenger traffic on a larger scale than ever. “Fifteen millions of people,” says Mr. H. A. Griffin, the Secretary of the Cleveland Board of Control (Engineering Magazine, iv., 819), “now live upon the shore lines of the lakes, or within six hours’ travel by rail, and nearly all of that population is south of the United States boundary line. The territory directly tributary to the lakes, north and south of the line, is capable of easily maintaining a population of 100,000,000.... It does not require a very lively imagination to foresee the Great Lakes surrounded by the most prosperous and progressive people on earth, and crossed and recrossed by scores of lines of passenger steam-ships, in addition to a still greater number of freight lines.” The number of first-class passenger steamers already launched or on the stocks is an indication that the revival of passenger traffic will not lag or be delayed.

The unique conditions and requirements of this lacustrine traffic were bound to lead to types of vessels differing in many respects from the steam-ships to be seen in the harbours of Great Britain. The introduction of iron shipbuilding gave a great impetus to the construction of the lake steamers, for vessels of more than 3,000 tons could be built with a comparatively shallow draught of water (15½ feet), which was one of the 146necessities of the situation. As far back as 1872, iron shipbuilding had been fully established at Cleveland and Detroit, and at the latter place scores of splendid steel steam-ships have been turned out. The Cleveland builders have not been far behind, and Buffalo, Milwaukee, Chicago, and other places, have followed suit. At the beginning of 1893, there were on the lakes more than fifty vessels of over 2,000 tons each, while the total number of steam vessels of all kinds was considerably over 1,600, and sailing vessels with steam-tugs counted over 2,000. The tonnage of the ships on the lakes has been estimated at about 36 per cent. of the whole mercantile marine of the United States, and it is said that 40,000 men are employed upon the vessels. The total freight passing Detroit in 1892 was calculated to exceed 34,000,000 tons, an amount greater than the whole foreign and coasting trade of the port of London. There are more than thirty shipbuilding concerns on the lakes, and some of them possess large dry docks of their own; but there are also independent companies owning dry docks of great size. Some of these shipbuilding establishments have turned out steel ocean-going tugs, paddle and screw passenger steamers, cargo-carrying boats, vessels for carrying railway trains across the Detroit river, etc., etc.

Fig. 68a.—A Whaleback Steamer, No. 85, Built at West Superior, Wisconsin.

The extent and importance which steam navigation has attained in a definite region have been indicated in the preceding paragraphs; but an attempt to show by illustration and description the several characteristic forms the steam-ship has now assumed in these lacustrine waters would carry us far beyond our allotted limits. The steam vessels now on the lakes are almost exclusively actuated by screw-propellers, whether they are passenger or freight boats. The boilers and engines are near the stern, and the hulls are usually of great length; in fact, some of these steamboats will compare in dimensions with the Persia, which was the transatlantic marvel about the year 1857. (See p. 137.) Such is the Mariposa, launched in 1892, which is 350 feet long and 45 feet broad, carrying 3,800 net tons, with a draught of only 15½ feet. There are others, 380 feet long, with engines of 7,000 horse-power, steaming at 20 miles an hour, and providing 147ample accommodation for 600 passengers. The newest and most novel type of steam-ship on the lakes is the “whaleback.” The celerity with which ships of this kind have been constructed on occasion is perfectly marvellous. One of them, named the Christopher Columbus, designed to carry passengers to and from the World’s Fair at Chicago in 1893, was launched in fifty-six days after the keel had been laid, yet it was a ship intended to carry 5,000 passengers, having a length over all of 362 feet, breadth 42 feet, depth 24 feet. The “whaleback” steamers are designed to give the greatest carrying capacity with a given draught of water, and all the structures usually fitted to the upper deck of a steamer are in them replaced by the plain curved and closed deck, over which, when the vessel is in a storm, waves may sweep harmlessly, thus avoiding the shocks received by ships with high sides.

The river steam-boat was, as we have seen, nearly coeval with the nineteenth century, and although its practicability was first demonstrated in British waters, regular steam navigation was not established until a few years afterwards, when, in 1807, Robert Fulton placed on the River Hudson its first steam-boat. To this others were soon added, so that in 1813 there were six steam-boats regularly plying on the Hudson before a single one ran for hire on the Thames. An article by Mr. Samuel Ward Stanton, in a recent number of The Engineering Magazine, gives a very full account of the Hudson River steam-boats from the beginning down to 1894, and to this article we are mainly indebted for the details we are about to give.

The Hudson River washes the western shore of Manhattan Island, on which stands by far the greater part of the city of New York, with its vast population. The river is here straight, and has a nearly uniform width of one mile; at New York it is commonly called the North River, because of the direction of its course, for it descends from almost the due north. It is not one of the great rivers of the United States as regards length or extent of navigation; not, e.g., like the Mississippi and the Missouri, which are ascended by steam-boats to thousands of miles above their mouths; but it has one of the world’s great capitals on its shores, and at the quays, which occupy both its banks to the number of eighty or more, may be seen in multitudes some of the finest ocean-going steamships, trading to every considerable port in the world. The North River separates New York from what are practically the populous suburbs of Jersey City and Hoboken, though these are controlled by their own municipalities.

It was on the River Hudson that steam navigation was inaugurated by Fulton with a vessel which was 133 feet long, 18 feet broad, and 7 feet deep, and was named the Clermont. The speed attained was but five miles an hour. The first trip was made on the 7th August, 1807, to Albany, 150 miles up the river from New York, with twenty-four passengers on board, and the new kind of locomotion was so well patronised that during the following winter, when the Hudson navigation had to be suspended on account of the ice, it was considered expedient to enlarge the capacity of the boat by adding both to her length and width; at the same time her name was changed to The North River, and she plied regularly for several seasons afterwards. Her speed down the river with the current was evidently greater than that of the first trip up the river, for on 9th November, 1809, the New York Evening Post announced that 148“The North River steam-boat arrived this afternoon in twenty-seven and a half hours from Albany, with sixty passengers.”

The paddle-wheels were of a primitive form, and as they were unprovided with paddle-boxes, the arrangement had the appearance of a great undershot mill-wheel on each side of the boat, above the deck of which was placed the steam-engine, a position it has retained in all these river-boats, in which a huge, rhombus-shaped beam, oscillating high above the deck, is a conspicuous feature. Another boat of much larger dimensions was built the following year, having a tonnage of nearly 300, and from that time there has been a more or less regular increase in the sizes of the vessels, until in 1866 a tonnage of nearly 3,000 was reached. In 1817 a vessel called the Livingstone was launched, which was able to go up to Albany in eighteen hours. In 1823 was launched the James Kent, a novel feature in which vessel was the boiler made of copper, and weighing upwards of 30 tons. It was so planned that if it happened to burst, the hot water would be carried through the bottom of the vessel by tubes or hollow pillars. From this it appears that considerable apprehension existed as to the liability of the boilers exploding. We are told that the cost of the copper boiler was in this case nearly one-third of that of the whole vessel. The cabins are described as having been very handsomely fitted up, and the speed was such that fourteen hours sufficed for the trip up river to Albany. Many fine boats were placed on the river during the twenty following years, and these were marked by various improvements, as when, in 1840, anthracite coal was for the first time substituted for wood as the fuel for the furnaces, with the effect of reducing the cost of this item to one-half. Then, in 1844, iron began to be used for constructing the hulls, and a few years afterwards, steamers having a speed of twenty miles an hour and over, became quite common. In 1865, and again in the eighties, some four screw-propeller boats were built; but this type does not appear to have found much favour on the Hudson, for the large paddle-wheels and the single or double beam, working high above the deck, have continued the almost universal form of construction. A very popular and famous boat was placed on the Hudson in 1861. This was the Mary Powell, called the “Queen of the Hudson,” which, although a boat of moderate tonnage (983), was able on occasion to steam at the rate of twenty-five miles an hour. This vessel was placed on the line between New York and Rondont, and was still running in 1894.

One of the most modern and most elegant boats on the Hudson is the New York, launched in 1887, and declared by Mr. Stanton to be one of the finest river steam-boats in the world, well arranged, and beautifully finished and furnished. She is built on fine lines, is 311 feet long, 40 feet broad, and with a tonnage of 1,552, draws only 12¼ feet of water. She can steam at twenty miles an hour, and is placed on one of the New York and Albany lines. Throughout the summer there are both day and night boats for Albany, and the latter especially are of great size, three stories high, and provided with saloons, state-rooms, and, in fact, all the accommodation of a luxurious first-class hotel. The vessels named in this notice include but a few of the splendid boats that ply on the River Hudson, and, in respect of their numbers, speed, and comfort, it may safely be asserted that they cannot be equalled on any other river in the world.

PLATE X.

THE “NEW YORK.”

149

Fig. 69.H.M.S. Devastation in Queenstown Harbour.

SHIPS OF WAR.

“Take it all in all, a ship of the line is the most honourable thing that man, as a gregarious animal, has ever produced. By himself, unhelped, he can do better things than ships of the line; he can make poems, and pictures, and other such concentrations of what is best in him. But as a being living in flocks, and hammering out with alternate strokes and mutual agreement, what is necessary for him in those flocks to get or produce, the ship of the line is his first work. Into that he has put as much of his human patience, common sense, forethought, experimental philosophy, self-control, habits of order and obedience, thoroughly wrought hand-work, defiance of brute elements, careless courage, careful patriotism, and calm expectation of the judgment of God, as can well be put into a space of 300 ft. long by 80 ft. broad. And I am thankful to have lived in an age when I could see this thing so done.” So wrote Mr. Ruskin about forty years ago, referring, of course, to the old wooden line-of-battle ships. It may be doubted whether he would have written thus enthusiastically about so unpicturesque an object as the Glatton, just as it may be doubted whether the armour-plated steamers will attain the same celebrity in romance and in 150verse as the old frigates with their “wooden walls.” Certain it is that the patience, forethought, experimental philosophy, thoroughly wrought hand-work, careful patriotism, and other good qualities which Mr. Ruskin saw in the wooden frigates, are not the less displayed in the new ironclads.

Floating batteries, plated with iron, were employed in the Crimean War at the instigation of the French Emperor. About the same time the question of protecting ships of war by some kind of defensive armour was forced upon the attention of maritime powers, by the great strides with which the improvements in artillery were advancing; for the new guns could hurl projectiles capable of penetrating, with the greatest ease, any wooden ship afloat. The French Government took the initiative by constructing La Gloire, a timber-framed ship, covered with an armour of rolled iron plates, 4½ in. thick. The British Admiralty quickly followed with the Warrior, a frigate similar in shape to the wooden frigates, but built on an iron frame, with armour composed of plates 4½ in. thick, backed by 18 in. of solid teak-wood, and provided with an inner skin of iron. The Warrior was 380 ft. long, but only 213 ft. of this length was armoured. The defensive armour carried by the Warrior, and the ironclads constructed immediately afterwards, was quite capable of resisting the impact of the 68 lb. shot, which was at that time the heaviest projectile that could be thrown by naval guns. But to the increasing power of the new artillery it soon became necessary to oppose increased thickness of iron plates. The earlier ironclads carried a considerable number of guns, which could, however, deliver only a broadside fire, that is, the shots could, for the most part, be sent only in a direction at right angles to the ship’s length, or nearly so. But in the more recently built ironclads there are very few guns, which are, however, six times the weight of the old sixty-eight pounders, and are capable of hurling projectiles of enormous weight. The ships built after the Warrior were completely protected by iron plates, and the thickness of the plates has been increased from time to time, with a view of resisting the increased power which has been progressively given to naval guns. A contest, not yet terminated, has been going on between the artillerist and the ship-builder; the one endeavouring to make his guns capable of penetrating with their shot the strongest defensive armour of the ships, the other adding inch after inch to the thickness of his plates, in order, if possible, to render his ship invulnerable.

Fig. 70.Section of H.M.S. Hercules.

One of the finest of the large ironclads is the Hercules, of which a section amidships is presented on the next page. This ship is 325 ft. in length, and 59 ft. in breadth, and is fitted with very powerful engines which will work up to 8,529 indicated horse-power. The tonnage is 5,226; weight of hull, 4,022 tons; weight of the armour and its backing, 1,690 tons; weight of engines, boilers, and coals, 1,826 tons; total with equipment and armament, 8,676 tons. Although the Hercules carries this enormous weight of armour and armament, her speed is very great, excelling, in fact, that of any merchant steamer afloat, for she can steam at the rate of nearly 17 miles an hour. She also possesses, in a remarkable degree, the property which naval men call handiness; that is, she can be quickly turned round in a comparatively small space. The handiness of a steamer is tested by causing her to steam at full speed with the helm hard over, when the vessel will describe a circle. The smaller the diameter of that circle, and the shorter the time required to complete it, the better will the vessel execute the movements required in naval tactics. Comparing the performances of the Warrior and the Hercules, we find that the smallest circle the former 152can describe is 1,050 yards in diameter, and requires nine minutes for its completion, whereas the latter can steam round a circle of only 560 yards diameter in four minutes. The section (Fig. 70) shows that, like the Great Eastern, the Hercules is constructed with a double hull, so that she would be safe, even in the event of such an accident as actually occurred to the Great Eastern, when a hole was made by the stripping off of her bottom plates, 80 ft. long and 5 ft. wide. The defensive armour of the Hercules is, it will be observed, greatly strengthened near the water-line, where damage to the ship’s side would be most fatal. The outer iron plates are here 9 in. thick, while in other parts the thickness is 8 in., and in the less important positions 6 in. The whole of the hull is, however, completely protected above the water-line, and the iron plates are backed up by solid teak-wood for a thickness of from 10 in. to 12 in. The teak is placed between girders, which are attached to another iron plating 1½ in. thick, supported by girders 2 ft. apart. The spaces between these girders are also filled with teak, and the whole is lined with an inner skin of iron plating, ¾ in. thick. The belt along the water-line has thus altogether 11¼ in. of iron, of which 9 in. are in one thickness, and this part is, moreover, backed by additional layers of teak, as shown in the section; so that, besides the 11¼ in. of iron, the ship’s side has here 3 ft. 8 in. total thickness of solid teak-wood. The deck is also covered with iron plates, to protect the vessel from vertical fire. The Hercules carries eight 18–ton guns as her central battery, and two 12–ton guns in her bow and stern: these guns are rifled, and each of the larger ones is capable of throwing a shot weighing 400 lbs. The guns can be trained so as to fire within 15° of the direction of the keel; for near the ends of the central battery the ports are indented, and the guns are mounted on Scott’s carriages, in such a manner that any gun-slide can be run on to a small turn-table, and shunted to another port, just as a railway-carriage is shunted from one line to another. Targets for artillery practice were built so as to represent the construction of the side of the Hercules, and it was found, as the result of many experiments, that the vessel could not be penetrated by the 600 lb. shot from an Armstrong gun, fired at a distance of 700 yds. The production of such iron plates, and those of even greater thickness which have since been used, forms a striking example of the skill with which iron is worked. These plates are made by rolling, and it will be understood that the machinery used in their formation must be of the most powerful kind, when it is stated that plates from 9 in. to 15 in. thick are formed with a length of 16 ft. and a breadth of 4 ft. The plates are bent, while red hot, by enormous hydraulic pressure, applied to certain blocks, upon which the plates are laid, the block having a height adjusted according to the curve required. The operation requires great care, as it must be accomplished without straining the parts in a manner injurious to the strength of the plate.

Fig. 71.Section of H.M.S. Inconstant.

Fig. 71 on the next page is the section of another ship of war, the Inconstant, which has not, like the Hercules, been designed to withstand the impact of heavy projectiles, but has been built mainly with a view to speed. The Inconstant has only a thin covering of iron plating, except in that portion of the side which is above water, where there is a certain thickness of iron diminishing from the water-line upwards, but not enough to entitle the Inconstant to be classed as an armoured vessel. This ship, however, may be a truly formidable antagonist, for she carries a considerable number of heavy guns, which her speed would enable her to use with great effect against an adversary incapable of manœuvring so rapidly. She could give 153chase, or could run in and deliver her fire, escaping by her speed from hostile pursuit in cases where the slower movements of a ponderous ironclad would be much less effective. The Inconstant carries ten 12–ton guns of 9 in. calibre, and six 6–ton 7 in. guns, all rifled muzzle-loaders, mounted on improved iron carriages, which give great facilities for handling them 154The ship is a frigate 338 ft. long and 50 ft. broad, with a depth in the hold of 17 ft. 6 in. She is divided by bulkheads into eleven water-tight compartments. The engines are of 6,500 indicated horse-power, and the vessel attains an average speed of more than 18½ miles per hour.

Fig. 72.Section, Elevation, and Plan of Turret of H.M.S. Captain.

Fig. 73.H.M.S. Captain.

A new system of mounting very heavy naval guns was proposed by Captain Coles about 1861. This plan consists in carrying one or two very heavy guns in a low circular tower or turret, which can be made to revolve horizontally by proper machinery. The turret itself is heavily armoured, so as to be proof against all shot, and is carried on the deck of the ship, which is so arranged that the guns in the turret can be fired at small angles with the keel. The British Admiralty having approved of Captain 156Coles’ plans, two first-class vessels were ordered to be built on the turret system. These were the Monarch and the Captain—the latter of which we select for description on account of the melancholy interest which attaches to her. On page 155 a diagram is given representing the profile of the Captain, in which some of the peculiarities of the ship are indicated—the turrets with the muzzles of two guns projecting from each being easily recognized. The Captain was 320 ft. long and 53 ft. wide. She was covered with armour plates down to 5 ft. below the water-line, as represented by the dark shading in the diagram. The outer plating was 8 in. thick opposite the turrets, and 7 in. thick in other parts. It was backed up by 12 in. of teak; there were two inner skins of iron each ¾ in. thick, then a framework with longitudinal girders 10 in. deep. The deck was plated in the spaces opposite the turrets with iron 1½ in. thick. The Captain was fitted with twin screws—that is, instead of having a single screw, one was placed on each side, their shafts being, of course, parallel with the vessel’s length. The object of having two screws was not greater power, for it is probable that a single screw would be more effectual in propelling the ship; but this arrangement was adopted because it was considered that, had only one screw been fixed, the ship might easily be disabled by the breaking of a blade or shaft; whereas in the case of such an accident to one of the twin screws, the other would still be available. The twin screws could also be used for steering, and the vessel could be controlled without the rudder, as the engines were quite independent of each other, each screw having a separate pair. The diameter of the screws was 17 ft. The erections which are shown on the deck between the turrets afforded spacious quarters for the officers and men. These structures were about half the width of the deck, and tapered off to a point towards the turrets, so as leave an unimpeded space for training the guns, which could be fired at so small an angle as 6° with the length of the vessel. Above these erections, and quite over the turrets, was another deck, 26 ft. wide, called the “hurricane deck.” The ship was fully rigged and carried a large spread of canvas. But the special features are the revolving turrets, and one of these is represented in detail in Fig. 72, which gives a section, part elevation, and plan. Of the construction of the turret, and of the mode in which it was made to revolve, these drawings convey an idea sufficiently clear to obviate the necessity of a minute description. Each turret had an outside diameter of 27 ft., but inside the diameter was only 22 ft. 6 in., the walls being, therefore, 2 ft. 3 in. thick—nearly half this thickness consisting of iron plating. Separate engines were provided for turning the turrets, and they could also be turned by men working at the handles shown in the figures. Each turret carried two 25–ton Armstrong guns, capable of receiving a charge of 70 lbs. of gunpowder, and of throwing a 600 lb. shot.

After some preliminary trials the Captain was sent to sea, and behaved so well, that Captain Coles and Messrs. Laird, her designer and contractors, were perfectly satisfied with her qualities as a sea-going ship. She was then sent in the autumn of 1870 on a cruise with the fleet, and all went well until a little after midnight between the 6th and 7th September, 1870, when she suddenly foundered at sea off Cape Finisterre. The news of this disaster created a profound sensation throughout Great Britain, for, with the exception of nineteen persons, the whole crew of five hundred persons went down with the ship. Captain Coles, the inventor of the turrets, was in the ill-fated vessel and perished with the rest, as did also Captain Burgoyne, the gallant commander, and the many other distinguished naval 157officers who had been appointed to the ship; among the rest was a son of Mr. Childers, then First Lord of the Admiralty. Although the night on which this unfortunate ship went down was squally, with rain, and a heavy sea running, the case was not that of an ordinary shipwreck in which a vessel is overwhelmed by a raging storm. It might be said, indeed, of the loss of the Captain as of that of the Royal George:

“It was not in the battle;
No tempest gave the shock;
She sprang no fatal leak;
She ran upon no rock.”

Fig. 74.

Fig. 75.

One of the survivors, Mr. James May, a gunner, related that, shortly after midnight he was roused from his sleep by a noise, and feeling the ship uneasy, he dressed, took a light, and went into the after turret, to see if the guns were all right. He found everything secure in the turret, but that moment he felt the ship heel steadily over, and a heavy sea having struck her on the weather side, the water flowed into the turret, and he got out through the hole in the top of the turret by which the guns were pointed, only to find himself in the water. He swam to the steam-pinnace, which he saw floating bottom upwards, and there he was joined by Captain Burgoyne and a few others. He saw the ship turn bottom up, and sink stern first, the whole time from her turning over to sinking not being more than a few minutes. Seeing the launch drifting within a few yards, he called out, “Jump, men! it is your last chance.” He jumped, and with three others reached a launch, in which were fifteen persons, all belonging to the watch on deck, who had found means of getting into this boat. One of these had got a footing on the hull of the ship as she was turning over, and he actually walked over the bottom of the vessel, but was washed off by a wave and rescued by those who in the meantime had got into the launch. It appears that Captain Burgoyne either remained on the pinnace or failed to reach the launch. Those who were in that boat, finding the captain had not reached them, made an effort to turn their boat back to pick him up, but the boat was nearly swamped by the heavy seas, and they were obliged to let her drift. One man was at this time washed out of the boat and lost, after having but the moment before exclaimed, “Now, lads, I think we are all right.” After twelve hours’ hard rowing, without food or water, the survivors, numbering sixteen men and petty officers and three boys, reached Cape Finisterre, where they received help and attention. On their arrival in England, a court-martial was, according to the rules of the service, formally held on the survivors, but in reality it was occupied in investigating the cause of the catastrophe. The reader may probably be able to understand what the cause was by giving his attention to some general considerations, which apply to all ships whatever, and by a careful examination of the diagrams, Figs. 74 and 75, which are copied from diagrams that were placed in the hands of the members of the court-martial. The letters b and g and the arrows are, however, added, to serve in illustration of a part of the explanation. The vessel is represented as heeled over in smooth water, and the gradations on the semicircle in Fig. 74 will enable the reader to understand how the heel is measured by angles. If the ship were upright, the centre line would coincide with the upright line, marked o on the semicircle, and drawn from its centre. Suppose a level line drawn through the centre of the semicircle, and let the circumference between the point where the last line cuts it and the point o be divided into ninety equal parts, and let these parts be numbered, and straight lines 158drawn from the centre to each point of division. In the figure the lines are drawn at every fifth division, and the centre line of the ship coincides with that drawn through the forty-fifth division. In this case the vessel is said to be inclined, or heeled, at an angle of forty-five degrees, which is usually written 45°. In a position half-way between this and the upright the angle of heel would be 22½°, and so on. The reader no doubt perceives that a ship, like any other body, must be supported, and he is probably aware that the support is afforded by the upward pressure of the water. He may also be familiar with the fact that the weight of every body acts upon it as if the whole weight were concentrated at one certain point, and that this point is called the centre of gravity of the body. Whatever may be the position of the body itself, its centre of gravity remains always at the same point with reference to the body. When the centre of gravity happens to be within the solid substance of a body, there is no difficulty in thinking of the force of gravitation acting as a downward pull applied at the centre of gravity. But this point is by no means always within the substance of bodies: as often as not it is in the air outside of the body. Thus the centre of gravity of a uniform ring or hoop is in the centre, where, of course, it has no material connection with the hoop; but in whatever position the hoop may be placed, the earth’s attraction pulls it as if this central point were rigidly connected with the hoop, and a string were attached to the point and constantly pulled downwards. This explanation of the meaning of centre of gravity may not be altogether superfluous, for, when the causes of the loss of the Captain were discussed in the newspapers, it became evident that such terms as “centre of gravity” convey to the minds of many but very vague notions. One writer in a newspaper enjoying a 159large circulation seriously attributed the disaster to the circumstance of the ship having lost her centre of gravity! The upward pressure of water which supports a ship is the same upward pressure which supported the water before the ship was there—that is, supported the mass of water which the ship displaces, and which was in size and shape the exact counterpart of the immersed part of the ship. Now, this mass of water, considered as a whole, had itself a centre of gravity through which its weight acted downwards, and through which it is obvious that an equal upward pressure also acted. This centre of gravity of the displaced water is usually termed the “centre of buoyancy,” and, unlike the centre of gravity, it changes its position with regard to the ship when the latter is inclined, because then the immersed part becomes of a shape different for each inclination of the ship. Now, recalling for an instant the fundamental law of floating bodies—namely, that the weight of the water displaced is equal to the weight of the floating body—we perceive that in the case of a ship there are two equal forces acting vertically, viz., the weight of the ship or downward pull of gravitation acting at G, Fig. 74, the centre of gravity of the ship, and an equal upward push acting through B, the centre of buoyancy. It is obvious that the action of these forces concur to turn a ship placed as in Fig. 74 into the upright position. It is by no means necessary for this effect that the centre of gravity should be below the centre of buoyancy. All that is requisite for the stability of a ship is, that when the ship is placed out of the upright position, these forces should act to bring her back, which condition is secured so long as the centre of buoyancy is nearer to the side towards which the vessel is inclined than the centre of gravity is. When there is no other force acting on a ship or other floating body, these two points are always in the same vertical line. The two equal forces thus applied in parallel directions constitute what is called in mechanics a “couple,” and the effect of this in turning the ship back into the upright position is the same as if a force equal to its weight were applied at the end of a lever equal in length to the horizontal distance between the lines through B and 160G. The righting force, then, increases in proportion to the horizontal distance between the two points, and it is measured by multiplying the weight of the ship in tons by the number of feet between the verticals through G and B, the product being expressed in statical foot-tons, and representing the weight in tons which would have to be applied to the end of a lever 1 ft. long, in order to produce the same turning effect. When a ship is kept steadily heeled over by a side wind, the pressure of the wind and the resistance of the water through which the vessel moves constitute another couple exactly balancing the righting couple. The moment of the righting couple, or the righting force, or statical stability as it is also called, is determined by calculation and experiment from the design of the ship, and from her behaviour when a known weight is placed in her at a known distance from the centre. Such calculations and experiments were made in the case of the Captain, but do not appear to have been conducted with sufficient care and completeness to exhibit her deficiency in stability. After the loss of the ship, however, elaborate computations on these points were made from the plans and other data. The following table gives some of the results, with the corresponding particulars concerning the Monarch for the sake of comparison:

  Monarch. Captain.
I. Angle at which the edge of the deck is immersed 28° 14°
II. Statical righting force in foot-tons at the angle at which the deck is immersed 12,542 5,700
III. Angle of greatest stability 40° 21°
IV. Greatest righting force in foot-tons 15,615 7,100
V. Angle at which the righting force ceases 59° 54°
VI. Reserve of dynamical stability at an angle of 14° in dynamical foot-tons 6,500 410

From No. V. in the above table we learn that if the Captain had been heeled to 54°, the centre of gravity would have overtaken the centre of buoyancy—that is, the two would have been in one vertical line. Any further heeling would have brought the points into the position shown in Fig. 75, where it is obvious that the action of the forces is now to turn the vessel still more on its side, and the result is an upsetting couple instead of a righting couple.

These figures and considerations refer to the case of the vessel floating in smooth water, but the case of a vessel floating on a wave is not different in principle. The reader may picture to himself the diagrams inclined so that the water-line may represent a portion of the wave’s surface; then he must remember that the very action which heaves up the water in a sloping surface is so compounded with gravity, that the forces acting through G and B retain nearly the same position relatively to the surface as before.

No. VI. in the foregoing table requires some explanation. To heel a ship over to a certain angle a certain amount of work must be done, and in the scientific sense work is done only when something is moved through a space against a resistance. When the weight of a ton is raised 1 ft. high, one foot ton of work is said to be done; if 2 tons were raised 1 ft., or 1 ton were raised 2 ft., then two foot-tons of work would be done, and so on. The 161same would be the case if a pressure equal to those weights were applied so as to move a thing in any direction through the same distances. It should be carefully noticed that the foot-ton is quite a different unit in this case from what it is as the moment of a couple. If we heel a ship over by applying a pressure on the masts, it is plain that the pressure must act through a certain space, and the same heel could be caused either by means of a smaller pressure or a greater, according as we apply it higher up or lower down; but the space through which it must act would vary, so that the product of the pressure and space would, however, be always the same. No. VI. shows the amount of work that would have to be done in order completely to upset each of the vessels when already steadily heeled over to 14°. The amounts in the two cases are so different that we can easily understand how a squall which would not endanger the Monarch might throw the Captain over. A squall suddenly springing up would do more than heel a vessel over to the angle at which it is able to maintain it: it would swing it beyond that position by reason of the work done on the sails as they are moving over with the vessel, and the latter would come to a steady angle of heel only after a series of oscillations. Squalls, again, which, although suddenly springing up in this manner, could not heel the ship over beyond the angle where the stability vanishes, might yet do so if they were intermittent and should happen to coincide in time with the oscillations of the ship—just as a series of very small impulses, coinciding with the time of the vibrations of a heavy pendulum, may accumulate so as to increase the range of vibration to any extent. It is believed that in the case of the Captain the pressure of the wind on the underside of the hurricane assisted in upsetting the vessel. This, however, could only have exerted a very small effect compared to that produced by the sails. The instability of the Captain does not appear to have been discovered by such calculations as were made before the vessel went to sea. It was observed, however, that the ship when afloat was 1 ft. 6 in. deeper in the water than she should have been—in other words, the freeboard, or side of the ship out of the water, instead of being 8 ft. high as intended, was only 6 ft. 6 in., and such a difference would have a great effect on the stability.

Fig. 76.H.M.S. Glatton.

The turret system has been applied to other ships on quite a different plan. Of these the Glatton is one of the most remarkable. Her appearance is very singular, and totally unlike that which we look for in a ship, as may be seen by an inspection of Fig. 76, page 162. The Glatton, which was launched in 1871, is of the Monitor class, and was designed by Mr. E. J. Reed, who has sought to give the ship the most complete protection. With this view the hull is covered with iron plates below the water-line, and the deck also is cased with 3 in. iron plates, to resist shot or shell falling vertically. The base of the turret is shielded by a massive breastwork, which is a peculiarity of this ship. The large quantity of iron required for all these extra defences has, of course, the effect of increasing the immersion of the vessel, and therefore of diminishing her speed. The freeboard when the ship is in ordinary trim is only 3 ft. high, and means are provided for admitting water to the lowest compartment, so as to increase the immersion by 1 ft., thus reducing the freeboard to only 2 ft. when the vessel is in fighting trim, leaving only that small portion of the hull above water as a mark for the enemy. The water ballast can be pumped out when no longer needed. The Glatton is 245 ft. long and 54 ft. broad, and she draws 19 ft. of water with the freeboard of 3 ft., displacing 4,865 tons of water, while, with the 2 ft. freeboard, the displacement is 5,179 tons. This ship 162cost £210,000. Mr. Reed wished to construct a vessel of much larger size on the same plan—a proposal to which, however, the Admiralty did not then consent. The Glatton is, nevertheless, one of the most powerful ships of war ever built, and may be considered as an impregnable floating fortress. Above the water-line the hull is covered with armour plates 12 in. thick, supported by 20 in. of teak backing, and an inner layer of iron 1 in. thick. Below the water-line the iron is 8 in. thick, and the teak 10 in. The revolving turret carries two 25–ton guns, firing each a 600 lb. shot, and is covered by a massive plating of iron 14 in. in thickness. Besides this the base of the turret is protected by a breastwork rising 6 ft. above the hull. This breastwork is formed of plates 12 in. thick, fastened on 18 in. of teak. The turret rises 7 ft. above the breastwork, and therefore the latter in no way impedes the working of the guns. The Glatton has a great advantage over all the other turret ships in having a perfectly unimpeded fore range for her guns, for there is no mast or other object to prevent the guns being fired directly over the bow. There are no sails, the mast being intended only for flying signals and hoisting up boats, &c. The hull is divided by vertical partitions into nine water-tight compartments, and also into three horizontal flats—the lowest being air-tight, and having arrangements for the admission and removal of water, 163as already mentioned. The stem of the ship is protruded forwards below the water for about 8 ft., thus forming a huge ram which would itself render the Glatton a truly formidable antagonist at close quarters even if her guns were not used. The engines are capable of being worked up to 3,000 horse-power, giving the ship a speed of 9½ knots per hour, and means are provided for turning the turret by steam power. The turret can be rotated by manual labour, requiring about three minutes for its complete revolution, but by steam power the operation can be effected in half a minute. The commander communicates his orders from the pilot-house on the hurricane deck to the engine-room, steering-house, and turret, by means of speaking-tubes and electric telegraphs. The Glatton was not designed to be ocean-going, but is intended for coast defence.

Fig. 77.H.M.S. Thunderer.

The British navy contains two powerful turret-ships constructed on the same general plan as the Glatton, but larger, and capable of steaming at a 164greater speed, and of carrying coal for a long voyage. These sister ships are named the Devastation, Fig. 69, and the Thunderer, Fig. 77. The Thunderer has two turrets and a freeboard of 4 ft. 6 in. Space is provided for a store of 1,800 tons of coal, of which the Glatton can carry only 500 tons. The vessel is fitted with twin screws, turned by two pairs of independent engines, capable of working up to 5,600 horse-power, and she can steam at the rate of 12 knots, or nearly 14 miles, an hour. With the large supply of coal she can carry, the Thunderer could make a voyage of 3,000 miles without re-coaling. Though the freeboard of the heavily-plated hull is only 4 ft. 6 in., a lighter iron superstructure, indicated in the figure by the light shading, rises from the deck to the height of 7 ft., making the real freeboard nearly 12 ft. This gives the ship much greater stability, and prevents her from rolling heavily when at sea. The length is 285 ft. and the width 58 ft., and the draught 26 ft. The hull is double, the distance between the outer and inner skins of the bottom being 4 ft. 6 in. The framing is very strong and on the longitudinal principle, and the keel is formed of Bessemer steel. Each turret is 24 ft. 3 in. in internal diameter, and is built with five layers of teak and iron. Beginning at the inside, there is a lining of 2⅝ in. iron plates; then 6 in. of teak in iron frames, arranged horizontally; 6 in. of armour plates; 9 in. of teak, placed vertically; outside of all, 8 in. armour plates. Each turret carries two Fraser 35–ton guns, rifled muzzle-loaders. The turrets revolve by hand or by steam-power. There are no sails, and thus a clear range for the guns is afforded fore and aft. The bases of the turrets are protected by the armoured breastwork, of which a portion is seen in the figure in advance of the fore turret.

Another very powerful ship of war, which possesses some special features, is represented in the diagram on page 165, Fig. 78. This vessel, named the König Wilhelm, was built at Blackwall for the Prussian Government by the Thames Ironworks and Steam Shipbuilding Company, from designs by Mr. Reed. Her length is 365 ft., width 60 ft.; burthen, 6,000 tons; displacement, 8,500 tons. She is framed longitudinally, that is, girders pass from end to end, about 7 ft. apart, and the stem projects into a pointed ram. In this case also the hull is double; there is, in fact, one hull within another, with a space of 4½ ft. between them. The armour plates are 8 in. in thickness, with 10 in. of teak backing; but on the less important parts the thickness of the iron is reduced to 6 in., and in some places to 4 in. This ship has a broadside battery, and there are no turrets, but on the deck there are, fore and aft, two semicircular shields, formed of iron plates and teak, pierced with port-holes for cannon, and also with loop-holes for muskets. From these a fore-and-aft fire may be kept up. The ship is fully rigged, and has also steam engines of 7,000 horse-power, by Maudslay and Co. Her armament consists of four three-hundred-pounders, capable of delivering fore-and-aft as well as broadside fire, and twenty-three other guns of the same size between decks. These guns are all Krupp’s steel breech-loaders.

Fig. 78.The König Wilhelm.

Fig. 78a.—The “Victoria” leaving Newcastle-on-Tyne.

The great contest of armour plates versus guns has already been alluded to, and to the remarks then made it may be added that, while on the one hand, guns weighing 110 tons are mounted in turrets, ships are already designed with 18 in. and even 20 in. of steel armour plates. It would be very difficult to predict which side will sooner reach the limit beyond which increase of size and power cannot go. The gradual increase of thickness of plating, attended by increased weight of guns, projectiles, and charges 166of powder, may be illustrated by stating in a condensed form a few details of some ships, as regards the thickness of armour, and its resisting power, which is nearly in proportion to the square of its thickness; and also some particulars respecting the guns originally carried by those ships.

Warrior. Hercules. Glatton. Thunderer. Victoria.
Date when completed 1861 1868 1872 1877 1889
Thickness of iron plating in inches 9 12 14 18
Relative resisting power of plating 20 81 144 196 324
Guns carried Cast iron, smooth bore Wrought iron, rifled Wrought iron, rifled Wrought iron, rifled Steel, Rifled
Weight of guns in tons 18 25 35 111
Charge of powder in lbs. 16 60 70 120 960
Weight of projectiles in lbs. 68 400 600 700 1,800
Destructive power of projectiles in foot-tons 452 3,863 5,165 8,404 56,000

167One of the latest additions out of the thirty or forty armoured ships that have been added to the British Navy since the preceding pages were written is included in the above table for the sake of comparison. Our ironclad fleet now includes vessels protected and armed in many different ways. Some have the protective armour extended continuously along the water-line, others have it for only a greater or less part of their length. The armaments are also very diverse as to the size of the guns and the way in which they are mounted. A few carry one or two of the huge 110–ton gun mounted in massive revolving turrets; others have their guns in central batteries, or in barbettes, and others again are arranged as broadside ships; while these plans are also variously combined so as to form a great number of different types. In the ships built within the last 15 years, steel has been almost invariably used instead of iron for the armour-plating. A great increase of speed has been obtained in late years. The largest British armoured ships yet launched have displacements between 10,000 and 12,000 tons, but another class of first-rate line-of-battle ships of still greater size is in process of construction, and of these it is estimated that four will be completed in 1893. They are all of the same design and armament, and will have a displacement of 14,150 tons, a length of 380 feet, and a breadth of 75 feet. The armour plates at the sides will be 18 inches thick. Each ship will carry four 67–ton breech loading rifled guns, ten 6–inch quick firing guns, and 18 other smaller guns, also quick firing. These vessels are expected to realize a speed of about 20 miles per hour; but this is somewhat less than a few of the heavy ironclads now afloat have given by actual trial, a rate equal to 21⅓ miles an hour having been attained by some. Several of our rapid unarmoured cruisers are able to steam at 25 miles an hour.

Before the close of 1894, the British navy possessed no fewer than eight of the largest armoured line of battle-ships mentioned in the foregoing paragraph, each being of 14,150 tons displacement, and having engines of 13,000 horse-power. At the same period there were in course of construction four ships surpassing even these in tonnage, though of somewhat less engine-power. Two were building at Portsmouth, to be called the Majestic and the Royal George, whilst the Jupiter was in progress at Glasgow and the Mars at Birkenhead. All these are very heavily armoured vessels, each displacing 14,900 tons, provided with engines of 12,000 horse-power, and a very effective armament of guns. Among the powerful ships of the navy may now also be noted the Blake, the Blenheim, which, although the displacement is only 500 tons greater than that of König Wilhelm, have engines of nearly three times the power, namely, of 20,000 horse-power. Of large armoured ships, namely, those of 9,000 tons and upwards, Great Britain now has afloat at least fifty; and the advance that has taken place in the size and power of war-ships during the last twenty years may be inferred by reference to the foregoing paragraphs giving the dimensions, &c., of the Glatton and the Thunderer, which paragraphs are, for the sake of comparison, allowed to appear as they did in the first edition (1876) of this book. Besides these very large armoured vessels, of which the smallest is nearly twice as big as the largest of twenty-five years ago, the British navy comprises ships of every size and for every purpose, and so many of them that their names and classifications would occupy many pages.

Two recent additions representing new type of ships claim notice before this article is concluded. These are first the Terrible, with a 168sister ship the Powerful. The former, of which a representation[3] is given in Plate V., is pronounced, for its size, armour, armament, and speed taken together, to be the most powerful cruiser in the world. The length is 538 ft., breadth 71 ft., depth 43 ft., and the displacement is 14,250 tons. A special object in the design of this vessel was high speed, and she is provided with twin-screws and two engines, the combined effort of which is equal to 25,000 horse-power. There are forty-eight boilers and four funnels, the ship being capable of carrying 3,000 tons of coal. The vessel is built on the lines of the great Atlantic steamers, and the engines, guns, and magazines are protected by a thick curved armour deck. The vessel has a speed of 22 knots, or 25⅓ miles per hour. Her armament consists of two 22–ton guns, twelve 6–in. quick-firing, and many other smaller machine guns, and she carries besides four submerged torpedo tubes. A second ship to be noted is amongst those designed mainly to exceed all other craft in speed, and ranging in tonnage from 3,800 to 4,500. The Janus, a torpedo-boat destroyer of this class, was found, at a recent trial over a measured mile, to attain the then unexampled speed of 28 knots, or 32¼ miles per hour. But even this has been beaten by a new torpedo-boat destroyer, built by Messrs. Yarrow at Poplar for the Russian Government, and launched in August, 1895. This vessel, within a few hours after leaving the stocks, cut through the water at the rate of 30·285 knots, or nearly 35 miles, per hour.

3.  From Graphic, 1st June, 1895.

A sad fate befell the Victoria, which was one of the heaviest armed of British ships (vide page 129), when taking part in some naval manœuvres off Tripoli, on the Syrian coast, where she was the flag-ship of Admiral Tryon, commander-in-chief of the squadron. On the 22nd June, 1893, in consequence of an inconsiderate order given by the admiral himself, the Victoria was struck by the formidable ram of the Camperdown (10,600), and in fifteen minutes turned over and sank in sight of the whole fleet, carrying down with her the admiral, 30 officers, and 320 men, out of a crew of 600. [1895.]

Fig. 78b.—Firing at a floating battery.

PLATE XI. H.M.S. “TERRIBLE.”

169

Fig. 79.Krupp’s Works, at Essen, Prussia.

FIRE-ARMS.

The invention of gunpowder—or rather its use in war—appears at first sight a device little calculated to promote the general progress of mankind. But it has been pointed out by some historians that the introduction of gunpowder into Europe brought about the downfall of the feudal system with its attendant evils. In those days every man was practically a soldier: the bow or the sword he inherited from his father made him ready for the fray. But when cannons, muskets, and mines began to be used, the art of war became more difficult. The simple possession of arms did not render men soldiers, but a long special training was required. The greater cost of the new arms also contributed to change the arrangements of society. Standing armies were established, and war became the calling of only a small part of the inhabitants of a country, while the majority were left free to devote themselves to civil employments. Then the useful arts of life received more attention, inventions were multiplied, commerce began to be considered as honourable an avocation as war, letters were cultivated, and other foundations laid for modern science. If such have really been the indirect results of the invention of gunpowder, we shall hardly share the regret of the fine gentleman in “Henry IV.”:

“That it was great pity, so it was,
That villanous saltpetre should be digged
Out of the bowels of the harmless earth,
Which many a good tall fellow had destroyed
So cowardly.”

We often hear people regretting that so much attention and ingenuity as are shown by the weapons of the present day should have been expended 170upon implements of destruction. It would not perhaps be difficult to show that if we must have wars, the more effective the implements of destruction, the shorter and more decisive will be the struggles, and the less the total loss of life, though occurring in a shorter time. Then, again, the exasperated and savage feelings evoked by the hand-to-hand fighting under the old system have less opportunity for their exercise in modern warfare, which more resembles a game of skill. But the wise and the good have in all ages looked forward to a time when sword and spear shall be everywhere finally superseded by the ploughshare and the reaping-hook, and the whole human race shall dwell together in amity. Until that happy time arrives—

“Till the war-drum throbs no longer, and the battle flags are furl’d
In the Parliament of man, the Federation of the world—
When the common sense of most shall hold a fretful realm in awe,
And the kindly earth shall slumber, lapt in universal law,”—

we may consider that the more costly and ingenious and complicated the implements of war become, the more certain will be the extension and the permanence of civilization. The great cost of such appliances as those we are about to describe, the ingenuity needed for their contrivance, the elaborate machinery required for their production, and the skill implied in their use, are such that these weapons can never be the arms of other than wealthy and intelligent nations. We know that in ancient times opulent and civilized communities could hardly defend themselves against poor and barbarous races. But the world cannot again witness such a spectacle as Rome presented when the savage hordes of Alaric swarmed through her gates, and the mighty civilization of centuries fell under the assaults of the northern barbarians. In our day it is the poor and barbarous tribes who are everywhere at the mercy of the wealthy and cultivated nations. The present age has been so remarkably fertile in warlike inventions, that it may truthfully be said that the progress made in fire-arms and war-ships within the second half of the nineteenth century surpasses everything that had been previously accomplished from the time gunpowder came into use. Englishmen have good reason to be proud of the position taken by their country, and may feel assured that her armaments will enable her to hold her own among the most advanced nations of the world.

The subject of fire-arms embraces a very wide ground, as will appear if we consider the many different forms in which these weapons are constructed in order best to serve particular purposes. Pertaining to this subject, attention must also be directed to the modern projectiles and to the newer explosives that have largely taken the place of ordinary gunpowder. The shot gun, fowling-piece, and sporting rifle properly come under the head of fire-arms, and in the march of improvement these forms have most commonly been in advance of military muskets and rifles, the ingenuity bestowed on all their details being worthy of admiration. Nevertheless it is to the implements of war that general interest attaches; for on them depends so much the fate of battles and the destiny of nations, that whenever any country is engaged in war the question of arms becomes one of surpassing importance, enlisting the patriotic instincts of every citizen. Hence in the following pages our space will be devoted mainly to weapons of war, and more particularly to those that have been adopted by our own country.

Everyone of course is aware that guns, cannon, and gunpowder are by no means inventions of the nineteenth century; but there are fewer 171acquainted with the fact that rifling, breech-loading, machine guns, and revolvers were all invented and tried hundreds of years before. The devices by which some of these ideas were sought to be realised in past ages appear to us in some instances very primitive, not to say childish, when compared with modern work: but it must be remembered that nearly all the appliances required for producing such weapons had themselves to wait for their invention until the nineteenth century; such, for instance, as the steam-hammer, powerful and accurate tools, refined measuring implements, material entirely reliable such as the new steel, and also scientific investigations of all the conditions involved. The military fire-arms are of so many different forms and patterns that we can deal here with but a selection from the various services. If a rough classification had to be made, the most obvious distinction would be between the weapons the soldier carries in his hands (small-arms) and those which are mounted on some kind of carriage and discharge projectiles of much greater weight (ordnance). Ordnance again includes guns mounted on forts, carried in ships, or taken with an army into the field, in each case coming into action under different conditions. Partaking somewhat of the nature of both field-guns and of small-arms are the machine guns, of which the French mitrailleur was the first example, afterwards developing into much more effective weapons in the hands of Gatling, Gardner, Nordenfelt, Maxim, and Hotchkiss.

As much will have to be said about rifling the bores of muskets and cannon, we may here explain the nature and object of this device. The projectiles used in all guns down to comparatively recent times were almost invariably of spherical form, and could indeed scarcely be otherwise with smooth-bore weapons. As the diameter of the shot would necessarily be something less than that of the bore of the barrel, a considerable loss of power would result from the escape of the powder gases between the shot and the barrel, which escape is known as windage. Another disadvantage of the spherical projectile is that for the same weight of metal the air offers a greater resistance to its passage, and consequently checks its speed more quickly than that of any other circular form; for the air resistance is proportional to the square of the diameter, and therefore if we take a ball of 1 in. diameter and a cylinder of 1 in. in length, each having the same weight of metal, the diameter of the cylindrical shot will be a little more than four-fifths of an inch, and the air resistance to the ball will be exactly half as much again as to the cylinder, that is, in the proportion of 3 to 2. Again, the passage of the spherical shot within the barrel of the gun will not be in a straight line, but in a series of rebounds from side to side, and its direction on leaving the muzzle will depend upon which part of the bore it just before impinges on, as from that it will also take a rotatory “twist” that will in part determine its path through the air.

Now if an elongated projectile were fired from a smooth-bore gun, its course through the air would be erratic to a degree impossible to the spherical shot, for it would turn end over end with deviations that would make aiming impracticable. But if the elongated projectile is made to spin rapidly enough about its longitudinal axis, it flies through the air quite steadily, the axis of rotation remaining parallel to that of the gun throughout the whole flight. The steadiness due to rapid rotation has familiar examples in spinning tops, in gyroscopic tops, in the way arrows are feathered so that the air may cause them to revolve axially, and so 172on. The axial rotation of the projectile is effected by ploughing out in the cylindrical barrel of the gun a number of spiral or twisting grooves, which the projectile is compelled to follow as it travels along the barrel, either by means of corresponding protuberances formed upon its surface in the first instance, as in Jacob’s bullets, or by studs let into it, as in the studded shots and shells for ordnance which constituted at one time the regulation plan adopted by the British Government; or otherwise by making the force of the explosion expand some portion of the projectile in such a manner that this portion shall completely fill up the grooves, thus preventing windage, and causing the projectile to follow the twist of the grooves. This is the more general method, especially since the adoption of breech-loading. The Lancaster rifling, and that advocated by Whitworth, are the same in principle, but differ in appearance, from the section of the barrel being made in the one case oval, in the other hexagonal or polygonal, but with the twist necessary to produce rotation.

Incident to the discharge of all fire-arms, great and small, is a phenomenon of which we have to speak, because it is one which in the mounting of heavy ordnance especially has to be taken into account. And as it also illustrates in a very direct way one of the most general laws of nature, while people often have very vague and erroneous ideas of its cause and operation, it deserves the reader’s attention. In gunnery it is called the recoil, and is familiar to anyone who has ever fired a pistol, fowling-piece, or rifle, in the kick backwards felt at the moment of the discharge. This law is in operation whenever the condition of a body in respect to its rest or motion is changing. That is, whenever a body at rest has motion given to, or if when already moving it is made to go faster or slower, or to stop, or when the direction of the motion is changed from that in a straight line. Now although these changes or actions are frequently occurring before our eyes, the operation in them of Newton’s third law of motion does not generally present itself to common observation. This third law was stated by Sir Isaac Newton thus:—“To every action there is always an opposite and equal reaction.” Now the expanding gases due to the gunpowder explosion press the bullet forwards and the barrel (with its attachments) backwards, with the same pressure in both cases, but at the end of the bullet’s passage along the bore the same velocity is not imparted to the two bodies, because the same pressure acting for the same time on bodies of unequal mass always produces velocities that are inversely proportional to the masses. The reader should try to acquire this conception of mass, remarking that it is a something quite distinct from that of weight. A given lump of metal, for instance, would have exactly the same mass in any part of the universe, whereas its weight would depend upon its position; as, for instance, at the distance from the earth of the moon’s orbit, it would weigh only as 1
3600
th part of its weight at the earth’s surface, and if it could be carried to the very centre of the earth it would there have no weight at all. Though the lump of metal will have different weights at different parts of the earth’s surface, it has been found (by experiment) that the weights of bodies at any one place are proportional to their masses. Therefore the same numbers that express the weights of bodies might also express their masses; but for certain good reasons these quantities are referred to different units. In England a piece of metal weighing 32 lbs. under standard conditions is said to have mass = 1; and so on. As with the same pressure acting for the same time, the velocities imparted are inversely proportional to the 173masses, it follows that the number expressing the velocity multiplied by that representing the mass in each such case of action and reaction will give the same product, or in other words the amount of motion (momentum) will be the same. This is what Newton meant by saying the reaction is equal to the action. We may now by way of illustration calculate the velocity of recoil of a rifle under conditions similar to those that might occur in practice. Let us suppose that the rifle, including the stock and all attachments, weighs 10 lbs., and that from it is fired a bullet weighing one-sixteenth of a pound, with a velocity at the muzzle of 1,200 ft. per second. To obtain the amount of motion or the momentum, we should here multiply the number expressing the mass of the bullet by 1,200, but for our present purpose the weight numbers may be used for the sake of simplicity; therefore 1
16
x 1,200 = 75 will represent (proportionately) the forward momentum of the bullet, and according to Newton’s law the backward momentum of the rifle will be, on the same scale, 75 also. We must therefore find the number which multiplied by 10 will give 75, and this obviously is 7·5. That is as much as to say that at the instant the bullet is leaving the muzzle, the rifle itself, if free to move, would be moving backward at the speed of 7½ ft. per second. Observe that this result would be the same if the rifle were fired where weight is non-existent; nor is the recoil due, as sometimes is erroneously supposed, to the resistance of the air to the passage of the bullet along the barrel, for even if the air were abolished, the recoil, so far as due to the masses and velocities, would remain the same, as indeed may be seen from the fact of our calculation taking no account of the bore of the rifle or of the shape of the bullet, circumstances of the utmost importance where atmospheric resistance is concerned.

The foregoing calculation however involves an assumption not in exact conformity with actual conditions, by taking for granted that the centre of gravity of the rifle is in the line of the axis of the barrel, while in fact this centre is almost always lower, and therefore the kick of the recoil acts in part as a turning-over push, tending to tilt up the muzzle of the gun, and for that reason the firer must hold the weapon very firmly or he will miss his aim. When such a rifle as we have supposed is fired, say from the shoulder, it would follow from the above calculation that the backward kick of the recoil is equivalent to a blow from a 10–lb. weight moving at the speed of 7½ ft. per second. This would certainly be a very uncomfortable experience, but the backward momentum must be met somehow. We have supposed that the gun is free to move, but we know the firer presses it firmly against the muscles of his shoulder, and the stock of the gun is spread out and provided with a smooth hollow heel plate, so that any pressure from it is felt as little as possible, especially as the muscle against which it is applied acts as an elastic pad. With the rifle thus firmly held we may regard the marksman and his rifle as forming only one mass, and the centre of gravity of this being now much below the axis of the barrel, the effect of the recoil tends to overthrow the man backwards; but he learns to resist this by standing firmly, so that the elasticity of his whole frame comes into play; and besides this, the mass factor of the momentum being now so large, the velocity factor becomes comparatively insignificant.

Although the momenta of gun and projectile are, according to Newton’s law, equal and opposite, the case is very different with regard to their energies, or powers of doing work, for the measure of these is jointly mass 174and the square of the velocity. The energy (vis viva) of a body of weight in pounds = W, moving with the velocity of v feet per second is always Wv2
64·4
, that is, it will do this number of foot-lbs. units of work before it comes to rest. It would require too much space to demonstrate and fully explain here what this means, but the reader may refer to our index under the entries “Energy” and “Work,” or to any modern elementary treatise on dynamics. If the calculation be made of the energies of the ball and of the rifle due to our calculated velocities of recoil, it will be found that that of the ball is 160 times greater than that of the other, and the ball possesses this energy in a much smaller compass.

Fig. 80.Trajectory of a Projectile.

The course or track of a projectile through the air after it leaves the gun is called the trajectory, and this has been studied both experimentally and theoretically, with interesting results. Assuming that the shot passed through empty space, or that the air offered no resistance to its passage, it would be very easy to trace the path of a projectile. Let us suppose that Fig. 80 represents a gun elevated at a high angle. The moment the projectile leaves the muzzle, gravity begins to act upon it, causing it to move vertically downwards with ever-increasing velocity until it finally reaches the ground; the onward uniform movement parallel to the axis of the piece being continued all the time. We could find the position of the projectile at the end of successive equal periods of time by drawing a straight line AC, a prolongation of the axis of the piece, or a line of the same inclination; on this we mark off equal distances representing by scale the velocity of the projectile per second, the points B, C, D, E being the positions the projectile would be in at the end of each successive second if gravity did not act. In order to bring the diagram within moderate compass, we suppose the projectile to have only the small velocity of 115 ft. per second. At the end of the first second it would be at B, but now suppose that gravity is allowed to act for one second, it would at the end of that time have fallen 16 ft. vertically below B and have arrived at b. Similarly we may set off by scale on verticals through C, D, and E distances representing 64 ft., 144 ft., and 256 ft. respectively. Because, for instance, the ball, without gravity acting, would at the end of 3 seconds be at D, where we may suppose its course arrested and gravity then allowed to act for 3 seconds to pull the ball down from its position of rest at D; at the end of this period, gravity alone acting, its position would be 144 ft. vertically below D, because gravity pulls a body that distance in 3 seconds, and the actual position 3 seconds after the ball had left the muzzle would be at d, after it had described the curved 175path A, b, c, d. Supposing d to be the highest point of the trajectory, another 3 seconds would bring the ball along a downward curve, and at the end of 6 seconds from the discharge it would be at a point on the same level as A. Now the complete curve would be symmetrical on each side of a vertical line through its highest point, and it would be in fact a regular parabola with its vertex at d.

The foregoing presupposes that the air offers no resistance to the passage of the projectile through it. The fact however is quite otherwise, for no sooner does the projectile begin its flight than its velocity is constantly diminished by the air’s resistance. Now this resistance is complex, depending upon a number of different conditions, the effect of which can be taken into account only by extremely complex calculations. Obviously it will vary according to the area of the section presented by the projectile to the line of its flight, and again by the shape of its front, for a pointed shot will cleave the air with less resistance than one with a flat front. Then the density of the air at the time will also enter into the calculation. The mass of the projectile and also its velocity, upon which depend its vis viva, energy, or power of overcoming resistance in doing work, will also have to be considered. Most complex of all is the law, or rather laws (i.e. relations), which connect the air resistance with the velocity; for this relation no definite expression has been found. It is a function of the velocity (known only by experiment under defined conditions), and varying with the velocity itself. Thus for velocities up to 790 ft. per second, it is a function (determined experimentally) of the second power or square of the velocity; between 790 ft. per second and 990 ft. per second the law of resistance is changed and becomes a function of the third power of the velocity; between 990 ft. and 1,120 ft. velocity the law again changes and is related to the sixth power of the velocity; between 1,120 ft. and 1,330 ft. the resistance is again related to the third power of the velocity; and with higher speeds than that last named it is again more nearly related to the square of the velocity. It will be seen that to calculate the path of a projectile is really a very difficult mathematical problem, and indeed one which can be solved only approximately when all the known data are supplied.

The air resistance to the motion of a projectile is much greater than before trial would be supposed. Let us take an experiment that has actually been recorded, in which a bullet three-quarters of an inch in diameter, weighing one-twelfth of a pound, was found to have a velocity of 1,670 ft. per second at a distance of 25 ft. from the gun, and this 50 ft. farther was reduced to 1,550 ft. per second. Now if the reader will calculate, according to the formula we have given above, the energy due to the bullet’s velocity at these points, he will find it must have done 500 foot-lbs. units of work in traversing the 50 ft., and as this could have been expended only in overcoming the resistance of the air, we learn that this last must have been equivalent to a mean or average pressure of 10 lbs. thrusting the bullet backwards.

It will be interesting to compare the difference in the trajectory of a projectile under defined conditions, worked out with the air resistance taken into account, compared with the trajectory when the air is supposed to be non-existent. We find an example of the former problem fully worked out by many elaborate mathematical formulæ in Messrs. Lloyd and Hadcock’s treatise on Artillery. The problem is thus stated:—“An 11–in. breech-loading howitzer” (a howitzer is a piece of ordnance used for firing 176at high angles) “fires a 600–lb. projectile with an initial velocity of 1,120 foot-sec. at an elevation of 20°. Find the range, time of flight, and angle of descent.” We shall calculate these points on the suppositions adopted with regard to Fig. 80, and with no higher mathematics than common multiplication and division.

It will have been observed that we supposed two motions that really take place simultaneously to take place successively and independently: one in the direction of the line of fire, due to the initial velocity; the other vertically downwards, due to the action of gravity, the final result being the same. This affords an excellent illustration of another of Newton’s laws of motion, and should be considered by the reader in this connection. The law itself admits of being stated in various ways, as thus:—“Whenever a force acts on a body, it produces upon it exactly the same change of motion in its own direction, whether the body be originally at rest or in motion in any direction with any velocity whatever—whether it be at the same time acted on by other forces or not.” Or again: “When two forces act in any direction whatever on a body free to move, they impress upon it a motion which is the superposition (or compounding) of those that it would receive if each force acted separately.” The law is given also in the following form (Thomson and Tait):—“When any forces act on a body, then, whether the body be originally at rest or moving with any velocity and in any direction, each force produces in the body the exact change of motion which it would have had had it acted singly on the body originally at rest.” In all of these expressions the word “forces” is used, and a very convenient word it is, but it may be noted in passing, nothing but a word; for it stands for no real self-existing things, since, apart from observed changes of motion in bodies, forces for us have no existence. Nevertheless, it is useful for the sake of abbreviating statements about changes of motion, to regard these actions as produced by imaginary agents—imagined for the time and for this purpose, and therefore vainly to be sought for in the realm of reality.

Fig. 81.Diagram.

In dealing with the trajectory of the howitzer’s projectile through airless space we have no concern with its diameter nor with its weight. We use the little diagram, Fig. 81, to represent the motions,—c being a horizontal line, a, a vertical one, the angle at B is therefore a right angle, and we assume that at A to be 20°. Now, the most elementary geometry teaches us that every triangle having these angles will have the lengths of its sides in the same invariable proportions one to another whatever may be the size of the triangle itself, and it has been found convenient to calculate these proportions once for all, not merely for angle 20°, but for every angle up to 90°. Besides this, distinct names have been given to the proportions of every side of the triangle to each of the other two sides. Thus in the triangle before us, if we take a, b, and c to represent the numbers expressing the lengths of the sides against which they are placed, a divided by b, that is a ÷ b, or a/b, is called the sine of angle 20°, while c/b is named the cosine of that angle, etc. These therefore are numbers which are given in mathematical tables, and we find by these that sine 20° = 0·3420201, and cosine 20° = 0·9396926, and these with the 177initial velocity give us all the data we require. We may first find the time the projectile would take to reach the ground level, or strictly that of the muzzle of the gun at B. Taking t to stand for this time, we know that AC = 1,120 × t, but CB will be the distance that a body would fall from rest at C by the influence of gravity in that same time, t, and it is known by experiment that this distance is 16·1 feet multiplied by the square of the time from rest in seconds. We have now therefore the length of the line CB, and put a
b
= CB
AC
= 16·1 × t2
1,120 × t
= sine 20° = ·3420201, and dividing numerator and denominator by t and multiplying the above 3rd and 5th expressions by 1,120, we have

16·1 × t = 1,120 × ·3420201  
 
    1,120 × ·3420201  
and therefore t =
= 23·7927 secs.
    16·1  

Having obtained the time, it will be easy to work out the lengths b and a as 26,648 ft. and 9114·1 ft. respectively; and as c/b = cosine 20°, we have c = 26,648 × ·9396926 = 25040·8 ft., which is the range. The trajectory will be a curve (parabola) symmetrical on each side of a vertical line half-way between A and B, and the length of this line within the triangle will be equal to half of a, and in half of 23·7927 seconds the projectile, supposed to move only along the line AC, would reach the point where this vertical axis intersects AC. If during this half-time it had been falling from rest at the same intersection, it would have reached a point below by a space just one quarter of CB (the spaces fallen through being as the squares of the times), and therefore at this its highest point its distance above AB would also be one quarter the length of a = 2278·525 ft., which distance is called the height of the trajectory; and the descending curve being in every respect symmetrical to the ascending branch, the angle at which this would be inclined to AB would be 20°, but in the opposite direction to BAC, while the velocity would be the same as at A. We may now compare these results with those calculated when the air resistance is taken into account:—

  Without air With air  
  resistance. resistance. Difference.
Time of descent 23·7927 secs. 22·61 sec. –1·18 sec.
Angle of descent 20° 23° 49´ +3° 49´
Velocity of descent 1120 foot-secs. 868·8 foot-secs. –251·2 f.-s.
Range 25040·8 ft. 20,622 ft. –4418·8 ft.
Height of trajectory 2278·5 ft. 1989 ft. –288·5 ft.

With the air resistance the trajectory will no longer be a symmetrical curve: its highest point, instead of being on the vertical line midway between A and B, will be on one 1,050 ft. nearer to B than to A, and the descending branch will be steeper than the ascending. The total time, it will be observed, is less, although the final, and therefore the mean, velocity, is also less; but this shortening of the time is due to the trajectory itself being much less in length. The range of the projectile is decreased 178by 4,418 ft., or 1,473 yards, or more than four-fifths of a mile. The loss of velocity at the descent is very notable, and the reader will find it interesting to calculate the corresponding loss of energy by the formula already given.

The reader should now easily understand that the projectile from a rifle or gun discharged horizontally through airless space at the height of 16·1 ft. above a level plain would strike the ground in one second at a range or distance from the gun exactly equal to the initial velocity, or if the gun were on a tower and its axis 64·4 ft. above the plain, the range would then be 2V. It will be seen therefore that, corresponding to the range intended, there must be in general a certain inclination given to the axis of the piece in aiming, and this is done by means of the sights, one of which near the muzzle is usually fixed, while that next the breech is adjustable by sliding along an upright bar, which is graduated so that the proper elevation may be given for any required range. These graduations are made from experiments, and of course have reference only to some standard quantity and quality of ammunition and a standard of weight, shape, and material in the projectile. Sometimes large pieces of ordnance are laid by elevation in degrees, etc., marked on their mounting, the angles being taken from a table prepared for that particular gun and ammunition, from experiments at different ranges.

After these generalities about fire-arms we may enter upon certain particulars about the construction of some varieties, beginning with

THE MILITARY RIFLE.

Fig. 82.Muzzle-loading Musket and Rifles (obsolete patterns).

A. Brown Bess and Bayonet; B. Brunswick Rifle; C. Enfield Rifle and Bayonet.

In Fig. 82 are represented the muzzle-loading musket and muzzle-loading rifles which formed the regulation weapons of the British infantry from the beginning of the century up to the year 1864. Somewhat slow in its earlier stages was the development of the modern military rifle from the old smooth bore musket with its flint-lock, which was the ordinary weapon of the British and other armies up to nearly the middle of this century. Partly, perhaps, owing to the inherent conservatism of government departments, and partly to the very serious outlay involved in arming all the troops of a nation with a new weapon, it has happened that many improvements in small arms were in use as applied to sporting guns, long before they were adopted in the regulation weapons of armies. The advance towards the modern arm of precision has been made along all the several directions that converge in the latest product, and it may be said that the most obvious of these are spiral rifling, breech-loading, and improved ammunition. The improvements in any one of these particulars would have been of little advantage unless the others had been kept in line with it. How long antiquated systems may continue in use may be illustrated by the case of the flint-lock, which was retained in the British army from the time it superseded the old match-lock, in the latter part of the seventeenth century, down to almost the middle of this present nineteenth. It is quite possible that not a few readers still in their fifties may never have seen a flint-lock outside of a museum, yet this was the firing apparatus of the weapon that used to be affectionately known to our soldiers as “Brown Bess,” and that for a century and a half continued the regulation arm of British troops helping Wellington 180to win his victories, and superseded by the percussion musket only in 1842. The “Brown Bess” of the earlier part of the century had a smooth-bore barrel of three-quarters of an inch diameter (0·753 inch), and 39 inches long; this musket weighed, with its bayonet, 11 lbs., 2 oz. The bullet was spherical, and made of lead, in weight a little over one ounce. The diameter of the bullet was slightly smaller than the bore of the barrel, because a closely fitting ball could not be used, on account of the great force required to push it home with a ram-rod. The bullet was therefore wrapped in loosely fitting material, called a “patch,” and this made the gun easy to load, even when the barrel was “fouled” by the solid residues that always remain after the explosion of gunpowder. “Brown Bess” was credited with a range of 200 yards, but its want of accuracy was such that the soldier was directed not to fire until he could see the whites of the enemies’ eyes. But in 1800 one or two British regiments were armed with the muzzle-loading rifle known as Baker’s, and again in 1835 these were provided with the Brunswick rifle. These regiments afterwards became known as the Rifle Brigade. The bullets in both cases were spherical, and as the earlier pattern had a seven-grooved barrel, there was so much difficulty in introducing the bullets into the muzzles that mallets had to be used. The bullet of the Brunswick rifle was encircled by a projecting band, which fitted into two rather deep grooves diametrically opposite to each other in the barrel. This bullet, wrapped in some slightly greased material, could be readily dropped into the muzzle, and rammed home without difficulty. Moreover, whereas in Baker’s rifle the grooves made only a quarter of a turn in the length of the barrel, the grooves of the Brunswick rifle made more than one complete turn. This was so much an improvement on “Brown Bess” that the effective range was more than doubled. For the rank and file of the infantry regiments the flint-lock smooth-bore musket was, however, the regulation weapon until 1842, when it was superseded by the percussion musket. The percussion-cap is now comparatively little used, as, since the introduction of cartridges containing their own means of ignition, it is rapidly becoming a thing of the past. The copper percussion-cap, in the form it still retains, was invented about 1816, and was universally adopted for sporting-guns a long time before it was used for the military weapon. In 1842 the percussion musket was definitely adopted as the weapon of the British army, but up to that date the flint-locks still continued to be made at Birmingham.

The barrel of the percussion musket then issued was shortly afterwards rifled, when about the year 1852 the Minié system was adopted, and the Government awarded to M. Minié, a Frenchman, the sum of £20,000 for the bullet he had invented. What the meaning of this improvement was may now be explained, and we must begin by mentioning the various forms of grooving, or, at least, such forms as found some approval during the present century, for grooved barrels had been tried long before. At first the grooves appear to have been intended merely to receive the fouling, and these were often made without any twist or spiral, but parallel to the axis of the barrel. The grooves are hollow channels of greater or less depth, and of various forms; square, triangular, rounded, or of such a form that the inner line of a section of the barrel would present the form of a ratchet wheel. The numbers of the grooves made use of have varied between two and twelve, or more, and different rates of twist, or numbers of turns of the spiral in the length of the barrel have been resorted to, 181these ranging from half a turn to twelve turns. The Brunswick rifle had been found wanting in accuracy, when at length in 1846 General Jacobs proposed the adoption of the conical bullet with projecting spiral ridges which fitted into grooves cut in the rifle barrel. The difficulty in using muzzle-loading rifles consisted in the force required to ram down the bullet, which had to adapt itself to the grooves, and fill them up so that the gases due to the explosion of the powder should not escape. If the bullet simply dropped into the bore of the rifle easily, it did not effectually fill the grooves, which then became channels of this windage, and if, on the other hand, the leaden bullet was made to fill the grooves from the muzzle, great force was required, and the time and effort expended in ramming the missile home, detracted enormously from the efficiency of the rifle as a military weapon. Mr. Lancaster produced rifles having a slightly oval, instead of a circular, bore, making, of course, the necessary twist within the barrel. A bullet of the corresponding section, but nearly globular, much as if the projecting belt of the Brunswick bullet had been laterally extended to its opposite poles, could be easily dropped in at the muzzle, without force being required to make it take grooves, the barrel being internally smooth throughout. It was, however, soon found that this easy-fitting ball allowed a considerable amount of windage, and the Minié system was definitely adopted, in which advantage was taken of a fact observed some years before by a French artillery officer, who found that an elongated leaden bullet, if hollowed out at the base, was so expanded by the pressure of the powder gases that the material was forced into the grooves of a rifle. Minié made his bullet elongated, pointed in front, and hollowed out part of its length by a conical space, the widest part of which was at the base, and was covered by a small iron cup, that, when driven inwards by the pressure of the gases, caused an expansion of the bullet by which the lead was forced into the grooves of the rifling. But the forces operating on the base of the bullet would at times cause the iron cup to cut the bullet in two, and propel the anterior portion only, leaving the base in the form of a ring clinging to the rifling. The military authorities had many comparative trials carried out between the smooth-bore percussion musket and the Minié rifle. The greater accuracy of the latter may be inferred from the results of practice made by men firing at a target 6 feet high and 20 feet broad; when at 100 yards distance, 74 hits out of 100 shots were made from the musket, against 94 from the rifle; and the superiority of the latter, at longer ranges, was increasingly marked. Thus at 260, 300, and 400 yards the respective percentages of hits were for the musket 42, 16, 4½, but for the same ranges the rifle gave 80, 55, 52.

Fig. 83.The Minié Bullet.

Curiously enough, the principle of the expanding bullet had been brought forward by the late Mr. W. Greener seventeen years before the government prize was awarded to M. Minié. Mr. Greener’s bullets were of an oval form, being half as long again as their diameter, with one end flattened where the lead was excavated in a narrowing hollow nearly through the bullet. In this opening was inserted the end of a tapering plug of hard metal, and when the rifle was fired this plug was driven home, and the lead thus expanded took the grooves, so preventing windage, and giving range and accuracy; while allowing the piece to be loaded with as 182much ease as the smooth-bore musket. The invention, though favourably reported on by the military authorities at the time, did not receive the attention it would seem to have deserved. However, in 1857, Mr. Greener’s claim of priority for the first suggestion of the expanding bullet was acknowledged by a government award of £1,000.

Fig. 84.Greener’s Expanding Bullet.

Sir Joseph Whitworth, having been invited by the British military authorities to institute experiments with a view to producing the best type of rifle, with the help of the most perfect machinery, constructed the barrels with a polygonal bore, a plan which he had before adopted for large guns. The barrels were accurately bored out to a hexagonal section, and experiments were made to find what number of turns in the twist would give the projectile a sufficient rapidity of rotation to maintain it during its flight parallel to its axis. It was found that one turn in 20 inches was sufficient, and the projectile was made by machinery to fit accurately but easily into the rifled bore, so that it dropped into its place, and the loading could be expeditiously performed. The bullet was long, compared with the bore, which was made smaller than before, and it was found that the explosion caused it to expand sufficiently to fill up the corners of the hexagon, so that there was no loss from windage. The accuracy of aim of the Whitworth rifle was superior to that of any weapon of the kind that had, up to that time, been produced. When officially tried against the Enfield, its mean deviation at 500 yards range was only 4½ inches, while that of the Enfield at the same range was 27 inches. Mr. Whitworth had proved the advantages of using a small bore, an elongated bullet, and a sharp twist in the rifling; and it was acknowledged that as a military weapon his rifle was superior to all other arms of similar calibre that had before been produced. Some doubt appears to have been entertained, however, as to whether the mechanical perfection of the trial rifles could be maintained if they came to be manufactured on the large scale, and also as whether an adequate supply of the polygonal ammunition would be procurable when required. The Whitworth rifle was never adopted into the government service, and soon after these trials in 1857, the adoption of another type of weapon became imperative, as the results obtained by the Germans with their needle-gun, demonstrated the enormous advantages of a breech-loading rifle.

Fig. 85.The Chassepot Rifle.—Section of the Breech.

The French then adopted the Chassepot rifle (so called after its inventor), which embodied the same principle as the needle-gun, but with improvements. This arm has a rifled barrel, with a breech mechanism of great simplicity, which is represented in section in Fig. 85. The piece marked B corresponds to what is called the “hammer” in the old lock used with percussion-caps, and the first operation in charging 183the rifle consists in drawing out B, as shown in the cut, until, by the spring, C, connected with the trigger, A, falling into a notch, the hammer, if we may so term it, is retained in that position. The effect of this movement is to draw out also a small rod attached to the hammer, and terminated in front by a needle, about ½ in. long, at the same time that a spiral spring surrounding the rod is compressed, the spring being fastened to the front end of the rod, and abutting against a screw-plug, which closes the hinder end of F, and permits only the rod to pass through it. The piece F, which is also movable, has projecting from its front end a little hollow cylinder, through the centre of which the needle passes, and this little cylinder has a collar, serving to retain its position, an india-rubber ring surrounding a portion of the cylinder, and forming a plug to effectually close the rear end of the barrel. It will be noticed that the cylinder is continued by a smaller projection, which forms a sheath for the point of the needle. The movable breech-piece, F, is provided with a short lever, E, by which it is worked. The second movement performed by the person who is charging the piece is to turn this lever from a horizontal to a vertical position, which thus causes the piece F to turn 90° about its axis, and then by drawing the lever towards him he removes the piece F from the end of the barrel, which, thus exposed, is ready to receive the cartridge. The cartridge contains the powder and the bullet in one case, the posterior portion containing also a charge of fulminate in the centre, and it is by the needle penetrating the case of the cartridge and detonating this fulminate that the charge is exploded. When the cartridge has been placed in the barrel, the piece F is pushed forward, the metallic collar and india-rubber ring stop up the rear of the barrel, and on turning the lever, E, into a horizontal position, the breech is entirely closed. If now the trigger be drawn, the hammer is released, and the spring carries it forward, at the same time impelling the needle through the base of the cartridge-case, where it immediately causes the explosion of the fulminate. The bullet is conical, and its base having a slight enlargement, the latter moulds itself to the grooves with which the barrel is rifled. When the piece has not to be fired immediately, the lever is not placed horizontally, but in an inclined position, in which the hammer 184cannot move forward, even if the trigger be drawn. The Chassepot has an effective range of 1,093 yards, and the projectile leaves the piece with a velocity of 1,345 ft. per second, the trajectory being such that at 230 yards the bullet is only 18 in. above the straight line. The piece can be charged and fired by the soldier in any position, and it was found that it could be discharged from seven to ten times per minute, even when aim was taken through the sights with which it is furnished, and fourteen or fifteen times per minute without sighting. The ordinary rifled musket, which this arm superseded, could only be fired twice in a minute, and could only be loaded when the soldier was standing up.

Other nations followed either by adopting as their infantry arm some form of breech-loader, or by converting their muzzle-loaders into breech-loaders as a temporary expedient, pending the selection of some more perfect type. When in 1864 a committee which had been appointed to investigate the question of proper arms for our infantry, recommended that that branch of the service should be supplied with breech-loaders, our Government, considering that no form of breech-loader had up to that time been invented which would unequivocally meet all the requirements of the case, wisely determined that, pending the selection of a suitable arm, the service muzzle-loaders should meanwhile be converted into breech-loaders. The problem of how this was to be done was solved by the gunmaker Snider, and in the “Converted Enfield” or “Snider” the British army was provided for a time with an arm satisfying the requirements of that period. This change of weapon was effected at a comparatively small outlay, for the conversion cost less than twenty shillings an arm. The breech action in the Snider consisted of a solid piece of metal which closed the breech end of the barrel, and, being hinged on the right-hand side parallel to the barrel, could be turned aside, making room for the insertion into the conically widened bore of a metallic cartridge case, invented by Colonel Boxer, which contained the projectile, the powder charge, and the means of ignition in itself. A short backward movement of the breech-lock caused a claw acting on the base of the spent cartridge case to withdraw it from the barrel, and then the reaction of a spring brought the breech-block back into position, after insertion of a new cartridge. This cartridge proved very effective in increasing the range and accuracy of the weapon. It should be mentioned that all the breech-loading mechanisms are provided with arrangements by which the metallic cases of the spent cartridges are automatically extracted from the barrel. The authorities having, in 1866, offered gunmakers and others handsome prizes for the production of rifles best fulfilling certain conditions, nine weapons were selected out of 104 as worthy to compete. No first prize was awarded, but the second was given to Mr. Henry, while Mr. Martini was seventh on the list. In order to obtain a weapon fulfilling all the requirements, a vast number of experiments were made by the committee appointed for that purpose, as to best construction of barrel, size of bore, system of rifling, kind of cartridge, and other particulars, and assistance was rendered by several eminent gunsmiths and engineers.

Fig. 86.Section of Martini-Henry Lock.

After a severe competition it appeared that the best weapon would be produced by combining Henry’s system of rifling with Martini’s mechanism for breech-loading. The parts constituting the lock and the mechanism for working the breech, shown in Fig. 86, are contained in a metal case, to which is attached the woodwork of the stock, now constructed in two parts. To this 185case is attached the butt of the rifle by a strong metal bolt 6 in. in length, A, which is inserted through a hole in the heel-plate. The part that closes the breech—termed the “block”—is marked B. It turns loosely on a pin, C, passing through its rear end and fixed into the case at a level somewhat higher than the axis of the barrel. The end of the block is rounded off so as to form with the rear end of the case, D, which is hollowed out to receive it in a perfect knuckle joint. Let it be observed that this rounded surface, which is the width of the block, receives the whole force of the recoil, no strain being put on the pin, C, on which the block turns. In the experiments a leaden pin was substituted, and the action of the mechanism was not in the least impaired. This arrangement serves greatly to diminish the wear and the possibility of damage from the recoil. As the pin on which the block turns is slightly above the axis at the barrel, it follows that the block, when not supported, immediately drops down below the barrel. Behind the trigger-guard is a lever, E, working on a pin, F, fitted into the lower part of the case. To this lever is attached a much shorter piece called the “tumbler,” which projects into the case, G. It is this tumbler which acts as a support for the block, and raises it into its firing position or lowers it according as the lever, E, is drawn toward a firer or pushed forward. How this is accomplished will be readily understood by observing the form of the notch, H, in which the upper end of the tumbler moves. It will be noticed that the piece being in the position for firing, if the lever be pushed back, G slides away from the shallower part of the notch into the deeper, and the block accordingly falls into the position shown in the figure; and if again the lever is drawn backward, G acting on H will raise the block to its former position. The block or breech-piece is hollowed out on its upper surface, I, so as to permit the cartridge to be readily inserted into the exploding chamber, J. The centre of the block is bored out, and contains within the vital mechanism for exploding the cartridge, namely, a spiral spring, of which the little marks at K are the coils in section. These coils pass round apiece of metal called the “striker,” which is armed with a point, capable of passing through a hole in the front 186face of the block exactly behind the percussion-cap of the cartridge when the block is in the firing position. When the lever handle is moved forward, it causes the tumbler, which works on the same pin, to revolve, and one of its arms draws back the striker, compressing the spring in so doing, so that as the block drops down the point of the striker is drawn inwards. In this position the piece receives the cartridge into the chamber. The lever, E, being now drawn backward, the piece is forced into the notch, H, and the block is kept firmly in its place; besides this, there is a further compression of the spring by the tumbler, and in this position the spring is retained by the rest-piece, L, which is pushed into a bend in the tumbler. By pulling the trigger this piece is released, so that the tumbler can revolve freely, and relieve the pent-up spring, whose elasticity impels the striker forward, so that this enters the carriage directly. A very important and ingenious part of this arrangement is the contrivance for extracting the case of the exploded cartridge. The extractor turns on the pin, M, and has two arms pointing upwards, N, which are pressed by the rim of the cartridge pushed home into two grooves cut in the sides of the barrel. It has another arm, O, bent only slightly upwards and pointing towards the centre of the case, and forming an angle of about 80° with the above-mentioned upright arm; when, by pushing forward the lever, its short arm drops into the recess, the block, no longer supported, falls, and hits the point of the bent arm of extractor, so causing the two upright arms to extract the cartridge-case a little way.

Fig. 87.The Martini-Henry Rifle.

A, ready for loading; B, loaded and ready for firing.

The barrel is of steel; the calibre is 0·451 in. It is rifled on Mr. Henry’s patent system. The section of the bore may be generally described as a heptagon with re-entering angles at the junctions of the planes, so that there are fourteen points of contact for the bullet, viz., one in the middle of each plane, and one at each of the re-entering angles. The twist of rifling is one turn in 22 in. The charge consists of 85 grains of powder, and a bullet weighing 480 grains, of a form designed by Mr. Henry. The cartridge is of the same general construction as the “Boxer” cartridge, used in the Snider rifle, but it is bottle-shaped, the diameter being enlarged from a short distance in rear of the bullet, in order to admit of its being made shorter, and consequently stronger, than would be otherwise possible. A wad of bees’-wax is placed between the bullet and powder, by 187which the barrel is lubricated at each discharge. The sword-bayonet to be used with this rifle is of a pattern proposed by Lord Elcho. It is a short sword, broad towards the point, and furnished on a portion of the back with a double row of teeth, so as to form a stout saw. It is so balanced as to form a powerful chopping implement, so that, in addition to its primary use as a bayonet, it will be useful for cutting and sawing brushwood, small trees, &c.

The following are the principal particulars of weight, dimensions, &c., of the Martini-Henry rifle:

  Without bayonet 4 ft. 1 in.
Length of rifle With bayonet fixed 5 ft. 8 in.
  Of barrel 2 ft. 9·22 in.
 
Calibre       0·451 in.
 
Rifling Grooves 7  
  Twist 1 turn in 22 in.
 
Weight Without bayonet 8 lbs. 7 oz.
  With bayonet 10 lbs. 4 oz.
 
Bayonet Length 2 ft. in.
  Weight without scabbard 1 lb. 8 oz.
 
Charge of powder   85 grains.
Weight of bullet   480 grains.
 
The rifle is sighted to 1,400 yards.

As an evidence of the accuracy of fire in this rifle, it may be stated that of twenty shots fired at 1,200 yards, the mean absolute deflection of the hits from the centre of the group was 2·28 ft. The highest point in the trajectory at 500 yards is rather over 8 ft. so that the bullet would not pass over a cavalry soldier’s head within that distance. The trajectory of the Snider at the same range rises to nearly 12 ft. The bullet will pass through from thirteen to seventeen ½ in. elm planks placed 1 in. apart at 20 yards distance; the number pierced by the Snider under similar circumstances being from seven to nine. As regards rapidity of fire, twenty rounds have been fired in 53 seconds; and one arm which had been exposed to rain and water artificially applied for seven days and nights, and had during that time fired 400 rounds, was then fired, without cleaning, twenty rounds in 1 minute 3 seconds.

Rifles of the Martini-Henry and Chassepot type were soon superseded, for as early as 1876 Switzerland had armed her troops with a magazine rifle of a smaller calibre than any then in use, and this weapon was found so effective that in a few years after every European nation had followed suit, as also had the United States and Japan, each country adopting some particular pattern of a weapon with certain modifications. Of these the Mannlicher and the Mauser are much used. A magazine rifle is one that can be fired several times successively without reloading. Like revolvers, the magazine arms repeat their fire, but instead of having several distinct firing chambers, they have but one, from which the empty cartridge cases are automatically extracted by the breech mechanism, for the magazine rifle is necessarily a breech-loader. The magazine rifle carries a supply of cartridges, which one after another are brought into the firing chamber by the simple action of the breech mechanism, so that the soldier is enabled to discharge several rounds in any position without reloading. The several varieties of the magazine rifle may be classed 188according to the position of the magazine. This may be: First, in the stock; second, under the barrel; third, in a box under the breech; or fourth, in a box above the breech. In the first and second variety the cartridges are in line in a tube, out of which they are moved on by a spiral spring, and this was the earlier form of the weapon. The box above or below the breech is the later development, and has the advantage of holding the cartridges lying side by side, and thus in a position in which they are not so liable to injure each other as in the tubular arrangements. Then, again, the movement of the cartridge in the breechbox in arriving at the firing chamber is much less than in the linear magazines, and the centre of gravity of the whole changes but little when the supply is exhausted. With any of the varieties of magazine a suitable modification of the mechanism may be adopted, so that the weapon can at will be used as a single firing rifle, but changeable in an instant to the magazine form. Again, the box magazine may be made as a fixture on the rifle, or it may be detachable. Commissions of military authorities had for several years been deliberating upon the best models for their respective nations, while Professor Hebler was working out his researches as to the best calibre for military rifles. Hebler published a work showing the great advantages of a bore one-third less in diameter than that commonly in use, which was about 0·45 inch, as in our Martini-Henry. The small-calibre rifle shoots straighter and hits harder than the large bore one, and the recoil is less, and so is the weight of the weapon. Lead is found to be too soft a material for the bullet of the small-bore rifles, as it does not keep in the rifling, which has a sharper turn than that in the older weapon; hence the bullets are now cased in steel or nickel. These bullets have remarkable power of penetration. Some will go through a steel plate 1¼ inch thick, making a clean hole in it, and the Lebel bullet penetrates 15 inches of solid oak, at a distance of 220 yards. Such a missile would, therefore, be capable of going completely through the bodies of several men or horses.

Fig. 88.The Mannlicher Magazine Rifle.

The Germans, about 1888, adopted a magazine rifle known as the Mauser. It had a fixed tubular magazine for eight rounds below the barrel, and a breech mechanism of the Remington-Keene type. The French followed suit with their famous Lebel gun, the construction of which was long kept secret. It also has a fixed under barrel tubular magazine, and the cartridges used with it contain smokeless powder. It is said that a new gun of practically the same pattern has been adopted by Russia, but with a detachable magazine to contain five rounds. The Russian gun will also use smokeless powder. In England, a small-bore rifle of 0·303 inches calibre is now issued to all troops. It has an under breechbox magazine, modified from the Lee rifle. The box is detachable, so that the weapon could normally be used as a single loader, and the magazine attached only when required. But the British authorities have decided that the 189magazine box is to be attached to the weapon by a chain. The first issue of this pattern of rifle to British soldiers took place early in 1890. The Austrians are adopting the Mannlicher pattern, in which the magazine idea is embodied in a complete and practical form. This rifle has a fixed box magazine below the breech. From this box, in which the cartridges—five in number—lie side by side, they are fed up by springs as they are disposed of by the movement of the breech mechanism. The magazine is recharged by placing in it a tin case containing five cartridges, and the case drops out when all the cartridges have been fired. In this form there is of course no necessity for providing any mechanism for holding the magazine in reserve while the rifle is used as a single loader. As to calibre, the Austrian authorities follow other countries in adopting a small bore, namely, 0·315 inch. Italy has converted her single-fire Vetterli rifle into a magazine arm, with a box something like the Mannlicher, and Belgium has adopted a gun of the same type. The rate of fire from charged magazines of such guns as the “Lee,” “Mannlicher” and “Vetterli,” worked with the right hand without bringing the piece down from the shoulder is, for all of them, about one shot per second; but the time that is required to recharge the magazines varies much according to the contrivance used. The number of rounds the magazine of a rifle is capable of containing when fully charged is from 5 to 12, or more, according to the difference of system. It is considered that in the detachable Lee or the quick recharging Mannlicher five rounds are ample for use at a critical moment.

Fig. 89.The Magazine and Breech of the Mannlicher Rifle.

The calibre of the military rifle has been decreased with almost every new pattern adopted. Thus, while the old “Brown Bess” had a calibre of 0·75 inch, in the last issue of it the bore was reduced to 0·693 inch; the Enfield (1852) had a bore of 0·577 inch; the Martini-Henry, 0·451 inch, which, in a newer pattern adopted in 1887, was reduced to 0·400 inch; and, finally, in the Lee-Metford, the calibre is only 0·303 inch. A similar consecutive reduction of bores has taken place in the rifles adopted by other countries, and one of the latest type, issued for the use of the United States Navy, has a bore of only 0·236 inch, and it is even expected that a still smaller one will become general. The advantage of the narrow and lighter projectile is that while it has a higher initial velocity with a given charge, its flight is less checked by the resistance of the atmosphere, the section it presents being so much less. Thus the bullet of 0·236 inch diameter has a section little more than one-fourth that of the 0·45 inch 190bullet. The difference is well shown in the comparative heights of the trajectory (or path of the bullet) of the Martini-Henry 0·450 inch bullet, and that of the 0·303 inch Lee-Metford (the latter with cordite ammunition); for at a range of 1,000 yards the former reaches to 48 feet above the line of sight, while the latter rises to only 25 feet.

Some form of repeating or magazine rifle has now been adopted by all the most important nations of the world. The number of shots contained in the magazines varies from 5 to 12. In the British detachable box magazine there are ten charges. The calibres of the barrels range in the infantry patterns of different nations from 0·256 inch to 0·315 inch; the explosive used in every case is some kind of smokeless powder, and this, in the cartridge for the Lee-Metford, is cordite. The bullets are not made simply of lead, but of lead coated with a harder metal or alloy such as steel, cupro-nickel, nickel steel, or they consist entirely of some of these alloys.

Although the magazine rifle is now the regulation weapon of the infantry of all great armies, it is not improbable that at no distant future it maybe superseded by one in which, as in certain machine guns, the force of the recoil will be used for actuating the breech and lock movements. Many patents have already been taken out for rifles on this principle, and several patterns have actually been constructed, in which a merely momentary contact of the breech-piece with the end of the barrel is sufficient; the recoil of the barrel with the reaction of a spring performs all the requisite movements with such rapidity that an amazing speed of firing has been obtained. It is said that such an automatic gun can send forth bullets at a perfectly amazing rate. Of course the mechanism of such a gun is somewhat intricate, and it is impossible to explain its construction and action without a great number of diagrams and much description.

RIFLED CANNON.

Having briefly sketched in the foregoing section the development of the military rifle from such weapons as our own “Brown Bess,” down to the repeating or magazine rifle, we now purpose to adopt a similar course with regard to ordnance, giving also some particulars of the methods of manufacture, etc., and following in general the order of history.

Naturally there is nothing that accelerates progress in warlike inventions so much as the exigences of war itself. This is well exemplified in circumstances attending the Crimean War, which was waged in 1854 by England and France in alliance against Russia. The desire of having ships that could run the gauntlet of the heavy guns mounted on Russian forts led to the construction of La Gloire and other armour-plated vessels, as we have already seen, and a suggestion of the French Emperor, as to improving metal for guns, made to Mr. Bessemer, led incidentally but ultimately to the great revolution in the manufacture of steel, although it is true that Krupp of Essen had begun to produce small cast-steel ordnance as early as 1847. But what determined the necessity for rifled ordnance was more particularly the greater comparative effects obtained by the muzzle-loading rifles over the field artillery 191then in use in the several engagements that took place in the Crimea, especially in the battle of Inkerman (1854). The rifles so much surpassed in accuracy at long ranges the smooth-bore field-pieces firing spherical projectiles, that field artillery was on the point of losing its relative importance, and even in the matter of range the latter lost so much by windage that the men serving the artillery could sometimes be leisurely picked off by the rifle sharp-shooters. Inventors were soon at work on devising methods of increasing the accuracy of ordnance fire with both light and heavy pieces, and before the end of the war some cast-iron guns rifled on Lancaster’s plan had been mounted on forts and in ships, without proving very successful except in regard to increase of range when elongated pointed projectiles were used with them.

Fig. 90.32–pounder, 1807.

Now let us see of what kind was the ordnance used for some years after the middle of the century, in order that we may be the better able to appreciate the progress that has since been made. Ordnance is, as already noticed, of several species, as guns mounted on fortresses, naval guns, siege guns, field-guns, etc., and the size of the pieces under each of those heads is distinguished sometimes in one, sometimes in another of three different ways. We may name it by the weight of the gun itself in tons or hundredweights, as “a 35–ton gun,” etc.; or by the weight of its projectile, as “a 68–pounder,” etc.; or by its calibre, that is the diameter of its bore, as “a 4–inch gun,” etc. We may take the naval guns with which Nelson won his battles (Trafalgar, 1807) as representative of all except field ordnance up to about 1856. They were all made of cast iron, threw spherical projectiles, and were very rudely mounted. The gun most commonly mounted on board our ships of war was the 32–pounder, weighing 32 cwt., shown with its carriage in Fig. 90. The carriage was of wood, and consisted of two side pieces joined back and front by two transverse pieces and carried by four low wooden wheels. The trunnions of the gun fitted into bearings at the top of the side-pieces, and were secured by iron plates that passed over them in a semi-cylindrical form and were bolted down to the wood. The position of the trunnions on the gun was always such that the breech end of the gun preponderated, being supported on an adjustable wooden wedge; and when the muzzle of the gun had to be lowered, this was done by raising the breech end with handspikes and pushing in the wedge so far as to prevent the 192breech from dropping down again. There was a vent or narrow passage to contain a train of powder from the touch-hole at the upper part of the breech to the rear of the charge. When the gun was fired, with its muzzle protruding a little way out of the port-hole, the recoil would trundle it inwards about its own length, when its course would be stayed by a thick rope attached to the sides of the vessel; and by other tackle it would be kept in position until loaded, when it would be allowed to roll back, or would be drawn by ropes and pulleys out to the port-hole, and by the same means such lateral inclination as might be required could be given. This last adjustment was called training the gun. A 32–pounder required the services altogether of a dozen or fourteen men, but these by virtue of constant drill would learn to handle the clumsy machine with a certain amount of expedition. If we except a notch on the highest point of the muzzle, the pieces were devoid of anything of the nature of sights, though sometimes marks were made on the adjustable wedge under the breech to correspond with certain elevations. Nor were sights required; for the mode of fighting then was to get quite close to the adversary’s ship and pour in a broadside by firing simultaneously all guns on the enemy’s side when they had been trained (by rough methods), so as to concentrate their effect as much as possible on one point of the antagonist. Nelson’s famous ship the Victory carried a few larger guns than the 32–pounders, namely, two 68–pounders, called carronades (from having first been cast at Carron in Scotland), and some 42–pounders. The 32– and 42–pounders numbered together thirty, and there were also as many 24–pounders, with forty 12–pounders. These were all simply cast of the required dimensions, and were not made with the one single improvement which after two centuries’ use of cast-iron guns had been introduced into France about fifty years before, namely, the boring of the chase out of a solid casting.

On the outbreak of the Crimean War (1854) the minds of many inventors were occupied by the problem of ordnance construction, and this also engaged the attention among others of two of the most eminent British mechanical engineers of the day. These were Sir W. Armstrong and Sir J. Whitworth, who, with others, were invited by our War Department to submit the best models of field and heavy guns their skill was severally able to produce. Two years afterward, Sir W. Armstrong had, after many experiments, completed a gun of 1·88 in. calibre. This had a forged steel barrel 6 feet in length; but it was only after eight such forgings had been bored and rejected on account of flaws revealed only by the boring that a sound barrel was at length obtained. This barrel was strengthened on the outside by jackets made from coils of wrought iron bars welded into a piece and shrunk on while hot (of which process we shall have something more to say presently); the barrel was rifled with many shallow grooves, and the pointed projectile, 3 calibres long, was made of lead, for which afterwards iron coated with lead was substituted. This gun was a breech-loader, the breech being closed by a block let into a slot after loading, and then pressed against the barrel by some turns of a screw which advanced parallel to the axis of the piece, and was made hollow for loading through, before the closing block was put in. In a trial of the various pieces ready in 1857, it was found that the Armstrong gun made as just described had an accuracy and range immensely greater than any weapon that had ever been tested, and the Government authorities approved of the system of construction, except that they preferred muzzle-loading pieces to breech-loading, as being simpler in 193action, more easily kept in repair, and cheaper in original cost and ammunition.

When Sir Joseph Whitworth’s gun was, in 1863, submitted to a competitive trial against the Armstrong, as to their endurance and mode of ultimate failure when fired with ever-increasing charges of powder and shot, at the forty-second round the Armstrong breech-loader split, and at the sixtieth the Armstrong muzzle-loader had one of its coils cracked; while it was not until the ninety-second round that the Whitworth gun burst violently into eleven pieces. These competing guns were 12–pounder field-guns weighing 8 cwts., and from each 2,800 regulation rounds had been fired before they were subjected to the bursting proofs. The result of these trials being that the authorities considered that steel was not then sufficiently reliable, and they decided to adopt the system of building up rifled guns with iron jackets over an inner tube of steel. Sir Joseph Whitworth made his guns entirely of steel, and they were striking examples of beautiful and accurate workmanship. His system of rifling consisted in forming the bore of the gun so that its section is a regular hexagon, and the projectile is an elongated bolt with sides exactly fitting the barrel of the gun: the projectile is, in fact, a twisted hexagonal prism. Fig. 91 shows at the left-hand side the section of the barrel, and on the right we see the form of the projectile on a smaller scale, this last representing, in fact, the exact size and shape of the bullet of the Whitworth rifle mentioned on another page. Sir Joseph’s guns were muzzle-loaders, and they were remarkable for their long range and accuracy of fire. One of these guns, with a charge of 50 lbs. of gunpowder, threw a 250–lb. shot a distance of nearly six miles, and on another occasion a 310–lb. shell was hurled through the air, and first touched the ground at a distance of more than six and a quarter miles from the gun. These distances are greater than any to which shot or shell had previously been thrown.

Fig. 91.Whitworth Rifling and Projectile.

As the material of these Whitworth guns was very costly, and very perfect workmanship was required in the formation of the barrel and the shots, the expense attending their manufacture and use was much greater than that incurred in the case of the Armstrong guns. Sir W. Armstrong’s 194estimate for a 35–ton gun was £3,500, and Sir J. Whitworth’s, £6,000. The gun, as constructed at Woolwich on Mr. Fraser’s plan, was estimated to cost £2,500. The first cost of a gun is a matter for consideration, since each piece, even the strongest, is able only to fire a limited number of rounds before it becomes unsafe or useless. It appears that no cannon has yet been constructed capable of withstanding without alteration the tremendous shocks given by the explosion of the gunpowder, and these alterations, however small at any one discharge, are summed up and ultimately bring to an end what may be termed the “life of the piece.”

Fig. 92.600–pounder Muzzle-loading Armstrong Gun.

About the year 1858 Sir William Armstrong (afterwards Lord Armstrong) established at Elswick, Newcastle-on-Tyne, a manufactory of ordnance, which has since developed into the great arsenal now so well known all over the world. Here all the resources of science have been applied to the problems of artillery, and experiments carried on with a prodigality of cost and promptness of execution impossible at a government establishment trammelled with official regulations. Here, and also at Woolwich, our national ordnance factory, guns have since always been constructed on the building-up plan advocated by Sir W. Armstrong, whose principle consists in disposing of the fibre of the iron so as best to resist the strains in the several parts of the gun. Wrought iron being fibrous in its texture has, like wood, much more strength in the direction of the grain than across it. The direction of the fibre in a bar of wrought iron is parallel to its length, and in that direction the iron is nearly twice as strong as it is transversely. A gun may give way either by the bursting of the barrel or by the blowing out of the breech. The force which tends to produce the first effect acts transversely to the axis of the gun; hence the best way to resist it is to wrap the iron round the barrel, so that the fibres of the metal encircle it like the hoops of a cask. The force which tends to blow out the breech is best resisted by disposing the fibres of the iron so as to be parallel to the axis of the gun; hence Sir W. Armstrong makes the breech-piece from a solid forging with the fibre in the required direction. But the 195Elswick building-up principle involves much more than the direction of the fibres of the iron, for each coil or jacket, after having its spires welded together, was bored out on a lathe, and the exterior of the part of the gun on which it was to be placed was also turned with the utmost exactness, so that when the enveloping piece was heated to a certain temperature and in this state brought into position, it would in cooling compress the parts it encircled just to that degree which careful calculations showed would best strengthen the gun without unduly straining the metal at any part. The Elswick guns being built up of several superimposed jackets of calculated lengths and thicknesses, the means was afforded of distributing the tensions throughout the whole mass of metal to the best advantage. In the simpler form, arranged by Mr. Fraser, and for the sake of economy adopted by the authorities at Woolwich in 1867, the greater part of the benefit derivable from adjustment of tension was no doubt sacrificed to cheapness of manufacture. These, and also the forms of Armstrong guns that have not yet been described, ceased to be made after 1880, by which time steel had replaced iron in every part of the construction and fittings of guns, and muzzle-loading had been definitely abandoned in favour of breech-loading.

Fig. 93.35–ton Fraser Gun.

Now, in 1874, when the first edition of the present work was in preparation, the Fraser-Woolwich guns were in full vogue, being spoken of by the public press as the ne plus ultra of artillery construction in size, efficiency, and economy. When, accordingly, the author had been privileged to visit the arsenal and witness the production of these guns in every stage of their manufacture, he wrote a description of it which is here retained as printed at the time, seeing that it may not be without historical interest, particularly since great numbers of these guns must still be extant, mounted on our forts in various parts of the world, and seeing also that the description of the simpler formations may render more easily to be understood future references to similar operations in gun-making as have been retained in the later developments. Of course, the following description was written in the present tense, and therefore in perusing it the reader must constantly bear in mind that the guns with 196which our ships of war have since been equipped are in every respect entirely different from

The Fraser-Woolwich Guns, 1867–1880.

Fig. 94.Section of 9 in. Fraser Gun.

Until the year 1867 the guns made at Woolwich were constructed according to the original plan proposed by Sir W. Armstrong, and on this system one of the large guns consisted of as many as thirteen separate pieces. These guns, though unexceptionable as to strength and efficiency, were necessarily so very costly that it became a question whether anything could be done to lessen the expense by a simpler mode of construction or by greater economy in the material. The problem was solved in the most satisfactory manner by Mr. Fraser, of the Royal Gun Factory, who proposed an important modification of the original plan, and the adoption of a kind of iron cheaper than had been previously employed, yet perfectly suited for the purpose. Mr. Fraser’s modification consisted in building up the guns from only a few coils, instead of several, the coils being longer than Sir W. Armstrong’s, and the iron coiled upon itself two or even three times: a plan which enabled him to supersede the breech-piece, formerly made in one large forging, by a piece formed of coils. In order to perceive the increased simplicity of construction introduced by Mr. Fraser, we need but glance at the section of a 9 in. gun constructed according to his system, Fig. 94, and remember that a piece of the same size made after the original plan had ten distinct parts, whereas the Fraser is seen to have but four. Compare also Figs. 92 and 93. We shall now describe the process of making the Fraser 9 in. gun. The parts of the gun as shown in the section, Fig. 94, are: 1, the steel barrel; 2, the B tube; 3, the breech-coil; 4, the cascable screw. The inner steel barrel is made from a solid cylinder of steel, which is supplied by Messrs. Firth, of Sheffield. This steel is forged from a cast block, the casting being necessary in order to obtain a uniform mass, while the subsequent forging imparts to it greater solidity and elasticity. After the cylinder has been examined, and the suitable character of the steel tested by trials with portions cut from it, the block is roughly turned and bored, and is then ready for the toughening process. This consists in heating the tube several hours to a certain temperature in an upright furnace, and then suddenly plunging it into oil, in which it is allowed to remain for a day. By this treatment the tenacity of the metal is marvellously increased. 197A bar of the steel 1 in. square previous to this process, if subjected to a pull equal to the weight of 13 tons, begins to stretch and will not again recover its original form when the tension is removed, and when a force of 31 tons is applied it breaks. But the forces required to affect the toughened steel in a similar manner are 31 tons and 50 tons respectively. The process, unfortunately, is not without some disadvantages, for the barrel is liable to become slightly distorted and even superficially cracked. Such cracks are removed by again turning and boring; the hardness the steel acquires by the toughening process being shown by the fact that in the first boring 8¼ in. diameter of solid steel is cut out in 56 hours, yet for this slight boring, in which merely a thin layer is peeled off, 25 hours are required; and lest there should be any fissures in the metal, which, though not visible to the eye, might make the barrel unsound, it is filled with water, which is subjected to a pressure of 8,000 lbs. per square inch. If under this enormous pressure no water is forced outwards, the barrel is considered safe. It is now ready to have the B tube shrunk on it.

The B tube, like certain other portions of these guns, is constructed from coiled iron bars, and this constitutes one great peculiarity of Sir W. Armstrong’s system. It has the immense advantage of disposing the metal so that its fibres encircle the piece, thus applying the strength of the iron in the most effective way. The bars from which the coils are prepared are made from “scrap” iron, such as old nails, horse-shoes, &c. A pile of such fragments, built up on a wooden framework, is placed in a furnace and intensely heated. When withdrawn the scraps have by semi-fusion become coherent, and under the steam hammer are soon welded into a compact mass of wrought iron, roughly shaped as a square prism. The glowing mass is now introduced into the rolling-mill, and in a few minutes it is rolled out, as if it were so much dough, into a long bar of iron. In order to form this into a coil it is placed in a very long furnace, where it can be heated its entire length. When sufficiently heated, one end of the bar is seized and attached to an iron core of the required diameter, and the core being made to revolve by a steam engine, the bar is drawn out of the furnace, winding round the core in a close spiral, so that the turns are in contact. The coil is again intensely heated, and in this condition a few strokes of the steam hammer in the direction of its axis suffice to combine the spires of the coil into one mass, thus forming a hollow cylinder.

The B tube for the 9 in. gun is formed of two double coils. When the two portions have been completely welded together under the steam hammer, the tube, after cooling, is roughly turned and bored. It is again fine bored to the required diameter, and a register of the diameter every few inches down the bore is made. These measurements are taken for the purpose of adapting most accurately the dimensions of the steel barrel to the bore of the B tube, as it is found that perfect exactness is more easily obtained in turning than in boring. The steel barrel is therefore again turned to a size slightly larger than the bore of the B tube, and is then placed muzzle end upwards, and so arranged that a stream of water, to keep it cool, shall pass into it and out again at the muzzle, by means of a syphon, while the B tube, which has been heated until it is sufficiently expanded, is passed over it and gradually cooled.

If now the B tube were allowed to cool spontaneously, its ends would, by cooling more rapidly than the central part, contract upon the steel barrel and grip it firmly at points which the subsequent cooling would tend to draw nearer together longitudinally, and thus the barrel would be subjected 198to injurious strains. In order to prevent this, the B tube is made to cool progressively from the breech end, by means of jets of water made to fall upon it, and gradually raised towards the muzzle end, which has in the meanwhile been prevented from shrinking by having circles of gas-flames playing upon it.

The breech-coil, or jacket, is formed of three pieces welded together. First, there is a triple coil made of bars 4 in. square, the middle one being coiled in the reverse direction to the other two. After having been intensely heated in a furnace for ten hours, a few blows on its end from a powerful steam hammer welds its coils perpendicularly, and when a solid core has been introduced, and the mass has been well hammered on the sides, it becomes a compact cylinder of wrought iron, with the fibres all running round it. When cold it is placed in the lathe, and the muzzle end is turned down, leaving a shoulder to receive the trunnion-ring. The C coil is double, welded in a similar manner to the B coil, and it has a portion turned off, so that it may be enclosed by the trunnion-ring.

The trunnion-ring is made by punching a hole in a slab of heated iron first by a small conical mandrel, and then enlarging by repeating the process with larger and larger mandrels. The iron is heated for each operation, and the trunnions are at the same time hammered on and roughly shaped—or, rather, only one has to be hammered on—for a portion of the bar which serves to hold the mass forms the other. The trunnion-ring is then bored out, and after having been heated to redness, is dropped on to the triple breech-coil which is placed muzzle end up, and the turned end of the C coil (of course, not heated) is then immediately placed within the upper part of the trunnion-ring. The latter in cooling contracts so forcibly as to bind the ends of the coils together, and the whole can thus be placed in a furnace and heated to a high temperature, so that when removed and put under the steam hammer, its parts are readily wielded into one mass. The breech-coil in this state weighs about 16 tons; but so much metal is removed by the subsequent turnings and borings, that it is reduced to nearly half that weight in the gun. It is then turned in a lathe of the most massive construction, which weighs more than 100 tons. Fig. 34, page 95, is from a drawing taken at Woolwich, and shows one of the large guns in the lathe. No one who witnesses this operation can fail to be struck with the apparent ease with which this powerful tool removes thick flakes of metal as if it were so much cheese. The projections of the trunnions prevent the part in which they are situated from being finished in this lathe, and the gun has to be placed in another machine, where the superfluous metal of the trunnion-ring is pared off by a tool moving parallel to the axis of the piece. Another machine accomplishes the turning of the trunnions, the “jacket” being made to revolve about their axis. The jacket is then accurately bored out with an enlargement or socket to receive the end of the B tube, and a hollow screw is cut at the breech end for the cascable.

The portion of the gun, consisting of the steel barrel with the B tube shrunk on it, having been placed upright with the muzzle downwards, the breech-piece, strongly heated, is brought over it by a travelling crane, and slips over the steel barrel, while the recess in it receives the end of the B tube. Cold water is forced up into the inside of the barrel in order to keep it cool. As the breech cools, which it is allowed to do spontaneously, it contracts and grips the barrel and B tube with great force. The cascable requires to be very carefully fitted. It is this piece which plays so important a part in resisting the force tending to blow out the end of the barrel. The 199cascable is a solid screw formed of the very best iron, and its inner end is wrought by scraping and filing, so that when screwed in there may be perfect contact between its face and the end of the steel barrel. A small annular space is left at the circumference of the inner end, communicating through a small opening with the outside. The object of this is, that in case of rupture of the steel barrel, the gases escaping through it may give timely warning of the state of the piece.

Besides minor operations, there remain the important processes of finishing the boring, and of rifling. The boring is effected in two operations, and after that the interior is gauged in every part, and “lapping” is resorted to where required, in order to obtain the perfect form. Lapping consists in wearing down the steel by friction against fine emery powder and oil, spread on a leaden surface. The piece is then ready for rifling. The machinery by which the rifling is performed cannot be surpassed for its admirable ingenuity and simplicity.

In this operation the gun is fixed horizontally, its axis coinciding with that of the bar, which carries the grooving tools. This bar is capable of two independent movements, one backwards and forwards in a straight line in the direction of the length of the bar, and the other a rotation round its axis. The former is communicated by a screw parallel to the bar, and working in a nut attached to the end of it. For the rotatory movement the bar carries a pinion, which is engaged by a rack placed horizontally and perpendicularly to the bar, and partaking of its backward and forward movement, but arranged so that its end must move along another bar placed at an angle with the former. It is this angle which determines the pitch of the rifling, and by substituting a curved guide-bar for the straight one, an increasing twist may be obtained in the grooves.

The projectile used with these guns is of a cylindrical form, but pointed at the head, and the moulds in which these shots are cast are so arranged that the head of the shot is moulded in iron, while the body is surrounded with sand. The rapid cooling induced by the contact of the cold metal causes the head of the shot to solidify very quickly, so that the carbon in the iron is not separated as in ordinary casting. In consequence of this treatment, the head of the shot possesses the hardness of steel, and is therefore well adapted for penetrating iron plates or other structures. The projectiles are turned in a lathe to the exact size, and then shallow circular cavities are bored in them, and into these cavities brass studs, which are simply short cylinders of a diameter slightly larger than the cavities, are forced by pressure. The projecting studs are then turned so as accurately to fit the spiral grooves of the guns. Thus the projectile in traversing the bore of the piece is forced to make a revolution, or part of a revolution, about its axis, and the rapid rotation thus imparted has the effect of keeping the axis of the missile always parallel to its original direction. Thus vastly increased accuracy of firing is obtained.

Fig. 95.Millwall Shield after being battered with Heavy Shot.—Front View.

Fig. 96.Rear View of the Millwall Shield.

Shells are also used with the Woolwich rifled guns. The shells are of the same shape as the solid shots, from which they differ in being cast hollow, and having their interior filled with gunpowder. Such shells when used against iron structures require no fuse; they explode in coming into collision with their object. In other cases, however, the shells are provided with fuses, which cause the explosion when the shot strikes. Fig. 93, page 195, represents one of the 35–ton guns, made on the plan introduced by Mr. Fraser. This piece of ordnance is 16 ft. long, 4 ft. 3 in. in diameter at the breech, and 1 ft. 9 in. at the muzzle. The bore is about 1 ft. Each 200gun can throw a shot or bolt 700 lbs. in weight, with a charge of 120 lbs. of powder. It is stated that the shot, if fired at a short range, would penetrate a plate of iron 14 in. thick, and that at a distance of 2,000 yards it would retain sufficient energy to go through a plate 12 in. thick. The effect of these ponderous missiles upon thick iron plates is very remarkable. Targets or shields have been constructed with plates and timber backing, girders, &c., put together in the strongest possible manner, in order to test the resisting power of the armour plating and other constructions of our ironclad ships. The above two cuts, Figs. 95 and 96, are representations of the appearance of the front and back of a very strong shield of this description, after having been struck with a few 600 lb. shots fired from the 25–ton gun. The shots with chilled heads, already referred to, sometimes 201were found to penetrate completely through the 8 in. front plate, and the 6 in. of solid teak, and the 6 in. of plating at the back. The shield, though strongly constructed with massive plates of iron, only served to prove the relative superiority of the artillery of that day, which was at the time when our century had yet about thirty years to run. Up to 1876 no confidence was placed in steel as a resisting material, a circumstance perhaps not much to be wondered at, as its capabilities had not then been developed by the newer processes of manufacture, described in our article on Iron; nor had mechanicians acquired the power of operating with large masses of the metal. Since then it has come about that only steel is relied upon for efficiently resisting the penetration of projectiles, iron being held of no account except as a backing. There has always been a rivalry between the artillerist and the naval constructor, and this contest between the attacking and the defending agencies is well illustrated in the table on page 166, where the parallel advance in the destructive power of guns and in the resisting power of our war-ships is exhibited in a numerical form.

Fig. 97.Comparative Sizes of 35 and 81 ton Guns.

A, 35–ton; B, 81–ton.

The 35–ton Fraser guns were at the time of their production humorously called in the newspapers “Woolwich infants”; but it was not long before they might in another sense be called infants in comparison with a still larger gun of 81 tons weight constructed at Woolwich shortly before iron-coiling and muzzle-loading were set aside. Fig. 97 shows the relative dimensions of the 35–ton and 81–ton guns: the latter was built up in the same way as the 9–inch gun described above, but the coils were necessarily longer and the chase was formed in three parts instead of two. The total length of this gun was 27 feet, and the bore was about 24 feet long and 14 in. in diameter, and the weight of the shot about 1000 lbs., with sufficient energy to penetrate at a considerable distance an iron plate 20 in. in thickness. It was for the manufacture of these very large guns that the great steam hammer, represented in Plate III., was erected at Woolwich.


The 81–ton gun was the largest muzzle-loader ever made in the national gun factory at the time when such huge weapons were in request; but in 1876 its dimensions were surpassed by those of a few 100–ton guns built at Elswick to the order of the Italian Government for 202mounting on their most formidable ironclads. These guns have a calibre of 17·72 inches, and are provided with a chamber of somewhat larger bore to receive the charge of powder. They are built up on the Armstrong shrinkage principle, and comprise as many as twenty different tubes, jackets, hoops, screws, etc., and are undoubtedly the most powerful muzzle-loading weapons ever constructed. It happened, just as these guns were completed, that the British Government, apprehensive at the time of a war with Russia, exercised its rights of purchasing two of them, one to be mounted at Gibraltar, the other at Malta.

The Elswick establishment soon afterwards surpassed all its former achievements in building great guns, by designing and constructing the huge breech-loaders, one of which forms the subject of our Plate XII. These are known as the Armstrong 110–ton guns; they are formed of solid steel throughout, and their weight is accurately 247,795 lbs., or 110 tons 12 cwts. 51 lbs. The total length of the gun is 43 ft. 8 in., and of this 40 ft. 7 in. is occupied by the bore, along which the rifling extends 33 ft. 1 in. The calibre of the rifled part is 16¼ in., and the diameter of the powder chamber is somewhat greater. The regulation charge of powder weighs 960 lbs., although the guns are tested with still greater charges. The weight of the projectile is 1,800 lbs., and it leaves the muzzle with a velocity of 2,128 ft. per second, which is equivalent to a dynamical energy of 56,520 foot-tons. What this means will perhaps be better understood, not by describing experiments such as those on the Millwall Shield, the results of which are depicted in Figs. 95 and 96, but by stating that if the shot from the 110–ton gun encountered a solid wall of wrought iron a yard thick, it would pass through it. The Elswick 110–ton gun is, in fact, the most powerful piece of ordnance that has ever been constructed. There are no trunnions to these great guns, but they are encircled by massive rings of metal, between which pass strong steel bands that tie the gun to its carriage, or, rather, to the heavy steel frame on which it is mounted, and which slides on a couple of girders. The force of the recoil acts on a hydraulic ram that passes through the lower part of the supporting frame. The whole working of the gun is done by hydraulic power, and, indeed, the same method has been applied by the Elswick firm to the handling of all heavy guns. By hydraulic power, maintained automatically by a pumping engine exercising a pressure of from 800 lbs. to 1,000 lbs. per square inch, are operated the whole of the movements required for bringing the cartridge and the projectile from the magazine; for unscrewing the breech block, withdrawing it, and moving it aside; for pushing home the shot and the cartridge to their places in the bore; for closing the breech and screwing up the block; for rotating the turret within which the gun is mounted, or in other cases for ramming the piece in or out, and for elevating or depressing it. It is, indeed, obvious that such ponderous masses of metal as form the barrels and projectiles of these 110–ton and other guns of the larger sizes could not be handled to advantage by any of the ordinary mechanical appliances. But by the application of the hydraulic principle, a very few men are able to work the largest guns with the greatest ease, for their personal labour is thus reduced to the mere manipulation of levers. On board ship the power required for working large guns has lately been sometimes supplied by a system of shafting driven by a steam engine and provided with drums and pulleys, exactly as in an engineer’s workshop. Great care has also been bestowed upon the mounting of the smaller guns, which are so nicely 203poised on their bearings and provided with such accurately fitted racks, pinions, etc., that a steel gun of 10 ft. in length can easily be pointed in any direction by the touch of a child’s hand. The mechanical arrangements are now so admirably adapted for facility of working that, unless in the rude shocks of actual warfare the nicely adjusted machinery is found to be liable to be thrown out of gear, these applications of the engineer’s skill may be considered as having done all that was required to bring our modern weapons to perfection.

PLATE XII.

THE 110–TON ARMSTRONG GUN.

With the construction of the 110–ton we arrive at a period when commences a new era in guns—and especially in the armament of war-ships—necessitated by various circumstances, amongst which may be named the invention of torpedoes and the building of swiftly moving torpedo-boats, and of still swifter “torpedo-boat catchers or destroyers”; so that guns that could be worked only at comparatively long intervals were at a great disadvantage. Again, about 1880, were published the records of a most elaborate and important series of researches conducted by Captain Noble and Sir F. Abel, the chemist of our War Department. They had investigated all the conditions attending the combustion of gunpowder in confined spaces, the nature and quantities of the products, the temperature and pressures of the confined gases, etc. The information thus afforded was extremely valuable; but besides this, direct experiments made with actual guns were carried out, more particularly at Elswick, in which the speed of the projectiles at every few inches of their travel along the bore of the piece was ascertained, and also the pressures of the powder gases at any point. The way in which this is done we shall explain on another page. (See article on Recording Instruments.)

So long as muzzle-loading was in use, guns were necessarily made short, for had they not to be run in from the port-holes and embrasures of forts in order to be loaded? Now there was an obvious disadvantage in this, for the projectile left the gun before the expansive force of the gases had been spent that could have imparted additional velocity. When however muzzle-loading was abandoned, and especially when strong and trustworthy steel became available for the construction of the gun throughout, there was no reason to waste in this way the power of the charge, so that barrels were made lighter, much longer in proportion to the calibre, and every part accurately adapted in strength to the strain to be resisted. For instances of increasing length, take the 38–ton 12–inch guns built up at Woolwich (of only seven pieces) for H.M.S. Thunderer (see Fig. 93), on Mr. Fraser’s plan. These had a bore equal to only 16 times their calibre, while in the Armstrong 100–ton guns the bore is 21 calibres long; and in the 110–ton guns the total length of the chase is 31 times the diameter of the rifled part. It has since been the practice to make the bore of guns from 30 to 40 calibres in length.

The effect of a longer chase used with an appropriate charge is very clearly and instructively shown by the diagram Fig. 98, which is by permission copied from the very comprehensive work by Messrs. E. W. Lloyd and A. G. Hadcock, entitled Artillery: its Progress and Present Position. The reader should not pass over this diagram until he has thoroughly understood it, for it is an excellent example of the graphic method of presenting the results of scientific investigations. At the lower part of the diagram there are drawn to scale half-sections of a long and of a short gun. The horizontal line above is marked in equal parts representing feet numbered from the base of the projectiles. The upright 204line on the left numbered at every fourth division is the scale for the pressures in tons per square inch on the base of the projectile, and these are represented by the height of the plain curves above the horizontal line at each point in the travel of the shot. The dotted lines represent in the same way, but not on the same scale as the former, the velocity with which the base of the projectile passes every point in the chase. The figures 2, 4, and 6 on the upright line at the right-hand side refer only to pressures: the velocities scale is such that the point where the dotted meets the right-hand one is 2,680 units above the horizontal line, as the middle upright in the same way is 1,561 high, and the heights of the dotted lines represent each on the same scale the velocities of the bases of the projectiles at the corresponding parts of the chases. The shorter gun has the rifled part of the chase 15·4 calibres long; the corresponding part of the longer is nearly 33 calibres. The short 7–inch gun has a charge of 30 lbs. of gunpowder, and its projectile weighed 115 lbs. The longer 6–inch gun was not charged with gunpowder, but with the more powerful modern explosive cordite (see Index), of which there was 19·5 lbs., and its projectile weighed 100 lbs. The charges were so adjusted that the shots had the same initial maximum pressure of 20 tons per square inch applied to them. Now the cordite, though much more powerful than gunpowder (that is, a given weight will produce far more gas), is slower in its ignition, continuing longer to supply gas. The maximum pressure, 20 tons in both cases, is suddenly attained by the gunpowder gases, when the shot has hardly moved 6 inches onward, and the pressure declines rapidly as the moving shot leaves more space for the gas; while the cordite gases produce their greatest pressure more gradually at a part where the shot is already about 20 inches on its way, and not only do their highest pressures continue for a greater distance,—but the decline is far less rapid than in the other case. It will be observed by the intersection of the dotted lines, that when the shots in each case have moved about 2 ft. their velocities are equal. They finally leave the muzzles with the velocities marked on the diagram, and if the reader will apply the formula given on page 174 he will obtain their respective energies in foot-lbs.; but for large amounts like these it is more usual to state the energy in foot-tons, which of course will be arrived at by dividing the foot-lbs. numbers by 2,240, and these will work out in the one case to 4978·9 ft.-tons, and in the other to 1942·5 ft.-tons. The shot from the long gun will therefore have more than 2½ times the destructive power of the other.

Fig. 98.Diagram of Velocities and Pressure.

The operations required in constructing guns are multiform, and have to be very carefully conducted so that the workmanship shall be of the best quality. The finest ores are selected for reduction, and the steel is obtained by the Siemens-Martin process already described. It must be free from sulphur and phosphorus, and contain such proportions of carbon, silicon, and manganese as experience has shown to be best, and its composition is ascertained by careful chemical analysis before it is used. The fluid steel is run into large ladles lined with fire-brick, and provided with an opening in the bottom from which the metal can be allowed to run out into the ingot moulds, the size and proportions of these being in accordance with the object required; some admitting of as much as 80 tons at one operation. When a barrel or hoop is required of not less than 6 inches internal diameter the ingot is cut to the required length and roughly bored. The ingot is then heated, a long cylindrical steel bar 206is put through the hole, and under a hydraulic press the hot metal is squeezed into greater length and less diameter. The hole first bored through the ingot is of somewhat greater, and the steel bar (called a mandril) of less, diameter than required in the finished piece. Portions are cut from each end of what is now called the forging and subjected to mechanical tests: if these are satisfactory, the forging is rough bored and turned on the outside. It is then annealed, by being heated and allowed to cool very slowly. The next operation is to harden the metal by raising it to a certain temperature, at which it is immersed in rape oil until cold. Then the piece is again annealed, and fine-turned and bored. All these operations have to be performed not only on the barrel, but also on each hoop, before the hoops are shrunk on, and the greatest nicety of measurement is required in each piece. Then the gun has to be turned on the outside, the screw for the breech piece cut, the bore rifled, etc. The object of the annealing is to relieve the metal from internal strains. It will not be wondered at that months are required for the construction of the larger kind of guns. Thus at Elswick a 6 in. quick firing gun, upon which men are employed night and day, cannot be completed in less than five months, and sixteen months are required for making a 67–ton gun.

We may take as an illustration of the progress of modern artillery one of the products of the Elswick factory which has just been referred to, and for which the demand from all quarters has been unprecedentedly great, namely, the 4·7 inch gun. This weapon is mounted in various manners according to the position it has to occupy, whether for a land defence, or on ship-board between decks, or on the upper deck. The arrangement shown in Fig. 99, which is reproduced from Messrs. Lloyd & Hadcock’s work, is known as the centre pivot mounting, and is suitable for such a position as the upper deck of a ship. The reader should compare the proportions and mounting of this weapon with those of the old 32–pounder sketched in Fig. 90, observing the very much greater comparative length of the modern weapon, and the mechanism for elevating and training it (which, however, the scale of the drawing crowds into too small a space to show as it deserves). C is a projection from the breech, to which is attached the piston of the recoil press; at T is the handle for training, which actuates a worm at V; the elevation is regulated by the turning of the four-armed wheel. The long chase of the gun projects in front; but the mounting and the breech machinery are protected by shields of thick steel, of which the sections of two plates are denoted by the dark upright parts in front. These are fixed; but a movable plate above the gun can be raised or lowered into an inclined position, for better taking sights. In the figure this is shown as open and in a horizontal position. This gun is provided with sights by which it can be aimed at night; that is, the sights can be illuminated by small electric lamps suitably placed; the wires connecting these with voltaic battery cells carried on the mounting are indicated. The figure represents the gun as constructed about 1893, but the improvements that are continually being made have brought about some modifications in the details.

Fig. 99.Elswick 4·7 inch Q. F. Gun on Pivot Mounting.

Very notable among the productions of the great Elswick factory are the quick firing guns. These were at first confined to guns of small calibre, such as the 6–pounders. They are, of course, all breech-loaders, and the powder and shot are both contained in a single metallic cartridge 208case. A more formidable weapon of the same class is the 45–pounder rapid firing gun, which, like the rest, is constructed entirely of steel, with a total length of 16 ft. 2½ in., a calibre of 4·724 in., and a length of bore equal to 40 diameters. The weight of this gun is 41 cwt., and it throws a shell of 45 lbs. weight with a 12–lb. charge of gunpowder. Quick firing guns having a calibre of 6 in. are now also made in great numbers for arming our ironclads. The breech block in the quick firing guns turns aside on a hinge, and after the introduction of the cartridge it is closed and screwed up to its place by a slight turn of a handle. The piece is then pointed and trained by aid of mechanical gearing as in the case of the heavier guns. But Mr. Hotchkiss has introduced a simpler method of elevating and training his 3–pounder and 6–pounder quick firing guns, by attaching to the rear, and unaffected by the recoil, a shoulder piece against which the marksman can lean, and move the weapon as he takes his aim. Though these guns weigh respectively 4½ cwt. and 7 cwt., they can thus be pointed with the greatest ease. The firing is done by pulling a trigger in what seems like the stock of a pistol. The empty cartridge case is automatically extracted from the firing chamber by the act of opening the breech, and it drops to the ground. Ten or twelve rounds per minute can be fired from these guns, and Lord Armstrong has advocated the use of a number of them for naval armament in preference to that of a few ordinary breech-loaders of more unwieldy dimensions. He has calculated that in a given time a far greater weight of metal can be projected from a vessel armed with quick firing guns than from one provided only with the heavier class of cannons.

The breech pieces in the Elswick guns are closed on the “interrupted screw” system—that is, a very large screw thread of V-shaped section is cut in the barrel at the breech end, and a corresponding thread on the principal part of the breech block, which is, of course, capable of rotating about the axis. The screw threads, however, are not continuous, segments parallel to the axis being cut away, the spaces in the outer thread corresponding with the projecting parts in the inner, and vice versâ, so that when the block is pushed home, one very small part of a turn suffices to engage all the threads. The screw is also made conical, and is so cut into steps, as it were, that great resisting power is brought into play. The Elswick guns are provided with hydraulic buffers for checking the recoil, and the principle is applied in various modified forms. In some cases the pistons allow for the water a passage, which towards the end gradually diminishes. This is the arrangement for the 3–pounder rapid firing Hotchkiss gun, and the force of the recoil is made at the same time to compress two springs, which serve to return the gun to the firing position. This very handy gun is said to be able to fire twenty rounds per minute. In Mr. Vavasseur’s plan of mounting, the recoil is checked by ports, or openings, in the piston of a hydraulic cylinder being gradually closed, which is easily arranged by making a spiral groove within the cylinder, which gives a small axial motion to part of the piston.

Fig. 100.The Moncrieff Gun raised and ready for firing.

Fig. 101.Moncrieff Gun lowered for loading.

An extremely effective plan for the defence of coasts and harbours was originated by Colonel Moncrieff, when about 1863 he contrived a method of mounting large guns on the disappearing system, by which almost complete protection against hostile fire is given to both gun and gunners. He utilizes the recoil as a means of bringing the gun down into a protected position the moment it has been fired, and retains this energy by a simple arrangement until the piece has been reloaded, when it is 209allowed to expend itself by again raising the gun above the parapet into the original firing position. The configuration and action of Colonel Moncrieff’s gun-carriage will be understood by an inspection of the annexed illustrations, where in Fig. 100 is shown the gun raised above 210the parapet and ready for firing. When the discharge takes place, the gun, if free, would move backwards with a certain speed, but the disposition of the mounting is such that this initial velocity receives no sudden check, the force being expended in raising a heavy counterpoise, and at the same time the gun is permitted to descend, while maintaining a direction parallel to its firing position. At the end of the descent, which, it must be understood, is caused by the force of the recoil, and not by the counterpoise, for this more than balances the weight of the gun, the latter is retained as shown in Fig. 101 until it has been reloaded; and when it has again to be fired, it is released so as to allow the descent of the counterpoise to raise it once more into position. The great advantage of this invention is the protection afforded to the artillerymen and gun while loading; and even the aiming can be accomplished by mirrors, so that the men are exposed to no danger, except from “vertical fire,” which involves but little risk.

Colonel Moncrieff took out a patent for his invention in 1864, but committed the practical working out of his idea to the firm of Sir W. G. Armstrong & Co., in whose hands the design was ultimately transformed from the original somewhat cumbersome arrangement of the mounting into the compact and manageable form shown in Fig. 102, which represents a 13·9 inch 68–ton breech-loading disappearing gun on the Elswick hydro-pneumatic mounting. The principle of hydraulic power is fully explained in our article on that subject, and an example of its application to cranes as devised by Sir W. Armstrong is there described. When guns began to be made very large, and projectiles weighing several cwts. had to be dealt with, the application of power in some form became essential for loading, running out, elevating, training, etc.; and though steam-power naturally was first used, hydraulic power was adopted at Elswick, and has been there applied to the mountings of large guns with the greatest success by Mr. G. W. Rendel. To mention the various arrangements in which this power is applied, or to attempt any description of the elaborate machinery by which it is regulated, would carry us far beyond our limits. But the powerful weapon depicted in Fig. 102 is designed to be worked only by the manual effort of a few men. In this mounting the pressure of condensed air sustains the gun in the firing position; that pressure, acting upon the water in the recoil presses, having previously forced up their rams so as to turn into a nearly vertical position the strong brackets or beams on which the trunnions are supported. The recoil is checked in the usual way by the forcing of the water through small ports or valves as the ram descends, but these valves are so arranged that the water is in part forced back into the air chamber, and there recompresses the air, to restore the power for again raising the gun. The pressure in the air chamber when the gun is down may be about 1,400 lbs. per square inch; when it is up this will be reduced to perhaps one half by the expansion of the air in doing work. We have here the reaction of compressed air taking the place of the gravity of the counterpoise originally designed. There are in this hydro-pneumatic mounting a number of adjusting appliances, such as forcing pumps, brakes, etc., for regulating the pressures, or quantity of liquid, as, for instance, when lowering the gun without any recoil action in operation. Then again, with any change in the weight of projectile or in the powder charge, there would be a corresponding change in the power of the recoil, and therefore the necessity for compensatory adjustments, which are made 212with great readiness. The nicety with which the parts are adapted to each other in this mounting must be obvious, when we observe the magnitude of the mass to be moved with the least delay, and brought to rest, quite gently and exactly, in a new position. Details cannot here be given even of the method by which the valves in the recoil cylinders are automatically controlled for this purpose. Means are also supplied for setting the gun, while still in its protected position, to the required angle of elevation or depression. The adjustment is made by the long rods attached near the breech and set at their lower ends to the position giving the intended angle to the raised gun. The varied and powerful strains to which the parts of this mechanism are subject, and which have had to be calculated and provided for, may be inferred from the enormous recoil energy of the gun, which under ordinary conditions amounts to no less than 730 foot-tons. The gun is provided with ordinary, and also with reflecting, sights, so that no one need be exposed to the enemy’s fire. Protective armour above the gun is not required, as the pit itself being usually on some elevation is imperceptible to the enemy, and the gun is visible but for a few seconds, forming a quite inconspicuous object. The pit in which the gun is mounted is commonly lined with concrete. Italy, England, Norway, Japan and other countries have appreciated the advantages of the disappearing system in providing the most powerful coast defences yet devised, and a great many guns have been mounted on this principle.

Fig. 102.68–ton Gun on Elswick Hydro-Pneumatic Mounting.

An extraordinary piece of ordnance is represented in Fig. 103. It is one of two huge mortars, the idea of which presented itself to Mr. Mallet during the Crimean War, the intention being to throw into the Russian lines spherical shells a yard in diameter, which would, in fact, have constituted powerful mines, rendering it impossible for the fortifications to continue tenable. Mallet’s original design was to project these shells from mortars of no less than 40 tons weight. When it was pointed out that the transport of so heavy a mass would be impracticable, the design was changed to admit of the mortar being made in pieces not exceeding eleven tons in weight, and built up where required. During the most active period in the siege of Sebastopol this plan was submitted to Lord Palmerston, who at once ordered two of these apparently formidable pieces to be constructed, without waiting for official examinations of the scheme, and the usual reports of experts,—promptness in this case being considered of the utmost importance. A contract was made with a private firm, who undertook to deliver them in ten weeks. But the difficulties attending such constructions not being understood at the time, delays arose, the contractors failed, and two years elapsed before the mortars were completed. In the meantime peace had been concluded, and the mortars were never fired against any hostile works; but experiments were made with one of them at Woolwich. The heaviest of the shells it was intended to project weighed 2,940 lbs., and for this it was proposed to use a charge of 80 lbs. of gunpowder. In the experiments the charges first used were low, but gradually increased: when it was found that after every few rounds repairs became necessary in consequence of the weak points in the construction, and after the nineteenth round the mortar was so much damaged that the trials were definitely discontinued. The other mortar, though mounted, was never fired, but remains at Woolwich, an object of some interest to artillerists, especially since there has been some talk of reverting to this very old-fashioned form of 213ordnance as a means of attacking ironclads in their most vulnerable direction by the so-called vertical fire. In one of the rounds of the Mallet mortar tried at Woolwich, a shell weighing 2,400 lbs. was thrown by a charge of 70 lbs. of gunpowder a distance of more than a mile and a half, and it buried itself in the soil to a very great depth.

Fig. 103.Mallet’s Mortar

For high-elevation firing, howitzers will more probably be the form of ordnance most in use. The range of the howitzer is determined by the angle at which it is elevated, whereas with the mortar it is chiefly by variation of the powder charge that the aim is adjusted. Many of the old short 9 in. muzzle-loaders have already been converted into 11 in. 214rifled howitzers, and these are likely to prove of great service in defending our harbours and channels against war vessels.

Some account has been given in a preceding article of the great steel works of Krupp & Co. at Essen, and the place has been noted as one of the greatest gun factories in the world during the second half of our century. The process there practised of casting crucible steel ingots, and already described, is precisely that used in the first stage of gun-making. The steel for guns put into the crucibles is a carefully adjusted mixture of one quality of iron puddled into steel and subjected to certain treatment; the other portion is made from a different quality of iron from which all the carbon has been puddled out. The cast ingot is forged under a great steam hammer, bored, turned, and steel hoops shrunk upon it, in several layers, and other operations are performed upon it like those which have already been mentioned. A 14 in. gun is said to require sixteen months for its manufacture, and its cost to be about £20,000.

Fig. 104.32–pounder Krupp Siege Gun, with Breech-piece open.

Artillerists had long carried on a warm controversy as to the relative merits of wrought iron and steel in gun construction, the latter material being regarded with shyness on account of its want of uniformity as formerly produced. Krupp however began as early as 1847 to make guns of his excellent crucible steel, and through bad report and good report confined himself to this material until, it is asserted, by 1878 he had supplied over 17,000 steel guns of all calibres. He began by making a 3–pounder gun, but soon produced pieces of larger size, all of which were bored and turned out of solid masses of metal. At a later period the plan of shrinking on strengthening hoops of steel was adopted. The Krupp guns have found extensive favour, and many very heavy ones have been made, some indeed of greater weight than the 110–ton Armstrong; but the excess of weight is due to the mass of metal which the Krupp construction of the breech mechanism requires. Thus Krupp’s 120–ton gun has a muzzle energy of but 45,796 foot-tons, while that of the Elswick piece is 55,105 foot-tons.

Fig. 105.The Citadel of Strasburg after the Prussian Bombardment.

The breech arrangement in the Krupp guns consists of a lateral slot into which slides a closing block after the charge has been inserted from the rear. An obsolete form of this breech piece is seen in Fig. 104, which 215represents a 32–pounder gun such as was used in sieges by the Prussians in the Franco-German War. It will be observed here that the slot and breech piece are of rectangular form; but this shape, causing the piece to be weak where most strength was required, was afterwards altered into a D-shaped section, the curved side being of course to the rear. That difficulty which baffled the earliest attempts at breech-loading is the same that has given much trouble to modern gunmakers. It consists in so closing the breech that no escape of the powder gases can take place there at the moment of discharge. When we remember that the momentary pressure of the gases in the powder chamber may amount to more than 40 tons on the square inch, we can well understand the enormous velocity with which they will rush forth from even the smallest interspace between the base of the gun and the breech block, but we can hardly realise without actual inspection the mechanical action they produce in their passage: when once the escape occurs, a channel is cut in the metal as if part had been removed by an instrument, and the piece in that condition is disabled for further use. Several devices are in use obtaining perfect closure of the breech, which is technically called obturation (Latin, obturare, to close up). One of these consists in fitting closely into the circumference of the bore a ring of very elastic steel, turned up at the edges towards the powder chamber. The gas pressure forces the edge of this ring still more closely against the interior of the powder chamber, much in the same way as the Bramah collar acts in the hydraulic press (see Fig. 165). The shaded circle shown on the breech piece in Fig. 104 is an additional device for obtaining obturation. The Broadwell 216ring, as the above-mentioned contrivance is called, is not used in English guns, but another plan of obtaining a gas-joint has been much adopted, in which a squeezable pad is by compression forced outwards to close up the bore.

A very long range was claimed for Krupp’s guns at the time of the Franco-German War, for at the siege of Paris (1870) it was said they could hurl projectiles to the distance of five miles, though probably there was some exaggeration in this statement. There is no doubt however that the Prussians had very effective and powerful artillery, as may be gathered from Fig. 105, which is taken from a photograph of part of the fortifications of Strasburg after the bombardment of that fortress. The explosive shells used by the Prussians against masses of troops were not precisely segment shells of the form already described, but the principle and effect were the same, for the interior was built up of circular rings, which broke into many pieces when the shell exploded.

Out of the very numerous forms in which modern ordnance is constructed, we have been able to select but a few examples for illustration and description. These will suffice, it is hoped, to give an idea of the progress that the century has witnessed. It would be beyond our scope to give details of the ingenious mechanical devices that have come to be applied to guns: such as the breech-closing arrangements, the various ways in which recoil is controlled and utilized, etc. A good illustration, had space permitted, of the scientific skill applied to ordnance would be found in the contrivances fitted to certain projectiles in order to determine their explosion at the proper moment. These are very different from the cap or time fuse that did duty in the first half of the century. We have indeed said little of the projectiles themselves beyond mention of the Palliser chilled shot and the obsolete studded projectiles. We have not explained how bands of copper, or other soft metal, are put round a certain part of the shot or shell, in order that, being forced into the grooves, the axial rotation may be imparted, or how windage is prevented by “gas checks” attached to the base of the projectiles. We must now be contented to conclude this section by showing the structure of two kinds of explosive shells which have been much used.

Shrapnel shell takes its name from Lieutenant Shrapnel, who was its inventor about the end of last century, but the projectile began to be used only in 1808. Fig. 105a is a section showing the shell as a case containing a number of spherical bullets, of which in the larger shells there are very many, the interspaces being filled with rosin, poured in when melted; the bullets are thus prevented from moving about. The figure shows the shell without the fuse or percussion apparatus, which screws into the hollow at the front. The bursting charge of gunpowder is behind the bullets, and when it explodes they travel forward with a greater velocity than the shell, but with trajectories more or less radiating, carrying with them wide-spreading destruction and death.

A shrapnel shell may be said to be a short cannon containing its charge of powder in a thick chamber at the breech end; the sides of the fore part of the shell are thinner than those of the chamber, and may be said to form the barrel of the cannon. This cannon is loaded up to the muzzle with round balls, which vary with the shell in size. An iron disc between the powder and the bullets represents the wad used in ordinary fowling-pieces. A false conical head is attached to the shell, so that its outward appearance is very similar to that of an ordinary cylindro-conoidal shell: 217that is to say, it looks like a very large long Enfield bullet. The spinning motion which had been communicated to the shell by the rifling of the gun from which it had been fired causes the barrel filled with bullets to point in the direction of the object at which the gun has been aimed. Consequently, when the shrapnel shell is burst, or rather fired off, the bullets which it contained are streamed forward with actually greater velocity than that at which the shell had been moving; and the effect produced is similar to firing grape and canister from a smooth-bore cannon at a short range.

Fig. 105a.—The Shrapnel and Segment Shells.

Segment shells were first brought into use by Lord Armstrong in 1858 in connection with his breech-loading guns. The segment shell consists of a thin casing like a huge conical-headed thimble, with a false bottom attached to it. It is filled with small pieces of iron called “segments,” cast into shapes which enable them to be built up inside the outer casing into two or more concentric circular walls. The internal surface of the inmost wall forms the cavity of the compound or segment shell, and contains the bursting charge. The segment shell is fitted with a percussion fuse, which causes it to explode when it strikes. In the shrapnel shell, the powder charge is situated in rear of the bullets, and consequently produces the chief effect in a forward direction. In the segment shell, the powder is contained inside the segments, and therefore produces the chief effect in a lateral direction. When the shrapnel shell is burst at the right moment, its effect is greatly superior to that of the segment shell; on the other hand, the segment shell, when employed at unknown or varying distances, is far more unlikely to explode at the proper time.

Shrapnel and segment shells can be used with field artillery, i.e., 2189–pounders, 12–pounders, 16–pounders; and also with heavy rifled guns in fortresses, viz., 40–pounders, 64–pounders, 7–in. and 9–in. guns. But the conditions of their service are very different in each case. With regard to field artillery, the distance of the enemy is rarely known, and is constantly changing, and hence the men who have to adjust the fuses would probably be exposed to the fire of the enemy’s artillery, and, consequently, could not be expected to prepare the fuses with the great care and nicety which are absolutely necessary to give due effect to the shells. There are, however, some occasions when the above objections would not hold good—as, for instance, when field artillery occupy a position in which they wait the attack of an enemy advancing over ground in which the distances are known.

Segment shells require no adjustment of their percussion fuse. They enable the artillerymen to hit off the proper range very quickly, since the smoke of the shell which bursts on striking tells them at once whether they are aiming too high or too low.

With regard, however, to the service of heavy rifled guns in fortresses, the conditions are quite different. In the first place, the distance of all objects in sight would be well known beforehand; and in the second place, the fuses of the shells would be carefully cut to the required length in the bomb-proofs, where the men would be completely sheltered. The 7–in. shrapnel contains 227 bullets, and a 9–in. shrapnel would contain 500 bullets of the same size, and these shells could be burst with extraordinary accuracy upon objects 5,000, 6,000, or 7,000 yards off.

MACHINE GUNS.

The name of machine guns has been applied to arms which may be regarded as in some respects intermediate between cannons and rifles, since in certain particulars they partake of the nature of both. Like the former, they are fired from a stand or carriage, and in some of their forms require more than one man for their working: in the calibre of their barrels and the weight of their projectiles, they are assimilated to the rifle, but they are capable of pouring forth their missiles in a very rapid succession—so rapid indeed as practically to constitute volley firing. The firing mechanism of the machine gun has always an automatic character, but the rifle has acquired this feature, so that it cannot be made a distinguishing mark: on the other hand, since machine guns have been made to discharge projectiles of such weights as 1 lb. or 3 lb. there is nothing to separate them from quick-firing ordnance unless it be the automatic firing.

The idea of combining a number of musket-barrels into one weapon, so that these barrels may be discharged simultaneously or in rapid succession, is not new. Attempts were made two hundred years ago to construct such weapons; but they failed, from the want of good mechanical adjustments of their parts. Nor would the machine gun have become the effective weapon it is, but for the timely invention of the rigid metallic-cased cartridge. Several forms of machine guns have in turn attracted much attention. There is the Mitrailleur (or Mitrailleuse), of which so much was heard at the commencement of the Franco-German War, and of whose deadly powers the French managed to circulate terrible and mysterious reports, while the weapon itself was kept concealed. 219Whether this arose from the great expectations really entertained of the destructive effects of the mitrailleur, or whether the reports were circulated merely to inspire the French troops with confidence, would be difficult to determine. Our own policy in regard to new implements of war is not to attempt to conceal their construction. Experience has shown that no secret of the least value can long be preserved within the walls of an arsenal, although the French certainly apparently succeeded in surrounding their invention with mystery for a while. The machine gun, or “battery,” invented by Mr. Gatling, an American, is said by English artillerists to be free from many defects of the French mitrailleur. In 1870 a committee of English military men was appointed to examine the powers of several forms of mitrailleur, with a view to reporting upon the advisability or otherwise of introducing this arm into the British service. They recommended for certain purposes the Gatling battery gun.

Fig. 105b.—The Gatling Gun.—Rear View.

In the Gatling the barrels, ten in number, are distinct and separate, being screwed into a solid revolving piece towards the breech end, and passing near their muzzles through a plate, by which they are kept parallel to each other. The whole revolves with a shaft, turning in bearings placed front and rear in an oblong fixed frame, and carrying two other pieces, which rotate with it. These are the “carrier” and the lock cylinder. Fig. 105b gives a rear view, and Fig. 105c a side view, of the Gatling battery gun. The weapon is made of three sizes, the largest one firing bullets 1 in. in diameter, weighing ½ lb., the smallest discharging bullets of ·45 in. diameter. The small Gatling is said to be effective at a range of more than a mile and a quarter, and can discharge 400 bullets or more in one minute. Mr. Gatling thus describes his invention:

“The gun consists of a series of barrels in combination with a grooved 220carrier and lock cylinder. All these several parts are rigidly secured upon a main shaft. There are as many grooves in the carrier, and as many holes in the lock cylinder, as there are barrels. Each barrel is furnished with one lock, so that a gun with ten barrels has ten locks. The locks work in the holes formed in the lock cylinder on a line with the axis of the barrels. The lock cylinder, which contains the lock, is surrounded by a casing, which is fastened to a frame, to which trimmers are attached. There is a partition in the casing, through which there is an opening, and into which the main shaft, which carries the lock cylinder, carrier, and barrels, is journaled. The main shaft is also at its front end journaled in the front part of the frame. In front of the partition in the casing is placed a cam, provided with spiral surfaces or inclined planes.

“This cam is rigidly fastened to the casing, and is used to impart a reciprocating motion to the locks when the gun is rotated. There is also in the front part of the casing a cocking ring which surrounds the lock cylinder, is attached to the casing, and has on its rear surface an inclined plane with an abrupt shoulder. This ring and its projection are used for cocking and firing the gun. This ring, the spiral cam, and the locks make up the loading and firing mechanism.

“On the rear end of the main shaft, in rear of the partition in the casing, is located a gear-wheel, which works to a pinion on the crank-shaft. The rear of the casing is closed by the cascable plate. There is hinged to the frame in front of the breech-casing a curved plate, covering partially the grooved carrier, into which is formed a hopper or opening, through which the cartridges are fed to the gun from feed-cases. The frame which supports the gun is mounted upon the carriage used for the transportation of the gun.

“The operation of the gun is very simple. One man places a feed-case filled with cartridges into the hopper; another man turns the crank, which, by the agency of the gearing, revolves the main shaft, carrying with it the lock cylinder, carrier, barrels, and locks. As the gun is rotated, the cartridges, one by one, drop into the grooves of the carrier from the feed-cases, and instantly the lock, by its impingement on the spiral cam surfaces, moves forward to load the cartridge, and when the butt-end of the lock gets on the highest projection of the cam, the charge is fired, through the agency of the cocking device, which at this point liberates the lock, spring, and hammer, and explodes the cartridge. As soon as the charge is fired, the lock, as the gun is revolved, is drawn back by the agency of the spiral surface in the cam acting on a lug of the lock, bringing with it the shell of the cartridge after it has been fired, which is dropped on the ground. Thus, it will be seen, when the gun is rotated, the locks in rapid succession move forward to load and fire, and return to extract the cartridge-shells. In other words, the whole operation of loading, closing the breech, discharging, and expelling the empty cartridge-shells is conducted while the barrels are kept in continuous revolving movement. It must be borne in mind that while the locks revolve with the barrels, they have also, in their line of travel, a spiral reciprocating movement; that is, each lock revolves once and moves forward and back at each revolution of the gun.

“The gun is so novel in its construction and operation that it is almost impossible to describe it minutely without the aid of drawings. Its main features may be summed up thus: 1st.—Each barrel in the gun is provided with its own independent lock or firing mechanism. 2nd.—All the locks revolve simultaneously with the barrels, carrier, and inner breech, when the 221gun is in operation. The locks also have, as stated, a reciprocating motion when the gun is rotated. The gun cannot be fired when either the barrels or locks are at rest.”

There is a beautiful mechanical principle developed in the gun, viz., that while the gun itself is under uniform constant rotary motion, the locks rotate with the barrels and breech, and at the same time have a longitudinal reciprocating motion, performing the consecutive operations of loading, cocking, and firing without any pause whatever in the several and continuous operations.

The small Gatling is supplied with another improvement called the “drum feed.” This case is divided into sixteen sections, each of which contains twenty-five cartridges, and is placed on a vertical axis on the top of the gun. As fast as one section is discharged, it rotates, and brings another section over the feed aperture, until the whole 400 charges are expended.

Fig. 105c.—The Gatling Gun.—Front View.

After a careful comparison of the effects of field artillery firing shrapnel, the committee concluded that the Gatling would be more destructive in the open at distances up to 1,200 yards, but that it is not comparable to artillery in effect at greater distances, or where the ground is covered by trees, brushwood, earthworks, &c. The mitrailleur, however, would soon be knocked over by artillery if exposed, and therefore will probably only be employed in situations under shelter from such fire. An English officer, who witnessed the effects of mitrailleur fire at the battle of Beaugency, looks upon the mitrailleur as representing a certain number of infantry, for whom there is not room on the ground, suddenly placed forward at the proper moment at a decisive point to bring a crushing fire upon the enemy. Many other eye-witnesses have spoken of the fearfully deadly effect of the mitrailleur in certain actions during the Franco-German War.

Mr. Gatling contends that, shot for shot, his machine is more accurate than infantry, and certainly the absence of nerves will ensure steadiness; 222while so few men (four) are necessary to work the gun that the exposure of life is less. No re-sighting and re-laying are necessary between each discharge. When the gun is once sighted its carriage does not move, except at the will of the operator; and the gun can be moved laterally when firing is going on, so as to sweep the section of a circle of 12° or more without moving the trail or changing the wheels of the carriage. The smoke of battle, therefore, does not interfere with its precision.

Whatever may be the part this new weapon is destined to play in the wars of the future, we know that every European Power has now provided itself with some machine guns. The Germans have those they took from the French, who adhere to their old pattern. The Russians have made numbers of Gatlings, each of which can send out, it is said, 1,000 shots per minute, and improvements have been effected, so as to obtain a lateral sweep for the fire.

Fig. 105d.—The Montigny Mitrailleur.

A competitor to the Gatling presents itself in the Belgian mitrailleur, the Montigny, Fig. 105d. This gun, like the Gatling, is made of several different sizes, the smallest containing nineteen barrels and the largest thirty-seven. The barrels are all fitted into a wrought iron tube, which thus constitutes the compound barrel of the weapon. At the breech end of this barrel is the movable portion and the mechanism by which it is worked. The movable portion consists mainly of a short metallic cylinder of about the same diameter as the compound barrel, and this is pierced with a number of holes which correspond exactly with the position of the gun-barrels, of which they would form so many prolongations. In each of the holes or tubes a steel piston works freely; and when its front end is made even with the front surface of the short cylinder, a spiral spring, which is also contained in each of the tubes, is compressed. The short cylinder moves as a whole backwards and forwards in the direction of the axis of the piece, the movement being given by a lever to the shorter arm of which the movable piece is attached. When the gun is to be loaded this piece is drawn backwards by raising the lever, when the spiral springs are relieved 223from compression, and the heads of the pistons press lightly against a flat steel plate in front of them. The withdrawal of the breech-block gives space for a steel plate, bored with holes corresponding to the barrels, to be slid down vertically; and this plate holds in each hole a cartridge, the head of each cartridge being, when the plate has dropped into its position, exactly opposite to the barrel, into which it is thrust, when the movable breech-block is made to advance. The anterior face of this breech-block is formed of a plate containing a number of holes again corresponding to the barrels, and in each hole is a little short rod of metal, which has in front a projecting point that can be made to protrude through a small aperture in the front of the plate, the said small apertures exactly agreeing in position with the centres of the barrels, and being the only perforations in the front of the plate. The back of the plate has also openings through which the heads of the pistons can pass, and by hitting the little pieces, or strikers, cause their points to pass out through the apertures in front of the plate, and enter the base of the cartridges, where fulminate is placed. The plate filled with cartridges has a bevelled edge, and the points of the strikers are pushed back by it as it descends. The heads of the pistons are separated until the moment of discharge from the recesses containing the strikers by the flat steel plate or shutter already mentioned. The effect, therefore, of pushing the breech-block forward is to ram the cartridges into the barrels, and at the same time the spiral springs are compressed, and the heads of the pistons press against the steel shutter which separates them from the strikers, so that the whole of the breech mechanism is thus closed up. When the piece is to be fired a handle is turned, which draws down the steel shutter and permits the pistons to leap forward one by one, and hit the strikers, so that the points of the latter enter the cartridges and inflame the fulminate. The shutter is cut at its upper edge into steps, so that no two adjoining barrels are fired at once. The whole of the thirty-seven barrels can be fired by one and a quarter turns of the handle, which may, of course, be given almost instantly, or, by a slower movement, the barrels can be discharged at any required rate.

The barrels of the machine guns we have described do not, as is generally supposed, radiate; on the contrary, they are arranged in a perfectly parallel direction. In consequence of this, the bullets are at short ranges directed nearly to one spot. The Gatling gun was adopted as a service weapon by the British navy, and in several minor actions it had proved effective, but in its original form it was superseded by the Gardner gun, in which the barrels are fixed horizontally side by side, and are in number five or fewer; each barrel is able to fire 120 rounds per minute. A new system of feed was afterwards applied to the Gatling gun by Mr. Accles, by means of which this gun was greatly improved and its rate of firing was increased to more than 1,000 rounds per minute; indeed, 80 rounds have been fired from it within 2 seconds. The Gatlings in this improved form have ten barrels, and are provided with feed drums, each containing 104 cartridges, and capable, when empty, of being almost instantly replaced by a full one. The contents of one drum can, if necessary, be discharged in about 2¼ seconds, so that in this time 104 rifle bullets would be fired; or considerably more than the rate of 1,000 rounds per minute could easily be maintained. The weapon is so mounted, that without moving its carriage it can be pointed at any angle of elevation or depression, and through a considerable lateral range.

Mr. Nordenfelt has brought out a machine gun, which, on account of 224the simplicity and strength of its firing mechanism, has proved the most reliable weapon of its class, and it also has been adopted into the British service, and indeed into that of nearly every nation in the world. In this gun there are five barrels arranged as in the Gardner, but the firing is operated by a lever working backwards and forwards at the rate of 600 rounds per minute.

Fig. 105e.—A Hotchkiss Gun.

In the firing of all these weapons, by turning a crank, or moving a lever at one side, any attempt at exact aiming must obviously be difficult if not impossible, from the liability of the gun to get moved. Several designs have been proposed for making the firing mechanism entirely automatic so as to require no effort on the part of the firer, whose attention can then be directed solely to pointing the piece. It would not be 225easy to explain in detail the way in which this is accomplished in these very ingenious guns; for while the principle of their action is sufficiently clear, namely, that the force of the recoil is made to extract the spent cartridge, open the breech, insert a fresh cartridge, close the breech, and fire the charge, the mechanism of the reacting springs, etc., by which this is effected could scarcely, even by the aid of elaborate diagrams, be made intelligible to any other than a gunsmith. The Maxim is one of those automatic guns: it has but one barrel, and after the first discharge it will go on firing with marvellous rapidity the cartridges supplied to it in a continuous chain, and this without any deviation from such direction as may be given to it by the operator, for he has neither crank to turn nor lever to move, but merely sits behind an iron shield directing the weapon at will, which, without interference, fires hundreds of shots per minute from one barrel, so long as the long bands of cartridges are supplied to it.

Mr. Nordenfelt and Mr. Hotchkiss have also both contrived quick firing guns for 1–lb., 3–lb., and 6–lb. projectiles, and these, it has been thought, will be of great service in naval warfare as against torpedo boats.

Though the automatic mechanism, whereby the breech operations are all performed by the force of the recoil of the barrel, which is allowed to slide backwards, and is then returned to its place by a spring, is too complicated for illustration here, mention may be made of a quite recent device by which the recoil action is dispensed with, and the mechanism so far simplified that scarcely more than half the number of parts in the lock mechanism are required. Imagine a closed tube beneath the barrel, parallel to it, and communicating with it only by a small boring near the muzzle; through this opening the expanding gases will pass, in a degree depending on its size and position, and by their action on a piston near the breech, impulses are supplied that will actuate the lock mechanism so long as cartridges are supplied, as they may be in a continuous band. A weapon of this construction has been already tried, and its discharges are so rapid that the sound of them is described as being quite deafening. This plan appears to be equally applicable to small arms, and to machine or field guns. A very effective gun of the kind, which fires ordinary rifle bullets, has been contrived by Mr. Hotchkiss, and is represented in Fig. 105e. It is capable of sending forth as many as 1,000 shots in one minute.

Modern ordnance has required certain modifications in the making of gunpowder, so that the original name of powder would now hardly be applicable at all. The large charges now used, if introduced in the form of fine powder, would certainly shatter the guns from the suddenness of the exploding force. Hence the material is made up into larger or smaller masses, generally rounded like small pebbles. The explosive used for the huge 110–ton guns presents itself in the form of chocolate-coloured hexagonal prisms, two or three inches long and about an inch in diameter. These are obtained by compressing the specially prepared material into moulds with a hydraulic press. The reason for this process is that, in order to obtain precision and uniformity in the effects, not only must the composition of the powder be always the same, but the size, shape, weight, and number of the several portions that make up the charge must be invariable. It has not been found possible to fire one of these monster guns many times without such signs of deterioration as 226would suggest a short “life” for each of them. But the greatest necessity for modern fire-arms is a smokeless powder or other explosive. It is obvious that the advantages of quick firing, whether of large or of small fire-arms, are greatly reduced if the soldier or gunner is prevented by smoke from taking aim. The invention of a smokeless gunpowder has several times been announced, and great advances have, indeed, been made towards its realization. Certain compositions, which appeared to meet the requirement of being practically smokeless, have, however, been found liable to chemical changes, or to corrode the bore, or to possess other objectionable properties. In this country the explosive coming into use as best adapted for quick firing guns, etc., presents itself in appearance like whitish or grey strings, and has hence received the name of cordite. The composition and mode of manufacture of these new substitutes for gunpowder are not readily disclosed, each military authority jealously guarding its own secrets. The problem of smokeless powder has, however, been almost completely solved, for at a military review that took place on the Continent in 1889, the discharge of the rifles (loaded with blank cartridges, of course) is said to have been attended with no more smoke than the puff of a cigar. The new invention will cause some changes in military tactics, for the manœuvres formerly executed under cover of the battle smoke will no longer be possible. Some particulars as to the nature of smokeless powders will be found in the article on “Explosives.”

227

Fig. 106.Harvey’s Torpedo. Working the Brakes.

TORPEDOES.

The notion of destroying ships or other structures by explosions of gunpowder, contained in vessels made to float on the surface of the water, or submerged beneath it, is not of very modern origin. Two hundred and fifty years ago the English tried “floating petards” at the siege of Rochelle. During the American War of Independence similar contrivances were used against the British, and from time to time since then “torpedoes,” as they were first termed by Fulton, have been employed in warfare in various forms; but up to quite a recent period the use of torpedoes does not appear to have been attended with any decided success, and it is probable that but for the deplorable Civil War in the United States we should have heard little of this invention. During that bitter fratricidal struggle, however, when so much ingenuity was displayed in the contrivance of subsidiary means of attack and defence, the torpedo came prominently into notice, having been employed by the Confederates with the most marked effects. It is said that thirty-nine Federal ships were blown up by Confederate torpedoes, and the official reports own to twenty-five having been so destroyed. This caused the American Government to turn their attention to the torpedo, and they became so convinced of the importance of this class of war engine that they built boats expressly for torpedo warfare, and equipped six Monitors for the same purpose.

It has been well remarked that the torpedo plays the same part in naval warfare as does the mine in operations by land. This exactly describes the 228purpose of the torpedo where it is used defensively, but the comparison fails to suggest its capabilities as a weapon of offence. There are few occasions where a mine is made the means of attack, while the torpedo readily admits of such an employment, and, used in this way, it may become a conspicuous feature of future naval engagements. Many forms of this war engine have been invented, but all may be classified, in the first place, under two heads: viz., stationary torpedoes, and mobile or offensive torpedoes; while independent distinctions may be made according to the manner of firing the charge; or, again, according to the mode of determining the instant of the explosion. The stationary torpedo may be fixed to a pile or a raft, or attached to a weight; the offensive torpedo may be either allowed to float or drift against the hostile ships, or it may be propelled by machinery, or attached to a spar of an ironclad or other vessel. The charge may be fired by a match, by percussion, by friction, by electricity, or by some contrivance for bringing chemicals into contact which act strongly upon each other, and thus generate sufficient heat to ignite the charge. The instant of explosion may be determined by the contact of the torpedo with the hostile structure (in which case it is said to be “self-acting”), or by clockwork, or at the will of persons directing the operations. In some cases lines attached to triggers are employed; in others electric currents are made use of.

Fig. 107.Submerged Torpedo.

In the American Civil War the stationary torpedoes at first laid down were self-acting, that is, they were so arranged as to explode when touched by a passing vessel. Such arrangements present the great disadvantages of being as dangerous to friendly as to hostile ships. The operation of placing them is a perilous one, and when once sunk, they can only be removed at great risk. Besides this, they cannot be relied on for certain 229action in time of need, as the self-acting apparatus is liable to get out of order. The superiority of the method of firing them from the shore when the proper instant arrived, became so obvious that the self-acting torpedo was soon to a great extent superseded by one so arranged that an observer could fire it at will, by means of a trigger-line or an electric current. Similar plans had often been previously employed or suggested. For example, during the war between Austria and Italy the Austrian engineers at Venice had very large electric torpedoes sunk in the channels which form the approaches to the city. They consisted of large wooden cases capable of containing 400 lbs. of gun-cotton, moored by chains to a wooden framework, to which weights were lashed that sufficed to sink the whole apparatus, Fig. 107. A cable containing insulated wires connected the torpedo with an electrical arrangement on shore, and the explosion could take place only by the operator sending a current through these wires. The torpedo was wholly submerged, so that there was nothing visible to distinguish its position. There was no need of a buoy or other mark, as in the case of self-acting torpedoes, to warn friendly vessels off the dangerous spot, and therefore nothing appeared to excite an enemy’s suspicions. But it is, however, absolutely necessary that the defenders should know the precise position of each of their submarine mines, so that they might explode it at the moment the enemy’s ship came within the range of its destructive action. This was accomplished at Venice in a highly ingenious manner, by erecting a camera obscura in such a position that a complete picture of the protected channels was projected on a fixed white table. While the torpedoes were being placed in their positions an observer was stationed at the table, who marked with a pencil the exact spot at which each torpedo was sunk into the water. Further, those engaged in placing the torpedoes caused a small boat to be rowed round the spot where the torpedo had been placed, so as to describe a circle the radius of which corresponded to the limit of the effective action of the torpedo. The course of the boat was traced on the picture in the camera, so that a very accurate representation of the positions of the submarine mines in the channels was obtained. Each circle traced on the table was marked by a number, and the wire in connection with the corresponding torpedo was led into the camera, and marked with the same number, so that the observer stationed in the camera could, when he saw the image of an enemy’s ship enter one of the circles, close the electric circuit of the corresponding wire, and thus instantly explode the proper torpedo. The events of the war did not afford an opportunity of testing practically the efficiency of these preparations.

Another mode of exploding torpedoes from the shore has been devised by Abel and Maury. It has the advantage of being applicable by night as well as by day. The principle will be easily understood with the assistance of the diagram, Fig. 108, in which, for the sake of simplicity, the positions of only three torpedoes, 1, 2, 3, are represented.

Fig. 108.Mode of Firing Torpedo.

In this arrangement two observers are required at different stations on the shore. At each station—which should not, of course, be in any conspicuous position—is a telescope, provided with a cross-wire, and capable of turning horizontally about an upright axis. The telescope carries round with it, over a circular table of non-conducting substance, a metallic pointer which presses against narrow slips of metal let into the circumference of the table. To each slip of metal a wire passing to a torpedo is attached, and another wire is connected with the axis of the pointer, so as to be put into electric contact with each of the others when the pointer touches the 230corresponding piece of metal on the rim of the table. The mode in which these wires are connected with the torpedoes, the telescopes, and the electric apparatus is shown by the lines in the diagram. At each station is a key, which interrupts the electric circuit except when it is pressed down by the operator. There are thus four different points at which contacts must be simultaneously made before the circuit can be complete or a torpedo explode. In the diagram three of these are represented as closed, and in such a condition of affairs it only remains for the observer to depress the handle of the key at station B to effect the explosion of torpedo No. 2. The observer at station a is supposed to see the approaching vessel in the line of torpedo No. 2, and recognizing this as an enemy’s ship, he depresses the key at his station. The operator at B, by following the course of the vessel with his telescope, will have brought the pointer into contact with the wire leading to No. 2 torpedo, and he then causes the explosion to take place by completing the circuit by depressing his key. A modification of this plan is proposed by which the position of the torpedoes is indicated by placing marks, such as differently-coloured flags, or by night lamps with coloured glasses, throwing their light only towards the telescopes. These marks are placed in the line of direction of each torpedo from the telescope as at c1, c2, c3 and b1, b2 3; and if they can be put at some distance, the position of the torpedo is determined with great accuracy by the intersection of the lines of sight of the two telescopes. Electric wires connect the stations and the torpedoes in the same manner as we have before described. Such methods of firing torpedoes are no doubt the most efficient, for the destructive charge may be sunk so far below the surface that not a ripple or an eddy can excite an enemy’s suspicion, or the channel appear otherwise than free and unobstructed, while friendly ships may pass and repass without risk; for the current which determines the explosion only passes when the two sentinels complete the circuit by simultaneously depressing their keys.

231Attempts have often been made to convert the torpedo into an offensive weapon, by causing vessels containing explosive charges to drift by currents, or otherwise, into contact with the enemy’s ships. The results have been always unsatisfactory, as there is great uncertainty of the machine coming into contact with its intended mark. Besides, it is easy to defend vessels against such attacks by placing nets, &c., to intercept the hostile visitors, especially if the attack is made by day, and by night the chance that a torpedo drifting at random would strike its object is very small indeed. One condition essential to the success of such attacks is that the approach of the insidious antagonist may be unobserved. Accordingly divers schemes have been projected for propelling vessels wholly submerged beneath the surface of the water, so that they may approach their object unperceived, and exert their destructive effect precisely at that part of the vessel where damage is most fatal, and where an ironclad vessel is most vulnerable, namely, below the water-line. Vessels have been built, propelled by steam and so contrived that their bodies are wholly submerged, only the funnel being visible above the surface. These quasi submarine ships carry small crews, and are fitted with a long projecting spar in front, at the end of which is carried the torpedo.

Fig. 109.Explosion of Whitehead’s Torpedo.

Fig. 110.Effect of the Explosion of Whitehead’s Torpedo.

The Federal navy sustained several disasters from torpedo-boats of this kind. For example, the commander of the United States steamer Housatonic reported the loss of that vessel by a rebel torpedo off Charleston on the evening of the 17th February, 1864, stating that about 8·45 p.m. the officer of the deck discovered something in the water about 100 yards from, and moving towards, his ship. It had the appearance of a plank moving in the water. It came directly towards the ship, the time from when it was first seen till it was close alongside being about two minutes; and hardly had it arrived close to the ship before it exploded, and the ship began to sink. The torpedo-boat, with its commander and crew, were lost, having, it is supposed, gone into the hole made by the explosion, and sunk with the Housatonic. In general, however, the performance of submarine boats has been unsatisfactory. There is the difficulty of determining accurately the 232course of the boat; there is great danger to the men manning it, as exemplified in the case above; and there is again the problem of providing a means of propulsion which shall enable such a boat to advance or retreat for, say, a mile or more, without making its presence conspicuous by smoke or otherwise. The latter condition would appear to exclude the use of steam for such purposes, as the inevitable smoke and vapour would betray the presence of the wily craft. Another power which has been proposed is air strongly compressed, and recently a still more portable agent has been suggested in solid carbonic acid, which is capable of exerting a pressure of forty atmospheres by passing into the gaseous form. A locomotive form of torpedo, invented by Mr. Whitehead, has the explosive charge, which consists of about 18 lbs. of glyoxyline, placed in the front part of a cigar-shaped vessel, the other part containing mechanism for working a screw-propeller, by means of compressed air contained in a suitable reservoir. This torpedo having been sunk a few feet below the water, the motive power may be set in action by drawing a cord attached to a detent, when the mechanical fish proceeds in a straight line under the water. It is said that this torpedo is effective at 500 yards from the ship attacked, and may even be made sufficiently powerful to travel 1,000 yards under the water. The great objection to such arrangements is the uncertainty of the missile arriving at its destination, for even supposing that the water were without currents, the least deviation from the straight course would cause the torpedo to pass wide of the mark at 1,000 yards distant. It is said that at the experimental trials more than one projector of such war engines has been startled by his machine, after pursuing a circuitous submarine course, exploding in dangerous proximity to the place whence it was sent off, the engineer narrowly escaping 233being “hoist with his own petard.” The experiments which have been made with Whitehead’s torpedo in smooth water appear, however, to have been so far successful that we may probably hear of this invention being put in practical operation in certain cases. Fig. 109 shows the upthrow of water produced by the explosion of one of these torpedoes against an old hulk. The large mass of water thus heaved up is a proof of the mechanical energy of the explosion, and the effect on the hulk is shown in Fig. 110, which exhibits the damage done to her timbers, from the effects of which, it need hardly be said, she immediately sank. In Fig. 112 we have the representation of the explosion of one of Whitehead’s torpedoes containing 67 lbs. of gun-cotton, instead of the glyoxyline. The accurate delineation of these pyramids of water could not have been obtained but by the aid of instantaneous photography, and it constitutes a good example of the great value of such an application of that art, for the instantaneous photographs obtained in these experiments enabled the engineers to calculate accurately the volume and height of the column of water, which thus furnishes a measure of the power of the explosion.

Fig. 111.Experiment made by the Royal Engineers with a Torpedo charged with 10 lbs. of Gun-Cotton.

The ordinary torpedo adopted by the British authorities for coast defence consists of a cylinder of boiler plate, 4 ft. long and 3 ft. in diameter. It is intended to contain 432 lbs. of loose gun-cotton, equivalent in explosive energy to about a ton of gunpowder. The effect of one of these torpedoes exploded 37 ft. beneath the surface of the water is depicted in Fig. 113, 234and in Fig. 114 is shown the effect produced when the same charge was exploded at the depth of 27 ft. below the surface. Gun-cotton appears to be the most effective explosive for torpedoes, if we may judge by the large volume of water heaved up, as witness Fig. 111, which shows the result with a small torpedo, containing only 10 lbs. of gun-cotton, exploded at a less depth than those already mentioned. The ordinary torpedoes are moored by an anchor attached to the torpedo, and floating above it is a buoy shaped like an inverted cone. This cone contains a mechanical arrangement of such a nature that when it is struck by a passing vessel, an electric circuit is closed by bringing into contact two wires connecting the torpedo with a voltaic battery on shore. While the apparatus may thus be at any moment made fatal to a hostile vessel touching it, from the control it is under by the engineer having the management of the battery contacts, friendly vessels may pass over it with impunity.

Fig. 112.Explosion of Whitehead’s Torpedo, containing 67 lbs. of Gun-Cotton.

The employment of torpedoes develops, as a matter of course, a system of defence against them. Nets spread across a channel will catch drifting torpedoes, and stationary ones may be caused to explode harmlessly by nets attached to spars pushed a great distance forward from the advancing ship.

Before the final adoption of Whitehead’s torpedo, presently to be described, the British Government had, after various official trials, approved of a towing torpedo designed for offensive operations. It is the invention of Commander Harvey, and is worthy of a detailed description for the ingenuity of its construction.

Fig. 113.Explosion of 432 lbs. of Gun-Cotton in 37 feet of Water.

Fig. 114.Explosion of 432 lbs. of Gun-Cotton in 27 feet of Water.

The shape of Harvey’s torpedo, as may be noticed on reference to Fig. 118, is not symmetrical, but it has some remote resemblance to a boat, though constructed with flat surfaces throughout. The outside case is formed of wood well bound with iron, all the joints being made thoroughly water-tight. The length is 5 ft. and the depth 1¾ ft., while the breadth is only 6 in. Within this wooden case is another water-tight case made of 235thick sheet copper, from the top of which two very short wide tubes pass upwards to what we may term the deck of the wooden case. These are the apertures through which the charge of gunpowder or other explosive material is introduced; and when the tubes have been securely stopped with corks, brass caps are screwed on. The centre of the internal case is occupied by a copper tube, g, Fig. 115, which passes the entire depth, and is soldered to the top and bottom of the copper case, so that the interior of the tube has no communication with the body of the torpedo, the principal charge merely surrounding it. Thus the tube forms a small and quite independent chamber in the midst of the large one, which latter is capable of containing 80 lbs. of gunpowder. The copper tube or priming-case contains also a charge, a, which when exploded bursts the tube, and thus fires the torpedo in its centre. The priming charge is put in from the lower end of the tube, which is afterwards closed by a cork and brass cap, h; 236for the centre of the priming-case is occupied by a brass tube, b, closed at the bottom, but having within a pointed steel pin projecting upwards. In this tube works the exploding bolt c d, which requires a pressure of 30 or 40 lbs. to force it down upon the steel pin. This pressure is communicated to the bolt by the straight lever working in the slot at its head, d, and itself acted on at its extremity by the curved lever to which it is attached. Thus from the mechanical advantage at which the levers act a moderate downward pressure suffices to force the exploding bolt to the bottom of the brass tube. The lower end of this bolt has a cavity containing an exploding composition sufficient in itself to fire the torpedo, even independently of the priming charge contained in the copper tube. This composition is safely retained in the end of the bolt by a metallic capsule, c, which, when the bolt is forced down, is pierced through by the steel pin at the bottom of the brass tube, and then the explosion takes place. The bolts are not liable to explosion by concussion or exposure to moderate heat, and they can be kept for an indefinite period without deterioration.

Fig. 115.Section of Priming-Case and Exploding Bolt.

The mode of producing the explosion is not stated: it consists probably of an arrangement for bringing chemicals into contact. Besides the two levers already mentioned, a shorter curved lever working horizontally will be noticed. The object of this is to make a lateral pressure also effective in forcing down the bolt—a result accomplished by attaching to the short arm of the lever a greased cord, which, after passing horizontally through a fairleader, runs through an eye (see Fig. 117) in the straight lever, and has its extremity fastened so that a horizontal movement of the short lever draws the other down. A very important part of the apparatus is the safety key, f, Fig. 115, a wedge which passes through a slot in the exploding bolt, and resting on the brass-work of the priming-case, retains the muzzle 1 in. above the pin. Through the eye of the safety key and round the bolts passes a piece of packthread, e, which being knotted is strong enough to keep the key securely in its place, but weak enough to yield when the strain is put on the line, , used for withdrawing the safety key at the proper moment. This line is attached to the eye of the key, and passes through one of the handles forming the termination of the iron straps. As represented in Fig. 117, it forms the centre one of the three coils of rope. The bottom of the torpedo is ballasted with an iron plate, to which several thicknesses of sheet lead can be screwed on as occasion requires. Fig. 117 shows the arrangement of the slings by which the torpedo is attached to the tow-rope, and it will be seen that another rope passes backwards through an eye in the stern to the spindle-shaped object behind the torpedo. This is a buoy, of which two at least are always used, although only 237one is represented in the figure. Each buoy, in length 4½ ft., is made of solid layers of cork built up on an iron tube running through it lengthways, so that the buoys admit of being strung upon the rope.

Fig. 116.Harvey’s Torpedo.

Having thus described the construction of the torpedo, we proceed to explain how it is used. It must be understood that if the torpedo and its attached buoys are left stationary in the water, the tow-rope being quite slack, the torpedo will, from its own weight, sink several feet below the surface. But when they are towed, the strain upon the tow-line brings the torpedo to the surface, to dip below it again as often as the tow-line is slackened. There is another peculiarity in the behaviour of the torpedo, and that is that, when towed, it does not follow in the wake of the vessel, but diverges from the ship’s track to the extent of 45°. Its shape and the mode in which it is attached to the tow-line are designed so as to obtain this divergence. But, according as the torpedo is required to diverge to the right or to the left, there must be the corresponding shape and arrangement of tow-line and levers; hence two forms of torpedo are required, the starboard and the port. The figures represent the port torpedo, or that which is launched from the left side of the torpedo-ship, and diverges to the left of its course. The efficiency of the torpedo depends upon the readiness and certainty with which it can be brought into contact with the hostile ship, and this is accomplished by duly arranging the course of the torpedo vessel, and by skilfully regulating the tow-line so as to obtain the requisite amount of divergence, and to cause the torpedo to strike at the proper depth. The tow-rope is wound on a reel, furnished with a powerful brake, the action of which will be readily understood by inspection of Fig. 116, 238which represents also a similar smaller reel for the line attached to the safety key. Leather straps, sprinkled with rosin to increase the friction, encircle the drums of the reels, and can be made to embrace them tightly by means of levers, so that the running out of the lines can be checked as quickly as may be desired. Handles are attached to the straps, so that they can be lifted off the drum when the line is being drawn in by working the handles. When the torpedo is ready for action and has been launched, a suitable length of tow-line, which is marked with knots every ten fathoms, is allowed to run off its reel, while the safety key-line is at the same time run off the small reel, care being taken to avoid fouling or such strains on the line as would prematurely withdraw the key. Fig. 106 will make clear the mode of controlling the lines, but it is not intended to represent the actual disposition in practice, where the men and the brakes would be placed under cover. On the left of the figure a starboard torpedo is about to be launched; on the right a port torpedo has been drawn under the ironclad and is in the act of exploding, the safety key having been withdrawn by winding in its line when the torpedo came into proximity to the attacked vessel.

Fig. 117.Harvey’s Torpedo.

Fig. 118.Harvey’s Torpedo.

Fig. 119.Official Trial of “Harvey’s Sea Torpedo,” February, 1870.

When the torpedo has been launched over the vessel’s side, the latter being in motion, the torpedo immediately diverges clear of the ship; and when the buoys have also reached the water, the men working the reels pay out the line steadily, occasionally checking the torpedo to keep it near the surface, but avoiding a sudden strain upon the slacked tow-rope, which would cause the torpedo to dive, and in shallow water this might lead to the injury or loss of the torpedo. The torpedo can be gradually veered out to the distance required, at the same time that the safety-key is so managed that sufficient strain may be put upon it to prevent it from forming a long 239bight astern of the torpedo, but avoiding such a strain as would break the yarn holding the safety-key in its place. The distance to which the tow-line may be paid will depend upon the circumstances of the attack. More than 50 fathoms is, however, a disadvantage, as the long bight of tow-lines makes the torpedo drag astern. The torpedo can always be made to dive several feet below the surface by suddenly letting out two or three fathoms of tow-line. The torpedo vessel should, of course, be a steamer of 240considerable speed—able to outstrip when necessary all her antagonists, and, as a rule, it is found best to make the attack at night. Let us imagine two ships of war at anchor, and parallel to each other at perhaps a distance of 60 fathoms; and suppose that, under cover of darkness, a hostile torpedo vessel boldly steams up between them, having launched both its starboard and port torpedoes. In such a case neither ship could fire at the torpedo vessel for fear of injuring the other, while the torpedo vessel would in all probability succeed in bringing its floating mines into contact with both its enemies.

Fig. 120.Model of Submarine Guns.

Another device for submarine attacks upon vessels on which much ingenuity has been expended is the submarine gun. It has been sought to propel missiles beneath the surface of the water, these missiles being usually provided with a charge which, on contact with the vessel’s side, would explode, and by making a hole below the water-line, cause the certain destruction of the ship. It is obvious that such a mode of attack would reach the only vulnerable parts of a thickly-plated ironclad, and therefore the project has been recently revived in several forms. Fig. 120 is taken from the photograph of a model of an invention of this kind. The guns which are to propel the submarine projectiles, have port-holes formed by valves in such a manner that the gun when loaded can be run out without allowing water to enter; it can then be fired while the muzzle is below the surface, and again drawn in without the port being at any time so opened that water can pour into the vessel. All contrivances of this kind have hitherto been failures; indeed, it does not appear possible that they could succeed, except at very close quarters, for the resistance offered by water to a body moving rapidly in it is extremely great, and, as we have already had occasion to state, the resistance increases as the square of the velocity, and probably in even a higher degree for very great velocities. Any one who will remember the effort it 241requires to move one’s hand quickly backwards and forwards through water will easily understand that the resistance it presents would, in a comparatively short space, check the speed of a projectile, however great that speed might be at first. A good many years ago Mr. Warner produced a great sensation by an invention which appears to have been essentially a floating torpedo. The cut below, Fig. 121, represents the result of an experiment publicly made by him off Brighton, in 1844, upon a barque, which was towed out by a steamer to a distance of a mile and a half from the shore. Mr. Warner was on board the steamer, and the barque was 300 yards astern. Five minutes after a signal had been made from the shore, the torpedo was caused to explode, striking the barque amidships, throwing up a large column of water and débris, shooting the mainmast clean out of the vessel, the mizen going by the board, and dividing the hull into two parts, so that she sank immediately. Yet this invention, though apparently so successful, does not seem to have ever been put in practice.

Fig. 121.The Warner Experiment off Brighton.

The stationary torpedoes of the kind mostly used in the American Civil War were, as already stated, self-acting; that is, they exploded when touched by a passing vessel. They would now be more generally called self-acting mines, and are to be distinguished from that form of the weapon in which the explosion is determined by some manipulation on shore, such as the closing of an electric circuit, when the hostile vessel comes within the area of destructive action. This form receives the name of observation mines. Stationary mines are essentially instruments of defence, and as such are employed for the protection of rivers and harbours. The self-acting varieties usually contain a charge of 70 lbs. to 24280 lbs. of gun-cotton, and are commonly arranged in lines. Of course, when the occasion for which such mines have been laid down is past, they must be removed, and the operation of picking them up is one of great danger. The observation mines, on the other hand, do not require immediate removal, and they can be taken up with little risk. In the British service the observation mine contains about 500 lbs. of gun-cotton, and a line of these is sometimes moored in a water-way, from 35 feet to 50 feet below the surface. The area of destructive action in this case is a circle of about 30 feet radius, and therefore a line of seven such mines laid across a channel at intervals of 120 feet apart would ensure the almost certain destruction of any war vessel of ordinary breadth that might attempt to pass up a river of 840 feet in width. This is about the distance across the Thames near the Tower of London, but the depth of the river there being only 12 feet at low-water and 33 feet at high-water, would not suffice to give effect to the full energy of so large a charge of gun-cotton; for it has been found that, for a given charge, there is a certain depth under water at which its explosion will produce the maximum effect, and this depth will be greater with heavier charges than with light ones. The regulation “observation mine” of the British service has a cylindrical case of stout plate-iron, 32 inches in diameter and 34 inches high, with domed ends. Within this gun-cotton is contained, in a wet condition, in a number of copper envelopes, which have holes for access of water to wet the charge from time to time as occasion requires, the wet condition being the safest for the carriage of gun-cotton. The centre of the case is a tin charged with some discs of dry gun-cotton, and the detonator required to bring about the explosion of the whole charge when the electrical contact is made, fires the fuze contained within the primer. These cases are arranged to have a certain buoyancy, and are moored with wire ropes to heavy iron sinkers, the mooring ropes being of such length as to keep the explosive case at the proper depth below the surface, and of sufficient strength to resist the force of the currents in the waterway. There is also another type of submarine mine, operated by an electric current, the circuit of which is closed by contact of a passing vessel, if at the time a battery on shore is included in the circuit. In this way the mines can be made harmless or dangerous for passing vessels at the will of the operator on shore. The passing vessel is made to complete the circuit by tilting over the cylindrical case so far that some mercury contained in a small part of it is upset, and makes the requisite metallic contact. This arrangement is known as the electro-contact mine.

In former pages of this article on torpedoes will be found representations of the effects produced by Whitehead’s torpedo, which, being automobile and travelling altogether under the surface of the water, was capable of being made a very formidable weapon of offence. When the earlier editions of this work were going through the press, it was understood that the Whitehead torpedo left much to be desired as regards speed, certainty of direction through the water, and perhaps in other points, the inventor being constantly engaged in effecting improvements. At that time particular pains were taken to keep secret the nature of the most important parts of the internal mechanism. The work of construction was carried on in a room with locked doors, blocked-out windows, and a military guard outside. The earlier experimental forms of this automobile torpedo were constructed in complete secrecy by the inventor himself, with the help of only one trusted, skilled mechanic and a boy, 243who was no other than Mr. Whitehead’s own son. The history of the invention is very interesting, and exemplifies the power of skill and perseverance to overcome a multitude of difficulties, the result being a machine which is simply a marvel of ingenuity and of delicate nicety of adaptation.

The first notion of the automobile torpedo appears to have occurred to an Austrian naval officer; but it took rather the form of a small vessel containing within itself some propelling power by which it could move along the surface of the water, its course being directed by ropes or guiding lines from the shore or from a ship. The fore part of the little vessel was to hold an explosive, to be fired automatically by the self-propelled torpedo coming into contact with the side of the hostile vessel. The propelling power, as first suggested, was clockwork, if that could be made efficient, or steam as an alternative. The Austrian authorities, however, considered that it would be impracticable to direct the course of the torpedo in the manner proposed, and that there were also great objections to each of the methods of obtaining motive power. The assistance of a thoroughly competent and skilful mechanician was then sought, and Mr. Whitehead, at that time the director of an engineering establishment at Fiume, devoted himself to solving the problem of devising a torpedo which should be able to travel beneath the surface of the water, and, when once started, should require no external guidance to keep it on its proper course. After some years of experimental labours, Mr. Whitehead produced the first form of the weapon with which his name is associated, but to this he has since added from time to time many ingenious improvements. A committee of experts having been appointed by the Austrian Government to test the capabilities of the new invention, it was made the subject of a long series of trials, after which the committee recommended its immediate adoption in the Austrian navy. The earlier form of the Whitehead torpedo had, however, the defect already mentioned, of being sometimes very erratic in its course; its speed was small (6 knots) compared with that of the more recent patterns (30 knots), and its range of travel proportionately less. The British Admiralty having invited Mr. Whitehead to visit England with some specimens of his invention, a committee was appointed to make complete trials of the capabilities of two weapons he had brought with him. Although by this time great improvements had been made on the original design, and in particular, Mr. Whitehead had almost completely overcome the difficulty of keeping the torpedo at a uniform depth during its course, by means of delicate adjustments in what we may call the steering chamber (to be presently mentioned), much remained to be accomplished before the weapon attained the perfection of the modern patterns. Indeed, the inventor may be said to have from time to time redesigned his contrivances, as when in 1876 the speed was increased to 18 knots, and again in 1884 more powerful engines brought up the speed to 24 knots. Further improvements have been made by Mr. Whitehead, who designed a new form of the weapon in 1889, and some of the more recent patterns can now show a speed of 30 knots or more. The committee appointed by the Admiralty to conduct experiments with the first pair of torpedoes brought to England, after having tested them in various ways for a period extending over six months, reported that they believed that “any maritime nation failing to provide itself with submarine locomotive torpedoes, would be neglecting a great source of power, both for offence and defence.” 244Upon this recommendation the Admiralty immediately purchased from Mr. Whitehead for £15,000 the secret of the internal mechanism of his invention and the rights of manufacturing it. The self-adjusting apparatus within the steering chamber, by means of which the torpedo was kept at its due depth, was then a jealously-guarded secret; but when the arrangement with Mr. Whitehead was effected, the Government immediately set about the manufacture of these torpedoes on a large scale. The artificers employed in making the Whitehead torpedoes were now numerous, and the internal structure of these weapons could not advantageously be altogether concealed from those who had to handle them on board of the ships, so that it inevitably happened that some details of their construction leaked out, and came into the possession of other powers, whereupon all the maritime states followed the example of Great Britain by providing their navies with Whitehead or some such form of locomotive torpedo. It is no part of our plan to enter into the mechanical minutiæ of the Whitehead torpedo. We may, however, give the reader such an idea of the external appearance and internal arrangement of the Whitehead torpedo as will enable him to appreciate to some extent the ingenuity and skill that have been brought to bear upon its construction.

There are in existence many different patterns of the weapon—twenty-four, it is said—and this is what might be expected from the fact of its being produced at several different manufactories, each striving to effect whatever improvements its resources will supply. Some torpedoes have been made at Fiume, very many at Mr. Whitehead’s works at Portland, as also at the Government establishment at Woolwich, while private enterprise in this direction is encouraged by contracts with some private firms, such as that of Messrs. Greenwood & Bately at Leeds. The greatest diameter of the large torpedo is 18 inches, but in some it is rather more, in others 14 inches or 16 inches; and the length may vary between 14 feet and 19 feet. Many of our Whitehead torpedoes are made of polished steel, but in the later patterns phosphor-bronze is partly made use of, as being not liable to corrode. The interior of the torpedo is divided by transverse partitions into five distinct compartments. The foremost of these, called the “head,” contains the explosive charge when the weapon is ready for use in actual warfare. This section, which may occupy about one-sixth of the total length, is an air-tight case made of phosphor-bronze, one-sixteenth of an inch thick, and it is kept permanently charged with slabs of wet gun-cotton, which may amount to 200 pounds weight in all, and is ready to be attached by a screw and bayonet joint to the body of the torpedo; but this is done only at the time immediately before it is required for its destructive employment. Its place at other times, as when the torpedo is used for drill practice, and to test its running powers, is occupied by a dummy head of steel, of exactly the same shape and size, and packed with wood in such a manner that its weight and centre of gravity are like those of the explosive head when the latter is ready for action. The wet gun-cotton requires a detonative explosive of dry material close to it, in order to determine its own detonation. The explosive heads of the Whitehead are not fitted with the pistol and priming tube until all is ready for the discharge of the weapon, as this would render the handling of the torpedo highly dangerous. This priming apparatus is merely a metallic tube that slips into a corresponding hollow in the explosive head so far as to reach well within the wet gun-cotton 245charge, although still separated from the latter by a metal casing. The posterior extremity of the priming tube contains a few ounces of dry gun-cotton, and just in front of this is a copper cap containing some fulminate of mercury, which readily explodes when struck by the point of a steel rod, occupying the centre of the tube and projecting a short distance out at the “nose” of the torpedo, so as to be driven inwards by the impact of the latter on a ship’s side. The explosion of the fulminate causes the detonation of the dry gun-cotton at the bottom of the priming tube, and this is taken up by the whole mass of the explosive with destructive effect. The danger of premature or accidental explosion by anything coming in contact with the projecting striker is obviated by several checks which prevent any chance blow driving the rod home against the fulminate charge. The anterior projecting end of the rod has a screw thread worked upon it, and on this turns freely a nut provided with wings like a small fan, revolving in such a manner that as the torpedo is moved through the water, the nut is spun off, and the striker is free to be driven back, except in so far as it is still retained by a small copper pin, the breaking of which requires a considerable blow. Again, the little fan above mentioned cannot begin to spin off the rod until another pin or wedge has been withdrawn, which operation is performed just before launching the weapon.

Immediately behind the exploding head of the torpedo is the air-chamber, which occupies a considerable space in the length, i.e., about one-third of the whole. This part is made of the toughest steel, nearly ⅓ of an inch thick, and contains the power actuating the motor, in the form of air forced into it by powerful pumps on board the ship, until the pressure reaches the enormous amount of 1,300 lbs. or more on the square inch, or, at least, this is what is made use of in the newer patterns when charged for action. In the largest size of the weapon the weight of air injected may be more than 60 lbs., and, of course, considerably detracts from the buoyancy of this part.

Behind the air-chamber comes another much shorter compartment we have called the “steering chamber,” in which are contained the most ingenious and delicate parts of the apparatus, namely, the mechanism by which this extraordinary artificial fish adjusts itself, after the manner of a living thing, to the required conditions. Among other contrivances, it contains several valves controlling the action of the compressed air on the engines, etc. The enormous pressure to which the air-chamber is charged, if allowed to act unchecked, would give at first a power almost sufficient to shatter the machinery, and, in order to prevent this, a “reducing valve” is interposed so that only a moderate and uniform pressure of air is allowed to act upon the engines. Then there is the “starting valve” by which the air is admitted or cut off from the engines, and still another valve which is contrived to delay the action of the compressed air for the short interval during which the torpedo is passing from the discharging tube until it enters the water. For during this interval the propellers not having to act against the water, but only against the resistance of the atmosphere, would be whirled round at an enormous speed, and the machinery would sustain such shocks and strains as might endanger the whole apparatus. It is to prevent this that the “delay action valve” is provided.

The automatic apparatus by which the torpedo’s course is regulated is a very remarkable part of the invention, and it admits of the nicest adjustments. 246This was the crown of Mr. Whitehead’s ingenuity, but the details were, by an arrangement between the government and the inventor, not to be made public, though necessarily communicated to certain officers in the service, and known to the chief artisans employed in their fabrication. These persons are all, we believe, required to give pledges not to divulge the arrangement of particular parts. But such details could scarcely be made intelligible, even should they be interesting, to the general reader. The principles upon which the controlling apparatus are arranged may, however, be comprehended without difficulty.

The tail of the torpedo is provided with two rudders, one in its central vertical plane, and the other in its central horizontal plane. Their action in directing the torpedo’s course is exactly that which the tail supplies to a fish, or the rudder to a boat. Suppose that while the torpedo is passing through the water the vertical rudder is by any means turned towards one side, the course of the metallic fish will be diverted towards that side; or again, a turning upwards of the horizontal rudder would have the effect of directing the nose towards the surface, and would make the torpedo rise, and so on. Now the positions of the horizontal rudder are regulated from the “steering chamber,” in which a heavy weight is suspended like a pendulum, so as to be capable of swinging fore and aft. This pendulous weight actuates the horizontal rudder through a system of rods and levers, so that when it hangs vertically the horizontal rudder is level, but if from any cause the nose of the torpedo were directed downwards, the pendulous weight would come to a more forward position in the steering chamber, and would raise the rudder, and thus turn the nose towards the surface until the original horizontal position were regained. In the contrary case, of course, the reverse action would take place. But the torpedo, while preserving a horizontal position, might tend to sink to too great a depth, or rise too near the surface, and this is prevented by another adjustment, namely, a piston receiving the pressure of the water, which, on the other side, is opposed by a spring. If the torpedo sinks a little the pressure increases, the piston, which moves with perfect freedom without allowing water to pass in, is forced inwards, and its movement is communicated to the same levers that connect the pendulous weight with the horizontal rudder, the latter is raised, and then the nose of the torpedo is directed upwards, and it consequently approaches the surface again. In the contrary case the spring, relieved from some of the external pressure, operates the levers in the other direction.

The compartment immediately behind the “steering chamber” contains the engines which are of the Brotherhood type, provided with three single acting cylinders. The three-fold throw prevents any possibility of the engine getting on a “dead point.” Though this compartment is the shortest in the torpedo, the engines in the larger sizes are capable of indicating as much as thirty horse power. It has for simplicity been stated above that the pendulous weight and the balanced piston act by means of rods on the horizontal rudder; this was so in the early patterns of the torpedo, but it was soon found that they did not do so with sufficient steadiness and promptitude, and the force they could apply was in the larger and swifter forms quite ineffective. Nowadays the engine compartment always contains a little piece of apparatus which is an arrangement of cylinder and piston, upon which the compressed air acts in one or the other direction according to the way its slide-valve is moved. It is this slide-valve that the rods from the “steering chamber” move, and allow 247the force of the compressed air to turn the rudder up or down. This auxiliary apparatus has the same relation to the torpedo rudder that the steam-steering apparatus of a large vessel has to its rudder. Although it is only about a few inches long, its power and delicacy are such that the pressure of half an ounce on its slide admits to its piston a force equal to 160 lbs., and its introduction has given the torpedo the power of steadily steering itself.

Behind the engine compartment, but completely shut off from it, is another almost empty division occupying a considerable part of the length of the torpedo, and known as the “buoyancy chamber.” But it contains, attached to the bottom of it, a certain amount of ballasting, so adjusted to balance the weights of the other parts that the whole floats horizontally, and at the same time preserving the tube in one vertical position as regards its transverse diameter, i.e., so that the horizontal rudder is always horizontal. The shaft from the engine passes through this compartment, as also the rod from the small motor that moves the horizontal rudder. These, of course, pass through water-tight bearings.

At the tail of the torpedo, behind the rudders, are two three-bladed screw propellers, of which the anterior one is mounted on a tubular shaft having a common axis with the other, but made to revolve in the opposite direction by means of a bevel wheel mounted on each independent shaft, with a third such wheel connecting them. The object of the double screw is to obviate “slip,” that is, ineffective motion of the blades through the water, and by this means the full power of the engines can be developed; while any tendency to deviation to right or left, due to the rotation, is reduced to a minimum. We have spoken of one horizontal and one vertical rudder, although externally there appear to be two of each kind, right and left, above and below, on the tail of the torpedo. These pairs, however, are so connected as to be always in the same respective planes. The controlling mechanism acting in two different ways on the horizontal rudder has been already indicated, but nothing has yet been said about the vertical rudder. It is not moveable by anything within the torpedo, but is commonly fixed by clamping screws in or about the same vertical plane as the axis of the torpedo, and it performs the same function as a kind of back fin, which, in the earlier forms, extended nearly the whole length of the tube; and that is obviating any tendency of the torpedo to roll about its axis. The vertical rudder can also be fixed at a considerable inclination to the axis should occasion require, and the effect of that would be to cause the torpedo to pursue a circular course of greater or less radius, according to the less or greater degree of inclination. Very rarely, however, would this be required, and the vertical rudder may be considered as fixed in the axial plane, or having such slight inclination as may, on trial, have been found necessary to counteract any tendency to lateral deviation.

There are several different methods for discharging the Whitehead torpedoes from ships. They may be sent from a tube below the water-line, but the arrangements for that purpose are complicated and difficult to manage, while, on the other hand, the launch of the weapon is not perceived by the enemy, and it is at the same time out of the reach of any blow from a hostile missile while yet in its discharging tube. More commonly the discharging tube is arranged above the water-level. On regular torpedo boats, the tubes are sometimes mounted on pairs upon a revolving table, provided with many nice adjustments, and even the 248single above-water torpedo tube, as used between decks, is an apparatus having somewhat complicated appliances. The torpedo is expelled from the tube now preferably by a small charge of cordite. But in the Royal Navy no fewer than some twenty different patterns of torpedo tubes have been in use for the various sizes of torpedoes. In some of these, compressed air, in others gunpowder or cordite, in others, again, mechanical impulse propels the torpedo into its element. It would obviously be impossible within our limits to enter into details of these various constructions, or to attempt descriptions of all the ingenious contrivances applied to the torpedo itself, or to give an account of the means of defence against mines and torpedoes, this last being a matter belonging to naval tactics. The adoption of the torpedo as a naval weapon has given rise to special types of boats adapted for its employment, and these again have required other boats to destroy them (“torpedo-boat destroyers” or “catchers”). Light draught and high speed were desired in these last; but in many cases the intended speed was inferior to that of the torpedo boats that were to be caught.

The following particulars about the British torpedo-boat destroyer Daring may be compared with those given of the cruiser Majestic. The Daring is 185 feet long, 7 broad, and she draws only 7 feet of water. Her speed is about 28½ knots per hour, with a steam pressure in the boilers of 200 lbs. per square inch, and an air pressure in the stoke-holds equivalent to 3 inches of water (forced draught.)

The importance attached to the prospective use in war of the automobile torpedo may be shown by the fact that at the end of 1890 the number of torpedo boats built or laid down for England was 206, and for France 210, while other nations followed with numbers proportionate to their means. Forty “torpedo-boat destroyers” were in building for the British Navy towards the close of the year 1896, and now (March, 1897) it is announced that the number of torpedo boats and torpedo-boat destroyers in the French Navy is to be increased by 175.

249

Fig. 122.M. Ferdinand de Lesseps.

SHIP CANALS.

Artificial canals are amongst the oldest of inventions, for, centuries ago, they have been constructed, even of very large dimensions, in various parts of the world. There is in China, for instance, a great canal, 900 miles in length and 200 feet broad, which is supposed to have been made 800 years ago. The advantages of canals did not escape the attention of the Egyptians, Greeks and Romans. We read of very early attempts to cut through isthmuses, in order to form a water communication between regions where other carriage would be long and difficult. It appears to be admitted that canals connecting the Red Sea with the Mediterranean existed some centuries before the Christian era, and to cut the Isthmus of Corinth by a waterway was a cherished project with several Roman Emperors, and now it appears that in this nineteenth century this project will shortly be realized. But as the canal-lock is but a comparatively modern invention, dating only from the fourteenth century, and first used in Holland, all the canals anterior to that period had to be designed as level cuts, a restriction which greatly increased the difficulties of the problem. Canals were in use in various parts of Europe, 250particularly in Holland and France, long before any were constructed in England, as, for example, the Languedoc Canal, which, by a cut of 150 miles, connects the Bay of Biscay with the Mediterranean. It is 60 feet broad, and attains, at its highest level, an elevation of 600 feet above the sea. The canal system in England was first introduced in the middle of the eighteenth century, and soon afterwards, the Duke of Bridgewater engaged the famous Brindley to construct a canal, connecting his collieries at Worsley with Manchester, about seven miles distant, and afterwards extended his scheme, so as to open up a more direct water communication between Manchester and Liverpool. Before the making of this canal, the cost of the carriage of goods between these towns had been forty shillings per ton by land, and twelve shillings by water. After that, they were conveyed with regularity for six shillings per ton. The system was soon extended, so as to connect the Trent with the Mersey, and the boldness of both the projectors and their engineer in carrying out this scheme is memorable in the history of such undertakings. Brindley was equal to the task of coping with the difficulty of carrying his canal over what had hitherto been supposed an insuperable obstacle, for he pierced Harecastle Hill with a tunnel more than a mile and a half in length—a then unheard of piece of engineering—to say nothing of several shorter tunnels, many aqueducts, and scores of locks. The Duke of Bridgewater, who at one period had been unable to raise £500 on his own bond for the prosecution of his scheme, died in 1803, in receipt of a princely income from the profits of his useful undertaking. For its creation, he had, however, denied himself the present enjoyments of his patrimonial revenue, by reducing his expenses at one period to the modest sum of £400 per annum. Before his death, the Duke, for taxation purposes, estimated his income at £110,000 per annum. Before the railway system was fully established a network of canals had united the most populous places in England, the total length of the waterways being not much less than two thousand miles. With the rise of railways the importance of canals as channels for the conveyance of merchandise declined. But, nevertheless, in consequence of the continued increase of traffic and the great cheapness with which goods can be carried by water, canals are often able to compete with railways in the carriage of bulky or heavy goods when speed of transit is not an object. The English canals have, therefore, never been disused or abandoned, notwithstanding the ubiquitous ramifications of the railway lines. Nay, the value of the Bridgewater Canal system, about to be superseded so far as concerns the communication between Liverpool and Manchester by the greater scheme we have presently to describe, is such that £1,710,000 is now required for its purchase; and that is the value in spite of four lines of railway connecting those great towns, and all competing for the carriage of goods. In these canals, designed for inland communication only, the navigation is confined to boats or barges of very insignificant dimensions compared with the sea-going ships that some great modern canals are constructed to receive.

To the present century belongs the famous “Caledonian Canal,” as the waterway is often called that extends in a straight line for more than 60 miles across Scotland, in north-east and south-west directions. The canal work here was commenced in 1802, under the direction of Telford, and though it was opened for traffic in 1822, the work as it now exists was not completed until 1847. But the length of the actual canal 251construction in this case did not much exceed 23 miles, for a natural waterway, navigable for ships of any burden, is formed by the series of narrow lakes that fill what is called the “Great Glen of the Highlands.” This glen has many of the characteristics of a great artificial ditch: its highest point is only 90 feet above the tide level in Loch Linnhe; a circumstance not a little remarkable in so mountainous a country. What is also remarkable is the great depth of these lakes, which in some places exceeds 900 feet. The banks also are generally very steep, and indeed at one time it was impracticable to pass along the shores of Loch Ness, the longest of the lakes. But there are now good roads along both banks. Although the ground traversed by the artificial channels of the Caledonian Canal is chiefly alluvial, the cost of the undertaking proved to be great, amounting, it is said, to about one and a quarter million pounds sterling. Indeed, had it not been for the introduction of steam navigation before the completion of the work, and the consequent increase and facility of water conveyance, it is doubtful whether the utility of this canal would have been commensurate with its cost, or its receipts have made any profit for its promoters. By the Caledonian Canal large steamers and other vessels may pass from sea to sea, and in the summer time the steamers that traverse it are crowded with tourists attracted by the magnificent scenery it presents throughout the greater part of its length.

But whatever had previously been done in canal construction was surpassed in enterprise and importance by Lesseps’ great work in Egypt.

THE SUEZ CANAL.

As we have already seen, the idea of opening a waterway between the Red Sea and the Mediterranean is by no means a product of the present century. The ancient Egyptians do not appear to have cut directly through the Isthmus, but Herodotus describes a canal made by Necho about the year 600 B.C., from Suez through the Bitter Lakes to Lake Timsah and then westward to Bubastis on the Nile. He mentions certain water gates, and states that vessels took four days in sailing through. This canal became silted up with sand ages ago, but it was cleared out again and re-opened in the seventh century of our era by the Caliph Omar, and traces of it are still visible. According to some recent discoveries in the chief archives of Venice, as early as the end of the fifteenth century, when Vasco da Gama had discovered the Cape of Good Hope, and the Portuguese took that new route to India, hitherto the exclusive property of the Venetian and Genoese merchants, a re-cutting of the Isthmus of Suez was thought of. Plans were prepared and embassies sent to Egypt for paving the way for the accomplishment of this great enterprise, which, it is said, was only foiled by the persistent opposition of some patricians, who were probably bribed by foreign gold to prevent the execution of the plan. One of our Elizabethan poets, Christopher Marlowe, appears, in the following lines, to have anticipated M. de Lesseps:—

“Thence marched I into Egypt and Arabia,
And here, not far from Alexandria,
Whereat the Terrene and the Red Sea meet,
Being distant less than full a hundred leagues.
I meant to cut a channel to them both,
That men might quickly sail to India.”

252For at that period travellers going to India in the famous sailing ships, called “East Indiamen,” were obliged to sail round the Cape of Good Hope and pass from the Southern to the Indian Ocean. The reader who wishes to understand the importance of the Suez Canal should look at the map of the Eastern Hemisphere, where he will have no difficulty in finding the position of the vast continent of Africa, which is washed on the north by the Mediterranean Sea, on the west by the Atlantic, on the south by the Southern Ocean, and on the east and north-east by the Indian Ocean and the Red Sea. If he now traces the waterway round Africa, on coming to the head of the Red Sea he will find the only interruption of the oceanic continuity in the narrow neck of land called the Isthmus of Suez. But for this, ships might long ago have made complete circuits round this vast, and, even as yet, but partially explored continent. The circuit would, indeed, be a great one of some 15,000 miles; but the barrier that the Isthmus presented to inter-oceanic communication between the eastern and the western worlds was a piece of physical geography which has undoubtedly been a most important factor in determining the course of history. It has been said that had there existed at Suez a strait like that of Gibraltar or that of Messina, instead of a sandy isthmus, the achievements of Diaz, Vasco da Gama, and Columbus would have lost much of their significance; but the advantages to the world’s commerce would have been incalculable, and the progress of the race might have been more rapid.

The Emperor Napoleon I. had the idea of restoring the old canal; but it was only when steam navigation had taken its place on the seas that the scheme was looked upon as offering any chance of financial success. But General Chesney, who made some surveys for the French Government in 1830, had come to the conclusion that there was a considerable difference of level between the two seas—a difference, he calculated, of about 30 feet. The existence of such a state of things would, of course, have been very unfavourable for the undertaking; but the General’s supposition was soon proved to have been erroneous.

The suggestion of carrying out the project of constructing a ship canal through the Isthmus was seriously revived by Père Enfantin, the St. Simonian, in the year 1833. He then induced M. Ferdinand Lesseps, the French vice-consul, and Mehemet Ali, the Pasha of Egypt, to take some practical measures towards its accomplishment. Surveys were made, but owing to the breaking out of a plague, and to other causes, not much more was heard of the scheme till 1845. In 1846 La Société d’Etude du Canal de Suez was formed, and among those who turned their attention to the subject was Robert Stephenson. His report was wholly unfavourable to the enterprise. He recommended the construction of a railway through Egypt, and a line was accordingly made between Alexandria and Suez. But, notwithstanding the opinion of Mr. Stephenson, M. Lesseps persevered with wonderful energy, believing, on the report of other engineers, that the scheme could be successfully carried out. It is right, however, to state that Mr. Stephenson did not say it was impossible to complete the Suez Canal—he merely gave it as his opinion that the cost of making the canal, and keeping it in a proper state for navigation, would be so great that the scheme would not pay. However, in 1854, the Viceroy of Egypt signed the concession, and in 1860 the work was actually commenced, but not on a plan that was advocated by the English engineers of making the canal 25 feet above the sea level. 253There were also some political and financial difficulties to be overcome. The Suez Canal Company, it was said, had expended twelve millions of money in what was considered to be chiefly shifting sands.

Fig. 123.The Sand-Glass.

When the Suez Canal was projected, many prophesied evil to the undertaking, from the sand of the Desert being drifted by the wind into the canal, and others were apprehensive that where the canal was cut through the sand, the bottom would be pushed up by the pressure of the banks. They imagined that the sand would behave exactly like the ooze of a soft peat-bog, through which, when a trench has been cut, the bottom of the trench soon rises, for the soft matter has virtually the properties of a liquid: it acts, in fact, exactly like very thick treacle. Sand, however, is not possessed of liquid properties; it has a definite angle of repose, which is not the case with thin bog. This behaviour of sand is familiarly illustrated in the sand-glass, which the diagram Fig. 123, will recall to mind. It may be observed that the sand falling in a slender stream from the upper compartment is in the lower one heaped up in a little mound, the sides of which preserve a nearly constant inclination of about 30°. In this property it is distinctly different from peat-bog or such-like material, which has no definite angle of repose. It need hardly be said that all apprehensions as to the safety of the canal from the causes here alluded to have proved unfounded.

But if some English engineers appeared to oppose the project, another eminent one, Mr. Hawkshaw, certainly helped it on at a moment when the Viceroy of Egypt was losing confidence; and, had his opinion been adverse to the project reported upon, the Viceroy would certainly not have taken upon himself additional liability in connection with the undertaking, and the money expended up to that date would have been represented only by some huge mounds of sand and many shiploads of artificial stone, thrown into the bottom of the sea to make the harbour of Port Saïd. And that M. Lesseps appreciated the good offices of Mr. Hawkshaw is shown from the fact that, when he introduced that engineer to various distinguished persons, on the occasion of the opening of the canal, he said, “This is the gentleman to whom I owe the canal.” It cannot, therefore, be said of the English nation that they were jealous of the peaceful work of their French neighbours, or opposed it in any other sense but as a “non-paying” and apparently unprofitable scheme.

The Canal was opened in great state by Napoleon III.’s Empress Eugénie, in November, 1869, when a fleet of fifty vessels passed through, and the fact was thus officially announced in Paris:—“The canal has been traversed from end to end without hindrance, and the Imperial yacht, Aigle, after a splendid passage, now lies at her moorings in the Red Sea.

“Thus are realized the hopes which were entertained of this great undertaking—the joining of the two seas.

“The Government of the Emperor cannot but look with satisfaction upon the success of an enterprise which it has never ceased to encourage. A work like this, successfully accomplished in the face of so many 254obstacles, does honour to the energetic initiative of the French mind, and is a testimony to the progress of modern science.”

An Imperial decree was then issued, dated the 19th of November, appointing M. de Lesseps to the rank of Grand Cross of the Legion of Honour, in consideration of his services in piercing the Isthmus of Suez.

The Suez Canal is 88 geographical, or about 100 statute miles long: its average width is 25 yards, and the minimum depth, 26 feet. At intervals of five or six miles, the canal is widened, for a short space, to 50 yards, forming thus sidings (gares) where only vessels can pass each other. At these, therefore, a ship has often to wait until a file of perhaps twenty steamers, coming the other way, has passed. Occasionally a ship gets across, or “touches,” and then the canal is blocked for hours. So much inconvenience has been found from the restricted dimensions of the work, that in 1886 it was proposed to widen the canal, or, alternatively, to construct a second canal, and use the two like the lines of a railway, so that vessels would never have occasion to pass each other. The amount of traffic is very large, and has been steadily increasing. Thus, in 1874, the tonnage of the vessels passing through was 5,794,400 tons; in 1880, the tonnage was 8,183,313, and the receipts of the Company amounted to £2,309,218. In 1875, the British Government purchased, from the Khedive, £4,000,000 worth of shares.

Fig. 124.A Group of Egyptian Fellahs, and their Wives.

The Suez Canal is not so much a triumph of engineering as a monument of successful enterprise and determination on the part of its great promoter, M. Lesseps, in the face of great difficulties. According to the original programme, the canal was to have been constructed by forced labour, supplied by the Viceroy. The unhappy peasantry of the country, called “fellahs,” were compelled to give their labour for a miserable pittance of rice. No doubt, in ancient times, when forced labour was in use, every peasant might cheerfully work, because it was for the general benefit to bring sweet water from the Nile to other dry and thirsty places in Egypt; but to be obliged to work at a waterway of salt, which was only to be of 255use to foreigners who passed through the country, could not be expected of human beings, and therefore the carrying out of the work was not unaccompanied by cruelties of the nature attending slave labour in other lands. This was one of the reasons why the late Lord Palmerston opposed the canal scheme, for the kind hearted statesman bore in mind the loss of health and life occasioned to poor Egyptians by this mode of labour, and the more so because it had been originally proposed that one of the conditions on which the French Company was to take up the project should be the execution of the work by free labour. In consequence, no doubt, of representations from free countries, the Porte was induced to put a veto on the employment of forced labour, and everyone thought that this would be the deathblow to the completion of the canal: but M. Lesseps did not give way to despair, and he since stated that if he had depended on the labours of the fellahs only, the difficulties of the work never could have been surmounted; and that, in fact, the successful prosecution of the work was owing to his having turned his attention to the mechanical contrivances used for dredging on the Thames and the Clyde, from which he obtained better results in half the time and at half the cost.

Fig. 125.Dredges and Elevators at Work.

Fig. 126.Map of the Suez Canal.

The dredges used in the construction of the canal were of a new description. They were wonderful mechanical contrivances, and but for them the canal would not have been finished. They were not the contrivance of M. Lesseps, but of one of the contractors, a distinguished engineer, who received his technical education in France but his practical experience in England. The use of the dredging machines was prepared for by digging out a rough trough by spade work, and as soon as it had been dug to the depth of from six feet to twelve feet, the water was let in. After the water had been let in, the steam dredges were floated down the stream, moored along the bank, and set to work. The dredges were of two kinds. The great couloirs consisted of a long, broad, flat bottomed barge, on which stood a huge framework of wood, supporting an endless chain of heavy iron buckets. The chain was turned by steam, and the height of the axle was shifted from time to time, so that the empty buckets, as they revolved round and round, should always strike the bottom of the canal at a fixed angle. As they were dragged 256over the soil they scooped up a quantity of mud and sand and water, and as each bucket reached its highest point in the round, it discharged its contents into a long iron pipe which ran out at right angles to the barge. The further extremity of this pipe stretched for some yards beyond the bank of the canal, and therefore, when the dredging was going on, there was a constant stream of liquid mud pouring from the pipe’s mouth upon the shore, and thus raising the height of the embankment. When the hollow scooped out by the buckets had reached the required depth, the dredge was moved to another place, and the same process was repeated over and over again. These stationary dredges, however, though very effective, required much time in moving, and the lighter work of the canal was chiefly effected by movable dredges of a smaller size. These machines were of the same construction as those described; the only difference was that the mud raised by their agency was not poured directly on shore by pipes attached to the dredges, but was emptied in the first instance into large barges moored alongside the dredge. These barges were divided into compartments, each of which contained a railway truck, and when the barge was filled it steered away to the bank, where an elevator was fixed. The trucks, filled with mud were raised by a crane worked by steam power, and placed upon inclined rails, attached to the elevator, which sloped upwards at an angle of 45 degrees towards the bank. They were then drawn up the rails by an endless rope, and as each truck reached the end of the rails its side fell open, the mud was shot out upon the bank, and the empty truck returned by another set of rails to the platform on which the elevator was placed, and was thence lowered into the barge to which it belonged. As the elevator could unload and re-load a barge much faster than the dredges could fill it with mud, each elevator 257was fed by half a dozen dredges, and thus the mud raised from the canal by several dredges was carted away without difficulty at one and the same time. As these floating dredges were much easier to shift than those encumbered by the long couloir pipes, the work of excavating the bed went on much more rapidly. But in places where there was any great mass of earth or sand to be removed, the large couloirs could scoop out a given volume in a shorter time.

The traveller who wishes to see the canal should go to France, and, embarking at the port of Marseilles, cross the Mediterranean Sea, and steam to Port Saïd, which is about 150 miles east of the port of Alexandria, where the isthmus is crossed by the railroad, and is used by travellers to India, being known as the “overland route.” And this railway conveys the mail to and from India, thus saving the great sea voyage round Africa and the Cape of Good Hope. Nevertheless, it involves two transhipments—from the steamer to the rail at Alexandria, and from the railway to the steamer at Suez.

Fig. 127.Port Saïd, the Mediterranean entrance to the Suez Canal.

Let us notice in order the places passed by the traveller in going from Port Saïd to Suez and the Red Sea. The arrow (Fig. 126) points in the direction of the compass, and shows that the canal runs very nearly from north to south. Port Saïd is the little town at the northern or Mediterranean entrance to the canal, situated on the flat sands at the entrance of the canal, and is built chiefly of wood, with straight wide streets and houses, and although it now contains several thousand inhabitants, before the making of the canal was begun one hundred people could hardly have been got together. The town contains nothing deserving of notice, and has a striking resemblance to the newly settled cities of America. But in it reside agents who represent numerous varied interests—administrative, financial, mercantile and political. It is provided with docks, basins, quays and warehouses, and has a harbour stretching out a couple of miles or so into the sea, for to that distance two piers, or rather breakwaters, run out.

258Fig. 128 shows these two converging breakwaters, which have been built out into the Mediterranean from the coast, the larger and more westerly one being one mile and a half long, the shorter about a mile and a quarter, and the distances between the two lighthouses erected on the extremities of the breakwater being half a mile.

The piers are made of concrete which was cast in blocks weighing 10 tons each. This composition has of late years been greatly approved by engineers where stone cannot be procured. The sea-face of the great canal in Holland is composed of a similar artificial stone, and it is found to bear the wear and tear of the waves almost, if not quite, as well as ordinary stone. It is stated that 25,000 blocks, each weighing 10 tons, were used. They were not laid with the regularity of ordinary masonry, but had been dropped from large barges, so that they presented a very rugged and uneven appearance (Fig. 129); but the object of throwing out these great bulwarks is for the purpose of preventing the sand brought down by the Nile silting in and closing up the canal. Along the western pier there is, from this cause, a constant settlement of sand, which was partially washed through the interstices left between the blocks of artificial stone, and might have given some trouble by forming sandbanks in the harbour; but this was prevented by the introduction of smaller stones, which could readily be carried out in boats at the low tide.

Fig. 128.Bird’s-eye View of Port Saïd.

Beginning with the Mediterranean Sea and Port Saïd, there is a run of 28 miles to Kantara, through Lake Menzaleh. Although called a lake, it is, in truth, nothing but a shallow lagoon or swamp, in which water-fowl of all kinds are very abundant, the great flocks of white pelicans and pink flamingoes being especially striking. The waters of this 259lagoon cover lands that once were fertile, and the salt sea-sands doubtless conceal the remains of many an ancient town.

Fig. 129.One of the Breakwaters at Port Saïd.

Of all portions of the undertaking, this one, M. Lesseps states, was the most arduous and difficult, though, at the time, it attracted the least attention. A trough had to be dredged out of the bed of the shallow lagoon, and on either side of this hollowed out space high sandbanks had to be erected, and the difficulty of making a solid foundation for these sand banks was found to be extreme. The difficulty, however, was surmounted, and such is the excellence of the work, that the water neither leaks out, nor does any of the brackish water of the lagoon infiltrate and undermine the great embankments.

Fig. 130.Lake Timsah and Ismaïlia.

At Kantara, the canal crosses the track of the highway between Cairo and Syria—a floating bridge carries the caravans across; and near this spot is stationed an Egyptian man-of-war, which supplies the police for the proper watch and ward of the canal. From Kantara to El Fendane is a distance of 15 miles—that is to say, to the southern extremity of Lake 260Ballah, where the canal still passes through sand embankments, raised within a mere. The lake is, however, almost dried up, and therefore the difficulties which had to be surmounted at Lake Menzaleh were not felt here.

The traveller may now be supposed to have arrived at Lake Timsah, where, no doubt, in the days of the Pharaohs, a lake existed. When taken in hand by M. Lesseps, it was a barren, sandy hollow, containing a few shallow pools, through which a man could easily wade, but now it is filled with the waters of the Mediterranean Sea. It is a pretty, inland, salt water lake, about three miles in width. On the northern shore stands the town, or, rather, small settlement of Ismaïlia, which is, in fact, the “half way house” where most of the officials of the Suez Canal Company resided, as they could get to either end of the canal with greater facility, or to Cairo by the railroad, which comes to this point, and continues, with the canal, to Suez.

Fig. 131.Railway Station at Ismaïlia.

When the canal was opened, in November, 1869, Ismaïlia was the scene of the most brilliant part of the opening ceremony, in which the French Empress Eugénie, the Empress of Austria, the Crown Prince of Prussia, and other distinguished personages took share. The Khedive built himself a summer palace, and M. Lesseps erected a villa, and the town was most artistically laid out, with every prospect of becoming a flourishing place. But the drainage had been so entirely overlooked, that it is said the sewage found its only outlet in the fresh water canal; and the consequence was fever broke out and so infected the town, that it was soon almost quite deserted. In 1882, Ismaïlia was once more the scene of bustle and activity, for here was the base of Sir Garnet Wolseley’s operations in his brilliant campaign against Arabi. The British Navy entered the canal, and took possession of Ismaïlia, where the army and the military stores were rapidly concentrated. From this place, Sir Garnet advanced along the route of the railway and the Sweet Water Canal, and, after storming the lines of Tel-el-Kebir, occupied Cairo, without further resistance, after a campaign of only three weeks’ duration.

From Lake Timsah to the Bitter Lakes the canal again passes for eight miles or so through the desert, where, by partial excavations by hand labour and subsequent flooding to admit the dredges, it was considered 261that a sufficiently deep channel could be made. The couloirs were set to work, when suddenly “a lion arose in their path” in the shape of a great rock, about 80 feet in length, and lying 12 feet only below the surface, and right in the middle of the main channel. If anything could show the indomitable energy of M. Lesseps it was his courage in dealing with this difficulty, and at a time when a few months only could elapse before the advertised day of the opening. He attacked the sunken rock with gunpowder. A large raft, or floor, supported on barges, was moored over the sunken rock, and from this men, armed with long poles shod with steel, drilled numerous holes, into which charges of gunpowder were placed, and fired in the usual manner by the electric battery. This temporary obstruction occurred opposite to the landing place at Sérápeum.

Fig. 132.The Viceroy of Egypt cutting the last embankment of the Reservoir of the Plain of Suez, to unite the two seas—the Mediterranean and the Red Sea.

Passing by Sérápeum, the traveller arrives at a vast expanse of water called the “Bitter Lakes,” because the dry sandy hollow formerly contained a marsh, or mere, of very brackish water. The possibility of keeping this great area filled with sea water had been denied by the opponents of the canal, who said the water would sink into the sand or be evaporated by the intense heat of the sun; but none of these prognostications have been verified, and it is now a great inland sea, far surpassing Lake Timsah, being 25 miles long and from six to seven miles wide. The only difficulty in filling this enormous natural basin arose from the rapidity and force with which the waters flowed in. This was done when the water at Suez was at low tide, and then subsequently the Red Sea was allowed to flow in. Though the expanse of water in the Bitter Lakes is great enough, the available channel is still narrow. But the steamers can proceed at full speed, as here there are no banks to be washed away.

Since the two seas have joined their waters, a strong current has set in from south to north, but there is no eddy or fall at the place where the 262waters meet. The tide runs up the canal with great force, and there is a difference of six or seven feet between high and low water: but the tide does not extend beyond the Bitter Lakes, where it is gradually diffused and lost. The colour of the current of water from Suez is said to be green, whilst that portion fed by the Mediterranean is blue. Since the Bitter Lakes have been filled the mean temperature of the districts on the banks has fallen 5° Centigrade. It is also stated that, although the canal swarms with sea fish they keep to their respective ends of the canal, as if the Mediterranean fish would not consort with those of the Red Sea, or, rather, make themselves at home in strange waters. There is also, perhaps, another cause, and that is the very bitter nature of the water at the northern end of the Bitter Lakes, which acts as a natural barrier, through which the fish may decline to pass.

The bed of the Bitter Lakes is the only portion of the canal’s course in which it was not necessary to make a cutting. Buoys are laid down to mark the best channel, but such is the width and depth of the water that vessels need not exactly keep within them. Quitting the Bitter Lakes we again enter the canal proper. In order to reach the vast docks which the Suez Canal Company has constructed on the western coast of the Red Sea, the canal is now quitted, and the vessel crosses the neck of the Red Sea. The Cairo and Alexandria Railway has been extended two miles, and is carried through the sea on an embankment, which lands the train close to the docks and quays of the canal, so that passengers by the overland route are able to embark from the train on board the steamer, and thus escape the troublesome transhipment of themselves and luggage.

THE MANCHESTER SHIP CANAL.

The project of constructing a ship canal to connect Manchester with the sea appears to have been started just before the railway era, but it was then abandoned, as the opening of the Liverpool and Manchester Canal brought about an immediate reduction in the rates of carriage. Perhaps it was the success of the Suez Canal which caused the revival of this scheme, in 1880, combined with the depression of the cotton trade at that period, when the Liverpool dock dues and the comparatively high railway rates proved a heavier tax than usual on the great Lancashire industry. The first definite steps were taken two years afterwards, when two plans were submitted for the selection of a committee. One scheme proposed to construct the canal without any locks; but, as Manchester is 60 feet above the sea level, there would, it was felt, be certain inconveniences in loading or unloading ships in a deep depression. The other plan was submitted by Mr. Leader Williams, a well known canal engineer, who proposed to take the canal from Runcorn, a distance of 20 miles, and making use of locks. When Parliament was applied to for powers authorizing the prosecution of the enterprise, there was, of course, much opposition offered by the various interests involved, and the inquires before the Committees of each House of Parliament were unusually protracted, for they extended in all to 175 days, and the cost to the promoters is said to have amounted to £150,000. Then, when the Bill had passed, it was found that the capital (£8,000,000) could not be raised owing to the financial depression, and partly also to some want of confidence in 264the soundness of the undertaking on the part of the Lancashire capitalists. But the promoters submitted the whole scheme to a representative committee, who should consider any possible objections. This committee reported (after sitting almost daily for five weeks) upon every point, and were unanimous in pronouncing the undertaking to be perfectly practicable and commercially sound. After this there was no difficulty in raising the required capital, which was subscribed by corporate bodies as well as private persons. The contract was let for £5,750,000, and the work was commenced in November, 1887, the contractor undertaking to have the canal completed and ready for traffic by January 1st, 1892.

Fig. 133.Western Portion.

Fig. 134.Eastern Portion.

Figs. 133 and 134.Map of the Manchester Ship Canal.

The Manchester Docks of this canal will cover an area of nearly 200 acres at the south-western suburb of that city, and from there the canal traverses the Valley of the Irwell, following, indeed, the general course of the river, but not its windings, so that the bed of the river is, in the distance of eight miles, or down to its junction with the Mersey, repeatedly crossed by the line of the canal. From the confluence of the rivers, the canal traverses the Valley of the Mersey, for this is the name retained by the combined streams. The course of the river, in its progress towards the sea, now makes wider bends, but the canal proceeds, by a slight and nearly uniform curve, to Latchford, near Warrington, passing to the south of which last named place it follows a straight line to Runcorn, which is at a distance of 23 miles from Manchester. Here it reaches what is now the estuary of the Mersey, but the embankments are continued along the southern shore to Eastham, where the terminal locks are placed. In this part of the canal, the engineer had difficulties to overcome of a different nature from those encountered in the upper part, where it was chiefly a matter of cutting across the ground intervening between the bends of the river, so as to form for its waters a new and direct channel everywhere of the requisite breadth and depth. But when Runcorn has been passed, and Weston Point rounded, there is the mouth of the River Weaver to be crossed, and this is marked by a great expanse of loose and shifting mud. Other affluents of the Mersey are dealt with by means of sluices, and in one instance the waters of a river are actually carried beneath the course of the canal by conduits of 12 feet in diameter. The total length of the canal from Manchester to the tidal locks at Eastham is 35 miles.

Fig. 135.A Cutting for the Manchester Ship Canal.

Fig. 136.Blasting Rocks for the Manchester Ship Canal.

The minimum width of the canal at the bottom is 120 feet, its depth 26 feet. But for several miles below Manchester this width will be increased, so that ships may be moored along the sides, and yet sufficient space left for the up and down lines of traffic in the middle. In this way, works and manufactories on the banks will be able to load and unload their cargoes at their own doors, and it may be expected that the advantages so offered will cause the banks of the canal to be much in request for the sites of works of all kinds. At the several places where the locks are placed there will be a smaller and a larger one, side by side, so that water shall not be needlessly used in passing a moderate sized vessel through the greater locks. As these last are 550 feet long and 60 feet wide, they are capable of receiving the largest ships, whilst the smaller locks are 300 feet long and 40 feet wide. Again, both the larger and the smaller are provided with gates in the middle, so that only half their length may be used when that is found sufficient. Coming down the canal from Manchester, the first set of locks will be at Barton, about three miles distance, just below the place where the Bridgewater Canal is carried across the Irwell, which 266is now to become the ship canal, by means of the aqueduct of 1760, by which Brindley became so famous. There is a story told about Brindley being desirous of satisfying the duke about the practicability of his plan, and requesting the confirmatory opinion of another engineer. When, however, this gentleman was taken to the place where it was proposed to construct the aqueduct, he shook his head, and said that he had often heard of castles in the air, but had never before been shown where any of them were to be erected. This aqueduct is about 600 feet long, and the central one of its three arches spans the river at a height of nearly 40 feet above the water. But the Manchester Ship Canal requires a clear headway of 75 feet, and Mr. Williams is going to replace the fixed stone structure by a swinging aqueduct, or trough of iron, which can be turned round, so as to give a clear passage for ships in his canal. This trough, or great iron box, will have gates at each end, and gates will be provided in the aqueduct at each side, so that no water will be lost when the water bridge is turned aside. But more than this; hydraulic lifts have been designed, so that, in a few minutes, vessels can be lowered from the Bridgewater Canal into the Manchester Canal, or raised from the latter into the former while still floating in water. The supply of water for the canal will be ample, as it has the rivers Irwell, Mersey and Bollin, with their tributary streams, to draw from. It should be mentioned that the terminal locks at Eastham will be of somewhat larger dimensions than those already referred to, and will be three in number. The largest, 267which is on the south or landward side, will be 600 feet by 80 feet, the middle one 350 feet by 50 feet, and the smallest one 150 feet by 30 feet. These three locks will be separated by concrete piers 30 feet wide, on which will be placed the hydraulic machinery for opening and closing the gates. Besides the ordinary gates, there will be provided for each lock at Eastham an outer pair of storm-gates that will be closed only in rough weather. These gates will shut from the outside against the lock sills, and, by resisting the force of wind and waves, will protect the ordinary tidal gates from being forced open. The lock gates throughout will be made of a wood obtained from British Guiana, and known as greenheart. This timber is the product of a large tree (Nectandra Rodiœi) belonging to the laurel family. It is a very heavy and close grained wood, the strength and endurance of which have been proved many years ago by its use in ship-building, etc., and some of the logs imported for the canal are remarkably fine specimens, being 22 inches square and 60 feet long. A pair of the largest gates weigh about 500 tons. The gates of the tidal locks at Eastham will all be open for half the time of each tide, when there will be a depth of water, above the sills, greater by 11 feet than that of any dock in Liverpool or Birkenhead.

Fig. 137.Manchester Ship Canal Works, Runcorn.

The way in which the difficulty is overcome of crossing the several busy lines of railway that intersect the course of the new canal, so that their traffic shall not be impeded, is one of special interest in this bold scheme. The London and North Western Railway crosses the Mersey 268at Runcorn by a bridge that leaves a clear headway of 75 feet at high water, and it was determined that this headway should be maintained in the bridges over the canal. The use of swing bridges on lines of railway over which trains are constantly passing being out of the question, it is necessary that the railways be carried over the canal at the required height. It is accordingly laid down in the Act of Parliament that before the Canal Company can cut the existing lines of railway it shall construct permanent bridges, and carry over them lines rising by gradients not exceeding 1 in 135, and not only so, but these deviation lines must be previously given up to the several railway companies for six months to be tried experimentally in that period for goods traffic. The cost of constructing these deviation lines, which, in all, will not be far short of 12 miles of new railway, will not be much less than £500,000. The traffic of the canal will probably have great feeders at certain points in the other canals and the railway lines that reach it. For instance, the Bridgewater Canal, now incorporated with the greater undertaking, will bring traffic from the Staffordshire potteries, the river Weaver brings salt laden barges from Cheshire, and at other points the railways will bring the produce of the excellent coal fields of South Yorkshire and South Lancashire, which will be automatically transferred from the waggons into ocean going steamships.

Fig. 137a.The French Steam Navvy.

Fig. 137b.—The English Steam Navvy.

Though the general notion of the construction of the canal as a deep, wide trench, or cutting following the course shown on the map, is sufficiently simple, the operation of carrying this into practice involves the exercise of great skill and ingenuity in dealing with mechanical 269obstacles. Man’s operations in the world consist but in changing the position of masses of matter; and the properties of matter—its inertia, cohesion, gravitation, etc., are the forces that oppose his efforts. The quantity of matter to be shifted in excavating this trench of thirty-five miles long across the country was no less than sixty millions of tons. The number of “navvies” employed at one time has been 15,000; but even this army of workmen would have made but slow progress with a cutting of this magnitude, had not the “strong shouldered steam” been also called into operation for scooping out the soil. The illustrations (Figs. 137a and #137b:fig137b) will show the arrangement of two forms of “steam navvies” that were much used on the works. One (Fig. 137a) is similar to the dredgers used for clearing mud out of rivers and canals: it consists of a series of scoops, or buckets, mounted on an endless chain, so as to scrape the material from an inclined embankment and tip it into waggons for removal. The other (Fig. 137b) may be compared to a gigantic ladle made to scrape against the face of a cutting in rising, and filling each time its bucket with nearly a ton of the material. It is most interesting to witness the perfect control which the man at the levers exercises over this machine, the movements of which he directs with as much precision as if he were handling a spoon. One of these steam navvies is able to 270fill 600 waggons or more—that is, to remove 3,000 tons of material—in one day; and as many as eighty of them have been simultaneously used on the Canal works. The value of the plant employed by the contractor is estimated at £700,000, and the length of temporary railway lines (see Fig. 137), for transport of the “spoil,” etc., is said to exceed 200 miles. There is a main line running through from one end of the canal to the other, and known to the workmen as the “Overland Route.” From this diverge numerous branches, some to the bottom of the excavations in progress, others to embankments down which is tipped out the “spoil,” as the dug out material is called; while others connecting with brickfields and quarries, or with existing canals and railway lines, serve to bring supplies of the materials used in the constructions. Some 150 locomotives are constantly at work on these temporary lines, and the coal consumed by them, and by the steam navvies, steam cranes, pumping engines, etc., is equivalent to about two train loads every day.

Though the Manchester Ship Canal is to be nearly twice as wide as the Suez Canal, its width for some miles below Manchester will be still greater, for there the banks will form long continuous wharves for the accommodation of the works and factories that are certain to be attracted to the spot. Indeed, so obvious are the advantages of ocean shipment, and so extensive the industries of South Lancashire, that it is not improbable the whole course of the canal may, in process of time, be lined with wharves, and the two great cities of Manchester and Liverpool may be united by a continuous track of dense population. Be that as it may, there seems every reason to believe that the undertaking will be a financial success. Calculation has shown that if the cotton alone that enters and leaves Manchester were carried by the canal at half the rates charged by the railways, there would result not only an annual saving of £456,000 to the cotton trade, but a clear profit to the canal company sufficient to pay more than 3 per cent. interest on its own capital. And, again, the railway and other local interests that have hitherto been opposed to this great enterprise can hardly fail to be in the long run benefited by the enlarged prosperity and increased general trade and manufactures it will develop. So that it will presently be found that there is room enough and work enough for both canal and railways.

The Manchester Ship Canal, so far from having been ready for traffic on the 1st January, 1892, was not completed until the end of 1893, and it was only on the 16th December, 1893, that the directors and their friends made the trial trip throughout its entire length, accomplishing the distance of 35½ miles in 5½ hours. The total cost of the canal was greatly in excess of the estimates, which placed it at eight million pounds, as fifteen millions is the sum actually expended upon it. With such a vast capital expenditure, it may be some time before the ordinary shareholders can look for dividends, especially as there has not been any sudden rush of traffic, such as many sanguine people expected. On the other hand, traffic is continuously and steadily increasing, and there is reason to believe that this great work will ultimately prove a commercial, as it has an engineering, success.

271

Fig. 137c.Sketch Map of The North Sea Canal.

THE NORTH SEA CANAL.

Like several other canals for sea going ships this last addition to the achievements of modern engineering is but the realisation of a project conceived at a long past period. The idea of a canal to connect the Baltic and the North Sea dates back into the Middle Ages, and indeed a short canal was constructed in 1389, which by uniting two secondary streams of the peninsula really did provide a waterway between the two seas. The inefficiency of this means of communication may be inferred from the fact of there having been proposed since that period no fewer than sixteen schemes of canalisation between these two seas, of which the recently completed North Sea Canal is the sixteenth, and it need hardly be said the greatest, so that in comparison with it the rest vanish into insignificance. The canal was commenced in 1887, and on the 20th of June, 1895, it was opened by the reigning Emperor of Germany, William II., with a very imposing naval pageant in which nearly a hundred ships of war from the great navies of the world took part. A glance at the accompanying sketch-map will show the great importance of this canal as a highway of commerce. The entrance to the Baltic has hitherto been round the peninsula of Denmark and through the narrow “belts” and “sounds” that divide the Danish Islands, a course beset with imminent perils to navigators, for the channels abound in rocks and dangerous reefs, to say nothing about the frequent storms and the impediments of ice floes. Yet as many as 35,000 vessels have lately had to take that course annually, these representing a total tonnage of no less than 20,000,000 tons. The figures speak for the magnitude of the Baltic shipping intercourse with the rest of the world; while the losses incurred 272in traversing these forbidding waters may be gathered from the statement that since 1858, nearly 3000 ships have been wrecked in them, and a greater number much damaged. Indeed, for large vessels, there is hardly a more dangerous piece of navigation in all Europe. The importance of this canal must not therefore be estimated solely by the saving of length in ships’ course, though that is great, as the map shows.

The North Sea Canal is 61 miles long, 200 ft. wide at the surface, 85 ft. wide at the bottom, and it will admit of vessels of 10,000 tons register passing through, the average time of transit being about twelve hours. The estimated cost of this undertaking was nearly eight and a quarter million pounds sterling, and about one-third of this sum was contributed by Germany, for whom the canal is of the greatest strategic importance in case of war, for her fighting ships need not then traverse foreign waters. The construction was therefore pushed forward with unusual energy, as many as 8,600 men having been engaged on the works at one time. An important naval station already exists at Kiel, the Baltic end of the canal, where there is a splendid harbour. The engineer and designer of this water-way is Herr Otto Baensch, who has devised much ingenious machinery in connection with the immense tidal locks at the extremities of the canal, and the swing bridges by which several lines of railway are carried across it. In the construction of this canal there were no vast engineering difficulties to be overcome, and hence striking feats of mountain excavation or valley bridging are not to be met with in its course, though in places there are some deep cuttings. The methods of excavating and of steam dredging that were made use of have already been illustrated in relation to the other works described in this article. The country through which the canal passes does not present any unusually picturesque features.

THE PANAMA AND NICARAGUA CANAL PROJECTS.

The several undertakings described in our chapter on Ship Canals are now all completed and in active operation, and but for financial mis-management and dishonest speculations, the same might probably have been said of another great project, the name of which was on everyone’s lips a short time ago, but in which public interest has lately waned; perhaps from a mistaken impression that the construction itself is involved in a common ruin with the fortunes of so many of its promoters, or that the scheme was frustrated by some unforeseen and insurmountable engineering difficulties. These assumptions have so little justification that it is quite probable that Lesseps’ last great project may yet be completed under more favourable auspices, and the Panama Canal unite the Atlantic and Pacific Oceans. The Panama Canal Company still exists, and possesses not only a very large part of the work almost quite finished, but 273all the extensive plant in perfect condition for resuming operations. The original scheme provided for a tidal water-way between the two oceans, without the intervention of a single lock. The canal was to be nearly 47 miles in length, 100 feet wide at the surface of the water, 72 feet wide at the bottom, and 29 feet deep. The entrances are at Colon on the Atlantic side, and at Panama on the Pacific. The latter is the eastern extremity, and the western one is on the Atlantic side, owing to the configuration of the isthmus which curves round the Panama Gulf that opens to the south. A railway crosses the isthmus between the points already named, and the route of the canal is laid down almost parallel with this railway, from which it is nowhere far distant. For the first 20 miles from the Atlantic side the land is only at a very moderate elevation above the sea-level, say 25 or 30 feet, but the next 11 miles is more hilly, the elevations reaching at some points 150 to 170 feet, but these are only for short distances. A few miles farther on, they rise still higher, until at Culebra the highest point is met with, about 323 feet above the sea-level, and a cut of this depth, 1,000 feet long, would be required. Through this highest part it has been proposed to drive a tunnel, but the total extent of the deep cutting at this part of the canal would be nearly 2 miles in length. This would no doubt be a work of the most formidable magnitude, for it has been calculated that no less than 24,000,000 cubic yards of material, consisting for the most part of solid rock, would have to be removed. It is not supposed, however, to offer any great difficulty in an engineering point of view. Doubtless it would be costly, and would take some time to accomplish. Another heavy piece of work would consist in constructions for controlling a mountain torrent called the Rio Chagres, through the valley of which the canal passes. This stream is very variable in the quantity of water it discharges, rising in the rainy season 45 feet above its ordinary level, and sending down forty times as much water as it does in the dry season.

Mr. Saabye, an American engineer, who examined unofficially the works of the Panama Canal in 1894, considers that about one half of the total excavation has already been done, and one half of the total length of the canal almost finished, and remaining in comparatively good condition. At both ends, including 15 miles on the Atlantic side, there is water 18 to 24 feet deep. “Besides the work already done, the Canal Company has on hand, distributed at both terminals, and at convenient points along the canal route, an immense stock of machinery, tools, dredges, barges, steamers, tug-boats, and materials for continued construction. At Panama, La Boca, and Colon, as well as along the canal, are numerous buildings—large and small—for offices, workshops, storehouses, and warehouses, and for lodging and boarding the men who were employed on the work. The finished work, as well as all the machinery, tools, materials, buildings, etc., are well taken care of and looked after. The Canal Company employs one hundred uniformed policemen, besides numerous watchmen, machinists, and others, whose sole duty consists in watching the canal and looking after needed repairs of plant and care of materials. In fact, the work and the whole plant is in such a condition, so far as I could ascertain, that renewed construction could be taken up and carried to a finish at any time it is desired to do so, after the Company’s finances will permit.”

An enormous amount of money has already been expended on the Panama Canal, and much of it lavishly and unnecessarily. A reorganised 274company may probably be able to form such estimates of the probable cost of completing the work under careful and efficient management, that financial confidence in it maybe restored. The canal not only already possesses the requisite plant, but the route has the special advantages of assistance in transport from the railway everywhere at but a short distance from it, and fine commodious harbours for its ocean mouths. If it were finished as originally designed, vessels could pass through it with one tide, say in about six hours. It is understood that before the Panama enterprise is again proceeded with, the Company think that a sum of about £25,000 should be expended in a complete survey and re-study of all the conditions, and the results submitted to the most eminent engineers.

A rival scheme for carrying a ship canal across the isthmus that divides the Atlantic and Pacific Oceans is that known as the Nicaragua Canal, as the proposed route is to cross Lake Nicaragua, an extensive sheet of water situated some 400 or 500 miles north-west of the Panama Canal. The lake is 110 miles long and 45 miles broad, and is on its western side separated from the Pacific by a strip of land only 12 miles wide, having at one point an elevation not exceeding 154 feet, which is probably the lowest on the isthmus. The lake drains into the Caribbean Sea on the east, by the San Juan river, a fine wide stream, 120 miles in length, which is navigable for river boats from the Caribbean Sea up to the lake, except near its upper part, where some rapids at certain times prevent the passage of the boats. This canal project first took definite form in 1850, when a survey was made and routes reported on. The scheme attracted some attention in the United States, and in 1872, and again in 1885, further surveys and estimates were made at the instance of the States Government. The earlier schemes provided for the rise and fall between sea and lake-–108 feet, a considerable number of locks—eleven on each side, making the total length from sea to sea 181 miles. The report of the latter advocated the canalization of the San Juan by a very bold measure, namely, the construction of an immense dam, by which the waters were to be retained in the valley for many miles at the level of the lake. A company was formed to promote the project, and again in 1890 there were more surveys and estimates made. This company actually expended a considerable sum of money in attempting to improve the harbour at Greytown, which would have formed the eastern terminus, but had become silted up. But it was found afterwards that it would be better to recommend the formation of an artificial harbour at another point, by constructing two long piers running out into the sea, although this change would involve the abandonment of a few hundred yards of canal already excavated by the company near Greytown. The company has also laid down about 12 miles of railway along the proposed route, with wooden and iron sheds as workshops, offices, etc., and, moreover, had dredges and other appliances at work. At this stage it was proposed that the United States Government should guarantee the bonds of the Nicaragua Canal Company to the extent of more than twenty million pounds sterling. By an Act of Congress passed in March, 1895, a commission of engineers was appointed for the purpose of ascertaining the feasibility, permanence, and cost of construction and completion of the Nicaragua Canal by the route contemplated. The report of this commission is an elaborate and exhaustive review of the whole scheme based upon a personal examination of the route, and on the plans, surveys, and estimates made for the company, whose records, however, are stated in the 275report to be deficient in the supply of many important data. The Canal Company’s project provided for the improvement of Greytown harbour, as already stated, and from that place the canal was to proceed westward at the sea-level to the range of high ground on the eastern side of the isthmus, which elevation was to be ascended by three locks of unusual depth, and a deep cut more than 3 miles in length, through rock to a maximum depth of 324 feet. After passing this enormous cut, the route provides for a series of deep basins, in which the water is confined by numerous dams or embankments, the canal excavations being confined to short sections through higher ground separating these basins. The total length of these embankments will be about 6 miles, and their heights will vary from a few feet to more than seventy. About 31 miles from Greytown the canal reaches the San Juan river, which, however, by means of an enormous dam across the valley at a place called Ochoa, 69 miles below the point at which it receives the waters of Lake Nicaragua, is there practically converted into an arm of the lake. This dam, which would raise the water of the river 60 feet above its present level, and would, of course, flood the valley back to the lake, is the most notable feature of the project. Its maximum height would be about 105 feet, and the weirs on its crest, to discharge the surplus water, would require a total length of nearly a quarter of a mile. Twenty-three smaller embankments would also be needed for retaining the waters; the river would have to be deepened in the upper part, and a channel dredged out in the soft mud of the lake for 14 miles beyond the river. The big Ochoa dam is said to have no precedent in engineering construction, on account of its great height and the enormous volume of the waters it is intended to retain. No doubt its construction and safe maintenance are within the range of engineering skill, when a thoroughly exhaustive survey of the site has been made, and the necessary funds are forthcoming. From the western shore of the lake its level would also be extended by another great dam crossing the valleys of the Tola and the Rio Grande, with a length of 2,000 feet and a height of 90 feet. The canal would then be carried to the sea-level by a series of locks. The length of the canal from sea to sea would be 170 miles, but of this only 40 miles of channel would require to be excavated. The total cost of the work, as estimated by the Nicaragua Canal Company, would be about fifteen million pounds sterling, but the State Commission of Engineers thinks about double that amount would be a safer calculation, and taking into account the imperfection of the data, even this might be exceeded in certain contingencies. The Government of the United States has been urged to expend a few thousand pounds on another engineering commission, to make complete surveys, and consider all the practical problems involved, including the final selection of a route.

276

Fig. 138.Britannia Bridge, Menai Straits.

IRON BRIDGES.

The credit of having invented the arch is almost universally assigned to the ancient Romans, though the period of its introduction and the date of its first application to bridge building are unknown. That some centuries before the Christian era, the timber bridges of Rome had not been superseded by those of more permanent construction is implied in the legend of the defence of the gate by Horatius Cocles—a tale which has stirred the heart of many a schoolboy, and is known to everybody by Macaulay’s spirited verses, in which

“Still is the story told,
How well Horatius kept the bridge,
In the brave days of old.”

Some of the arched bridges built by the Romans remain in use to this day to attest the skill of their architects. The Ponte Molo at Rome, for example, was erected 100 B.C.; and at various places in Italy and Spain many of the ancient arches still exist, as at Narni, where an arch of 150 ft. 277span yet remains entire. Until the close of the last century the stone or brick arch was the only mode of constructing substantial and permanent bridges. And in the present century many fine bridges have been built with stone arches. The London and Waterloo Bridges across the Thames are well-known instances, each having several arches of wide span, attaining in the respective cases 152 ft. and 120 ft. The widest arch in England, and one probably unsurpassed anywhere in its magnificent stride of 200 ft., is the bridge across the Dee at Chester, built by Harrisson in 1820. At the end of last century cast iron began to be used for the construction of bridges, a notable example being the bridge over the Wear at Sunderland, of which the span is 240 ft. But with the subsequent introduction of wrought iron into bridge building a new era commenced, and some of the great results obtained by the use of this material will be described in the present article. In order that the reader may understand how the properties of wrought iron have been taken advantage of in the construction of bridges, a few words of explanation will be necessary regarding the strains to which the materials of such structures are exposed.

Such strains may be first mentioned as act most directly on the materials of any structure or machine, and these are two in number, namely, extension and compression. When a rope is used to suspend a weight, the force exerted by the latter tends to stretch the rope, and if the weight be made sufficiently great, the rope will break by being pulled asunder. The weight which just suffices to do this is the measure of the tenacity of the rope. Again, when a brick supports a weight laid upon it, the force tends to compress the parts of the brick or to push them closer together, and if the force were great enough, the brick would yield to it by being crushed. Now, a brick offers so great a resistance to a crushing pressure, that a single ordinary red brick may be capable of supporting a weight of 18 tons, or 40,320 lbs.—that is, about 1,000 lbs. on each square inch of its surface. Thus the bricks at the base of a tall factory chimney are in no danger of being crushed by the superincumbent weight, although that is often very great. The tenacity of the brick, however, presents the greatest possible contrast to its strength in resisting pressure, for it would give way to a pull of only a few pounds. Cast iron resembles a brick to a certain extent in opposing great resistance to being crushed compared to that which it offers to being pulled asunder, while wrought iron far excels the cast metal in tenacity, but is inferior to it in resistance to compression.

The following table expresses the forces in tons which must be applied for each square inch in the section of the metals, in order that they may be torn apart or crushed:

Tenacity per square inch, in tons. Crushing pressure per square inch, in tons.
Cast iron 8 50
Wrought iron 30 17
Iron wire 40 ...

Besides the direct strains which tend to simply elongate or compress the materials of a structure or of a machine, there are modes of applying forces which give rise to transverse strains, tending to twist or wrench the pieces 278or to bend them, or rupture them by causing one part of a solid to slide away from the rest. Strains of this kind no doubt come into play in certain subordinate parts of bridges of any kind; but if we divide bridges according to the nature of the strains to which the essential parts of the structure are subject, we may place in a class where the materials are exposed to crushing forces only, all bridges formed with stone and brick arches; and in a second class, where the material is subjected to extension only, we can range all suspension bridges; while the third class is made up of bridges in which the material has to resist both compression and extension. This last includes all the various forms of girder bridges, whether trussed, lattice, or tubular. The only remark that need be here made on arched bridges is, that when cast iron was applied to the construction of bridges, the chief strength of the material lying in its resistance to pressure, the principle of construction adopted was mainly the same as that which governs the formation of the arch; but as cast iron has also some tenacity, this permitted certain modifications in the adjustment of the equilibrium, which are quite out of the question in structures of brick and stone.

Fig. 139.

Fig. 140.

Fig. 141.

Fig. 142.

The general principle of the construction of girder bridges is easily explained by considering a simple case, which is almost within everybody’s experience. Let us suppose we have a plank supported as in Fig. 139. The plank will by its own weight sink down in the centre, becoming curved in the manner shown; or if the curvature be not sufficiently obvious, it may always be increased by placing weights on the centre, as at g. If the length of the plank had been accurately measured when it was extended flat upon the ground, it would have been found that the upper or concave surface, a b, had become shorter, and the lower or convex surface, c d, longer when the plank is supported only at the ends—a result sufficiently obvious from the figure it assumes. It is plain, then, that the parts of the wood near the upper surface are squeezed together, while near the lower surface the wood is stretched out. Thus, the portions in the vicinity of the upper and lower surfaces are in opposite conditions of strain; for in the one the tenacity of the material comes into play, and in the other its power of resisting compression. There is an intermediate layer of wood, however, which, being neither extended or compressed, receives no strain. The position of this is indicated by the line e f, called the neutral line. If the plank, instead of being laid flat, is put upon its edge, as in Fig. 140, the deflection caused by its weight will hardly be perceptible, and it will in this position support a weight which in its former one would have broken 279it down. There is in this case a neutral line, e f, as before; but as the part which is most compressed or extended is now situated at a greater distance from the neutral line, the resistance of the material acts, as it were, at a greater leverage. Again the portions near the neutral line are under no strain; they do not, therefore, add to the strength, although they increase the weight to be supported, and they may, for that reason, be removed with advantage, leaving only sufficient wood to connect the upper and lower portions rigidly together. The form of cast iron beams, Fig. 141, which were used for many purposes, depends upon these principles. The sectional area of the lower flange, which is subjected to tension, is six times that of the upper one, which has to resist compression, because the strength of cast iron to resist pressure is about six times greater than its power of resisting a pull. If the upper flange were made thicker, the girder would be weaker, because the increased weight would simply add to the tension of the lower one, where, therefore, the girder would be more ready to give 280way than before. If we suppose the vertical web divided into separate vertical portions, and disposed as at Fig. 142, the strength of the girder, and the principle on which that strength depends, will be in no way changed, and we at once obtain the box girder, which on a large scale, and arranged so that the roadway passes through it, forms the tubular bridge. It is only necessary that the upper part should have strength enough to resist the compressing force, and the lower the extending force, to which the girder may be subject; and wrought iron, properly arranged, is found to have the requisite strength in both ways, without undue weight. The various forms of trussed girders, the trellis and the lattice girders, now so much used for railway bridges, all depend upon the same general principles, as does also the Warren girder, in which the iron bars are joined so as to form a series of triangles, as in Fig. 143.

Fig. 143.

Girders have been made of wrought iron up to 500 ft. in length, but the cost of such very long girders is so great, that for spans of this width other modes of construction are usually adopted.

GIRDER BRIDGES.

Fig. 144.Section of a Tube of the Britannia Bridge.

The Britannia Bridge, which carries the Chester and Holyhead Railway across the Menai Straits, is perhaps the most celebrated example of an iron bridge on the girder principle. It was designed by Stephenson, but the late Sir W. Fairbairn contributed largely by his knowledge of iron to the success of the undertaking, if he did not, in fact, propose the actual form of the tubes. Stephenson fixed upon a site about a mile south of Telford’s great suspension bridge, because there occurred at this point a rock in the centre of the stream, well adapted for the foundation of a tower. This rock, which rises 10 ft. above the low-water level, is covered at high water to about the same depth. On this is built the central tower of the bridge, 460 ft. from the shore on either side, where rises another tower, and at a distance from each of these of 230 ft. is a continuous embankment of stone, 176 ft. long. The towers and abutments are built with slightly sloping sides, the base of the central or Britannia tower being 62 ft. by 52 ft., the width at the level where the tubes pass through it, a height of 102 ft., being reduced by the tapering form to 55 ft. The total height of the central tower is 230 ft. from its rock foundation. The parapet walls of the abutments are terminated with pedestals, the summits of which are decorated by huge lions, looking landwards. As each line of rails has a separate tube, there are four tubes 460 ft. long for the central spans, and four 230 ft. long for the shorter spans at each end of the bridge. Each line of rails, in fact, traverses a continuous tube 1,513 ft. in length, supported at intervals 281by the towers and abutments. The four longer tubes were built up on the shore, and were floated on pontoons to their positions between the towers, and raised to the required elevation by powerful hydraulic machinery. The external height of each tube at the central tower is 30 ft., but the bottom line forms a parabolic curve, and the other extremities of the tubes are reduced to a height of 22¾ ft. The width outside is 14 ft. 8 in. Fig. 144 shows the construction of the tube, and it will be observed that the top and bottom are cellular, each of the top cells, or tubes, being 1 ft. 9 in. wide, and each of the bottom ones 2 ft. 4 in. The vertical framing of the tube consists essentially of bars of -iron, which are bent at the top and bottom, and run along the top and bottom cells for about 2 ft. The covering of the tubes is formed of plates of wrought iron, rivetted to - and -shaped ribs. The thickness of the plates is varied in different parts from ½ in. to ¾ in. The plates vary also in their length and width in the different parts of the tubes, some being 6 ft. by 1¾ ft., and others 12 ft. by 2 ft. 4 in. The joints are not made by overlapping the plates, but are all what are termed butt joints, that is, the plates meet edge to edge, and along the juncture a bar of -iron is rivetted on each side, thus: . The cells are also formed 282of iron plates, bolted together by -shaped iron bars at the angles. The rails rest on longitudinal timber sleepers, which are well secured by angle-iron to the -ribs of the framing forming the lower cells. More than two millions of rivets were used in the work, and all the holes for them, of which there are seven millions, were punched by special machinery. The rivets being inserted while red hot, and hammered up, the contraction which took place as they cooled drew all the plates and ribs very firmly together. In the construction of the tubes no less than 83 miles of angle-iron were employed, and the number of separate bars and plates is said to be about 186,000. The expansion and contraction which take place in all materials by change of temperature had also to be provided for in the mode of supporting the tubes themselves. This was accomplished by causing the tubes, where they pass through the towers, to rest upon a series of rollers, 6 in. in diameter, and these were arranged in sets of twenty-two, one set being required for each side of each tube, so that in all thirty-two sets were needed. There are other ingenious arrangements for the same purpose at the ends of the tubes resting on the abutments, which are supported on balls of gun-metal, 6 in. in diameter, so that they may be free to move in any manner which the contractions and expansions of the huge tubes may require. Each of the tubes, from end to end of the bridge, contains 5,250 tons of iron. The mode in which these ponderous masses were raised into their elevated position is described in the article on “Hydraulic Power,” as it furnishes a very striking illustration of the utility and convenience of that contrivance. The foundation-stone of the central tower was laid in May, 1846, and the bridge was opened in October, 1850. The tubes have some very curious acoustic properties: for example, the sound of a pistol-shot is repeated about half a dozen times by the echoes, and the tubular cells, which extend from one end of the bridge to the other, were used by the workmen engaged in the erection as speaking-tubes. It is said that a conversation may thus be carried on with a person at the other end of the bridge, a distance of a quarter of a mile. The rigidity of the great tubes is truly wonderful. A very heavy train, or the strongest gale, produces deflections in the centre, vertical and horizontal respectively, of less than one inch. But when ten or a dozen men are placed so that they can press against the sides of the tube, they are able, by timing their efforts so as to agree with the period of oscillation proper to the tube, to cause it to swing through a distance of 1¼ in.—an illustration of facts of great importance in mechanics, showing that even the most strongly built iron structure has its own proper period of oscillation as much as the most slender stretched wire, and that comparatively small impulses can, by being isochronous with the period of oscillation, accumulate, as it were, and produce powerful effects. Bridges are often tried by causing soldiers to march over them, and such regulated movements form the severest test of the freedom of the structures from dangerous oscillation. The main tubes of the Britannia Bridge make sixty-seven vibrations per minute. The expansion and contraction occurring each day show a range of from ½ in. to 3 in. The total cost of the structure was £601,865.

A stupendous tubular bridge has also been built over the St. Lawrence at Montreal, and the special difficulties which attended its construction render it perhaps unsurpassed as a specimen of engineering skill. The magnitude of the undertaking may be judged of from the following dimensions: Total length of the Victoria Bridge, Montreal, 9,144 ft., or 1¾ miles; length of tubes, 6,592 ft., or 1¼ miles: weight of iron in the tubes, 9,044 283tons; area of the surface of the ironwork, 32 acres; number of piers, 24, with 25 spans between the piers, each from 242 ft. to 247 ft. wide.

Fig. 145.Albert Bridge, Saltash.

Another singular modification of the girder principle occurs in the bridge built by Brunel across a tidal river at Saltash, Fig. 145. Here only a single line of rails is carried over the stream, which is, however, 900 ft. wide, and is crossed by two spans of about 434 ft. wide. A pier is erected in the very centre of the stream, in spite of the obstacles presented by the depth of the water, here 70 ft., and by the fact that below this lay a stratum of mud 20 ft. in depth before a sound foundation could be reached. This work was accomplished by sinking a huge wrought iron cylinder, 37 ft. in diameter and 100 ft. in height, over the spot where the foundation was to be laid. The cylinder descended by its own weight through the mud, and when the water had been pumped out from its interior, the workmen proceeded to clear away the mud and gravel, till the rock beneath was reached. On this was then built, within the cylinder, a solid pillar of granite up to the high-water level, and on it were placed four columns of iron 100 ft. high, each weighing 150 tons. The two wide spans are crossed by girders of the kind known as “bow-string” girders, each having a curved elliptical tube, the ends of which are connected by a series of iron rods, forming a catenary curve like that of a suspension bridge. To these chains, and also to the curved tubes, the platform bearing the rails is suspended by vertical suspension bars, and the whole is connected by struts and ties so nicely adjusted as to distribute the strains produced by the load with the most beautiful precision. When the bridge was tested, a train formed wholly of locomotives, 284placed upon the entire length of the span, produced a deflection in the centre of 7 in. only. This bridge has sometimes been called a suspension bridge because of the flexible chords which connect the ends of the bows; but this circumstance does not in reality bring the bridge as a whole under the suspension principle. The section of the bow-shaped tube is an ellipse, of which the horizontal diameter is 16 ft. 10 in. and the vertical diameter 12 ft., and the rise in the centre about 30 ft. Beside the two fine spans which overleap the river, the bridge is prolonged on each side by a number of piers, on which rest ordinary girders, making its total length 2,240 ft., or nearly half a mile; 2,700 tons of iron were used in the construction. As in the case of the Britannia Bridge, the tubes were floated to the piers, and then raised by hydraulic pressure to their position 150 ft. above the level of the water. The bridge was opened by the late Prince Consort in 1860, and has received the name of the Albert Bridge.

SUSPENSION BRIDGES.

The general principle of the suspension bridge is exemplified in a chain hanging between two fixed points on the same level. If two chains were placed parallel to each other, a roadway for a bridge might be formed by laying planks across the chains, but there would necessarily be a steep descent to the centre and a steep ascent on the other side. And it would be quite impossible by any amount of force to stretch the chains into a straight line, for their weight would always produce a considerable deflection. Indeed, even a short piece of thin cord cannot be stretched horizontally into a perfectly straight line. It was, therefore, a happy thought which occurred to some one, to hang a roadway from the chains, so that it might be quite level, although they preserved the necessary curve. In designing such bridges, the engineer considers the platform or roadway as itself constituting part of the chain, and adjusts the loads in such a manner that the whole shall be in equilibrium, so that if the platform were cut into sections, the level of the road would not be impaired.

Public attention was first strongly drawn to suspension bridges by the engineer Telford, who, in 1818, undertook to throw such a bridge across the Menai Straits, and the work was actually commenced in the following year. The Menai Straits Suspension Bridge has been so often described, that it will be unnecessary to enter here into a lengthy account of it, especially as space must be reserved for some description of other bridges of greater spans. The total length of this bridge is 1,710 ft. The piers are built of grey Anglesea marble, and rise 153 ft. above the high-water line. The distance between their centres is 579 ft. 10½ in., and the centres of the main chains which depend from them are 43 ft. below the line joining the points of suspension. The roadway is 102 ft. above the high-water level, and it has a breadth of 28 ft., divided into two carriage-ways separated by a foot-track. The chains are formed of flat wrought iron bars, 9 ft. long, 3¼ in. broad, and 1 in. thick. In the main chains, of which there are sixteen, no fewer than eighty such bars are found at any point of the cross section, for each link is formed of five bars. These bars are joined by cross-bolts 3 in. in diameter. The main chains are connected by eight 285transverse stays formed of cast iron tubes, through which pass wrought iron bolts, and there are also diagonal ties joining the ends of the transverse stays. The time occupied in the construction was 6½ years, and the cost was £120,000. This bridge has always been regarded with interest for being the first example of a bridge on the suspension principle carried out on the large scale, and also for its great utility to the public, who, instead of the hazardous passage over an often stormy strait, have now the advantage of a safe and level roadway.

Fig. 146.Clifton Suspension Bridge, near Bristol.

The Clifton Suspension Bridge over the Avon, near Bristol, is noted for having a wider span than any other bridge in Great Britain, and it is remarkable also for the great height of its roadway. The distance between the centres of the piers—that is, the distance of the points between which the chains are suspended—is more than 702 ft. Part of the ironwork for this bridge was supplied from the materials of a suspension bridge which formerly crossed the Thames at London, and was removed to make room for the structure which now carries the railway over the river to the Charing Cross terminus. Five hundred additional tons of ironwork were used in the construction of the Clifton Bridge, which is not only much longer than the old Hungerford Bridge, but has its platform of more than double the width, viz., 31 ft. wide, instead of 14 ft. A view of this bridge is given in Fig. 146, where its platform is seen stretching from one precipitous bank of the rocky Avon to the other, and the river placidly flowing more than 200 ft. below the roadway. The picturesque surroundings of this elegant structure greatly enhance its appearance, and the view looking south from the centre of the bridge itself is greatly admired, although the 286position may be at first a little trying to a spectator with weak nerves. The work is also of great public convenience, as it affords the inhabitants of the elevated grounds about Clifton a direct communication between Gloucestershire and Somersetshire, thus avoiding the circuitous route through Bristol, which was required before the completion of the bridge.

Fig. 147.

The use of iron wire instead of wrought bars has enabled engineers to far exceed the spans of the bridges already described. The table on page 199 shows that iron wire has a tenacity nearly one-third greater than that of iron bars, and this property has been taken advantage of in the suspension bridge which M. Chaley has thrown over the valley at Fribourg, in Switzerland. This bridge has a span of no less than 880 ft., and is constructed entirely of iron wires scarcely more than ⅒ in. in diameter. The main suspension cables, of which there are two on each side, are formed of 1,056 threads of wire, and have a circular section of 5½ in. diameter. The length of each cable is 1,228 ft., and at intervals of 2 ft. the wires are firmly bound together, so as to preserve its circular form. But as the cable approaches the piers, the wires are separated, and the two cables on each side unite by the spreading out of the wires into one flat band of parallel wire, which passes over the rollers at the top of the piers, and is again divided into eight smaller cables, which are securely moored to the ground. Each of the mooring cables is 4 in. in diameter, and is composed of 528 wires. In order to obtain a secure attachment for the mooring cables, shafts were sunk in the solid rock 52 ft. deep, and the ingenious mode in which, by means of inverted arches, an anchorage in the solid rock is formed for the cables, will be understood by a reference to Fig. 147. The cables pass downwards through an opening made in each of the middle stones, and are secured at the bottom by stirrup-irons and keys. The suspension piers are built of blocks of stone, very carefully shaped and put together with cramps and ties, so as to constitute most substantial structures. These piers are embellished with columns and entablatures, forming Doric porticoes, enclosing the entrances to the bridge, which are archways 43 ft. high and 19 ft. wide. The roadway is 21 ft. wide, and is supported on transverse beams, 5 ft. apart, upon which is laid longitudinal planking covered by transverse planking. The roadway beams are suspended to the main cables by vertical wire cables, 1 in. in diameter. The length of these suspension cables of course varies according to their position, the shortest being ½ ft. and the longest 54 ft. in length. Each suspension cable is secured by the doubling back of the wires over a kind of stirrup, through which passes a plate of iron, supported by the two suspension cables, the latter being close together, and, indeed, only separated by the thickness of the suspension cables, which hang between them. The roadway has a slight rise towards the centre, its middle point being from 20 to 40 in. above the level of the ends, according to the temperature.

287To test the stability of the bridge, fifteen heavy pieces of artillery, accompanied by fifty horses and 300 people, were made to traverse it at various speeds, and the results were entirely satisfactory. Indeed, a few years afterwards the people of Fribourg had another wire bridge thrown over the gorge of Gotteron, at about a mile from the former. This, though not so long (640 ft.), spans the chasm at a great height, and in this respect is probably not surpassed by any bridge in the world—certainly not by any the length of which can compare with its own. The height of the roadway above the valley is 317 ft., or about the same as that of the golden gallery of St. Paul’s Cathedral above the street. The structure is very light, and the sensation experienced when, looking vertically downwards through the spaces between the flooring boards, you see the people below diminished to the apparent size of flies, and actually feel yourself suspended in mid-air, is very peculiar, as the writer can testify.

The Americans have, however, outspanned all the rest of the world in their wire suspension bridges. They have thrown a suspension bridge of 800 ft. span over the Niagara at a height of 260 ft. above the water, to carry not only a roadway for ordinary traffic, but a railway. Suspension bridges are not well adapted for the latter purpose, but there seemed no other solution of the problem possible under the circumstances. The bridge, however, combines to a certain extent the girder with the suspension principle. The girder which hangs from the main cables (for they are made of wire), carries the railway, and below this is the suspended roadway for passengers and ordinary carriages. The engineer of this work was Roebling, who also designed many other suspension bridges in America.

The spans of any European bridges are far exceeded by that of the wire suspension bridge which crosses the Ohio River at Cincinnati, with a stride of more than 1,000 ft.; and this is, in its turn, surpassed by another bridge which has been thrown over the Niagara. This bridge, which must not be confounded with the one mentioned above, or with the Clifton Bridge in England already described, merits a detailed description from the audacity of its span, which is nearly a quarter of a mile, and entitles it to the distinction of being the longest bridge in the world of one span.

Fig. 147a.—Clifton Suspension Bridge, Niagara.

The new suspension bridge at the Niagara Falls, called the Clifton Bridge, of which a view is given in Fig. 147a, is intended for the use of passengers and carriages visiting the Falls, and it is also the means of more direct communication between several small towns near the banks of the river. The bridge is situated a short distance below the Falls, crossing the river at right angles to its course at a point where the rocks which form the banks are about 1,200 ft. apart. The distance between the centres of the towers is 1,268 ft. 4 in., and the bridge has by far the longest single span of any bridge in the world, the distance between the points of suspension being more than twice that of the Menai Bridge, and more than six times the span of the widest stone bridge in England. This remarkable suspension bridge was constructed by Mr. Samuel Keefer, and was opened for traffic on the 1st of January, 1869, the actual time employed in the work having been only twelve months. The cables and suspenders are made of wire, which was drawn in England at Warrington and Manchester, and the wires for the main cables were made of such a length, that each wire passed from end to end of the cable without weld or splice. The length of each of the two main cables is 1,888 ft., and of this length 1,286 ft. usually hangs between the suspending towers, the centre being about 90 ft. below the level of the points of suspension. This last distance, however, 289varies considerably with the temperature, for in winter the contraction produced by the cold brings up the centre to 89 ft. below the level line, while in summer it maybe 3 ft. lower. The centre of the bridge is about 190 ft. above the water in summer, and 193 ft. in winter. The cables are each formed of seven wire ropes, and each rope consists of seven strands, each strand containing nineteen No. 9 Birmingham gauge wires of the diameter of 0·155 in. The cables of this bridge do not hang in vertical planes, since in the centre they are only 12 ft. apart; while at the towers, where they pass over the suspension rollers, they are 42 ft. apart. The end of the platform which rests on the right bank is 5 ft. higher than the other, and if a straight line were drawn from one end to the other, the centre of the roadway would be in winter 7 ft. above it, and in summer 4 ft. From each point of suspension twelve wire ropes, called “stays,” pass directly to certain points of the platform. The stays are not attached to the cables, but pass over rollers on the tops of the towers, and are anchored in the rock, independently of the cables. The longest stays are tangential to the curve formed by the main cables, and they are fixed to the platform at a point about half-way to the centre. Other stays proceed from the platform at intervals of 25 ft., between the longest and the end of the bridge. The thickness of the stays is varied according to the strain they have to bear, and they form not only a great additional support to the platform, but they also serve to stiffen the bridge and lessen the horizontal oscillations to which the platform would be liable from the shifting loads it has to bear. There are also stays which transversely connect the two cables. The wire ropes by which the platform is suspended to the main cables are ⅝ths of an inch in diameter, and have such a strength that the material would only yield to a strain of 10 tons. These suspenders are placed 5 ft. apart and are 480 in number, the lengths, of course, being different according to the position. To each pair of suspenders is attached a transverse beam, 13½ ft. long, 10 in. deep, and 2½ in. wide. Upon these beams—which are, of course, 5 ft. apart from centre to centre—rests the flooring, formed of two layers of pine planking 1½ in. thick; and the roadway thus formed constitutes a single track 10 ft. in width. Along each side of the platform is a truss the whole length of the bridge, formed of an upper and a lower beam, 6½ ft. apart, united by ties and diagonal pieces. The lower chord of the truss is 2 ft. below the road, and on it rolled iron bars are bolted continuously from one end of the bridge to the other. The last arrangement contributes greatly to stiffen the platform, vertically and horizontally. In the central part of the bridge the flooring-boards are bolted up to the cables, and there are studs formed of 2 in. iron tubes, so that the platform cannot be lifted vertically without raising the cables also; and as thus 81 tons of the weight of the cables vertically rest upon the platform, great steadiness is secured, inasmuch as the central part of the cables must partake of any movement of the platform, and their weight greatly increases the inertia to be overcome. In order still further to prevent oscillations as much as possible, a number of “guys” are attached to the bridge. These are wire ropes of the same thickness as the suspenders, and they connect the platform with various points of the bank—some going horizontally to the summit of the cliffs, others vertically, but the majority obliquely. There are twenty-eight guys on the side of the bridge next the falls, and twenty-six on the other side. The thickness of the wire rope of which they are made being little more than ½ in., they are scarcely visible, or rather appear like spider lines. About 400 ft. of the length of the bridge in the centre is without either 290guys or stays except two small steel ropes, which, tightly strained from cliff to cliff, cross each other nearly at right angles at the centre of the bridge. The suspension towers are pyramidal in form and are built of white pine, the timbers being a foot square in section and very solidly put together, so that they are capable of bearing forty times the load which can ever be put upon them. The towers are surmounted by strong frames of cast iron, to which are fixed the rollers carrying the cables and stays to their anchorage. The weight of the bridge itself, together with the greatest load it can be required to bear, amounts to 363 tons. Its cost was £22,000, and it was constructed without a single accident of any kind.

The foam of the great falls is carried by the stream beneath the bridge, and in sunshine the spectator who places himself on the centre of its platform sees in the spray driven by the wind, not a mere fragment of a rainbow, or a semicircular arc, but the complete circle, half of which appears beneath his feet. The gorge of the Niagara is very liable to furious blasts of winds, for by its conformation it seems to gather the aërial currents into a focus, so that a gentle breeze passing over the surrounding country is here converted into a strong gale, sweeping down with great force between the precipitous banks of the river. Indeed, one would suppose that the cavern from which Æolus allows the winds to rush out, must be situated near Niagara Falls. The bridge is not disturbed by ordinary winds, although during its construction, before the stays and guys were fixed, it was subject to considerable displacement from this cause. The peculiar arrangement of the cables, by which they hang, not vertically, but widening out from the centre of the bridge, giving what has been termed the “cradle” form, has proved of the highest advantage, so that, with the aid of the guys and stays, and the plan of attaching the central part of the roadway to the cables, the bridge is believed to be capable of withstanding without damage a gale having the force of 30 lbs. per square foot, although its total pressure on the structure might then amount to more than 100 tons. The stability of the structure was severely tested soon after its erection by a furious gale from the south-west, by which the guys were severely strained; in fact, many of them gave way. In one case an enormous block of stone, 32 tons in weight, to which one of the guys was moored, was dragged up and moved 10 ft. nearer the bridge. This and some lateral distortion of the platform, which was easily remedied, was all the damage sustained by the bridge. By an increase of the strength of the guys, &c., and the addition of the two diagonal steel wire ropes mentioned above, the bridge was soon made stronger than before. Some years ago, when the Menai suspension bridge was exposed to a storm of like severity, that structure suffered great damage, the platform having been broken and some of it swept away. In the great gale which swept down upon the Niagara bridge, although the force of the wind was so great that passengers and carriages could not make headway, the vertical oscillations of the bridge never exceeded 18 in., an amount which must be considered extremely satisfactory in a bridge of the kind, having a span of nearly a quarter of a mile.[4]

4.  Notwithstanding the skill displayed in its construction, this bridge has, since the above account was written, been destroyed by a tremendous hurricane.

291

Fig. 147b.—Living Model of the Cantilever Principle.

CANTILEVER BRIDGES.

The great Forth Bridge, now (December, 1889) approaching completion, is the first bridge on the cantilever and central girder principle that has been erected in Great Britain, and it has also the distinction of being by far the widest spanned bridge in all the world. We are told by the engineers of the bridge that the cantilever and girder principle is by no means new, for it has been adopted hundreds of years ago by comparatively rude tribes in the construction of timber bridges, to which it readily lends itself. Such bridges are described as having been erected by the natives of Hindoostan, Canada, Thibet, etc., even at remote periods. The principle of the cantilever and girder construction was well illustrated by Mr. Baker, one of the engineers of the bridge, at a lecture given by him at the Royal Institution, by means of what he termed “a living model,” of which (Fig. 147b) shows the general arrangement. Two men, seated on chairs, extend their arms and hold in their hands sticks, of which the other ends butt against the chairs. The central girder is represented by a shorter stick, suspended at a and b. We have here the representation of two double cantilevers, the ropes at c and d, connected with the weights, representing the anchorages of the landward arms of the cantilevers. When a weight is placed on a b, which was done in the “living model,” by a third man seating himself thereon, a tensile strain comes into action in the ropes and in the men’s arms, while the sticks abutting on the chairs have to resist a compressing force, and the weight of the whole is borne by the legs of the chairs, also under compression. Now let the reader imagine the men’s heads to be 360 feet above the ground, and about a third of a mile apart, while the distance between a and b is 350 feet, and he will have a rough but sufficiently clear idea, not only of the principle upon which the Forth Bridge is constructed, but also of the magnitude of one of its spans. To complete the comparison, Mr. Baker further invited his hearers to suppose that the pull upon each arm 292of the men is equal to 10,000 tons, and that the legs of each chair press on the ground with the weight of more than 100,000 tons.

The Forth Bridge spans the estuary at Queensferry nine miles north-west from Edinburgh, and its purpose is to afford uninterrupted railway communication along the eastern side of Scotland. It will, in effect, shorten the railway journey between Edinburgh and Perth, or Aberdeen, by nearly two hours. Queensferry had long been established as a usual place for crossing the Forth, and readers of Scott’s “Antiquary” will remember that the first chapter describes how Monkbarns and Lovel, by some accidental delays to the coach, lost the tide, and had to wait, to sail “with the tide of ebb and the evening breeze,” finding themselves, in the meanwhile, pretty comfortable over a good dinner at the “Hawes Inn.” This inn still stands, its situation being close to the southern end of the great bridge. A design for the erection of a light suspension bridge at the same spot was published at the beginning of the present century, but although the spans were to be equal to those of the present bridge (17,000 feet), the different scale of the projects may be inferred from the total weight of iron to be used being estimated at 200 tons, while 50,000 tons will be required for the structure now approaching completion.

In 1873, an Act of Parliament was obtained authorizing the construction of a suspension bridge at Queensferry, to carry the railway over the estuary. The design comprised practically two bridges, each carrying a single line of rails, the bridges being braced together at intervals. The central towers were to have been 600 feet high, or about 100 feet loftier than any other erection then existing in the world. The designer was the late Sir Thomas Bouch, and preparations were made for carrying out the plans by the erection of workshops and the manufacture of bricks for the piers. But the project was knocked on the head by the terrible disaster at the Tay Bridge, in December, 1879, when several of the central piers were overturned by the force of the wind, with swift destruction to a passing train, which was precipitated into the water, and every one of about ninety persons in the train perished. Sir Thomas Bouch having been the designer of the Tay Bridge, public confidence in his plan was shaken to such an extent, that the four railway companies who were promoting the construction of the suspension bridge abandoned the project in favour of a design on the cantilever and central girder system, which was then brought forward by Mr. (now Sir John) Fowler and Mr. Baker. When the Bessemer process had made steel attainable at a cheap rate, these engineers recognized the advantages which cantilever bridges, made of that material, presented for the wide spans required for carrying railways across navigable rivers, and in 1865 they had designed such a bridge, with 1,000 feet spans for a viaduct, across the Severn, near the position of the present tunnel. It was not, however, until 1881 that the designs for the Forth Bridge were published in English and American engineering journals. These designs at once attracted attention, and scarcely a year had elapsed before a railway bridge was built for the Canadian and Pacific Railway, on the same principle, and this has been followed by others since. It is, however, absurd to allege that the engineers took their ideas from America, merely because these smaller undertakings have been completed before the great work that dwarfs them all was open for traffic. The construction of the Forth Bridge on its present design was commenced in January, 1883. Its site at Queensferry is at a point where the estuary narrows, and where, in the very middle of the channel, there is a small 293rocky island, called Inchgarvie, that furnishes a solid foundation for the great central pier. On each side of this island the channels are about one-third of a mile wide, and more than 200 feet deep, and through them the tide rushes with great velocity. The impossibility of building up any intermediate piers, under such circumstances, is sufficiently obvious—the currents must be crossed at one span, if a railway bridge had to be made. The formation of the piers for such a work presented many novel problems, and much of the work had to be commenced in deep water; that is, the ground of rock or hard clay had to be prepared, in some parts, as far as 90 feet below high water. Each pier stands on four caissons, which are great tubes or drums of iron and steel, filled up with concrete. Each weighed, when empty, about 400 tons, but when filled up with concrete, the weight would be about 3,000 tons. The diameter of each is 70 feet, and the deepest one is sunk 89 feet below the water, and it was with no little labour that some of them were put in their places. Each caisson has an outer and an inner tube, is 70 feet in diameter at the base, and 60 feet at the top. Seven feet from the bottom, an air-tight partition formed a chamber in the lower part of the caisson, about 70 feet in diameter, by 7 feet high, and shafts sufficiently large to admit the passage of men and tools led from the top. Air was forced into this chamber, when the caisson had been sunk, expelling the water, and then men descended through the shafts and locks, in which a high pressure of air was also maintained, and excavated the material at the bottom, until the caisson had, by its own weight, sunk to the depth required. The work in this air chamber was carried on by means of electric lights, and ten or twelve weeks were occupied in sinking each caisson. The pressure of the air in the working chamber was sometimes as high as 35 pounds per square inch, or sufficient to maintain the mercurial column in a barometer 72 inches high, instead of the ordinary 29 or 30 inches. It was found that the labour in the compressed air chamber could not be done by our home workmen, as they were quite unaccustomed to the high air pressures required to keep out the water; but arrangements were made for the assistance of a staff of French workmen, inured to the conditions by long working under water in the construction of the docks at Antwerp.

PLATE XIII.

THE FORTH BRIDGE.

The stores, offices and workshops, situated on a slight eminence near the south end of the bridge, are very extensive, occupying, it is said, an area of 50 acres. Here are great furnaces, cranes and machinery for shaping and fitting the steel plates and bars ready for taking their appointed places in the vast structure. An hydraulic crane may, for instance, be seen lifting a ton weight flat steel plate that has been heated to redness in a regenerative gas furnace, and transferring it to an hydraulic press, where it is quickly and quietly bent to the required shape. The plate is then cooled, and, when the edges have been planed, it is placed in position with the adjoining plates, and the rivet holes are drilled by an ingenious machine, specially designed by Mr. Arrol, the contractor, for that purpose. It works upon 8–feet lengths of the tubes, and simultaneously cuts ten rivet holes at different points in the circumference. All the different parts of the structure are temporarily fitted together to ascertain that every piece is properly adjusted. They are then marked according to the position they are to take, and are laid aside until they are wanted. Thus the work at the bridge has proceeded without any awkward hitches arising from ill adjusted sections being brought together. At times, 1,800 tons of finished steel-work has been turned out of these shops in a month, and 294this material, which was supplied by the Steel Company of Scotland, has been found thoroughly trustworthy in every respect. Its strength is one-half greater than that of the best wrought-iron, and the plates have thrice the ductility of iron plates. The steel plates for the great tubes are supplied in lengths of 16 feet, and of different thicknesses, between ⅜ths of an inch and 1¼ inch.

Fig. 147c.—Principal Dimensions of the Forth Bridge.

The sketch, Fig. 147 c, shows the general dimensions of the bridge proper, or that part of the viaduct which will actually span the estuary. Of the three great piers that support the cantilevers, it will be observed that the central one, which rests on Inchgarvie, is wider than the other two. Each consists mainly of four tubes, 12 feet in diameter, made of plates of steel 1¼ inch in thickness, and these rise to the highest part of the bridge, which is 361 feet above the water, so that the structure is as lofty as St. Paul’s Cathedral. These great tubes are not placed vertically, but incline inwards towards the top, so that while the “straddle legs” of each pair are 120 feet apart at the base, they are only 33 feet apart at the top. These lofty columns are also braced together diagonally by other steel tubes—that is, a tube passes from the foot of every column to each of the other three. At the base of each column, the lowest spanning member springs also (which appears like an arch, but is not so), as a tube of 12 feet diameter. Thus abutting or resting on enormously thick plates of steel that cap the masonry of each pier, are five tubular steel limbs, three of which are 12 feet in diameter, and two are 8 feet, and, besides these five, girder members diverge from nearly the same centre. One of the large tubular members is the first strut that rises obliquely to support the upper structure. From the point where this strut meets the upper member, a stay passes downwards with an opposite inclination to the lower member, from its point of junction with which another strut rises, and so on. All the struts, as being subject to compressing force, are made of steel tubes; the straight upper members and the stays are lattice braced girders of rectangular section. The apparent curve of the lower member—for it is really made up of sections of straight tubes—may suggest the notion of an arch; but the reader must remember that the principle of this bridge has no relation to that of the arch. The cantilevers do not unite the long arms they stretch, but each is an independent structure with its own perfect stability, and it will not be clutched on or locked up to its neighbours by the central girders. The weight of one of these 1,700 feet spans is about 16,000 tons, and the heaviest train loads might be two coal trains, weighing together, say 800 tons, or only one-twentieth of the 295dead weight of the structure. But, what would not generally be supposed, the pressure of the wind is an element of much more importance in considering the stability of the bridge than the weight of the rolling load. It is to resist the wind pressure that the lofty columns that are only 33 feet apart at the top across the bridge, plant their bases 120 feet asunder. The estimated lateral pressure of the wind on one of the cantilevers, assuming it as equal to 56 lbs. per square foot, would amount to 2,000 tons. These strains are so fully provided for that the engineers are confident that a hurricane of such a force as would desolate the country would leave the Forth Bridge intact, even if the wind blew in opposite directions on the two arms of the cantilever. To rend asunder the top ties, a pull equivalent to the weight of 45,000 tons would be required, whilst the utmost strain that passing trains could possibly bring upon these ties would be less than 2,000 tons. A striking illustration of the strength of these huge brackets was lately given by Mr. Baker himself, when in a public lecture he assured his audience that half a dozen of our ponderous modern ironclads might be hung from the cantilevers. Everyone knows that a bracket requires to be strongest nearest the base, and the lower steel arms that stretch out 680 feet each diminish in diameter until at the end it has decreased to five feet, and the pairs approach each until, from being 120 feet apart at the base, they are only 33 feet apart at the ends. The central girders will each weigh about 1,000 tons, and only one end of each will be attached to a cantilever, the other ends will simply rest on what are called “rocking columns,” so that there may be freedom of motion to allow play for the changes of position that will be induced by changes of temperature expanding or contracting the huge masses of metal.

The reader can hardly have failed to observe that the chief element in the stability of the structure depends upon balancing a great mass of metal on the one side of a pier by an equal mass on the other side. But while each end of the central cantilever bears half the weight of a central girder, the two shoreward cantilevers have this load at their inner ends only. How is their balance maintained? In this way: the shoreward arms are made about 10 feet longer than those that stretch over the water and their extremities are also loaded with about 1,000 tons of iron, built up within the shore piers.

The lofty columns of the piers were erected without any external staging, from a temporary platform surrounding the piers and supporting the necessary machinery. The weight of this platform with the machinery on it was about 400 tons, and as the work proceeded it was raised as required by hydraulic machines placed within the vertical columns. As the height of these increased, the men and materials had to be conveyed to the platform by cages moving between guide ropes and worked by steam engines. From this platform were constructed not only the main columns, but the great diagonal tubes, the bracing girders, and the viaduct girder. The cantilevers were also put together without scaffolding. When the first few feet of the lower member had been built out from the base, a movable platform was hung round it, and on this platform were the cranes for putting the plates into position, the furnace for heating the rivets, and the hydraulic riveter of specially designed construction, without noise or hammering, the riveting being completed by the application of a pressure equal to 3 tons per square inch. The building up of the cantilever arms on either side of each pier always proceeded at the same rate, 296so that the balance was constantly maintained. This building out from each side of the pier, without the necessity of relying upon any temporary scaffolding from below, is one great advantage of the cantilever system, as it is both easier and safer than a system which relies upon the temporary scaffolding raised from below. The Forth is for the time the longest spanned bridge in the world; but it may not retain that honour long, for the legislature of the United States has already authorized the construction of a cantilever bridge, the spans of which are to be 2,480 feet. Still more gigantic is the project lately put forward by some competent French engineers of bridging the English Channel from Folkestone to Cape Grisnez in 70 spans on the cantilever system. The designs have been completed and the calculations made, and no one doubts of the engineering practicability of the scheme. But the cost is estimated at about 34 million pounds sterling, or nearly six times as much as that required for constructing the proposed Channel Tunnel; so that the scale could be turned in favour of the bridge only if the political reasons that were opposed to the tunnel were held not to be applicable to the bridge. But it is difficult to conceive that the existing traffic could ever be developed to such an extent as to make an undertaking of this magnitude a commercial success.

Since the above account was written, the Forth Bridge was formally opened on the 4th March, 1890, by the Prince of Wales, in the presence of a great gathering of railway directors, eminent engineers, and other distinguished persons from all parts. A very strong gale was blowing at the time, and at this very hour the bridge was therefore subjected to another severe but undesigned test of its stability. The perfect steadiness and security of the structure impressed all who were present on that occasion, and the train crossed the bridge, exposed to a wind pressure, registered by the gauge, of 25 lbs. per square foot. At the luncheon following the opening ceremony, the Prince announced that baronetcies had been conferred upon Mr M. W. Thompson (the chairman of the Bridge Company) and upon Sir John Fowler, and that Mr. Baker and Mr. Arrol, the contractor for the works, were to be knighted. Sir John Fowler, the engineer-in-chief, was born in 1817, and has been engaged in many other important works of railway construction in Yorkshire, in that of the London and Brighton Railway, in the Sheffield Waterworks, &c. The Metropolitan Railway in London, which also was carried out by Sir John Fowler, would alone suffice to make him famous as an engineer. Sir Benjamin Baker is a much younger man, who has had a large and varied practice in railway engineering in various parts of the world. He is in much request on the American continent, and is now engaged in carrying out a ship railway in Canada and a tunnel under the Hudson at New York. Sir William Arrol began life at nine years of age as a “piecer” in a cotton mill, but was afterwards apprenticed as an engineer. Subsequently he was employed as a foreman by engineering firms in Glasgow. In 1866, he began business on his own account at Dalmarnock, and obtained contracts at first for smaller then for larger works connected with bridge and viaduct building. He is distinguished for the energy and inventive resources he displays in carrying out his undertakings.

297

THE TOWER BRIDGE, LONDON.

A little more than four years after the opening of the Forth Bridge, in June 1894, another great enterprise which had been commenced eight years before, was inaugurated by the Prince and Princess of Wales as representatives of Her Majesty the Queen. This was the Tower Bridge, which not only is one of the most important public works of the century, but one that presents features of interest and novelty that have never before been combined in any single structure. The want of an adequate communication between the shores of the Thames eastward of London Bridge had long been felt, and was for years a subject of serious consideration for the Metropolitan authorities. The congested state of the traffic across London Bridge has often furnished a spectacle for the sight-seer, and figures are not wanting to show that the number of foot-passengers alone who daily traverse that bridge, which altogether is only 54 feet wide, would be equal to the whole population of many considerable cities: for in 1882 a count showed the daily average of pedestrians to be 110,525, while the number of vehicles was 22,242. There was much difference of opinion as to the best method of providing the required means of communication; but there was an almost universal agreement as to its position being selected just eastward of the Tower of London. The map of the districts connected by the Tower Bridge which is given in Fig. 147d, will show a reader who has any acquaintance with London the suitability of the site. The problem of traversing the river at this point involved complex conditions as affecting the vehicular traffic and the navigation, and many different schemes were proposed and examined, comprised under the three heads of bridges, tunnels and ferries. But a ferry is always an imperfect means of communication, liable to accidents and interruptions from fogs, and in severe weather from ice, rendering the transit impossible for sometimes many days together. A tunnel beneath the river would, of course, leave the navigation without impediment, but among its special disadvantages are the great expense of construction and maintenance, for it has been found that tunnels beneath waterways are very costly in both respects. Besides, there would have to be long inclined approaches at each end, and the cost would be enormously increased by the amount of valuable land these would occupy. It was indeed proposed that the tunnel should be provided instead with hydraulic lifts at each end, like those often found in connection with the sub-ways at railway stations; but such would have to be of Brobdignagian dimensions, and would daily entail heavy expense. Then, as regards the bridges, schemes of various kinds were proposed, some even bridging the whole 850 feet width of the river at a single span, but all distinguishable by these important characteristics: they either provided a high level roadway which requires long inclines to reach it, but permitted lofty-masted ships to pass under it; or, on the other hand, the roadway was to be made at a low level with a clear headway above the water of moderate height. While avoiding the inclined approaches, this plan would either prevent fully rigged vessels passing to the wharves above the bridge, or some part of the structure would have to open or swing aside, that the ships might pass through the opening, thus completely interrupting the pedestrian and 298vehicular traffic for the time, with an amount of inconvenience that may be imagined when, as often happens, twenty large ships or more might pass in the course of a day, each causing a stoppage of five minutes in the road traffic. Nor would it be without risks that large vessels could pass through a comparatively narrow opening in a strong tide-way. Plans for sub-ways, for high level roadways and for low level roadways, were examined by Parliamentary Committees when powers to construct the works were successively applied for by the Metropolitan authorities, and much valuable evidence having been given, such objectionable features of each scheme as have been already referred to were duly noted. At length in 1878, Mr. Horace Jones, the late architect to the City of London, in a report on the various projects, suggested the general plan on which the present bridge is built, and this having been approved of by the Common Council, steps were taken to obtain Parliamentary powers to raise the necessary capital and to proceed with the works; but, for various reasons, it was not until 1885 that the Act authorising the undertaking was passed. In the meantime Mr. John Wolfe Barry was appointed engineer of the structure, while Mr. Jones was to superintend the architectural details; but after having received the honour of knighthood in 1885, he died in the same year; and Mr. Barry, reconsidering the joint design, introduced some new features and somewhat modified the architectural expression of the structure. One striking point of originality about the Tower Bridge is that while it is essentially an iron and steel construction as much as the Forth Bridge, the heavy stiff metal-work is encased in masonry of elegant and appropriate architectural design, by which the general desire that the bridge should harmonize so far as might be, with the ancient historical fortress it adjoins, has been happily realised. Then again, by the ingenious engineering, the public have the advantage of a low level roadway, while the largest vessels may pass freely through a wide space without risk. These apparently incompatible advantages have been obtained by the adoption of what is the bascule principle on a hitherto unattempted scale. Bascule is a French engineering term, which is probably less familiar to most of our readers than the thing itself. It is applied to the platform of a draw-bridge which turns as the lid of a box does on its hinges, to afford a passage over the stream or moat when it is horizontal, and when drawn up vertically denies such passage. Smaller bascule bridges on exactly the same plan as in the Tower Bridge may often be seen in places having docks or canals, such as Hull, &c. In these a flap or platform is let down from each side from the vertical position, in which the water-way is open until the free edges meet together to form the roadway. These platforms turn on horizontal pivots, and are counterpoised by loads of stone or metal, so that they are without difficulty raised and lowered by a winch or handle that turns a cogged pinion engaging the teeth of a large quadrant.

PLATE XIV.

THE TOWER BRIDGE IN COURSE OF CONSTRUCTION.

The Engineer”      Swain Eng.

Fig. 147d.—Map of the Tower Bridge and its Approaches.

The following general description of the Tower Bridge is mainly abstracted from a very full and excellent account of it drawn up in 1894 by Mr. J. E. Tuit, engineer to Sir W. Arrol & Co., the contractors, in which are embraced the whole of the technical details of the structure. The map, Fig. 147d, shows the site of the bridge and its approaches, of which the northern one begins close to the mint and passes along the east side of the Tower of London to the northern abutment. This approach is formed of a series of brick arches, and is nearly 1,000 feet long and 35 feet wide in the roadway, with a footpath 12½ feet wide on either side of it. The 300incline is only a rise of 1 in 60, but the southern approach is slightly steeper, namely, 1 in 40 leaving the street level at Tooley Street. At each abutment there are also stairs connecting the banks of the river with the roadway of the bridge. The width of the river between the two abutments is 880 feet, and this is divided, as shown in Fig. 147e, into two side spans, each 270 feet wide, and one central span of 200 feet clear, making together 740 feet, the river piers, each of which is 70 feet wide, completing the total span. The clear headway above high water, when the bascules or leaves are down, is, in the middle span, 29½ feet in the centre, but only 15 feet at the ends; but when the leaves are raised for ships to pass, it is about 143 feet. The headway at the shore sides of the piers is 27 feet, but this is lessened to 23 feet and 20 feet at the north and south abutments respectively. The roadway and footpaths are continued along the side spans of the same width as on the approaches, but over the central span the road is 32 feet, and each footway 8½ feet wide. The river piers are said to be the largest in the world of the same kind, and their great area was necessitated by the nature of the London clay on which they rest, which was found incapable of bearing a load much exceeding four tons per square foot without some risk of undue settlement.

The part of the piers below the bed of the river is formed of concrete, while the upper part is brickwork, set in cement and faced with Cornish granite. Upon each of the river piers rest four octagonal columns, built up of flat steel plates, connected together at their edges by splayed angle-bars. The columns are 120 feet high, and 5½ feet in diameter; those on each pier are securely braced together, at certain stages also by plate girders, 6 feet deep, to form a floor or landing, and the tops of the columns are similarly joined together. At the height of 143 feet above high water there are two footways, each 12 feet wide and 230 feet long, carried on girders over the central span, and supported by the columns on each pier. It must be noted that all the roadway, and, in fact, all the practical and useful structure of the bridge, depend upon the steel-work alone, which is supported mainly by the eight octagonal columns just mentioned. The architectural features, which so appropriately clothe all the steel columns, are added for æsthetic considerations, and their masonry takes no part in bearing the weights and strains of the structure. Indeed, the stone-work of the towers is carefully separated from the columns, which were covered with canvas while the masonry was built round them, and spaces were left at every point where compression of the steel-work would bring weight upon the stone-work. This investment of the metal-work by beautiful architecture is, as already mentioned, one of the most original features of the Tower Bridge. The view of the work in progress, as given in Plate VIII., which is one of the many beautiful illustrations in Mr. Tuit’s book, will give the reader an opportunity of judging how much the structure gains in sightliness by the addition of the architectural features. Two hydraulic lifts are placed in each tower to convey pedestrians to and from the higher level footways, when the moving parts of the bridge are open, and stairs also are provided for the same purpose for those who prefer them to using the lifts.

Fig. 147e.The Tower Bridge.

Length of Bridge with its approaches 2680 feet.
Length of Northern approach 1000 feet.
Length of Southern approach 800 feet.
Width between N. and S. abutments 830 feet.
Width of central span 200 feet.
Width of side spans, each 270 feet.
Depth of River at high water under central span 33½ feet.
Depth of River at lowest tides under central span 12 feet.
Clear headway at high water when the leaves are down (varies from one part of the bridge to another) 20 to 29½ feet.
Clear headway in centre span at high water with the leaves raised 143 feet.

The side spans are really suspension bridges, but the chains have only two links, connected at the lowest point by a pin 2½ feet in diameter, while their higher ends are supported on the columns of the piers, and on similar but shorter columns on the abutments. The horizontal pulls of the chains on the piers are made to balance each other by connecting the 302chains to tie bars stretching across the central span, and the landward ends of the chains, after passing over the lower columns of the abutments, are securely anchored in enormous masses of concrete.

Each of the opening parts, or bascules, or leaves, as they may be called, consists of four girders 18½ feet apart, rigidly braced together, and connected at the pier end with a great shaft, 48 feet long and 1 foot 9 inches in diameter, which turns in massive bearings, resting upon four fixed girders. The leaf is counterbalanced on the shore side of the pivot shaft by 350 tons of lead and iron; the short leverage of the centre-weight and small space available for it required the greater part of this weight to be of lead, rather than of the less expensive metal. The pivot shaft passes through the centre of gravity of the whole, so that, although the total weight is nearly 1,200 tons, no very great power is required to set it in motion, as the pivot shaft rests on rollers to diminish the friction. The power for moving the leaf is applied to toothed quadrants of 42 feet radius, of which two are fixed to the outside girders of each leaf, and are geared into cogs moved by eight large hydraulic engines, with six accumulators, into which water is pumped by two engines, each of 360 horse-power.

The total length of the bridge, including the approaches, is just half a mile, and the height of the towers from the foundations is 293 feet, so that if one of them were placed beside St. Paul’s Cathedral, it would compare with it in height as shown in the sketch, Fig. 147f.

Fig. 147f.—Sketch.

303

THE GREAT BROOKLYN BRIDGE.

The Clifton Bridge at Niagara Falls, which for a time had the distinction of being the longest in span of any suspension bridge in the world, has been fully described in previous pages; but more recently this bridge has been surpassed in span, and in all other respects, by a structure that immediately connects two of the most populous localities in the United States of America. The Island of Manhattan, which is occupied by the city of New York proper, has a population of nearly two millions, and a strait on its eastern side, connecting Long Island Sound with New York Harbour, alone divides it from the other great seats of population, called respectively Long Island City and Brooklyn. This channel is about ten miles long, and of a varying width, which may average three-quarters of a mile. There are many ferries between the opposite shores, and the waters are busy with steamers, sailing-boats, tugs, and craft of all kinds, engaged either in traffic with ports near at hand, or in trade with distant lands. At the southern end of this strait, near the point of its junction with New York Bay, is the narrowest part of its course, and it is here that it is crossed by the magnificent suspension bridge, known indifferently as the East River Bridge, or Brooklyn Bridge, which provides land communication between New York, with its population of two millions, and Brooklyn, the fourth city of the States in point of size, with inhabitants numbering about one million. Brooklyn is largely a residential place for persons whose daily business is in New York. It has wide, well-planned streets, many shaded by the luxuriant foliage of double rows of trees, and possesses parks, public buildings, institutes, churches, etc., on a scale commensurate with its importance.

The central span of Brooklyn Bridge, from tower to tower, is 1,595 feet, and each shore part, extending from the tower to the anchorage of the cables, is 930 feet span, while the two approaches beyond the anchorage together add 2,534 feet to the total length, which is 5,989 feet, or considerably over a mile. The centre span, it will be observed, is much greater than that of the Niagara Falls Clifton Bridge, which was less than one quarter of a mile, whereas the Brooklyn Bridge span extends to something approaching one-third of a mile, or, more exactly, a few yards longer than three-tenths. The width of the Brooklyn is another one of its remarkable features, for this is no less than 85 feet, and includes two roadways for ordinary vehicles, and two tramway tracks, on which the carriages are moved by an endless cable, worked by a stationary engine on the Brooklyn side. There is also a footpath, 13 feet wide, for pedestrians. In this structure, as in many other suspension bridges, advantage has been taken of the great tenacity of steel wire as compared with iron bars. But here the wires are not twisted in strands like ropes, but are laid straight together, and bound into a cylindrical form, each wire being 3,572 feet long, and extending from end to end of the cables, which are four in number, each calculated to bear a strain of 12,200 tons. The number of wires in each cable is very great, for instead of about the thousand of which the stranded wire cables usually consist, there are 5,296 steel wires wrapped closely round, and forming a cylinder 15¾ inches in diameter. Each wire is galvanised, that is, coated with zinc, and then coated with oil. The towers over which the cables pass are of 304masonry, and rise to 272 feet above high-water; their dimensions at the water level are 140 feet by 50 feet, which offsets diminish until at the top they are 120 feet by 40 feet. At the anchor structures, the cables enter the masonry at nearly 80 feet above high-water, and pass 28 feet into the stonework for connection with the anchor chains. The anchorages are masses of masonry, measuring at the base 129 feet by 119 feet, and at the top 117 feet by 104 feet, with a height of 89 feet in front and 85 feet in the rear. The weight of each anchor-plate is 23 tons. The roadway of the bridge is suspended from the cables above the buildings and streets between the towers and the anchorages. The approaches, on the Brooklyn side 971 feet, on the New York side 1,563 feet, are carried on stonework arches, which are utilised as warehouses, but where these approaches cross streets, iron bridges are thrown over. The clear headway between the centre of the roadway over the river at high-water is 135 feet, so that there is no obstruction to navigation, and the headway at the towers is 119 feet, so that the roadway rises towards the centre about 3 feet 3 inches in 100 feet. The two towers comprise more than 85,000 cubic yards of masonry, and for various purposes 13,670 tons of concrete were used. The work was commenced in January, 1870, and the first wire was carried across on 29th May, 1877. The bridge was opened to the public on the 24th of May, 1883, and the tramway four months later. The bridge was made free for pedestrians in 1891, and in 1894 the tram-car fares were reduced to five cents (2½d.) for two journeys. In that year, 41,927,122 passengers were carried on the cars. The average number of persons daily crossing the bridge is estimated at about 115,000, although on one day (11th Feb., 1895) as many as 225,645 passengers have been carried on the cars. The cost of the work connected with this great bridge was $15,000,000 (£3,125,000).

In relation to the subject of wide-spanning bridges, the erection has been contemplated of structures which would surpass in magnitude and boldness any of those yet named. Thus, in 1894, the New York Chamber of Commerce proposed to throw across the River Hudson, which washes the western side of New York, a bridge with a clear span of 3,200 feet (six-tenths of a mile), and 500 feet clear height; and the project was declared by an eminent and experienced engineer to be quite feasible.

PLATE XV.

THE BROOKLYN BRIDGE.

305

Fig. 148.Newspaper Printing-Room, with Walter Machines.

PRINTING MACHINES.

A volume might be filled with descriptions of the machines which in every department of industry have taken the place of slow and laborious manual labour. But if even we selected only such machines as from the beautiful mechanical principles involved in their action, or from their effects in cheapening for everybody the necessaries and comforts of life, might be considered of universal interest, the limits of the space we can afford for this class of inventions would be far exceeded. The machines for spinning, for weaving fabrics, for preparing articles of food, are in themselves worthy of attention; then there is a little machine which in almost every household has superseded one of the most primitive kinds of hand-work, and that is the sewing machine. But all these we must pass over, and confine our descriptions of special machines to a class in which the interest is of a still more general and higher character, since their effect in promoting the intellectual progress of mankind is universally acknowledged. We need hardly say that we allude to Printing Presses, and if we add a few lines on printing machines other than those which have given us cheap literature, it is because these other machines also have contributed to the general culture by giving us cheap decorative art, and in their general principles they are so much akin to the former that but little additional description is necessary.

306

LETTERPRESS PRINTING.

The manner in which the youthful assistants of printers came to receive their technical appellation of “devils” has been the subject of many ingenious explanations. One of these is to the effect that the earlier productions of the press, having imitated the manuscript characters, the uninitiated supposed the impressions were produced by hand-copying, and in consequence of their rapid production and exact conformity with each other, it was thought that some diabolical agency must have been invoked. Another story relates that one of Caxton’s first assistants was a negro boy, who of course soon became identified in the popular mind with an imp from the nether world. A very innocent explanation is put forward in another tale, relating that one of the first English printers had in his employment a boy of the name of De Ville, or Deville, which name was soon corrupted into the now familiar title, and became the inheritance of this youth’s successors in the craft. Perhaps a more probable and natural explanation might be found in the personal appearance which the apprentices must have presented, with hands, and no doubt faces also, smeared over with the black ink which it was their duty to manipulate. For the ink was formerly always laid upon large round pads or balls of leather, stuffed with wool. When these balls, Fig. 149, which were, perhaps, about 12 in. in diameter, had received a charge of ink, the apprentice dabbed the one against the other, working them with a twisting motion, and after having obtained a uniform distribution of the ink on their surfaces with many dexterous flourishes, he applied them to the face of the types with both hands, until all the letters were completely and evenly charged. The operation was very troublesome, and much practice was required before the necessary skill was obtained, while it was always a most difficult matter to keep the balls in good working condition.

Fig. 149.Inking Balls.

Fig. 150.Inking Roller.

The first important step towards the possibility of a printing machine was made, when for these inking balls was substituted a cylindrical roller, mounted on handles, Fig. 150. The body of the roller is of wood, but it is thickly coated with a composition which unites the qualities of elasticity, softness, and readiness to take up the ink and distribute it evenly over the types. The materials used for this composition are chiefly glue and treacle, and sometimes also tar, isinglass, or other substances. Glycerine and various other materials have also been proposed as suitable ingredients for 307these composition rollers, but it is doubtful whether the original compound is not as efficacious as any yet tried. The composition is not unlike india-rubber in its appearance and some of its properties. Fig. 150 represents equally the mode in which the roller is applied to the type in hand presses, and that in which it is charged with ink, by being moved backwards and forwards over a smooth table upon which the ink has been spread.

From the time of the first appearance of printing presses in Europe down to almost the beginning of the present century, a period of 350 years, no improvement in the construction appears to have been attempted. They were simply wooden presses with screws, on exactly the same plan as the cheese-presses of the period. Earl Stanhope first, in 1798, made a press entirely of iron, and he provided it with an excellent combination of levers, so that the “platen,” or flat plate which overlies the paper and receives the pressure, is forced down with great power just when the paper comes in contact with the types. Such presses are capable of turning out about 250 impressions per hour, and it should be noted that the very finest book printing is still done by presses upon this principle. One reason is that in such cases, where it is desired to print with the greatest clearness and depth of colour, the ink employed is much thicker, or stiffer, and requires more thorough distribution and application to the type than a machine can effect. Stanhope’s press was not of a kind to meet the desire for rapid production, to which the increasing importance of newspapers gave rise. The first practical success in this direction was achieved by König, who, in 1814, set up for Mr. Walter, the proprietor of the “Times,” two machines, by which that newspaper was printed at the rate of 1,100 impressions per hour, the machinery being driven by steam power.

The “Times” of the 28th November, 1814, in the following words made its readers acquainted with the fact that they had in their hands for the first time a newspaper printed by steam power:

“Our journal of this day presents to the public the practical result of the greatest improvement connected with printing since the discovery of the art itself. The reader of this paragraph now holds in his hand one of many thousand impressions of ‘The Times’ newspaper, which were taken off by a mechanical apparatus. A system of machinery almost organic has been devised and arranged, which, while it relieves the human frame of its most laborious efforts in printing, far exceeds all human powers in rapidity and dispatch. That the magnitude of the invention may be justly appreciated by its effects, we shall inform the public that after the letters are placed by the compositors, and enclosed in what is called the ‘form,’ little more remains for man to do than to attend upon and watch this unconscious agent in its operations. The machine is then merely supplied with paper, itself places the form, inks it, adjusts the paper to the form newly inked, stamps the sheet, and gives it forth to the hands of the attendant, at the same time withdrawing the form for a fresh coat of ink, which itself again distributes, to meet the ensuing sheet now advancing for impression, and the whole of these complicated acts is performed with such a velocity and simultaneousness of movement that no less than 1,100 sheets are impressed in one hour. That the completion of an invention of this kind, not the effect of chance, but the result of mechanical combinations, methodically arranged in the mind of the artist, should be attended with many obstructions and much delay may be readily admitted. Our share in this event has, indeed, only been the application of the discovery, under an agreement with the patentees, to our own particular business; yet few can conceive, even with this limited 308interest, the various disappointments and deep anxiety to which we have for a long course of time been subjected. Of the person who made the discovery we have little to add. Sir Christopher Wren’s noblest monument is to be found in the building which he erected: so is the best tribute of praise which we are capable of offering to the inventor of the printing machine comprised in the preceding description, which we have feebly sketched, of the powers and utility of his invention. It must suffice to say further, that he is a Saxon by birth, that his name is König, and that the invention has been executed under the direction of his friend and countryman, Bauer.”

Fig. 151.Diagram of Cowper and Applegath’s Single Machine.

Each of the machines erected by König for the “Times” printed only one side of the sheet, so that when they had been half printed by one machine, they had then to be passed through the other, in order to be “perfected,” as it is technically termed. These machines were greatly improved by Messrs. Applegath and Cowper, who contrived also a modification by which the sheets could be perfected in one and the same machine. As the principle of these machines has been followed, with more or less diversity of detail, in most of the printing machines at present in use, it is very desirable to lay that principle clearly before the reader. The diagram, Fig. 151, will make the action of Applegath and Cowper’s single-printing machine easily understood. The type is set up on a flat form, A B, which occupies part of the horizontal table, C D, the rest of which, A C, is the inking table. E is a large cylinder, covered with woollen cloth, which forms the “blanket.” The paper passes round this cylinder, and it is pressed against the form. The small black circles, f, g, h, k, l, m, n, represent the rollers for distributing the ink. f is called the ductor roller. This roller, which revolves slowly, is made of metal, and parallel to it is a plate of metal, having a perfectly straight edge, nearly, but not quite, touching the cylinder, and at the other side, as well as at the extremities, bent upwards, so as to form a kind of trough, to contain the ink, as a reservoir. The slow rotation of the ductor conveys the ink to the next roller, which is covered with composition, and being made to move backwards and forwards between the ductor roller and the table at certain intervals, it is termed the vibrating roller. The ink having thus reached the inking-table, is spread evenly thereon by the distributing rollers, h, k, and it is taken up from the inking table, as the latter passes under, by the inking rollers, l, m, n. The table, C D, as a whole is constantly moving right and left in a horizontal direction, 309so that the form passes alternately under the impression cylinder, E, and the inking rollers, l, m, n. The axles of the inking and distributing rollers are made long and slender, and instead of turning in fixed bearings, they rest in slots or notches, in order that, as the form passes below them, they may be raised, so that they rest on the inking slab, and on the types, only by their own weight. They are placed not quite at right angles to the direction of the table, but a little diagonally. The sliding motion caused by this, helps very much in the uniform spreading of the ink. By these arrangements the form is evenly smeared with ink, since each inking roller passes over it twice before it returns to meet the paper under E.

Fig. 152.Diagram of Applegath and Cowper’s Perfecting Machine.

Fig. 153.Cowper’s Double Cylinder Machine.

Fig. 152 is a similar diagram, to show the action of the double or perfecting printing machine, in which the sheets are printed on both sides. It will be observed that the general arrangement of impression cylinder, rollers, &c., is represented in duplicate, but reversed in direction. There are also two cylinders, B B, the purpose of which, as may be gathered from an inspection of the diagram, is to reverse the sheets of paper, so that after one side has been printed under the cylinder, , the blank surface may be turned downward, ready to receive the impression from the form, A B. Fig. 153 gives a view of the Cowper and Applegath double machine, as actually constructed. The man standing up is called the feeder or layer-on. He pushes the sheets forward, one by one, towards the tapes, which carry them down the farther side of the more distant cylinder, under which they pass, receiving the impression; and so on in the manner already indicated 310in the diagram, Fig. 152, until finally they reach a point where, released by the separation of the two sets of tapes, they are received by the taker-off (the boy who is represented seated on the stool), and are placed by him on a table. The bed or table which carries the form moves alternately right and left, impelled by a pinion acting in a rack beneath it, in such a manner that the direction of the table’s motion is changed at the proper moment, while the driving pulley continues to revolve always in the same direction. The movements of the table and of the cylinders are performed in exact harmony with each other, for these pieces are so connected by trains of wheels and rack-work that the sheets of paper may always receive the impression in the proper position as regards the margins, and therefore, when the sheets are printed on both sides, the impressions will be exactly opposite to each other. This gives what is technically called “true register,” and as this cannot be secured unless the paper travels over both cylinders at precisely the same rate, these are finished with great care by turning their surfaces in a lathe to exactly the same diameter. The action of the machine will not be fully understood without a glance at the arrangement of the endless tapes which carry the paper on its journey. The course of these may be followed in Fig. 154, and a simple inspection of the diagram will render a tedious description unnecessary.

Fig. 154.Tapes of Cowper’s Machine.

In Fig. 155 we have a representation of a steam-power printing machine, such as is now very largely used for the ordinary printing of books, newspapers of moderate circulation, hand-bills, &c., and in all the ordinary work of the printing press. In this the table on which the form is placed has a reciprocating motion, but the large cylinder moves continuously always in the same direction. The feeder, or layer-on, places the sheet of paper against certain stops, and at the right moment the sheet is nipped by small steel fingers, and carried forwards to the cylinder, which brings it into contact with the inked type. This is done with much accuracy of register, for the impression cylinders gear in such a manner with the rest of the parts that their revolutions are synchronous. This is a perfecting machine, for the paper, after having received the impression on one side, is carried by tapes round the other cylinder, where it receives the impression on the other side, “set-off sheets” being passed through the press at the same time. The axles of the impression cylinders are mounted at the 312ends of short rocking beams, by small oscillations of which the cylinders are alternately brought down upon, or lifted off, the form passing below them. A machine of this kind can print 900 impressions per hour, even of good bookwork, and for newspaper or other printing, where less accuracy and finish are required, it may be driven at such a rate as to produce 1,400 perfected impressions per hour.

Fig. 155.Messrs. Hopkinson and Cope’s Perfecting Machine.

The machines used for lithographic printing by steam power are almost identical in their general arrangement with that just described, which may be taken as a representative specimen of the modern printing machine.

To such machines as those already described the world is indebted for cheap books, cheap newspapers, and cheap literature in general. But when, with railways and telegraphs, came the desire for the very latest intelligence, the necessities of the newspaper press, as regards rapidity of printing, soon required a greater speed than could possibly be attained by any of the flat form presses; for in these the table, with the forms placed upon it, is unavoidably of a considerable weight, and this heavy mass has to be set in motion, stopped, moved in the opposite direction, and again stopped during the printing of each sheet. The shocks and strains which the machine receives in these alternate reversals of the direction of the movement impose a limit beyond which the speed cannot be advantageously increased. When Mr. Applegath was again applied to by the proprietors of the “Times” to produce a machine capable of working off a still larger number of impressions, he decided upon abandoning the plan of reciprocating movement, and substituting a continuous rotary movement of the type form. And he successfully overcame the difficulties of attaching ordinary type to a cylindrical surface. The idea of placing the type on a rotating cylinder is due to Nicholson, who long ago proposed to give the types a wedge shape, so that the pieces of metal would, like the stones of an arch, exactly fit round the cylindrical surface. The wedge-shaped types were, however, so liable to be thrown from their places by the centrifugal force, that Nicholson proposed also certain mechanical methods of locking the types together after they had been placed on the circumference of the drum. The plan he suggested for this purpose involved, however, such an expenditure of time and trouble that his idea was never carried into practice. Mr. Applegath used type of the ordinary kind, which was set up on flat surfaces, forming the sides of a prism corresponding to the circumference of his revolving type cylinder, which was very large and placed vertically. The flat surfaces which received the type were the width of the columns of the newspaper, and the type forms were firmly locked up by screwing down wedge-shaped rules between the columns at the angles of the polygon. These form the “column rules,” which make the upright lines between the columns of the page, and by their shape they served to securely fix the type in its place. The diameter of the cylinder to which the form was thus attached was 5 ft. 6 in., but the type occupied only a portion of its circumference, the remainder serving as an inking table. Round the great cylinder eight impression rollers were placed, and to each impression roller was a set of inking rollers. At each turn, therefore, of the great cylinder eight sheets received the impression. These cylinders were, as already stated, placed vertically, and, as it was necessary to supply the sheets from horizontal tables, an ingenious arrangement of tapes and rollers was contrived, by which each sheet was first carried down from the table into a vertical position, with its plane directed towards the impression roller, in which position it was stopped for an instant, then moved horizontally forwards round the 313impression cylinder, and was finally brought out, suspended vertically, ready for a taker-off to place on his pile. This machine gave excellent results as to speed and regularity. From 10,000 to 12,000 impressions could be worked off in an hour, and the advantage was claimed for it of keeping the type much cleaner, by reason of its vertical position. The power of this machine may be judged of from one actual instance. It is stated that of copies of the “Times” in which the death of the Duke of Wellington was announced, 14th November, 1852, no less than 70,000 were printed in one day, and the machines were not once stopped, either to wash the rollers or to brush the forms. It may be mentioned, in order to give a better idea of the magnitude of the operation of printing this one newspaper, that one average day’s copies weigh about ten tons, and that the paper for the week’s consumption fills a train of twenty waggons.

At the “Times” office and elsewhere, the vertical machine has some years ago been superseded by others with horizontal cylinders. The fastest, perhaps, of all these printing machines is that which is now known as the “Walter Press,” so called either because its principle was suggested by the proprietor of the “Times,” or merely out of compliment to him. The improvements which are embodied in the Walter Press have been the subject of several patents taken out in the names of Messrs. MacDonald and Calverley, and it is to these improvements that we must now direct the attention of the reader. But we must premise that such machines as the Walter Press became possible only by the discovery of the means of rapidly producing what is called a stereotype plate from a form of type. A full account of the methods of effecting this is reserved for a subsequent article, but here it may suffice to say, that when a thick layer of moist cardboard, or rather a number of sheets of thin unsized paper pasted together and still quite moist, is forced down upon the form by powerful pressure, a sharp even mould of the type is obtained, every projection in the latter producing a corresponding depression in the papier maché mould. When the paper mould is dry, it may be used for forming a cast by pouring over it some fusible metallic alloy, having the properties of becoming liquid at a temperature which will not injure the mould, of taking the impressions sharply, and of being sufficiently hard to bear printing from. One of the improvements in connection with the Walter Press is in the mode of forming cylindrical stereotype casts from the paper mould. For this purpose the mould is placed on the internal surface of an iron semi-cylinder, with the face which has received the impression of the type inwards. The central part of the semi-cylinder is occupied by a cylindrical iron core, which is adjusted so as to leave a uniform space between its convex surface and the concave face of the mould. Into this space is poured the melted metal, and its pressure forces the mould closely against the concave cylindrical surface to which it is applied, so that the thickness becomes quite uniform. The iron core has a number of grooves cut round it, and these produce in the cast so many ribs, or projections, which encircle the inner surface, and serve both to strengthen the cast and afford a ready means of obtaining an exact adjustment. Not the complete cylinder, but only half its circumference, is cast at once, the axis of the casting apparatus being placed horizontally, and the liquid metal poured in one unbroken stream between the core and the mould from a vessel as long as the cylinders. Fig. 156 is a section of the casting apparatus, in which a is the core, b the papier maché mould, c the iron semi-cylinder containing it, d the metal which has been poured in at the widened space, e. When the metal has solidified, 314the core is simply lifted off, and the cast is then taken out, in the form of a semi-cylinder, the internal surface of which has exactly the diameter of the external surface of the roller of the machine on which it is to be placed, in company with another semi-cylindrical plate, so that the two together encircle half the length of the roller, and when another pair of semi-cylinders have been fixed on the other part of the roller, the whole matter of one side of the newspaper sheet, usually four pages, is ready for printing. One great advantage of working from stereotype casts made in this way is that the form-bearing cylinder of the machine has no greater circumference than suffices to afford space for the matter on one side of the paper. The casts are securely fixed on the revolving cylinder by elbows, which can be firmly screwed down. The casts are usually made to contain one page each, so that four semi-cylinders, each half the length of the revolving cylinder, are fixed on the circumference of the latter. The process of casting in no way injures the paper mould, which is in fact generally employed to produce several plates.

Fig. 156.

Fig. 157.Diagram of the Walter Press.

The Walter Machine is not fed with separate sheets of paper, but takes its supply from a huge roll, and itself cuts the paper into sheets after it has impressed it on both sides. This is done by a very simple but effective plan, which consists in passing the paper between two equal-sized rollers, the circumference of which is precisely the length of the sheets to be cut. These rollers grip the paper, but only on the marginal spaces; and on the circumference of one of them, and parallel to its axis, is a slightly projecting steel blade, which fits into a corresponding recess, or groove, in the circumference of the other, and at this time the whole width of the sheet is firmly held by a projecting piece acted on by a spring. Although the Walter Machine, as actually constructed, presents to the uninitiated spectator an apparently endless and intricate series of parallel cylinders and rollers, yet it is in reality exceedingly simple in principle, as may be seen by the diagram given in Fig. 157. In this we may first direct the reader’s attention to the two cylinders, F1, F2, which bear the stereotype casts—one of the matter belonging to one side of the sheet, the other of the matter belonging to the other side, for the Walter Press is a perfecting machine—and the web of paper having been printed by F1, against which it is pressed by the roller, P1, passes straight, as shown by the dotted line, to the second pair of cylinders, in order to be printed on the other side; and here, of course, the form cylinder, F2, is below, and the impression cylinder, P2, above, and an endless cleaning blanket is supplied to the latter to receive 315the set-off. The web of paper then passes between the cutting rollers, C, C1, by which it is cut in sheets. But the knife has a narrow notch in the centre, and one at each end, so that the paper is not severed at those parts, narrow strips or tags being left, which maintain for a while a slight connection. But the tapes, t1, t2, between which the paper is now carried, are driven at a rather quicker rate than the web issues from C, C1; and the result is, that the tags are torn, and the sheet becomes separated from the portion next following it. Thus, as a separate sheet, it arrives at the horizontal tapes, h, and is brought to another set of tapes mounted on the frame, r, rocking about the centre, c, by which it is brought finally to the tapes, f1, f2, which by the movement of r receive the sheets alternately. A sheet-flyer, s, oscillates between the tapes, f1, f2; and as fast as the sheets arrive, lays them down right and left alternately, and it only remains for the piles, p1, p2 so formed, to be removed. The inking apparatus of each form-cylinder is indicated by the series of rollers marked I1, I2; and in this part of the machine there are also some improvements over former presses, for the distributing rollers are not made of composition, but of iron, turned with great exactness to a true surface, and arranged so as not quite to touch each other. At D is an apparatus for damping the paper, in which there are hollow perforated cylinders, covered by blanket, and filled with some porous material, which is kept constantly wet. These cylinders being made to rotate rapidly, the centrifugal force causes the water to find its way uniformly to the outside. Here the paper also passes between rollers intended to flatten and to stretch it. At R is the great roll of paper, from which the machine takes its supply. These rolls contain, perhaps, five miles length of paper, and at first it was a matter of some difficulty to fix them firmly on their wooden axles, so that they might be steadily unwound; but the 316contrivers of the Walter Press make these spindles as tight as may be required by forming them in wedge-shaped pieces, which can be made to increase the thickness of the spindle by drawing one upon another by screws.

The great speed of the Walter Machine is secured by the paper being drawn by the machine itself from a continuous web, instead of being laid on in a separate sheet, so that the machine is not dependent on the dexterity of the layers-on, who are besides necessarily highly-skilled workmen, and therefore a great economy of wages results from using a machine which does not require their services; and as the Walter Press also itself lays down the perfected sheets, the necessary attendants are as few as possible. The waste of paper and loss of time by stoppages are said to be extremely small with this machine.

Fig. 148 will give some idea of the appearance of the printing-room where one of the leading London daily papers is being printed by Walter Presses.

Another fast printing machine is the type revolving cylinder machine invented by Colonel Richard M. Hoe, and manufactured by the well-known firm of Hoe and Company, New York, with whose name the history of fast printing machines must ever be associated. In these machines the type is placed on the circumference of a cylinder which rotates about a horizontal axis, and the difficulties of securely locking up the type are successfully overcome. The machines are made with two, four, six, eight, or ten impression cylinders, and at each revolution of the great cylinder the corresponding number of impressions are produced. The engraving on the opposite page, Fig. 158, represents the two-cylinder machine, and an examination of the figure will render its general action intelligible. The form of type occupies about one-fourth of the circumference of the great cylinder, the remainder being used as an ink-distributing surface. Round this main cylinder, and parallel to it, are placed smaller impression cylinders, from two to ten in number, according to the size of the machine. When the press is in operation, the rotation of the main cylinder carries the type form to each impression cylinder in succession, and it there impresses the paper, which is made to arrive at the right time to secure true register. One person is required for each impression cylinder, to supply the sheets of paper, which have merely to be laid in a certain position, when, at the proper moment, they are seized by the “grippers,” or fingers of the machine, and after having been printed, are carried out by tapes, and laid in heaps by self-acting sheet-flyers, by which the hands which are required to receive and pile the sheets in other machines are dispensed with. The ink is contained in a fountain placed beneath the main cylinder, and is conveyed by means of rollers to the distributing surface of the main cylinder. This surface, being lower than that of the type forms, passes by the impression cylinders without touching them. For each impression cylinder there are two inking rollers, receiving their supply of ink from the distributing surface of the main cylinder. These inking rollers, the bearings of which are, by springs, drawn towards the axis of the main cylinder, rise as the form passes under them, and having inked it, they again drop on to the distributing surface. Each page of the matter is locked up on a detachable segment of the large cylinder, which segment constitutes its bed and chase. The column-rules are parallel with the shaft of the cylinder, and are consequently straight, while the head, advertising, and dark rules have the form of segments of a circle. The column-rules are in the shape of a wedge, 318with the thin end directed towards the axis of the cylinder, so as to bind the types securely. These wedge-shaped column-rules are held in their place by tongues projecting at intervals along their length, and sliding in grooves cut crosswise in the face of the bed. The spaces in the grooves between the column-rules are accurately fitted with sliding blocks of metal level with the surface of the bed, the ends of the blocks being cut away underneath, to receive a projection on the sides of the tongues of the column-rules. The locking up is effected by means of screws at the foot of each page, by which the type is held as securel