NRLF
B ^ Ebl 7MD
LJ N 1VERSITY OF CALIFORNIA.
G-IFT OF
THE ''CLASS OF 1883.
X
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.
PLATE II.
JKON IN ARCHITECTURE- THE CRYSTAL PALACE, SYPENHAM
DISCOVERIES AND
INVENTIONS
OF THE
NINETEENTH CENTURY.
BY
ROBERT ROUTLEDGE, B.Sc., F.O.S.,
Assistant Examiner in Chemistry and in Natural Philosophy to tke University of London.
WITH NUMEROUS ILLUSTRATIONS.
FIFTH EDITION.
LONDON:
GEORGE ROTJTLEDGE AND SONS,
THE BROADWAY, LUDGATE.
NEW YORK : 416 BROOME STREET.
1881.
SAME AUTHOR.
A POPULAR
HISTORY OF SCIENCE.
BY ROBERT ROUTLEDGE,
.Sc. (LondJ, f.C.S.
WITH MORE THAN THREE HUNDRED PORTRAITS,
ILLUSTRATIONS, AND DIAGRAMS.
'2/Z^'d
SCIENCE IN SPORT
MADE
PHILOSOPHY IN EARNEST.
EDITED BY
ROBERT ROUTLEDGE,
.Se. (LondJ, F.C.S.
BEING AN ATTEMPT TO ILLUSTRATE SOME
ELEMENTARY PRINCIPLES OF PHYSICAL KNOWLEDGE
BY MEANS OF TOYS AND PASTIMES.
WITH NUMEROUS ILLUSTRATIONS.
PREFACE.
IN the following pages an attempt has been made to present a
popular account of remarkable discoveries and inventions which
characterize the present century. 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 progress of our age. The topics
comprise chiefly those great applications of mechanical, engineering,
physical, and chemical science, in which every intelligent person
feels concerned; and a few articles only are devoted to certain purely
scientific discoveries which are exciting general interest.
The Author has aimed at giving a concise, but clear, description of
the several subjects ; and he has endeavoured to indicate, if not to ex-
plain, the principles involved in each discovery and invention; 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 ordi-
nary education. The design has been to treat the subjects as fami-
liarly 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.
A book on a plan somewhat similar to, but by no means identical
with, that of the present work, was projected two or three years ago,
by Mr. J. H. PEPPER ; and, in fact, several sheets were in type, when
its progress was permanently interrupted by that gentleman's removal
to a distant part of the world. The matter in type, which had become
viii PREFACE.
the property of the Publishers, and also a number of woodcuts (re-
lating chiefly to warlike inventions) which had been prepared under
Mr. PEPPER'S direction, were placed at the Author's disposal. He
has found it convenient to make use of some portion of this material;
hence, the article on " The Suez Canal," the sections on " Shells and
Explosive Bullets," and on "Sand Experiments," and the paragraphs
giving numerical particulars regarding the Martini-Henry rifle, are from
the pen of Mr. PEPPER.
The articles in this work are, in general, independent of each other ;
although in a few cases an acquaintance with preceding pages may be
found to render the subject more easy for the general reader. The
nature of the subjects treated of allows little opportunity for any
regularly classified arrangement ; it may, however, be stated that the
earlier part of the book deals with matters having reference mainly
to mechanical and engineering achievements; these are followed by
accounts of discoveries and inventions having some relation to the
so-called physical forces ; while the chapters involving chemical con-
siderations are placed in the latter part of the work ; and these last
articles include a glimpse of some theories necessary for a real com-
prehension of the subject. In the final article the Author has essayed
to attract attention to a grand discovery, which, as yet, has seldom
been introduced into books intended for the widest circle of readers.
In some of the articles the reader is recommended to try certain easily
performed and inexpensive experiments, which will give him or her an
otherwise unattainable grasp of the principles involved.
CONTENTS.
Page
INTRODUCTION... ... ... ... ... ... ... i
STEAM ENGINES ... ... ... ... ... ... 3
THE LOCOMOTIVE ... ... ... ... ... ... 14
PORTABLE ENGINES... ... ... ... ... ... 2O
THE STEAM HAMMER ... ... ... ... ... 21
IRON ... ... ... ... ... ... ... ... 25
TOOLS... ... ... ... ... ... ... ... 43
THE BLANCHARD LATHE ... ... ... ... ... 54
SAWING MACHINES ... ... ... ... ... ... 56
RAILWAYS ... ... ... ... ... .., ... 59
THE METROPOLITAN RAILWAYS ... ... ... ... 72
THE PACIFIC RAILWAY ... ... ... ... ... 74
STEAM NAVIGATION ... ... ... ... ... ... 83
THE BESSEMER CHANNEL STEAMER ... ... ... ..." 93
THE CASTALIA ... ... ... ... ... .,. 96
SHIPS OF WAR ... ... ... ... ... ... 99
FIRE-ARMS
117
RIFLED CANNON ... ... '
118
BREECH-LOADING RIFLES
... 131
MITRAILLEURS, OR MACHINE GUNS ...
136
SHELLS AND EXPLOSIVE BULLETS* ...
142
TORPEDOES
147
THE SUEZ CANAL*
162
SAND ...
179
SAND EXPERIMENTS*
179
THE SAND BLAST ...
184
IRON BRIDGES ...
187
GIRDER BRIDGES
191
SUSPENSION BRIDGES
195
PRINTING MACHINES ...
201
LETTERPRESS PRINTING
202
PATTERN PRINTING...
217
HYDRAULIC POWER
22O
PNEUMATIC DISPATCH ...
... 2 3 6
ROCK BORING ...
245
THE MONT CENIS TUNNEL ...
- 247
ROCK-DRILLING MACHINES ...
THE CHANNEL TUNNEL
- 251
260
LIGHT...
26 7
SOME PHENOMENA OF LIGHT
269
VELOCITY OF LIGHT
271
By Mr. J. H. PEPPER
CONTENTS.
LIGHT continued. p a ge
REFLECTION OF LIGHT ... ... ... ... ... 275
REFRACTION ... ... .. ... ... ... 283
DOUBLE REFRACTION AND POLARIZATION ... ... ... 285
CAUSE OF LIGHT AND COLOUR ... ... ... ... 294
THE SPECTROSCOPE ... ... ... ... ... ... 302
CELESTIAL CHEMISTRY AND PHYSICS ... ... ... ... 322
SIGHT... ... ... ... ... ... ... ... 332
THE EYE ... ... ... ... ... ... ... 334
VISUAL IMPRESSIONS ... ... ... ... ... 348
ELECTRICITY ... ... ... ... ... ... ... 359
ELEMENTARY PHENOMENA OF ELECTRICITY AND MAGNETISM ... 361
THEORY OF ELECTRICITY ... ... ... ... ... 365
ELECTRIC INDUCTION ... ... ... ... ... 366
DYNAMICAL ELECTRICITY ... ... ... ... ... 368
INDUCED CURRENTS ... ... ... ... ... 380
MAGNETO-ELECTRICITY ... ... ... ... ... 384
THE GRAMME MAGNETO-ELECTRIC MACHINE ... ... ... 388
THE ELECTRIC TELEGRAPH ... ... ... ... ... 397
TELEGRAPHIC INSTRUMENTS... ... ... ... ... 403
TELEGRAPHIC LINES ... ... ... ... ... 422
LIGHTHOUSES ... ... ... ... ... ... ... 432
PHOTOGRAPHY ... ... ... ... ... ... ... 446
PRINTING PROCESSES ... ... ... ... ... ... 459
STEREOTYPING ... ... ... ... ... ... 459
LITHOGRAPHY ... ... ... ... ... ... 463
OTHER PROCESSES ... ... ... ... ... ... 467
RECORDING INSTRUMENTS ... ... ... ... ... 472
AQUARIA ... ... ... ... ... ... ... 484
THE CRYSTAL PALACE AQUARIUM ... ... ... ... 486
THE BRIGHTON AQUARIUM ... ... ... ... ... 491
GOLD AND DIAMONDS ... ... ... ... ... ... 496
GOLD ... ... ... ... ... ... ... 496
DIAMONDS >.. ... ... ... ... ... ... 501
NEW METALS ... ... ... ... ... ... ... 505
INDIAN-RUBBER AND GUTTA-PERCHA ... ... ... ... 513*-
INDIAN-RUBBER ... ... ... ... ... ... 513
GUTTA-PERCHA ... ... ... ... ... ... 517
ANAESTHETICS ... ... ... ... ... ... ... 520
EXPLOSIVES ... ... ... ... ... ... ... 529
MINERAL COMBUSTIBLES ... ... ... ... ... 537
COAL ... ... ... ... ... ... ... 537
. PETROLEUM ... ... ... ... ... ... 543
PARAFFIN ... ... ... ... ... ... ... 547
COAL-GAS ... ... ... ... ... ... ... 550
COAL-TAR COLOURS ... ... ... ... ... ... 561
THE GREATEST DISCOVERY OF THE AGE... .. ... ... 579
LIST OF ILLUSTRATIONS.
Fif. Page
Heading Wind, Steam, and Speed
(after Turner) i
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 GifFard's Injector n
7. Bourdon's Pressure Gauge 12
8. Steam Generator 13
9. Section of Locomotive 15
10. Stephenson's Link Motion 17
ii. Explosion of Boiler 19
1 2. Hancock's Steam Omnibus 19
13. Nasmyth's Steam Hammer 23
14. Merryweather's Steam Fire-Engine 24
15. A Foundry 25
1 6. Aerolite in the British Museum 26
17. Blast Furnace 27
18. Section of Blast Furnace 28
19. Plan of Blast Furnace 29
20. Cup and Cone 32
21. Rolling Mill 33
22. Fibrous Fracture of Wrought Iron... 35
23. Experiments at Baxter House ^7
24. Bessemer Converter 39
25. Apparatus for Making Bessemer Steel 40
26. Cupola Furnace 42
27. Portrait of Sir Joseph Whitworth ... 43
28. Whitworth's Screw Dies and Tap ... 44
29. Screw-cutting Lathe 45
30. Whitworth's Measuring Machine ... 47
31. Whitworth's Drilling Machine 49
32. Whitworth's Planing Machine 51
33. Pair of Whitworth's Planes or Surface
Plates 52
34. Interior of Engineer's Workshop ... 53
35. Blanchard Lathe t 54
36. Vertical Saw 56
37. Circular Saw 57
38. Pit-Saw 58
39. Box Tunnel 59
40. Coal-Pit, Salop 60
41. Sankey Viaduct 61
42. Rails and Cramp-gauge 62
43. Fish-plate 63
44. Section of Rails and Fish-plates 64
45. Conical Wheels 65
46. Centrifugal Force 65
47- Points 66
48. Signal-Box on North London Rail-
way 67
49. Post Office Railway Van 69
50. Gower Street Station, Metropolitan
Railway 73
51. Map of the Route of Pacific Railway 75
52. Trestle Bridge 76
53. American Canyon 77
54. Cape Horn 79
55. Snow Plough 80
56. First Steam Railroad Train in America 81
Fig. Page
57. Railway Embankment 82
58. The Great Eastern at Anchor 83
59. Casting Cylinder of a Marine Steam
Engine 85
60. Screw-Propeller 86
61. Section of Great Eastern amidships 88
62. The Great Eastern in course of Con-
struction 89
63. The Great Eastern ready for Launch-
ing 90
64. Comparative sizes of Steamships ... 91
65. The Great Eastern at Night 92
66. Saloon of the Bessemer Steamer 93
67. The Castalia in Dover Harbour 97
68. The same. End View 98
69. H.M.S. Devastation in Queenstown
Harbour 99
70. Section of H.M.S. Hercules 101
71. Section of H.M.S. Inconstant 103
72. Section, Elevation, and Plan of Tur-
ret of H.M.S. Captain 104
73. H.M.S. Captain 105
74. Diagram of H.M.S. Captain 108
75 Ditto 109
76. H.MS. Glatton 112
77. H.M.S. Thunderer 113
78. The Koiue Wilhelm 115
Firing at Floating Battery 116
79. Krupp's Works at Essen, Prussia ... 117
80. Section of 9 in. Fraser Gun 119
81. The 35-ton Fraser Gun 123
82. Mill wall Shield after being battered
with Heavy Shot. Front View... 124
83. Rear View of the Millwall Shield ... 124
84. Comparative sizes of 35 and 8i-ton
Guns 125
85. The 7-pounder Rifled Steel Gun 126
86. The 1 10 - pounder Breech - loading
Krupp's Gun ; open, ready to load 126
87. The same, ready for firing 127
88. The 32 - pounder Prussian Krupp
Siege Gun 127
89. Appearance of the Deckofa Shipafter
the Bursting of a large Gun 128
90. Another view of the same disaster... 128
91. The Citadel of Strasburg after the
Prussian Bombardment 129
92. Moncrieff *s Gun - Carriage ; Gun
lowered for loading 130
93. The same, raised and ready for firing 130
94. 6oo-pounder Muzzle -loading Arm-
strong Gun 131
95. Section of Martini-Henry Lock ....... 132
96. Martini-Henry Rifle 134
97. The Chassepot Rifle. Section of the
Breech 135
98. The Catling Battery Gun. Rear
View 137
99. The same. Front View 139
loo. The Montigny Mitrailleur 141
loi. Mallet's Mortar 143
102. The Shrapnel and Segment Shells... 143
XI
Xll
LIST OF ILLUSTRATIONS.
Fig. Page
103. Norton's Explosive Bullets and Rifle
Shells 145
104. General John Jacob's Explosive Bul-
lets 146
105. Major Fosbery's Explosive Bullets 146
106. Henry's Torpedo. Working the
Brakes 147
10 7 Submerged Torpedo 148
108. Mode of Firing Torpedo 150
109. Explosion of Whitehead's Torpedo... 151
no. Effect of the Explosion of White-
head's Torpedo 152
in. Experiment with a Torpedo charged
with 10 Ibs. Gun-Cotton 153
112. Explosion of Torpedo containing 67
Ibs. Gun-Cotton 154
113. Explosion of 432 Ibs. Gun-Cotton in
37ft. Water 155
114. The same in 27 ft. Water 155
115. Section of Priming-Cas* and Explod-
ing Bolt 156
116. Harvey's Torpedo 157
117. The same 158
118. The same 159
119. Official Trial of "Harvey's Sea Tor-
pedo" 159
120. Model of Submarine Guns 160
121. The Warner Experiment offBrighton 161
Portrait of M. Lesseps 162
122. Port Said 165
123. One of the Breakwaters at Port Said 166
124. Bird's-eye View of Port Said 166
125. Map of the Suez Canal 167
126. A Group of Egyptian Fellahs and
their Wives 168
127. Dredges and Elevators at Work 170
128. Railway Station at Ismailia 171
129. Lake Timsah and Ismailia 172
130. The Viceroy of Egypt cutting Em-
bankment 174
131. Apparatus for showing Sand Experi-
ments 180
132. Model marked like Chevrons 181
133. Iron Cylinder, Sand, and Eggs 181
134. The Three Cylindrical Vessels and
Tubes 182
135. Framework to represent Pail 182
136. Tube, Sand, and Sledge-Hammer .. 182
137. Hour-Glass on Screen at Polytechnic 183
138. Britannia Bridge, Menai Straits 187
139. Diagram showing Strains 189
140. Ditto 190
141. Girder 190
142. Ditto 190
143. Ditto 191
144. Section of a Tube of the Britannia
Bridge 192
145. Albert Bridge, Saltash itfe
146. Clifton Suspension Bridge ,... 196
147. Section of Shaft 197
148. Newspaper Printing-Room 201
149. Inking Balls 202
150. Inking Roller 202
151. Diagram of Single Machine 204
152. Diagram of Perfecting Machine ... 205
153. Cowper's Double Cylinder Machine 205
154. Tapes of Cowper's Machine 206
155. Hopkinson and Cope's Perfecting
Machine 207
156. Section of Casting Apparatus 210
157. Diagram of the Walter Press 211
158. Hoe's Type Revolving Cylinder
Machine 213
Fig. Page
159. Hoe's "Railway" Machine 215
160. Napier's Platen Machine 216
161. Roller for Printing Wail-Papers 218
162. Machine for Printing Paper-Hang-
ings 219
163. Chain-Testing Machine 220
164. Pascal's Principle 221
165. Collar of Hydraulic Cylinder 222
166. Hydraulic Press 223
167. Section of Hydraulic Lift Graving
Dock 227
168. Section of Column 228
169. SirW. Armstrong's Hydraulic Crane 231
170. Raising Tubes of Britannia Bridge 232
171. Press for Raising the Tubes 233
172. Head of Link- Bars 234
173. Apparatus to prove Transmission of
Pressure 235
174. Pneumatic Tubes and Carriages 236
175. Diagram of Tubes, &c 238
176. Sending and Receiving Apparatus... 239
177. Section of Receiving Apparatus 240
178. Sommelier Boring Machines 245
179. Transit by Diligence over Mont Cenis 249
180. Burleigh Rock Drill on Tripod 252
181. The same on Movable Column 254
182. The same Mounted on Carriage 255
183. Diamond Drill Crown 256
184. Diamond Drill Machinery 259
185. Chart of the Channel Tunnel 263
186. Section of the Channel Tunnel 264
187. View of Dover 265
188. Contrasts of Light 2.67
189. Rays 269
190. Diagram 270
191. Telescopic Appearance of Jupiter and
Satellites 271
192. Diagram 273
193, 194, 195. Diagrams 275
196. Diagram 276
197. Polemoscope 277
198. Apparatus for Ghost Illusion 278
199. Illusion produced by Mirrors 280
200. A Stage Illusion 281
201. View of Venice Reflections 282
202. Refraction ; , 283
203. Diagram 284
204, 205. Diagrams of Crystals 286
206. Diagram 287
207. Diagram 289
208. Diagram 290
209. Polariscope 292
210. Section showing Polarization 293
211. Iceland Spar, showing Double Re-
fraction 293
212. Diagram 294
213. Diagram 296
214. Diagram 298
215. Portrait of Professor Kirchhoff 302
216. Diagram 303
217. Newton's Experiment 304
218. Bunsen's Burner on Stand 307
219. Spectroscope with One Prism 309
220. Miniature Spectroscope 312
221. The Gassiot Spectroscope 313
222. Browning's Automatic Adjustment
of Prisms 315
223. Apparatus for Spark Spectra :.. 316
224. The Sorby-Browning Micro-Spectro-
scope 319
225. Section of Micro-Spectroscope, with
Micrometer 320
226. Diagram 321
LIST OF ILLUSTRATIONS.
Xlll
Fig. Page
227. Section of Micro-Spectroscope 322
228. Solar Eclipse, 1869 325
229. The Planet Saturn 326
230. Solar Prominences, No. i 328
231. Ditto, No. 2 329
232. Section of Amateur Star Spectro-
scope 330
233. Portrait of Professor Helmholtz 332
234. Vertical Section of the Eye 334
235. Section of Retina 336
236. Diagram 337
237. Muscles of Eyes 339
238. Diagram 341
239. Diagram 344
240. Diagram 345
241. Ruete's Ophthalmoscope 346
242. Diagram 347
243. Wheatstone's Reflecting Stereoscope 349
244. Diagram 350
245. Diagram 351
246. The Telestereoscope 353
247. Lines 355
248, 249. Diagrams 356
250, 251. Diagrams 357
252. Portrait of SirW. Thompson 359
253. A simple Electroscope 363
254. The Gold-leaf Electroscope 367
255. The Leyden Jar 368
256. A Voltaic Element 369
257. Ampere's Rule 370
258. Galvanometer 371
259. Daniell's Cell and Battery 373
260. Grove's Cell and Battery 373
261. Wire Ignited by Electricity 374
262. Duboscq's Electric Lantern and
Regulator 375
263. Decomposition of Water 376
264. Electro-plating 377
265. A Current producing a Magnet 378
266. An Electro-magnet 379
267. Ruhmkorff's Coil 381
268. Discharge through Rarefied Air 382
269. Appearance of Spark on Looking-
glass 384
270. Magneto-electric Spark 385
271. A Magnet producing a Current 386
272. Clarke's Magneto- electric Machine 386
273. Magneto-electric Light 387
274. Diagram 388
275. Gramme Machine 389
276. Insulated Coils 390
277. Hand Gramme Machine 390
278. Gramme Machine, with Eight Verti-
cal Electro-magnets 393
279. Gramme Machine, with Horizontal
Electro-magnets 395
280. Gramme Machine 395
281. Portrait of Professor Morse 397
282. Double-Needle Instrument 404
283. Electro-magnetic Bells 405
284. Portable Single-Needle Instrument 406
285. Connections of Telegraph Line 408
286. Morse Recording Telegraph 409
287. Morse Transmitting Key 411
288. Morse Transmitting Plate 412
289. Step-by-step Movement 417
290. Froment's Dials 417
291. Wheatstone's Universal Dial Tele-
graph 418
292. Mirror Galvanometer 420
293. Telegraph Post and Insulators 423
294. Ditto ; 423
Fig.
295. Wire Circuit 424
296. Wire and Earth Circuit 424
297. Submarine Cable 425
298. Making Wire for Atlantic Cable 427
299. Instrument-Room at Valentia 428
300. Breaking of the Cable 429
301. Atlantic Telegraph Cable, 1866 430
302. Diagram 430
Lig-hthouse (heading) 432
303. Eddystone Lighthouse 433
304. Eddystone in a Storm 434
305. Revolving Light Apparatus 440
306. Stephenson's Holophotal Light 443
307. Camera 446
308. Camera and Slide 454
309. Folding Camera 455
310. Lenses 456
311. Bath 458
312. Portrait of Aloysius Senefelder 459
313. Press for Stereotyping by Clay pro-
cess 460
314. Recording Anemometer 472
315. Registration of Height of Barometer
and Thermometer 474
316. Electric Chronograph 476
317. Negretti's Deep-Sea Thermometer... 480
318. Ditto, General Arrangement 481
319. Atmospheric Recording Instrument 482
320. Domestic Aquarium 484
321. The Opelet 488
322. Viviparous Blenny 489
323. The Lancelet 490
324. Sea-Horses 492
325. Proteus anguinus 493
326. Mud-fish 494
327. The Axolotl 495
328. Sorting, Washing, and Digging at the
South African Diamond-Fields ... 496
329. Gold Miners' Camp 498
330. Gold in Rocks 499
331. "Cradle "for Gold-washing 499
332. Pniel, from Jardine's Hotel 502
333. Sifting at the " Dry Diggings" 503
334. Vaal River, from Spence Kopje 504
335. Portrait of Sir Humphrey Davy 505
336. Apparatus 508
337. Portrait of Mr. Thomas Hancock ... 513
338. Portrait of Sir James Young Simp-
son, M.D .'.: 520
339. Railway Cutting 529
340. View on the Tyne 537
341. Fossil Trees in a Railway Cutting... 538
342. Impression of Leaf in Coal Measures 539
343. Possible Aspect of the Forests of the
Coal Age 540
344. The Fireside 542
345. View on Hyde and Egbert's Farm,
Oil Creek 547
2^6. View of City of London Gas-works... 550
347 . Section of Gas-making Apparatus... 551
348. The Retort 553
34Q . The Gas Governor 555
350. Bunsen's Burner 557
3 5 j. Faraday's Ventilating Gas-burner ... 558
352. Apparatus for making Magenta 561
353. Iron Pots for making Nitro-Benzol... 564
354. Section of Apparatus for making
Nitro-Benzol 565
355. Apparatus for making Aniline 56*
35 6. Section of Hollow Spindle 567
357. Portrait of J. Prescott Joule, F.R.S. 569
Tailpiece , 588
LIST OF PLATES.
PLATE I.
Drawn by
THE GREAT STEAM HAMMER Royal) p Tr tivntp . v
Gun Factory, Woolwich J P< HUNE
PLATE II.
IRON IN ARCHITECTURE The Crystal ">
Palace, Sydenham J
PLATF. III.
INTERIOR OF A PULLMAN CAR on the")
Midland Railway J
PLATE IV.
CLIFTON SUSPENSION BRIDGE, Niagara ,,
PLATE V.
THE GHOST ILLUSION
PLATE VI.
SPECTRA (Coloured Plate) '.
From
The Object
To face
... Page 24
PLATE VII.
LARGE INDUCTION COIL at the Polytechnic >
Institution )
PLATE VIII.
INTERIOR OF THE BRIGHTON AQUARIUM
PLATE IX.
RETORT HOUSE OF THE IMPERIAL GAS-")
WORKS, King's Cross, London $
... A Photograph ... Title page
The Object
... Page 70
A Design by \
the Author $
... 198
,, 278
... 308
The Object
A Photograph
The Object
.. 384
49*
554
Wind, Steam, and Speed (after TURNER).
INTRODUCTIONltn* I? 7
INLY 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 observa-
tion 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 length-
ened life ; it has mitigated pain ; it has extinguished diseases ; it has in-
creased 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 accele-
rated motion ; it has annihilated distance ; it has facilitated intercourse,
correspondence, all friendly offices, all dispatch of business ; it has enabled
\nan 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 yes-
terday was invisible is its goal to-day, and will be its starting-point to-
morrow." MACAULAY.
INTRODUCTION,
Thus every new invention, every triumph of engineering skill, is the
embodiment of some scientific idea ; and experience has proved that dis-
coveries 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 cheap-
ness of production which has placed comforts, elegancies, and refinements
unknown to our fathers within the reach of the humblest, are traceable in
"a high degree to that 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 in-
creased 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 copy-
ing, 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 pro-
duced 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 ^m^mber 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
<:team-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 inven-
tions and discoveries which distinguish the present age it is the purpose of
this work to give some account.
STEAM ENGINES.
*T* O track the steps which led up to the invention of the Steam Engine,
-* and fully describe the improvements by which the genius of the illus-
trious Watt perfected it at least in principle, are not subjects falling within
the province of this work, which deals only with the discoveries and inven-
tions 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 remove^, 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 /&, 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
12
STEAM ENGINES.
of cold water from the cistern, ^, 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
FIG. 2. Ncwcomeris Steam Engine.
the rod, m. The water which entered the cylinder from the cistern, toge-
ther with that produced by the condensation of the steam, flowed out of
the cylinder by the opening, /, the pipe from which was conducted down-
wards, 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 improve-
ments 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."
" 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
STEAM ENGINES.
FlG. 3. Watfs Double-action Steam Engine.
call 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 appli-
cation 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
STEAM ENGINES.
otherwise. 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."
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 per-
fection to which the steam engine was brought by Watt. The steam is con-
veyed to the cylinder through a pipe, B, the supply being regulated by the
FIG. ^.Governor and Throttle- Valve.
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 uni-
form ; 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//
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
STEAM ENGINES.
the 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, com-
municating 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 versa.
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 posi-
tion, 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,^ 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 pistori,
namely, where it is changing its direction, in which there is no force what-
ever 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 re-
moved, 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
8
STEAM ENGINES.
anchor, 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 ; c D, the
air-pump links,
from the centre
of which the air-
pump-rod is sus-
pended; c D
moves about the
fixed centre, c,
while D E is mov-
able about the
centre D, itself
moving in an arc,
of which c is the
centre. The dot-
ted 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 posi-
tion 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 in-
STEAM ENGINES.
ventions, but 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
FIG. 5. Slide Valve.
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 com-
municates 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 tem-
perature 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.
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 con-
sists simply of a very small cylinder, in which works a piston, very accu-
rately 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
i o STEAM ENGINES.
is 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 pres-
sure 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 atmo-
sphere 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 accu-
rately 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 sted.ni 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 /..,
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 Ibs. thirty-
three feet high, or the raising of thirty-three pounds i,opo 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 an-
STEAM ENGINES. it
other; for 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.
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 en-
graving 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 in-
vented 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
FIG. 6. Section of Giffard's Injector.
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 IB through the
holes. The nozzle of this tube is of a conical shape, and its centre is occu-
pied 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 conies 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 pro-
pelled 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
12
STEAM ENGINES.
water. 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, unrtil the pressure in H be-
comes 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. To explain the principle on which this apparatus acts has been
somewhat of a puzzle for engineers, for it certainly appears paradoxical that
the steam should force the water into the boiler against its own pressure.
We must observe, however, that the net result of the operation is a lessen-
ing of the pressure in the boiler ; for the entrance of the feed-water pro-
duces 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 sta-
tionary, locomotive, or marine engines.
Steam boilers are now always provided with one
QiBourdorfs 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 communi-
cates 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 wheel work, 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.
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 b>
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 oressures, such as several
FIG. 7. Monrdotfs
Pressure Gauge.
STEAM ENGINES.
FIG. 8. Steam Generator.
thousand 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.
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 con-
trivances 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
i 4 THE LOCOMOTIVE.
generating 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 accord-
ing 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 con-
densers. 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 in-
clined. 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 leak-
age 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.
/ T % HE first locomotive came into practical use in 1804. Twenty years
-1 before, Watt had patented but had not constructed a locomotive
engine, the application of steam to drive carriages having first been sug-
gested 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 impor-
tant 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
\vaggons along the tramways of obscure collieries. The progress of the
locomotive in the path of improvement was, however, slow, until about
'825, when George Stephenson applied the blast-pipe, and a few years
/ater 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 4|
tons, and at the trial drew a load of tenders and carriages weighing 12 ;;
tons. Its average speed was 14 miles an hour, and its greatest, 29 miles
THE LOCOMOTIVE.
FIG. 9. Section of Locomotive.
an hour. This engine, the parent of the powerful locomotives of the pre-
sent day, may now be seen in the Patent Museum at South Kensington.
Since 1829, numberless variations and improvements have been made in
16 THE LOCOMOTIVE.
the details of the locomotive. Its weight may now be 50 tons, its load
from 50 to 500 tons, and its speed from 10 to 60 miles an hour.
Fig. 9 represents the section of a locomotive as now constructed. 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 \\ 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 f 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 or a Giffard's Injector. 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 alter-
nately, 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-
THE LOCOMOTIVE,
shaft, and their rods joined to the ends of the curved bar or link, CD. 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
FIG. io.Stephensotfs Link Motion.
of the link and the eccentric rods is counterpoised with a weight, K, at-
tached 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 for-
ward, and vice 'versa; hence the engine will be reversed. When the link
is so placed that the stud is exactly in the centre, the slide-valve will re-
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.
!8 THE LOCOMOTIVE.
The 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 resist-
ance of the 7 oad 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 1 5 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 locomo-
tive 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 I2olbs. 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 Ibs. per square inch should not be employed, if it were found otherwise
desirable. It need hardly be said that locomotives are invariably con-
structed 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. 1 1 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.
Locomotive engines for propelling carriages on common roads were
THE LOCOMOTIVE.
FIG. II. Explosion of Boiler.
invented 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
FIG. 12. Hancock's Steam Omnibus.
been successfully realized in the traction engines lately introduced. Pro-
bably 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
2 2
20 PORTABLE ENGINES.
locomotion, as the prejudices and interests which have always to be over-
come 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 wiil 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 the city of Manchester, a great centre of engineering industry, not
having as yet a single tramway, while in all the populous cities of the
United States, and in almost every European capital, tramways have been
in successful operation for many years.
PORTABLE ENGINES.
nnHE 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 hori-
zontally 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 com-
municate 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 mate-
rials, 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 repre-
THE STEAM HAMMER. 21
sents a 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.
There can be little doubt that before long it will be quite common to
have such domestic work as grinding coffee, mincing meat, cleaning knives,
&c., done by steam power. Already an efficient little engine has been
introduced for working drawing-room sewing-machines. This miniature
engine (for it is small enough to be carried in the pocket) is very simply
constructed, with an oscillating cylinder, and can be instantly attached to
a sewing machine, small lathe, &c. It is connected with its boiler merely
by a flexible india-rubber tube, while another similar tube conducts the
waste steam from the apartment. The boiler, which is somewhat orna-
mental in construction, is heated by gas or paraffin, and the little engine
is capable of working a sewing machine at double the ordinary speed, at
the cost, it is said, of only one halfpenny per hour. The speed is regulated
by a lever, which controls the admission of steam. When this little motor
is used to drive a sewing machine, the lever is attached by a cord to the
pedal of the machine in such a manner that when the pedal is held down
steam is admitted in proportion to the pressure, while the removal of the
foot shuts off the steam. This little engine is so cheap, portable, and easily
applied that it will probably be largely used for many other purposes where
a rotatory movement of small power is required.
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 ham-
sner having been lifted by cams and otha 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 dia-
meter 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
22 THE STEAM HAMMER.
the 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 ham-
mer 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 & 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 work-
shops ? 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.
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,
THE STEAM HAMMER.
during 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 Wool-
wich, 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 fur-
naces and powerful cranes, carrying the huge iron tongs that are to grasp
the glowing masses. The hammer descends not merely with its own weight
FlG. 13. Nasmyttis Steam Hammer.
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 enor-
mous 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
THE STEAM HAMMER.
soberly and 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 I.
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 sta-
tionary, 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 strikirg 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. nMerryweather's Steam Fire-Engine.
" Daily Telegraph.*
FIG. 1 5. A Foundry.
IRON.
' T RON and coal," it has been well said, "are kings of the earth." No
substance can indeed be named possessing so many useful qualities
and capable of such a variety of applications as iron. The employment of this
metal has been so vastly extended by modern improvements in the modes
of manufacturing it, and by increased knowledge of its properties and
behaviour, that we should be passing over some of the most important
inventions of the age were we to omit a description of Bessemer's process
and certain other operations, which facilitate the production of unlimited
quantities of excellent iron and steel from the dull stony ore. The nature
and value of these recent inventions will, however, be quite unintelligible to
a reader not possessing some knowledge of the ordinary mode of extracting
iron, and of the modifications in the properties of the metal produced by the
presence in it of small quantities of certain other substances. We shall,
therefore, begin by a few words on the smelting of iron, noticing some of
the more remarkable improvements.
Iron is the most common of the metals, in more than the ordinary sense.
It is so widely diffused that almost every mineral contains some iron, and
it is a chief constituent of a great many. It is not absent from the organic
kingdoms, and in the blood of all vertebrate animals occurs in notable pro-
portions. It is not a little remarkable that while this commonest of metals
25
26 IRON.
is never found in the metallic state amongst terrestrial minerals, the aero-
lites or meteoric stones, which fall upon our planet from out of the realms of
immeasurable space, consist usually of little else than metallic iron, alloyed
with a little nickel. These meteorites are sometimes of a considerable size ;
for example, one found in South America is calculated to weigh fourteen
tons ; but they fall too rarely to be of any value as a source of iron, although
the natives of India and other places have sometimes forged swords from
FIG. 1 6. Aerolite in the British Museum.
the sky-descended masses. The minerals which yield iron are plentiful
and easily obtained, but in them not a particle of iron exists in a metallic
state, the metal being combined with oxygen and other bodies, so that all
the properties of the simple substance are entirely disguised. The richest
and most valuable ores of iron are oxides, such as the magnetic iron ore of
Sweden, and haematite, which is abundant in certain parts of England and
France. The chief source, however, of the large quantity of iron produced
in Great Britain is the clay ironstone of South Wales and Staffordshire.
This contains an impure carbonate of iron, mixed with clay, lime, oxide
of manganese, and other minerals. It has the great advantage of being
IRON.
27
FIG. i-]. Blast Furnace.
associated with strata yielding coal and lime, and this circumstance more
than compensates for the small per-centage of iron it contains as compared
with the oxide ores. It is not definitely settled how far iron was used in
ancient times, but it is certain that if it were known at all it must have been
obtained directly from the oxides by the simple process of heating the ore
with charcoal in a small furnace or on a hearth, the necessary temperature
being attained by urging the fire with some rude blowing apparatus. In
certain localities, where the nature of the ore is suitable and fuel abun-
dant, malleable iron is still obtained from the ore by a single process.
This is practised in the Pyrenees, and on a larger scale in the bloomery
forges of North America. But in Great Britain the enormous quantity of
iron produced from the clay ironstone is first obtained in the state of cast
iron by the process of smelting.
In this process the clay ironstone is roasted after having been broken up
28 IRON.
into lumps. This operation is now almost invariably performed in large
calcining kilns, which are charged with ore intermixed with a small pro-
portion of the cheapest kind of coal. This preliminary treatment removes
all the volatile matters, expelling the whole of the carbonic acid, and entirely
driving off, in great clouds of steam, the water which is contained in iron-
stone in notable quantity. The calcined ore is then ready for the blast
furnace, represented in section in Fig. 18.
This is a structure about 70 to 100 ft. high, and from 20 to 30 ft. in in-
ternal diameter at the widest part. At E is the crucible, the bottom of
which is termed the hearth, and is usually formed of a certain kind of very
FIG. 1 8. Section of Blast Furnace.
infusible sandstone ; A is called the tympstone, and above it is an opening
through which the slag overflows. At O is one of the openings for the
pipes or tuyeres, which are connected with blowing machines supplying
a constant blast of air at a pressure of about 3 Ibs. per square inch. The
arrangement of the tuyeres is shown in the plan, Fig. 19. At the lowest
point of the furnace is the tap-hole, which is completely closed by sand and
clay, except when it is opened at certain intervals to allow the melted metal
to be drawn off. Surrounding the chimney or throat of the furnace is a
gallery, and at C is an opening through which the charges are introduced.
Access is obtained to this gallery by the gangway of which a portion is
shown on the left-hand side of the figure.
IRON. 29
The interior of the furnace is lined with the very best fire-bricks, and
the exterior is formed of a casing of solid masonry strengthened with iron
hoops. Great care and expense are bestowed in the construction of these
furnaces, and when the fire has been kindled it is never allowed to go out
until the furnace needs repairs ; so that such a furnace will continue in
activity without intermission for a period of ten years, being regularly sup-
plied at proper intervals with alternate charges of coal and a mixture of
roasted ore with limestone in fragments. The limestone is added in order
to render fusible the clay, and other earthy matter, which are associated
with the carbonate of iron ; these matters melt and form the glassy-looking
slags that in a molten state are continually flowing over the tympstone.
FIG. 19. Plan of Blast Furnace.
The air which issues from the tuyeres is soon deprived of its oxygen by
the excess of carbon, producing carbonic oxide, and this gas ascending,
penetrates the heated ore, rendered porous by the previous roasting.
Carbonic oxide is a combustible gas, and at the high temperature of the
furnace it takes away oxygen from the iron, which then combines with a
small proportion of the carbon in the coal, fuses, and, together with the
melted slag, drops into the crucible of the furnace, where it sinks to the
lowest part ; while the slag floats on its surface, and flows over the tymp-
stone as it accumulates at the same time covering the surface of the melted
iron, which otherwise would be oxidized by the blast, and would, in fact,
burn by again uniting with oxygen.
The iron which thus prepared always contains from 2 to 5 per cent, of
carbon is drawn off at intervals of 12 or 24 hours by the removing with
an iron rod the plug of clay stopping the tap-hole. The liquefied metal is
allowed to run into a series of shallow channels formed in sand, where it
solidifies, and when cold, is broken into suitable lengths, and then presents
itself in the form of the bars commonly known as pig iron. This is the
crude cast iron; and here it will be desirable to refer to the fact that cast
iron is not simply iron, but a chemical compound of iron and carbon. As
it runs from the smelting furnace, however, it contains many other sub-
stances, such as silicon, uncombined carbon, manganese, and other metals,
phosphorus, sulphur, &c. The properties of the metal are greatly modified
by these bodies, even when present in very small proportions. In the'
variety of cast iron known as white, perhaps the carbon is chemically com-
bined with the metal, while in the grey and mottled varieties some of the
carbon is separated from the iron, and is merely mechanically diffused
IRON.
throughout the mass in the form of small crystals, similar to those of graphite
or plumbago. The following table shows the per-centage composition of
some samples of cast iron :
White.
White.
Mottled.
Grey.
Iron
88-81
89-304
QV2Q
00-376
Combined carbon
4.-Q4.
2'4-t;?
278
I'O2I
Graphite, or uncombined carbon.
0-871
I'QQ
2 '64. 1
Silicon
O'7C
I 'I2A
O'7I
vo6i
Sulphur ... .
trace
2-1:16
trace
I'l 3Q
Phosphorus
O'I2
O'QIT
I '2~l
O'Q28
Manganese
rs8
2-8I5
trace
O'8^4.
These examples will suffice to show that the composition of cast iron
varies greatly ; and there are also wide differences in the mechanical pro-
perties of each variety. Grey iron, that which is commonly produced from
the furnace, is not so hard as the other kinds of cast iron ; it can be filed, or
drilled, or turned in a lathe. The mottled variety is very tough, and on
that account is preferred for casting guns. White cast iron has, when
broken across, a white lustre, and the fracture presents a lamellar crystal-
line texture. It is more fusible than the others, but it is very brittle, and
so hard that it cannot be worked with steel tools. Iron possesses a pro-
perty which is by no means common to all the metals a property upon
which chiefly depends its admirable suitability for receiving any required
form by casting. At the moment that a mass of the fluid metal solidifies, its
bulk increases, so that this metal is capable of receiving even delicate
markings from the moulds in which it is cast.
No greater improvement was ever effected in any art by simple means
than that introduced into iron smelting about forty-five years ago by
Neilson's substitution of hot air for cold in the blast furnace. So great
was the saving of fuel, especially in Scotland, where the hot blast first came
into use, that the trade of iron smelting was completely revolutionized.
Thus, at the Clyde Ironworks, in 1829, the production of each ton of iron
required 153 cwts. of coal, and 10^ cwts. of limestone ; whereas, in 1833,
after the hot blast had been adopted, 59 cwts. of raw coal, and 7 cwts. of
limestone, sufficed for the same work. In carrying his invention into
practice Neilson had to encounter many difficulties. The iron ovens in
which he at first heated the air were very rapidly oxidized ; and when thick
cast iron pipes were substituted, it was found that they were very liable
to leak at the joints on account of the expansions and contractions caused
by the alterations of temperature. Like other new inventions, this also had
to contend with established prejudices and misconceptions. The iron-
masters having observed that the quantity of ore reduced was greater in
winter than in summer, attributed this to the coldness of air blown in
overlooking the fact that with equal volumes of cold air and warm air, the
quantity or weight of oxygen must be greater in the former.
The quantity of air blown into a blast furnace is enormous, its weight
being greater than that of all the coke, ore, and limestone put together.
It is calculated that the weight of the air passing through a smelting fur-
nace amounts, in some cases, to between 2,000 and -3,000 tons in a week.
IRON. 31
At the ironworks at Dowlais an engine of 650 horse-power is appro-
priated to the blowing apparatus, in which a piston moving in a cylinder
12 ft. in diameter, and the same in length, is constantly forcing air at a
pressure of 3^ Ibs. per square inch through the immense mains or discharge-
pipes, 5 ft. in diameter, by which it is conducted to the furnaces.
Various theories have been advanced to explain why i cwt. of fuel ex-
pended in heating the blast should do the work of perhaps 4 cwt. burnt in
the furnace itself. Recently, however, furnaces have been built of larger
dimensions, some having as much as six times the capacity of those formerly
in use ; and experience has shown that this increase of size, of itself, pro-
duces results similar to those which were obtained when the hot blast was
applied to smaller furnaces. Nevertheless, the use of the hot blast has
not been abandoned ; for as the air can thus be heated by cheap coal at a
less cost than by the fuel within the furnace, Neilson's invention still affords
very important advantages. There is, however, much difference of opinion
among practical metallurgists as to the temperature which should be given
to the blast, and as to its influence on the quality of the iron produced.
The common practice has been to pass the air through a series of pipes or
chambers heated by a separate furnace, so that it might enter the smelting
furnace at a temperature sufficiently high to melt a strip of lead held in a
current of it, that is at about 620 F.
Mr. Siemens has recently introduced a mode of still further economizing
fuel by causing the hot gases which escape from the smelting furnace to
pass through a chamber filled with fire-bricks, so arranged that the gases
circulate freely round them ; and when the bricks are by this means heated
to redness, the current of gases is shut off from the chamber, and conducted
through another precisely similar ; while the blast of cold air is made to
circulate through the heated chamber, and thus acquires a temperature of
1,200 or 1,300 F. Two of these chambers are used alternately, so that
while one is employed in heating the blast, the other is acquiring from the
furnace gases the heat necessary for it to perform the same duty. In this
manner a great part of the heat of the waste gases is utilized. Other modes
of employing the gases escaping from the chimneys of the smelting furnaces
have also been adopted.
It will be remembered that the most active agent in the reduction of the
metal is the carbonic oxide gas produced in the furnace by the incomplete
combustion of the carbon of the coal. A large excess of this gas is pro-
duced, and escapes from the chimney of the furnace. The unconsumed
carbonic oxide so escaping, together with the hydrogen and other combus-
tible gases, forms more than a third of the gases issuing from the furnace.
It is the combustion of these inflammable gases which produces the lam-
bent flames often seen at the mouths of smelting furnaces, and imparting
its most striking features to the night view of an iron-smelting region.
Now, until recently, all the heat produced by these flames was absolutely
wasted, but by various expedients a portion or the whole of these gases is
now drawn off and allowed to burn in such a manner that the heat is
available for raising steam or for heating the air-blast. It is obvious that
if the gases are withdrawn from the furnace without checking the upward
current, the processes could not suffer in any way. One very effective
manner of doing this is shown in Fig. 20, 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 the required position by
32 IRON.
the chain e, and is also provided with a counterpoise, f. In this position
the mouth of the furnace is closed, and the gases find an exit by the opening
g, seen behind the cones, and leading into a passage through which the
gases are conveyed to the place where they are required to be 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 materials resting in 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 is at once closed.
FlG. 20. Cup and Cone.
By such contrivances as we have described, and by minor improvements,
the consumption of coal in iron smelting has been so much economized in
recent years that Mr. I. L. Bell-, in his presidential address to the members
of the Iron and Steel Institute in 1873, mentions that in the quantity of
coal consumed for iron smelting an annual saving of three and a half mil-
lions of tons had been effected over that consumed fifteen years before,
although the quantity of iron produced had very greatly increased.
Cast iron, it is well known, cannot be wrought with the hammer ; it can-
not be rolled into plates, nor welded on an anvil ; it is not readily filed or
worked with steel tools ; and it possesses no ductility, and little tenacity,
or power to resist a pulling force. On the other hand, wrought iron pos-
sesses all these properties in the highest degree, but can be fused only by
an extremely intense heat. In chemical composition the latter is essentially
pure iron, whereas the former is essentially a compound of iron and carbon.
Cast iron is converted into wrought iron by the processes of refining and
puddling. The object of these operations is, as may be imagined, the
removal of the carbon and other substances. The pig iron is re-melted on
the hearth of a furnace in such a manner that it is exposed to the action of
the air for about two hours. The silicon, most of the carbon, and some of
the iron itself are oxidized in this process. At one stage in the process the
metal appears to boil, owing to the escape of jets of carbonic acid gas,
formed by the union of oxygen and carbon in the midst of the mass. The
oxidizing action is carried on through the whole, for the puddler stirs it up,
so that every part is brought into contact with the oxygen, or with the oxide
of iron formed on the surface, and carried by the stirring into the heart o
IRON.
33
FIG. 21. Rolling Mill.
fromthentT i is sometimes mixed with oxide of iron
from the forge. As the iron loses its carbon it becomes less fusible, and at
dTm^l H m Th >f C meS a maSS 1 lo Sely adherin S Drains, like so much
damp sand. The heat is now raised, and the grains begin to fuse and be-
come more adherent, so that the puddler is able to collect all the metal at
the end of an iron rod into a spongy mass. He forms this into balls or
blooms, weighing about 70 Ibs. each. The blooms consist of particles of
nearly pure iron, partly fused together, but retaining in the interstices
between them a portion of the fused slags, oxides, and other extraneou
>,T' Ji Y a !" e n w dellvered to the shingUr, by whom they are sub-
Bitted whilst still intensely hot, to the action of a steam hammer or other
heavy hammer, or subjected to strong compression in a shingling press or
comnrl tr? n i^ aSS !T e iro * rollere - Th ^ design of this treatment is to
compress the half-fused particles of iron into a compact mass, and to tho-
F Ut thC ^ and fused Oxide ' In a ^ case the ^ration
^ Y PaS ?u g the metal between ^ ooved rollers > b y wh 'ch it is
roffi rS ; / T ^ afterwards cut into lengths/re-heated, and
5 rolling repeated, and so on several times, when the icon is required to
possess great tenacity. The rolling of the blooms into bars i^s riki-
34 IRON.
spectacle. The furnace door is opened, the workman pulls out a white-hot
ball, he throws it on the ground, whence it is instantly snatched up by an
attendant Vulcan, armed with a pair of tongs, and applied to the largest-
sized groove in a pair of massive rollers. The lump of iron is shot through
the rolls, and is doubled in length by their pressure. No sooner has ii
come out than it is again seized and tossed back over the rollers, to be
again passed through a smaller groove ; and it thus passes backwards and
forwards several times, increasing its length and improving in quality with
each passage through the grooves. The whole operation is effected in
an incredibly short time, and before the spectator has been able fully to
comprehend the process the result is before him a long, straight, finished
bar of glowing iron is stretched on the sand. Scarcely has the bar been
laid out to cool than another fiery mass is following the same course through
the rolls. The view of a rolling mill given in Fig. 21 will enable the
reader to understand the nature of the operation we have just described.
If the spectator's gaze is not entirely fascinated by the glowing metal,
he may perceive a massive fly-wheel, perhaps 20 ft. in diameter and as
many tons in weight, spinning through the air at the rate of sixty revolu-
tions per minute, and communicating by certain toothed wheels the rotary
motion to the powerful rolls. At Dowlais each pair of rolls has an iron
fly-wheel, 20 ft. in diameter, with a rim 12 in. square, and the engine driving
these mills has itself a fly-wheel 25 ft. in diameter and 2 ft. wide. The rolls
themselves are 1 1 in. in diameter in the grooves, and elsewhere double that
diameter. The reader, from these details, and from the fact that such
massive fly-wheels are made to revolve at the rate of sixty or a hundred
revolutions per minute, may form some idea of the enormous momentum
possessed by them. The following, from the " Times " of November 22,
1859, may enable him to realize the amount of force stored up in a heavy
body in rapid motion :
" About eleven o'clock on the night of Friday last a most destructive
accident occurred at the extensive ironworks of Messrs. Gibbs Brothers,
Deepfield, near Wolverhampton, by which a large iron- rolling mill was
levelled with the ground, one man killed, and several others severely injured.
A number of the workmen had fortunately gone to supper, and others were
disengaged while some alteration was being made in the rollers, when sud-
denly the large driving-wheel, some tons in weight, broke into fragments,
which were propelled on all sides with great force. Several of the iron
pillars that supported the roof, the principal iron beam, and several of the
lesser ones were broken, and the entire roof shortly afterwards came down.
Of the men who were in the mill at the time, one, named John Taylor,
was dug out of the debris insensible, and expired shortly afterwards, three
others sustained severe fractures and other injuries, and two or three
escaped unhurt in a manner little short of miraculous. The whole place
looks as if it had been blown up with gunpowder, and the damage is esti-
mated at about ,3,000."
Wrought iron is never pure, but always contains a small proportion of
carbon, varying from one-fifth to one-half per cent. The presence of this
small quantity of carbon enhances rather than impairs its useful qualities ;
but some of the other ingredients of cast iron, if not entirely removed in
the refining and puddling processes, act most injuriously upon the qualities
of the wrought iron. For example, the presence of a small proportion of
phosphorus renders wrought iron brittle and rotten when cold, although at
a red heat it may be forged. Iron having this defect is technically said to
IRON.
35
be cold short, while the term red short is applied to metal which when hot
breaks and crumbles under the hammer, a condition occasioned by the
presence of a small quantity of sulphur or of silicon. Wrought iron is quite
unlike cast iron in texture, for while the latter when broken across shows
a distinctly crystalline structure, which we may compare to that of loaf-
sugar, the former exhibits a fibrous grain, not unlike that of a piece of wood.
This fibrous structure depends upon the mechanical treatment the iron has
received, and in bars the fibres always arrange themselves parallel to the
length of the bar. Fig. 22 shows the 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 across.
Consequently, to obtain the greatest advantage from the strength of wrought
FlG, 22. Fibrous Fracture of Wrought Iron.
iron, the metal must be so applied that the chief force may act upon it in
the direction of the fibres.
Steel is a nearly pure compound of iron with carbon, the proportion of
the latter element being much less than in cast iron, and always less than
one-fiftieth. Good steel contains from 07 to 17 per cent, of carbon, and
some excellent qualities have been found to have from 1*3 to 1*5 per cent,
of carbon, together with o'i per cent of silicon. Steel is thus, as regards
carbon, intermediate in composition between wrought and cast iron, and
in a great measure possesses the most valuable properties of both. It may
be wrought on the anvil at a white heat, and at a higher temperature it may
be melted and cast in a mould. It is distinguished from cast iron by its
fine, close grain, and still more by its remarkable tenacity, in which pro-
perty it excels wrought iron, for while a bar of the best wrought iron, i in.
square, breaks with a load of thirty tons, a bar of good steel of the same
size will sustain seventy-five tons, and if the steel has been subjected to
certain processes, its tenacity may even reach a hundred and twenty tons.
Still more remarkable is the wonderful property possessed by steel by
which it may at will be made soft or hard, tough or elastic. If suddenly
quenched in water when it is red hot, it acquires a hardness rivalling that
3 2
36 IRON.
of the diamond, and is also rendered very brittle and extremely elastic.
The hardness and brittleness can be reduced by tempering 'to any required
extent. Steel may be made either by stopping the processes by which carbon
is removed from cast iron at such a stage as to leave the requisite quantity .
of carbon in combination with the iron, or by reversing the decarbonizing
process and re-combining wrought iron with carbon. In the latter plan bars
of the finest wrought iron are heated for a week in a closed receptacle,
lightly packed with powdered charcoal.
But all the older plans for producing steel by the partial decarbonization
of cast iron have been eclipsed in interest and importance by Bessemer's
discovery that the carbon and silicon may be readily removed by forcing
currents of cold air through a mass of the fused metal. This discovery was
first announced to the world in a paper read before the British Association
by Mr. Bessemer at the meeting in 1856. This paper bore the startling
title : " On the Manufacture of Iron and Steel without Fuel." In this pro-
cess the whole mass of melted iron is exposed to the action of atmo-
spheric air without the intervention of the puddler with his stirring-rod, the
stirring being performed by the air itself, while the heat produced by the
combustion of the silicon and carbon, and of a considerable proportion of
the iron itself, maintains the metal in a perfectly fluid state, even when all
the extraneous matters have been burnt off. Thus Mr. Bessemer showed the
world the unprecedented spectacle of several tons of pure or malleable iron
in a molten state. Mr. Bessemer's first patent, dated iyth October, 1855,
was for " forcing currents of air, or of steam, or of air and steam, into and
among the particles of molten crude iron, or of re-melted pig or refined
iron, until the metal so treated is thereby rendered malleable, and has
acquired other properties common to cast steel, and still retaining the fluid
state of such metal, and pouring or running the same into suitable moulds."
It was found that the steam had an injurious effect, but when air alone
was forced through the metal, the temperature rose from a red to a white
heat. Mr. Bessemer afterwards took out other patents for improvements
in his process and in the apparatus, using air alone. The experiments re-
quisite for the perfection of the invention were carried out at Baxter House,
where Mr. Bessemer then resided, and Dr. Percy describes the process,
as he there witnessed it, as the most startling and impressive metallur-
gical operation he had ever seen. " After the blast was turned on," he says,
" all proceeded quietly for a time, when a volcano-like eruption of flame and
sparks suddenly occurred, and bright red-hot scoriae or cinders were forcibly
ejected, which would have inflicted serious injury on any unhappy by-
standers whom they might perchance have struck. After a lew minutes all
was again tranquil, and the molten malleable iron was tapped off. At first
I doubted whether the metal which I saw flowing was actually malleable
iron ; and after the analysis in my laboratory of a portion of this identical
iron, and the detection in it of phosphorus somewhat exceeding i per cent,
my scepticism was rather confirmed than otherwise. However, I soon
became convinced that Mr. Bessemer was correct in asserting that he had
succeeded in producing a temperature higher than ever before attained in
metallurgical operations ; sufficient, indeed, to render malleable iron as
liquid as water." The apparatus used in these experiments was a cylin-
drical vessel, like a large crucible, in the bottom of which were a number
of clay nozzles, or tuyeres, through which the blast from a blowing machine
could be forced (see Fig. 23.) The first experiments were not undertaken
with a view to the production of steel, but to ascertain the possibility of
IRON.
37
obtaining malleable iron without submitting the metal to the ordinary re-
fining and puddling operations. Into the cylindrical vessels Mr. Bessemer
caused crude iron from a blast furnace to be poured until the liquid metal
filled the vessel to about the depth of two feet. But the blast of air was
turned on before the metal was allowed to enter the vessel, and thus the
tuyeres were kept clear, for the pressure of air in the blast sent through
them supported the weight of the liquid column of metal. The air rushing
FIG. 23. Experiments at Baxter House.
through the liquid kept it in constant agitation, and the union of the oxygen
with the carbon not only maintained the temperature of the mass, but even
caused it to increase greatly. In about fifteen or twenty minutes, all the
carbon diffused through the iron having been burnt up, the metal itself
began to combine with the oxygen, producing oxide, which, being well
mixed with the rest by the violent ebullition going on, was brought in con-
tact with any silica or earthy matter which might be present, and thus
rendered them fusible, and caused them to appear as frothy slags. At the
end of from thirty to thirty-five minutes the process was complete, and the
fluid decarbonized iron was run out at a tap-hole. It cannot properly be
said that the operation is conducted without fuel ; for not only the carbon
burnt off forms the fuel, but a large quantity of the iron itself burns into
oxide, which helps to form the slag, and this quantity, most of which must
be accounted as loss, amounts to upwards of twenty per cent. In the
manner just described, the iron may be completely decarbonized, and it is
plain that if the process were stopped at precisely the right point, which
38 IRON.
would leave the proper proportion of carbon in combination with the iron,
the result should be good cast steel. There is, however, great difficulty
in ascertaining the exact point of decarbonization at which the operation
is to be stopped, and although valuable indications are afforded by the
colour of the flame which issues from the vessel, especially when this is
examined by the spectroscope, it is found better in practice to obtain the
required composition in another manner.
The Bessemer process was on its first announcement welcomed with
great enthusiasm, but the earlier results obtained by it disappointed the
expectations of every one, for both the iron and steel made by it were of
bad quality. Thus, Dr. Percy, in the foregoing account of the process,
mentions the large per-centage of phosphorus he found in the product, and
we have already referred to bad effects produced by the presence of this
element in iron. In fact, though by this process silicon and carbon are com-
pletely removed from the iron, it appears that sulphur and phosphorus are
not eliminated. Hence it is necessary to employ cast iron free from these
impurities, and metal containing even so small a quantity of phosphorus
as seven parts in ten thousand must be rejected. But this is not all, for even
when very pure pig iron, containing but mere traces of substances other
than carbon, has been employed, the product has been found valueless for
practical purposes. At one time it seemed that the new process would
prove a failure in practice, when the happy thought occurred to Mr. Mushet
that the defects of the method as regards steel might be remedied by the
addition of manganese to the contents of the converter. The presence of
manganese in the iron best adapted for making into steel had long before
been pointed out. It having also been found that in the production of
steel it was very difficult to determine with any certainty the proper mo-
ment for arresting the decarbonization, the Bessemer process was modified
in the manner described above, by adding to the completely decarbonized
metal such a quantity of good cast iron (spiegeleisen}, containing about ten
per cent, of manganese, as would convert it into steel of the finest quality.
Spiegeleisen (literally mirror-iron}, a white hard cast iron, has had that
name given to it by the Germans from the fact that when it is broken across,
the fractured surfaces present numerous little mirror-like faces of crystals,,
having a pure silvery lustre. This iron is procured from ores which con-
tain manganese, and it also retains a very large proportion of carbon. The
composition of an average specimen of spiegeleisen may be stated as
showing 4 to 4! per cent, of carbon, 10 per cent, of manganese, and I per
cent, of silicon. The precise composition of the spiegeleisen about to be
used in the Bessemer operation is always first determined with great accu-
racy ; and, according to its richness in carbon, a quantity is added which
will convert the iron contained in the Bessemer vessel into good steel.
The quantity thus added to the contents may form a proportion varyjng
from, 5 to 10 per cent. Manganese is by no means the only metal the pre-
sence of which in small quantities has been found to improve the quality
of steel, for silver, rhodium, and chromium have also been observed to
produce a beneficial effect, and Mr. Mushet obtained a patent for the
addition of titaniferous iron to steel. A short account of the manner in
which the Bessemer operation is now conducted will, with the annexed
figures, serve to render the process easily intelligible.
The vessel in which the operation is conducted is termed a converter,
and its construction will be understood by reference to Fig. 24. It is an
egg-shaped vessel, about 3! ft. in diameter, made of wrought iron in two
I It OAT.
39
parts, and lined in the inside with a thick infusible coating made from
ground fire-bricks and a certain kind of sandstone. The two portions are
united by flanges strongly bolted together, and the converter swings on
trunnions, one of which is hollow and admits the air-blast by the pipe b to
the base of the vessel. This pipe, which of course turns on the trunnion with
die converter, conducts the air to a kind of chamber, d, from which it passes
into the vessel through about fifty holes of ^ in. diameter. To the other
FlG. 24. Bessemer Converter.
A, Front view, showing the mouth, c ; B, Section.
trunnion a toothed wheel is attached, which engages the teeth of a rack
receiving motion from hydraulic pressure in a cylinder. The iron for the
operation is melted in a furnace having its hearth above the level of the
converter, which is turned so that its axis is horizontal and its mouth up-
wards. In this position it is ready to receive the molten iron, which is con-
veyed to it by a trough, lined with sand, when the furnace is tapped. The
metal is allowed to pour in until its surface is nearly at the level of the lowest
holes through which the air enters. Usually about five tons of iron are
thus operated on. The blast having first been turned on at a pressure of
1 5 Ibs. to the square inch, the hydraulic power is set to work and the con-
verter is slowly brought back to an upright position. The pressure of the cur-
rent of air prevents any of the fluid metal from entering the blow-holes, and
the blast of cold air is continued for a period varying from twelve to twenty
minutes until, in fact, all the silicon and carbon have been entirely con-
sumed. The converter is then slowly turned back into the horizontal posi-
tion, and the blast is shut off, while a certain weight of melted cast iron of
a particular composition is run in ; the blowing is resumed, the vessel
brought to the upright position, and the blast continued for about five
minutes, in order thoroughly to incorporate the ingredients. At the end of
this time the vessel is again lowered, the blast is shut off, and the contents
of the converter are run off into a vessel of wrought iron, lined with sand
and provided with an iron plug, coated with sand, fitting into a socket, so
that, when required, the plug may be raised, and the molten steel allowed
to flow out into the moulds, which it does in a stream about an inch in dia-
4 o
IRON.
IRON. 41
meter. In this process it will be observed that the steel is not produced
by stopping the decarbonization at a certain stage, but by adding to it cast
iron containing such a proportion of carbon as, when added to the pure
iron in the converter, will produce good steel.
In a paper read before the Institute of Civil Engineers the effects when
the blast of cold air is put on are described : " The process is then in an
instant brought into full activity, and small, though powerful, jets of air
spring upwards through the fluid mass. The air, expanding in volume,
divides itself into globules, or bursts violently upwards, carrying with it
some hundredweights of fluid metal, which again falls into the boiling mass
below. Every part of the apparatus trembles under the violent agitation
thus produced. A roaring flame rushes from the mouth of the vessel, and
as the process advances, it changes its violet colour to orange, and finally
to a voluminous pure white flame. The sparks, which at first were large,
like those of ordinary foundry iron, change to small hissing points, and
these gradually give way to small floating specks of bluish light as the
state of malleable iron is approached. There is no eruption of cinder, as
in the early experiments, although it is formed during the process ; the
improved shape of the converter causes it to be retained, and it not only
acts beneficially on the metal, but it helps to confine the heat, which during
the process has risen from the comparatively low temperature of melted
pig iron to one vastly greater than the highest known welding heat, by
which malleable iron only becomes sufficiently soft to be shaped by the
blows of the hammer. But here it becomes perfectly fluid, and even rises
so much above the melting-point as to admit of its being poured from .the
converter into a foundry ladle, and from thence transferred to several suc-
cessive moulds."
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 beau-
tiful 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 handles seen at H. The crane, 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 posi-
tively marvellous to a spectator.
Although the results of the process are not perfect, yet the method has
already caused a new development of the applications of steel. Not only
was the production of five tons of malleable metal from pig iron, in one
operation, in the short space of half an hour, a surprise for metallurgists ;
but there was the unprecedented circumstance of this mass of metal being
in a state of perfect fusion. By the modified method 400,000 tons of steel,
or steely iron, are now produced annually in this country ; and a substance
which has hitherto been so costly as to be employed only for knives, springs,
42 IRON.
and other small articles, is now produced on a scale which admits of its
being used in the construction of bridges, railways, and buildings, or, in
fact, applied to any purpose where great tenacity, hardness, elasticity, or
durability would be desirable. The production of large castings in steel
was long a matter of impossibility, for steel cannot be fused, except in com-
paratively small crucibles ; but by Bessemer's process large castings may
be made, for quantities of pig iron, about ten tons in weight, are now
sometimes operated on in the converter. The great difficulty, however, in
steel castings is to obtain them perfectly uniform in texture throughout.
Sir. J. Whitworth applies to the steel, after it has been run into the mould,
a very powerful pressure, by which process excellent results have been ob-
tained in cases where uniformity of texture is of the highest importance,
as, for example, in castings intended for the construction of cannons.
But everything that has previously been done in the way of casting steel
of uniform texture has been surpassed by the scale on which the German
firm of Krupp and Co. carry on their operations. The largest mass of steel
ever made in one piece was exhibited by this firm at the London Inter-
national Exhibition of 1862. Its weight was 21 tons, and it had been pur-
posely broken across, to show that its texture was sound throughout ; yet
this enormous piece of metal had been formed in separate portions of
perhaps not more than 70 Ibs. each, melted in separate crucibles, and poured
so continuously and regularly into the mould as to form one uniform cast-
ing without flaw or defect. When we consider how many crucibles con-
taining 70 Ibs. of metal each would be required to make up such a casting,
we see that a large number of men must have been employed, and that there
must have been a perfect organization and harmony in their working. Krupp
is largely engaged in making steel cannons for the German and other govern-
ments, and his works are the largest of the kind in the world, no fewer than
10,000 men being employed in them.
FIG. 26. Cupola Furnace.
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
43
44
70OLS.
simple example of the copying principle, which is so widely applied in
machines for manufacturing ; for, in all of these, materials are shaped 01
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.
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
FIG. T&.WhitwortKs Screw Dies and Tap.
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 uni-
formity 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
al3o to produce in metal a hollow screw. The reader may have observed
gasfitters and other workmen performing the first operation by an instru-
ment 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.
TOOLS, 45
The 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
wse, 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, /, 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 repre-
sented in the lower part of Fig. 28.
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
FIG. 29. Screw-cutting Lathe.
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 cut-
ting 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, , and the tool receives another longitudinal movement from the
46 TOOLS.
handle, 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 dis-
tance. 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 cut-
ting 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 revo-
lutions 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 $ inch pitch.
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 im-
part 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 -^ in.;
half a turn y^ in. ; a quarter of a turn, ^o, 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 parsed the index, cause the screw
to advance through ^j of -^ inch, or 10 ^ oQ 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,
TOOLS. 47
intended 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 thumb-
screw. 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
FlG. 30. Whitworttts Measuring Machine.
fraction of an inch the size of the work measured differs from a certain
standard piece. Each headstock carries a screw of ^ 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 -^ of the ^ of an inch, that is, lQ Soo f an mcn -
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,
48 TOOLS.
with 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 divi-
sions 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. 3 1 , 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 T^ 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 divi-
sion passes the index, advanced through a space equal to ^Q X ^o X
ch. This
TOOOQOO f an mcn J that i s > 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 TQOOOOO f
an inch is shown by the gravity-piece remaining suspended instead of fall-
ing, and the piece falls again when the tangent-screw is turned back
through -^(j of a revolution, a difference of reading representing a possible
movement of the measuring surface through only TOO 000 f 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 reauired by passing the strap from one pair of pulleys to
TOOLS.
49
another. 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
\htfeed 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 communi-
cate a more rapid movement to I, so as to raise up the drill in a position to
FIG. 31. WHUwortKs Drilling Machine.
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.
The visitor to an engineer's workshop cannot fail to be struck with the
50 TOOLS.
operation 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 V-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 him-
self 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, , 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,
<:, 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 horizon-
tally, 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 regu-
lated 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
TOOLS.
32
52 TOOLS.
of the cylinders which carry the cutters is drawn in alternate directions at
the end of each stroke, the effect being to turn the cutters h?.lf round, so
as always to present their cutting edges to the work. There are also con-
trivances 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 V-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.
The copying principle is evident in this machine ; for the plane surface
results from the combination of the straightness of the bed with the straight-
ness of the tran verse slide along which the tools are moved. It should, more-
over, 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
FIG. 33. Pair of Whitworth' s Planes, or Surface Plates.
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 com-
parison ? This was first perfectly done by Sir J. Whitworth, about thirty
years ago. Three pieces of iron have each a face wrought into comparatively
plane surfaces ; they are compared together, and the parts which are pro-
minent 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. i 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. i), then No. 3 must be exactly similar to No. 2, and conse-
quently when No. 2 was applied to No. 3, hollow would be opposed to
TOOLS.
S3
Tiollow 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, ap-
proach 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.
5'-
TOOLS.
FIG. 35. The Blanchard Lathe.
THE BLANCHARD LATHE.
THIS machine affords a striking example of the application of the copy-
ing principle which is the fundamental feature of modern manufac-
turing 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 con-
structed 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 head-
stock 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
TOOLS. 55
bottom, 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, /*, 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 /. 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, how-
ever, 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, , 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 head-stocks. It is extremely inte-
resting 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.
TOOLS.
FIG. "2 6. Vertical Saw,
SAWING MACHINES.
"\17ITH 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 imple-
ments 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 accu-
rate 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
TOOLS.
57
history 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.
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 illustra*
tion, this class of tools presents the special advantage of being readily
understood as regards their purpose and mode of action, while their sim-
FIG. 37. Circular Saw.
plicity in these respects does not prevent them from showing the advan
tages 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 mo-
tion 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 tne next descent of the saw-frame. This push-
ing 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, moves forward the car-
riage on which the piece of timber is firmly fixed, so that when the blades
TOOLS.
of 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 dimen-
sions 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.
FlG. 38. Pit-Saw,
*T*O WARDS the end of last century, tramways formed by laying down
-1 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 i_, 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 \vere 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
59
6o
RAIL WA VS.
century 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
FIG. 40: Coal-pit, Salop.
was applied for, the canal companies succeeded in retarding, by their in-
fluence, the passing of that Act for two years. It was passed, however, ir
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 insti-
gation 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 unprecendented 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
AIL WAYS.
6r
FIG. 41. Sankey Viaduct.
and 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 rail-
way, and continued their exorbitant charges and tardy conveyance, pocket-
ing 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 iri 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
62
It AIL WAYS.
as 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 Com-
mittee, in which we find the opinions and fears of the best informed men
of fifty years ago, and trace the frantic efforts of the holders of the " vested
interests " to retain them, however obstructive of the public good.
">
fei- N .
^^"-7*- _. -~V
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 ob-
stacles, 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 con-
sideration, 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, em-
bankments, 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 origin-
ally in distinction to the temporary tramways laid down by the contractors
during the progress of the works. The permanent way is formed first of
RAILWAYS.
o.i
ballast^ 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 em-
bedded 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 trans-
versely 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
! B
tramp guage, the chairs having previously been securely attached to the
sleepers by bolts or nails. The double T 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 si 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.
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 ex-
pansion 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 ^th f an mcn apart, at 30
y^th of an inch apart, and so on. The neglect of this precaution has some-
times 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 mid-
6 4
KAIL WAYS.
day heat so expanded the iron, that the rails became in some places ele-
vated 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.
The distance between the rails in Great Britain is 4 ft. 8^ in., that width
having been adopted by George Stephenson in the construction of the
earlier lines. Brunei, the engineer of the Great Western, adopted, however,
in the construction of that railway, a gauge of 7 ft., with a view of obtain-
ing greater speed and power in the engines, steadiness in the carriages,
FIG. 44. Section of Rails and Fish-plates.
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 construc-
tion 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
56| in. The Great Western line has engines, bridges, tunnels, viaducts,
c., on a larger scale than any other railway in Britain. The difference of
gauge has, however, been felt to involve so much inconvenience that lines
which adopted the 7-ft. gauge have since relaid the tracks at the more
common width. In all probability the Great Western line will soon be
completely reconstructed on the narrow gauge system, in order that trains
may run without interruption in connection with other lines.
The Avheels of railway carriages and engines differ from those of ordinary
AIL WAYS.
carriages 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
i in 20 ; that is, in a
wheel 5 in. broad the
radius of the outer edge
is ^ 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 circum-
-. ference,wouldcausethe
J wheels to roll towards
the other side. The
conical shape produces
"l IN 20
Lk.
FIG. ^.Conical Wheels.
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 junc-
tions. 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 hori-
zontally. The resultant or com-
bined 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
FIG. 46. Centrifugal Force.
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 raite
5
66
RAIL WA YS.
are placed so that the slope counteracts the centrifugal force when the
train travels at about the rate of twenty miles per hour.
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 car-
riages 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
SHORT TONGUE
FIG. 47 Points.
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
RAILWAYS.
FIG. 48. Signal-box on the North London Railway
like spectacles in front of it. The meanings of the various coloured lights
and the corresponding semaphore signals are these :
I
1
1
White
Green
Red .
All right
Caution .
Danger .
Go on.
Proceed slowly.
Stop.
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 de-
scribes the signalling
68 RAILWAYS.
"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, indi-
cating 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 Belvi-
dere two, three, or four blows, according as the train is for Greenwich,
jor 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, be-
tween 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 .with-
drawn, 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 re-
RAIL WA VS.
C 9
quired ; distant 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 sym-
pathy 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 confu-
sion in it ; one head and hand directs the whole, so that there are no con-
flicting interests and no misunderstandings ; all is done in perfect tran-
quillity, 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 descrip-
tion 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."
Post Office Railway Van.
Most of the carriages used on railways are so familiar to every one^that
it is unnecessary to give any description of them. We give, however, Illus-
trations of two forms which have special features of interest. The first
of these is the 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 appa-
ratus, 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.
70 RAILWAYS.
This 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.
The other illustration shows the interior of one of the Pullman's Cars, so
much used in the United States, and in one of its forms lately introduced
into England on the Midland Railway. Some of these vehicles on the
American railways are luxurious hotels upon wheels ; they contain accom-
modation 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, pillow-
cases, &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 in-
stance, 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 re-
mainder of the car, which room contains two large and comfortable arm-
chairs 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 sit-
ting 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, and, unless
you have eaten too heartily of antelope or elk, will sleep as soundly."
RAILWAYS.
An 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 tram-
ways 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 car-
riages now running on English lines, especially in the first-class carriages,
where, in the curved lines of the mouldings which are supposed to orna-
ment 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 improve-
ments, and in forms more in harmony with the railway system, than the
conservatism of English ideas, still cleaving to the stage coach type, per-
mitted to be attempted in this country. The perfection of comfort in
railway travelling appears to be attained in the famous Pullman Cars, of
which travellers in the States have long enjoyed the benefit, while, in the
birthplace of railways, no attempt has been made to effect any material
improvements in the general plan of the carriages. Quite recently, how-
ever, the Midland Railway Company, to their credit be it said, have entered
into an agreement with the Pullman Car Company, by which, for the first
time, these luxurious vehicles are placed within reach of the English tra-
veller. In Plate III. we give a representation of the interior of one of these
cars as now fitted up for the Midland line, and known as the Parlour Car.
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
72 RAILWAYS.
directly sn 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 Ca/ represented in our plate.
The great engineering feats which have been accomplished in the con-
struction of railways are numerous enough to fill volumes. We give, there-
fore, only a short notice of one or two recently constructed lines which have
features of special interest, passing over, for want of space, even such
remarkable constructions as the railway by which the traveller may now go
up the Righi> and the railway which is to ascend Mount Vesuvius.
JHE METROPOLITAN RAILWAYS.
'XIT'HEN 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 con-
struction 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 occu-
pied about three years, and it was opened for traffic in 1863. The line
commences at Paddington, and passing beneath Edgware Road at right
angles, it 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 a junc-
tion with the Great Northern and Midland system is effected. Here the
line bends sharply southwards, and proceeds to Farringdon Street Station,
near Smithfield Market, from which point it again takes an easterly direc-
tion and reaches Moorgate Street, the present 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 I 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
JRAJLWAYS. 73
FIG. 50. Cower Street Station, Metropolitan Railway.
inventiveness 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 repre-
sents 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 ven-
tilation. 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.
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, when it
74 RAILWAYS.
leaves the bank of the river to reach its terminus at the Mansion House
Station. This line, taken in conjunction with the Metropolitan, forms the
" inner circle" of the railway communication in London. But the circuit is
not complete, being broken at the east by the want of connection between
the Mansion House Station and that at Moorgate Street, although these
stations are but little more than half a mile apart. A line connecting these
two points will probably soon be constructed, and then the public will
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.
HP HE 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.
The road/rom 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 com-
menced in November, 1865, and completed in May, 1869. There are at
Omaha extensive workshops provided with all the appliances for construc-
ting 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 dis-
tance 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 dis-
trict 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.
RAIL WA YS.
75
Cheyenne, 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 Can-
yon, for example, the rise in five miles
is 574 ft. , or about 1 2 1 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 sum-
mit 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 co-
vered 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 pre-
vent it from blocking the line by being
drifted into the cuts by the high wind.
A few miles beyond Dale Creek at Sher-
man is the largest bridge on the line.
It is a trestle bridge, 650 ft. long and
126 ft. high, and has a very light ap-
pearance 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 j and forming a tableland lying be-
7 6
RAILWAYS.
FIG. 52. -Trestle Bridge.
tween the 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
RAIL WA VS.
77
horse 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 Moun-
tains.
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.
FIG. 53. American Canyon.
Where the road could not be carried round or over the spurs of the moun-
tains 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.
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 Rail-
road, 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 re-
markable engineering feat of laying 10 miles of railway in one day was
performed. It was thus accomplished : when the waggon loaded with the
78 RAILWAYS.
rails 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 opera-
tions proceeded was about 240 ft. of track in 77^ 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 Ibs. ! Four thousand men and hundreds of waggons were re-
quired, 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 moun-
tain 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
RAIL WA YS.
79
FlG. 54. Cape Horn.
the 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.)
These lines of railway, connecting Omaha with Sacramento, are remark-
able 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
RAIL WA YS.
FIG. 55. Snow Plough.
named 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 loco-
motives, 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 nVe country merchants, unskilled in
RAILWAYS. 8 1
railway making, unaided by public support, and even discouraged in their
project by their own friends. The financial and legal obstacles they suc-
cessfully 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 pre-
pare 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 suc-
cessfully 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 Fran-
cisco 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 bav
for 2.\ 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 em-
bark 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 Fran-
cisco 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 steam-
ships ply regularly, carrying mails to China, Japan, Panama, South America,
Australia, &c., and there are, of course, hundreds of other steamers and
ships.
6
RAIL WA YS.
The 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 direc-
tions 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 not half a century ago. We in England should also have pride
in remembering that the growth of the railways here is due to the enter-
prise, 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.
I
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 after-
wards 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, how-
ever, 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, d
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
83 6 2
84 STEAM NA VIGA TION.
} moreover 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 techni-
cally 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 re-
quire 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
flie 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 cross-
head, 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 oscil-
lating cylinders. The paddle-wheels are constructed with an iron frame-
work, 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
STEAM NA VIGA TION.
FIG. 59. Casting Cylinder of a Marine Steam Engine.
mechanism 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.
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 ad-
vance 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,
86
STEAM NA VI G A TION.
and 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 fundamen-
tal 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 re-
sistance 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 for-
ward 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 pro-
pelled, 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 vita 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 appro-
priate 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.
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
FIG. 60. Screw- Propeller.
STEAM NA VIGA TION. 87
float, 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 ad-
vantage is lost whenever a side-wind inclines the ship to one side, or when-
ever 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 re-
quired 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 SirW.
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 prin-
ciples 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. Brunei, 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 1 5
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 con-
fidence 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 hurri-
cane 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, has 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 Bmnels for the
Thames Tunnel was, commercially, a failure ; the Great Western Railway,
with its magnificent embankments, cuttings, and tunnels, is reverting to
88
STEAM NA VIGATION.
the narrow gauge, and therefore the extra expenses 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 achieve-
ments 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 woulw
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
FlG. 61. Section of Great Eastern Amidships.
Great Eastern had existed, we should not now have had an Atlantic Tele-
graph. Possibly this huge ship is but the precursor of other 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.
The accidents which had happened to the ship had not, however, materi-
ally 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. 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
STEAM NA VIGATION.
89
FIG. 62. The Great Eastern in course of Construction.
many 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 pro-
menade 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 f 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, \ in. thick. These are
350 ft. long and 60 ft. high, and are crossed at intervals by transverse bulk-
heads, in such a manner that the ship is divided into nineteen compart-
ments, 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
9
STEAM NA VIGAT10N.
FIG. 63. The Great Eastern ready for Launching.
turned 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 accommo-
dation 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, 1 2 tons of coal are burnt every hour, and the
total displacement of the vessel laden with coal is more than 20,000 tons.
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 threefold, and every reader knows that there
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 belong-
ing to the Peninsular and Oriental Company. The steamers on the Holy-
head and Kingston line may be taken as good examples of first-class pas-
senger 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
STEAM NA VIGA TION.
about ,75,000. The average passage between the two ports a distance
of 65! miles occupies 3 hours 52 minutes, and at the measured mile the
vessel attained the speed of 2O'8i i 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
i oft. 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.
1858
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-one miles per hour appears to be about the highest i
ever attained by a steamer. This is probably near the limit beyond whicriV
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
fourfold. 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
STEAM NA VIGA TION.
of the engine must be increased in proportion to the cube of the velocity ;
so that to propel a boat at the rate of 1 5 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.
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 re-
lative 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 in-
cludes 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 \Vestern ...
Paddles
236 ft.
36ft.
1$M4
Great Britain . . .
322
CI
i8t;6
Persia . . . .
Paddles
^QO
4.C ..
1858
Great Eastern ...
Screw and paddles
690
TO
83
FIG. 65. The Great Eastern at Ni%ht.
STEAM NA VIGATION.
93
FlG. 66. Bessemer Steamer.
THE BESSEMER CHANNEL STEAMER.
T^HE latest, most novel, and most ingenious invention connected with
-* steam navigation is certainly the steamer which Mr. Bessemer has
built at Mull. This invention will entirely abolish all the unpleasant sensa-
tions which landsmen are apt to experience in a sea voyage. The problem
of effectually removing the cause of the distressing malde mer now appears
likely to be successfully solved. Mr. Bessemer's ship is built for plyi
between the shores of France and England, and the method in which he
purposes to carry passengers over the restless sea which separates us from
our Gallic neighbours is bold and ingenious in the highest degree. He
will carry the passengers in a spacious saloon, which, instead of partaking
of the rolling and tossing of the ship, will be maintained in an absolutely
level position. The saloon will be suspended on pivots, much in the same
way as a mariner's compass is suspended ; and, by an application of
hydraulic power, forces will be applied to counteract the motion of the
ship and maintain the swinging saloon perfectly horizontal. It was origin-
ally intended that the movements should be regulated by a man stationed
for that purpose, where he may work the levers that bring the machinery
into action, so as to preserve the saloon in the required position. This
plan has, however, been improved upon, and the adjustments will be auto-
matic. It may be well to mention that it is a mistake to suppose that any-
thing freely suspended, like a pendulum, on board a ship rolling with the
waves, will hang vertically. If, however, we cause a heavy disc to spin
very rapidly, say in a horizontal plane, the disc cannot be moved out of the
94 STEAM NA VIGA TION.
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 makes use of 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. The following interesting details regarding Mr.
y/Bessemer's latest invention are extracted from the " Daily Telegraph " of
/* the 23rd September, 1874:
" At the water-line Mr. Bessemer's ship is 350 ft. long, and each end, for
a distance of 48 ft., will be only about 4 ft. from the line of floating. In
rough weather the water will wash over the ends, which have been rounded,
so as to throw it off as easily as possible. These cigar-shaped extremities
are fitted with capstans, worked by Messrs. Brown's (Edinburgh) hydraulic
apparatus, and the vessel is provided with two of Martin's patent anchors.
When at sea there will seldom be any necessity for any one to go upon the
ends, but they will be used chiefly when the vessel is entering a harbour
or port. Above the low ends a breastwork is raised, about 8 ft. high, 254 ft.
long, and extending the entire length of the vessel. In the centre, and
occupying the space of 90 ft., is the swinging saloon, which is intended for
first-class passengers. At either end of this apartment are the engines and
boilers; on the breastwork deck are deck-houses, for private families or
parties, smoke-rooms, refreshment bars, &c. Although both extremities
of the vessel have the same appearance, each being fitted with a rudder
sheeted by Messrs. Brown's hydraulic machinery, they may for convenience
be named the fore and after ends. As the latter will be the part first to
take the water at the launching, temporary bulwarks are being erected, so
that as little wash as possible may be caused. At the after-part of the
vessel, and entirely independent of the swinging saloon, is the accommo-
dation for second-class passengers. On the first floor is a spacious cabin
for ladies, and two other cabins, which can be used by families or other
persons requiring privacy. On the next floor is the second-class saloon,
5 1 ft. in length. The entrances to the engine-rooms are of a convenient
character, and there is every probability that in fine weather this part of the
vessel will be frequently resorted to by passengers. Running in all direc-
tions in the engine-room are huge pipes, conveying steam to different
engines, and water to the numerous pumps situated in various parts of the
vessel.
" The engines are oscillating and expansive, working up to 4,600 horse-
power, which, should it be required, can be increased to as much as 5,000;
but it is expected that the former will be quite sufficient to drive the ship
at the required speed of twenty miles per hour. There are 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 Ibs.
pressure per square inch, supplied from four box-shaped boilers, each boiler
having four large furnaces. The paddle-wheels, of which there are a pair
on either side of the vessel, are 27 ft. 10 in. in diameter outside the outer
ring, and each wheel has twelve feathering floats. It is expected the leading
pair of wheels, when working at full speed, will make thirty-two revolutions
per minute. The following pair of wheels will of course move faster, as
they will receive some of the wash from the leading ones. Every care has
been taken to so secure the engines in their places that when developing
their enormous power they shall not strain or injure the ship. For starting,
stopping, and reversing the engines, Brown's hydraulic starting-gear has
STEAM NA VIGA TION. 95
been adopted. All orders to the engineers will be conveyed from the bridges
to the engine-room by telegraph. The whole of the levers for working an
engine are brought within a space of three feet, so that the engineer, with-
out moving from the spot, can reach any one of them. Great care has been
taken to make the gear as simple as possible, so that one engineer only will
be required to actually work the engines, and either can be started and
reversed in a few seconds. The levers, in fact, are so easily worked that
a child could set the engines in motion or stop them. There will be no
necessity for the stokers ever to appear on deck. Those engaged in stoking
for the after engine can walk along a passage which brings them to the
fore engine, near which their bunks are situated. This passage will also
enable the engineers to get at once from one engine-room to the other, in
case anything should be the matter with the machinery.
" Entrance to the Bessemer saloon is gained by two broad staircases lead-
ing to one landing, and a flexible passage from this point to the saloon will
be laid. The saloon rests on four steel gudgeons, one at each end, and
two close together near the middle. These are not only employed to support
the saloon, but are also utilized for conveying the water to the hydraulic
engines, by which the saloon is kept steady. For this purpose the after
one has been made hollow, and is connected with the water mains from
two pairs of powerful engines made by Messrs. Galloway and Co., Man-
chester, and also with a supply-pipe leading to a central valve-box, by
means of which the two hydraulic cylinders on either side are supplied
with water. Between the two middle gudgeons is placed a gyroscope,
worked by a small turbine, filled with water from one of the gudgeons.
The introduction of this gyroscope has enabled Mr. Bessemer to dispense
with the services of a man, and has thus completed his scheme of a steady
saloon, by making the machinery completely automatic ; but should at any
time the gyroscope fail to act, it is so arranged that a man can at once take
charge of the controlling machinery, and thus prevent the cabin becoming
useless for its first object. The saloon is 70 ft. long, 35 ft. wide, and 20 ft.
high. On the left-hand side, just within the apartment, is a spacious stair-
case leading to the top, and thus enabling passengers to enjoy the sea breeze,
and at the same time be free from feeling the motion of the ship, and this
without having first to traverse any portion of the vessel proper. On the
right-hand side of the engine will be a retiring-room, so that if, even in the
saloon, any person should find the * sea air ' too much for him, he can with-
draw from the public gaze. Ranged round the saloon will be a row of seats,
and it is intended to ornament the sides in a very tasteful manner with
panels. There will be carved oak shields bearing the monogram ' B. S. C.'
(Bessemer Steamship Company), and above these will be handsome oil
paintings. At the far end of the saloon is a retiring-room to be used by
ladies, and over that another. It may be mentioned that the different names
and uses of the various auxiliary cabins have not yet been definitely decided
upon, and they will remain in abeyance until the requirements of the traffic
have made themselves manifest
" One great desideratum in a ship's saloon is good ventilation, and this
has been attended to with the greatest care. Two fans or blowers are
employed, and are worked by the small auxiliary engine. One fan forces
fresh air into long tubes passing under the seats and throughout the whole
length and breadth of the saloon, and the pipes are punctured with small
holes, so as not to create a draught in any particular part. The air thus
supplied will be kept at a convenient temperature by passing through a
96 STEAM NA VIGA TION.
heating apparatus, resembling very much an ordinary surface condenser.
Thus, in cold weather, by regulating the supply of steam to the apparatus,
the temperature may be comfortably warmed, and, by always maintaining
a supply of fresh air, it will never become in any degree vitiated. The heat
is obtained from the exhausted steam from one of Galloway's engines. The
other fan draws the foul air from the saloon, and discharges it overboard.
The tubes conveying the air from the blowers are connected with those in
the saloon by means of an intermediate pipe fitted with flexible joints. It
is confidently expected that the arrangement of the saloon, together with
the steadiness of the vessel, will entirely prevent sea-sickness. The recent
addition to the original plan has been the placing of two light masts, one
at either end : sails attached to these will tend to materially steady the
steamer ; but another great consideration was to give the vessel some as-
sistance in turning, which, owing to her great length, would probably have
been a somewhat slow process, as she would have to be moved in a wide
circle. Entrance-ports or gangways are situated at the outer side of the
paddle-box, so as to insure a safe and easy landing-place. The steering
apparatus will be under the control of the officer on the bridge, which is
fitted between each pair of paddle-boxes. The kitchens are on the spon-
sons at the fore end, and are capable of serving up a hot dinner. In the
fore part is the accommodation for the crew, and a large space is appro-
priated to the stowage of luggage. For the latter purpose a crane is being
fitted on board, and such arrangements are made as to prevent the boxes
and other property of the passengers from being tumbled about, as is some-
times the case. The vessel will be provided with two large life-rafts, on
the principle patented by Mr. Christie, and four other boats will be ranged
along the side of the vessel."*
THE CASTALIA.
A NOTHER very remarkable ship has recently been constructed for
** carrying passengers across the English Channel without the unplea-
sant rolling which is experienced in the ordinary steamboats. The vessel
which has received the above name has been 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 pro-
ject 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 has built a vessel with
two hulls, each of which acts 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
* Since the above account was written, the Bessemer has been tried at sea. Her speed has by
no means realized the expectations of her designers. The automatic regulator will not be adopted
at present ; and the swinging saloon has not yet (Aug. 1875) been brought into operation.
STEAM NAVIGATION.
97
FIG. 67. The Castalia in Dover Harbour.
the section amidships has a form like this . . .
The two hulls are connected by what we may term
" girders," which extend completely across their sec-
tions, forming transverse partitions or bulkheads,
and these girders are strongly framed together, so
as to form rigid triangles. These unite the two hulls so completely, that
there is not the least danger of the vessel being strained in a sea-way. The
decks are also formed of iron although covered with wood, so that the whole
vessel really forms a box girder of enormous section.
The reason why the steamers which have hitherto run between Dover
and Calais, Folkestone and Boulogne, and other Channel ports, are so
small, is because the harbours on either side could not receive vessels with
such a draught as the fine steamers, for example, which run on the Holy-
head and Kingston line. Now, the Castalia draws only 6 ft. of water, or
i ft. 6 in. less than the present small Channel steamers, and she will there-
fore be able to enter the French ports at all states of the tide. Yet the
extent of the deck space is equalled in few passenger ships afloat, except
the Great Eastern and some of the Atlantic steamers. The vessel is 290 ft.
in length, with an extreme breadth of 60 ft. The four spacious and ele-
gantly-fitted saloons two of which are 60 ft. by 36 ft., and two 28 ft. by
26 ft., and the roomy cabins, retiring-rooms, and lavatories, offer the
greatest possible contrast to the " cribbed, cabined, and confined " accom-
modation of the ordinary Channel steamers. There are also a kitchen and
all requisites for supplying dinners, luncheons, &c., on board. But besides
the above-named saloons and cabins, there is a grand saloon, which is
9 8
STEAM NAVIGATION.
FIG. 68. The Castalia in Dover Harbour End View.
1 60 ft. long and 60 ft. wide ; and the roof of this forms a magnificent pro-
menade 14 ft. above the level of the sea. There is comfortable accommo-
dation in the vessel for more than 1,000 passengers.
The inner .sides of the hulls are not curved like the outside, but are
straight. The space between them is 35 ft. wide, and the hulls are each
20 ft. in breadth, and somewhat more in depth. There are two paddle-
wheels, placed abreast of each other in the water-way between the two
hulls, and each of these contains boilers and powerful engines. The de-
signers of this vessel calculated that she would attain a speed of I4f knots
per hour, but this result has not been realized. Probably there were no
data for the effect of paddles working in a confined water-space. The posi-
tion of the paddles is otherwise an advantage, as it leaves the sides of the
vessel free and unobstructed. The ship is of the same form at each end,
so that it can move equally well in either direction. There are rudders at
both ends, and the steering qualities of the ship are admirable. Although
the speed of the Castalia is below that intended, the vessel is quite a
success as regards steadiness, for the rolling and pitching have been
vry greatly reduced, and the miseries and inconveniences of the Channel
passage have, it is hoped, been at length obviated.
The Castalia is represented in Figs. 67 and 68. 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 has caused a delay in placing the vessel on her station.
FIG. (x)H.M.S. Devastation in Queenstown Harbour.
SHIPS OF WAR.
'"T
*
AKE 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, un-
helped, 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 nearly twenty
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 Glutton, just as it may be doubted whether
the armour-plated steamers will attain the same celebrity in romance and in.
TOO SHIPS OF WAR.
verse 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 ques-
tion 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 con-
structing La Gloire, a timber-framed ship, covered with an armour of rolled
iron plates, 4| 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 4! in. thick, backed by 18 in.
of solid teak-wood, and provided with an inner skin of iron. The Warrior
is 380 ft. long, but only 213 ft. of this length is armoured. The defensive
armour carried by the Warrior, and the ironclads constructed immediately
afterwards, was quite capable of resisting the impact of the 68 Ib. 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 iron-
clads 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 cap-
able 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 gi^en 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 pene-
trating 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 pos-
sible, to render his ship invulnerable.
One of the finest of the large ironclads is the Hercules, of which a section
amidships is presented on the opposite 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; weight of equipment and arma-
ment, 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 handinessj 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
SfffPS OF WAR.
101
FIG. 70. -Section ofH.M.S. Hercules,
102 SffJPS OF WAR.
can 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 \\ 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, f in. thick. The belt
along the water-line has thus altogether I \\ 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 1 1^ 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 1 8-ton guns as her central battery, and two 1 2-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 Ibs. The guns can be
trained so as to fire within 1 5 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 Ib. 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 1 5 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. 7 1 on the next page is the section of another ship of war, the Incon-
stant, 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 manoeuvring so rapidly. She could give
SHIPS OF WAR.
103
FIG. 71. Section of H.M.S. Inconstant.
chase, or could run in and deliver her fire, escaping by her speed from
hostile pursuit in cases where the slower movements of a ponderous iron-
clad would be much less effective. The Inconstant carries ten 1 2-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-
IO4
SHIPS OF WAR.
The 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 com-
partments. The engines are of 6,500 indicated horse-power, and the
vessel attains an average speed of more than 1 8| miles per hour.
A new system of mounting very heavy naval guns was proposed by
FIG. 72. Section, Elevation, and Plan of Turret of H. M.S. Captain.
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 sho.t, 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
SHIPS OF WAR.
io6 SHIPS OF WAR.
Coles' 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 at-
taches to her. On page 105 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 repre-
sented 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 f in. thick,
then a framework with longitudinal girders 10 in. deep. The deck was
plated in the spaces opposite the turrets with iron i^ 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 Ibs. of gunpowder, and of throwing a 600 Ib. shot.
After some preliminary trials the Captain was sent to sea, and behaved
so well, that Captain Coles and Messrs. Laird, her designer and contrac-
tors, 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
SHIPS OF WAR. 107
officers 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 tempe>t gave the shock ;
She sprang no fatal leak ;
She ran upon no rock."
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 dia-
grams 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 illus-
tration 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
io8
SNIPS OF WAR.
drawn 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 22^, 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
FIG. 74.
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 ; Lut in whatever
position the hoop may be placed, the earth's attraction pulls it as z/"this cen-
tral 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
rJie 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
SHIPS OF WAR. 109
large 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 down-
wards, 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 posi-
tion 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
FIG. 75-
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 shipj 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
no
SHIPS OF WAR.
G. The righting force, then, increases in proportion to the horizontal dis-
tance 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
i ft. long, in order to produce the same turning effect. When a ship is kept
steadily heeled over by a side wind, the presence of the wind and the re-
sistance of the water through which the vessel moves constitutes 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, are
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 dis-
tance 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 :
I. Angle at which the edge of the deck is immersed
II. Statical righting force in foot-tons at the angle
at which the deck is immersed
III. Angle of greatest stability
IV. Greatest righting force in foot-tons
V. Angle at which the righting force ceases
VI. Reserve of dynamical stability at an angle of
14 in dynamical foot-tons
Monarch. \ Captain.
28'
12,542
^9 15
6,500
54
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 slop-
ing 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 I ft. high,
one foot ton of work is said to be done; if 2 tons were raised i ft., or I tori
were raised 2 ft., then two foot-tons of work would be done, and so on. The
SHIPS OF WAR. in
same 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
j>r 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 under-side of the hur-
ricane 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 I 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.
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 appear-
ance 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 112. 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 fall
ing 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 immer-
sion 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 im-
mersion by i 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
112
SHIPS OF WAR.
cost ,210,000. Mr. Reed
wished to construct a vessel
of much larger size on the
same plan a proposal to
which, however, the Ad-
miralty did not then con-
sent. The Glatton is, never-
theless, 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 I 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 Ib. 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, fast-
ened on 1 8 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 Glattoru has a great
advantage over all the other
turret ships in having a per-
fectly unimpeded fore range
for her guns, for there is no
mast or other object to pre-
vent the guns being fired
directly over the bow. There
are no sails, the mast being
intended only for flying sig-
nals and hoisting up boats,
&c. The hull is divided by
vertical partitions into nine
water-tight compartments,
and also into three horizon-
tal flats the lowest being
air-tight, and having ar-
rangements for the admis-
sion and removal of water,
SHIPS OF WAR.
IT3
as already mention-
ed. The stem of the
ship is protruded
forwards below the
water for about 8 ft.,
thus forming a huge
ram which would it-
self render the Glat-
ton a truly formid-
able 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
9^ knots per hour,
and means are pro-
vided for turning
the turret by steam
power. The turret
can be rotated by
manual labour, re-
quiring about three
minutes for its com-
plete revolution, but
by steam power the
operation can be
effected in half a mi-
nute. The comman-
der 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.
The British navy
contains two pow-
erful turret -ships
constructed on the
same general plan
as the Glatton, but
larger, and capable
of steaming at a
8
n 4 SHIPS OF WAR.
greater speed, and of carrying coal for a long voyage. These sister ships
are named the Devastation, Fig. 69, and the Thunderer ; Fig. 77. The Thun-
derer 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 2f in. iron plates ; then 6 in. of teak in iron frames,
arranged horizontally ; 6 in. of armour plates ; 9 in. of teak, placed verti-
cally ; 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 the opposite page, Fig. 78. This vessel,
named the Konig Wilhelm, was built at Blackwall for the Prussian Govern-
ment 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 4! 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.
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 80 tons in weight are in course of construction, ships are already
designed with 18 in. and even 20 in. of iron 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
SHIPS OF WAR
u6
SHIPS OF WAR.
of powder, may be illustrated by stating in a condensed form some details of
ships already named, as regards the thickness of armour, and its resisting
power, which is nearly in proportion to the square of its thickness ; and
some particulars respecting the guns carried by those ships are also given.
Warrior.
Hercules.
Glatton.
Thunderer.
Thickness of iron pla-
tin r in inches
4.1
Q
12
Relativeresisting power
of plating
2O
8 1
M4
1 06
Guns carried
Cast iron,
Wrought iron,
Wrought iron,
Wrought iron,
Weight of guns in tons
Charge of powder in Ibs.
Weight of projectiles in
Ibs
smooth bore.
4l
16
68
nned.
18
60
4.00
nned.
25
70
6OO
rifled.
35
1 20
700
Destructive power of
projectiles at 1,000
yards range, in foot-
tons
4.C2
7,863
s,i6s
8.4O4.
In official trials the power of iron plates to resist projectiles was tested
not only by firing at targets built to resemble the sides of the vessels,
but real floating batteries, like that represented below, were made the sub-
ject of experiment ; and although the sides of the battery here depicted
were formed of 4^ in. slabs of iron, backed by 22 in. of teak, Sir J. Whit-
worth's flat-headed projectiles completely penetrated them, punching a
clean six-sided hole in the iron plates. The bright flash of light emitted
at the instant of the impact is shown in the cut, and the effect to a spectator
was much the same as if a gun had been fired from the battery in reply.
FlG. 79. AV////V 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 intro-
duction 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
117
n8 FIRE-ARMS.
upon 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 exaspe-
rated 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 every-
where 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 elabo-
rate 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 last few years surpasses that of the three previous centuries.
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. We shall bring
before the reader a description of some of the improvements in artillery,
beginning with
RIFLED CANNON.
n^HE large guns which are now constructed at Woolwich, though often
-* called Armstrong guns, are not the production of one inventive mind
only, but may be described more fully as wrought iron guns built on Sir W.
Armstrong's principles, improved by Mr. Anderson's method of hooping
the coils,^-with solid-ended steel tubes toughened in oil, rifled on the
French system, modified as recommended by the Ordnance Committee to
suit projectiles studded according to Major Palliser's plan. Sir W. Arm-
strong's 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
FIRE-ARMS. 119
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.
Until the year 1867 the guns made at Woolwich were constructed accord-
ing 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 pro-
posed an important modification of the original plan, and the adoption of
a kind of iron cheaper than had been previously employed, yet perfectly
BREECH'COIL
FIG. 80. Section of 9 in. Fraser Gun.
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. 80, 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. Com-
pare also Figs. 8 1 and 94. We shall now describe the process of making the
Fraser 9 in. gun. The parts of the gun as shown in the section, Fig. 80, are :
i, 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 heat-
ing 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.
120 FIRE-ARMS.
A bar of the steel I 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 tough-
ened 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 8| 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 Ibs. 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. Arm-
strong'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 fur-
nace, winding round the core in a close spiral, so that the turns are in con-
tact. 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.
Jf 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
FIRE-ARMS. 121
to 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, go 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 pro-
cess 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 from 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 re-
moved 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 mas-
sive construction, which weighs more than 100 tons. Fig. 34, page 53, 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 ac-
curately 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
122 FIRE-ARMS.
cascable 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 per-
fect 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 finish-
ing 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 per-
pendicularly to the bar, and partaking of its backward and forward move-
ment, 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 there-
fore well adapted for penetrating iron plates or other structures. The pro-
jectiles 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 keep-
ing the axis of the missile always parallel to its original direction. Thus
vastly increased accuracy of firing is obtained.
There is a very curious deviation to which the projectiles from rifled
cannon are liable, a deviation which is not caused by the wind, but is con-
stant in amount for the same gun with the same projectile and charge of
powder. A shot deviates to the right or left according to the twist of the
rifling of the piece, and according to the form of the head of the shot.
This is found to depend upon certain laws which govern all rotating bodies.
To explain these laws fully would be to exceed our limits, but the reader
who is interested in this subject may see them in operation in the gyroscope,
a simple form of which is now a cheap and common toy. When the axis
FIRE-ARMS. 123
of the disc is placed in an inclined position, the unsupported extremity
would, if the disc were not rotating quickly, be depressed by gravity ; but
when the disc is in rapid rotation, it descends very slowly, and the axis at
the same time slowly moves round horizontally about the supported point.
It is easy to see that the projectile from the rifled cannon is under similar
conditions, for the reaction on its head of the air through which it moves
tends to depress or to elevate the anterior end of the axis, according as the
projectile is flat-headed or pointed. The constant deflection of shot here
mentioned is allowed for in pointing the piece, its direction and amount
having once been determined by experiment.
FIG. 81. They^-ton Fraser Gun.
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 east
hollow, and having their interior filled with gunpowder. Such shells when
used against iron structures require no fuse : they explode on coming into
collision with their object. In other cases, however, the shells are provided
with fuses, which cause the explosion when the shot strikes. The cut above,
Fig. 81, 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. 8 in. in diameter at
the breech, and i ft. 9 in. at the muzzle. The bore is about I ft. Each
gun can throw a shot or bolt 700 Ibs. in weight, with a charge of 120 Ibs.
of powder. It is stated that the shot, if fired at a short range, would pene-
trate 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,
graders, &c., put together in the strongest possible manner, in order to test
the resisting power of the armour plating and other constructions of our
iron-clad ships. The next two cuts, Figs. 82 and 83, are representations
of the appearance of the front and back of a very strong shield of this de-
scription, after having been struck with a few 600 Ib. shots fired from the
25-ton gun. The shots with chilled heads, already referred to, sometimes
were 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.
Other plans of constructing guns quite different from that adopted at
124
FIRE-ARMS.
Woolwich have been proposed. Sir Joseph Whitworth makes his guns of
steel, and they are striking examples of beautiful and accurate workman-
ship. His system of rifling consists in forming the bore of the gun so that
its section is a regular polygon, and the projectile is an elongated bolt with
FlG. 82. Millwall Shield after being battered with Heavy Shot. Front
View.
sides exactly fitting the barrel of the gun : the projectile is, in fact, a twisted
prism, usually hexagonal. Sir Joseph's guns are breech-loaders, and they
are remarkable for their long range and accuracy of fire. One of these
FIG. 83. Rear View of the Millwall Shield.
guns with a charge of 50 Ibs. of gunpowder threw a 250 Ib. shot a distance
of nearly six miles, and on another occasion a 310 Ib. 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 are the greatest distances to
which shot or shell have ever been thrown.
FIRE-ARMS. 125
As the material of which these guns are constructed is costly, and very-
perfect workmanship is required in the formation of the barrel and the
shots, the expense attending their manufacture and use is much greater
than that incurred in the case of the Armstrong guns. Sir W. Armstrong's
estimate for a 35-ton gun was .3,500, and Sir J. Whitworth's 6,000. The
gun, as constructed at Woolwich on Mr. Eraser's plan, is 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." By means of
.1 kind of pressure-gauge, in which the compression of a piece of metal
produced by the force of the gases in the powder-chamber is compared
with the amount of compression produced in the same metal by a known
FlG. 84. Comparative sizes of '35 and'&i-ton Guns.
A. 35-ton. B. 8i-ton.
pressure, it was estimated that in the 35-ton gun a pressure of more than 47
tons must have been applied to every square inch of the internal surface
of the powder-chamber. When we remember that these enormous pres-
sures are applied so suddenly that they partake rather of the nature of a
blow than of a pressure gradually applied, we cannot be surprised at the
ultimate failure of even the strongest piece of ordnance. The great 35-ton
guns, hitherto the most powerful of cannon, have been humorously called
" Woolwich Infants ; " but if the reader will refer to Fig. 84, he will see that
even these impressive pieces of ordnance are, indeed, " infants " in almost a
literal sense, compared with the monsters which are now in course of con-
struction. The figure represents the 35-ton and the 8i-ton gun on the same
scale. The new gun will weigh 8 1 tons, the length will be 27 ft., with a length
of bore equal to about 24ft., and the diameter of the bore will be 14 in. in
the first instance ; but if after experiments it be found desirable, the bore
may be enlarged, first to 15 and afterwards to 16 in. The trunnions for
this gun will be 16 in. in diameter. The shot for the 14 in. bore will weigh
about 1,000 Ibs, and with the larger bores 1,200 Ibs. The energy of the
1,000 Ib. projectile when it leaves the muzzle will, it is calculated, be equal
to 11,700 foot-tons, and that of 1,200 Ib. shot will exceed 14,000 foot-tons,
or nearly double that possessed by the shot from the 35-ton gun. Such
projectiles will completely penetrate plates of iron 20 in. in thickness. The
126
FIRE-ARMS.
Si-ton gun will be built up in the same manner as the 35-ton, but the coils
will necessarily be much longer, and the chase is formed in three parts
instead of two. It was for the manufacture of these enormous guns that
the great steam hammer (represented in the frontispiece) was erected at
Woolwich. An extreme contrast to the 8i-ton gun is presented in the little
gun which forms the subject of Fig. 85. This piece weighs only 148 Ibs.,
and with a charge of 8 oz. of gunpowder has been found to hit with shot
or shell a target with great precision at
a distance of 1,000 yards. It has been
found admirably adapted for mountain
warfare and in situations where the ab-
sence of good roads would make heavier
pieces an impediment to an army on the
march. In the wars in Abyssinia and in
Ashantee these little weapons jocosely
called " steel pens "-were found of great
service. In the battle which preceded the
fall of Magdala and the death of King
Theodore, the shells thrown by these
little guns at a distance of several hun-
dred yards cut up and threw into con-
fusion the great bodies of men which the
Abyssinian King had collected.
The Armstrong and the Whitworth
guns are not the only ordnance which
claim attention on account of their power
, ~ and accuracy of fire. There are tKe
The founder Rifled Steel Gun. sted guns of the famous Krupp? whose
works at Essen in Prussia are of enor-
mous extent. The head-piece to this chapter gives but a very faint idea
of the 500 acres of ground covered by this huge gun factory, where 310
steam engines are at work, and more than 100 furnaces are burning night
FIG. 85.
FlG. 86. The \\v-pojinder Breech-loading Krupp's Gun, with Breech-
piece, or Slide, open and ready to load.
Rnd day. The forges, the lathes, and the steam hammers may be reck-
oned by hundreds, and to crown all, more than 10,000 men are busily
engaged in feeding and controlling the innumerable machines. These
works originally were not devoted exclusively to the manufacture of
guns, but now the production of the cast steel breech-loading ordnance
absorbs much attention at these gigantic steel works. The peculiarity of
FIRE-ARMS.
127
these steel guns is the perfectly uniform character of the steel and its free-
dom from flaws. Krupp has exhibited solid cylinders of steel, 2 ft. in
diameter, broken across in order to show that the steel was perfectly sound
and uniform throughout the mass. The details of the processes by which
these castings are made are kept secret.
FlG. 87. The \\Q-po :>r.dcr Breech-loading Krupp Siege Gun, loaded,
the Slide pusiied in and fixed, and ready for firing.
The hundred-and-ten-pounder breech-loading gun, as constructed by
Krupp, is represented in Figs. 86 and 87. In the former the sliding breech-
piece is drawn out, and the piece is ready for loading ; in the latter the slide
is pushed in, and fixed ready for firing. The reader will, of course, under-
stand that the gun is represented in these figures without its carriage and
FlG. 88. The yz-pounder Prussian Krupp Siege GUJI, a Breech-loader,
with Breech-piece open for admission of the Shell and Gunpowder.
other adjuncts. These guns, it lias been stated, will throw a shot a distance
of five miles, although at the siege of Paris, where they were used by the
Prussians, the utmost range of the shells was about four and a half miles,
or more usually three and a half miles. A much lighter Krupp gun, a thirty-
two-pounder, is represented in Fig. 88, mounted on a traversing platform
and well-constructed gun-carriage, with an ingenious contrivance for re-
ceiving the force of the recoil. Krupp also makes guns throwing heavy
projectiles, 600 Ibs. and upwards. These large guns were at one time consi-
FIRE-ARMS.
FIG. 89. Appearance of the Deck of a Ship after the bursting of a large Gun,
dered by British artillerists as very unreliable weapons, because steel is a
material subject to certain unobserved flaws, that occasionally cause the
guns to burst in the most capricious manner. As a matter of fact, a few
FIG. 90. Another view of the same disaster, at which, strange to say, no
one was killed.
Krupp guns have burst, and in one case with disastrous consequences. The
reader may picture to himself the probable results to the gunners of an
accident of this kind. He will doubtless understand that every part of
the interior of the powder- chamber receives at the moment of the discharge
FIRE-ARMS.
129
FIG. 91. The Citadel of btrasburg after the Prussian Bombardment.
a sudden strain or blow of the same power as that which urges on the shot.
It is v the effect of this strain acting on the end of the barrel which pro-
duces the recoil of the gun in ordinary cases. But if the breech of the gun
is blown in pieces, these pieces are hurled about with as much force as
would have otherwise been expended on the shot. The cuts, Figs. 89 and 90,
are from photographs taken on board ship immediately after the bursting of
a large gun. The reader cannot fail to notice the manner in which a rnast
has been completely cut away by a fragment of metal.
The Krupp guns, as may be imagined from the scale of their production
are, however, finding great favour with continental nations. Austria, for
example, has resolved upon completely changing her armament, by intro-
ducing these weapons, in power and accuracy of fire they having been found
on investigation to surpass the Austrian artillery in the proportion of five
to one. The power of the Krupp guns may be illustrated by the reproduc-
tion of a photograph, given in Fig. 91, of a portion of the fortifications of
Strasburg after the Prussian bombardment of that fortress.
This section may fitly close with the two drawings Fig. 92 and 93, and a
few words of description of the truly scientific and ingenious invention of
Captain Moncrieff, by which he utilizes the force of the recoil as a power
for raising the gun into a firing position, after it has been loaded under
cover. The mode in which Captain MoncriefFs gun-carriage acts will be
understood by a simple inspection of the figures. Fig. 93 represents the
gun raised above the parapet and ready for firing. When thfc discharge
takes place the gun would, if free, move backwards with a speed which
would be greatest at the first. The arrangements of the carriage are such
I 3 o
FIRE-ARMS.
FIG. 92. Moncrieff's Gun-carriage j gun lowered j or loading.
_.- ./
FIG. 93. The Moncrieff Gim raised and ready for firing.
that this initial velocity does not receive a sudden check, but the force is
made to expend itself in raising a heavy counterpoise ; at the same time
the gun is permitted to descend, retaining a direction parallel to its first
position. At the end of the descent of the gun (which, it must be under-
stood, is not caused by its weight, but by the force of the recoil, for the
FIRE-ARMS. 13 i
counterpoise more than balances the gun) it is retained in that position
until it has been re-loaded, and when released the counterpoise descending
brings the gun up again into the firing position. The great advantage of
this invention is that the artillerymen are not exposed to any danger while
loading; and even when pointing the gun expedients may be adopted
whereby the whole danger is reduced to that arising from " vertical fire,"
by which little harm is likely to be done. The plan of using a counter-
poise in the manner just described would manifestly be inapplicable with
naval guns, but Captain Moncrieff has matured a most elegant application
of the elastic force of compressed air. The force of the recoil is made to
urge a piston, so as to compress the air, and the reaction is used, like the
descent of the counterpoise, to bring the gun back into the firing position.
FlG. 94. foo-pounder Muzzle-loading Armstrong Gun.
BREECH-LOADING RIFLES.
"VX/TIEN 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 gun-
maker 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
arrangement was confessedly only temporary, and the Snider-Enfield has
been passed on to the volunteers and reserve, while the line are now pro-
vided with a still more effective weapon in the Martini-Henry rifle. The
9 2
132
FIRE-ARMS.
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. 95. Section of M artinir 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. 95, are contained in a metal case, to which
is attached the woodwork of the stock, now constructed in two parts. To this
case 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 levei some-
what 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
FIRE-ARMS. 133
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 observ-
ing 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 in-
serted 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 a piece of metal called the " striker,"
which is armed with a point, capable of passing through a hole in the front
face 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 for-
ward, 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 abend 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 cartridge 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.
The barrel is of steel ; the calibre is 0*45 1 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 en-
larged 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
which 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
134
FIRE-ARMS.
as to form a powerful chopping implement, so that, in addition to its pri-
mary use as a bayonet, it will be useful for cutting and sawing brushwood,
small trees, &c.
FIG. 96. The Martini-Henry Rifle.
A, ready for loading ; B, loaded and reaay for nriiig.
The following are the principal particulars of weight, dimensions, &c,,of
the Martini-Henry rifle :
C Without bayonet . 4 ft. I in.
< With bayonet fixed
I Of barrel
Length of rifle
Calibre .
Rifling
Weight .
Bayonet .
Charge of powder
?) w
9-22
0-451
Grooves
7
Twist .
i turn in 22 in.
Without bayonet.
8 Ibs. 7 oz.
With bayonet
Jo 4
Length .
2 ft. i% in.
Weight without 7
scabbard J
I lb. 8 oz.
85 grains.
Weight of bullet . ' . . . . 480
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 ^ in. elm planks placed I 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
I minute 3 seconds.
A competent military authority, after instituting a careful comparison
between the breech-loading small arms of Prussia, France, and England,
FIRE-ARMS.
'35
concludes that in the Martini-Henry we have a weapon "giving great
accuracy at long ranges, combined with a very flat trajectory, and therefore
fearfully destructive at shorter ranges, with terrible smashing power and
great penetration, not liable to fouling, easily cleaned, and not injured by
being left uncleaned, with grooves which do not lead or wear out ; a breech
mechanism easily constructed by machinery, easily worked, not liable to
get out of order, utterly unaffected by rust or dirt, wearing well, quickly
loaded, light, handy, strong, and durable."
FIG. wThe Chassepot Rifle. Section of theHYeech. "^
Another breech-loading military rifle of note is the Chassepot, the weapon
of the French infantry, of which we heard so much before and during the
disastrous campaign against the Germans. This arm has a rifled barrel,
with a breech mechanism of great simplicity, which is represented in section
in Fig. 97. 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
the 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
xs to draw out also a small rod attached to the hammer, and terminated in
front by a needle, about \ 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
i 3 6 FIRE- ARMS.
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 levef, 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
cannot 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.
MITRAILLEURS, OR MACHINE GUNS.
'"PHE idea 01 combining a number of musket-barrels into one weapon, so
- 1 - that these barrels may be discharged simultaneously or in rapid suc-
cession, is not new. Attempts were made two hundred years ago to con-
struct 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 recent invention of the rigid metallic-
cased cartridge. Several forms of machine guns have recently attracted
much attention. There is the Mitrailleur (or Mitrailleuse), of which we
heard so much at the commencement of the Franco- German War, and of
whose deadly powers the French managed to circulate terrible and mys-
terious reports, while the weapon itself was kept concealed. Whether 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 awhile. The machine gun, or " battery," invented by Mr.
Catling, 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
FIRE-ARMS.
137
this arm into the British service. They recommend for certain purposes
the Catling Battery Gun.
In the Catling 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. 98
gives a rear view, and Fig. 99 a side view, of the Catling battery gun. The
weapon is made of three sizes, the largest one firing bullets i in. in dia-
meter, weighing \ lb., the smallest discharging bullets of -45 in. diameter.
FIG. gS.Ttie Gatling Battery Gun. Rear View.
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
carrier 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
irrto 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.
i 3 8 FIRE-ARMS.
" 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 sup-
ports 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 car-
tridges, 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 : ist. 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
gun 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 longi-
tudinal reciprocating motion, performing the consecutive operations of
loading, cocking, and firing without any pause whatever in the several and
continuous operations."
The small Catling 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
FIRE-ARMS.
FlG. 99. The Catling Battery Gun. Front View.
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.
The committee of military officers before referred to caused many experi-
ments to be performed, with a view of testing the power of the new weapon.
The nature of some of the experiments will be understood from the follow-
ing table :
TRIAL OF MONTIGNY AND SMALL CATLING MITRAILLEURS v.
12-pouNDER BREECH-LOADER AND 9-POUNDER MUZZLE-
LOADING RIFLED GUNS,
At 800 yards, against three rows of 45 ft. X 9 ft. targets, 15 yards apart,
representing columns of infantry and cavalry.
(Tffftfj two minutes.)
1
Range.
Nature
of Ordnance.
Projectile.
Number
of
rounds
fired.
Total
number
of hits
on three
screens.
Total
Cavalry
dis-
abled.
Total
Infantry
dis-
abled.
Remarks.
ab
nit
yards.
c
Numerous frag-
800
i2-pr. breech-
loader, rifled
1 Seg-
j raent
6
496
62
93 1
ments, yth round
in the gun when
V.
time was up.
Two rounds prema-
9-pr. muzzle-
loader, rifled
) Shrap-
) nel
7
254
45
59 ]
ture and one burst
over. Total effec-
(^
tive rounds, 4.
Mitrailleur
n
81
34
21 {
1 2th plate in gun.
Fired in volleys.
(
Gun worked stiff-
Small Catling
*-
82
191
Si
H
ly, and the tire
checked twice by
t
cartridge jamming.
i 4 o FIRE-ARMS.
After a careful comparison of the effects of field artillery firing shrapnel,
the committee concluded that the Catling 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. Catling contends that, shot for shot, his machine is more accurate
than infantry, and certainly the absence of nerves will insure steadiness ;
while 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 dis-
charge. 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.
The small Catling 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.
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 Catlings, each of which can send out, it is said, i ,000 shots per
minute, and improvements have been effected, so as to obtain a lateral
sweep for the' fire.
A competitor to the Catling presents itself in the Belgian mitrailleur,
the Montigny, Fig. 100. This gun, like the Catling, is made of several diffe-
rent sizes, the smallest containing nineteen barrels and the largest thirty-
seven. The barrels are all fitted into a wrought iron tube, which thus con-
stitutes 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
from 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
FIRE-ARMS. 141
FIG. ioo. The Montigny Mitrailleur.
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 project-
ing 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, vfhzre 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. It is found that at the proper ranges the bullets spread suffi-
ciently, for there are many causes which prevent them from pursuing a
perfectly parallel course.
142
FIRE-ARMS.
FIG. loi. Mallefs Mortar,
SHELLS AND EXPLOSIVE BULLETS.
PHESE missiles were formerly called "bombs," from the Latin bombus,
, ,. 1T } allu sion to the noise they make when exploded. The bomb is a
hollow iron globe cast pretty thick, and having a round aperture by which
it can be filled and lighted. After being carefully examined, to ascer-
tain if there are any flaws, it is nearly filled with gunpowder, and a fuse
inven m. Bombs are now called "shells," whether discharged from
FIRE-ARMS.
143
mortars or guns. The largest formerly used in the British service had a
diameter of 13 in. ; was rather more than 2 in. thick ; it contained about
10 Ibs. of gunpowder ; and weighed I cwt. 3 qrs. 2 Ibs.
The shells now in use vary from a few pounds to many hundreds of
pounds : the largest naval guns throwing a shell weighing 700 Ibs. the
Mallet, 36 in. Mortar, remains unsurpassed in respect of the weight of
metal which it is capable of throwing, viz., 2,986 Ibs.! This enormous
weight was thrown one mile and a half at the Plumstead practice range.
The shells were embedded to a great depth ; a few were dug up, but most
of them were buried fully 30 feet ; and as it costs about 21 to recover
FIG. 102. The Shrapnel and Segment Shells.
them, they are allowed to remain. Two mortars were made at a cost of
^5,000 each ; only one has been fired, and they weigh 35 tons being the
precise weight of " England's Thunderer," the 7oo-pounder already alluded
to. Mallet's mortar gave way with charges of from 60 to 70 Ibs. of gun-
powder. The 7oo-pounder fires 120 Ibs. of powder.
The most destructive shells now used are those called " The Shrapnel "
and " Segment Shells." The shrapnel consists of an iron case containing
a number of bullets. The bursting charge of gunpowder is behind them,
and when exploded by the fuse, which is ignited by the flash of the gun,
they travel forward with a greater velocity than the shell, and, spreading
out like the sticks of a lady's fan, carry death and destruction before
them. The segment shell is made up of forty-nine pieces of iron, some of
which are shown between the two shells in Fig. 102. The pieces of cast
iron are held together with lead ; the bursting charge is placed in the
centre, and is ignited by a percussion fuse, which explodes when the shell
strikes any object.
i 4 4 FIRE-ARMS.
A military authority writing on this subject says : "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 : that is to say.
it looks like a very large long Enfield bullet. When fired, the flash of the
gun lights a time-fuse in the head of the shell, which at the proper moment
communicates with the powder charge in the chamber through a pipe
which lies in the axis of the shell. 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 had 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.
" 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 likely to explode at the proper
time.
" Shrapnel and segment shells can be used with field artillery, i.e^
9-pounders, 12-pounders, i6-pounders ; and also with heavy rifled guns in
fortresses, viz., 4o-pounders, 64-pounders, 7-in. and Q-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 it is very difficult to cut the time-fuse of the shrapnel
shell to the proper length. Moreover, the men who have to adjust the fuses
would probably be exposed to the fire of the enemy's artillery, and conse-
quently 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. This authority, therefore, coincides with
FIRE-ARMS.
that of the Dartmoor Committee, who decided that both shrapnel and
segment shells should be served out in certain proportions to field batteries.
" 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."
This admirable digest was written in answer to the statement in the
" Times," that shrapnel shells were rarely used with very heavy guns, and
the author goes on to say " that there is nothing to prevent strategical
fortresses in England from being armed with 7-in. and 9-in. rifled shell guns,
and thus it would be easy to estimate the chances of success with which
any invading army could attack a properly constructed fortress armed with
rifled guns firing 7-in. and 9-in. shrapnel shells."
Captain C. Orde-Browne, Royal Artillery Laboratory Instructor at the
Royal Arsenal, Woolwich, in a recent lecture given by him in speaking
of the changes which had taken place in guns and projectiles remarked
that the bullets from a shrapnel shell might kill and wound a great number
of men, while the fragments of a common shell in bursting could only
blow one or two into atoms. In the late experiments at Dartmoor against
rows of targets representing columns of troops, it was shown that a single
field battery advantageously placed, and firing the improved shell, could
kill or disable 20,000 men in one hour.
FIG. 103. Norton's Explosive Bullets or Rifle Shells.
The Prussians used the ogivo-cylindrical form of percussion shell. These
projectiles burst by means of fuses called "percutent." At the moment
when the shell strikes the ground, a small metallic rod or stalk, terminat-
^ g iJ n a ? mt ' acts upon a fu } minatin g capsule screwed on the head of the
shell, and the powder is ignited. The shell bursts, and the fragments to
the number of twenty or more of different sizes are violently scattered,
mostly in front, to a distance of several hundred yards. The shell has a
leaden covering which is separated from the shell, and adds to the de-
structive effect produced by the cast-iron fragments.
This article will hardly be complete without some reference to Explosive
Bullets, which have been well described, and their proper use indicated,
by Major Fosbery. Of course, such bullets are in fact shells in miniature,
and it has been mercifully urged that it is quite sufficient to maim or
otherwise render useless an enemy, without blowing him into a shapeless
10
146
FIRE-ARMS.
mass, or causing increased torture by making the bullet that penetrates
the body explode instantly. Explosive bullets or rifle shells have been,
and are now, regularly used in shooting elephants, lions, tigers, and other
larger animals ; and the advocates for their use declare it is more merciful
to kill an animal with one blow and flash, than to condemn it to a slow
and lingering death by a number of single bullet wounds.
The first rifle shell was prepared by Captain Norton in the year 1826,
and is shown in Fig. 103. In one case, a, the bullet is exploded by some
FIG. 104. General John Jacobs' Explosive Bullet.
percussion powder, fired by a wooden plug ; in the other, <:, the bullet
contained a small tin tube fitted into the hollow; this was filled with
gunpowder, and a percussion cap placed on the end of the tube, which
explodes on contact ; b represents the external shape of Norton's explosive
bullet. This was succeeded by another invented by General John Jacobs.
FIG. 105. Major Fosbery's Explosive Bullets.
The next were the Metford and Boxer Shells, succeeded by Major Fosbery's
invention. This rifle shell was carefully tried in India in 1863, and used
for the purpose of blowing up artillery tumbrils. It was subsequently
employed by Major Fosbery, not for destroying human life, but for judging
distances in the hill country of India ; and with the greatest success at the
Umbeyla Pass, where, by watching the smoke and detonation on the rocks,
they were enabled to judge the distance and aim the mountain guns with
just as much precision, as they might have done on level ground.
FIG. 106. Harvey's Torpedo. Working the Brakes.
TORPEDOES.
'T^HE notion of destroying ships or other structures by explosions of gun-
* powder, 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
117 10 2
148 TORPEDOES.
purpose of the torpedo where it is used defensively, but the comparison
fails to suggest its capabilities as a weapon of offence. There are few occa-
sions 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 con-
trivance 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 clock-
work, 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.
FlG. 107. Submerged lurpeao.
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
I 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
TORPEDOES. 149
action 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 ap-
proaches to the city. They consisted of large wooden cases capable of con-
taining 400 Ibs. 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 posi-
tion. 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 there-
fore 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 posi-
tions 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 assist-
ance of the diagram, Fig. 108, in which, for the sake of simplicity, the
positions of only three torpedoes, I, 2, 3, are represented.
In this arrangement two observers are required at different stations on
the shore. At each station which should not, of course, be in any con-
spicuous 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
TORPEDOES.
C l-l A N N E. L
KEY
KEY
FIG. 108. Mode of Firing Torpedo.
corresponding piece of metal on the rim of the table. The mode in which
these wires are connected with the torpedoes, the telescopes, and the elec-
tric 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 ex-
plode. 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 com-
pleting 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
c \-> C
, containing 67 Ibs.
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.
Another very interesting form of torpedo, which is adapted for offensive
operations, has been approved by the English Government after satisfac-
tory results had been obtained with it in various official trials. It is the
invention of Commander Harvey, and is worthy of a detailed description
for the ingenuity of its construction.
The shape of Harvey's torpedo, as may be noticed on reference to Fig.
1 1 8, 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 if ft, while the breadth is
only 6 in. Within this wooden case is another water-tight case made of
TORPEDOES.
thick 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
FIG. 113. Explosion of^lbs. ofGun-Cotton in 37 feet of Water.
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 in-
FIG. 114. Explosion 0/432 Ids. of Gun-Cotton in 27 feet of Water.
dependent chamber in the midst of the large one. which latter is capable
of containing 80 Ibs. of gunpowder. The copper tube or priming-case con-
tains 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 ;
TORPEDOES.
for 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 Ibs. 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 cap-
sule,*:, which, when the bolt is forced down,
is pierced through by the steel pin at the
bottom of the brass tube, and then the ex-
plosion takes place. The bolts are not
liable to explosion by concussion or expo-
sure to moderate heat, and they can be
kept for an indefinite period without de-
terioration.
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
T, c, j- r> effective in forcing down the bolt a result
FIG. ^.-Section of Priming- accomplished . b y attaching to the short
arm of the lever a greased cord, which,
after passing horizontally through a fair-
leader, 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,/, Fig. 1 1 5, a wedge which passes through a slot in the exploding
bolt, and resting on the brasswork of the priming-case, retains the muzzle
i in. above the pin. Through the eye of the safety key and round the
bolts passes a piece of packthread, *?, 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, d', 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 repre-
sented 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 tor-
pedo. This is a buoy, of which two at least are always used, although only
Case and Exploding Bolt.
TORPEDOES.
157
FIG. 1 1 6. Harvey's Torpedo.
one is represented in the figure. Each buoy, in length 4^ 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.
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 star-
board 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 inspoction of Fig. 116,
i 5 8
TORPEDOES.
which 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
FIG. 117. Harvey's Torpedo.
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 iron-
clad 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.
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
TORPEDOES.
159
FIG. 1 1 8. Harvey's Torpedo.
bight 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
FIG. 119. Official Trial of" Harvey's Sea Torpedo? February, 1870.
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
i6o TORPEDOES.
considerable 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 tor-
pedo 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. 1 20. Model of Submarine Guns.
Another device for submarine attacks upon vessels on which much inge-
nuity 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 ex-
plode, and by making a hole below the water-line, cause the certain destruc-
tion 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 photo-
graph 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 resist-
ance 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
TORPEDOES.
161
requires to move one's hand quickly backwards and forwards through
water will easily understand that the resistance it presents would, in a com-
paratively short space, check the speed of a projectile, however great that
speed might be at first. Then the currents in the water will have a great
effect on the path of the projectile, so that taking an aim would under such
circumstances be practically impossible. For these reasons and others,
submarine guns could, therefore, be used only at very close quarters, where
probably other modes of attack, such as torpedoes attached to long spars,
would be more effective.
The real power of the offensive torpedo in actual warfare remains yet to
be proved, for the few cases recorded during the Civil War in America have
by no means settled the point ; and many inventions which appear quite
successful when tested merely in deliberate experiments, where everything
is previously arranged to insure the most favourable conditions, completely
fail when applied in actual warfare. Many years ago Mr. Warner pro-
duced a great sensation by an invention which appears to have been essen-
tially 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 debris, 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.
11
Portrait of M. Lesseps.
THE SUEZ CANAL.
THE reader who wishes to understand the exact position of the great
engineering work called the Suez Canal must take down his atlas,
and look for the Eastern Hemisphere, when no difficulty will be experienced
in discovering the position of the vast continent of Africa, of which many
parts still remain unexplored. Africa is washed on the north by the Medi-
terranean Sea, on the west by the Atlantic, on the south by the Southern
Ocean, and by the Indian Ocean and Red Sea on the east and north-east.
The traveller who went to India in the famous sailing ships called East
Indiamen was obliged formerly to sail round the " cape of storms," the Cape
of Good Hope, and would pass from the Southern to the Indian Ocean.
If the waterway round Africa is now traced out, we come to the Red Sea,
and find that the only obstacle which would have prevented a ship making
the circuit of 15,000 miles is a narrow neck of land, called the Isthmus of
Suez.
It has been well said that had there been a strait like that of Gibraltar,
or that of Messina, at Suez, instead of a sandy isthmus, the achievements
of Bartholomew Diaz, Vasco da Gama, and Columbus might have lost
162
THE SUEZ CANAL. 163
much of their significance ; but the progress of the human race would have
been infinitely more rapid, and the advantages to the world's economy
would have been incalculable.
If the names of these hardy mariners would have come less prominently
forward, it is fair to suppose that we should not have heard of another
great man, viz., Monsieur Ferdinand Lesseps, whose portrait graces the
head of this chapter, and who has been the persevering and successful
pioneer and engineer to achieve the completion of the work. It would
appear that there are many claimants for the honour of having first sug-
gested the feasibility of the plan for cutting through the Isthmus of Suez.
According to some recent discoveries in the chief archives of Venice, it
was so 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, it was already at that period that a re-cutting of the Isthmus
of Suez was thought of. Plans were compiled 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
(probably bribed by foreign gold) which prevented the execution of the plan.
The ancient Egyptians did not cut through the entire isthmus, although
they formed therein certain canals, the remains of which are visible to this
day.
One of the early English poets, Christopher Marlowe, born in the reign
of King Edward VI., educated at Cambridge, and who appeared on the
stage in the reign of Elizabeth, and was unfortunately assassinated with
his own sword by a footman, appears to have anticipated M. de Lesseps, in
the following lines :
" 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."
But the idea of carrying out the project, it is stated by Lord Houghton,
was due to Pere Enfantin, of the St. Simonians, who, in the year 1833,
interested M. Ferdinand Lesseps, the French vice-consul, and Mehemet
Ali, the Pasha of Egypt, in taking practical measures towards its accom-
plishment.
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 Societe d* Etude du Canal de Suez was formed, and among the names
of those who then applied their attention to the subject was to be found
that of Robert Stephenson. But he instituted inquiries, the result of which
was wholly unfavourable to the enterprise. He recommended the con-
struction of a railway through Egypt, and a line was made between Alex-
andria 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. Lord
Houghton very properly said that M. Lesseps had not invented the Suez
Canal. In fact, who did invent anything ? An invention is the result oi
the information and the deductions of thousands of other men. M. Lesseps
undertaking was the complement of what had already been done by other
men ; but no less honour was due to him because it was so.
112
1 64 THE SUEZ CANAL.
It is right 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.
If a great English engineer 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 Said.
The canal is, however, an accomplished fact, and the magnitude of the
enterprise may be appreciated when it is remembered that fourteen years
have elapsed in carrying it out, and that in round numbers the Suez Canal
is 100 miles long, 100 yards wide, having a minimum depth of 26 ft. The
Suez Canal Company, it is said, has expended twelve millions of money in
what was considered to be chiefly shifting sands. 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.
No opposition, however influential, can now hinder the Suez Canal route
from being the sea highway between Europe and India. The iron ship
trade is at present yielding immense profits, and numbers of iron vessels are
still being built for this particular route. It does not require much com-
prehension to understand that the distance from London or Liverpool to
Bombay by the Suez Canal as compared with that by the Cape is some
5,000 less out of 10,000 miles, and that in due time the whole course of
trade between East and West will be changed by the piercing of the Isthmus
of Suez.
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 Said, 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 by the cognomen of 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.
Port Said is the little town at the northern or Mediterranean entrance of
the canal. It is chiefly built of wood, with straight wide streets and
houses, and although now containing a population of six thousand inhabi-
tants, it would have been difficult to have got together one hundred people
at that spot twenty years ago. It is said to have a very flourishing and
bright appearance, as seen from the canal, and, like all the other towns on
the Suez route, has a striking resemblance to the newly settled cities of
America, and being composed of very combustible materials, would be
burnt down in a very short space of time.
Port Said is provided with docks, basins, quays, and warehouses, and
THE SUEZ CANAL. 165
FIG. 1 22. Port Said, the Mediterranean entrance to the Suez Canal.
has a harbour stretching out a couple of miles or so into the sea, which is
enclosed by two piers, or rather breakwaters. One of the most serious
obstacles to the advancement of Port Said is the absence of fresh water,
which is supplied from the "fresh-water canal" at Ismailia, where two
engines of 25 -horse power are at work night and day pumping the water
through a distance of 40 miles. If the canal which carries the beautiful
Nile- water from Cairo to Ismailia was prolonged to Port Said, this diffi-
culty would no longer prevail, but it could only be carried out by a great
expenditure of time and money.
The harbour (Fig. 1 24)however, is now completed ; two converging break-
waters have been built out into the Mediterranean from the coast, where a
lighthouse is erected, the larger and more westerly one being one mile and a
half long, the shorter about a mile and a quarter, and the distance between
the two lighthouses erected on the extremities of the breakwater being
half a mile.
The piers are made of concrete and sand, cast into 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 now being completed 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 are not laid with the regularity of
ordinary masonry, but have been dropped from large barges, so that they
present a very rugged and uneven appearance. (Fig. 1 23.) Experienced naval
officers say that Port Sa'id is superior to Alexandria as a port, and 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 Suez Canal.
Along the western pier there is a constant settlement of sand from this
cause, which, they say, is partially washed through the interstices left be-
tween the blocks of artificial stone, and may in time give some trouble by
i66
THE SUEZ CANAL.
FIG. 123. One of tke Breakwaters at Port Said.
forming sand-banks in the harbour ; but it is quite possible to conceive that
this will be easily prevented by the introduction of smaller stones, which
could be readily inserted by workmen from boats, going out at the low tide.
FIG. 124. Bird's-eye View of Port Said.
" Rob Roy" describes Port Said as " a little town at the north entrance
of the canal. It is built of wood, with wide straight streets, and houses
that look like brown paper, and that would burn from end to end in ten
THE SUEZ CANAL.
167
FIG. i2$.-Map of the Suez Canal.
minutes. Hotels, cafe's, shops, and
bazaars are crowded by six thousand
people of every nation, but with the
Greek and Levantine element largely
preponderating."
At Port Said are seen vessels of con-
siderable tonnage waiting their turn to
enter the canal, which is indicated by
two obelisks (Fig. 122), being part of the
festive arrangements prepared for the
reception of Her Majesty the Empress
of the French. They consist of a frame-
work of wood, covered with painted
canvas, and will no doubt be some day
replaced by granite. Having now fairly
entered the canal, it is quite as well to
consult the map (Fig. 125), in order to
know the precise localities of the places
passed by the traveller in going from
Port Said to Suez and the Red Sea.
The arrow points in the direction of
the compass, and shows that the canal
runs very nearly from north to south.
Beginning with the Mediterranean Sea
and Port Sa'id, there is a run of 28 miles
through Lake Menzaleh to Kantara.
Although called a lake, it is in truth
nothing but a shallow lagoon or swamp,
and here it was found better to enclose
the canal with high embankments of
sand, in order to keep out the waters
of the lake, which were of no practical
service in the feeding of the canal, but
were very detrimental to its completion.
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
sand-banks 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 sur-
mounted, and such is the excellence
and stability of the work that the water
of the canal neither leaks out, nor does
any of the brackish water of the lagoon
infiltrate and undermine the great em-
bankments. A passenger on board a
steamer going through this part of the
168 THE SUEZ CANAL.
FIG. 126. A Group of Egyptian Fellahs ', and their Wives.
canal states that " the only curiosity worthy of notice is the constant appear-
ance of the curious effect of the ' mirage/ which brought up on the horizon
the illusory effect of trees and houses, that could not have 'existed in the
position where they were seen. The waters of the lake were covered with
wild ducks, and white pelicans stalked about in the marshy places."
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. There are two hotels here, which
condescend to supply the traveller at exorbitant prices.
From Kantara to El Fendane is a distance of 15 miles, that is to say,
to the southern extremity of Lake Ballah, where the canal still passes
through sand embankments raised within a mere. This lake is, however,
almost dried up, and therefore the difficulties which had to be surmounted
at Lake Menzaleh were not felt here.
According to the original programme, the canal was to have been con-
structed by forced labour, supplied by the Viceroy. The unhappy peasantry
of the country, called "fellahs" (Fig. 126) were to be induced, by a liberal
supply of stick, to give their labour for a miserable pittance of rice.
No doubt, in ancient times, the corve, or forced labour, was in use, when
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 water, which was only to
be of use to foreigners who passed through their country, could not be
expected of frail human beings, and thus the cruelties of the work fre-
quently equalled the horrors of other slave countries. 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
THE SUEZ CANAL. 169
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
every one thought that this would be the death-blow to the completion of
the canal ; but M. Lesseps did not give way to despair, and has since
stated that if he had depended only on the labour of the fellahs, the
gigantic difficulties of the work never could have been surmounted, and,
in fact, that he owed the success of his canal to his not having had labourers
of that sort, because he had turned his attention to the mechanical con-
trivances used for dredging on the Thames and Clyde, and the result was
that the work had been done in half the time and at half the expense that
would have been necessary if the dredging had been done by the manual
labour of the poor fellahs.
Mr. Fowler, the eminent engineer, has stated that the dredges used in
the construction of the canal were of a new description. They were won-
derful 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 6 ft. to
12 ft. 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. These dredges are of two kinds. The great " couloirs " * consist
of a long, broad, flat-bottomed barge, on which there stands a huge frame-
work of wood, supporting an endless chain of heavy iron buckets. The
chain is turned by steam, and the height of the axle is shifted from time
to time, so that the empty buckets, as they revolve round and round, shall
always strike the bottom of the canal at a fixed angle. As they are dragged
over the soil they scoop up a quantity of mud and sand and water; and
as each bucket reaches its highest point in the round, it discharges its
contents into a long open iron pipe, which runs out at right angles to the
oarge. The further extremity of this pipe stretches for some yards beyond
the bank of the canal ; and, therefore, when the dredging is going on there
is 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 has reached the required depth, the dredge is
moved to another place, and the same process is repeated over and over
again. These stationary dredges, however, though very effective, require
much time in moving, and the lighter work of the canal has been chiefly
effected by movable dredges of a smaller size. These machines are of the
same construction as those described ; the only difference is, that the mud
raised by their agency is not poured directly on shore by pipes attached
to the dredges, but is emptied in the first instance into large barges, divided
into partitions, and moored alongside the dredge. Each partition contains
a railway truck, and when the barge is filled it steers away to the bank,
where an elevator is fixed. The trucks filled with mud are raised by a
crane worked by steam power, and placed upon inclined rails, attached to
the elevator, which slope upwards at an angle of 45 towards the bank.
They are then drawn up the rails by an endless rope, and as each truck
' " Couloir " signifies a long open pipe, in allusion to the pipe attached to the dredging machine.
i7o THE SUEZ CANAL.
FIG. 127 '.Dredges and Elevators at Work.
reaches the end of the rails, its side falls open, the mud is shot out upon
the bank, and the empty truck returns by another set of rails to the plat-
form on which the elevator is placed, and is thence lowered into the barge
to which it belongs. As the elevator can unload and re-load a barge much
faster than the dredges can fill it with mud, each elevator is fed by half a
dozen dredges, and thus the mud raised from the canal by several dredges
is carted away without difficulty at one and the same time. As these
floating dredges are much easier to shift than those encumbered by the long
couloir pipes, the work of excavating the bed goes on much more rapidly.
But in places where there is any great mass of earth or sand to be removed,
the large couloirs can scoop out a given volume in a shorter time.
The chief contractor, M. Lavalle, calculated that the expense of keeping
the canal clear from silting up might be estimated at about ,40,000 per
annum ; but it does not appear that this is the case, and happily so, from
the following authentic statement in the "Times," made I7th June, 1871,
by Sir David A.' Lange, English director of the Suez Canal Company:
" The following are the measures adopted for maintaining the Suez Canal
at its present minimum depth of 26 English feet of water.
" Two dredgers will be assigned for dredging the channel of the outer
harbour at Port Said, and removing any silt which may have accumulated
during last year.
" Two other dredgers are to be employed in excavating the new circular
basin to be formed on the Asiatic shore of the canal, and to continue
dredging operations in the Cherif basin.
*' A fifth dredger is destined to maintain the canal along the entire line
of section terminating at kilometre 60*500.
" The second section, commencing at kilometre 60-500, will only have
two dredgers at work one for widening the bend north of El-Guisr, and
the other to complete the siding at the Bitter Lakes.
"All along the Suez section a single dredger has been deemed sufficient
to maintain the canal."
The marvellous nature of the operations required to push on the canal
to completion appears to have struck many independent observers, and
amongst them none are more entertaining than " Rob Roy," who says :
" The sensation of wonder at the prodigious scale of the operations in
THE SUEZ CANAL.
171
progress increases day by day as one moves along what seems to be a wide
river, with villages on the banks, and smoky funnels and white sails on the
surface. The hydraulic machines, which groan and snort and rattle their
chains as they work, are of enormous size; and though each of them
seems to be pouring forth a volume of mud, yet the mind finds it hard to
believe that all of these together can lift up and throw over the banks
enough to make any appreciable progress between yesterday and to-day.
The sand dredged from below is either carried out to sea in barges, or
(farther inland) is delivered in a stream from a lofty iron tube, 220 ft. long,
with its mouth over one bank, or it is hoisted up an iron inclined plane and
cast upon the shore, until the heap on each side of the water is 50 ft. high.
The engines for this purpose are forty in number, and each of them cost
^40,000. The expenses at present amount to ^200 coo every month, and
the work has already absorbed eight millions sterling.**
From El Fendane, at the end of Lake Ballah, to Lake Timsah, a distance
of about five miles, the canal was dug out by the " fellahs ; " nearly 60,000
men were engaged upon it, organized in separate great gangs, 35,000 work-
ing by day and 25,000 by night. A tramway was laid down, and the sand
was taken in ballust-trucks and shot into the desert.
The traveller is now 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 Ismaiiia, which is, in fact, the " half-way house,"
where most of the officials of the Suez Canal Company reside, as they can
get to either end of the canal with greater facility, or to Cairo, by the rail-
road, which comes to this point and continues with the canal to Suez.
Before the station and railroad were constructed the desert was perfectly
solitary, varied only by the tents of half-naked and ragged Arabs ; now it
is a scene of bustle and prosperity. The Viceroy of Egypt is building a
stone palace ; here and there are a few villas and an hotel. The chief
reason why Ismaiiia is likely to become a flourishing place is because the
172
THE SUEZ CANAL.
FIG. 129. Lake 'limsah and Ismailia.
settlement is well supplied with water, which has been brought from Cairo
by canal, and called very properly " The Sweet-Water Canal." " Rob Roy "
speaks most enthusiastically of it.
" The Sweet- Water Canal is already a blessing to Egypt. It is from 30
to 40 ft. wide, and boats with all sorts of cargoes are towed through it by
men on foot, or sail along gaily if there is a breeze to fill their snowy wings.
My canoe excited the greatest delight among all this river population, both
when she skimmed over the water with her blue sails, or rested by the bank
with her cabin rigged up, and my dinner cooked, and my little reading lamp
and mosquito curtains arranged for the night. I managed to sleep thus in
the canoe very comfortably, though the nights were cold ; and on Lake
Timsah a jackal paid me a visit at a very unfashionable hour by moonlight.
During one day a violent gale swept across the canal. To look at the
desert was to see a vast yellow picture of men and camels dimly floating
in a sea of sand without any horizon. The quantity of sand whisked from
the plain, and cast into the canal-water by a wind like this, will be a serious
matter to deal with. An ounce of sand per square yard amounts to 500
tons on the whole canal, and the wind sometimes blows in this way for a
month together."
The palace of the Viceroy is situated on the Fresh-Water Canal, and M.
Lesseps has built a pretty villa at this spot, and within eight days of the
opening of the canal, took to himself, in the little church of Ismailia, a
young and handsome wife.
Travellers speak highly of the beautiful gardens on the banks of this
canal, and indeed vegetation has sprung up on all sides ; orange trees and
acacias, tall enough to shelter you from the noontide sun, are to be found
in the garden of M. Lesseps. Lake Timsah is the head-quarters of the
land works, and, in fact, the depot of the company, where vessels going
up or down the Suez Canal may cross each other safely. The course is
marked out with buoys. It commences at the north-east corner, and after
sweeping round in a wide curve, passes out at the south-east.
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 that a
THE SUEZ CANAL. 173
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 ft. in length, and lying 12 ft. only below the surface, and right in
the middle of the main channel. If anything could show the indomitable
energy of M. Lesseps, it would be his courage in dealing with this diffi-
culty, and at a time when a few months only could elapse before the adver-
tised 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 Serapeum, which is an interesting spot, where the remains
of the ancient canal of the Pharaohs exist, in reference to which Lord
Houghton observes :
" Looking at the vast works that had been executed in Egypt ages ago,
he could not but think that if the canal had been regarded as a necessary
undertaking in former days, it would have been accomplished in those days.
He believed that inventions were carried out when they were wanted, and
that consequently the Suez Canal was the result of a want of our own
time.
" When he looked at the works of irrigation that had been constructed
in Egypt from the days of the Pharaohs to the days of the Ptolemies, he
felt convinced that if the canal had been wanted it would have been made
before the nineteenth century. The truth was no one had wanted it. In
former times, the Egyptians would have regarded the intersection cf the
isthmus by a canal as a contrivance which would lead to the unnecessary
intrusion of foreigners, and to the destruction of the nationality of Egypt,.
In the times to which he referred, the Egyptians were anxious for free
communication between the Nile and the Red Sea, but not for free com-
munication between the Red Sea and the Mediterranean?
Passing by Se'rapeum, 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. Here it was that theory pro-
claimed and bitterly contested the impossibility of keeping such an enor-
mous area filled with sea-water. The opponents of the canal said it 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 6 to
7 miles wide. The only difficulty in filling this enormous natural basin
arose from the rapidity and force with which the waters flowed in, which
carried away certain great barriers, erected to prevent accident. This was
done when the water at Suez was at the low tide, and then subsequently
the Red Sea was allowed to flow in.
The last embankment which separated the two oceans was cut through
by the Viceroy in person, and at last the two seas were united.
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
waters meet. The tide runs up the canal with great force, and there is a
difference of 6 or 7 ft. 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
174
THE SUEZ CANAL.
FIG. iy>.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.
been filled the mean temperature of the districts on the banks has fallen
5 Centigrade. It is also stated that, although the canal literally 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 has not been 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 keep exactly within them. On quitting the Bitter
Lakes the canal proper is again entered, and the work is reported to be
very complete for ten miles from this point, passing Chalouf, where " Rob
Roy " makes the following note :
" At Chalouf I found 14,000 men at work. They labour very hard indeed,
running up the hill with baskets of sand on their heads. About 1,000
donkeys walk in long lines with neat mat baskets on their backs. In curious
and close contrast to these simple carriers the mighty power of steam toils
and puffs as it hurls up huge bulks of heavy clay ; and it is, perhaps, only
in Egypt one could see human and animal power exerted in such competi-
tion with steam power. The labourers are sent from all parts of Egypt.
They must come, but they are highly paid from 2 francs to 3 francs a day.
Prices both of labour and of food have risen very much since the canal
has been begun, but the supply of fish has rapidly increased."
In order to reach the vast docks which the Suez Canal Company has
erected 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 for a distance of
THE SUEZ CANAL. 175
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.
At the opening of the canal M. Lesseps showed his cleverness and
courage by permitting a flotilla of fifty vessels to pass through, and on the
2 ist November, 1869, the following statement was made by the " Official
Journal" of Paris, announcing the arrival of the Empress at Suez :
" 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 under-
taking the joining of 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
obstacles, 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 iQth November, appoint-
ing 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 report of Captain Richards, Hydrographer to the Admiralty, con-
taining information from Captain S. S. Nares, of H.M. surveying vessel
Newport, is so very comprehensive and important, as further elucidating
the important question of the pilotage and future prospects of the canal,
that it is given here in extenso.
" The coast in the neighbourhood of Port Sa'id is unusually low, being
out of sight at three miles distance. The lighthouse, town, and shipping
are the only objects seen from the offing. At present there are two tall
obelisks, one on each side of the canal entrances, but as they are merely
built of boarding they can only be temporary. At six miles to the west
the coast is marked by a Gemileti tower, a low square building, standing
by itself on a low sandy coast ; but to the eastward of the port there is
nothing to mark the low shore. The current off the coast is very uncertain.
It generally runs with the wind, from to \\ knots an hour. The general
set is to the eastward. Owing to the current and low shore, more than usual
caution is necessary in approaching the harbour. The harbour is formed
by two concrete breakwaters running off from the sandy shore. Inside the
piers the harbour is at present constantly silting up, in consequence of the
current, heavily laden with sand, running through numerous openings in
the piers, and depositing the sand in the quieter water inside. A good
straight channel of 26 ft. of water has been dredged, leading into the inner
basins, about 100 yards inside, and parallel to the west pier. It is marked
by black buoys on the east side, and red ones on the west side ; and it may
be presumed that the authorities will be careful to keep it clear. The basins
inside the harbour have a depth of 26 ft. water : they are sufficiently large
for the trade which may be expected ; if not, there is ample space for en-
larging them. On the outer end of each breakwater there is a low light
red on the west pier, and green on the east one. The Port Sa'id lighthouse
is a tall white stone tower, 180 ft. high, standing close to the inshore end
of the west breakwater. It shows a flashing white lime-light, visible
18 miles. The pilot-boats carry a Blue Peter flag. The best anchorage
in 6 fathoms is with the low red light on with the high lighthouse ; or
J7 6 THE SUEZ CANAL.
the west pier-head a little open of the lighthouse on either side. The
bottom is mud and very good holding ground. A bank with 12 ft. water
has been formed to the eastward of the harbour. The east pier-head light
(green) on with the high lighthouse leads over the west edge of the bank ;
therefore, these marks must be kept well open. In approaching, allowance
must be made for a bank which is forming outside the west pier end. In
November, 1869, there was 6 fathoms at half a mile from the pier end,
with the anchorage marks in one. The entrance to the canal is conveniently
situated at the inner end of the basins. The usual depth of water is from
26 to 29 ft. ; immediately south of the Campement de Cap is a short bank
of 24 ft. ; and a mile north of Kantara, opposite the 43rd kilometre mark,
is a bank of 23 ft. The whole of this distance, 24^ miles, with the excep-
tion of one-sixth of a mile at the Campement, which is higher, the canal
runs through a wet, flat sandy plain scarcely higher than the level of the
water on the east side, and a little below it on the west side, which, with a
'high Nile' is completely overflooded, and the sand rendered firm by the
deposit of mud from the river. In this part of the canal there is no sand-
drift, and it may be considered as completed. The debris thrown upon
the banks is firm, black, sandy mud, protecting the canal from the water
in Lake Menzaleh, without any opening in the whole distance. The canal
passes through sand-hills from 20 to 30 ft. high, and has a depth of from
26 to 28 ft. This part of the canal is completed, but it is subject to a very
severe sand-drift in high winds. The canal here passes through a lagoon,
with a depth varying from 19 to 24 ft. ; but the dredges are still at work.
There is constant trouble in this part of the canal, in consequence of the
banks on each side, which are composed of fine sand- debris, not being firm
enough to resist the constant ebb and flow of the water between the lake
and the canal, which, carrying large quantities of sand with it, is constantly
altering the depth of water. In this cutting the sand-hills are about 40 ft.
high. The depth in the canal varies from 22 to 24 ft. ; but there is work
still going on in the shallow parts. All this part is subject to heavy sand-
drift.
" For about four miles in the neighbourhood of El Guisr the canal is cut
through a stratum of soft lime or sandstone. The sharp turns between El
Guisr and Lake Timsah are probably owing to the engineers having fol-
lowed the softest part of the rock. Ships can pass round the curves without
trouble. The central station in the canal is well situated for a stopping-
place. There is at present only 22 ft. in the middle of the lake ; but the
dredges will soon give deeper water. The depth varies from 22 ft. to
27 ft., except one bank of 20 ft., in the lagoon. The debris banks here,
of pure sand, like those in Lake Ballah, are not adhesive enough to form
a barrier between the canal and the lagoons, to keep the silt from run-
ning into the channel, but the canal is sufficiently wide to allow dredges
to work without stopping the traffic. In this cutting the canal is carried
through a stratum of sandstone, with depths from 22 ft. to 24 ft., except in
one place a mile south of Serapeum, where for about 30 yards there is a
narrow ridge, with only 18 ft. water over hard rock. A strong party of
men are at work, and the obstruction will soon be reduced. At the south
end of the cutting the deep channel is narrow and incomplete. This cut-
ting is subject to a very heavy sand-drift. From the debris on the bank it
would appear that the narrow ridge of stone running across the canal had
only lately been discovered. The margin of the deep water in the lake i \
miles from the entrance is marked on the east side by a red iron pillar
THE SUEZ CANAL. 177
lighthouse, 40 ft. high, showing a fixed white light, visible 10 or 12 miles.
The excavated channel leading into the deep water has a depth of from
24 ft. to 29 ft. It is conspicuously marked on each side by iron beacons^
15 ft. high, with a black ball 3 ft. in diameter on the top. As we passed, each
beacon was lighted; but whether the lamps are to remain could not be
ascertained. The margin of the deep water at the south end of the lake is,
conspicuously marked on the east side by a lighthouse similar to the north
one, and by a buoy on the west side. A straight run may be made between
the lighthouses (a distance of 8 miles) with not less than 22 ft. depth of
water ; 26 ft. may be obtained by passing nearer to the west shore of the
lake. The water in this part of the lake being shallower, a cutting has
been made, giving from 26 ft. to 27 ft. depth. The channel is well marked
by numerous iron beacons on each side (from four to six to a mile) similar
to those at the north end of the lake. This part is quite complete, with
hard banks and depths of water from 26 ft. to 30 ft. at low water. It is
subject to sand-drifts. At Chalouf the cutting is carried through sand-
stone; the debris is hard and lumpy. South of latitude 30 6' N. the canal
passes through sand-hills, it increases in width, and the debris on the bank
is more than usually large. At Madama the banks are of firm marl or
soft clay. This part of the canal is incomplete : the debris banks are sand.
The soundings were irregular, the depth varying from 21 ft. to 26 ft. at low
water. A large number of men are still at work here. At the entrance a
good stone wall is built on the west bank, but it requires to be raised and
extended. Another is much wanted on the east side, where the curve
already shows the usual signs of scouring out on the outer, and depositing
on the inner side. The south end of the canal may be said to extend if
miles beyond the two red lights, passing the Suez creek and the new dock
and harbour works, into the Gulf of Suez, with not less than 27 ft. at low
water. With a flood tide a great quantity of silt pours into the canal from
the sand-bank on the east side of the entrance ; but doubtless means will
be taken to prevent it. A breakwater has already been carried across the
sea-face of the bank. The mouth of the canal is marked by a red light on
the west side at the extreme end of the new harbour works, and by a green
light on the opposite side on the nearest end of the breakwater. Both lights
are at present only hoisted on temporary poles. Outside these marks the
channel is further shown by a line of buoys, white on the east side and red
on the west side. The dry dock is 430 ft. long, 83 ft. broad, and can dock
a ship drawing 23 ft. when the channel outside is completed.
" The current depends on any variation in the height of water in the
Mediterranean. The banks show that the canal here is subject to a rise
and fall of one foot, the current and height lessening as the distance from
the entrance increases. There is no tide or current in Lake Timsah or
the upper Bitter Lake. The tidal influence extends from Suez to four miles
north of the southern end of the Bitter Lakes. The stream commences to
flow from two or three hours after low water at Suez. A spring tide rises 6 ft.
at Suez, 2 ft. at Madama, i ft. at Chalouf, and \ ft. at the south entrance
of the Bitter Lakes. At Kabiet there is no rise and fall. The immense
reservoir of water in the Bitter Lakes with an ebb tide, and in the Gulf of
Suez with the flood, will prevent the tide ever having a greater range. With
a strong southerly wind in the Gulf of Suez the water rises to from 8 ft. to
9 ft. at the head of the Gulf, and may affect the water in the canal to some
small extent. From two to three hours before high water at Suez the flood
spring tide was running i\ knots at Chalouf, increasing to 2 or 2\ knots at
178 THE SUEZ CANAL.
Madama, with the water very much discoloured. By starting from Suez an
hour before low water a vessel will arrive in the Bitter Lake before the flood
tide overtakes her, and having nearly slack water all the way. Every five or
six miles a short widening in the canal (a gare) gives room for a vessel to haul
in and allow another to pass her with ease. Vessels can pass each other
at any part by using warps ; but they cannot do so without stopping, except
at a great risk of running on shore, and delaying the whole traffic of the
canal. A single ship could pass through in from fourteen to sixteen hours ;
and two small ships, entering one at each end, could pass each other with-
out slackening speed. But it is impossible to carry a train of large ships
through in one day. Lake Timsah and the town of Ismailia are conveniently
situated and sufficiently large for a stopping-place ; and, doubtless, arrange-
ments will be made for ships to start from each end on one day, for all to
meet and anchor for the night at Lake Timsah, and to start for their re-
spective ends the following morning. This, allowing eight hours for passing
through each end of the canal, and twelve hours for remaining at Ismailia,
will give twenty-eight hours for the transit. With a full moon, a handy
ship, by entering the canal in the evening and arriving at Ismailia in the
morning early enough to join the train of vessels, might perform the voyage
in from sixteen to twenty hours. With a train of only two or three ships,
and no delay at nights, the transit would occupy about eighteen hours.
There is no doubt that every vessel will cause more or less damage to the
banks on passing, but screw ships only going five or six knots will hurt the
canal very slightly, except in the lagoons, where the banks are formed of
very fine sand. The Pera, a large paddle-wheel steamer, on passing with
great speed (8 knots), and displacing the water in the whole breadth of the
canal, did considerable damage, the wave she made swamping several boats.
Large vessels should be made to reduce speed more than small ones.
Should a vessel touch the ground in any part of the canal, except in the
tidal part at the Suez end, she will sustain no damage, merely being thrown
out of her turn in the line. A good coating of sand has formed at the bottom
of the canal in the sandstone cuttings. In the tidal part near Suez, if a vessel
is passing through with a following tide, and the bow touches either bank,
there will be great danger of her swinging across the canal, with a two-
knot current running against her broadside. With a wind blowing across
the canal, vessels touching the lee side will be blown at once against the
bank, but without any damage. The present pilots will rapidly gain expe-
rience ; with trained leadsmen and a lead going on each side of the ship,
there is no difficulty whatever in navigating the canal and keeping in mid
channel."
SAND.
HTHE foregoing account of the Suez Canal is by Mr. J. H. Pepper, being,
- in fact, the substance of a lecture delivered nightly by him at the
Polytechnic Institution, in Regent Street, at the time when the canal was
the latest novelty of the day. The lecture was illustrated by some experi-
ments, designed to exhibit certain properties of sand which had reference
to the construction of the canal ; and though the properties in question are
by no means to be classed among recent discoveries, yet the experiments
were novel in form, and well calculated to interest a popular audience.
The want of cohesion among the sand-particles, which is the cause of the
lateral pressure, although it is also the great feature of liquids, is far from
conferring upon sand all the characteristic properties of liquids. 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, with which material the experiments described in the following pages
could not possibly be performed. The behaviour of sand, which became
a matter of interest to the public in connection with the Suez Canal, was,
however, popularly confounded with that of peat-bog and similar materials;
but it need not be said that all the apprehensions as to the safety of the
canal have proved unfounded.
The following account of the experiments shown at Mr. Pepper's lecture
is given in his own words.
The first experiment may be made by filling a large corked funnel (sup-
ported by a proper stand) with dry sand ; and attention must be paid to this
point, viz., dryness, as the property of cohesion is conferred on the separate
particles of sand if they are at all wet, or even damp ; and thus fine white
sand, from which all salt has been carefully washed, is the best kind to use
in these experiments ; and if any salt remains, the sand becomes humid
in damp weather, and the particles will not roll properly one upon the
other, but stick or cling together. The corked funnel containing the sand
being arranged and standing on a tray, the oxy-hydrogen light is thrown
on and the cork removed. The sand flows out with great regularity, and
forms a heap below, which takes the form of a cone, having a certain angle,
which may be determined by a quadrant, and is found to be 30. By the
sea-side, in the summer months, the sand is frequently very dry, and by
burying a child's hoop half-way in the sand, and then allowing some loose
sand to fall, a cone is obtained, and if the half of the hoop has been roughly
graduated, the angle at which the particles of sand will remain in a posi-
179 122
i8o
SAND.
FIG. 131. Apparatus for showing Sand Experiments.
A, funnel from which the sand is flowing ; B, scale and wedge to show angle at which sand
rolls ; c, model of section of cylinder, with chalk-marks to show direction of the pressure ;
r>, E, F, tin vessels with tubes ; G, press to contain eggs and sand ; H, tube and piston ; i, j,
K, K, American pails, containing sand for the experiments, and prepared with tissue-paper ;
L, framework and sides of tissue-paper to represent a pail ; N, oxy-hydrogen light to show
experiments.
tion of stability is readily determined. It follows, therefore, from this cir-
cumstance that the pressure of sand is not perpendicular, but lateral, and
it is well shown by taking a wooden section of a tube, having a sliding
piece of wood, the sides of which have been cut to an angle of 30. The
piece of wood is first brought to the lower part of the model, and the out-
line marked with a piece of chalk. It may then be moved higher up and
chalked again, and by repeating this three or four times, certain lines are
marked on the model, which are intended to show that, after allowing for
the weight of the cone of sand having its sides sloping at an angle oi 30,
and which covers the bottom of the tube, the remainder heaped upon the
first cone does not press upon the bottom, but almost entirely on the sides
of the containing vessel (Fig. 132).
The chalk-marks will remind the spectator of the chevrons, or good-
conduct badges, on the arms of soldiers. The direction of the pressure is
shown by putting some sand in a strong cylindrical iron vessel, and packing
therein some eggs (Fig. 133), the whole being well bedded and covered with
sand. On the upper part a thick piece of wood is now laid, and the operator
may take a 14 Ib. weight and bring it down with force upon the piece of
wood, and if the table upon which the arrangement is standing is strong
enough, several smart blows may be given with a sledge-hammer. This
being done, the 14 Ib. weight and the piece of wood are removed, and the
sand poured out into the tray, when the eggs will be found to be intact ;
and thus it is shown that when certain animals deposit their eggs in the
sand, they cannot be broken by any human being walking on the surface,
SAND.
181
and not even if the bulky hippopotamus should chance to be taking a pro-
menade and tread over the exact spot where the eggs are deposited.
FlG. 132. The Model marked with
Chalk in several places, like Che-
vrons.
FIG. 133. Iron Cylinder, Sand, and Eggs.
The principle of lateral pressure may now be strikingly illustrated by
taking an American wooden pail, and having previously cut a large circular
hole in the bottom, this is now covered with fine tissue-paper, which should
be carefully pasted on, to prevent the particles of sand flowing through the
small openings between the paper and the wood.
The pail with its paper bottom may be held before the oxy-hydrogen
light, to show the thinness of the tissue-paper, and being placed upright
and rapidly filled with sand, it may be carried about by the handle without
the slightest fear of the weight of the sand breaking through the thin
medium.
On ejecting the sand from the pail, it may be held as before in front of
the light, and if the hand is thrust through the tissue-paper, more evidence
is given of the peculiar manner in which sand presses, and that the wooden
sides of the pail receive the chief pressure, and not the bottom.
With large tin cylindrical cans, into which tubes of at least an inch in
diameter are inserted in various positions, other and very interesting expe-
riments may be performed. If the vessel is furnished with a tube standing
out at right angles, as shown at E, Fig. 134, and then filled with sand, on
removing the cork from the end of the tube, no sand will flow out, because
it forms a cone, one side of which crosses the tube at an angle of 30, and
effectually stops any further movement of the sand. The same result is
obtained by inserting a tube into the containing vessel, like the spout, or
rather in the same direction as the spout, of a tea-pot (D, Fig. 134). It
182
SAND.
matters not how high the sand may be piled above the level of the top of
the spout, it cannot flow out ; whereas, if it was filled with water, of course
:;hat fluid would flow out until it had found its level.
FlG. 1 34. The three Cylindrical Vessels and Tubes.
The third arrangement (F,Fig. 134) in which the tube is inserted at triQ
proper angle of 30, is the only one out of which the sand will move, and
even here it may be noted that the particles of sand require time for their
movement, as there is, first, the inertia of the particles to be overcome,
and, secondly, the friction is great. The sand flows out of vessel r(Fig. 134)
FlG. 135. Framework and sides of FlG. 136. Tube (one end closed -with
Tissue-paper to represent a Pail. Tissue-paper), Sand, and Sledge-
hammer.
and a very instructive result is obtained, because it stops when the sand
forms a cone inside the vessel, the sides of which correspond with the tube ;
and in flowing out on a sheet of paper it forms a cone of the same angle.
Probably one of the most convincing experiments is that which may be
performed with a cylindrical tube (Fig. 135)1 8 in. long and 2 in. wide, open at
SAND.
183
FIG. 137. The Hour-Glass on the Screen at the Polytechnic.
both ends. A piece of tissue paper is carefully pasted on one end, so that
when dried no cracks or interstices are left ; the tube is filled with dry sand to
a height say of 12 in. ; in the upper part is inserted a solid plug of wood 12
in. long, and of the same or very nearly the same diameter as the inside of
the tube, so that it will move freely up and down like the piston of an air-
pump. The tube, sand, and piston, being arranged as described, may now
be held by an assistant, and the demonstrator, taking a sledge-hammer,
may proceed to strike steadily on the end of the piston, and although the
paper will bulge out a little, the force of the blow will not break it. If the
assistant holding the tube allows it to jerk or rebound after each blow of the
hammer, the paper may break, because air and sand are driven down by
the succeeding blow, and therefore it must be held steadily, so that the
piston beds fairly on the sand each time.
A still more conclusive and striking experiment (Fig. 136) may be shown
with a framework of metal constructed to represent a pail, the sides of which
are closed up by pasting sheets of tissue-paper inside and over the lower
part. As before demonstrated, when a quantity of sand is poured into
the pail, the tissue-paper casing the bottom does not break, but if a suffi-
cient quantity is used, the sides formed of tissue-paper bulge out, and
usually give way, in consequence of the lateral pressure exerted by the
particles of sand exerted in the direction shown by the chalk-marks in
the model of the section of the cylinder, shown at Fig. 132.
One of the symbols of time is the hour-glass, a simple contrivance con-
sisting of a glass vessel contracted in the centre so as to leave a narrow
tube in communication with both sides. Fine dry sand is placed into one
1 84 SAND.
side, and the quantity is adjusted, so that it will run for a few minutes or
for the period of one hour.
By fitting a flattened hour-glass into a slide which was placed in a
powerful lantern, with achromatic lenses, and lighted with the oxy-hydrogen
light, a large picture of the " hour-glass " was projected on to the screen
at the Polytechnic. It was the more amusing because, the object being
inverted, the sand appeared to flow upwards instead of downwards, and
whilst flowing, it was noticed that as each particle of sand struck a tiny
blow on the top of the fallen cone of sand, the force passed down from the
top of the cone to the bottom in a wave-like figure, by the communicating
particles of sand, the angle being also well defined. The experiment was
satisfactory, as explaining the principle of the hour-glass, and why the sand
flows always at the same rate (see Fig. 137).
It is thus clearly shown that as sand rolls down, it will always maintain
a conical surface, whose inclination at the base is about 30, consequently,
if the banks of the Suez Canal are formed of dry sand, this angle, as
already demonstrated, must not be exceeded, as any attempt to construct
them at sharper angles must be labour in vain, because the sand would
roll off and fill up the hollow or cutting between.
THE SAND-BLAST.
THE properties of sand, which have been so fully illustrated by these
experiments of Mr. Pepper's, are perhaps not more interesting than
a recent application of sand to industrial purposes, almost entitling it to be
called a new mechanical agent. Persons who. have dwelt near the sea-
shore have often remarked how soon, by exposure to winds which drift the
sand, the glass of windows loses its polish. Engineers have noticed that
solid particles carried over mechanically with the steam from the boiler
of an engine soon erode the pipes, especially at places where there is a
deflection. Many instances might be given where a stream of small
rapidly-moving particles produces such effects that their wearing power has
to be taken into account and guarded against. It is remarkable that such
effects have been so long observed, and that no attempt appears to have
been made to turn this cutting power of moving particles to good account,
until a paper, communicated to the Franklin Institute, announced that Mr.
Tilghman had found that sand, impelled by a jet of steam escaping under
high pressure, constituted a very efficient means of grinding the surface of
glass, an operation often required for ornamental purposes. Mr. Tilghman
at first made use of high-pressure steam, into the midst of a current of
which he introduced a stream of sand. He found, however, that a very
high velocity was not necessary in order to obtain useful results. For re-
moving the polish from glass, a blast of air, giving a pressure equal only to
four inches of water, sufficed to impart enough impetus to the sand particles.
He then adopted an ordinary rotatory fan, making about fifteen hundred
revolutions per minute, and sending the current of air downwards through
an upright tube, 5 ft. in height, at the top of which the sand is supplied,
which, falling into the current of air, acquires additional velocity, and
is thus impelled against the plates of glass, which were slowly moved
SAND. 185
across the end of the tube at a little distance from it. The tube was of
a narrow oblong section, 2 ft. by I in., and sheets of glass moved slowly
forward at the rate of about five inches per minute were completely ground
by the sand-blast of i in. across, as ten or fifteen seconds' time was
found enough to enable the sand completely to depolish common glass.
Arrangements were made for an automatic replacement of the spent sand
at the top of the tube, and the dust produced was carried off by the air-
blast and re-conveyed into the fan, again to mix with the shower of sand
upon the glass. Glass ground in this manner shows under the microscope
a number of little indentations or cavities, produced by the impact of the
particles of sand, and the surface is much more uniform in its texture than
any that could be formed by rubbing. By covering portions of the surface
of the glass with paint, or by protecting it in part with lace, paper, collo-
dion, or other material preventing the access of the sand, patterns of any
kind may be very quickly engraved. Beautiful effects are produced in the
ordinary processes of glass-cutting by operating upon colourless glass,
which has been covered " flashed," as it is called by a thin layer of co-
loured glass. On removing the coloured layer to a greater or less depth,
varied tints or clear-cut patterns may be obtained. The sand-blast may
be employed to produce such effects in great perfection, by protecting the
portion in which it is desired to retain the colour by some tough or elastic
substance applied to the glass. The flashing of ordinary coloured glass is
cut through by the sand-blast in from four to twenty minutes.
If a current of air of less velocity be used (for example, one equivalent
in pressure to about an inch of water), it is found possible to depolish glass
with the sand long before a fern-leaf, or other delicate material, will be
pierced, and thus patterns having the outlines of leaves, &c., are readily
and directly transferred to the glass. By continuing the blast, the softer
parts of leaves may be cut through, while the glass is still protected by the
thicker veins and stems, and thus something more than a mere outline can
be obtained directly from natural leaves. A piece of common window-
glass, covered by a piece of wire gauze, exposed to the sand-blast, was com-
pletely cut through in the meshes of the gauze, thus producing from a solid
piece of glass a glass sieve, with meshes ^ in. wide, separated by portions
of glass only ^ in. thick. A photograph taken, on glass covered with a film
of gelatine and bichromate of potash, may be subjected to the sand-blast,
so that the parts not protected by the gelatine are acted on by the sand.
Beautifully engraved pictures produced by this elegant process were exhi-
bited by Mr. Tilghman, at a meeting of the Photographic Society of Phila-
delphia, in 1871. The process of engraving these occupied only from three
to ten minutes. The most delicate results were obtained by using finely
sifted sand and a blast of about one inch pressure of water, with a longer
time of exposure. That a material so hard as glass should be ground away
in the manner described, while a substance so delicate as a piece of lace
or a film of gelatine appears to resist the action, is explicable on the sup-
position that the soft materials yield to the impact of the grains of sand,
which may become for a moment half embedded on the surface, and then
be thrown off, while in the case of the glass the sharp angles of the sand
particles cut out a minute portion of the more unyielding body.
An instructive result was obtained in a series of experiments to elucidate
these singular facts. It was found that by imparting sufficient velocity to
even comparatively soft bodies, they may be made to wear the surfaces of
substances much harder than themselves. Thus a stream of fine leaden
i86
SAND.
shot, carried in a current of steam escaping from a pressure of 50 Ibs. to trie
square inch, worked out a cavity in a piece of hard quartz, and the shot
were found on examination to be but very slightly flattened by the blow.
Sharp hard sand has been made to cut a hole i^ in. diameter and i^ in.
deep through a piece of corundum, a substance much harder than sand
itself. This was accomplished by employing a steam-jet of very high pres-
sure, namely, 300 Ibs. to the square inch. But 100 Ibs. of steam sufficed to
urge the sand with a velocity that enabled it to perforate a file \ in. thick in
ten minutes. In using steam in this way, the sand is introduced in the
centre of the jet of steam, through a tube about in. in diameter. The
steam escapes from a larger pipe completely surrounding the sand-pipe,
and projecting 6 in. beyond its orifice. Thus the escaping steam, acting as
a piston, tends to produce a vacuum behind it, into which the rush of air
draws down the sand-particles from above, and they are impelled upon
the material to be operated upon, which is placed about one inch from the
end of the tube.
This invention is also applied to cutting stones, and for this purpose the
steam-jet is always used as the propelling agent. It has been found that
steam at a pressure of 125 Ibs. will enable the sand to cut away i^ cubic
inches of granite, 3 cubic inches of marble, or 10 cubic inches of sand-
stone in one minute. By making use of stencil-plates, patterns of any kind
may thus be quickly cut, even in the hardest stone. It is singular that
stencil-plates of metal soon curl up under the sand-blast, while a soft sub-
stance, like paper, is not liable to this defect. Hence metallic templates,
if used, have to be protected from the impact of the sand by some soft
material.
When the sand-blast is working on stone, a red light is perceptible. As
this does not appear to be due to heat, it may possibly be connected with
the luminous effects that are observed when certain crystals are split. It
has been suggested that the ancient Egyptian carvings, which are so neatly
executed in some of the hardest stone, may have been produced by a
similar process.- It is, perhaps, a great descent from Egyptian sculpture
to mention an application of the sand-blast so humble as that of cleaning
out the interior of cast iron pans. But to this purpose, however, it has
been advantageously applied, supplanting the operation of turning in a
lathe, which formerly was requisite, in order to obtain a clean surface for
tinning.
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 Codes 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
187
i88
IRON BRIDGES.
span 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, attain-
ing in the respective cases 1 52 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 pro-
perties 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, exten-
sion 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 com-
press 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 Ibs. that is, about 1,000 Ibs. 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 pres-
sure per square
inch, in tons.
Cast iron
8
CO
Wrought iron
-3Q
17
Iron wire
4
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.
IRON BRIDGES. 189
or 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 cer-
tain 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 ex-
tension. 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 pres-
sure, 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.
The general principle of the construction of girder bridges is easily
explained by considering a simple case, which is almost within every-
body's experience. Let us suppose we have a plank supported as in Fig. 1 39.
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 01 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, how-
ever, which, being neither extended or compressed, receives no strain. The
position of this is indicated by the line /, 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
1 90
IRON BRIDGES.
it 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
FIG. 140.
increase the weight to be supported, and they may, for that reason, be re-
moved with advantage, leaving only sufficient wood to connect the upper
and lower portions rigidly together. The form of cast iron beams, Fig. 141,
now so much used for many purposes, depends upon these principles. The
FIG. 141.
FIG. 142.
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
IRON- BRIDGES.
191
way 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.
/\/\/\/\l
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.
^PHE Britannia Bridge, which carries the Chester and Holyhead Rail-
way 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 abut-
ments 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
I 9 2
IRON BRIDGES.
FIG. 144. Section of a Tube of the Britannia Bridge.
by 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 22f 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 i ft. 9 in. wide, and
each of the bottom ones 2 ft. 4 in. The vertical framing of the tube con-
sists essentially of bars of T-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 T- and L-shaped ribs.
The thickness of the plates is varied in different parts from \ in. to f in.
The plates vary also in their length and width in the different parts of
the tubes, some being 6 ft. by if 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 T-iron is rivetted on each side, thus : ~. The cells are also formed
IRON BRIDGES. 193
of iron plates, bolted together by L-shaped iron bars at the angles. The
rails rest on longitudinal timber sleepers, which are well secured by angle-
iron to the T-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 1 86,000. 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 sup-
ported 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 i^ 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 mam
tubes of the Britannia Bridge make sixty-seven vibrations per minute. The
expansion and contraction occurring each day show a range of from \ 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 dimen-
sions : Total length of the Victoria Bridge, Montreal, 9,144 ft., or if miles ;
length of tubes, 6,592 ft., or i miles : weight of iron in the tubes, 9,044
13
I 9 4
IRON BRIDGES.
FIG. 145. A Ibert Bridge, Saltash.
tons ; 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.
Another singular modification of the girder principle occurs in the bridge
built by Brunei 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 loo 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 1 50 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 suspen-
sion 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 locomo-
IRON BRIDGES. 195
tives, placed upon the entire length of the span, produced a deflection in
the centre of 7 in. only. This bridge has sometimes been called a suspen-
sion 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 dia-
meter 1 2 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.
*T*HE 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 deflec-
tion. Indeed, even a short piece of thin cord cannot be stretched horizon-
tally 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, espe-
cially 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 579ft lo^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,
3^ in. broad, and I in. thick. In the main chains, of which there are six-
teen, 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
13 - -2
196
IRON BRIDGES.
i 1 IG. 146. Clifton Suspension Bridge, near Bristol.
transverse stays formed of cast iron tubes, through which pass wrought
iron bolts, and there are also diagonal ties joining the ends of the trans-
verse stays. The time occupied in the construction was 6| years, and the
cost was ;i 20,000. 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, in-
stead of the hazardous passage over an often stormy strait, have now the
advantage of a safe and level roadway.
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 re-
markable 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 precipi-
tous 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
IRON BRIDGES.
197
position 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 Gloucester-
shire and Somersetshire, thus avoiding the circuitous route through Bristol,
which was required before the completion of the bridge
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
1 88 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 Switzer-
land. This bridge has a span of no less than 880 ft, and is constructed
entirely of iron wires scarcely more than ^ 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 5^
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 to-
gether with cramps and ties, so as to constitute
most substantial structures. These piers are em-
bellished 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 ver-
tical wire cables, I in. in diameter. The length of these suspension cables
of course varies according to their position, the shortest being ^ 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 toge-
ther, 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.
FIG. 147.
198 IRON BRIDGES.
To test the stability of the bridge, fifteen heavy pieces of artillery, accom-
panied 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 pro-
bably 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 prin-
ciple. 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 Roeb-
ling, 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.
The new suspension bridge at the Niagara Falls, called the Clifton
Bridge, of which a view is given in Plate IV., 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, cross-
ing 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 sus-
pension being more than twice that of the Menai Bridge, and more than
six times the span of the widest stone bridge in England. This remark-
able suspension bridge was constructed by Mr. Samuel Keefer, and was
opened for traffic on the ist 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. usu-
ally hangs between the suspending towers, the centre being about 90 fL
level of the points of suspension. This last distance, however,
IRON BRIDGES. 199
varies considerably with the temperature, for in winter the contraction pro-
duced by the cold brings up the centre to 89 ft. below the level line, while
in summer it may be 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 plat-
form 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 road-
way wou'd 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 cer-
tain 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 f ths 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, 13! ft. long,
10 in. deep, and 2\ 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 i\ 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, 6^ 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 over-
come. 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 ^ 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
200 IRON BRIDGES.
guys 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 plat-
form sees in the spray driven by the wind, not a mere fragment of a rain-
bow, 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 aerial 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 ^Eolus 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 Ibs. 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. This work is a remarkable
testimony to the skill of its engineer, and a striking example of the enter-
prise of the American people.
FlG. 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 labo-
rious 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 them-
selves 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.
201
202 PRINTING MACHINES.
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 pro-
ductions of the press, having imitated the manuscript characters, the unin-
tiated 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. An-
other 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 pre-
sented, with hands, and no doubt faces also, smeared over with the black
Fro. 149. Inking Balls. FIG. 150. Inking Roller.
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 ftiem 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 work-
ing condition.
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
PRINTING MACHINES. 203
these 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. 1 50 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 con-
tact with the types. Such presses are capable of turning out about 250 im-
pressions 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. Stan-
hope'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 prac-
tical success in this direction was achieved by Konig, 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 ma-
chinery 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 l form,' little more re-
mains for man to do than to attend upon and watch this unconscious agent
i'i 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 simultaneous-
ness 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
204 PRINTING MACHINES.
interest, 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 Konig, and that
the invention has been executed under the direction of his friend and coun-
tryman, Bauer."
Each of the machines erected by Konig 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 im-
proved by Messrs. Applegath and Cowper, who contrived also a modifi-
cation 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
Cj
FlG. 151. Diagram of Cowper and ApplegatWs Single Machine.
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 t g, ^, /,/,#*, , 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 rota-
tion 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, /, m, n. The table,
C D, as a whole is constantly moving right and left in a horizontal direction,
PRINTING MACHINES.
205
so that the form passes alternately under the impression cylinder, E, and
the inking rollers, /, ?;z, 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 direc-
tion 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 arrange-
ments 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. 152 is a similar diagram, to show the action of the double or per-
fecting printing machine,.in which the sheets are printed on both sides. It
will be observed that the general arrangement of impression cylinder,
FIG. i^.Cowper^s Double Cylinder Machine.
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, E', 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 fat 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
206
PRINTING MACHINES.
in 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-ojf,
(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 rackwork that the sheets of paper may always receive the im-
pression in the proper position as regards the margins, and therefore, when
the sheets are printed on both sides, the impressions will be exactly oppo-
site to each other. This gives what is technically called " true register,"
FIG. 154. Tapes ofCowper's Machine.
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. 1 54, and a simple inspection of the diagram
will render a tedious description unnecessary.
In Fig. 1 5 5 we have a representation of a steam-power printing machine,
such as is now very largely used for the ordinary printing of books, news-
papers 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 impres-
sion 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
I
208 PRINTING MACHINES.
ends 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 liour, even of
good book-work, ana 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.
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 intelli-
gence, the necessities of the newspaper press, as regards rapidity of print-
ing, 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 recipro-
cating 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 circum-
ference, 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 hori-
zontal tables, an ingenious arrangement of tapes and rollers was contrived,
by which each sheet was first carried down from the table into a vertical posi-
tion, with its plane directed towards the impression roller, in which position
it was stopped for an instant, then moved horizontally forwards round the
PRINTING MACHINES.
209
impression 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, I4th November, 1852, no less than 70,000 were printed in
one day, and the machines were notionce 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 card-
board, 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 macht 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 form-
ing 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 cen-
tral 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 circum-
ference, 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
mache 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 solidi-
14
2io PRINTING MACHINES.
fied, the 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
FIG. 156.
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 gene-
rally employed to produce several plates.
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 project-
ing 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 spec-
tator 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, F 15 F 2 , 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 F T , against which it is pressed
by the roller, PJ, 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, F 2 , is below, and the impression cylinder, P 2 ,
above, and an endless cleaning blanket is supplied to the latter to receive
PRINTING MACHINES.
211
the set-off. The web of paper then passes between the cutting rollers, c, C 1?
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, / a , / 2 , between which the paper is now carried, are driven at a
rather quicker rate than the web issues from C, C x ; 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,
FIG. itf Diagram of the Walter Press.
h, and is brought to another set of tapes mounted on the frame, r, rock-
ing about the centre, ^, by which it is brought finally to the tapes, f-^fz,
which by the movement of r receive the sheets alternately. A sheet-flyer,
5-, oscillates between the tapes,/!, / 2 ; and as fast as the sheets arrive, lays
them down right and left alternately, and it only remains for the piles, p^p^
so formed, to be removed. The inking apparatus of each form-cylinder
is indicated by the series of rollers marked i x , I 2 ; 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 uni-
formly 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
14 2
212 PRINTING MACHINES.
contrivers of the Walter Press make these spindles as tight as may be re-
quired 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 im-
pression cylinders, and at each revolution of the great cylinder the corre-
sponding number of impressions are produced. The engraving on the
opposite page, Fig. 158, represents the two-cylinder machine, and an exa-
mination 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 per-
son 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 con-
tained 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 sur-
face 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 distri-
buting surface. Each page of the matter is locked up on a detachable seg-
ment of the large cylinder, which segment constitutes its bed and chase.
The column-rules are parallel with the shaft of the cylinder, and are con-
sequently 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.,
PRINTING MACHINES.
213
2i4 PRINTING MACHINES.
with the thin end directed towards the axis of the cylinder, so as to bind
the types securely. These wedge-shaped column-rulep 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 securely as in the ordinary
manner upon a flat bed. The main cylinder of the machine represented
in Fig. 158 has a diameter of 3 ft. 9 in., and its length is, according to the
size of the sheets to be printed, from 4 ft. 5 in. to 7 ft. 4 in. The whole is
about 20 ft. long, 10 ft. wide, including the platforms, and a height of 9 ft.
in the room in which it is placed suffices for its convenient working. The
steam power required is from one to two horse-power, according to the
length of the main cylinder. The speed of these machines is limited only
by the ability of the feeders to supply the sheets fast enough. The ten-
cylinder machine has, of course, ten impression cylinders, instead of two,
and there are ten feeding-tables, arranged one above the other, five on each
side. The main cylinder has a diameter of 4 ft. 9 in., and is 6 ft. 8 in. long.
The machine occupies altogether a space of 31 ft. by 1 6 ft., and its height is
1 8 ft. A steam engine of eight horse-power is sufficient to drive the ten-
cylinder machine, which is then capable of producing 25,000 impressions
per hour. The mechanism of the larger machines is precisely similar to
that of the two-cylinder machine, except such additional devices as are
necessary to carry the paper to and from the main cylinder at four, six,
eight, or ten points of its circumference. Much admirable contrivance is
displayed in the manner of disposing feeders as closely as possible round
the central cylinder.
In some machines, such as Messrs. Hoe's, Fig. 158, the sheet-flyers are
interesting features, for they form an efficient contrivance for laying down
and piling up, with the greatest regularity, sheet after sheet as it issues from
the press. The sheet-flyer is in fact an automatic taker-off, and therefore
it supersedes the services of the boy who would otherwise be required. It
is simply a light wooden framework of parallel bars, turning on one of its
sides as a centre ; and the tapes carrying the sheet, passing down between
the bars, bring the paper down upon the frame, where its progress is then
stopped, the frame makes a rapid turn on its centre, lays down the sheet,
and quickly rises to receive another from the tapes. One can hardly see a
printing machine in action without being struck with the deftness with which
the sheet-flyer does its duty ; for the precision with which it receives a sheet,
lays it down, and then quickly returns, to be ready for the next, suggest to
the mind of the spectator rather the movements of a conscious agent than
the motions of an unintelligent piece of mechanism. The sheet-flyer is seen
at the left-hand side of Fig. 158, where it is in the act of laying down a
sheet on the pile it has already formed.
The modern improvements in printing presses are well illustrated by
the machine represented on the opposite page, Fig. 1 59, which has been
designed by the Messrs. Hoe to work exclusively by hand. It is intended
for the newspaper and job work of a country office, and it works easily,
without noise or jar, by turning the handle always in the same direction,
producing 800 impressions in an hour. The bed moves backwards and
forwards on wheels running on rails, the reciprocating movement being
216 PRINTING MACHINES.
derived from the circular one by means of a crank. From the mode in
which the table is carried backwards and forwards, the manufacturers call
this the " Railway Printing Machine." The paper is fed to the underside
of the cylinder, which, after an impression has been given, remains sta-
tionary while the bed is returning, and while the layer-on is adjusting his
sheet of paper. The axle of the impression cylinder carries a toothed
wheel working in a rack on the bed or table, the wheel having at two parts
of its circumference the teeth planed off so as to permit of the return of
the table without moving the impression cylinder, which is again thrown
into gear with the rack by a catch, so that the same tooth of the rack always
enters the same space on the toothed wheel, and thus a good register is
secured. The impression cylinder remains unaltered, whatever may be the
size of the type form, it being only necessary to place the forward edge of
the form always on the same line of the bed. Machines of a very similar
FIG. 1 60. Napier's Platen Machine.
construction, but driven by steam power, are used in lithographic printing ;
and in some of these machines advantage is elegantly taken of the fact
that, when a wheel rolls along, the uppermost point of its circumference is
always moving forward at exactly twice the velocity of its centre. Hence,
if the table of a printing machine rests on the circumference of wheels, a
backward and forward movement of the centres of these wheels, produced
by the throw of a crank through a space of 2 ft, would produce a rectilineal
reciprocating movement through a distance of 4 ft. of a table resting on the
circumference of the wheels. Any reader who is interested in geometry
or mechanics would do well to convince himself that the lowest point of
the wheel of a railway carriage, for example, is stationary (considered while
it is the lowest point), that the centre of the wheel is moving forwards with
the velocity of the train, and that the highest point of the wheel is moving
forwards with just twice the speed of the train. There is no difficulty about
the rate of rectilineal motion of the centre, but the reader cannot possibly
perceive the truth of the statement regarding the lowest and highest points
unless he reflects on the subject, or puts it to the test of experiment An-
other form of press which is used for good book printing is represented
PRINTING MACHINES. 217
in the engraving, Fig. 160, which shows Napier's platen machine. There
the action is similar to that of the ordinary hand presses as regards the
mode in which the paper is pressed against the face of the type ; but the
movements are all performed by steam power, applied through the driving
belt, shown in the figure.
The various kinds of printing machines adapted to each description of
work are too numerous to admit of even a passing mention here ; but those
which have been described may fairly be considered as representing the
leading principles of modern improvements. This article relates only to
the mechanism by which an impression is transferred from a form to the
surface of paper : the interesting and novel processes by which the form
itself may be produced processes which have amazingly abridged the
printers' labour and extended the resources of the art deserve a separate
chapter, and will furnish matter for an article on Printing Processes, which
will be the better understood by being placed after chapters wherein the
scientific bases of some of these processes are discussed.
PATTERN PRINTING.
THE machines used for printing patterns are, in principle, very similar
to those for letterpress printing ; but the circumstance of several
different colours having frequently to go to the production of one pattern
leads to the multiplication, in the present class of machines, of the appa-
ratus for distributing the colours and impressing the materials. Pattern
printing machines are most extensively used for impressing fabrics, such
as calicoes, muslins, &c., and for* producing the wall-papers for decorating
apartments. The machines employed for calicoes and for papers are so
much alike, that to describe the one is almost to describe the other.
The papers intended for paper-hangings are, in the first instance, covered
with a uniform layer of the colour which is to form the ground, and this is
done even in the case of papers which are to have a white ground. The
colours thus laid on, and those which are applied by the machine, are com-
posed of finely-ground colouring matters mixed with thin size or glue to a
suitable consistence, and the ground-tint is given by bringing the upper
surface of the paper, as it is mechanically unwound from a great roll, into
contact with an endless band of cloth emerging from a trough containing
a supply of the fluid colour. The paper then passes over a horizontal table,
where the layer of colour is uniformly distributed over its surface by brushes
moved by machinery, and the paper, after having been thoroughly dried,
is ready to receive the impressions. The impressions may be given by
flat blocks of wood on which the pattern is carved in relief, or from revol-
ving cylinders on which the pattern is similarly carved. The former is the
process of hand labour called " block printing," and it requires much skill
and care on the part of the operator ; but with these, excellent results are
obtained, as a correct adjustment of the positions of the parts of the pat-
tern can always be secured. The latter is the mode of printing mechani-
cally on rollers, corresponding with the type-bearing cylinders of the
218 PRINTING MACHINES.
machines already described ; but for pattern printing on paper they are
made of fine-grained wood, mounted on an iron axle, and they are carved
so that the design to be printed stands out in relief on their surface. One
of these rollers is represented in Fig. 161, and it should be clearly under-
stood that each colour in the pattern on a wall-paper requires a separate
roller, the design cut on which corresponds only with the forms the parti-
cular colour contributes to the pattern. Such rollers being necessarily
somewhat expensive, as the pattern is usually repeated many times over
the cylindrical surface, the plan has been adopted of fastening a mass
of hard composition in an iron axle, and when this has been turned to a
truly cylindrical surface, it is made to receive plates of metal, formed of
a fusible alloy of lead, tin, and nickel These plates are simply casts
FIG. 161. Roller for Printing W all-Papers.
from a single carved wooden mould of the pattern, which has thus only
once to be formed by hand. The plates are readily bent when warmed,
and are thus applied to the cylindrical surface, to which they are then
securely attached. It is found advantageous to cover the prominent parts
of the rollers which produce the impressions with a thin layer of felt, as
this substance takes up the colours much more readily than wood or metal,
and leaves a cleaner impression.
The machine by which wall-papers are printed is represented in Fig. 162.
where it will be observed that the impression cylinder has a very large
diameter, and that a portion of its circumference forms a toothed wheel,
which engages a number of equal-sized pinions placed at intervals about
its periphery. Each pinion being fixed on the axle of a pattern-bearing
roller, these are all made to revolve at the same rate. There is, however,
some adjustment necessary before that exact correspondence of the impres-
sions with each other is secured, which is shown on the printed pattern by
each colour being precisely in its appointed place. The rollers are con-
stantly supplied with colour by endless cloths, which receive it from the
troughs that are shown in the figure, one trough being appropriated to each
roller. Some of these machines can print as many as eighteen or twenty
different colours at once, by having that number of rollers ; and it is easy
to see how, by dividing each trough into several vertical compartments, in
each of which a different colour is placed, it would be possible to triple or
even quadruple the number of colours printed by one machine.
The machinery by which calicoes are printed is almost identical in con-
struction with that just described, and presents the same general appear-
ance. There is, however, an important difference in the rollers, which in
calico printing are of copper or bronze, and have the design engraved upon
their polished cylindrical surface, not in relief, but in hollows. After the
whole surface of the roller becomes charged with colour, there is in the
machine a straight-edge, which removes the colour from the smooth sur-
PRINTING MACHINES.
219
FIG. 162. Machine for Printing Paper-Hangings.
face, leaving only what has entered into the hollow spaces of the design,
which, as the roller comes round to the cloth, yield it up to the surface of
the latter. Thus, by a self-acting arrangement, the rollers are charged with
colour, cleaned, and made to give up their impressions to the stuff by part-
ing with the colour in the hollows. Rollers having patterns in relief are
also used in calico printing, the mechanism being then almost identical
with that of the former machine. It need hardly be said that great pains
are taken in the construction of such machines to have each part very
accurately adjusted, so that the impression may fall precisely upon the
proper place, without any blurring or confusion of the colours, and the
fact that an intricate design, having perhaps eighteen or twenty tints, can
be thus mechanically reproduced millions of times speaks volumes for the
accuracy and finish of the workmanship which are bestowed on such
printing machines.
FlG. 163. Chain-Testing Machine at Messrs. Brown and Lenox's
Works, Millwall.
HYDRAULIC POWER.
I
F a hollow sphere, a, Fig. 173, be pierced with a number of small holes at
various points, and a cylinder, , provided with a piston, c^ fitted into
it, when the apparatus is filled with water, and the piston is pushed inwards,
the water will spout out of all the orifices equally, and not exclusively from
that which is opposite to the piston and in the direction of its pressure.
The jets of water so produced would not, as a matter of fact, all pursue
straight paths radiating from the centre of the sphere, because gravity
would act upon them ; and all, except those which issued vertically, would
take curved forms. But when proper allowance is made for this circum-
stance, each jet is seen to be projected with equal force in the direction
of a radius of the sphere. This experiment proves that when pressure is
applied to any part of a liquid, that pressure is transmitted in all directions
equally. Thus the pressure of the piston which, in the apparatus repre-
sented in the figure, is applied in the direction of the axis of the cylinder
only is carried throughout the whole mass of the liquid, and shows itself
by its effect in urging the water out of the orifices in the sphere in all direc-
tions ; and since the force with which the water rushes out is the same a^
every jet, it is plain that the water must press equally against each unit o
area of the inside surface of the hollow sphere, without regard to the
position of the unit.
220
HYDRA ULIC PO WER. 221
If we suppose the piston to have an area of one square inch, and to be
pushed inwards with a force of 10 Ibs., it cannot be doubted that the square
inch of the inner surface of sphere immediately opposite the cylinder will
receive also the pressure of 10 Ibs. ; and since the pressures throughout
the interior of the hollow globe are equal, every square inch of its area will
also be pressed outwards with a force equal to 10 Ibs. Hence, if the total
area of the interior be 100 square inches, the whole pressure produced will
amount to a hundred times 10 Ibs.
That water or any other liquid would behave in the manner just described
might be deduced from a property of liquids which is sufficiently obvious,
namely, the freedom with which their particles move or slide upon each
other. The equal transmission of pressure in all directions through liquids
was first clearly expressed by the celebrated Pascal, and it is therefore
known as " Pascal's principle." He said that " if a closed vessel filled with
water has two openings, one of which is a hundred times as large as the
other ; and if each opening be provided with
an exactly-fitting piston, a man pushing in the
small piston could balance the efforts of a
hundred men pushing in the other, and he
could overcome the force of ninety -nine."
Pascal's principle which is that of the hy-
draulic press may be illustrated by Fig. 164,
in which two tubes of unequal areas, a and
, communicate with each, and are supposed , \
to be filled with a liquid water, for example, " I
which will, of course, stand at the same level
in. both branches. Let us now imagine that
pistons exactly fitting the tubes, and yet quite
free to move, are placed upon the columns of
liquid the larger of which, , we shall suppose
to have five times the diameter, and there-
fore twenty-five times the sectional area, of the
smaller one. A pressure of i Ib. applied to the __^
smaller piston would, in such a case, produce _
an upward pressure on the larger piston of ?lG.i6^-PascaFs Principle.
25 Ibs. ; and in order to keep the piston at rest,
we should have to place a weight of 25 Ibs. upon it. Here then a certain force
appears to produce a much larger one, and the extent to which the latter
may be increased is limited only by the means of increasing the area of
the piston. Practically, however, we should not by any such arrangement
be able to prove that there is exactly the same proportion between the
total pressures as between the areas, for the pistons could not be made to
fit with sufficient closeness without at the same time giving rise to so much
friction as to render exact comparisons impossible. We may, however,
still imagine a theoretical perfection in our apparatus, and see what further
consequences may be deduced, remembering always that the actual results
obtained in practice would differ from these only by reason of interfering
causes, which can be taken into account when required. We have sup-
posed hitherto that the pressures of the pistons exactly balance each other.
Now, so long as the system thus remains in equilibrium no work is done ;
but if the smallest additional weight were placed upon either piston, that
one would descend and the other would be pushed up. As we have
supposed the apparatus to act without friction, so we shall also neglect the
222
HYDRA ULIC PO WER.
effects due to difference in the levels of the columns of liquid when the
pistons are moved ; and further, in order to fix our ideas, let us imagine
the smaller tube to have a section of I square inch in area, and the larger
one of 25 square inches. Now, if the weight of the piston, a, be increased
by the smallest fraction of a grain, it will descend. When it has descended
a distance of 25 in., then 25 cubic inches of water must have passed into b,
and, to make room for this quantity of liquid, the piston with the weight oi
25 Ibs. upon it must have risen accordingly. But since the area of the larger
tube is 25 in., a rise of i in. will exactly suffice for this ; so that a weight of
i Ib. descending through a space of 25 in., raises a weight of 25 Ibs. through
a space of i in. This is an illustration of a principle holding good in all
machines, which is sometimes vaguely expressed by saying that what ii,
gained in power is lost in time. In this case we have the piston, b, moving
through the space of i in. in the same time that the piston a moves through
25 in. ; and therefore the velocity of the latter is twenty-five times greater
than that of the former, but the time is the same. It would be more pre-
cise to say, that what is gained in force is lost in space ; or, that no machine,
whatever may be its nature or construction, is of itself capable of doing
work. The " mechanical powers," as they are called, can do but the work
done upon them, and their use is only to change the Relative amounts of
the two factors, the product of which measures the work, namely, space
and force. Pascal himself, in connection with the passage quoted above,
clearly points out that in the new mechanical power suggested fr r him in
the hydraulic press, " the same rule is met with as in the old ones such
as the lever, wheel and axle, screw, &c. which is, that the distance is in-
creased in proportion to the force ; for it is evident that as one of the open-
ings is a hundred times larger than the other, if the man who pushes the
small piston drives it forward i in., he will drive backward the large piston
one-hundredth part of that length only." Though the hydraulic press was
thus distinctly proposed as a machine
by Pascal, a certain difficulty pre-
vented the suggestion from becoming
of any practical utility. It was found
impossible, by any ordinary plan of
packing, to make the piston fit without
allowing the water to escape when the
pressure became considerable. This
difficulty was overcome by Bramah,
who, about the end of last century,
contrived a simple and elegant plan
of packing the piston, and first made
the hydraulic press an efficient and
useful machine. -Fig. 1 66 is a view of
an ordinary hydraulic press., in which
a is a very strong iron cylinder, re-
presented in the figure with a part
broken off, in order to show that inside
of it is an iron piston or ram, b, which
works up and down through a water-
tight collar ; and in this part is the in-
vention by which Bramah overcame
the difficulties that had previously been met with in making the hydraulic
press of practical use. Bramah's contrivance is shown by the section of
FIG. 165. Collar of Hydraulic
Cylinder.
HYDRA ULIC PO WER.
223
the cylinder, Fig. 165, where the interior of the neck is seen to have a groove
surrounding it, into which fits a ring of leather bent into a shape resembling
an inverted U- The ring is cut out of a flat piece of stout leather, well oiled
and bent into the required shape. The effect of the pressure of the water is
to force the leather more tightly against the ram, and as the pressure be-
comes greater, the tighter is the fit of the collar, so that no water escapes
even with very great pressures. To the ram, , Fig. 166, a strong iron table,
c, is attached, and on this are placed the articles to be compressed. Four
FIG. 1 66. Hydraulic Press.
wrought iron columns, d d d d, support another strong plate, *, and main-
tain it in a position to resist the upward pressure of the goods when the
ram rises, and they are squeezed between the two tables. The interior of
the large cylinder communicates by means of the pipe,//, with the suction
and force-pump, #-, in which a small plunger, o, works water-tight. Suppose
that the cylinders and tubes are quite filled with water, and that the ram
and piston are in the positions represented in the figure. When the piston
of the pump, g^ is raised, the space below it is instantly filled with water,
which enters from the reservoir, ^, through the valve, *", the valve k being
closed by the pressure above it, so that no water can find its way back
from the pipe,/, into the small cylinder. When the piston has completed
its ascent, the interior of the small cylinder is therefore completely filled
with water from the reservoir ; and when the piston is pushed down, the
valve, /, instantly closes, and all egress of the liquid in that direction being
prevented, the greater pressure in^ forces open the valve, , and the water
flows along the tube,/, into the large cylinder. The pressure exerted by the
plunger in the small cylinder, being transmitted according to the principles
already explained, produces on each portion of the area of the large plunger
equal to that of the smaller an exactly equal pressure. In the smaller
224 HYLTRA ULIC PO WER.
hydraulic presses the plunger of the forcing-pump is worked by a lever, as
represented in the figure at n; so that with a given amount of force applied
by the hand to the end of the lever, the pressure exerted by the press will
depend upon the proportion of the sectional area of b to that of 0, and also
upon the proportion of the length m n, to the length m I. To fix our ideas,
let us suppose that the distance from m of the point n where the hand is
applied is ten times the distance m I, and that the sectional area of b is a
hundred times that of o. If a force of 60 Ibs. be applied at , this will pro-
duce a downward pressure at m equal to 60X10, and then the pressure
transmitted to the ram of the great cylinder will be 60 X 10 x 100=60,000^5.
The apparatus is provided with a safety-valve at^J, which is loaded with a
weight ; so that when the pressure exceeds a desired amount, the valve
opens and the water escapes. There is also an arrangement at q for allow-
ing the water to flow out when it is desired to relieve the pressure, and the
water is then forced out by the large plunger, which slowly descends to
occupy its place. The body of the cylinder is placed beneath the floor in
such presses as that represented in Fig. i667in order to afford ready access
to the table on which the articles to be compressed are placed.
The force which may, by a machine of this kind, be brought to bear upon
substances submitted to its action, is limited only by the power of the mate-
rials of the press to resist the strains put upon them. If water be con-
tinually forced into the cylinder of such a machine, then, whatever may be
the resistance offered to the ascent of the plunger, it must yield, or otherwise
some part of the machine itself must yield, either by rupture of the hydraulic
cylinder, or by the bursting of the connecting-pipe or the forcing-pump.
This result is certain, for the water refuses to be compressed, at least to any
noticeable degree, and therefore, by making the area of the plunger of the
force-pump sufficiently small, there is no limit to the pressure per square
inch which can be produced in the hydraulic cylinder ; or, to speak more
correctly, the limit is reached only when the pressure in the hydraulic
cylinder is equal to the cohesive strength of the material (cast or wrought
iron) of which it is formed. It has been found that when the internal
pressure per square inch exceeds the cohesive or tensile strength of a rod
of the metal i in. square (see page 188), no increase in the thickness of the
metal will enable the cylinder to resist the pressure. Professor Rankine
has given the following formula for calculating the external radius, R, of a
hollow cylinder of which the internal radius is r, the pressure per square
inch which it is desired should be applied before the cylinder would yield
being indicated by p, while f represents the tensile strength of the
materials ;
We may see in this formula that as the value of/ becomes more and more
nearly equal to / the less does the divisor (fp) become, and therefore
the greater is the corresponding value of R; and when f=p, or fp=o,
the interpretation would be that no value of R would be sufficiently great
to satisfy the equation. Thus a cylinder, made of cast iron, of which the
breaking strain is 8 tons per square inch, would have its inner surface rup-
tured by that amount of internal pressure, and the water passing into the
fissures would exert its pressure with ever-increasing destructive effect.
With certain modifications in the proportions and arrangement of its
parts, the hydraulic press is used for squeezing the juices from vegetable
HYDRAULIC POWER. 225
substances, such as beetroots, c., for pressing oils from seeds, and, in fact,
all purposes where a powerful, steady, and easily regulated pressure is
needed. Cannons and steam boilers are tested by hydraulic pressure, by
forcing water into them by means of a force-pump, just as it is forced into
the cylinder of the hydraulic press described above. This mode of testing
the strength has several great advantages ; for not only can the pressure be
regulated and its amount accurately known ; but in case the cannon or
steam boiler should give way, there is no danger, for it does not explode
the metal is simply ruptured, and the moment this takes place, the water
flows out and the strain at once ceases.
The strength of bars, chains, cables, and anchors is also tested by hydraulic
power, and the engraving at the head of this article, Fig. 163, represents
the hydraulic testing machine at the works of Messrs. Brown and Lenox,
the eminent chain and anchor, manufacturers, of Millwall. Immediately
in front of the spectator are the force-pumps, and the steam engine by
which they are driven. It will be observed that four plungers are attached
to an oscillating beam in such a manner that the water is continuously
forced into the hydraulic cylinder. The outer pair of plungers are of much
larger diameter than the inner pair, in order that the supply of water may
be cut off from the former when the pressure is approaching the desired
limit, and the smaller pair alone then go on pumping in the water, the pres-
sure being thus more gradually increased. Behind the engine and forcing
pump is the massive iron cylinder, where the pressure is made to act on
a piston, which is forced towards that end of the cylinder seen in the
drawing. The piston is attached to a very thick piston-rod, moving through
a water-tight collar at the other end of the cylinder. The effect of tht
hydraulic pressure is, therefore, to draw the piston-rod into the cylinder,
and not, as in the apparatus represented in Fig. 166, to force a plunger out.
The head of the piston-rod is provided with a strong shackle, to which the
chains to be tested can be attached. In a line with the axis of the cylinder
is a trough, some 90 ft. long, to hold the chain, and at the farther end of
the trough is another very strong shackle, to which the other end of the
chain is made fast. A peculiarity of Messrs. Brown and Lenox's machine
is the mode in which the tension is measured. In many cases it is deemed
sufficient to ascertain by some kind of gauge the pressure of the water in
the hydraulic cylinder, and from that to deduce the pull upon the chain ;
but the Messrs. Brown have found that every form of gauge is liable to
give fallacious indications, from variations of temperature and other cir-
cumstances, and they prefer to measure the strain directly. This is accom-
plished by attaching the shackle at the farther extremity of the trough to
the short arm of a lever, turning upon hard steel bearings, the long arm of
this lever acting upon the short arm of another, and so on until the weight
of I Ib. at the end of the last le T , .^r will balance a pull on the chain of
2,240 Ibs., or i ton. The tension is thus directly measured by a system
of levers, exactly resembling those used in a common weighing machine,
and this is done so accurately that even when a chain is being subjected
to a strain of many tons, an additional pull, such as one can give to the
shackle-link with one hand, at once shows itself in the weighing-room.
The person who has charge of this part of the machine places on the end of
the lever a weight of as many pounds as the number of tons strain to which
the chain to be tested has to be submitted. The engineer sets the pump
in action, the water is rapidly forced into the cylinder, the piston is thrust
inwards, and the strain upon the chain begins ; the engineer then cuts off
15
226 HYDRA ULIC PO WER.
the water supply from the larger force-pumps, and the smaller pair go on
until the strain becomes sufficient to raise the weight, and then the person
in the weighing-room, by pulling a wire, opens a valve in connection with
the hydraulic cylinder, which allows the water to escape, and the strain is
at once taken off. This testing machine, which is capable of testing cables
up to 200 tons or more, was originally designed by Sir T. Brown, the late
head of the firm, and not only was the first constructed in the country, but
remains unsurpassed in the precision of its indications.
The testing of cables, which we have just described, is a matter of the
highest importance, for the failure of cables and anchors places ships and
men's life in great danger, since vessels have frequently to ride out a storm
at anchor, and should the cables give -way, a ship would then be almost
entirely at the mercy of the winds and waves. Hence the Government have,
with regard to cables and anchors, very properly made certain stringent
regulations, which apply not only to the navy but to merchant shipping. The
chain-cable is itself a comparatively modern application of iron, for sixty
years ago our line-of-battle ships carried only huge hempen cables of some
8 in. or 9 in. diameter. Chain-cables have now almost entirely superseded
ropes, though some ships carry a hempen cable, for use under peculiar cir-
cumstances. The largest chain-cables have links in which the iron has a
diameter of nearly 3 in., and these cables are considered good and sound
when they can bear a strain of 136 tons. Such are the cables used in the
British navy for the largest ships. Of course, there are many smaller-sized
cables also in use, and the strains to which these are subjected when they
are tested in the Government dockyards vary according to the thickness
of the iron ; but it is found that, nearly one out of every four cables sup-
plied to the Admiralty proves defective in some part, which has to be re-
placed by a sounder piece. The chain-cables made by Messrs. Brown and
Lenox for the Great Eastern are, as might have been expected, of the
very stoutest construction ; the best workmanship and the finest quality of
iron having been employed in their manufacture. These cables were tested
up to 148 tons, a greater strain than had ever before been applied as a test
to any chain, and it was found that a pull represented by at least 172 tons
was required to break them. It is difficult to believe that a teacup-full of
cold water shoved down a narrow pipe is able to rend asunder the massive
links which more than suffice to hold the huge ship securely to her anchors,
but such is nevertheless the sober fact. The regulations of the Board of
Trade require that every cable or anchor sold for use in merchant ships is
to be previously tested by an authorized and licensed tester, who, if he
finds it bears the proper strain, stamps upon it a certain mark.
The means which is afforded by hydraulic power of applying enormous
pressures has been taken advantage of in a great many of the arts, of which,
indeed, there are few that have not, directly or indirectly, benefited by this
mode of modifying force. An illustration, taken at random, may be found
in the machinery employed at Woolwich for making elongated rifle-bullets.,
The bullets are formed by forcing into dies, which give the required shape,
little cylinders of solid lead, cut off by the machine itself from a continuous
cylindrical rod of the metal. The rod, or rather filament, of lead is wound
like a rope on large reels, from which it is fed to the machine. It is in the
production of this solid leaden rope or filament that hydraulic pressure is
used. About 4 cwt. of melted lead is poured into a very massive iron
cylinder, the inside of which has a diameter of 7^ in., while the external
diameter is no less than 2 ft. 6 in,, so that the sides of the cylinder are
HYDRAULIC POWER.
227
actually \\\ in. thick. When the lead has cooled so far as that it has
passed into a half solid state, a ram or plunger, accurately fitting the bore
of the cylinder, is forced down by hydraulic pressure upon the semi-fluid,
metal. This plunger is provided with a round hole throughout its entire
length, and as it is urged against the half solidified metal with enormous
pressure, the lead yields, and is forced out through the hole in the plunger,
making its appearance at the top as a continuous cylindrical filament, quite
solid, but still hot. This is wound upon the large iron reels as fast as it
FlG. 167. Section of Hydraulic Lift Graving Dock.
emerges from the opening in the plunger, and these reels are then taken to
the bullet-shaping machine, which snips off length after length of the leaden
cord, and fashions it into bullets for the Martini-Henry rifle. The leaden
pipes which are so much used for conveying water and gas in houses are
made in a similar manner, metal being forced out of an annular opening,
which is formed by putting an iron rod, having its diameter of the required
bore of the pipe, in the middle of the circular opening. The lead in escaping
between the rod and the sides of the opening takes the form of a pipe, and
is wound upon large iron reels, as in the former case.
Another interesting application of hydraulic power is to the raising of
ships vertically out of the water, in order to examine the bottoms of their
hulls, and effect any necessary repairs. The hydraulic lift graving dock, in
which this is done, is the invention of Mr. E. Clark, who, under the direc-
tion of Mr. Robert Stephenson, designed the machinery and superintended
15 2
228
HYDRAULIC POWER.
the raising of the tubes of the Britannia Bridge, where a weight of i ; 8oo
tons was lifted by only three presses. The suitability of the hydraulic
press for such work as slowly raising a vessel was doubtless suggested to
him in connection with this circumstance, and the durability, economy, and
small loss of power which occurs in the action of the press, pointed it out
as particularly adapted for this purpose. The ordinary dry dock is simply an
excavation, lined with timber or masonry, from which the tide is excluded by
a gate, which, after the vessel has entered the dock at high water, is closed ;
and when the tide has ebbed, and left the vessel dry, the sluice through
which the water has escaped is also closed. In a
tideless harbour the water has to be pumped out
of the dock, an,d this last method is also adopted
even in tidal waters, so that the docks may be
independent of the state of the tides. The lift of
Clark's graving dock is a direct application of the
power of the hydraulic press, and we select for
description the graving dock constructed at the
Victoria Docks for the Thames Graving Dock
Company, whose works occupy 26 acres. Fig. 167
is a transverse section of this hydraulic lift grav-
ing dock, in which there are two rows of cast iron
columns, 5 ft. in diameter at the base, where they
are sunk 12 ft. in the ground, and 4 ft. in diameter
above the ground. The clear distance between
the two rows in 60 ft., and the columns are placed
20 ft. apart from centre to centre, sixteen columns
in each row, thus giving a length of 310 ft. to the
platform, but vessels of 350 ft. in length may prac-
tically be lifted. The bases of the columns, one
of which is represented in section in Fig. 168,
are filled with concrete, on which the feet of
the hydraulic cylinders rest. The outer columns
support no weight, but act merely as guides for
the crossheads attached to the plungers. The
height of the columns is 68^ ft., and a wrought
iron framed platform connects the columns at
the top. In order that any inequalities in the
height of the rams may be detected, a scale is
painted on each column, to mark the positions of
the crossheads. The hydraulic cylinders, which
are within these columns, have solid rams of
10 in. diameter, with a stroke of 25 ft., and on
the tops of these are fastened the crossheads,
7 1 ft. long, made of wrought iron, and supporting
at the ends bars of iron, to the other ends of
which the girders of the platform are suspended.
The girders are, therefore, sixteen in number, and
together form a gridiron platform, which can be raised or lowered with the
vessel upon it. The thirty-two hydraulic cylinders were tested at a pressure
of more than 3 tons per square inch. The water is admitted immediately
beneath the collars at the top (this being the most accessible position) by
pipes of only | in. diameter, leading from the force-pumps, of which there
are twelve, of "if in. diameter, directly worked by a fifty horse-power steam
FIG. 1 68. Section of
Column.
HYDRA ULIC PO WER. 229
engine. The presses are worked in three groups one of sixteen, and two
of eight presses, so arranged that their centres of action form a sort of
tripod support, and the presses of each group are so connected that perfect
uniformity of pressure is maintained. The raising of a vessel is accom-
plished in about twenty-five minutes, by placing below the vessel a pon-
toon, filled in the first instance with water, and then raising the pontoon
with the vessel on it, while the water is allowed to escape from the pontoon
through certain valves ; then when the girders are again lowered, the pon-
toon, with the vessel on it, remains afloat. Thus in thirty minutes a ship
drawing, say, 18 ft. of water is lifted on a shallow pontoon, drawing, perhaps,
only 5 ft, and the whole is floated to a shallow dock, where, surrounded
with workshops, the vessel, now high and dry, is ready to receive the neces-
sary repairs. The number of vessels which can thus be docked is limited
only by the number of pontoons, and thus the same lift serves to raise and
lower any number of ships, which are floated on and off its platform by
the pontoons. With a pressure in the hydraulic cylinders of about 2 tons
upon each square inch, the combined action of these thirty-two presses
would raise a ship weighing 5,000 tons.
Hydraulic power has been used not only for graving docks, as shown in
the above figures, but also for dragging ships out of the water up an inclined
plane. The machinery for this purpose was invented by Mr. Miller for
hauling ships up the inclined plane of " Martin's slip," at the upper end of
which the press cylinder is placed, at the same slope as the inclined plane,
and the ship is attached, by means of chains, to a crosshead fixed on the
plunger. Hydraulic power has also been used for launching ships, and the
launch of the Great Eastern is a memorable instance ; for the great ship
stuck fast, and it was only by the application of an immense pressure,
exerted by hydraulic apparatus, that she could be induced to take to the
water. Water pressure is also applied to hoists for raising and lowering
heavy bodies, and in such cases the pressure which is obtained by simply
taking the water supply from an elevated source, or from the water-main
of a town, is sometimes made use of, instead of that obtained by a forcing
pump. The lift at the Albert Hall, South Kensington, by which persons
may pass to and from the gallery without making use of the stairs, is
worked by hydraulic pressure in the manner just mentioned. In such lifts
or hoists there is a vertical cylinder, in which works a leather-packed piston,
having a piston-rod passing upwards through a stuffing-box in the top of
the cylinder. The upper end of the piston-rod has a pulley of 30 in. or
36 in. diameter, attached to it, and round this pulley is passed a chain, one
end of which is fixed, and the other fastened to the movable cage or frame.
So that the cage moves with twice the speed of the piston, and the length
of the stroke of the latter is one-half of the range of the cage.
Sir William Armstrong has applied hydraulic power to cranes and other
machines in combination with chains and pulleys. His hydraulic crane
is represented by the diagram, Fig. 169, intended to show only the general
disposition of the principal parts of this machine, which is so admirably
arranged that one man can raise, lower, or swing round the heaviest load
with a readiness and apparent ease marvellous to behold. Here it is
proper to mention once for all, that the pressure for the hydraulic machines
is obtained not only by natural heads of water, or by forcing-pumps worked
by hand, but very frequently by forcing-pumps worked by steam power. It
is usual to have a set of three pumps with their plungers connected re-
spectively with three cranks on one shaft, making angles of 1 20 with each
230 HYDRA ULIC PO WER.
other. A special feature of Sir W. Armstrong's hydraulic crane is the
arrangement by which the engines are made to be always storing up power
by forcing water into the vessel, a, called the " accumulator." The accu-
mulator which in the diagram is not shown in its true position may be
placed in any convenient place near the crane, and consists of a large cast
iron cylinder, <5, fitted with a plunger; c, moving water-tight through the neck
of the cylinder. To the head of the plunger is attached by iron cross-bars,
dd, a strong iron case filled with' heavy materials, so as to load the plunger,
Cj with a weight that will produce a pressure of about 600 Ibs. upon each
square inch of the inner surface of the cylinder. The water is pumped into
the cylinder by the pumping engines through the pipe,/; and then the
piston rises, carrying with it the loaded Ccise, guided by the timber frame-
work, g, until it reaches the top of its range, when it moves a lever that
cuts off the supply of steam from the pumping engine. When the crane is
working the water passes out of the cylinder, a, by the pipe, h, and exerts
its pressures on the plungers of the smaller cylinders ; and the plunger of
the accumulator, in beginning its descent again, moves the lever in con-
nection with the throttle-valve of the engine, and thus again starts the
pumps, which therefore at once begin to supply more water to the accu-
mulator. The latter is, however, large enough to keep all the several
smaller cylinders of the machine at work even when they are all in opera-
tion at once. Fig. 169 shows a sketch elevation and a ground plan of the
crane as constructed to carry loads of I ton, but the size of the cylinders
is somewhat exaggerated, and all details, such as pipes, guides, valves,
rods, &c., are omitted. The hydraulic apparatus is entirely below the
flooring only the levers by which the valves are opened and closed ap-
pearing above the surface. The crane-post, z, is made of wrought iron :
it is hollow and stationary ; the jib, k, is connected with the ties, /, by side-
pieces, , which are joined by a cross-piece at m, turning on a swivel and
bearing the pulley, u. The jib and the side-pieces are attached at o to a
piece turning round the crane-post, and provided with a friction roller,/,
which receives the thrust of the jib against the crane-post ; the same piece
is carried below the flooring and is surrounded with a groove, which the
links of the chain, q, fit. This chain serves to swing the crane round, and
for this purpose the hydraulic cylinders, r, r", come into operation. The
plungers of these have each a pulley, over which passes the chain q, having
its ends fastened to the cylinders, so that when, by the pressure of the
water, one plunger is forced out, the other is pushed in, and the chain
passing round the groove at s swings the jib round. The cylinders are
supplied with water by pipes omitted in the sketch, as are also those by
which the water leaves the cylinders. These pipes are connected with
valves also omitted on account of the scale of the diagram being too
small to show their details so that the movement of a lever, /, in one or
the other direction at the same time connects one cylinder with the supply
and the other with the exit-pipe. When the crane is swinging round, the
sudden closing of the valves would produce an injurious shock, and to
prevent this relief-valves are provided on both the supply and exit-pipes
communicating with each cylinder. When, therefore, the valves are closed,
Che impetus of the jib and its load acting on the chain, and through that
on the plungers, continues to move the latter, the motion is permitted to
take place by the relief- valves opening, and allowing water to enter or leave
the cylinders against the pressure of the water. There is also a self-acting
arrangement by which, when these plungers have moved to the extent of
HYDRA ULIC PO WER.
231
their range in either direction, the valves are closed. The chain of the
crane rests on guide pulleys, and passing over the pulley u, goes down the
centre of the crane-post to the pulley v<, and thence passes backwards and
forwards ovrer a series of three pulleys at iv and two at .*", and is fastened
at its end to the cylinder,/. As there are thus six lines of chain, when the
FIG. 169. Sir W. Armstrong's Hydraulic Crane.
plunger of the lifting cylinder comes I ft. out, 6 ft. of chain pass over the
guide pulley, u. The plunger, when near the end of its stroke in either
direction, is made to move a bar not shown which closes the valve.
When the crane is loaded, the load is lowered by simply opening the
exhaust-valve, when the lift-plunger will be forced back into its cylinder
by the pull on the chain. But as the chain may require to be lowered
when there is no load upon it, although a bob is provided at z to draw the
2 3 2
HYDRA UL1C PO WER.
chain down, it would be disadvantageous to in-
crease the weight of this to the extent required
for forcing back the lifting plunger. A return,
cylinder is therefore made use of, the plunger
of which has but a small diameter, and is con-
nected with the head of the lift-plunger, so that
it forces the latter back when the lift-cylinder
is put in communication with the exhaust-pipe.
I 1 1| The water is admitted to the lifting cylinder
from the accumulator by a valve worked by a
lever, which, when moved the other way, closes
the communication and opens the exhaust-pipe,
and then the pressure in the return cylinder,
which is constant, drives in the plunger of the
lifting cylinder. The principle of the accumu-
; lator may plainly be used with great advantage
p even when manual labour is employed, for a less
number of men will be required for working the
' pumps to produce the effect than if their efforts
\ had to be applied to the machine only at the
I time it is in actual operation, for in the intervals
! they would, in the last case, be standing idle.
Apparatus on the same plan has been used with
advantage for opening and shutting dock gates,
\ moving swing bridges, turn-tables, and for other
^ purposes where a considerable power has to be
occasionally applied.
A famous example of the application of hy-
\ draulic power was the raising of the great tubes
r of the Britannia Bridge. As already stated, the
!' tubes were built on the shore, and were floated
| to the towers. This was done by introducing be-
I neath the tubes a number of pontoons, provided
with valves in the bottom, so as to admit the
j water to regulate the height of the tube accord-
" ing to the tide. The great tubes were so skilfully
j guided into their position that they appeared to
| spectators to be handled with as much ease as
small boats. The mode in which they were raised
by the hydraulic presses will be understood from
Fig. 170, where A is one of the presses and C the
tube, supported by the chains, B. The tubes were
suspended in this manner at each end, and as the
great tubes weighed 1,800 tons, each press had,
therefore, to lift half this weight, or 900 tons.
The ram or plunger of the pump was i ft. 8 in.
in diameter, and the cylinder in which it worked
was 1 1 in. thick. Two steam engines, each 40
horse-power, were used to force the water into
the cylinders. These cylinders were themselves
remarkable castings, for each contained no less
than 22 tons of iron. Notwithstanding the great
thickness of the metal, an unfortunate accident
HYDRA ULIC PO WER.
233
occurred while the plungers were making their fourth ascent, for the bottom
of one of the cylinders gave way a piece of iron weighing nearly a ton and
a half having been forced out, which, after killing a man who was ascend-
ing a rope ladder to the press, fell on the top of the tube 80 ft. below, and
made in it a deep indentation. The accident occasioned a considerable
delay in the progress of the work, for a new cylinder had to be cast and
fitted. Such an accident would assuredly have caused the destruction of
the tube itself but for the foresight and prudence of the engineer in placing
FIG. 171. Press for Raising the Tubes.
beneath the ends of the vast tube as it ascended slabs of wood i in. thick,,
so that it was impossible for the tube to fall more than i in. It must be
stated that as the tube was lifted each step, the masonry was built up from
below, and then as the next lift proceeded inch by inch, a slab of wood was
placed under the ends. Although by the giving way of the cylinder of the
hydraulic press the end of the tube fell through no greater space than i in.,
the momentum was such that beams calculated to bear enormous weights
were broken. At the time of the accident the pressure in the cylinder did
not exceed that which it was calculated to bear or that which is frequently
applied in hydraulic presses for other purposes. Some scientific observers
attributed the failure of the cylinder to the oscillating of the tube. It had
234 HYDRA UL1C PO WER.
been found when the similar tubes of the bridge over the Conway were
being raised, that when the engines at each end made their strokes simul-
taneously, a dangerous undulation was set up in the tube, and it was there-
fore necessary to cause the strokes of the engines to take place alternately.
The chains by which the tubes were suspended were made of flat bars 7 in.
wide and about I in. thick, being rolled in one piece, with expanded portions
about the " eye," through which the connecting-bolts pass. The links of
the chain consisted of nine and eight of these bars alternately the bars of
the eight-fold links being made a little thicker than those of the nine-fold,
so as to have the same aggregate strength. _ The mode in which the
hydraulic presses were made to raise the tubes is very clearly described by
Sir William Fairbairn in his interesting wdrk on the Conway and Britan-
nia Bridges, and his account of the mode of raising the tubes is here given
in his own words, but with letters referring to Fig. 171 :
" Another great difficulty was to be overcome, and it was one which pre-
sented itself to my mind with great force, viz., in what manner the enor-
FiG. 172. Head of Link-Bars.
mous weight of the tube was to be kept suspended when lifted to the height
of 6 ft., the proposed travel of the pump, whilst the ram was lowered and
again attached for the purpose of making another lift. Much time was
occupied in scheming means for accomplishing this object, and after exa-
mining several projects, more or less satisfactory, it at last occurred to me
that, by a particular formation of the links (of the chain by which the
tubes were to be suspended) we might make the chains themselves support
the tube. I proposed that the lower part of the top of each link, immedi-
ately below the eye, should be formed with square shoulders cut at right
angles to the body of the link (Fig. 172). When the several links forming
the chain E were put together, these shoulders formed a bearing surface, or
"hold," for the crosshead B attached to the top of the ram A of the hydraulic
pump. But the upper part of this crosshead, C C, was movable, or formed of
clips, which fitted the shoulders of the chain, and were worked by means
of right- and left-handed screws, and could be made either to clip the chain
immediately under the shoulders when the ram of the pump was down and
a lift about to be made, or be withdrawn at pleasure. Attached to the large
girders F were a corresponding set of clips, D D, which were so placed and ad-
justed as to height that when the ram of the pump was at the top there was
distance between the two sets of clips equal to twice the length of the travel
of the pump, or the length of the two sets of the links of the chain. To
HYDRA UL1C PO WER.
235
render the action of the apparatus more clear, suppose the tube resting on
the shelf of masonry in the position that it was left in after the operation
of floating was completed, and the chains attached, and everything ready
for the first lift, the ram of the pump being necessarily down. The upper
set of clips attached to the crosshead are forced under the shoulders of the
links, and the lower set of clips attached to the frames resting upon the
girders are drawn back, so as to be quite clear of the chain ; the pumps are
put into action simultaneously at both ends of the tube, and the whole
mass is slowly raised until it has reached a height of 6 ft. from its original
resting-place. The clips attached to the crosshead, B, have so far been
sustaining the weight, but it will be observed that by the time the pump has
ascended to its full travel, the square shoulders of another set of links have
come opposite to the lower clips on the girders, D, and these clips are
advanced under the shoulders of the links, and the rams being allowed to
descend a little, they in their turn sustain the load and relieve the pumps.
The upper clips being withdrawn, the rams are allowed to descend, and
after another attachment, a further lift of 6 ft. is accomplished ; and thus,
by a series of lifts, any height may be attained. The fitness of this appa-
ratus for its work was admirable, and the action of the presses was, as Mr,
Stephenson termed it, delighfuL"
FIG. 173. Apparatus to prove Transmission of Pressure in all directions.
FlG. 174. Pneumatic Tubes and Carriages.
PNEUMATIC DISPATCH.
WHEN the use of the electric telegraph became general, it was found
necessary to establish in all large towns branch stations, from which
messages were conveyed to the central station, or to which they were sent,
either by messengers who carried the written despatch, or by telegraphing
between the central and branch stations. The latter had the disadvan-
tages of rendering the original message liable to an additional chance of
incorrect transmission, and when an unusually great number of despatches
had to be sent to or from a particular branch station, there was necessarily
great delay in the forwarding of them. The plan of sending the written
messages between the central stations by bearers was unsatisfactory on
account of the time occupied. These inconveniences led to the invention
of a system for propelling, by the pressure of air, the papers upon which
the messages were written through tubes connecting the stations. This
was first carried into practice by the Electric and International Telegraph
Company, who, in this way, connected their central station in London with
their City branch stations. The apparatus was designed and erected by
Mr. L. Clark and Mr. Varley in 1854. The first tube laid down was from
Lothbury and the Stock Exchange a distance of 220 yards. This tube
had an inside diameter of only i^ in. ; but a larger tube, having a diameter
of T.\ in. was, some years afterwards, laid between Telegraph Street and
Mincing Lane a distance of 1,340 yards and was used successfully. In
236
PNE UMA TIC DISPA TCH. 237
these tubes the carriers were pushed forward by the pressure of the atmo-
sphere, a vacuum having been produced in front by pumping out the air.
The plan of propelling the carrier by compressing the air behind it was
also tried with good results, and, in fact, with a gain of speed ; for, while a
carrier occupied 60 or 70 seconds in passing from Telegraph Street to
Mincing Lane when drawn by a vacuum, it accomplished its journey in
50 or 55 seconds when it was shot forwards by compressed air, the diffe-
rence in pressure before and behind it being the same in each case. A
great deal of trouble was occasioned when the vacuum system was used,
by water being drawn in at the joints of the pipes. This water sometimes
accumulated to such a degree, especially after wet weather, that it com-
pletely overcame the power of the vacuum to draw the air through it, by
lodging in the vertical portions of the tube, where they passed to the upper
floors of the central station. This was remedied by improving the con-
struction of the joints, and by arranging a syphon for drawing off any
water which might be present. The best construction of the carrier was
another matter which required some experience to discover. It was found
that gutta-percha, or papier mache covered with felt, was the most efficient
material. The tubes found by Mr. Varley to give the best results were
formed of lead covered externally with iron pipes. The joints were made
perfectly smooth in the inside by means of a heated steel mandrel, on which
they were formed, so that the tube was of one perfectly uniform bore
throughout. An ingenious arrangement was also adopted by which the air
itself was made to do the work of opening and closing the valves, and
even that of removing the carrier from the tube : when, by a telegraphic
bell, rung from the distant station, it was announced that a carrier was
dispatched, the attendant at the receiving station had only to touch for a
second a knob marked " receive," which put the tube in communication
with the vacuum, in which condition it remained until the arrival of the
carrier, which, by striking against a pad of india-rubber, released the de-
tent, and thus cut off the vacuum. The carrier then fell out of the re-
ceiver and dropped into a box placed to catch it. When a carrier was sent,
it was placed in the tube, and a button marked " send " was touched, by
which a communication was opened with a vessel of compressed air and the
end of the tube behind the carrier was immediately closed by a slide, the
movements being all performed by the air itself. On the arrival of the
carrier, the boy at the receiving station rang an electric bell to signal its
reception ; and the sender then touched another knob marked " cut off,"
which caused the supply of compressed air to be cut off, and the slide to
be withdrawn from the end of the tube, which was then ready either to
receive or send carriers. By this arrangement there was no waste of power,
for the reservoirs of compressed air or of vacuum were only drawn upon
when the work was actually required to be done.
The tubes laid down by the Telegraph Company are still in active opera-
tion ; but at the new Central Telegraph Station the automatic valves of
Messrs. Clark and Varley appear to be dispensed with, and the attendants
perform the work of closing the tube, shutting off the compressed air, &c.,
by a few simple movements.
In December, 1869, Messrs. Siemens were commissioned by the Post-
master-General to lay tubes on their system from the General Post Office
to the Central Telegraph Station ; and the work having been accomplished
in February, 1870, and proving perfectly satisfactory after six weeks' trial,
it was decided to connect in the same manner Fleet Street and the West
238 PNEUMATIC DISPATCH.
Strand office at Charing Cross with the Central Station. The system
proposed by the Messrs. Siemens consisted in forming a circuit of tubes,
through which the carriers might be continually passing in one direction.
The diagram, Fig. 175, will give an idea of the manner in which it was
designed to arrange the tubes between the Central Telegraph Station and
Charing Cross. The arrows indicate the direction in which the air rushes
through the tubes ; A is the piston in the cylinder, and valves are so
arranged as to pump air out of the chamber v, and compress it into the
chamber P. This plan has been departed from, so far as regards the
Charing Cross Station, for want of space "there prevented the tube being
curved with a radius large enough to convey the carriers without their
being liable to stick, and consequently, these are not carried round in the
FIG. 175. Diagram of Tubes,
tube. The passage of carriers being stopped here, there are, in point of
fact, two tubes : an " up " tube and a " down " tube. But these are con-
nected by a sharp bend, so that though the tube is continuous as regards
the air current, it is interrupted as regards the circulation of the carriers.
The tubes are of iron, 3 in. internal diameter, made in lengths of about 19 ft. ;
and for the turns and bends, pieces are curved with a radius of 12 ft. Both
lines are laid side by side in a trench at about a foot depth below the streets.
The ends of the adjacent lengths form butt joints, so that the internal sur-
face is interrupted as little as possible, and there is a double collar to fasten
the lengths together. Arrangements are also made for removing from the
inside of the tubes water or dirt, or matter which may in any manner have
got in.
One special feature of Messrs. Siemens' invention is the plan by which
the carriers are introduced into and removed from the tube at any required
station without the circulation of the air being interfered with. The simple
yet ingenious mechanism by which this is effected will be understood from
the sections shown in Figs. 176 and 177. The figures represent the posi-
tion of the apparatus when placed to receive a carrier ; A' is the receptacle
into which the carrier is shot by the air rushing from A towards A". This
receptacle is Q-shaped, the curve of the D corresponding with that of the
tube, and the upper flat part admitting of a piece of plate glass being in-
serted, through which the attendant may perceive when a carrier arrives.
The progress of the carrier is arrested by a perforated plate, B, which
allows the air to pass. The ends of this receptacle are fixed in two parallel
plates, F F 7 , which also receive the ends of the plain cylinder, having pre-
cisely the same diameter as the tube, A. These plates are connected also
PNEUMATIC DISPATCH.
239
by cross-pieces, D E, the whole forming a sort of frame, which turns upon
E as a centre ; and according as it is put in the position shown by the plain
line in Fig. 176, or in that indicated by the dotted lines, causes the receiving
tube or the hollow cylinder to form part of the main tube, the cross-piece,
D, serving as a handle for moving the apparatus. It should be remarked
that the plates are made to fit the space cut out of the main tube with great
nicety, otherwise much loss of power would result from leakage. When
FIG. 176. Sending and Receiving Apparatus. Transverse
Section.
the hollow cylinder is in a line with the main tube, it is plain that the
carrier will not be stopped, as the tube is then continuous and uninter-
rupted. In this hollow cylinder also the carrier to be sent is deposited
after the rocking frame has been placed on it, Fig. 177 ; then, on drawing
the handle, the hollow cylinder is brought into the circuit, and the carrier
at once shoots off. To stop a carrier, the receiving-tube is put in by another
movement of the handle, and when the carrier arrives, it is removed by
bringing the open cylinder, or through tube, into the circuit, and thus
making the receiver ready for having the carrier pushed out of it by a rod
which is made to slide out by moving a handle. In order to avoid the
obstruction to the movement of the air which would be caused by the
carrier while in the receiving-tube, a pipe, G, is provided, through which
240
PNE UMA TIC DISPA TCH.
the air chiefly passes when the perforations of the plate, B, are closed by
the presence of a carrier. In this pipe at H is a throttle-valve, which
is opened by tappets, K, on the rocking frames when the receiver is in
circuit, and again closed when the open tube is substituted. The current
thus suffers no interruption by the action of the apparatus.
The carriers are small cylinders of gutta-percha, or papier madid, closed
at one end, and provided with a lid at the other. They are covered with
felt or leather, and at the front they are furnished with a thick disc of
drugget or leather, like the leathers of a common water-pump, but fitting
quite loosely in the tube. Such a carrier, being placed in the tube at the
Central Station, Fig. 175, will be carried by the current in the direction of
the arrows to the Charing Cross Station, where its progress will be inter-
rupted \ but according to the original plan it would continue its journey until
FlG. 177. Receiving Apparatus. Longitudinal Section.
it again reached the Central Station, where it would be intercepted by the
diaphragm, Fig. 175. But the carrier is stopped, if at any station the re-
ceiving-tube is placed in circuit, and this is done when an electric signal
indicates to the station that a carrier intended for it has been dispatched.
The tubes are worked on the " block system," that is, each section is known
to be clear before a carrier is allowed to enter it, and a bell is provided,
which is struck by a little lever, moved by each carrier in its passage
through, so that the attendant at each station knows when a carrier has
shot along the " through tube " of the station. This mode of working the
tubes renders the liability to accidents much less, but their carrying power
might be increased by dispatching carriers at regular and very short inter-
vals of time, when the limit would be only in the ability of the attendants
to receive a carrier and open the circuit in sufficient time to allow the next
following one to proceed without stoppage. The length of the lines of tube
laid down on this system, with the times required for the carriers to traverse
them, are stated below, the pressure and the vacuum being respectively
equal to the absolute pressures of 22 Ibs. and $% Ibs. on each square inch
of the reservoirs during the experiments :
PNEUMATIC DISPATCH. 241
Telegraph Station to General Post Office
General Post Office to Temple Bar
Yards.
852
1, 2O6
M. S.
i 54
2 28
Temple Bar to General Post Office
1, 2O6
2 IO
General Post Office to Telegraph Station
8 5 2
i '3
4,1 16
7 45
When the air was not compressed, but the vacuum only was used, the
air being allowed to enter the other end of the tube at the ordinary atmo-
spheric pressure, the time required for the carrier to traverse the circuit
was 10 minutes 23 seconds. In this case the vacuum was maintained, so
that the air was constantly in movement; but when the experiment was
tried by allowing the air in the tube to become stationary, placing a carrier
at one end, and then opening communication with the vacuum reservoir at
the other, the carrier required 13^ minutes to complete the journey. This
is explained by the fact of the greater part of the air having to be exhausted
from the tube before the carrier could be set in motion.
The utility and advantage of the pneumatic system is well seen when its
powers are compared with the wires. Thus, a single carrier, which may
contain, say, twenty-seven messages, can be sent every eight minutes ; and
since not more than one message per minute could be transmitted by tele-
graph wire, even by the smartest clerks, the real average being about two
minutes for each message, it follows that only four messages could be sent
in the time required for a single carrier to traverse the up tube, and to do
the work which could be done by the tube seven wires and fourteen clerks
would be required.
Mr. R. S. Culley, the official telegraph engineer, states as his experience
of the relative wear and tear of the carriers in these iron tubes and in
the smooth lead tubes, that it had been found necessary to renew the felt
covering of eighty- two dozen of the carriers used for three months in the
iron tubes, while in the same period only thirty-eight dozen of those used
in the lead tubes required to be re-covered. The numbers of carriers
sent and received by the pneumatic tubes on the 2ist of November, 1871,
between 1 1 a.m. and 4 p.m., were :
Iron tubes 135
in. lead tubes 1,170! T /w,
in. 527) I>697
The mileage of the carriers sent was much greater in the lead than in
the iron pipes, although the total lengths of each kind were respectively
5,974 yards and 6,826 yards. The result is remarkable, as showing the
effect of apparently slight differences when their operation is summed up
by numerous repetitions.
The circuit at Charing Cross having been divided on account of the
difficulty mentioned above, the tubes act as separate pipes one for " up "
traffic (i.e., to Central Telegraph Station), the other for " down" (i.e., from
the Central Station). The air, however, still accomplishes a circuit, being
exhausted at one end and compressed at the other. A very noticeable and
curious difference is found between the times required by the carriers to
perform the " up " and the " down" journeys :
16
242 PNE UMA TIC DISPA TCH.
An " up " carrier requires 6*5 minutes
A " down " carrier requires I2'5
Together 19-0
When two pipes were separated at Charing Cross so that the air no
longer circulated from one to the other, but both were left open to the
atmosphere, while the " up " pipe was worked by a vacuum only and the
" down " pipe by pressure only, the times wefe for
An"up" carrier 8*5 minutes
A " down " carrier 11*3
Together 19-8
The time, therefore, for the whole circuit was practically the same
whether the tubes were worked by a continuous current of air or separated,
and one worked by the' vacuum and the other by pressure. It was also
seen that when the tubes were connected so that the air current was con-
tinuous, and the pump producing a vacuum at one end and a compression
at the other, the neutral point where the pressure was equal to that of the
atmosphere was not found midway between the two extremities that is,
at Charing Cross Station but much nearer the vacuum end. When the
tubes were disconnected, it appeared, as already shown by the figures given
above, that there was a gain of speed on the down journey, and a loss of
speed on the up journey ; and as the requirements of the traffic happened
to require greater dispatch for the down journeys, the tubes have been
worked in this manner.
It has been proposed to convey letters by pneumatic dispatch between
the General and Suburban Post Offices, and the Post Office authorities
have even consulted engineers on the practicability of sending the Irish
mails from London to Holyhead by this system. It was calculated,
however, that although the scheme could be carried out, the proportion
of expense for great speeds and long distances would be enormously
increased. A speed of 130 miles per hour was considered attainable, but
the wear and tear of the carriers would be extremely great at this high
velocity, and it was considered doubtful whether this circumstance might
not operate seriously against the practical carrying out of the plan. The
prime cost would be very great, for the steam power alone which would be
requisite would amount to 390 horse-power for every four miles. We thus
see that very high velocities would introduce a new order of difficulties in
the practical working. The case as regards the velocity with which electric
signals can be sent round the world is very different.
An amusing hoax appears to have been perpetrated by some waggish
telegraph clerk on an American gentleman at Glasgow, with regard to the
pneumatic system of sending messages; for the gentleman sent to the
" Boston Transcript" a letter, in which he relates that having sent a tele-
graphic message from Glasgow to London, he received in a few minutes a
reply which indicated a mistake somewhere, and then he went to the
Glasgow telegraph office, and asked to see his message.
" The clerk said, ' We can't show it to you, as we have sent it to London/
' But,' I replied, ' you must have my original paper here. I wish to see that/
He again said, ' No, we have not got it : it is in the post office at London/
- What do you rnean ?' I asked. ' Pray, let me see the paper I left here half
PNEUMATIC DISPATCH. 243
an hour ago.' ' Well, 1 said he, ' if you must see it, we will get it back in a
few minutes, but it is now in London.' He rang a bell, and in five minutes
or so produced my message, rolled up in pasteboard. ... I inquired
if I might see a message sent. ' Oh, yes ; come round here.' He slipped
a number of messages into the pasteboard scroll, popped it into the tube,
and made a signal. I put my ear to the tube and heard a slight rumbling
noise for seventeen seconds, when a bell rang beside me, indicating that
the scroll had arrived at the General Post Office, 400 miles off. It almost
took my breath away to think of it."
. In the journal called " Engineering," into which this curious letter was
copied, it is pointed out that to travel from London to Glasgow, a distance
of 405 miles, in seventeen seconds, the carrier must have moved at the rate
of 24 miles per second, or 5 miles a second faster than the earth moves in
its orbit, and the carrier would have in such a case become red hot by its
friction against the tube before it had travelled a single second.
A plan of conveying, not telegraph messages, but parcels, was proposed
and carried into effect some time ago, and more recently has been applied to
lines of tubes in connection with the General Post Office. These tubes pass
from Euston Station down Drummond Street, Hampstead Road, Totten-
ham Court Road, to Broad Street, St. Giles's, whence, with a sharp bend,
they proceed to the Engine Station at Holborn, and then to the Post Office.
The tube is formed chiefly of cast iron pipes of a Q-shaped section, 4 ft. 6 in.
wide and 4 ft. high, in 9 ft. lengths. There are curves with radii of 70 ft.
and upwards, and at these parts the tube is made of brickwork and not of
iron. The carriages run on four wheels, and are so constructed that the
ends fit the tubes nearly, and the interval left is partly closed by a project*
ing sheet of india-rubber all round. The carriages are usually sent through
the tube in trains of two or three, and the trains are drawn forward by an
exhausting apparatus formed by a fan, 22 ft. in diameter, worked by two
horizontal steam engines having cylinders 24 in. in diameter and a stroke
of 20 in. The air rushes by centrifugal force from the circumference of
the fan, and is drawn in at the centre, where the exhaust effect is produced.
The tubes which convey the air from the main tube open into the latter
at some distance from its extremities, which are closed by doors, so that
after the carriage passes the entrance of the suction tube, its momentum is
checked by the air included between it and the doors, which air is, of
course, compressed by the forward movement of the carriage. At the
proper moment the doors are opened by a self-acting arrangement, and the
carriage emerges from the tube. There are two lines of tube an " up "
and a " down " line and means are provided for rapidly transferring the
carriages from one to the other at the termini. The time occupied in the
transit is about 12 minutes. Some of the inclines have as much slope as
I in 14, yet loads of 10 or 12 tons weight are drawn up these gradients with-
out difficulty. The mails are sent between Euston Station and the Post
Office by means of these tubes. Passengers have also made the journey as
an experiment by lying down in the carriages. Fig. 174 shows one of the
carriages and the entrance to the tubes.
Great expectations have been formed by some persons of the applica-
tions of pneumatic force. Some have suggested its use for moving the
trains in the proposed tunnel between England and France. But calcula-
lations show that for long distances and large areas such modes of impart-
ing motion are enormously wasteful of power. Thus, in the tunnel alluded
to it must be remembered that not only the train, but the whole mass of
16 2
244 PNE UMA TIC DISPA TCH.
air in the tunnel would have to be be drawn or pushed forward. The
drawing of a train through by exhausting the air would be very similar to
drawing it through by a rope ; in fact, the mass of air may be regarded as
a very elastic rope, but by no means a very light one, or one that could be
drawn through without some opposing force which has a certain resem-
blance to friction coming into operation. Indeed, it has been calculated
that in the case named, only five per cent, of the total power exerted by
the engines in exhausting the air could possityy produce a useful effect in
moving the train.
Air has also been made the medium for conveying intelligence in another
manner than by shooting written messages through tubes, for its property
of transmitting pressure has been applied to produce at a distance signals
like those made use of in the electric telegraph system. A few years ago,
an apparatus for this object was contrived by Signer Guattari, whose in-
vention is known as the " Guattari Atmospheric Telegraph." In this there
is a vessel charged with compressed air by a compression-pump, and the
pressure is maintained by the same means, while the reservoir is being
drawn upon. A valve is' so arranged that the manipulator can readily
admit the compressed air to a tube extending to the station where the
signals are received, at which the pressure is made to move a piston as
often as the sender opens the valve. This movement is made to convey
intelligence when a duly regulated succession of impulses is sent into the
tube the receiving apparatus being arranged either to give visible or
audible signals, or to print them on slips of paper, according to any of the
methods in use with the electric telegraph. Certain advantages over the
electric system are claimed for this pneumatic telegraph as, for example,
greater simplicity and less liability to derangement. The tubes, which are
merely leaden piping of small .bore, are also exempt from the inconvenient
interruptions which electric communication sometimes suffers from elec-
trical disturbances in the atmosphere. The pneumatic system is easily
arranged, and from its great simplicity any person can in a few hours learn
to use the whole apparatus, while it is calculated that the expense of con-
struction and working would not be above half of that incurred for the
electric system. For telegraphs in houses, ships, warehouses, and short
lines, this invention will doubtless prove very serviceable ; but for long
lines a much greater force of compression would be required, and the time
needed for the production of an impulse at the distant ends of the tubes
would be considerably increased.
FIG. 178. The Sommeiller Boring Machines.
ROCK BORING.
A LLUSION has already been made to one great characteristic of our
*T*- age, namely, the replacement, in every department of industry, of
manual labour by machines. A brief notice of even the main features of
the various contrivances which have been made to take the place of men's
hands would more than occupy this volume. Accordingly, we must omit
all reference to many branches of manufacture, although the products may
be of very great utility, and the processes of very high interest ; and in
taking one example here and. another there, we must be guided mainly by
the extent and depth of the influence which the new invention appears
destined to exert. This consideration has, with scarcely an exception,
decided the selection of the topics already discussed, and it has also de-
termined the introduction of the present article, which relates to machines
of no less general importance than the rest, although at first sight it might
seem to enter upon the details of merely a special branch of industry. But
so general are the interests connected with the subject we are about to
lay before our readers, that we are not sure it would not have been more
logical to have placed the present article before all the rest. For whence
comes the iron of which our steam engines, tools, rails, ships, cannon,
bridges, and printing presses are made? whence 'comes the fuel which
supplies force to the engines? whence come, in fine, the substances
which form the materiel of every art ? Plainly from the earth the nurse
245
246 ROCK BORING.
and the mother of all, and in most cases from the bowels of the earth, for
her treasures are hidden far below the surface the coal, and the ores of
iron and other metals, are not ready to our hand, exposed to the light of
day. The railways also, and the canals, can be made only on condition that
we cut roads through the solid rocks, and pierce with tunnels the towering
mountains. Hence the tools which enable us to penetrate into the sub-
stance of the earth present the highest general interest from a practical
point of view, and this interest is enhanced by the knowledge of the struc-
ture and past history of our planet acquired in such operations.
The operations by which solid rocks are penetrated in the sinking of
shafts for mines, or in the driving of tunnels, drifts, headings, galleries, or
cuttings for railways, mines, or other works, are easily understood. In the
first place a number of holes perhaps 3 ft. or 4 ft. deep and 2 in. or 3 in. in
diameter are formed in the rock. The holes are then charged with gun-
powder or other explosive materials, a slow-burning match is adjusted, the
miners retire to a safe distance, the explosion takes place detaching,
shattering, and loosening masses of the rock more or less considerable ; and
then gangs of workmen clear away the stones and debris which have been
detached by the explosion, and the same series of operations is renewed.
The holes for the blasting charges are formed by giving repeated blows
on the rock with a kind of chisel called a jumper the end of which is
formed of very hard steel, so that the rock is in reality chipped away. The
dtbris resulting from this operation is cleared away from time to time by
a kind of auger or some similar contrivance. But for many purposes it is
necessary to drill holes in rocks to great depths, hundreds of feet perhaps,
as for example, in order to ascertain the nature of underlying strata, or to
verify the presence of coal or other minerals before the expense of sinking
a shaft is incurred. These bore-holes were commonly formed in exactly
the same manner as the blast-holes already mentioned, by repeated blows
of a chisel or jumper, which was attached to the end of a rod ; and as the
hole deepened, additional lengths of rod were joined on, and the rods were
withdrawn from time to time to admit of the removal of the debris by
augers, or by cylinders having a valve at the bottom. The reciprocating
movement is given to the chisels and rods either by hand or by steam or
water power. When the length of the rods becomes considerable, of course
the difficulty of giving the requisite blows in rapid succession is greatly
increased, for the whole length of rods has to be lifted each time, and if
allowed to fall with too much violence, the breaking of the chisel or the
rods is the inevitable result The time requisite for drawing out the rods,
removing the fragments chipped out, and again attaching the rods and
lowering, also increases very much as the bore gets deeper. Messrs.
Mather and Platt, the Manchester engineers, have, in order to obviate
these difficulties, constructed machines in which the chipping or cutting is
done by the fall of a tool suspended from a rope, the great advantage re-
sulting from the arrangement being the facility and rapidity with which
the tools used for the cutting and for the removal of the debris are lowered
to their work and drawn up. It is necessary in using the juniper, whether
in cutting blast-holes or bore-holes, to give the tool a slight turn after eac&
blow, in order that the rock may be chipped off all round, and the action of
the tool equalized. Many attempts have been made to drill rocks after the
fashion in which iron is drilled that is, by drilling properly so called, in
which the tool has a rapid rotary motion. But even in comparatively soft
rock, it is found that no steel can sufficiently withstand the abrading action
ROCK BORING. 247
of the rock, for the tool becomes quickly worn, and makes extremely slow
progress. We shall have presently to return to the subject of bore-holes ;
but now let us turn our attention to an example which will illustrate the
nature and advantages of the machinery which has in recent times been
applied to work the jumpers by which the holes for blasting are formed.
THE MONT CENIS TUNNEL.
/ "P HE successful construction, by the direction of Napoleon, of a broad and
* easy highway from Switzerland into Italy, crossing the lofty Alps amid
the snows and glaciers of the Simplon, has justly been considered a feat of
skill redounding to the glory of its designers. But we have recently wit-
nessed a greater feat of engineering skill, for we have seen the Alps con-
quered by the stupendous work known as the Mont Cenis Tunnel. This
tunnel is 7\ English miles in length ; but it is not the mere length which
has made the undertaking remarkable. The mountain which is pierced by
the tunnel is formed entirely of hard rock, and what added still more to
the apparently impracticable character of the proposal when first announced
was the circumstance that it was quite impossible to sink vertical shafts, so
that the work could not, as in the usual process, be carried on at several
points simultaneously, but must necessarily be continued from the two
extremities only, a restriction which would occasion a vast loss of time and
much expense, to say nothing of the difficulties of ventilating galleries of
more than three miles in length. The reader must bear in mind that the
importance of this question of ventilation depends not simply on the re-
newing of the air contaminated by the respiration of the workmen, but on
the quick removal of the noxious gases produced in the explosions of the
blasting charges. A work surrounded by such difficulties would probably
have never been attempted had not Messrs. Sommeiller and Co. invited
the attention of engineers to an engine of their invention, worked by com-
pressed air, and capable of automatically working "jumpers" which could
penetrate the hardest rock. These rock-boring machines, having been ex-
amined by competent authorities in the year 1857, were pronounced so
efficient that the execution of the long-spoken-of Alpine tunnel was at once
resolved upon, and before the close of that year the work had actually been
commenced, after a skilful and accurate survey of the proposed locality
had been made, and the direction of the tunnel set out. The tunnel does
not pass through Mont Cenis, although the post road from St. Michel to
Susa passes over part of Mont Cenis, which gives its name to the pass.
The mountain really pierced by the tunnel is known as the Grand Vallon,
and the tunnel passes almost exactly below its summit, but at a depth the
perpendicular distance of which is as nearly as possible one mile. The
northern end of the tunnel is near a village named Fourneaux.
Pending the construction of the Sommeiller machines, and other machi-
nery which was to supply the motive force, the work of excavation was
commenced at both ends, in 1857, in the ordinary manner, that is, by hand
labour, and in 1858 surveys of the greatest possible accuracy were mean-
while made, in order that the two tunnels might be directed so that they
would meet each other in the heart of the mountain. The reader will at
once perceive that the smallest error in fixing on the direction of the two
straight lines which ought to meet each other would entail very serious
248 SOCK BORING.
consequences. The difficulties of doing this may be conceived when we
remember that the stations were nearly 8 miles apart, separated by rugged
mountains, in a region of snows, mists, clouds, and winds, over which the
levels had to be taken, and a very precise triangulation effected. So suc-
cessfully were these difficulties overcome, and so accurately were the mea-
surements and calculations made, that the junction of the centre lines of
the completed tunnel failed by only a few inches^ a length utterly insigni-
cant under the conditions.
The work was carried on by manual labour only, until the beginning
of 1 86 1, for it was found, on practically testing the machinery, that many
important modifications had to be made before it could be successfully em-
ployed in the great work for which it was designed. After the machinery
had been set to work, at the Bardonneche end, breakages and imperfec-
tions of various parts of the apparatus, or the contrivances for driving it,
caused delay and trouble, so that during the whole of 1861 the machines
were in actual operation for only 209 days, and the progress made averaged
only 1 8 in. per day, an advance much less than could have been effected
by manual labour. The engineers, not disheartened or deterred by these
difficulties and disappointments, encountered them by making improve-
ment after improvement in the machinery as experience accumulated, so
that a wonderful difference in the rate of progress showed itself in 1862,
when the working days numbered 325, and the average rate of advance
was three feet nine inches per day.
At the Fourneaux extremity more time was required for the preparation
of the air-compressing machinery, and the machines had been at work in
the other extremity, with more or less interruption, for nearly two years
before the preparations at Fourneaux were completed.
The illustration at the head of this article, Fig. 178, represents the Som-
meiller machines at work, the motive power being compressed air, conveyed
by tubes from receivers, into which it is forced until the pressure becomes
equal to that of six atmospheres, or 90 Ibs. per square inch. The com-
pression was effected by taking advantage of the natural heads of water,
which were made to act directly in compressing the air ; the pressure due
to a column of water 160 ft. high being made to act upwards, to compress
air, and force it through valves into the receivers ; then the supply of water
was cut off, and that which had risen up into the vessel previously con-
taining air was allowed to flow out, drawing in after it through another
valve a fresh supply of air ; and then the operations were repeated by the
water being again permitted to compress the air, and so on, the whole of
the movements being performed by the machinery itself. The compressed
air, after doing its work in the cylinders of the boring tools, escaped into
the atmosphere, and in its outrush became greatly cooled, a circumstance
of the greatest possible advantage to the workmen, for otherwise, from the
internal warmth of the earth, and that produced by the burning of lights,
explosions of gunpowder, and respiration, the heat would have been into-
lerable. At the same time, the escaping air afforded a perfect ventilation
of the workings while the machines were in action. At other times, as after
the explosion of the charges, it was found desirable to allow a jet of air to
stream out, in order that the smoke and carbonic acid gas should be quickly
cleared away. Even had the work been done by manual labour alone, a
plentiful supply of compressed air would have been required merely for
ventilation, so that there was manifest advantage in utilizing it as the
motive power of the machines.
ROCK BORING.
249
FIG. 179. Transit by Diligence over Mont Cenis.
The experience gained in the progress of the work suggested from time
to time many improvements in the machinery and appliances, which finally
proved so effectual that the progress was accelerated beyond expectation.
At the end of 1864, when the machines had been in work about four years,
it was calculated that the opening of the tunnel might be looked for in the
course of the year 1875. But in point of fact it happened that on the 2$th
December, 1870, perforator No. 45 bored a hole from Italy into France, by
piercing the wall of rock, about 4 yards thick, which then separated the
workings from each other. The centre lines of the two workings, as set
out from the different sides of the mountain, failed to coincide by only a
foot, that set out on the Fourneaux side being this much higher than the
other, but their horizontal directions exactly agreeing. The actual length
of the tunnel was found to be some 1 5 yards longer than the calculated
length, the calculation having given 7*5932 miles for the length, whereas by
actual measurement it was found to be 7*6017 miles. The heights above
the sea-level of the principal points are these :
Feet.
Fourneaux, or northern entrance 3>8oi
Bardonneche, or southern entrance 4> 2 36
Summit of tunnel 4> 2 4-6
Highest point of mountain vertically over the tunnel 95 2 ?
250 ROCK BORING.
The tunnel is lined with excellent brick and stone arching, and it is con-
nected with the railways on either side by inclined lines, which are in part
tunnelled out of the mountain, so that the extremities of the tunnel referred
to above are not really entered by the trains at all ; but these lateral tunnels
join the other and increase the total distance traversed underground to
very nearly 8 miles, or more accurately, 7 '9^806 miles. The time required
by a train to pass from one side to the other is about 25 minutes. What a
contrast is this to the old transit over the Mont Cenis pass by "diligence" !
We have the scene depicted in Fig. 179, where we perceive, sliding down
or toiling up the steep zigzag ascents, a series of curious vehicles drawn by
horses with perpetually jingling bells.
The cost of the Mont Cenis Tunnel was about .3,000,000 sterling, or
upwards of ,200 per yard ; but as a result of the experience gained in this
gigantic work, engineers consider that a similar undertaking could now be
carried out for half this cost. It is supposed that the profit to the contrac-
tors for the Mont Cenis Tunnel was not much less than 100 per yard.
The greatest number of men directly employed on the tunnel at one time
was 4,000, and the total horse-power of the machinery amounted to 860.
From 1857 to 1860, by hand labour alone, 1,646 metres were excavated;
from 1 86 1 to 1870 the remaining 10,587 metres were completed by the
machines. The most rapid progress made was in May, 1865, in which
month the tunnel was driven forward at one end the length of 400 feet.
When the workings were being carried through quartz, a very hard rock,
the speed was greatly reduced as, for example, during the month of April,
1866, when the machines could not accomplish more than 35 ft.
The perforators used in the Mont Cenis Tunnel were worked by com-
pressed air, conveyed to a small cylinder, in which it works a piston, to the
rod of which the jumper is directly attached. The air, being admitted be-
hind the piston, impels the jumper against the rock, and the tool is then
immediately brought back by the opening of a valve, which admits com-
pressed air in front of the piston, at the same time that the air which has
driven it forward is allowed to escape, communication with the reservoir
of compressed air having previously been closed behind it. The whole
of these movements are automatic, and they are effected in the most
rapid manner, four or five blows being struck in every second, or. between
two and three hundred in one minute. Water was constantly forced into
the holes, so as to remove the debris as quickly as it was formed. A number
of these machines were mounted on one frame, supported on wheels, run-
ning on the tramway which was laid along the gallery. The perforators had
no connection with each other, for each one had its own tube for the con-
veyance of compressed air, and its own tube to carry the water used for
clearing out the hole, and the cylinders were so fixed on the frames that
the jumpers could be directed in any desired manner against any selected
portion of the rock. They were driven to an average depth of about -2\ ft.,
and the process occupied from forty to fifty minutes. When a set of holes
had thus been formed, the cylinders were shifted and another series com-
menced, until about eighty holes had been bored, the formation of the
whole number occupying about six or seven hours, and the holes being so
arranged that the next operation would detach the rock to the required
extent. The flexible tubes, which conveyed the air and water to the ma-
chines from the entrances, were then removed from the machines and
stowed away, the frame bearing the perforators was drawn back along the
tramway, 'workmen advanced whose duty it was to wipe out the holes,
ROCK BORING.
251
charge them with powder, and fire the fuses ready for the explosion. When
the slow-burning match was ignited, all retired behind strong wooden bar-
ricades, at a safe distance, until the explosion had taken place ; and after
the compressed air had been allowed to stream into the working, so as to
clear away all the smoke and gas generated by the explosion, the workmen
ran up on a special tramway the waggons which were to carry away all
the detached stones ; and when this had been done, the floor was levelled,
the tramways were lengthened, and the frame bearing the drilling machines
was brought up to begin a fresh series of operations, which were usually
repeated about twice in the course of every twenty-four hours. A great part
of the rock consists of very hard calcareous schist, interspersed with veins
of quartz, one of the hardest of all rocks, which severely tries the temper
of the steel tools, for a few blows on quartz will not unfrequently cause the
point of a jumper to snap off.
ROCK-DRILLING MACHINES.
O EVERAL forms of rock-drills, or perforators, have been constructed on
*-2 the same principle as that used in the Mont Cenis Tunnel, and a de-
scription of one of them will give a good notion of the general principle of all.
We select a form devised by Mr. C. Burleigh, and much used in America,
where it has been very successfully employed in driving the Hoosac Tunnel,
effecting a saving in the cost of the drilling amounting to one-third of the
expense of that operation, and effecting also a still greater saving of time,
for the tunnel, which is 5 miles in length, is to be completed in four years,
instead of twelve, as the machines make an advance of 1 50 ft. per month,
whereas the rate by hand labour was only 49 ft. per month. These ma-
chines are known as the " Burleigh Rock Drills," and have been patented
in England for certain improvements by Mr. T. Brown, who has kindly
supplied us with the following particulars :
The Burleigh perforator acts by repeated blows, like Bartlett and Som-
meiller's, but its construction is more simple, and the machine is lighter
and not half the size, while its action is even superior in rapidity and force.
The Burleigh machines are composed of a single cylinder, the compressed
air or steam acting directly on the piston, without the necessity of fly-
wheel, gearing, or shafting. The regular rotation of the drills is obtained
by means of a remarkably simple mechanical contrivance. This consists
of two grooves, one rectilinear, the other in the form of a spiral cut into the
piston-rod. In each of these channels, or grooves, is a pin, which works
freely in their interior : these pins are respectively fixed to a concentric
ring on the piston-rod. A ratchet wheel holds the ring, and the pin slides
into the curve, causing it to turn always in the same direction, without
being able to go back. By this eminently simple piece of mechanism, the
regular rotation of the drill-holder is secured. The slide-valve is put into
motion by the action of a projection, or ball-headed piston-rod, on a double
curved momentum-piece, or trigger, which is attached to the slide-rod or
spindle by a fork, thus opening and shutting the valve in the ascent and
descent of the piston. Fig. 180 represents one of the machines attached
in this instance by a clamp to the frame of a tripod. The principal parts
252
ROCK BORING.
of the machine are the cylinder, with its piston, and the cradle with guide-
ways, in which the cylinder travels. The action of the piston is similar to
that of the ordinary steam hammer, with this difference, that, in addition
FlG. 1 80. Bur high Rock Drill on Tripod.
to the reciprocating, it has also a rotary, motion. The drill-point is held in
a slip-socket, or clamp, at the end of the piston-rod, by means of bolts and
nuts. The drill-point rotates regularly at each stroke of the piston, making
a complete revolution in every eighteen strokes. For hard rocks it is gene-
rally made with four cutting edges, in the form of a St. Andrew's cross,
ROCK BORING. 253
thus striking the rock in seventy-two places in one revolution, each cut-
ting edge chipping off a little of the stone at each stroke in advance of the
one preceding. The jumper makes, on an average, 300 blows per minute,
and such is the construction of the machine, that the blows are of an
elastic, and not of a rigid, nature, thus preventing the drill-point from being
soon blunted. It has been found in practice, that a drill-point used in the
Burleigh machine can bore on an average 20 ft. of Aberdeen granite with-
out re-sharpening. As the drill pierces the rock, the machine is fed down
the guide-ways of the cradle by means of the feed-screw (see Fig. 180),
according to the nature of the rock and the progress made. When the
cylinder has been fed down the entire length of the feed-screw, and if
a greater depth of hole is required, the cylinder is run back, and a longer
drill is inserted in the socket at the end of the piston-rod. The universal
clamp may be attached to any form of tripod, carriage, or frame, according
to the requirements of the work to be done ; it enables the machines to
work vertically, horizontally, or at any angle.
The following advantages are claimed for this machine : Any labourer
can work it ; it combines strength, lightness, and compactness in a remark-
able degree, is easily handled, and is not liable to get out of order. No
part of the mechanism is exposed ; it is all enclosed within the cylinder, so
there is no risk of its being broken. It is applicable to every form of rock-
work, such as tunnelling, mining, quarrying, open cutting, shaft-sinking, or
submarine drilling ; and in hard rock, like granite, gneiss, ironstone, or
quartz, the machine will, according to size, progress at the incredible rate
of four inches to twelve inches per minute, and bore holes from in. up to
5 in. diameter. It will, on an average, go through 120 ft. of rock per day,
making forty holes, each from 2 ft. to 3 ft. deep, and it can be used at any
angle and in any direction, and will drill and clear itself to any depth up
to 20 ft.
The following extract from the " Times," September 24th, 1873, gives an
account of some experiments with the machine, made at the meeting of
the British Association in that year, before the members of the Section
of Mechanical Science :
" Yesterday, considerable interest was taken in this section, as it had
been announced that a * Burleigh Rock Drilling Machine ' would be work-
ing during the reading of a paper by Mr. John Plant. The machine was
not, however, in the room, but was placed in the grounds outside, where it
was closely examined by the members after the adjournment, and seen in
full operation, boring into an enormous block of granite. The aspect of the
machine cannot be called formidable in any respect, for it looks like a big
garden syringe, supported upon a splendid tripod ; but when at work, under
about Solbs. pressure of compressed air, it would be deemed a very revolu-
tionary agent indeed, against whose future power the advocates for manual
labour in the open quarry, the tunnel, and even the deep mine, may well
look aghast. Placed upon a block of granite a yard deep, the machine was
handled and its parts moved by the fair hands of many of the lady asso-
ciates of scientific proclivites ; but once the source of power was turned on,
the drill began its poundings, eating holes 2 in. in diameter in the block
of granite, and making a honeycomb of it as easily as a schoolboy would
demolish a sponge cake. It pounds away at the rate of 300 strokes, and
progresses forward about 12 in., in the minute, making a complete revolu-
tion of the drill in eighteen strokes, and keeping the hole free of the
pounded rock. The machine was fixed to work at any angle, almost as
254
ROCK BORING.
FIG. 1 8 1. BurleigJi Rock Drill on Movable Column.
readily as a fireman can work his hose ; and its adaptation to a wide range
of stone-getting, by drilling for blasting, and cutting large blocks for build-
ing and engineering, with a saving of capital and labour, was admitted by
many members of the section. The tool is called the ' Burleigh Rock
' Drill,' invented by Mr. Charles Burleigh, a gentleman hailing from Massa-
chusetts, United States. The patent is the property of Messrs. T. Brown
and Co., of London. The principal feature of this new machine is, that it
imitates in every way the action of the quarryman in boring a hole in the
rock."
Many forms of carriages and supports have, from time to time, been
made to suit the work for which the ' Burleigh ; machines have been
required. The machine is attached to these carriages, or supports, by
means of the universal clamp, by which it can be worked in any direction
and at any angle. Of these carriages we select for notice only two forms,
one of which is shown in Fig. 181. This carriage can be used to great
ROCK BORING. 255
advantage in adits and drifts. It consists of an upright column, with a
screw clamp-nut for holding and raising or lowering the machine, the
whole being mounted on a platform which can slide right across the
carriage, and thus the machine can be brought to work on any point of a
heading. It is secured in position by means of a jack-screw in the top of
the column ; and as the carriage is mounted on wheels, it is easily moved
to permit of blasting. Fig. 182 represents a carriage which is the result of
many years' experience with mining machinery, and it is considered a very
perfect appliance. It is constructed of wood and iron, and it runs on wheels.'
FIG. 182. Burleigh Rock Drills mounted on a Carriage.
The supports for the machines, four of which may be mounted at once, are
two horizontal bars, the lower of which can be raised or lowered, as may
be necessary. The two parallel sides of the carriage are joined only at the
upper side, and there is nothing to prevent it from being run into the head-
ing, though the way between the rails may be heaped up with broken rock,
if only the rails are clear. Drilling, and the removal of the broken rock,
may then proceed simultaneously ; for, by means of a narrow gauge inside
the carriage rails, small cars may be taken right up to the debris. It is
made in different sizes, to suit the dimensions of the tunnel required. To
give the carriage steadiness in working, it is raised from the wheels by
jack-screws, and held in position by screws in a similar manner to the car-
riage represented in Fig. 181.
An extremely interesting system of drilling cocks totally different from
that on which the machines we have just described are constructed has,
within the last few years, been introduced by Messrs. Beaumont and
Appleby. What does the reader think of boring holes in rocks wieh dia-
monds ? It has long been a matter of common knowledge that the dia-
256 ROCK BORING.
mond is the hardest of all substances, and that it will scratch and wear
down any other substances, while it cannot itself be scratched or worn by
anything but diamond. In respect to wearing down or abrading hard stones,
the diamond, according to experiments recentlymade by Major Beaumont,
occupies a position over all other gems and minerals to a degree far beyond
that which has been generally attributed to it ; for in these experiments it
was found that on applying a diamond, or rather a piece of the "carbonate"
about to be described, fixed in a suitable holder, to a grindstone in rapid
rotation, the grindstone was quickly worn down ; but on repeating a similar
experiment with sapphires and with corundum, it was these which were
worn down by the grindstone. Without, on the present occasion, entering
into the natural history of the diamond, we may say that there are, besides
the pure colourless transparent crystals so highly prized as gems, several
varieties of diamond, and that those which are tinged with pink, blue, or
yellow, are far from having the same value for the jeweller. Then there is
another impure variety called boort, which appears to be employed only to
furnish a powder by which the brilliants are ground and polished. In the
diamond gravels of Brazil, from which we derive our regular supply of these
gems, there was discovered in 1842 a curious variety of dark-coloured
diamond, in which the crystalline cleavage, or tendency to split in certain
directions (which belongs to the ordinary stones), appears to be almost
absent : and the substance might be regarded as a transition form between
the diamond and graphite but for its hardness. This substance was until
lately used for the same purposes as boort, which is a nearer relative of the
pure crystal and like it, splits along certain planes. It received from the
miners the name of *' carbonado ? 2d\& with regard to the application we are
considering, it has turned out to be a sort of Cinderella among diamonds ;
for its unostentatious appearance is more than compensated for by its
surpassing all its more brilliant sisters in the useful property to which re-
ference has been made. This Brazilian term is doubtless the origin of
the English name by which the substance in question is known among
the English diamond merchants, who call it " carbonate" an unfortunate
word, for it is used in chemistry with an entirely
different signification. " Carbonate" it is, how-
ever, which supplies the requirements of the rock-
drill, and the selected stones are set in a crown,
or short tube, of steel, represented by c in Fig.
183. In this they are secured as follows: holes
are drilled in the rim of the tube, and each hole
is then cut so that a piece of the diamond exactly
fits it, and when this piece has been inserted, the
metal is drawn round by punches, so as almost
to cover the stone, leaving only a point projecting,
b b. The portions of the crown between the stones
are somewhat hollowed out, as at a, for a purpose
which will presently be mentioned. The crown
thus set with the boring gems is attached to the
end of a steel tube, by which it is made to rotate
with a speed of about 250 revolutions per minute while pressed against the
rock to be bored. Water is forced through the steel tube, and passing out
between the rock and the crown, especially under the hollows, c c, makes
its escape between the outside of the boring-tube and the rock, thus wash-
ing away all the dttris and keeping the drill cool. The pressure with
ROCK BORING. 257
which the crown is forced forward depends, of course, on the nature of the
rock to be cut, and varies from 400 Ibs. to 800 Ibs. In this way the hardest
rocks are quickly penetrated sometimes, for example, at the rate of 4 in.
per minute, compact limestone at 3 in., emery at 2 in., and quartz at the rate
of i in. per minute. It is found that, even after boring through hundreds
of feet of such materials, the diamonds are not in the least worn, but as
fit for work as before : they are damaged only when by accident one of the
stones gets knocked out of its setting ; and this machine surpasses all in the
rapidity with which it eats its way through the firmest rocks. This, it must
be observed, is the special privilege of the diamond drill that, since the
begemmed steel crown and the boring-rods are alike tubular, the rock
is worn away in an annular space only, and a solid cylinder of stone is
detached from the mass, which cylinder passes up with the hollow rods,
where, by means of certain sliding wedges, it is held fast, and is drawn
away with the rods.
When the diamond drill is used merely for driving the holes for blasting,
this cylinder of rock is not an important matter ; but there is an application
of the drill where this cylinder is of the greatest value, furnishing as it does
a perfect, complete, and easily preserved section of the whole series of
strata through which the drill may pass when a bore-hole is sunk in the
operation of searching for minerals (which is so significantly called in the
United States " prospecting," a phrase which seems to be making its way
in England in mining connections) ; for the core is uniformly cylindrical,
the surface is quite smooth, and any fossils which may be present come up
uninjured, so far as they are contained in the solid core, and thus the strata
are readily recognized. Contrast this with the old method, where the bore-
hole in prospecting is made by the reciprocating action imparted to a steel
tool, and merely the pounded material is obtained, usually in very small
fragments, by augers or sludge-pumps : the fossils, which might afford the
most valuable indications, crushed and perhaps incapable of being recog-
nized ; and instead of the beautifully definite and continuous cylinder, a
mere mass of debris is brought up. In the prospecting-bores the diameter
of the hole is from 2 in. to 7 in. The size adopted depends on the nature
of the strata to be penetrated, and on the depth to which it is proposed to
carry the boring. When the strata are soft, the operation is commenced
with a bore of 7 in., and when this has been carried to an expedient depth,
the danger of the sides of the hole falling in is avoided by putting down
tubes, and then the diamond drill, fixed to tubes of a somewhat smaller
diameter, will be again inserted, and the boring recommenced; or the hole
can be widened, so as to receive the lining-tubes. Of course, in boring
through hard rocks, such as compact limestones, sandstone, &c., no lining-
tubes are necessary.
In a very interesting paper, read before the members of the Midland
Institute of Mining Engineers, by Mr. J. K. Gulland, the engineer of the
Diamond Rock-Boring Company, who have the exclusive right of working
the patents for this remarkable invention, that gentleman concludes by
remarking that " the leading feature of the diamond drill is that it works
without percussion, thus enabling the holing of rocks to be effected by a fat
simpler class of machinery than any which has to strike blows. Every
mechanical engineer knows, often enough to his cost, that he enters upon
a new class of difficulties when he has to recognize it as a normal state of
things with any machinery he is designing that portions of it are brought
violently to rest. These difficulties increase very much when the power, as
17
258 ROCK BORING.
in the case of deep bore-holes, has to be conveyed for a considerable dis-
tance. Where steel is used a percussive action is necessitated, as, if a
scraping action is used, the drill wears quicker than the rock. The extra-
ordinary hardness of the diamond places a new tool in our hands, as its
hardness, compared with ordinary rock, say granite, is practically beyond
comparison. Putting breakages on one side, a piece of " carbonate " would
wear away thousands of times its own bulk of granite. Irrespective of the
private and commercial success which this invention has attained, it is a
boon to a country such as ours, where minerals constitute in a great mea-
sure our national wealth and greatness."
The advantages of the diamond drill may be illustrated by the case of
what is termed the Sub-Wealden Exploration. From certain geological
considerations, which need not be entered upon here, several eminent
British and continental geologists have arrived at the conclusion that it is
probable that coal underlies the Wealden strata of Kent and Sussex, and
that it may be perhaps met with at a workable depth. If such should really
prove to be the case, the industrial advantages to the south of England
would be very great, for the existence of coal so comparatively near to the
metropolis would prove not only highly lucrative to the owners of the coal,
but confer a direct benefit upon thousands by cheapening the cost of fuel.
A number of property owners and scientific men, having resolved that the
matter should be tested by a bore, raised funds for the purpose, and a 9 in.
bore had been carried down to a depth of 313 ft. in the ordinary manner,
when a contract was entered into with the Diamond Rock-Boring Com-
pany for a 3 in. bore extracting a cylinder of rock 2 in. in diameter. The
company, as a precautionary measure, lined the old hole with a 5 in. steel
tube ; and in spite of some delay caused by accidents, they increased the
depth of the hole to 1,000 ft. in the interval from 2nd February, 1874, to
1 8th June, 1874 the progress of the work being regarded with the greatest
interest by the scientific world. Unfortunately ( the further progress of the
work has been prevented by an untoward event, namely, the breaking of
the boring-rod, or rather tube ; and, although the company is prepared
with suitable tackle for extracting the tubes in case of accidents of this
kind, and generally succeeds in lifting them by a taper tap, which, entering
the hollow of the tube, lays hold of it by a few turns yet, in this instance,
where there have been special difficulties, the extraction of so great a
length of tubes is, as the reader may imagine, by no means an easy task.
Six attempts have been made to remove the boring-rods which have
dropped down ; but so difficult has this operation proved, that, all tfyese
efforts having failed, it has been decided to abandon the old work and
commence a new boring on an adjacent spot. A contract has been entered
into with the Diamond Boring Company, who have undertaken to com-
plete the first 1,000 ft. for .600, which is only ^200 more than it would
have cost to completely line the old bore-holes with iron tubes an opera-
tion which was contemplated by the committee in charge of the exploration.
The terms agreed to by the company are very favourable to the promoters
of the Sub-Wealden Exploration, although the cost of the second 1 ,000 ft.
will be ,3,000 more ; and the committee are relying upon the public for
contributions to enable them to carry on their enterprise. It is most pro-
bable that funds will be forthcoming, and should the boring result in the
finding of coal measures beneath the Wealden strata, all the nation will be
the richer and participate in the advantages resulting from an undertaking
carried on by private persons. Already a totally unexpected source of
POCK BORING.
259
FIG. 1 84. The Diamond Drill Machinery for deep Bores.
wealth has bsen met with by the old bore showing the existence of con-
siderable beds of gypsum in these strata, and the deposits of gypsum are
about to be worked. Whether coal be found or not found, there is no doubt
that a bore-hole going down 2,000 ft. will greatly increase our geological
knowledge, and may reveal facts of which we have at present no conception.
The boring-tubes, it maybe remarked, are made in 6ft. lengths, and are
so contrived that the joints are nearly flush that is, there is no projection
17 2
2 6o ROCK BORING.
at the junctions of the tubes. Fig. 184 is engraved from a photograph of
the machinery used for working the diamond drill when boring a hole for
" prospecting." This looks at first sight a very complicated machine, but
in reality each part is quite simple in its action, and is easily understood
when its special purpose has been pointed out. We cannot, however, do
more than indicate briefly the general nature of the mechanism. The
reader will on reflection perceive that, although the idea of causing a rod
to rotate in a vertical hole may be simple, yet in practically carrying it out
a number of different movements and actions have to be provided for in
the machinery. The weight of the rods cannot be thrown on the cutters,
nor borne by the moving parts of the machine hence the movable disc-
shaped weights attached to the chains are to balance the weight of the
boring-rods as the length of the latter is increased. There must also be a
certain amount of feed given to the cutters, regulated and adjusting itself
to avoid injurious excess : hence a nut which feeds the drill is encircled by
a friction-strap in which it merely slips round without advancing the cutter
when the proper pressure is exceeded. There must be means of throwing
this into or out of gear, or advancing the tool in the work and of withdraw-
ing it hence the handles seen attached to the brake-straps. Water must
be drawn from some convenient source, and caused to pass down the drill-
tube hence the force-pump seen in the lowest part of the figure. The
rods must be raised by steam power and lowered by mechanism under
perfect control hence suitable gearing is provided for that purpose.
The reader may be interested in learning what is the cost of " prospect-
ing " with this unique machinery. The company usually undertake to
bore the first 100 ft. for ^40, but the next 100 ft. cost ;8o that is, for
200 ft. ^120 would be charged ; the third looft. would cost ^120 that is
to say, the first 300 ft. would cost ^240, and so on each lower 100 ft. cost-
ing 40 more than the 100 ft. above it. Some of the holes bored have
been of very great depth, and have been executed in a marvellously short
space of time. Thus, in 54 days, a depth of 902 ft. was reached at Girrick
in a boring for ironstone ; another for coal at Beeston reached 1,008 ft. ;
and at Walluff in Sweden 304^ ft. were put down in one week !
These machines are peculiarly suitable for submarine boring, for they
work as well under water as in the air ; and they will no doubt be put into
requisition in the preliminary experiments about to be made for that great
project which bids fair to become a sober fact the Channel Tunnel be-
tween England and France ; and as, by the time these pages will be before
the public, the work of the greatest and boldest rock-boring yet attempted
will have commenced, and the scheme itself will be the theme of every
tongue, the Author feels that the present article would be incomplete with-
out some particulars of the great enterprise.
THE CHANNEL TUNNEL.
PHE notion of connecting England and France by a submarine line of
railways is not of the latest novelty, but has been from time to time
mooted by the engineers of both countries. The most carefully prepared
scheme, however, is embodied in the joint propositions of Sir J. Hawkshaw
ROCK BORING. 261
and Messrs. Brunlees and Low among English engineers ; and those of
M. Gamond on the French side, which these gentlemen have prepared at
the invitation of the promoters of the scheme, give the clearest and most'
authentic account of the considerations on which this gigantic enterprise
will be based, and from this document we draw the following passages :
The undersigned engineers, some of whom have been engaged for a
series of years m investigating the subject of a tunnel between France and
England, having attentively considered those investigations and the facts
which they have developed, beg to report thereon jointly for the informa-
tion of the committee.
These investigations supported the theory that the Straits of Dover were
not opened by a sudden disruption of the earth at that point, but had been
produced naturally and slowly by the gradual washing away of the upper
chalk ; that the geological formations beneath the Straits remained in the
original order of their deposit, and were identical with the formations of the
two shores, and were, in fact, the continuation of those formations.
Mr. Low proposed to dispense entirely with shafts in the sea, and to com-
mence the work by sinking pits on each shore, driving thence, in the first
place, two small parallel driftways or galleries from each country, connected
at intervals by transverse driftways. By this means the air could be made
to circulate as in ordinary coal-mines, and the ventilation be kept perfect
at the face of the workings.
Mr. Low laid his plans before the Emperor of the French in April, 1867,
and in accordance with the desire of his Majesty, a committee of French
and English gentlemen was formed in furtherance of the project.
For some years past Mr. Hawkshaw's attention has been directed to
this subject, and ultimately he was led to test the question, and to ascer-
tain by elaborate investigations whether a submarine tunnel to unite the rail-
ways of Great Britain with those of France and the Continent of Europe
was practicable.
Accordingly, at the beginning of the year 1866, a boring was commenced
at St. Margaret's Bay, near the South Foreland; and in March, 1866, an-
other boring was commenced on the French coast, at a point about three
miles westward of Calais ; and simultaneously with these borings an exa-
mination was carried on of that portion of the bottom of the Channel lying
between the chalk cliffs on each shore.
The principal practical and useful results that the borings have deter-
mined are that on the proposed line of the tunnel the depth of the chalk
on the English coast is 470 ft. below high water, consisting of 175 ft. of
upper or white chalk and 295 ft. of lower or grey chalk ; and that on the
French coast the depth of the chalk is 7 50 ft. below high water, consisting
of 270 ft. of upper or white chalk and 480 ft. of lower or grey chalk ; and
that the position of the chalk on the bed of the Channel, ascertained from
the examination, nearly corresponds with that which the geological inquiry
elicited.
In respect to the execution of the work itself, we consider it proper to
drive preliminary driftways or headings under the Channel, the ventilation
of which would be accomplished by some of the usual modes adopted in
the best coal-mines.
As respects the work itself, the tunnel might be of the ordinary form, and
sufficiently large for two lines of railway, and to admit of being worked
by locomotive engines, and artificial ventilation could be applied ; or it
262 ROCK BORING.
might be deemed advisable, on subsequent consideration, to adopt two
single lines of tunnel. The desirability of adopting other modes of trac-
tion may be left for future consideration.
Such are the essential passages of the report which, in 1868, was sub-
mitted to the Government of the Emperor Louis Napoleon, and was made
the subject of a special commission appointed by the Emperor to inquire
into the subject in all its bearings. The commission presented its report
in 1869, a-nd these are the chief conclusions contained in it
I. The commission, after having considered the documents relative to
the geology of the Straits, which agree in establishing the continuity, homo-
geneity, and regularity of level of the grey chalk between the two shores
of the Channel,
Are of opinion- that driving a submarine tunnel in the lower part of this
chalk is an undertaking which presents reasonable chances of success.
Nevertheless they would not hide from themselves the fact that its exe-
cution is subject to contingencies which may render success impossible.
II. These contingencies maybe included under two heads: either in
meeting with ground particularly treacherous a circumstance which the
known character of the grey chalk renders improbable ; or in an influx of
water in a quantity too great to be mastered, and which might find its way
in either by infiltration along the plane of the beds, or through cracks
crossing the body of the chalk.
Apart from these contingencies, the work of excavation in a soft rock like
grey chalk appears to be relatively easy and rapid ; and the execution of a
tunnel, under the conditions of the project, is but a matter of time and
money.
III. In the actual state of things, and the preparatory investigations
being too incomplete to serve as a basis of calculation, the commision will
not fix on any figure of expense or the probable time which the execution
of the permanent works would require.
The chart, Fig. 185, and the section, Fig. 186, will give an idea of the
course of the proposed tunnel, which will connect the two countries almost
at the nearest points. The depth of the water in the Channel along the
proposed line nowhere exceeds 180 ft. little more than half the height of
St. Paul's Cathedral, which building would, therefore, if sunk in the midst
of the Channel, stiii form a conspicuous object rising far above the waves.
But the tunnel will pass through strata at least 200 ft. below the bottom of
the Channel, rising towards each end with a moderate gradient ; and from
the lower points of these inclines the tunnel will rise slightly with a slope
of i in 2,640 to the centre, or just sufficient for the purposes of drainage.
On the completion of the tunnel a double line of rails will be laid down in
it, and trains will run direct from Dover to Calais. Companies have already
been formed in England under the presidency of Lord Richard Grosvenor,
and in France under that of M. Michel Chevalier, and the legislation of
each country has sanctioned the enterprise. Verily the real magician of
our times is the engineer, who, by virtually abolishing space, time, and
tide, is able to transport us hither and thither, not merely one or two
almost like the magicians we read of in the " Arabian Nights," with their
enchanted horses or wonderful carpets but by hundred? and by tens of
hundreds.
ROCK BORING.
263
FIG. 185. Chart of the Channel Tunnel.
The " Daily News " of January 22nd, 1875, in presenting its readers with
a chart of the proposed tunnel, offered also the following sensible and
interesting comment on the subject :
" This long-debated project has at length emerged from the region of
264
ROCK BORING.
speculation, and is entering the stage of practical
experiment. On this side the Channel a company
has been formed to carry out the work, and on the
other side the French Minister of Public Works
has presented to the Assembly a Bill authorizing a
French company to co-operate with the English en-
gineers. The enterprise is one worthy of the nations
which have in the present generation joined the two
shores of the Atlantic by an electric cable, and cut a
ship canal through the Isthmus of Suez, and of the
age which has obliterated the old barrier of the Alps.
All these gigantic undertakings seemed almost as
bold in conception and as difficult of execution as the
great work now about to commence. Those twenty
miles of sea have long been crossed by telegraph
lines ; they will soon be bridged, as it were, by
splendid steamers ; but even our own generation,
accustomed as it is to gigantic engineering works,
,has scarcely regarded the construction of a railway
underneath the waves as within the reach of possi-
bility. M. Thome* de Gamond, who first made the
suggestion five and thirty years ago, was long re-
garded as an over-sanguine person, who did not
recognize the inevitable limits of human skill and
power. A tunnel under twenty miles of stormy sea
seemed very much like an engineer's dream, and it
is only within the last few years that it has been
regarded as a feasible project. Of its possibility,
however, there seems now to be no manner of doubt.
It is merely a stream of sea-water, and not a fissure
in the earth, which divides us from the Continent
Prince Metternich was right in speaking of it as a
ditch. The depth is nowhere greater than one hun-
dred and eighty feet ; and so far as careful soundings
can ascertain the condition of the soil underneath
the water, it consists of a smooth unbroken bed of
' chalk. The success of the experiment depends on this
bed of chalk being continuous and whole. Should
any very deep fissure exist, which is extremely im-
probable, the tunnel may probably not be driven
through it. But given, what every indication shows
to exist, a homogeneous chalk bed some hundreds
of feet in thickness, the driving of a huge bore for
twenty miles through it is a mere question of time,
money, and organization, and as the engineers have
these resources at their command, they are sanguine,
and we may even say confident, of success.
"The method by which it is proposed that the
excavation shall be made is in some respects simi-
lar to that which was successfully employed in
tunnelling the Alps. Mont Cenis was pierced by
machinery adapted to the cutting of hard rock ;
the chalk strata under the Channel are to be bored
1 N
B
ROCK BORING.
265
FlG. 187. View of Dover.
by an engine, invented by Mr. Dickenson Brunton, which works in the
comparatively soft strata like a carpenter's auger. A beginning will be
made simultaneously on both sides of the Channel, and the effort will at
first be limited to what we may describe as making a clear hole through
from end to end. This small bore, or driftway as it is called, will be some
seven or nine feet in diameter. If such a communication can be success-
fully made, the enlargement will be comparatively easy. Mr. Brunton's
machine is said to cut through the chalk at the rate of a yard an hour. We
believe that those which were used in the Mont Cenis Tunnel cut less than
a yard a day of the hard rock of the mountain. Two years, therefore,
ought to be sufficient to allow the workers from one end to shake hands
with those from the other side. The enlargement of the driftway into the
completed tunnel would take four years' more labour and as many millions
of money. The millions, however, will easily be raised if the driftway is
made, since the victory will be won as soon as the two headways meet
under the sea. One of the great difficulties of the work is shared with the
Mont Cenis Tunnel, the other is peculiar to the present undertaking. The
Alps above the one, and the sea above the other, necessarily prevent the
use of shafts. The work must be carried on from each end ; and all the
debris excavated must be brought back the whole length of the boring, and
all the air to be breathed by the workmen must be forced in. The provi-
sion of a fit atmosphere is a mere matter of detail. In the great Italian
tunnel the machines were moved by compressed air, which, being liberated
when it had done its work, supplied the lungs of the workers with fresh
266 ROCK BORING.
oxygen. The Alpine engineers, however, started from the level of the
earth : the main difficulty of the Submarine Tunnel seerrts to be that it
must have as its starting-point at each end the bottom of a huge well
more than a hundred yards in depth. The Thames Tunnel, it will be re-
membered, was approached, in the days when it was a show place, by a
similar shaft, though of comparatively insignificant depth. This enterprise
may indeed be said to bear something like the relation to the engineering
and mechanical skill of the present day which Brunei's great undertaking
bore to the powers of an age which looked on the Thames Tunnel as the
eighth wonder of the world. Probably the danger which will be incurred
in realizing the larger scheme is less than that which Brunei's workmen
faced.
"It is, of course, impossible for any estimate to be formed of the risks
of this enormous work. They have been reduced to a minimum by the
mechanical appliances now at our disposal, but they are necessarily con-
siderable. The tunnel is to run, as we understand, in the lower chalk, and
there will be, as M. de Lesseps told the French Academy, some fifty yards
of soil a solid bed of chalk, it is hoped between the sea-water and the
crown of the arch. Moreover, an experimental half-mile is to be under-
taken on each side before the work is finally begun ; the engineers, in fact,
will not start on the journey till they have made a fair trial of the way.
Altogether the beginning seems to us to be about to be made with a com-
bination of caution and boldness which deserves success, even though it
should be unable to command it. Unforeseen difficulties may arise to
thwart the plans, but the enterprise, so far, is full of promise. The open-
ing of such a communication between this country and the Continent will
be a pure gain to the commercial and social interests on both sides. It
obliterates the Channel so far as it hinders direct communication, yet keeps
it intact for all those advantages of severance from the political complica-
tions of the Continent, which no generation has more thoroughly appre-
ciated than our own. The commercial advantages of the communication
must necessarily be beyond all calculation. A link between the two chief
capitals of Western Europe, which should annex our railway system to the
whole of the railways of the Continent, would practically widen the world
to pleasure and travel and every kind of enterprise. The 300,000 travellers
who cross the Channel every year would probably become three millions
if the sea were practically taken out of the way by a safe and quick com-
munication under it. The journey to Paris would be very little more than
that from London to Liverpool. It is, however, quite needless to enlarge
on these advantages. The Channel Tunnel is the crowning enterprise of
an age of vast engineering works. Its accomplishment is to be desired
from every point of view, and, should it be successful, it will be as benefi-
cent in its results as the other great triumphs of the science of our time."
FIG. 1 88.
LIGHT.
/ T*HE foregoing pages have been devoted to the description of inventions
* or operations in which mechanical actions are the most obvious
features. Some of the contrivances described have for their end and object
the communication of motion to certain bodies, others the arrangement of
materials in some definite form, and all are essentially associated with trie
idea of what is called matter. But we are now about to enter on another
region a region of marvels where all is enchanted ground a region in
which we seem to leave far behind us our grosser conceptions of matter,
and to attain to a sphere of more refined and subtile existence. For we
267
2 68 LIGHT.
are about to show some results of those beautiful investigations in which
modern science has penetrated the secrets of Nature by unfolding the
laws of light
" Light
Ethereal, first of things, quintessence pure."
The diversity and magnificence of the spectacles which, by day as well
as by night, are revealed to us by the agency of light, have been the theme
of the poet in every age and in every country. It cannot fail to arrest the
attention to find Science declaring that all the loveliness of the landscape,
the fresh green tints of early summer and the golden glow of autumn,
the brilliant dyes of flowers, of insects, of birds, the soft blue of the cloud-
less sky, the rosy hues of sunset and of dawn, the chromatic splendour of
rubies, emeralds, and other gems, the beauties of the million-coloured
rainbow, are all due to light to light alone, and are not qualities of the
bodies themselves, which merely seem to possess the colours. The follow-
ing quaint stanzas, in which a poet of the seventeenth century addresses
" Light " have a literal correspondence with scientific truth :
" All the world's bravery, that delights our eyes,
Is but thy several liveries;
Thou the rich dye on them bestowest,
Thy nimble pencil paints this landscape as thou goest.
"A crimson garment in the rose thou wearest:
A crown of studded gold thou bearest ;
The virgin lilies, in their white,
Are clad but with the lawn of almost naked light.
"The violet, Spring's little infant, stands
Girt in thy purple swaddling-bands:
On the fair tulip thou dost dote ;
Thou clothest it in a gay and parti-coloured coat."
All these beauties are indeed derived from the imponderable and invisible
agent, light ; and the variety and changefulness of the effects we may con-
stantly observe show that light possesses the power of impressing our visual
organs in a thousand different ways, modified by the surrounding circum-
stances, as witness that ever-shifting transformation scene the sky. In
the skies of such a climate as that of England there are ceaseless changes
and ever-beautiful effects, producing everywhere more perfect and diversi-
fied pictures than the richest galleries can show. In the night how changed
is the spectacle, when the sun's more powerful rays are succeeded by the soft
light of the moon, sailing through the azure star-bestudded vault! What
limitless scope for the artist is afforded by these innumerable modifications
of a single subtile agent, in light and shade, brightness and obscurity, in the
contrasts and harmonies of colours, and in the countless hues resulting from
their mixtures and blendings !
It will be necessary, before attempting to explain the discoveries and
inventions which prove how successfully science, aided by the powerful
mathematical analysis of modern times, has acquired a knowledge of the
ways of light, to discuss such of the ordinary phenomena as have a direct
bearing upon the subjects to be considered.
FIG. 189. Rays.
SOME PHENOMENA OF LIGHT.
IT may be considered as a matter of common experience that light is
able to pass through certain bodies, such. as air and gases, pure water,
glass, and a number of other liquids and solids, which, by virtue of this
passage of light, we term transparent, in opposition to another class ol
bodies, called opaque, through which light does not pass. That light tra-
verses a vacuum may be held as proved by the light of the sun and stars
reaching us across the interplanetary spaces ; but it may also be made the
subject of direct experiment by an apparatus described below, tig. 190.
Another fact, very obvious from common observation, is that light usually
travels in straight lines. Some familiar experiences may be appealed to
for establishing this fact. For example, every one has observed that the
beams of sunlight which penetrate an apartment through any small open-
ing pursue their course in perfectly straight lines across the atmosphere, in
270 LIGHT.
which their path is rendered visible by the floating particles of dust. It is
by reason of the straightness with which rays of light pursue their course
that the joiner, by looking along the edge of a plank, can judge of its truth,
and that the engineer or surveyor is able by his theodolite and staff to set
out the work for rectilinear roads or railways. On a grander scale than in
the sunbeam traversing a room, we witness the same fact in the effect repre-
sented in Fig. 189, where the sun. concealed from direct observation, is seen
to send through openings in the clouds, beams that reveal their paths by
lighting up the particles of haze or mist contained in the atmosphere. It
is not the air itself which is rendered visible ; but whenever a beam of sun-
light, or of any other brilliant light, is allowed to pass through an apartment
which is otherwise kept dark, the track of the beam is always distinctly
visible, and, especially if the light be concentrated by a lens or concave
mirror, the fact is revealed that the air, which under ordinary circum-
stances appears so pure and transparent, is in reality loaded with floating
particles, requiring only to be properly lighted up to show themselves.
FIG. 190.
Professor Tyndall, in the course of some remarkable researches on the
decomposition of vapours by light, wished to have such a glass tube as that
represented in Fig. 190, filled with air perfectly free from these floating par-
ticles. When the beam of the electric lamp passed through the exhausted
tube, no trace of the existence of anything within the tube was revealed,
for it appeared merely like a black gap cut out of the visible rays that tra-
versed the air ; thus proving that light, although the agent which makes all
things become visible, is itself invisible that, in fact, we see not light, but
only illuminated substances. When, however, air was admitted to the tube,
even after passing through sulphuric acid, the beam of the light became
clearly revealed within the tube, and it was only by allowing the air to stream
very slowly into the exhausted glass tube through platinum pipes, packed
with platinum gauze and intensely heated, that Professor Tyndall succeeded
in obtaining air " optically empty," that is, air in which no floating particles
revealed the track of the beams. The destruction of the floating matter
by the incandescent metal proves the particles to be organic ; but a more
convenient method of obtaining air free from all suspended matter was
found by Professor Tyndall to be the passing of the air through a filter of
cotton wool. It must not be supposed that it is only occasionally, or in
dusty rooms, laboratories, or lecture-halls, that the air is charged with
organic and other particles
"As thick as motes in the sunbeams."
" The air of our London rooms," says Tyndall, " is loaded with this
LIGHT.
271
organic dust, nor is the country air free from its pollution. However ordi-
nary daylight may permit it to disguise itself, a sufficiently powerful beam
causes the air in which the dust is suspended to appear as a semi-solid,
rather than as a gas. Nobody could, in the first instance, without repug-
nance, place the mouth at the illuminated focus of the electric beam and
inhale the dust revealed there. Nor is this disgust abolished by the reflec-
tion that, although we do not see the nastiness, we are drawing it in our
lungs every hour and minute of our lives. There is no respite to this con-
tact with dirt ; and the wonder is, not that we should from time to time
suffer from its presence, but that so small a portion of it would appear to
be deadly to man." The Professor then goes on to develope a very re-
markable theory, which attributes such diseases as cholera, scarlet fever,
small pox, and the like, to the inhalation of organic germs which may form
part of the floating particles. But we must return to our immediate subject
by a few words on the
VELOCITY OF LIGHT.
FlG. 191. Telescopic appearance of Jupiter and Satellites.
T T may be stated at once, that this velocity has the amazing magnitude
-"- of 185,000 miles in one second of time, and that the fact of light re-
quiring time to travel was first discovered, and the speed with which it
does travel was first estimated, about 200 years ago, by a Danish astro-
nomer, named Roemer, by observations on the eclipses of the satellites of
Jupiter. The satellites of Jupiter are four in number, and as they revolve
272
LIGHT.
nearly in plane of the planet's orbit, they are subject to frequent eclipses
by entering the shadow cast by the planet ; in fact, the thVee inner satel-
lites at every revolution. Fig. 191 represents the telescopic appearance of
the planet, from a drawing by Mr. De La Rue, and in this we see the well-
known "belts," and two of the satellites, one of which is passing across the
face of the planet, on which its shadow falls, and is distinctly seen as a
round black spot, while the other may be noticed at the lower right-hand
corner of the cut. The satellite next the planet (lo) revolves round its
primary in about 42 1 hours, and consequently it is eclipsed by plunging
into the shadow of Jupiter at intervals of 42^ hours, an occurrence which
must take place with the greatest regularity as regards the duration of the
intervals, and which can be calculated by known laws when the distance
of the satellite from the planet has been determined. Nevertheless, Roemer
observed that the actual intervals between the successive immersions of
lo in the shadow of Jupiter did not agree with the calculated period of
rotation when the distance between Jupiter and the earth was chang-
ing, in consequence chiefly of the movement of the latter (for Jupiter re-
quires nearly twelve years to complete his revolution, and may, therefore,
be regarded as stationary as compared for a short time with the earth).
Roemer saw also, that when this distance was increasing, the observed
intervals between the successive eclipses were a little greater, and that
when the distance was decreasing they were a little less, than the calculated
period. And he found that, supposing the earth, being at the point of its
orbit nearest to Jupiter, to recede from that planet, the sum of all the re-
tardations of the eclipses which occur while the earth is travelling to the
farthest point of its orbit, amounts to 16^ minutes, as does also the sum of
the deficiencies in the period when the earth, approaching Jupiter, is passing
from the farthest to the nearest point of her orbit. While, however, the
earth is near the points in her orbit farthest from, or nearest to Jupiter, the
distance between the two planets is not materially changing between suc-
cessive eclipses, and then the observed intervals of the eclipses coincide
with the period of the satellite's rotation. The reader will, after a little
reflection, have no difficulty in perceiving that the 16^ minutes represent the
time which is required by the light to traverse the diameter of the earth's
orbit ; or, if he should have any difficulty, it may be removed by comparing
the case with the following.
Let us suppose that from a railway terminus trains are dispatched every
quarter of an hour, and that the trains proceed with a common and uni-
form velocity of, say, one mile per minute. Now, a person who remains
stationary, at any point on the railway, observes the trains passing at
regular intervals of fifteen minutes, no matter at what part of the line
he may be placed. But now, let us imagine that a train having that very
instant passed him, he begins to walk along the line towards the place from
which the trains are dispatched : it is plain that he will meet the next train
before fifteen minutes he would, in fact, meet it a mile higher up the line
than the point from which he began his walk fourteen minutes before ; but
the train, taking a minute to pass over this mile, would pass his point of
departure just fifteen minutes after its predecessor. And our imaginary
pedestrian, supposing him to continue his journey at the same rate, would
meet train after train at intervals of fourteen minutes. Similarly, if he
walked away from the approaching trains, they would overtake him at
intervals of sixteen minutes. And again, it would be easy for him to cal-
culate the speed of the trains, knowing that they passed over each point of
LIGHT. 273
the line every fifteen minutes. Thus, suppose him to pass down the line a
distance known to be, say, a quarter of a mile ; suppose he leaves his sta-
tion at noon, the moment a train has passed, and that he takes, say an
hour, to arrive at his new station a quarter of a mile lower ; here, ob-
serving a train to pass at fifteen seconds after one o'clock, and knowing
that it passed his original station at one, he has a direct measure of the
speed of the trains. Here we have been explaining a discovery two cen-
turies old ; but our purpose is to prepare the reader for an account of how
the velocity of light has been recently measured in a direct manner, and
it certainly appears a marvellous achievement that means have been found
to measure a velocity so astounding, not in the spaces of the solar system,
or along the diameter of the earth's orbit, but within the narrow limits of
an ordinary room ! The reliance with which the results of these direct
measures will be received, will be greatly increased by the knowledge of
the astronomical facts with which they show an entire concordance. In
FlG. 192.
taking leave of Roemer, we may mention that his discovery, like many
others, and like some inventions which have been described in this book,
did not for some time find favour with even the scientific world, nor was
the truth generally accepted, until Bradley's discovery of the aberration of
light completely confirmed it.
To two gifted and ingenious Frenchmen we are indebted for independent
measurements of the velocity of light by two different methods. The general
arrangement of M. Fizeau's method is represented in Fig. 192, in which
the rays from a lamp, L, after passing through a system of lenses, fall upon
a small mirror, M N, formed of unsilvered plate-glass inclined at an angle of
45 to the direction of the rays ; from this they are reflected along the axis of
a telescope, T, by the lens of which being rendered parallel, they become a
cylindrical beam, B, which passes in a straight line to a station, D, at a
distance of some miles (in the actual experiment the lamp was at Suresnes
and the other station at Montmartre, 5^ miles distant) whence the beam is
reflected along the same path, and returns to the little plate of glass at
M N, passing through which it reaches the eye of the observer at E. At w
is a toothed wheel, the teeth of which pass through the point F, where the
18
274 LIGHT.
rays from the lamp come to a focus ; and as each tooth pksses, the light is
stopped from issuing to the distant station. This wheel is capable of re-
ceiving a regular and very rapid rotation from clockwork in the case, C,
provided with a register for recording the number of its revolutions. If the
wheel turns with such a speed that the light permitted to pass through
one of the spaces travels to the mirror and back in exactly the same time
that the wheel moves and brings the next space into the tube, or the second
space, or the third, or any space, the reflected light will reach the spectator's
eye just as if the wheel were stationary ; but if the speed be such that a
tooth is in the centre of the tube when the light returns from the mirror,
then it will be prevented from reaching the spectator's eye at all, so long
as this particular speed is maintained, but either a decrease or an increase
of velocity would cause the luminous image to reappear. Speeds between
those by which the light is seen, and those by which it entirely disappears,
cause it to appear with merely diminished brilliancy. It is only necessary
to observe the speed of the wheel when the light is at its brightest, and when
it suffers complete eclipse, for then the time is known which is required
for space and tooth respectively to take the place of another space and
hence the time required for the light to pass to the mirror and back is
found.
M. Foucault's method is similar in principle to that used by Wheatstone
in the measurement of the velocity of electricity. He used a mirror which
was made to revolve at the rate of 700 or 800 turns per second, and the
arrangement of the apparatus was such as to admit of the measurement of
the time taken by light to pass over the short space of about four yards !
More recently, however, he has modified and improved his apparatus by
adopting a most ingenious plan of maintaining the speed of the mirror at
a determined rate, which he now prefers should be 400 turns per second,
while the light is reflected backwards and forwards several times, so that it
traverses a path of above 20 yards in length. The time taken by the light
to travel this short distance is, of course, extremely small, but it is accu-
rately measured by the clockwork mechanism, and found to be about the
f a second ! The results of these experiments of Foucault's
make the velocity of light several thousand miles per second less than that
deduced from the astronomical observation of Roemer and Bradley, in
which the distance of the earth from the sun formed the basis of the calcu-
lations ; and hence arose a surmise that this distance had been over-esti-
mated. That such had, indeed, been the case was confirmed almost im-
mediately afterwards by a discussion among the astronomers as to the
correctness of the accepted distance, the result of which has been that the
mean distance, which was formerly estimated at 95 millions of miles, has,
by careful astronomical observations and strict deductions, been now esti-
mated at between 91 and 92 millions of miles. The recent transit of Venus,
December 9th, 187310 observe which the Governments of all the chief
nations of the world sent out expeditions derives its astronomical and
scientific importance from its furnishing the means of calculating, with
greater correctness than has yet been attained, the distance of the earth
from the sun.
LIGHT.
275
REFLECTION OF LIGHT.
LONG before plate glass backed by brilliant quicksilver ever reflected
the luxurious appointments of a drawing-room ; long before looking-
glass ever formed the mediaeval image of " ladye fair " ; long before the
haughty dames of imperial Rome were aided in their toilettes by specula;
long before the dark-browed beauties of Egypt peered into their brazen
mirrors ; long, in fact, before men knew how to make glass or to polish
metals, their attention and admiration must have often been riveted by
those perfect and inverted pictures of the landscape, with its rocks, trees,
and skies, which every quiet lake and every silent pool presents. Enjoyment
of the spectacle probably prompted its imitation by the formation artifi-
cially of smooth flat reflecting surfaces ; and no doubt great skill in the pro-
JL M
FIG. 194.
duction of these, and their application to purposes of utility, coquetry, and
luxury, preceded by many ages any attempt to discover the laws by which
light is reflected. The most fundamental of these laws are very simple, and
for the purpose we have in view, it is necessary that they should be borne
in mind. Let A B, Fig. 193, be a plane reflecting surface, such as the surface
of pure quicksilver or still water, or a polished surface of glass or metal,
and let a ray of light fall upon it in the direction, I O, meeting the surface at
O. it will be reflected along a line, O R, such that if at the point O we draw
a line, O P, perpendicular to the surface, the incident ray, I O, and the re-
flected ray, O R, will form equal angles with the perpendicular in other
words, the angle of incidence will be equal to the angle of refle :tion, and
the perpendicular, the incident ray, and the reflected ray, will all be in
one plane perpendicular to the reflecting plane. It would be quite easy to
18 2
27 6 LIGHT.
prove from this law that the luminous rays from any object falling on a
plane reflecting surface are thrown back just as if they came from an
object placed behind the reflecting surface symmetrically to the real object
The diagrams in Figs. 194 and 195 will render this clear. In the second
diagram, Fig. 195, it will be noticed that only the portion of the mirror be-
tween Q and P takes any part in the action, and therefore it is not necessary,
in order to see objects in a plane mirror, that the mirror 'should be exactly
opposite to them ; thus the portion o Q might be removed without the eye
losing any part of the image of the object A B.
There are many very interesting and important scientific instruments in
which the laws of reflection from plane surfaces are made use of such, for
example, as the sextant and the goniometers but passing over all these, we
FIG. 196.
may say a word about the formation of several images from one object by
using two mirrors. It has already been explained that the action of a plane
mirror is equivalent to the placing of objects behind it symmetrically dis-
posed to the real object The reflections, or virtual images in the mirror,
behave optically exactly as if they were themselves real objects, and are re-
flected by other mirrors in precisely the same manner. From this it follows
that two planes inclined to each other at an angle of 90 give three images
of an object placed between them, the images and the object apparently
placed at the four angles of a rectangle. When the mirrors are inclined to
each other at an angle of 60, five images are produced, which, with the
original object, show an hexagonal arrangement The formation of these by
the principle of symmetry is indicated in Fig. 196. It was these symmetri-
cally disposed images which suggested to Sir David Brewster the construc-
tion of the instrument so well known as the kaleidoscope, in which two or,
still better, three mirrors of black glass, or of glass blackened on one side,
are placed in a pasteboard tube inclined to ach other at 60 : one end of
the tube is closed by two parallel plates of glass ; the outer one ground,
but the inner transparent, leaving between them an interval, in which are
placed fragments of variously-coloured glass, which every movement of
LIGHT.
277
FlG. 197. Polemoscope.
the instrument arranges in new combinations. At the other end of the
tube is a small opening on applying the eye to which one sees directly
the fragments of glass, with their images so reflected that beautifully
symmetrical patterns are produced ; and this with endless variety. When
this instrument was first made in the cheap form in which it is now so
familiarly known, it obtained a popularity which has perhaps never been
equalled by any scientific toy, for it is said that no fewer than 200,000
kaleidoscopes were sold in London and Paris in one month.
By way of contrast to the mirrors of the kaleidoscope harmlessly pro-
ducing beautiful designs, by symmetrical images of fragments of coloured
glass, we show the reader, in Fig. 197, mirrors which are reflecting quite
other scenes, for here is seen the manner in which even the plane mirror
has been pressed into the service of the stern art of war. The mirrors are
employed, not like those of Archimedes, to send back the sunbeams from
every side, and by their concentration at one spot to set on fire the enemy's
works, but to enable the artillerymen in a battery to observe the effect of
their shot, and the movement of their adversaries, without exposing them-
selves to fire by looking over the parapet of their works. The contrivance
has received the appropriate name viPolemoscope (ToXe/*os, war, and cr/fOTrew.,
278
LIGHT.
FlG. 198. Apparatus for Ghost Illusion.
to view), and it consists simply, as shown in the figure, of two plane mirrors
so inclined and directed, that in the lower one is seen by reflection the loca-
lities which it is desired to observe.
We return once more to the arts of peace, in noticing the advantage
which has been lately taken of plane mirrors for the production of spectral
and other illusions, in exhibitions and theatrical entertainments, the im-
provement in the manufacture of plate-glass having permitted the produc-
tion of enormous sheets of that substance. Among the most popular exhi-
bitions of this class was that known as " Pepper's Ghost," the arrangement
of the mirrors having been the subject of a patent taken out by Mr. Pepper
and Mr. Dircks jointly. The principle on which the production of the
illusion depends, may be explained by the familiar experience of everybody
who has noticed that, in the twilight, the glass of a window presents to a
person inside of a room the images of the light or bright objects in the
apartment, while the objects outside are also visible through the glass.
As, by night coming on, the reflections increase in brilliancy, the darkness
outside is almost equivalent to a coat of black paint on the exterior surface
of the glass ; but, on the contrary, in the daylight no reflection of the in-
terior of the room is visible to the spectator inside, on looking towards the
window. The reflections are present, nevertheless, in the day-time as well
as at night, only they are overpowered and lost when the rays which reach
the eye through the glass are relatively much more powerful. Even in the
day-time the image of a lighted candle is usually visible, in the absence of
PLATE V.
THE GHOST ILLUSION
LIGHT. 279
direct sunshine, against a dark portion of the exterior objects as a back-
ground. The visibility, or otherwise, of the internal objects by reflection, and
of the external objects seen through the glass, depends entirely on the rela-
tive intensities of the illumination, for the more illuminated side overpowers
and conceals the other, just as the rising sun causes the stars " to pale their
ineffectual fires." Hence, on looking through the window on a dark night,
we cannot see objects out of doors unless we screen off the reflection of the
illuminated objects in the room. If the rays transmitted through the glass,
and those which are reflected, have intensities not very different, we see
then the reflected images mixed up in the most curious manner with the
real objects. It is exactly in this way that the ghosts are made to appear
in the illusion of which we are speaking. The real actors are seen through
a large plate of colourless and transparent glass, and from the front surface
of this glass rays are reflected which apparently proceed from a phantom
taking a part in the scene among the real actors. The arrangement is
shown in Fig. 198, where E G is the stage, separated from the auditorium,
H, by a large plate of transparent glass, E F, placed in an inclined position,
and not visible to the spectators, for the lights in front are turned down,
and the stage is also kept comparatively dark. Parallel to the large plate
of glass is a silvered mirror, c D, placed out of the spectators' sight, and
receiving the rays from a person at A, also out of sight of the spectators,
and strongly illuminated by an oxy-hydrogen lime-light at B. The manner
in which the rays are reflected from the silvered mirror to the plate-glass,
and hence reflected so as to reach the spectators and give them the im-
pression of a figure standing on the stage at G, is sufficiently indicated by
the lines drawn in the diagram. The apparitional and unsubstantial cha-
racter of the image is derived from its seeming transparency, and from
the manner in which it may be made to melt away, by diminishing the
brightness of the light which falls on the real person. The introduction of
the second mirror was a great improvement, for by this the phantom is
made to appear erect, while its original stands in a natural attitude. Where-
as, with only the plate-glass, E F, the ghost could not be made to appear
upright, unless, indeed, as was sometimes done, the plate was inclined at
an angle of 45, and the actor of the ghost lay horizontally beneath it. A
scene of the kind produced by the improved apparatus, is represented in
Plate V.
Another illusion is produced by the help of a large silvered mirror,
placed at an inclination of 45, sloping backwards from the floor, and,
in consequence, presenting to the spectators the image of the ceiling,
which appears to them the back of the scene. The mirror is perforated
near the centre by an opening, through which a person passes his head,
and, all his body being concealed by the mirror, the effect produced is that
of a head floating in the air. Means are provided of withdrawing the
mirror, when necessary, while the curtain is down, and then the real back
of the scene appears, which, of course, is exactly similar to the false one
painted on the ceiling. Fig. 199 represents a scene produced at the Poly*
technic by a somewhat similar arrangement of mirrors, under the manage-
ment of Mr. Pepper. Plane mirrors were employed in another piece of
natural magic which this gentleman exhibited to the public, who were
shown a kind of large box, or cabinet, raised from the floor, and placed
in the middle of the stage, so that the spectators might see under it and
all round it. Inside of the box were two silvered mirrors the full height of
it, and these were hinged to the farther angles, so that each one being
280
LIGHT.
FIG. 199. Illusion produced by Mirrors.
folded with its face against a side of the box, their backs formed the appa-
rent sides, and were painted exactly the same as the real interior of the
box. When the performer enters the box, the door is closed for an instant,
while he, stepping to the back, turns the mirrors on their hinges until their
front edges meet, where an upright post in the middle of the box conceals
their line of junction. The performer thus places himself behind the
mirrors in the triangular space between them and the back of the box,
while the mirrors, now inclined at angles of 45 to the sides, reflect
images of these to the spectators when the door is opened, and the spec-
tators see then the box apparently empty, for the reflection of the sides
appears to them as the back of the cabinet. The entertainment was some-
times varied by a skeleton appearing, on the door being opened, in the place
of the person who entered the cabinet. It is hardly necessary to say that
the skeleton was previously placed in the angle between the mirrors where
the performer conceals himself.
LIGHT.
281
FlG. 200. A Stage Illusion.
To the same inventive gentleman, whose ingenious use of plane mirrors
has thus largely increased the resources of the public entertainer, is due
another stage illusion, the effect of which is represented in Fig. 200 ; and,
although it does not depend on reflection, it may be introduced here as show-
ing how the perfection of the manufacture of plate-glass, which makes it
available for the ghost exhibition, can be applied in another way in dramatic
spectacles. The female form, here supposed to be seen in a dream by the
sleeper, is not a reflection, although she appears floating in mid-air, strangely
detached from all supports, but the real actress. This is accomplished by
making use of the transparency of plate-glass, a material strong enough to
afford the necessary support, and yet invisible under the circumstances of
the exhibition.
But it is not behind the turned-down footlights, or in the exhibitions of
the showman, that we find the most beautiful illustrations of the laws of
reflection. In the quiet mountain mere, amid the sweet freshness of nature,
we may often see tree, and crag, and cliff, so faithfully reproduced, that it
282
LIGHT.
needs an effort of the understanding to determine where substance leaves
off and shadow begins, a condition of the liquid surface indicated in twc
lines by Wordsworth :
" The swan, on still St. Mary's Lake,
Floats double, swan and shadow."
The landscape painter is always gratified if he can introduce into his
picture some piece of water, and it can hardly be doubted that much of the
charm of lakes and rivers is due to their power of reflecting. Look on
Fig. 201, a view of some buildings at Venice ; and, in order to see how much
of its beauty is owing to the quivering reflections, imagine the impression
it would produce were the place of the water occupied by asphalte pave-
ment, or a grass lawn. The condition of the reflections here represented
is perhaps even more pleasing than that produced by perfect repose: they
are in movement* and yet not broken and confused :
" In bright uncertainty they lie,
Like future joys to Fancy's eye."
FIG. 201. View of Venice Reflections.
LIGHT. 283
REFRACTION.
THAT light moves in straight lines is a statement which is true only
when the media through which it passes are uniform ; for it is easily
proved that when light passes from one medium to another, a change of
direction takes place at the common surface of the media in all rays that
meet this surface otherwise than perpendicularly. As a consequence of
this, it really is possible to see round a corner, as the reader may convince
himself by performing the following easy experiment. Having procured a
cup or basin, Fig. 202, let him, by means of a little bees'-wax or tallow,
attach to the bottom of the vessel, at R, a small coin. If he now places the
cup so that its edge just conceals the coin from view, and maintains his eye
steadily in the same position as at I, he
will, when water is poured into the cup,
perceive the coin apparently above the
edge of the vessel in the direction I R',
that is, the bottom of the cup will ap-
pear to have risen higher. Since it is
known that in each medium the rays
pass in straight lines, the bending which
renders the coin visible can therefore
only take place at the common junction
of the media, or, in other words, the
ray, R O, passing from the object in a
straight line through the water, is bent
abruptly aside as it passes out at the sur-
face of the water, A B, and enters the ,.,
air, in which it again pursues a straight * IG * 2O2<
course, reaching the eye at I, where it
gives the spectatoran impression of an object atR'. This experiment is also an
illustration of the cause of the well-known tendency we have tounder-estimate
the depth of water when we can see the bottom. The broken appearance pre-
sented by an oar plunged into clear water is due to precisely the same cause.
The curious exaggerated sizes and distorted shapes of the gold-fish seen in
a transparent globe have their origin in the same bending aside of the rays.
This deviation which light undergoes in passing obliquely from one medium
into another is known by the name of refraction, and it is essential for the
understanding of the sequel that the reader should be acquainted with some
of the laws of this phenomenon, although their discovery by Snell dates two
centuries and a half anterior to the present time. Let T O, Fig. 203, be a
ray of light which falls obliquely upon a plane surface, A B, common to two
different media, one of which is represented by the shaded portion of the
figure, A B c D, of which c D represents another plane surface, parallel to the
former. If the ray, T O, suffered no refraction, it would pursue its course
in a straight line to r'\ but as a matter of fact it is found that such a ray is
always bent aside at O, if the medium A B c D is more or less dense than
the other. If, for example, A B c D is water, and the medium above it glass,
then the ray entering at O will take the course O r ; but if A B C D is a plate
of glass with water above and below it, the ray will take the course T O,
o R, R B, suffering refraction on entering the glass, and again on leaving it,
284
LIGHT.
so that R B will emerge fromthe glass parallel to its original direction at T O.
If through the point of incidence, O, we suppose a line, O P, to be drawn
perpendicular to the surface, A B, then we may say that the ray in pass-
ing from the rarer medium (water, air, &c.) into the denser medium (glass,
&c.) is bent towards the perpendicular, or normal, as at O ; but that on
leaving the denser to enter the rarer medium, as at R, it is bent away from
the perpendicular. In other words, the angle b o a is less than the angle
m O T, and O R forms a less angle with R P 7 than R B' does. It is also a law
of ordinary refraction that the normal, o P, at the point of incidence, the
incident ray, T O, and the refracted ray, o R, are all in the same plane.
Besides, there is the important and interesting law discovered by Snell and
by Descartes, which may thus be explained with reference to Fig. 203. On
the incident and refracted rays, T o and O R, let us suppose that any equal
distances, O d and o , are measured off from o, and that from each of the
points a and , perpendiculars, a m and b , are drawn to the normal, P P,
which passes through o ; then it is found that, whatever may be the angle
of incidence, T o P, or however it is made to vary, the length of the line
a m bears always the same proportion to the line b n for the same two media.
Thus, if A B c D be water, and T o enters it out of the air, the length of the
line a m divided by the length of the line a b will always (whatever slope
f O may have) give the quotient I "33. This number is, therefore, a constant
quantity for air and water, and is called the index of refraction for air into
water. The law just explained is expressed by the language of mathematics
thus : For two given media the ratio of the sines of the angles of incidence
and of refraction is constant.
It is an axiom in optical science that a ray of light when sent in the oppo-
site direction will pursue the same path. Thus in Fig. 203 the direction
of the light is represented as from T towards B' ; but if we suppose B' R to be
an incident ray, it would pursue the path B' R, R O, O T, and in passing out
of the denser medium, A B c D at O, its direction is farther from the normal,
P P, or, as the law of sines, a m will be always longer than n d, and will bear
a constant ratio to it. Suppose the angle R O P to increase, then P o B will
LIGHT. 285
become a right angle ; that is, the emergent ray, O T, will just graze the sur-
face, A B, when the angle R O P has some definite value. If this last angle
be further increased, no light at all will pass out of the medium A B C D, but
the ray R o will be totally reflected at O back into the medium, A B c D,
according to the laws of reflection. The angle which R o forms with o P
when o T just skims the surface, A B, is termed the limiting angle, or the
critical angle, and its value varies with the media. The reader may easily
see the total reflection in an aquarium, or even in a tumbler of water, when
he looks up through the glass at the surface of the water, which has then
all the properties of a perfect mirror.
The power of lenses to form images of objects is entirely due to these laws
of refraction. The ordinary double-convex lens, for example, having its
surfaces formed of portions of spheres, refracts the rays so that all the rays
which from one luminous point fall upon the lens, meet together again at a
point on the other side, the said point being termed their focus. It is thus
that images of luminous bodies are formed by lenses. An explanation of
the construction and theory of lenses cannot, however, be entered into in
this place.
One important remark remains to be made namely, that in the above
statement of the laws of reflection and refraction, certain limitations and
conditions under which they are true and perfectly general have not been
expressed ; for the mention of a number of particulars, which the reader
would probably not be in a condition to understand, would only tend to
confuse, and the explanation of them would lead us beyond our limits.
Some of these conditions belong to the phenomena we have to describe,
and are named in connection with them, and others, which are not in im-
mediate relation to our subject, we leave the reader to find for himself in
any good treatise on optics.
DOUBLE REFRACTION AND POLARIZATION.
A BOUT two hundred years ago, a traveller, returning from Iceland,
** brought to Copenhagen some crystals, which he had obtained from
the Bay of Roerford, in that island. These crystals, which are remarkable
for their size and transparency, were sent by the traveller to his friend,
Erasmus Bartholinus, a medical man of great learning, who examined them
with great interest, and was much surprised by finding that all objects
viewed through them appeared double. He published an account of this
singular circumstance in 1669, and by the discovery of this property of
Iceland spar, it became evident that the theory of refraction, the laws of
which had been studied by Snell and by Huyghens a few years before, re-
quired some modification, for these laws required only one refracted ray, and
Iceland spar gave two. Huyghens studied the subject afresh, and was able,
by a geometrical conception, to bring the new phenomena within the general
theory of light. Iceland spar is chemically carbonate of lime (calcium car-
bonate), and hence is also called calc spar, and, from the shape of the
crystals, it has also been termed rhombohedral spar. The form in which
the crystals actually present themselves is seen in Fig. 204, which also repre-
sents the phenomenon of double refraction. Iceland spar splits up very
286
LIGHT.
readily, but only along certain definite directions, and from such a piece as
that represented in Fig. 204 a perfect rhombohedron, such as that shown in
Fig. 206, is readily obtained by cleavage ; and then we have a solid having
six lozenge-shaped sides, each lozenge or side having two obtuse angles of
101 55', and two acute angles of 78 5'. Of the eight solid corners, such
as A B c, &c., six are produced by the meeting of one obtuse and two acute
angles, and the remaining two solid corners are formed by the meeting of
three obtuse angles. Let us imagine that a line is drawn from one of these
FIG. 204.
angles to the other : the diagonal so drawn forms the optic axis of the
crystal, and a plane passing through the optic axis, A B, Fig. 205, and
through the bisectors of the angles, E A D and F B G, marks a certain defi-
nite direction in the crystal, to which also belong all planes parallel to that
just indicated. Any one of such planes forms what is termed a " principal
section," to which we shall presently refer.
It will be observed that in Fig. 204 the white circle on a black ground
seen through the crystal is doubled ; but that, instead of being white as the
circle really is, the images appear grey, except where they overlap, and
there the full whiteness is seen. If we place the crystal upon a dot made
on a sheet of paper, or having made a small hole with a pin in a piece of
cardboard, hold this up to the light, and place the crystal against it, we see
apparently two dots or two holes. The two images will, if the dot or hole
be sufficiently small, appear entirely detached from each other. Now, if,
keeping the face of the crystal against me cardboard or paper, the observer
turn the crystal round, he will see one of the images revolve in a circle
round the other, which remains stationary. The latter is called the ordinary
image, and the former the extraordinary image. Let us place the crystal
upon a straight black line ruled on a horizontal sheet of paper, Fig. 205, and
let us suppose, in order to better define the appearance, that we place it
LIGHT.
287
so that the optic axis, A B, is in a plane perpendicular to the paper, A being
one of the two corners where the three obtuse angles meet, and B the other,
and the face, A B C D, parallel to E G H B, which touches the paper. Then,
according to the laws of ordinary refraction, if we look straight down upon
the crystal, we should see through it the line I. K, unchanged in position
that is, the ray would pass perpendicularly through the crystal as shown
by L M and, in fact, a part of the ray does this, and gives us the ordinary
image, O o' ; but another part of the ray departs from the laws of Snell
and Descartes, and, following the course L N Y', enters the eye in the direc-
tion N Y', producing the impression of another line at I/, which is the ex-
traordinary ray, E E'. If the crystal be turned round on the paper, E E'
will gradually approach o o', and the two images will coincide when the
principal section is parallel to the
line I K ; but the coincidence is only
apparent, and results from the super-
position of the two images for a
mark placed on the line drawn on the
paper will show two images, one of
which will follow the rotation of the
crystal, and show itself to the right
or left of the ordinary image, ac-
cording as C is to the right or left
of A. So that there are really in
every portion of the crystal two
images on the line, one of which
turns round the other, and the coal-
escence of the two images twice in
each revolution is only apparent, for
the different parts of the lengths of
the images do not coincide. On continuing the revolution of the crystal after
they apparently coincide, the images are again seen to separate, the extra-
ordinary one being now displaced on the other side, or always towards the
point, C. Thus, then, the ray, on entering the crystal, bifurcates, one branch
passing through the crystal and out of it in the same straight line, just as it
would in passing through a piece of glass, while the other is refracted at
its entrance into the crystal, although falling perpendicularly upon its face,
and again at its exit. And again, when a beam of light, R r, Fig. 206, falls
obliquely on a crystal of Iceland spar, it divides at the face of the crystal
into two rays, r O, and r E ; the former, which is the ordinary ray, follows
the laws of ordinary refraction it lies in the plane of incidence, and obeys
the law of sines, just as if it passed through a piece of plate-glass. The
extraordinary ray, on the other hand, departs from the plane of incidence,
except when the latter is parallel to the principal section, and the ratio of
the sines of the angles of incidence and refraction varies with the incidence.
The reader who is desirous of studying these curious phenomena of double
refraction, and those of polarization, is strongly recommended to procure
some fragments of Iceland spar, which he can very easily cleave into rhom-
bohedra, and with these, which need not exceed half an inch square, or cost
more than a few pence, he can demonstrate for himself the phenomena, and
become familiar with their laws. He will find very convenient the simple
plan recommended by the Rev. Baden Powell, of fixing one of the crystals
to the inside of the lid of a pill-box, through which a small hole has been
made, and through the hole and the crystal view a pin-hole in the bottom
FlG. 206.
288 LIGHT.
of the box, turning the lid, and the crystal with it, to observe the rotation
of the image. The same arrangement will serve, by merely attaching
another rhomb of spar within the box, to study the very interesting facts
of the polarization to which we are about to claim the reader's attention.
The curious phenomena which have just been described, although in
themselves by no means recent discoveries, have led to some of the most
interesting and beautiful results in the whole range of physical science.
The examination and discussion of them by such able investigators as
Huyghens, Descartes, Newton, Fresnel, Malus, and Hamilton, have largely
conduced to the establishment of the undulatory hypothesis that compre-
hensive theory of light, which brings the whole subject within the reach of
a few simple mechanical conceptions.
It was at first supposed that it was only one of the rays which are pro-
duced in double refraction that departed from the ordinary laws, and Ice-
land spar was almost the only crystal known to have the property in ques-
tion. At the present day, however, the substances which are known- to
produce double refraction are far more numerous than those which do not
possess this property, for, by a more refined mode'of examination than the
production of double images, Arago has been able to infer the existence of
a similar effect on light in a vast number of bodies. Crystals have also
been found which split up a ray of light entering them into two rays, neither
of which obeys the laws of Descartes. It may, in fact, be said that, with
the exception of water, and most other liquids, of gelatine and other colloi-
dal substances, and of well-annealed glass, there are few bodies which do
not exercise similar power on light.
On examining the two rays which emerge from a rhomb of Iceland spar,
on which only one ray of ordinary light has been allowed to fall, we find
that these emergent rays have acquired new and striking properties, of
which the incident ray afforded no trace ; for, if we allow the two rays
emerging from a rhomb of the spar to fall upon a second rhomb, we shall
find, on viewing the images produced, that their intensity varies with the
position into which its second crystal is turned. Thus, if we place a rhomb
of the spar upon a dot made on a sheet of white paper, we shall have, as
already pointed out, two images of equal darkness. But, in placing a second
rhomb of the spar upon the first, in such a manner that their principal
sections coincide, and the faces of one rhomb are also parallel to the faces
of the other, we shall still see two equally intense images of the dot, only
the images will be more widely separated than before, and no difference
will be produced by separating the crystals if the parallelism of the planes
of their respective principal sections be preserved. Here, then, is at once
a notable difference between a ray of ordinary light and one that emerges
from a rhomb of Iceland spar ; for, in the case of rays of ordinary light, we
have seen that the second rhomb would divide each ray into two, whereas
it is incapable (in the position of crystals under consideration) of dividing
either the ordinary or the extraordinary ray which emerges from the first
rhomb. If, still keeping the second rhomb above the other, we make the
former rotate in a horizontal plane, we may observe that, as we turn the
upper crystal so that the planes of the principal sections form a small angle
with each, each image will be doubled, and, as the upper crystal is turned,
each pair of images exhibits a varying difference of intensity. The ordinary
ray in entering the second crystal is divided by it into a second ordinary
ray and a second extraordinary ray, the intensities of which vary accord-
ing to the angle between the principal sections. When the two principal
LIGHT. 289
sections are parallel to one plane, that is, when the angle between them is
either o or 180, the extraordinary image disappears, and only the ordinary
one is seen, and with its greatest intensity. When the two principal sections
are perpendicular to each other, that is, when the second crystal has been
turned through either 90 or 270, the extraordinary has, on the contrary,
its greatest intensity, and the ordinary one disappears. When the principal
section of the second crystal has been turned into any intermediate posi-
tion, such as through 45 and 135, or any odd multiple of 45, both images
are visible and have equal intensities. This experiment shows that the
two rays which emerge from the first crystal have acquired new properties,
that each is affected differently by the second crystal, according as the
crystal is presented to it in different directions round the ray as an axis.
FIG. 207.
The ray of light is no longer uniform in its properties all round, but appears
to have acquired different sides, as it were, in passing through the rhomb of
Iceland spar. This condition is indicated by saying that the ray is polarized \
and the first rhomb of spar is termed the polarizer, while the second rhomb,
by which we recognize the fact that both the ordinary and the extraordinary
rays emerge having different sides, has received the name of analyser. But,
in order to study conveniently all the phenomena in Iceland spar, we should
have crystals of a considerable size, otherwise the two rays do not become
sufficiently separated so as to make it an easy matter to intercept one of
them while we examine the other. A very ingenious mode of getting rid
of one of the rays was devised by Nicol, and as his apparatus is much used
for experiments on polarized light, we shall state the mode of constructing
NicoVs Prism. It is made from a rhomb of Iceland spar, Fig. 207, in which
a and b are the corners where the three obtuse angles meet, all equal. If we
draw through a and b lines bisecting the angles da c &s\&fhg, and join a ,
these lines will all be in one plane, which is a principal section of the crystal,
and contains the axis, a b. Now suppose another plane, passing through a b,
to be turned so that it is at right angles to the plane containing a b and the
bisectors : this plane would cut the sides of the crystal in the lines a t, ih,
bk,ka\ and in making the Nicol prism, the crystal is cut into two along
19
290
LIGHT.
this plane, and the two pieces are then cemented together by Canada balsam.
A ray of light, R, entering the prism, undergoes double refraction ; but the
ordinary ray, meeting the surface of the Canada balsam at a certain angle
greater than the limiting angle, is totally reflected, and passes out of the
crystal at o ; while the extraordinary ray, meeting the layer of balsam at a
less angle than its limiting angle, does not undergo total reflection, but
passes through the balsam, and emerges in the direction of E, completely
polarized, so that the ray is unable to penetrate another Nicol's prism of
which the principal section is placed at right angles to that of the first.
Among other crystals which possess the property of doubly refracting, and
therefore of polarizing, is the mineral called tourmaline, which is a semi-trans-
parent substance, different specimens having different tints. In Fig. 208, A,B,
represent theprismatic crystals of tourmaline, and C showsacrystal whichhas
been cut, by means of a lapidary's wheel, into four pieces, the planes of division
being parallel to the axis of the prism. The two inner portions form slices,
having a uniform thickness of about $ in., and when the faces of these have
FIG. 208.
been polished, the plates form a convenient polarizer and analyser. Let
us imagine one of the plates placed perpendicularly between the eye and a
lighted candle. The light will be seen distinctly through it, partaking, how-
ever, of the colour of the tourmaline ; and if the plate be turned round so
that the direction of the axis of the crystal takes all possible positions with
regard to the horizon, while the plane of the plate is always perpendicular
to the line between the eye and the candle, no change whatever will be seen
in the appearance of the flame. But if we fix the plate of crystal in a given
position, let us say with the axial direction vertical, and place between it
and the eye the second plate of tourmaline, the appearances become very
curious indeed, and the candle is visible or invisible according to the posi-
tion of this second plate. When the axis of the second is, like that of the
first, vertical, the candle is distinctly seen ; but when the axis of the second
plate is horizontal, no rays from the candle can reach the eye. If the second
plate be slowly turned in its own plane, the candle becomes visible or invi-
sible at each quarter of a revolution, the image passing through all degrees
of brightness. Thus the luminous rays which pass through the first plate
are polarized like those which emerge from a crystal of Jceland spar. It is
not necessary that the plates used should be cut from the same crystal of
tourmaline, for any two plates will answer equally well which have been
cut parallel to the axes of the crystals which furnished them. In the case
of tourmaline the extraordinary ray possesses the power of penetrating the
LIGHT. 291
substance of the crystal much more freely than the ordinary ray, which a
small thickness suffices to absorb altogether. It may be noted that in thfe
simple experiment we have just described, the plate of tourmaline next the.
candle forms the polarizer, and that next the eye the analyser; and thaV
until the latter was employed, the eye was quite incapable of detecting the.
change which the light had undergone in passing through the first plate, for
the unassisted eye had no means of recognizing that the rays emerged with,
sides. The usual manner of examining light, to find whether it is polarized,
is to look through a plate of tourmaline or a Nicol's prism, and observe
whether any change in brightness takes place as the prism or plate is
rotated. Now, it so happened that in 1808 a very eminent French man of
science, named Malus, was looking through a crystal of Iceland spar, and
seeing in the glass panes of the windows of the Luxembourg Palace, which
was opposite his house, the image of the setting sun, he turned the crystal
towards the windows, and instead of the two bright images he expected to
see, he perceived only one ; and on turning the crystal a quarter of a revo-
lution, this one vanished as the other image appeared. It was, indeed, by
a careful analysis of this phenomenon that Malus founded a new branch of
science, namely, that which treats of polarized light ; and his views soon
led to other discoveries, which, with their theoretical investigations, con-
stitute one of the most interesting departments of optical science, as re-
markable for the grasp it gives of the theory of light as for the number of
practical applications to which it has led.
The accidental observation of Malus led to the discovery that when a
ray of ordinary light falls obliquely on a mirror not of metal, but of any
other polished surface, such as glass, wood, ivory, marble, or leather it
acquires by reflection at the surface the same properties that it would ac-
quire by passing through a Nicol's prism or a plate of tourmaline : in a
word, it is polarized. Thus, if a ray of light is allowed to fall upon a mirror
of black glass at an angle of incidence of 54 35', the reflected ray will be
found to be polarized in the plane of reflection that is, it will pass freely
through a Nicol's prism when the principal section is parallel to the plane
of reflection ; but when it is at right angles to the latter, the reflected ray
will be completely extinguished by the prism that is, it is completely
polarized. If the angle of the incident ray is different from 54 35', then
the reflected ray is not completely intercepted by the prism it is not com-
pletely but only partially polarized. The angle at which maximum pola-
rization takes place varies with the reflecting substance ; thus, for water
it is 53, for diamond 68, for air 45. A simple law was discovered by Sir
David Brewster by which the polarizing angle of every substance is con-
nected with its refractive index, so that when one is known, the other may
be deduced. It may be expressed by saying that the polarizing angle is
that angle of incidence which makes the reflected and the refracted rays
perpendicular to each other. The refracted rays are also found to be pola-
rized in a plane perpendicular to that of reflection.
Instruments of various forms have been devised for examining the phe-
nomena of polarized light. They all consist essentially of a polarizer and
an analyser, which may be two mirrors of black glass placed at the pola-
rizing angle, or two bundles of thin glass plates, or two Nicol's prisms, or
two plates of tourmaline, or any pair formed by two of these. Fig. 209
represents a polariscope, this instrument being designed to permit any
desired combination of polarizer and analyser, and having graduations for
measuring the angles, and a stage upon which may be placed various sub-
192
292
LIGHT.
1 stances in order to observe the effects of polarized light when transmitted
through them. It is found that thin slices of crystals placed between the pola-
rizer and analyser exhibit varied and beautiful effects of colour, and by such
FIG. 209. Polariscope.
effects the doubly refracting power of substances can be recognized, wnere
the observation of the production of double images would, on account of
their small separation, be impossible. And the polariscope is of great service
LIGHT.
293
in revealing structures in bodies which with ordinary light appear entirely
devoid of it such, for example, as quill, horn, whalebone, &c. Except
liquids, well-annealed glass, and gelatinous substances, there are, in fact,
few bodies in which polarized light does not show us the existence of some
kind of structure. A very interesting experiment can be made by placing
FIG. 210.
in the apparatus, shown in Fig. 210, a square bar of well-annealed glass ;
on examining it by polarized light, it will be found that before any pres-
sure from the screw c is applied to the glass, it allows the light to pass
equally through every part of it ; but when by turning the screw the
particles have been thrown into a state of strain, as shown in the figure,
distinct bands will make their appearance, arranged somewhat in the
manner represented ; but the shapes of the figures thus produced vary
with every change in the strain and in the mode of applying the pressure.
FlG. 211. Iceland Spar showing Double Refraction,
294
LIGHT.
CAUSE OF LIGHT AND COLOUR.
Tl 7E have hitherto limited ourselves to a description of some of the
* V phenomena of light, without entering into any explanation of their
presumed causes, or without making any statements concerning the nature
of the agent which produces the phenomena. Whatever this cause or agent
may be, we know already that light requires time for its propagation, and
two principal theories have been proposed to explain and connect the facts.
The first supposes light to consist of very subtile matter shot off from
luminous bodies with the observed velocity of light ; and the second theory,
which has received its great development during the present century,
regards luminous effects as being due to movements of the particles of
a subtile fluid to which the name of " ether " has been given. Of the
existence of this ether there is no proof : it is imagined ; and properties
are assigned to it for no other reason than that if it did exist and possess
these properties, most of the phenomena of light could be easily explained.
This theory requires us to suppose that a subtile imponderable fluid per-
vades all space, and even interpenetrates bodies gaseous, liquid, and
solid ; that this fluid is enormously elastic, for that it resists compression
with a force almost beyond calculation. The particles of luminous bodies,
themselves in rapid vibratory motion, are supposed to communicate move-
ment to the particles of the ether, which are displaced from a position
LIGHT. 295
of equilibrium, to which they return, executing backwards and forwards
movements, like the stalks of corn in a field over which a gust of wind
passes. While an ethereal particle is performing a complete oscillation, a
series of others, to which it has communicated its motion, are also perform-
ing oscillations in various phases the adjacent particle being a little be-
hind the first, the next a little behind the second, and so on, until, in the
file of particles, we come to one which is in the same phase of its oscillation
as the first one. The distance of this from the first is called the " length
of the luminous wave." But the ether particles do not, like the ears of
corn, sway backwards and forwards merely in the direction in which the
wave itself advances : they perform their movements in a direction perpen-
dicular to that in which the wave moves. This kind of movement may
be exemplified by the undulation into which a long cord laid on the ground
may be thrown when one end is violently jerked up and down, when a wave
will be seen to travel along the cord, but each part of the latter only moves
perpendicularly to the length. The same kind of undulation is produced
on the surface of water when a stone is thrown into a quiet pool. In each
of these cases the parts of the rope or of the water do not travel along with
the wave, but each particle oscillates up and down. Now, it may some-
times be observed, when the waves are spreading out on the surface of a
pool from the point where a stone has been dropped in, that another set of
waves of equal height originating at another point may so meet the first
set, that the crests of one set correspond with the hollows of the other, and
thus strips of nearly smooth water are produced Dy the superposition of the
two sets of waves. Let Fig. 212 represent two systems of such waves pro-
pagated from the two points A A, the lines representing the crests of the
waves. Along the lines, b b, the crests of one set of waves are just over the
hollows of the other set ; so that along these lines the surface would be
smooth, while along c C the crests would have double the height. Now, if
light be due to undulation, it should be possible to obtain a similar effect
that is, to make two sets of luminous undulations destroy each other's effects
and produce darkness : in other words, we should be able, by adding light
to light, to produce darkness / Now, this is precisely what is done in a
celebrated experiment devised by Fresnel, which not only proves that dark-
ness may be produced by the meeting of rays of light, but actually enables
us to measure the lengths of the undulations which produce the rays.
In Fig. 213 is a diagram representing the experiment of the two mirrors,
devised by Fresnel. We are supposed to be looking down upon the
arrangement : the two plane mirrors, which are placed vertically, being
seen edgeways, in the lines, M o, o N, and it will be observed that the
mirrors are placed nearly in the same upright plane, or, in other words, they
form an angle with each other, which is nearly 180. At L is a very narrow
upright slit, formed by metallic straight-edges, placed very close together,
and allowing a direct beam of sunlight to pass into the apartment, this
being the only light which is permitted to enter. From what has been
already said on reflection from plane mirrors, it will readily be understood
that these mirrors will reflect the beams from the slit in such a manner as
to produce the same effect, in every way, as if there were a real slit placed
behind each mirror in the symmetrical positions, A and B. Each virtual
image of the slit may, therefore, be regarded as a real source of light at A
and at B ; thus, for example, it will be observed that the actual lengths of
the paths traversed by the beams which enter at L, and are reflected from
the mirrors, are precisely the same as if they came from A and B respectively.
296 LIGHT.
The virtual images may be made to approach as near to each other as may
be required, by increasing the angle between the two mirrors, for, when
this becomes 180, that is, when the two mirrors are in one plane, the two
images will coincide. If, now, a screen be placed as at F G, a very remark-
able effect will be seen ; for, instead of simply the images of the two slits,
there will be visible a number of vertical coloured bands, like portions of
very narrow rainbows, and these coloured bands are due to the two sources
of light, A and B ; for, if we cover or remove one of the mirrors, the bands
will disappear and the simple image of the slit will be seen. If, however,
we place in front of L a piece of coloured glass, say red, we shall no longer
see rainbow-like bands on the screen, but in their place we shall find a
number of strips of red light and dark spaces alternately, and, as before,
these are found to depend upon the two luminous sources, A and B. We
must, therefore, come to the conclusion that the two rays exercise a mutual
effect, and that, by their superposition, they produce darkness at some
FIG. 213.
points and light at others. These alternate dark and light bands are formed
on the screen at all distances, and the spaces between them are greater as
the two images, A and B, are nearer together. Further, with the same dis-
position of the apparatus, it is found that when yellow light is used instead
of red, the bands are closer together ; when green glass is substituted for
yellow, blue for green, and violet for blue, that the bands become closer
and closer with each colour successively. Hence, the effect of coloured
bands, which is produced when pure sunlight is allowed to enter at L, is
due to the superposition of the various coloured rays from the white light.
Let us return to the case of the red glass, and suppose that the distance
apart of the two images, A and B, has been measured, by observing the
angle which they subtend at C, and by measuring the distance, C O D, or
rather, the distance COL. Now, the distances of A and B from the centre
of each dark band, and of each light band, can easily be calculated, and it
is found that the difference between the two distances is always the same for
the same band, however the screen or the mirrors may be changed. On
comparing the differences of the distances of A and B in case of bright bands,
with those in the case of dark ones, it was found that the former could be
expressed by the even multiples of a very small distance, which we will call
d, thus :
o, 2^,4^; 6d, 8^ . . . :
LIGHT.
297
while the differences for the dark bands followed the odd multiples of the
same quantity, d, thus :
These results are perfectly explained on the supposition that light is a kind
of wave motion, and that the distance, d, corresponds to half the length of
a wave. We have the waves entering L, and pursuing different lengths of
path to reach the screen at F G, and, if they arrive in opposite phases of
undulation, the superposition of two will produce darkness. The undula-
tions will plainly be in opposite phases when the lengths of paths differ by
an odd number of half-wave lengths, but in the same phase when they
differ by an even number. Hence, the length of the wave may be deduced
from the measurement of the distances of A and B from each dark and light
band, and it is found to differ with the colour of the light. It is also plain
that, as we know the velocity of light, and also the length of the waves, we
have only to divide the length that light passes over in one second, by the
lengths of the waves, in order to find how many undulations must take place
in one second. The following table gives the wave-lengths, and the number
of undulations for each colour :
Colour.
Number of Waves
in one inch.
Number of Oscillations in one
second.
Red
AO Q6o
514 ooo ooo ooo ooo
Orange ...
43,560
5 57,000,000,000,000
Yellow
46,090
5 7 8,000,0^0,000,000
Green
49,600
62 1 ,ooo,oco ; ooo,ooo
Blue
53,470
670,000,000,000,000
Indigo
56,560
709,000,000,000,000
Violet
60,040
7 50,000,000,000,000
These are the results, then, of such experiments as that of Fresnel's, and
although such numbers as those given in the table above are apt to be con-
sidered as representing rather the exercise of scientific imagination than
as real magnitudes actually measured, yet the reader need only go care-
fully over the account of the experiment, and over that of the measurement
of the velocity of light, to become convinced that by these experiments
something concerned in the phenomena of light has really been measured,
and has the dimensions assigned to it, even if it be not actually the distance
from crest to crest of ether waves even, indeed, if the ether and its waves
have no existence. But by picturing to ourselves light as produced by the
swaying backwards and forwards of particles of ether, we are better able
to think upon the subject, and we can represent to ourselves the whole of
the phenomena by a few simple and comparatively familiar conceptions.
As an example of the facility with which the ether theory lends itself
3
A knowledge of their composition, he expressly asserted, could never be
attained, for we could have no means of chemically examining the matter
of which they are constituted. Such was the deliberate utterance of a man
by no means disposed to underrate the power of the human mind in the
pursuit of truth. And such might still have been the opinion of the learned
and of the unlearned, but for the remarkable train of discoveries which has
led us to the construction of instruments revealing to us the nature of the
substances entering into the constitution of the heavenly bodies. We have
now, for example, the same certainty about the existence of iron in our
sun, that we have about its existence in the poker and tongs on the hearth.
The last few years have seen the dawn of a new science ; and two branches
of knowledge which formerly seemed far as the poles asunder namely,
astronomy and chemistry have their interests united in this new science of
celestial chemistry. The progress which has been made in this depart-
ment of spectroscopic research is so rapid, and the field is so promising,
that the well-instructed juvenile of the future, instead of idly repeating the
simple lay of our childhood :
"Twinkle, twinkle, little star,
How I wonder what you are ! "
will probably only have to direct his sidereal spectroscope to the object of
his admiration in order to obtain exact information as to what the star is,
chemically and physically.
The results which have already been obtained in celestial chemistry, and
other branches of spectroscopic science, are so surprising, and apparently
so remote from the range of ordinary experience, that the reader can only
appreciate these wonderful discoveries by tracing the steps by which they
have been reached. A few fundamental phenomena of light have already
been spoken of in the foregoing article ; and an acquaintance with these
will have prepared the reader's mind
for a consideration of the new facts
we are about to describe. In discus-
sing, in the foregoing pages, the sub-
ject of refraction, we have, in order
that the reader's attention might not
be distracted, omitted all mention of
a circumstance attending it, when a
beam of ordinary light falls upon a
refracting surface, such as that re-
presented in Fig. 203. The laws
there explained apply, in fact, to ele-
mentary rays, and not to ordinary
white light, which is a mixture of a
vast multitude of elementary rays,
red, yellow, green, &c. When such
a beam falls obliquely upon a piece
of glass, the ray is, at its entrance,
broken up into its elements, for these,
being refracted in different degrees
by the glass, each pursues a different
path in that medium, as represented by Fig. 216. Each elementary ray
obeys the laws which have been explained, and therefore each emerges
from the second surface of the plate parallel to the incident ray, and, in
3 o4 THE SPECTROSCOPE.
consequence of this, the separation is not perceptible under ordinary cir-
cumstances with plates of glass having parallel surfaces. But, if the second
surface be inclined so as to form such an angle with the first that the rays
are rendered still more divergent in their exit, then the separation of the
light into its elementary coloured rays becomes quite obvious. Such is
the arrangement of the surfaces in a prism, and in the triangular pieces of
glass which are used in lustres.
For the fundamental experimental fact of our subject, we must go back
two centuries, when we shall find Sir Isaac Newton making his celebrated
analysis of light by means of the glass prism. We shall describe Newton's
experiment, for, although it was peformed so long ago, and is generally
well known, it will render our view of the present subject more complete ;
and it will also serve to impress on the reader an additional instance of
the world's indebtedness to that great mind, when we thus trace the grand
results of modern discovery from their source. " It is well," is the remark
of a clear thinker and eloquent writer, " to turn aside from the fretful din
of the present, and to dwell with gratitude and respect upon the services of
1 those mighty men of old, who have gone down to the grave with their
weapons of war,' but who, while they lived, won splendid victories over
ignorance."
The experiment of Sir Isaac Newton will be readily understood from
Fig. 217, where C is the prism, and A C represents the path of a beam of
sunlight allowed to enter into a dark apartment through a small round
FlG. 217. Newtorts Experiment.
hole in a shutter, all other light being excluded from the apartment. In
this position of the prism, the rays into which the sunbeam is broken at
its entrance into the glass were bent upwards, and at their emergence from
the glass they were again bent upwards, still more separated, so that when
a white screen was placed in their path, instead of a white 'circular image
of the sun appearing, as would have been the case had the light been
merely refracted and not split up, Newton saw on the screen the variously-
coloured band, D D, which he termed the spectrum. The letters in the
figure indicate the relative positions of the various colours, red, orange,
yellow, green, blue, &c., by their initial letters. The spectrum, or pro-
THE SPECTROSCOPE. 305
longed coloured image of the sun, is red at the end, R, where the rays are
least refracted, and violet at the other extremity, where the refraction is
greatest, while, in the intermediate spaces, yellow, green, and blue pass by
insensible gradations into each other. Newton varied his experiment in
many ways, as, for example, by trying the effect of refraction through a
second prism on the differently coloured rays. He found that the second
prism did not divide the yellow rays, for instance, into any other colour,
but merely bent them out of the straight course, to form on the second
screen a somewhat broader band of yellow, and similarly with regard to the
others. From these, and a number of other experiments described in his
" Opticks," (A. D. 1675), Newton concludes, "that if the sun's light consisted
of but one sort of rays, there would be but one colour in the whole world,
nor would it be possible to produce any new colour by reflections and re-
fractions, and, by consequence, the variety of colours depends upon the
composition of light." " And if, at any time, I speak of light and
rays, or coloured, or endued with colours, I would be understood to speak,
not philosophically and properly, but grossly, and accordingly to such con-
ceptions as vulgar people in seeing all these experiments would be apt to
frame. For the rays, to speak properly, are not coloured. In them there
is nothing else than a certain power and disposition to stir up a sensation
of this or that colour. For, as sound in a bell, a musical string, or other
sounding body, is nothing but a trembling motion, and in the air nothing
but that motion propagated from the object, and in the sensorium 't is a
sense of that motion under the form of a sound ; so colours in the object
are nothing but a disposition to reflect this or that sort of rays more copi-
ously than the rest : in the rays they are nothing but their dispositions to
propagate this or that motion into the sensorium, and in the sensorium
they are sensations of these motions under the form of colours."
These memorable investigations of Newton's have been the admiration
of succeeding philosophers, and even poets have caught inspiration from
this theme :
" Nor could the darting beam of speed immense
Escape his swift pursuit and measuring eye.
E'en Light itself, which everything displays,
Shone undiscovered, till his brighter mind
Untwisted all the shining robe of day ;
And, from the whitening undistinguished blaze,
Collecting every ray into his kind,
To the charmed eye educed the gorgeous train
Of parent colours. First the flaming red
Sprung vivid forth ; the tawny orange next ;
And next delicious yellow by whose side
Fell the kind beams of all-refreshing green ;
Then the pure blue, that swells autumnal skies,
Ethereal played ; and then, of sadder hue.
Emerged the deepened indigo, as when
The heavy-skirted evening droops with frost,
While the last gleamings of refracted light
Died in the fainting violet away.
These, when the clouds distil the rosy show,
Shine out distinct adown the watery bow ;
While o'er our heads the dewy vision bends
Delightful melting on the fields beneath.
Myriads of mingling dyes from these result,
And myriads still remain. Infinite source
Of beauty ! ever blushing ever new !
Did ever poet image aught so fair,
Dreaming in whispering groves, by the hoarse brook,
Or prophet, to whose rapture Heaven descends?"
The spectra which Newton obtained by admitting the solar beams
20
3 o6 THE SPECTROSCOPE.
through a circular aperture, were, however, not simple spectra. The cir-
cular beam may be considered as built up of flat and very thin bands of
light, parallel to the edges of the prism, and a simple ray would be formed
by one of these flat bands ; as the round opening would allow an indefinite
number of such rays to enter, each would produce its own spectrum on the
screen, and the actual image would be formed of a number of spectra
overlapping each other. When the aperture by which the light is admitted
consists merely of a narrow slit, or line, parallel to the edges of the prism,
we obtain what is termed a pure spectrum. When the prism is properly
placed, an eye, viewing the fine slit through it, sees a spectrum formed, as
it were, of a succession of virtual images of the slit in all the elementary
coloured rays.
The person who first examined the solar spectrum in this manner was the
English chemist Wollaston, who, in 1802, found that the spectrum thus ob-
served was not continuous, but that it was crossed at intervals by dark lines.
Wollaston saw them by placing his eye directly behind the prism. Twelve
years later, namely, in 1814, the German optician Fraunhofer devised a
much better mode of viewing the spectrum ; for, instead of looking through
the prism with the naked eye, he used a telescope, placing the prism and
the telescope at a distance of 24ft. from the slit, the virtual image of which
was thus considerably magnified. The prism was so placed that the in-
cident and refracted rays formed nearly equal angles with its faces, in
which circumstance the ray is least deflected from its direction, and the
position is therefore spoken of as being that of minimum deviation. It
can be shown that this position is the only one in which the refracted rays
can produce clear and sharp virtual images of the slit, and therefore it is
necessary in all instruments to have the prism so adjusted. Fraunhofer
then saw that the dark lines were very numerous, and he found that they
always kept the same relative positions with regard to the coloured spaces
they crossed ; that these positions did not change when the material of
which the prism was made was changed ; and that a variation in the re-
fracting angle of the prism did not affect them. He then made a very
careful map, laying down upon it the position of 354 of the lines out of about
600 which he counted, and indicated their relative intensities, for some
are finer and less dark than others. The most conspicuous lines he dis-
tinguished by letters of the alphabet, and these are still so indicated ; and
the dark lines in the solar spectrum are called " Fraunhofer's Lines." These
lines, as will appear in the sequel, are of great importance in our subject.
A few of the more obvious ones are shown in No. i, Plate VI. Fraun-
hofer found that these lines were always produced by sunlight, whether
direct, or diffused, or reflected from the moon and planets ; but that the
Ught from the fixed stars formed spectra having different lines from those
in the sun although he recognized in some of the spectra a few of the
same lines he found in the solar spectrum. The fact of these differences
in the spectra of the sun and fixed stars proved that the cause of the dark
lines, whatever it might be, must exist in the light of these self-luminous
bodies, and not in our atmosphere. It was, however, some years afterwards
ascertained that the passage of the sun's light through the atmosphere
does give rise to some dark bands in the spectrum ; for it was found that
certain lines make their appearance only when the sun is near the horizon,
and its rays consequently pass through a much greater thickness of air.
Sir D. Brewster first noticed in 1832 that certain coloured gases have the
power of absorbing some of the sun's rays, so that the spectrum, when the
THE SPECTROSCOPE.
307
rays are made to pass through such a gas before falling on the prism, is
crossed by a series of dark lines altogether different from Fraunhofer's
lines, though these are also present. The gas in which this property was
first noticed is that called " nitric peroxide" a brownish-red gas, of which
even a thin stratum produces a well-marked series of dark lines. The same
property was soon discovered in the vapours of bromine, iodine, and a cer-
tain compound of chlorine and oxygen. Each substance furnishes a system
of lines peculiar to itself : thus the vapour of bromine, although it has almost
exactly the same colour as nitric peroxide, gives a totally different set of
lines. These, therefore, do not depend on the mere colour of the gas or
vapour, and this is conclusively proved by the fact of many coloured vapours
producing no dark lines whatever : the vapour of tungsten chloride, for
example, although in colour so exactly like bromine vapour that the two
cannot be distinguished by the eye, yields' no lines whatever.
In Fig. 218 is represented a lamp for burning coal-gas, which is con-
stantly used by chemists as a source of heat. It is known as " Bunsen's
burner," from its inventor the celebrated German chemist. It consists of
a metal tube, 3 in. or 4 in. long, and \ in.
in diameter, at the bottom of which the
gas is admitted by a small jet communi-
cating with the elastic tube which brings
the gas to the apparatus. A little below
the level of the jet there are two lateral
openings which admit air to the tube.
The gas, therefore, becomes mixed with
air within the tube, and this inflammable
mixture streams from the top of the tube
and readily ignites on the approach of a
flame, the mixture burning with a pale
bluish flame of a very high temperature.
This little apparatus is not only the most
useful pieces of chemical apparatus ever
devised, but it furnishes highly instruc-
tive illustrations of several points in
chemical and physical science ; and to
some of these we invite the reader's
attention, as they have an immediate
bearing on our present subject. Coal-
gas is a mixture of various compounds of
the two elementary bodies, hydrogen and carbon ; and when the gas burns,
these substances are respectively uniting with the oxygen of the air, pro-
ducing water and carbonic acid gas. Now, when coal-gas is burnt in the
ordinary manner as a source of light, the supply of oxygen is too small to
admit of the complete combustion of all its constituents ; and as the oxygen
more eagerly seizes upon the hydrogen than upon the carbon, a large pro-
portion of the latter thus set free from its hydrogen compound is deposited
in the flame in the solid form, and is there intensely heated. The presence
of solid carbon in an ordinary gas flame is easily proved by holding in it a
cold fragment of porcelain, or a piece of metal, which will become covered
with soot. In the flame of the Bunsen burner there is no soot, because the
increased supply of oxygen, afforded by previously mixing the gas with air,
enables the whole of the constituents of the gas to be completely burnt ;
and this is of the greatest advantage to the chemist, who always desires to
20 2
n ,
2i%.-Bunsms Burntr on a
3 o8 THE SPECTROSCOPE.
have the vessels he heats free from soot, in order that he may observe what
is taking place within them. The flame of Bunsen's lamp becomes that of
an ordinary sooty gas flame, when the two orifices which admit the air at
the bottom of the tube are closed up, and then, of course, the temperature
cannot be so high as when the whole constituents of the gas are com-
pletely burnt, but the flame becomes highly luminous ; whereas when the
orifices are open it gives so little light, that in a dark room one cannot see
a finger held 20 in. from the lamp. Plainly the cause of this difference is
connected with the presence or absence of the heated particles of solid
carbon. The non-luminous flame contains no solid particles ; the bright
part of the other flame is full of them. To these heated particles of solid
carbon we are, then, indebted for the light which burning coal-gas supplies.
And, since we are able by such artificial illumination to distinguish colours,
the white-hot carbon must give off rays of all degrees of refrangibility, and
we should expect to find in the spectrum produced by such a flame, the red,
yellow, green, and other coloured rays. And such is indeed the spectrum
which these incandescent carbon particles produce : it resembles the solar
spectrum, but there is an entire absence of dark lines, so that the appear-
ance is that represented by No. I, Plate VI., if we suppose the Fraunhofer
lines removed. If the pale blue flame of the Bunsen's burner be similarly
examined, the spectrum, No. 14, Plate VI., shows that only a few rays of
certain refrangibilities are emitted, forming bright lines here and there, but
of little intensity, while the whole of the other rays are absent. This shows
that while the highly heated solid gives off all rays from red to violet with-
out interruption, the still more highly heated gases give off only a few
selected rays.
It has long been known that some substances impart certain colours
to flames, and such substances have been long employed to produce
coloured effects in fireworks, &c. But coloured flames do not appear to
have been examined by the prism until 1822, when Sir John Herschel
described the spectra of strontium, copper, and of some other substances,
remarking that " The colours thus communicated by the different bases to
flame afford in many cases a ready and neat way of detecting extremely
minute quantities of them." A few years later, Fox Talbot described the
method of obtaining a monochromatic flame, by using in a spirit-lamp
diluted alcohol in which a little salt has been dissolved. The paper in which
he describes this and other observations concludes thus : " If this opinion
should be correct and applicable to the other definite rays, a glance at the
prismatic spectrum of flame may show it to contain substances which it
would otherwise require a laborious chemical analysis to detect." Here we
have the first hint of that spectrum analysis which has provided the chemist
with a method of surpassing delicacy for the detection of metallic elements.
The spectra of coloured flames were also subsequently examined and
described by Professor W. A. Miller, but the most complete investigation
into the subject was made by Professors Kirchhoff and Bunsen, who also
contrived a convenient instrument, or spectroscope, for the examination and
comparison of different spectra. The instrument has received many im-
provements and modifications, but the essential parts are one or more
prisms ; a slit, through which the light to be examined is allowed to enter ; a
tube, having at the other end a lens to. render parallel the rays from the slit ;
a telescope, through which the spectrum is viewed ; and usually some appa-
ratus by which the positions of the different lines may be identified.
A very elegant instrument, made by Mr. John Browning, of the Strand, is
PLATE VI.
SPECTRA.
THE SPECTROSCOPE. 309
represented in Fig. 219. It has a single prism, made of glass, of great power
in dispersing the rays. The prism is supported on a little stage, placed in the
middle of a horizontal circular brass table about 6 in. in diameter. On the
left is seen a tube, about 1 5 in. long, at the outer extremity of which is the
slit, formed of pieces of metal very accurately shaped. One of these pieces
FIG. 219. Spectroscope 'with one Prism.
slides in a direction at right angles to the slit, and, by means of a spring
and a fine screw, can be very nicely adjusted, so that an opening of any
degree of fineness can be readily obtained. In front of the slit is a small
glass prism, with its edges parallel to the slit, but only half its height. The
bases of this prism are formed of two sides of a square and its diagonal,
and, as shown in the figure, one side is parallel to the face of the slit, and
the other to the axis of the tube. Rays of light coming from a source on
the left of the slit (as seen in the figure) will, therefore, enter this little
prism, and be totally reflected (see page 285) by the diagonal surface, down
the axis of the tube through the lower half only of the slit. This is the
only office of this prism, which has nothing to do with the dispersion of the
rays : the use to which it is put will be seen presently. It is fixed in such
a manner that, when required, it can be turned aside with the touch of a
finger, and the whole length of the slit exposed. A peculiarity in these
instruments of Mr. Browning's is the admirable arrangement for deter-
mining the position of any line in a spectrum. For this purpose, the eye-
piece of the telescope is provided with a pair of cross-wires, and the tele-
scope itself, which is about 1 8 in. in length, moves in a horizontal plane
round the axis of the circular brass table, from which an arm projects,
carrying a ring into which the telescope screws. This arm carries a vernier
along the limb of the circular table, which is very accurately divided into
thirds of degrees, so that with the aid of the vernier the angular position
of the telescope can be read off to a minute, that is, to g^th of a degree. The
arm carrying the telescope is provided with a screw for clamping it in any
desired position while the readings are taken. On placing in front of the
slit the flame of a Bunsen's burner, the spectrum produced by any substance
in this flame will, when the instrument is in proper adjustment, be seen on
3 io THE SPECTROSCOPE.
looking through the telescope, and the cross-wires being also in view, the
point of their intersection may be brought into coincidence with any line of
the spectrum, and the telescope being clamped in this position, the angular
reading thus taken determines the position of the line. Thus, for example,
the angular positions in which the principal Fraunhofer's lines are seen
having been observed and recorded, the angular position of any line in an-
other spectrum will at once determine its position among the Fraunhofer
lines ; or the spectrum may be mapped by laying down the angular read-
ings of the lines by means of a scale of equal parts. And, again, in the
little prism in front of the slit we have the means of bringing two spectra
in view at once, one being from a light directly in front, and the other from
a light at the side. The two spectra are seen one above the other, and the
coincidence or difference of their lines may be directly observed. When the
instrument is in use, the prism and the ends of the tube are covered with
a black cloth, loosely thrown over them, by which all stray light is shut out.
The author has had in use for several years one of these instruments, and
he cannot forbear expressing his perfect satisfaction with its powers, which
he finds amply sufficient for all ordinary chemical purposes, while the accu-
racy of the workmanship is really wonderful, considering the very moderate
price of the instrument.
The substances the spectra of which are most conveniently examined are
the metals of the alkalies and alkaline earths. Small quantities of the salts
of these metals, placed in a loop of fine platinum wire, impart characteristic
colours to the flame of a Bunsen burner or to that of a spirit-lamp. For the
examination of the spectra the former is to be preferred, as the lines come
out much more vividly. Indeed, at temperatures higher than that of the
Bunsen's burner, such as in the flame of pure hydrogen, or in the voltaic
arc, some substances give out additional lines. In Plate VI., Nos. 2 to 9,
is shown the appearance of the spectra produced by the Bunsen's burner
when salts of the metals are held in the flame in the manner already men-
tioned, and the spectra are examined with the instrument just described.
One of the simplest of these spectra is that produced by sodium compounds,
such as common salt. The smallest particle of this substance imparts an
intense yellow colour to the flame, and the spectrum is found to take the
form of a single bright yellow line No. 3. It has been estimated that the
presence of the iooojoooo^ P art f a S ra ^ H f sodium can be detected by
the production of this line. Indeed, the very delicacy of this sodium re-
action renders it almost impossible to get rid o this line, for sodium is
found to be present in almost everything, a fact the earlier observers of
spectra were not aware of, for they attributed this yellow line to water,
which was the only substance they knew to be so generally diffused. If a
platinum wire be heated in the flame of the Bunsen burner until all the
sodium indications have disappeared, it suffices to remove the wire, and,
without allowing it to come into contact with anything, to leave it exposed
to the air for a few minutes, to cause it again to give the characteristic
yellow colour when again plunged into the flame. This is due to the fact
that the element is contained in all the floating particles which pervade
the atmosphere. The spectroscope is not required to show the presence of
the sodium on the platinum which has been exposed to the air, the colour
imparted to the flame being plainly visible to the eye, and it needs only the
Bunsen burner and 2 in. of platinum wire to prove the fact, and also to show
that mere contact with the fingers is enough to highly charge the wire with
sodium compounds. Any volatile compound of potassium gives the spec-
THE SPECTROSCOPE. 311
trum represented by No. 2, the principal lines being a red line and one in
the extreme violet, the latter being somewhat difficult to observe. There
is also a third rather ill-defined red line, and a portion of a faint continuous
spectrum. Salts of strontium impart a bright red colour to the flame, and
the spectrum they produce is shown by No. 6, in which are seen several
bright red lines and a fainter blue one. Calcium, which also gives a red-
dish colour to flame, furnishes an entirely different set of lines (No. 5). and
barium salt another, containing numerous lines, especially some very vivid
green ones.
In all the cases we have named, and whenever bright-lined spectra are
furnished by substances placed in the flame of a lamp, or in burning hydro-
gen gas, or in the intensely hot voltaic arc, there is evidence that the sub-
stances are converted into vapour or gas. We have already seen how hot
solid carbon gives a continuous spectrum, while carbon in the state of
gaseous combination gives most of the bright lines seen in the spectrum
of coal-gas (No. 14). It is observed also that the more readily volatized
are the salts, the more vivid are the bright lines they produce when heated
in a flame. It must be understood that each element gives it own charac-
teristic lines, that these are always in precisely the same position in the
spectrum, that no substance produces a line in exactly the same position as
another, however near two lines due to different substances may, in some
cases, appear ; and also, that however the salts of the different metals are
mixed together, each produces its own lines, and each ingredient may be
recognized. And this is done in an instant by an experienced observer
a mere glance at the superposed spectra of, perhaps, half a dozen metals,
suffices to inform him which are present. There is also a peculiarity in
this optical mode of recognizing the presence of bodies which gives the
subject the highest interest, namely, the circumstance that the spectrum is
produced and the bodies recognized, however far from the observer the
luminous gas may be placed, the only condition required being that the
rays reach the instrument.
Until Kirchhoff and Bunsen's spectroscopic investigations, lithium was
supposed to be a rare metal, occurring only in a few minerals. It happens
that this substance yields a remarkable spectrum (No. 4), for it gives an
extremely vivid line of a splendid red colour, accompanied by only one
other, a feeble yellow line ; and the reaction is of very great delicacy, for
g-ou^Tnrath of a grain can easily be detected, and an eye which has once
seen the red line readily recognizes it again. A single drop of a mineral
water containing lithium has been found to distinctly produce the red line,
in cases where the quantity contained in a quart of the water would have
escaped ordinary chemical analysis. The spectroscope has shown that
lithium, so far from occurring in only four or five minerals, is a substance
very widely diffused in nature. In the waters of the ocean, in mineral and
river waters, in most plants, in wines, tea, coffee, milk, blood, and muscle,
this metal has been found. Dr. Roscoe states that the ash of a cigar, when
moistened with hydrochloric acid, and held in a platinum wire in the flame of
the Bunsen's burner, at once shows the principal lines of sodium, potassium,
calcium, and lithium. Salts of lithium and of strontium both impart a rich
crimson tint to flames, and it is hardly possible to detect any difference in
these colours with the naked eye; but, as the reader may see on comparing
spectra No. 4 and No. 6, the prism makes a wide distinction.
Matter for a very interesting chapter in the history of prismatic analysis
has been furnished by the discovery of four new elements by means of the
3 i2 THE SPECTROSCOPE.
spectroscope. In 1860 Bunsen observed that the residue, after evapora-
tion, of a certain mineral water, yielded spectra with bright lines which
he had not seen before. He concluded that they were due to some un-
known elements, and, in order to separate these, he evaporated many tons,
of the water, and was rewarded by the discovery of two alkaline metals,,
caesium and rubidium. The delicacy of the spectrum reaction may be
inferred from the fact of a ton weight of the water containing only three
grains of the salts of each of these substances. Rubidium gives a splendid
spectrum, containing red, yellow, and green lines, and also two character-
istic violet lines ; while caesium has orange, yellow, and green lines, and
two very beautiful blue lines, by which it is easily recognized.
About the same time, Mr. W. Crookes discovered, in a mineral from the
Hartz, another elementary body, the existence of which was first indicated
to him by the characteristic spectrum it produces, namely, a single splendid
green line (No. 8 spectrum). In 1864 two German chemists discovered,
also in the Hartz, a fourth new element, which was detected by two well-
defined lines in the more refrangible end of the spectrum (see spectrum
FIG. 220. Miniature Spectroscope.
No. 9, in the plate). This metal was named Indium, in reference to the-
colour of its lines, and the names of the other three caesium, rubidium,
and thallium, are also derived from the colours of their characteristic lines.
Although the reader may, from such representations of the spectra as.
those given in Plate VI., form some idea of their appearance, he would
find his knowledge of the subject much clearer if he had the opportunity
of examining for himself the actual phenomena. We have already recom-
mended the performance of certain easy experiments involving no outlay,
but, in the matter of spectroscopes, carefully finished optical and mechani-
cal work is absolutely necessary in the appliances. It fortunately happens
that one eminent optician, at least, has made it his study to produce good
spectroscopic apparatus at the lowest possible cost, and if the reader be
interested in this subject, and desirious of trying experiments himself, he
can, for a very moderate sum, be equipped with ail the appliances for
examining the phenomena we have described. He has only to procure, in
the first place, a small direct-vision spectroscope, such as that represented
of its actual size in Fig. 220, which is sold by Mr. Browning for twenty-
two shillings ; secondly, a Bunsen's burner, a few feet of india-rubber
tubing, two inches of platinum wire, and a few grains of the salts of lithium,
strontium, thallium, &c. The whole expense will probably be covered by
adding four shillings to the cost of the spectroscope, and the reader will
then be in a position to see for himself the principal Fraunhofer lines, the
spectra of the metals already referred to, and the absorption bands of the
THE SPECTROSCOPE.
3 is
gases which have been mentioned, as well as the absorption bands in liquids,
vrhich will be spoken of in the sequel.
The splitting up of a beam of light into its elements which it is the
office of the prism to produce is accomplished by a single prism to a cer-
tain degree only. It separates the red from the green, for example ; but
the colours pass into each by insensible gradations through orange, yellow,
3 i4 THE SPECTROSCOPE.
and greenish yellow. If we allow the rays to fall upon a second prism after
emerging from the first, the separation is carried further ; the red, for in-
stance, is spread out into different kinds of red, and so on with the rest.
And the greater the number of prisms, the greater is the extension which
is given to the spectrum. Now, just as by increasing the power of the tele-
scope, new stars become visible, whose light was before too faint, and
nebulas, or stars which before seemed single, are resolved into clusters, of
individual stars so, by increasing the power of the spectroscope by em-
ploying two, four, or more prisms^ lines which appear single by the less
powerful instruments are, in some instances, resolved into groups of lines,
and new lines come into view, which before were too faint to show them-
selves. For example, if we view the Fraunhofer lines through a spectro-
scope like that in Fig. 220, but having two prisms instead of one, we shall
see that the D line is not really a single line, but is formed of two lines
close together. If we use greater dispersive power by employing a greater
number of prisms, we shall observe with solar light that when these two D
lines are sufficiently separated, several other lines make their appearance
between them. In this way the number of dark lines in sunlight, which
have been carefully mapped by KirchhofT and others, amount to upwards
of 2,000; and no doubt there are many more lines waiting a still more
powerful instrument. Fig. 221 is copied from a large spectroscope made
by Mr. Browning for Mr. Gassiot. It has nine or more highly dispersive
glass prisms; the telescope and the tube bearing the slit have focal lengths
of 1 8 in., the lenses having a diameter of \\ in. ; the telescope is provided
with a slow motion for taking the angular position ; and there is a third
tube provided with a micrometer, by which the position of the lines can be
measured to TotWth of an inch.
The instruments we have mentioned, except the miniature spectroscope,
show only a portion of the spectra at once, a movement of the telescope
being requisite to bring each part into view. It has been already stated
that the only position of the prism which will make the lines clear and
well defined is that in which the deviation is the least. In using trains of
prisms it is therefore necessary to adjust each prism for the part of the
spectrum which may be under observation. This is a tedious process, and
it has been obviated by a useful invention of Mr. Browning's, by which the
adjustment is rendered automatic that is, the movements of the telescope
are communicated to the prisms in such a manner that they place them-
selves into the proper position for producing clear images of the slit, what-
ever may be the refrangibility of the rays under examination : Fig. 222
shows the arrangement as it appears when viewed from above. The train of
six prisms can be so arranged that the ray after passing through six of them
shall be totally reflected by a surface of the last prism, and pursue again
its path through the six prisms in the reverse direction, becoming more
and more dispersed by each prism until it emerges parallel to the axis of
the telescope. The power of the instrument is, therefore, equivalent to
that of one with twelve prisms ; but it can be used at pleasure with any
dispersive power, from two to twelve prisms.
By making use of one of the Bunsen burners, the lines which are charac-
teristic of some ten or twelve metals are readily seen when one of their more
volatile salts is converted into vapour. For this purpose their chlorides
are usually employed, but the reactions are common to all their salts. It is
necessary that the metal should exist in the flame in the state of highly
heated vapour or gas, in order that its characteristic rays should be given
THE SPECTROSCOPE.
off. We usually introduce compounds of these metals into the flame ; but
there is reason to believe that these are decomposed in the flame, and the
disassociated metal takes the form of glowing gas, a small quantity of
which suffices for the production of the bright lines. No doubt the other
constituent of the compound, the chlorine for example, is also set free in
the gaseous form ; but since the spectrum of the metal only is visible, we
may infer that at the temperature of the flame, the non -metallic elements
are not sufficiently luminous to produce a spectrum. When we repeat the
experiments with salts of the less volatile metals, we obtain no spectra
FIG. 222. Browning's Automatic Adjustment of Prisms.
the temperature of the flame not being sufficiently high to convert these
into vapour. Other methods have, therefore, to be resorted to, and advan-
tage is taken of the fact discovered by Faraday, that an electric spark is
nothing but highly heated matter. The spectroscope gives us reason to
believe that this matter, which is formed of the substances between which
the spark passes, is in the gaseous state; for it is found, on examining
sparks passing between two pieces of each metal, that characteristic bright
lines are produced. If one of the metals already named is submitted to
this examination, the same lines are found which are seen in the spectra
produced by the salts of the metal volatized in the flame, but in some cases
additional bright lines appear in the spark spectrum. With the heavier
metals the spark, or the electric arc, is, however, the only means of igniting
their vapours. The usual mode of doing this is to make the discharges of
a large induction coil pass between the two fine wires of the metals, placed
about a quarter of an inch apart. A Leyden jar is commonly employed to
condense the discharge, and thus produce a still higher temperature. Mr.
Browning has contrived the neat little apparatus shown in Fig. 223, in
which the jar is superseded by a more compact and convenient condenser
THE SPECTROSCOPE.
inside of the box, so that it is only necessary to attach one terminal of the
coil to the binding-screw, seen outside of the end of the box, and place the
other wire from the coil in the binding- screw of one or the other of the
pieces of apparatus supported by the upright rod. Of these it is the one on
the right which at present engages our attention. Within a small glass
cylinder are two sliding rods, terminated by screw-clips, which hold finely-
pointed pieces of the metal under examination. The slit of the spectroscope
FlG. 223. Apparatus jor Spark Spectra.
is placed close to the glass cylinder, and when a very rapid succession of
sparks is passing, the bright lines are seen continuously. The spectra of
metals examined in this way are found to yield a very large number of
lines. Thus the spectrum of calcium has 75 lines, and that of iron no fewer
than 450 lines. Our limits will not permit of an account of many interest-
ing particulars relating to these spectra, which include those of all the 50
metallic elements. It should, perhaps, be stated that a modified mode of
producing spectra by sparks is sometimes found useful. This consists in
causing sparks to pass between a solution of some salt of the metal and a
piece of platinum wire. The apparatus for this purpose is that shown on
the left side of the upright in Fig. 223.
It remains to describe the method of producing spectra of the gaseous
non-metallic elements, such as oxygen, nitrogen, hydrogen, &c. For this
purpose electricity is again made use of. It has been found that while an
electric discharge cannot take place across a perfect vacuum, and air or
gas, at ordinary densities, offers much resistance to the passage of elec-
tricity, on the other hand, a highly rarefied gas permits the discharge to
take place through it with great facility. This is seen in Geissler's tubes,
where a succession of discharges from a RuhmkorfPs coil causes the tubes
THE SPECTROSCOPE. 317
to appear filled with light due to the heating to incandescence of a very
minute quantity of the gas. The eye readily recognizes difference of colour
in the light given off by the different gases, and when this light is examined
by the spectroscope, bright lines, characteristic of each gas, are observed.
No. 12 and No. 13, in Plate VI., are the spectra of hydrogen and of nitrogen
respectively, which appear when the gases are examined in the manner just
described. In this manner the spectra of chlorine, bromine, iodine, oxygen,
sulphur, phosphorus, &c., may be studied. Silicon and some other solid
non-metallic elements present great difficulties to the spectroscopist, for
these elements cannot be volatized at any temperature we can command,
and the spectra of their elements can only be inferred from those of their
compounds. But unfortunately the spectra are found to vary with the nature
of the compound, and thus it happens that in the case of carbon, for
example, no definite spectrum can be assigned to the element. The flame
of coal-gas, burning in the air, as in the Bunsen burner, gives the spectrum
No. 14 ; but if this is compared with the spectrum of the flame of burning
cyanogen (a compound of carbon and nitrogen), the two are found to differ
greatly. The cyanogen spectrum has the two pale broad bands of violet-
blue, the four blue lines, the two green lines, and the brightest of the greenish
yellow which are seen in the coal-gas spectrum. But it has in addition a
characteristic series of violet lines, a series of bright blue, two or three
crimson and red lines, and bands in the orange, and several green lines,
none of which occur in the coal-gas spectrum. These additional lines are
not due to nitrogen, for, with perhaps the exception of some red lines, they
do not coincide in position with any of the nitrogen lines. The spectrum
of hydrogen, No. 12, should be noticed, as its three lines are very distinct,
and it will be observed that they exactly coincide in their position with the
three Fraunhofer lines, C, F, and G, in No. I.
There is another branch of this extensive subject to which we have now
to invite the reader's attention. The power of certain gases to absorb or
stop certain rays of an otherwise continuous spectrum has already been
mentioned ; but this property is by no means confined to gases, for certain
liquids and solids do this in a high degree. There is a remarkable metallic
element, named didymium. It is a rare substance, and its presence can-
not with certainty be detected by any ordinary tests. Its salts, however,
form solutions without colour, or nearly so, which have the power of strongly
absorbing certain rays. If we hold before the slit of the spectrum a small
tube containing a solution of any one of the salts, and allow the rays from
the sun, or from a luminous gas or candle-flame, to pass through it, we see
the spectrum crossed by certain well-defined very dark bands. A spectrum
of this kind is called an absorption spectrum, and the position, number,
width, &c., of dark bands are found to be as peculiar to each substance as
are the bright lines in the spectra of the elements. The method of observing
them when produced by solutions is very simple. The liquid is contained
in a small test-tube, which is placed in front of the slit ; or, more conve-
niently, the liquid is put into a wedge-shaped vessel, and thus the thickness
of the stratum of liquid through which the rays pass can easily be varied,
so that the best results may be obtained. The absorption spectra are pro-
duced by many compound substances. A striking absorption spectrum is
seen when a solution in alcohol of the green colouring matter of leaves
(chlorophyll] is examined ; for several distinct bands are seen, one in the red
being especially well marked. Many other coloured bodies exhibit charac-
teristic absorption bands, as, for example, permanganate of potash, uranic
3 i8 THE SPECTROSCOPE.
salts, madder, port wine, and magenta. The bands are so peculiar for each
substance, that if so-called port wine, for example, owe its colour to colouring
matter other than that of the grape, such as logwood, &c., the adulteration
can be instantly detected by a glance at the absorption spectrum. As, how-
ever, the absorption bands are not, like the bright lines of metals, definite
images of the slit, but rather broad portions of the spectra, it is very desir-
able in examining such spectra to compare them directly with those o{
known substances, by throwing two spectra into one field, by means of a
side reflecting prism, as already described.
Perhaps one of the most interesting examples of absorption spectra is
that of blood. A single drop of blood in a tea-cupful of water will show
its characteristic spectrum when it is properly examined. If the blood is
arterial or oxidized blood, two well-marked dark bands are visible ; but if
venous or deoxidized blood be used, we see, instead of the two dark bands.
a single one in an intermediate position. These differences have been
E roved to be due to oxidization and deoxidization of a constituent of the
lood, called hcemoglobin, and by using appropriate chemical reagents, the
same specimen of blood may be made to exhibit any number of alternations
of the two spectra, according as oxidants or reducing reagents are em-
ployed. It would be possible by an examination of the absorption spectrum
of a drop of arterial blood to pronounce that a person had died of suffoca-
tion from the fumes of burning charcoal. In such case, the supply of oxygen
being cut off, the haemoglobin of the whole of the blood in the system be-
comes deoxidized.
The beautiful delicacy of these spectrum reactions has permitted the
spectroscope to be applied to the microscope with signal success by Mr,
Browning, working in conjunction with Mr. Sorby, who has devoted great
attention to this subject. The Sorby-Browning instrument is a direct-vision
spectroscope, with a slit, lens, &c., placed above the eye-piece of the micro-
scope. By receiving the light through a single drop of an absorptive liquid:
placed under the object-glass of the microscope, the characteristic bands
are made visible. The micro-spectroscope is also a valuable instrument for
examining the absorption bands which are found in the light reflected from
solid bodies, for the smallest fragment suffices to fill the field of the micro-
scope. Mr. Sorby is able to obtain most unmistakably the dark bands
peculiar to blood from a particle of the matter of a blood-stain weighing
less than Y^njth part of a grain. It is plain from this that the spectroscope
must sometimes prove of great service in giving evidence of crime from
traces which would escape all ordinary observation.
The micro-spectroscope, in its most complete form, is represented in.
Fig. 224. As may be seen from the figure, the apparatus consists of several
parts. The prism is contained in a small tube, which can be removed at
pleasure ; below the prism is an achromatic eye-piece, having an adjust-
able slit between the two lenses ; the upper lens being furnished with a
screw motion to focus the slit. A side slit, capable of adjustment, admits,
when required, a second beam of light from any object whose spectrum it
is desired to compare with that of the object placed on the stage of the
microscope. This second beam of light strikes against a very small prism
suitably placed inside the apparatus, and is reflected up through the com-
pound prism, forming a spectrum in the same field with that obtained from
the object on the stage. A is a brass tube carrying the compound direct-
vision prism, and has a sliding arrangement for roughly focussing.
THE SPECTROSCOPE.
ii
FIG. 224. The Sorby-Br owning Micro-Spectroscope.
B, a milled head, with screw motion to finally adjust the focus of the
achromatic eye-lens.
C, milled head, with screw motion to open or shut the slit vertically.
Another screw, H, at right angles to C, regulates the slit horizontally. This
screw has a larger head, and when once recognized cannot be mistaken for
the other.
D D, an apparatus for holding a small tube, that the spectrum given by its
contents may be compared with that from any other object on the stage.
E, a screw, opening and shutting a slit to admit the quantity of light
required to form the second spectrum. Light entering the aperture near
E strikes against the right-angled prism which we have mentioned as being
placed inside the apparatus, and is reflected up through the slit belonging
to the compound prism. If any incandescent object is placed in a suitable
position with reference to the aperture, its spectrum will be obtained, and
will be seen on looking through it.
F shows the position of the field lens of the eye-piece.
G is a tube made to fit the microscope to which the instrument is applied.
To use this instrument, insert G like an eye-piece in the microscope tube.
Screw on to the microscope the object-glass required, and place the object
^ whose spectrum is to be viewed on the stage. Illuminate with stage mirror
.if transparent, with mirror and lieberkiihn and dark well if opaque, or by
Jside reflector, bull's-eye, &c. Remove A, and open the slit by means of the
Imilled head, H, at right angles to D D. When the slit is sufficiently open
3 the rest of the apparatus acts like an ordinary eye-piece, and any object
can be focussed in the usual way. Having focussed the object, replace A,
3 20
THE SPECTROSCOPE.
and gradually close the slit till a good spectrum is obtained. The spectrum
will be much improved by throwing the object a little out of focus.
Every part of the spectrum differs a little from adjacent parts in refran-
gibility, and delicate bands or lines can only be brought out by accurately
focussing their own parts of the spectrum. This can be done by the milled
head, B. Disappointment will occur in any attempt at delicate investiga-
tion if this direction is not carefully attended to. When the spectra of very
small objects are to be viewed, powers of from \ in. to i-2oth, or higher,
may be employed. Blood, madder, aniline dyes, permanganate of potash
solution, are convenient substances to begin experiments with. Solutions
that are too strong are apt to give dark clouds instead of delicate absorp-
tion bands. Small cells or tubes should be used to hold fluids for exami-
nation.
Mr. Browning has still further improved the micro-spectroscope by the
ingenious arrangement for measuring the positions of the lines, which is
represented in Fig. 225, and the construction and the use of which he thus
described in a paper read before the Microscopical Society :
Attached to the side is a small tube,
A A. At the outer part of this tube
is a blackened glass plate, with a fine
clear white pointer in the centre of
the tube. The lens, C, which is focus-
sed by sliding the milled ring, M, pro-
duces an image of the bright pointer
in the field of view by reflection from
the surface of the prism nearest the
eye. On turning the micrometer, M,
the slide which holds the glass plate
is made to travel in grooves, and the
fine pointer is made to traverse the
whole length of the spectrum.
It might at first sight appear as if
any ordinary spider's web or parallel
wire micrometer might be used in-
stead of this contrivance. But on
closer attention it-will be seen that
as the spectrum ; will not permit of
magnification by the use of lenses,
the line of such an ordinary micro-
meter could not be brought to focus
and rendered visible. The bright
pointer of the new arrangement pos-
sesses this great advantage that it
does not illuminate the whole field
of view.
_ If a dark wire were used, the bright
FIG. 225. Section of Micro-Spectro- diffused light wou id almost obscure
scopt with Micrometer. the faint light of the spe c t ra, and en-
tirely prevent the possibility of see-
ing, let alone measuring, the position of lines or bands in the most refrangible
part of the spectrum.
To produce good effects with this apparatus the upper surface of the
compound prism, P, must make an angle of exactly 45 with the sides of
THE SPECTROSCOPE.
321
the tube. Under these circumstances the limits of correction for the path
of the^rays in their passage through the dispersing prisms are very limited
and must be strictly observed. The usual method of correcting by the outer
surface is inadmissible. For the sake of simplicity, some of the work of
the lower part of the micro-spectroscope is omitted in the engraving. As
to the method of using this contrivance : With the apparatus just described,
measure the position of the principal Fraunhofer's lines in the solar spec-
trum. Let this be done carefully, in bright daylight. A little time given
to this measurement will not be thrown away, as it will not require to be
done again. Note down the numbers corresponding to the position of the
lines, and draw a spectrum from a scale of equal parts. About 3 in. will
be found long enough for this spectrum ; but it may be made as much
longer as is thought desirable, as the measurements will not depend in any
FlG. 226.
way on the distance of these lines apart, but only on the micrometric num-
bers attached to them. Let this scale be done on cardboard and preserved
for reference. Now measure the position of the dark bands in any ab-
sorption spectra, taking care for this purpose to use lamplight, as daylight
will give, of course, the Fraunhofer lines, which will tend to confuse your
spectrum. If the few lines occurring in most absorption spectra be now
drawn to the same scale as the solar spectrum, on placing the scales side
by side, a glance will show the exact position of the bands in the spectrum
relatively to the Fraunhofer lines, which thus treated form a natural and
unchangeable scale (see diagram, Fig 226). But for purposes of compari-
son it will be found sufficient to compare the two lists of numbers repre-
senting the micrometric measures, simply exchanging copies of the scale
of Fraunhofer lines, or the numbers representing them will enable observers
at a distance from each other to compare their results, or even to work
simultaneously on the same subject.
A simpler form of the micro-spectroscope is also made by Mr. Browning
at a very modest price, and if the reader possesses a microscope, and
desires to examine these interesting subjects for himself, he will do well to
procure this instrument, instead of that represented in Fig. 220, as it will
also answer better for other purposes. A section of the instrument is shown
in Fig. 227. When used with the microscope it is slipped into the place of
the eye-piece. There is an adjustable slit, a reflecting prism, by which two
different spectra may be examined at once, and a train of five prisms for
dispersing the rays. It can be used equally well for seeing the bright lines
21
322 THE SPECTROSCOPE.
of metals and the Fraunhofer lines, and for viewing any two spectra simul-
taneously. These direct-vision spectroscopes are better adapted for general
use by those who have not several different instruments, than such forms as
that shown in Fig. 229, for in the direct-vision instruments the whole extent
of the spectrum is visible at one view, which is by no means the case with
the larger instruments.
FIG. 227. Section of Micro-Spectrosoope.
CELESTIAL CHEMISTRY AND PHYSICS.
\ \ 7"E now approach that portion of our subject in which its interest cul-
* * minates, for however remarkable may be some of the above-named
results of this searching optical analysis, they are surpassed by those which
have been obtained in the field upon* which we are about to enter. The
cause of the dark lines which Fraunhofer observed in the light of the sun
and of certain stars remained unexplained, he only establishing the fact that
they must be due to some absorptive power existing in the sun and stars
themselves, and not to anything in our atmosphere. It was reserved for
Professor Kirchhoff, of the University of Heidelberg, to show the full signi-
ficance of the dark lines. Fraunhofer had, on his first observation of the
lines, noticed that the D lines were coincident with the bright lines in the
spectrum of sodium. This interesting fact may be readily observed with
any spectroscope which permits of the two spectra being simultaneously
viewed. The bright line (or lines if the spectroscope be powerful) of the
metal is seen as a prolongation of the dark D solar line. Even with an
instrument like that shown in Fig. 220 the coincidence may be noticed.
Let the observer receive into the instrument the rays in diffused daylight
only, when he will still see the principal Fraunhofer lines distinctly, and
let him note the exact position of the D line, while he brings in front of the
slit the flame of a spirit-lamp charged with a little salt. He will then see
the bright yellow line replacing the dark D line, and by alternately removing
and putting back the lamp he will be soon convinced of the perfectly iden-
tical position of the lines.
This fact remained without explanation from 1814 to 1859, when Kirchhoff
accidentally found, to his surprise, that the dark D line could be produced
THE SPECTROSCOPE. 323
artificially. He says : " In order to test in the most direct manner possible
the frequently asserted fact of the coincidence of the sodium lines with the
D lines, I obtained a tolerably bright solar spectrum, and brought a flame
coloured by sodium vapour in front of the slit. I then saw the dark lines
D, change into bright ones. The flame of a Bunsen's lamp threw the bright
sodium lines upon the solar spectrum with unexpected brilliancy. v In order
to find out the extent to which the intensity of the solar spectrum' could be
increased without impairing the distinctness of the sodium lines, I allowed
the full sunlight to shine through the sodium flame, and, to my astonish-
ment, I saw that the dark lines, D, appeared with an extraordinary degree
of clearness. I then exchanged the sunlight for the Drummond's or oxy-
hydrogen lime-light, which, like that of all incandescent solid or liquid
bodies, gives a spectrum containing no dark lines. When this light was
allowed to fall through a suitable flame, coloured by common salt, dark
lines were seen in the spectrum in the position of the sodium lines. The
same phenomenon was observed if, instead of the incandescent lime, a
platinum wire was used, which, being heated in the flame, was brought to
a temperature near its melting point, by passing an electric current through
it. The phenomenon in question is easily explained, upon the supposi-
tion that the sodium flame absorbs rays of the same degree of refrangi-
bility as those it emits, whilst it is perfectly transparent for all other rays."
(Quoted in Roscoe's Lectures on " Spectrum Analysis.") When the light
of ignited lime was similarly made to pass through flames containing the
incandescent vapours of potassium, barium, strontium, &c., the bright lines
which these substances would have produced had the lime-light not been
present were found to be in every case changed into dark lines, occupying
the very same positions in the spectrum. In such experiments the flames
containing the metals in the vapourized state do all the time really give
off those rays which are peculiar to each substance ; but when a more
intense illumination such as the lime-light, the electric arc, or direct
sunlight passes through them, the rays of the spectrum produced by the
intense light overpower those given off by the relatively feebly coloured
flames, and hence the portions of the spectrum which are occupied by
these, appear black. But as the intense light would give a perfectly con-
tinuous spectrum if the incandescent metallic vapour allowed the rays
corresponding to its lines to pass through it, the inference is obvious that
each vapour absorbs those particular rays which it has itself the power of
emitting, but allows all others to pass freely through it. Besides the experi-
mental proofs of this fact which have been already adduced, many others
might be named. The flame of a spirit-lamp with a salted wick appears
opaque and smoky when we look through it at a large flame of burning
hydrogen, also coloured by sodium ; for the rays emitted by the latter do
not penetrate the former, which, in consequence of its feebler light, appears
dark by comparison. Again, if an exhausted tube containing metallic
sodium be heated so as to convert the sodium into vapour, the tube viewed
by the light of a sodium flame appear to contain a black smoke, and the
light from the flame will no more pass through it than through a solid
object ; yet the tube appears perfectly transparent when viewed by ordi-
nary light, and the light from a lithium or other coloured flame would also
pass freely. Kirchhoff was led by purely theoretical reasoning to conclude
that all luminous bodies have precisely the same power of absorbing certain
rays of light as they have of emitting them at the same temperature, and
he thus brought luminous rays under the same general law which had
212
324 THE SPECTROSCOPE.
previously been established for radiant heat by Prevost, Dessains, Balfour
Stewart, and others. Here, then, a law was arrived at, and, abundantly
confirmed by direct experiment as regards the more volatile metals, it
was ready to supply the most satisfactory explanation of the coincidences
which were everywhere discovered to exist between the Fraunhofer lines
and those which belong to terrestrial substances. For Kirchhoff also
found, when mapping the very numerous lines seen in the spark spectrum
of iron, that for each of the 90 bright lines of iron which he then observed,
there was a dark line in the solar spectrum exactly corresponding in posi-
tion. The number of observed bright lines in the iron spectrum has been
since extended to 460, and yet each is found to have its exact counterpart
in a solar dark line.
So many coincidences as these made it certain that these dark lines and
the bright lines of iron must have a common cause, for the chances against
the supposition that the agreement was merely accidental are enormous.
Kirchhoff actually calculated, by the theory of probabilities, the odds against
the supposition. He found it represented by i ,ocx),ooo,oc)o,ooo,ooo,ooo to i.
The result arrived at in the case of sodium at once suggested the expla-
nation that these lines were produced by an absorptive effect of the vapour
of iron. Now, the existence of such a vapour in our atmosphere could not
be admitted, while the temperature of the sun was known to be exceedingly
high, far higher, indeed, than any temperature we can produce by electri-
city, or any other means. Hence, Kirchhoff concluded that his observa-
tions proved the presence of the vapour of iron in the sun's atmosphere
with as much certainty as if the iron had been actually submitted to chemi-
cal tests. By the same reasoning, Kirchhoff also demonstrated the existence
in the solar atmosphere of calcium, chromium, magnesium, nickel, barium,
copper, and zinc. To these, other observers have added strontium, cad-
mium, cobalt, manganese, lead, potassium, aluminium, titanium, uranium,
and hydrogen. It has also been demonstrated that a considerable number
of the Fraunhofer lines are due to absorption in our atmosphere by its gases
and aqueous vapour. This demonstration of the existence of iron and
nickel in the sun is an interesting pendent to the known composition of
many meteorites which reach us from interplanetary space.
Kirchhoff was led to believe that the central part of the sun is formed of
an incandescent solid or liquid, giving out rays of all refrangibility, just as
white-hot carbon does ; that round this there is an immense atmosphere,
in which sodium, iron, aluminium, &c., exist in the state of gas, where they
have the power of absorbing certain rays ; that the solar atmosphere ex-
tends far beyond the sun, and forms the corona ; and that the dark sun-
spots, which astronomers have supposed to be cavities, are a kind of cloud,
floating in the vaporous atmosphere.
During total eclipses of the sun, certain red-coloured prominences have
been noticed projecting from the sun's limb, and visible only when the glare
of its disc is entirely intercepted by the moon. Fig. 228 represents a total
eclipse, and will give a rude notion of the appearance of the red prominences
seen against the fainter light of the corona, which extends to a considerable
distance beyond the sun's disc. Now, two distinguished men of science
.Simultaneously and independently made the discovery of a mode of seeing
these red prominences, even when the sun was unobscured. M. Janssen
was observing a total eclipse of the sun in India, and the examination by
the spectroscope of the light emitted from the red prominences showed
him that they were due to immense columns of incandescent hydrogen, for
THE SPECTROSCOPE.
325
FIG. ill. Solar Eclipse, 1869.
he recognized the red line and blue lines which belong to the spectrum of
this gas (see No. 12, Plate VI.). Mr. Norman Lockyer at the same time
also succeeded in viewing the solar prominences in "London without an
eclipse. He found a red line per-
fectly coinciding in position with
Fraunhofer's C line and that of hy-
drogen, another nearly coinciding
with F, and a third yellow line near
D. Soon after this, Dr. Huggins dis-
covered a mode of observing the
shape of the red prominences at any
time, by using a powerful train of
prisms and a wide slit, so that the
changes in the forms of the red
flames can be followed. Now, since
the red prominences give off only a
few rays of particular refrangibility,
it is not difficult to understand that
the light of the sun might be, as it
were, so diluted by stretching out
the spectrum, by means of a train of
many prisms, that almost only the red
rays, C, should enter the telescope,
and occupy the field with sufficient
intensity to overpower all others, and produce an image of the object from
which they originated. The nature of this action may be illustrated thus : If
we hold vertically a prism, and look through it at a candle-flame, we may per-
ceive a lengthened-out image of the flame, showing the succession of pris-
matic colours, and formed, as it were, of a red image of the flame close to a
yellow one, and so on, but presenting no defined form. If, still viewing this
spectrum, we introduce into the flame on a platinum wire a piece of common
salt, we shall perceive a well-defined yellow image of the candle start out,
because the rays which are emitted by the incandescent sodium, being all
of one refrangibility, the prism simply refracts without dispersing them.
The dispersion which weakens the light of the continuous spectrum by
lengthening it out, does not sensibly detract from the brilliancy of the bright
lines, as their breadth is scarcely increased they are refracted but not dis-
persed. Hence, when a sufficient number of prisms is employed, the bright
lines of the solar chromosphere may be seen in full sunshine, in spite of the
greater intensity of the light emanating from the photosphere, which pro-
duces the continuous spectrum. The bright C line is, of course, a virtual
image of the slit produced by rays of that particular refrangibility ; but by
using a very high dispersive power, the slit may be opened so wide that the
C rays form in the telescope a red image of the prominence from which they
issue, since their light will predominate over that of any rays belonging to
the continuous spectrum.
In the hands of Mr. Norman Lockyer the science of the physical and
chemical constitution of the sun has made rapid progress, and new facts
are continually being observed, which serve to furnish more and more defi-
nite views. Mr. Lockyer considers that, extending to a great distance around
the sun is an atmosphere of comparatively cooler hydrogen, or perhaps of
some still lighter substance which is unknown to us. It is this which forms
what is termed the corona, or circle of light which is seen surrounding the
326 THE SPECTROSCOPE.
sun in a total eclipse. Immersed in this, and extending to a much smaller
distance from the nucleus of the sun, is another envelope, termed the chroma-
sphere, consisting of incandescent hydrogen and some glowing vapours of
magnesium and calcium. The brightest part of this envelope, which lies
nearest the sun, is that which gives off the red rays by which the promi-
nences may be observed without an eclipse. These prominences have been
shown to be tremendous outbursts of glowing hydrogen, belched up with
sometimes an enormous velocity from below, since they have been observed
to spring up 90,000 miles in a few minutes. Beneath the chromosphere,
and nearer to the body of the sun, are enormous quantities of the vapours
of the different elements sodium, iron, &c. to which the dark lines of the
solar spectrum are due. This stratum Mr. Lockyer calls the reversing layer,
because it reverses (turns to dark) the lines which would otherwise have
appeared bright, just as KirchhofFs sodium vapour did in the experiment
described on page 323. Beneath the reversing layer is the photo sphere, from
which emanates the light that is absorbed in part by the reversing layer,
and which there is good reason to believe is either intensely heated solid
or liquid matter.
In 1861 Dr. Huggins devoted himself, with an ardour which has since
known no remission, to the extension of prismatic analysis to the other
heavenly bodies. The difficulties of the investigations were great. There
was first the small quantity of light which a star sends to the spectator ;
this was obviated by the use of a telescope of large aperture, which ad-
mitted and brought to a focus many more rays from the star, and therefore
the brightness of the image was proportionately increased. Not so the
size of the image : the case of the fixed stars for this always remains a
mere point. It was, of course, necessary to drive the telescope by clock-
work, so that the light of the star might be stationary on the field of the
spectroscope. As the spectrum of the image of the star formed by the
object-glass would be a mere line, without sufficient breadth for an obser-
vation of the dark or light lines by which it might be crossed, it is necessary
to spread out the image so that the whole of the light may be drawn
out into a very narrow line, having a length no greater than will produce
a spectrum broad enough for the eye to distinguish the lines in it. This
is accomplished by means of a cylindrical lens placed in the focus of the
object-glass, and immediately in front of the slit Covering one-half of
the slit is a right-angled prism by which the light to be compared with that
of the star is reflected into the slit. The light is usually that produced
by taking electric sparks between wires of the metal in the manner already
described. The dispersive power of the spectroscope was furnished by two
prisms of very dense glass, and the spectrum was viewed through a tele-
scope of short focal length. Dr. Muggins's observations lead him to the
conclusion that the planets Mars, Jupiter, and Saturn possess atmospheres,
as does also the beautiful ring by which Saturn is surrounded ; for he
noticed in the spectrum of each different dark lines not belonging to the
solar spectrum.
Passing to the results obtained in the case of the fixed stars, we may
remind the reader of the enormous distance of the bodies which are sub-
mitted to the new method of analysis. Sir John Herschel gives the follow-
ing illustration of the remoteness of Sirius supposed to be one of the
nearest of the fixed stars : Take a globe, 2 ft. in diameter, to represent the
sun, and at a distance of 215 ft. place a pea, to give the proportionate size
and distance of the earth. If you wish to represent the distance of Sirius
THE SPECTROSCOPE. 327
on the same scale, you must suppose something placed forty thousand
miles away from the little models of sun and earth. But not only do we
know with certainty some of the substances contained in Sirius, but the
star spectroscope has taught us a great deal about orbs so remote, that
their distance is absolutely unmeasurable. About Aldebaran we know
that there are hydrogen gas and vapours of magnesium, iron, calcium,
sodium, and some four or five other elements. Generally the lines indicate
the presence of hydrogen in these distant suns ; but there is, at least, one
FIG. 229. The Planet Saturn.
remarkable exception in a Orionis, the spectrum of which yields no trace
of the hydrogen lines, although it is evident that magnesium, sodium,
calcium, &c., are present The spectra of celestial bodies are of several
kinds. Many of the stars have, like our sun, a continuous spectrum crossed
by dark lines. Such is that of Sirius, No. 10, Plate VI. Others have,
however, both dark and bright lines, and some are marked by only three
bright spaces. Of the spectra of the nebulae some have three bright lines
(see No. n, Plate VI.), and the bodies producing them are, therefore, to
be considered as masses of incandescent gas, while some give continuous
spectra. One of the bright lines in the spectra of the nebulae coincides
with one of the hydrogen lines, and another the brightest of the three
with one of the brightest nitrogen lines ; but the third does not agree with
any with which it has as yet been compared. The inference from these
appearances is that the nebulae contain hydrogen and nitrogen, but the
absence of the other lines of these substances has not been fully explained ;
although the observation of Dr. Huggins, that when the light of incande-
scent nitrogen and hydrogen is gradually obscured by interposing layers
of neutral tinted glass, the lines corresponding with those in the nebulas:
328 THE SPECTROSCOPE.
spectra are the last to disappear, seems to suggest a probable solution of
the difficulty.
There is another very interesting line of spectroscopic research in the
power the prism gives us of estimating the velocity with which the distances
of the stars from our system are increasing or diminishing. On closely
examining the hydrogen lines cf Sirius, and comparing them with the bright
lines of hydrogen rendered incandescent by electric discharges in a Geissler
tube, the spectrum of which his instrument enabled him to place side by
side with that of the star, Mr. Huggins was surprised to find that the lines
in the latter did not exactly coincide in position with those of the former,
but appeared slightly nearer the red end of the spectrum. This indicated
FIG. 230. Solar Prominences, No. i.
a longer wave-length, or increased period of vibration, according to the
theory of light, which would be accounted for by a receding motion between
Sirius and the earth, junt as the crest of successive waves of the sea would
overtake a boat going in the same direction at longer intervals of time than
those at which they would pass a fixed point, while, if the boat were meet-
ing the waves, these intervals would, on the other hand, be shorter. H ence,
if the position of the lines in the spectrum depends on the periods of vibra-
tion, that position will be shifted towards the red end when the luminous
body is receding from the earth with a velocity comparable to that of light,
and towards the violet end when the motion is one of approach. The change
in refrangibility observed by Mr. Huggins corresponded with a receding
velocity of 41-4 miles per second, and when from this was subtracted the
known speed with which the earth's motion round the sun was carrying us
from the star at the time, the remainder expressed a motion of recession
THE SPECTROSCOPE.
329
amounting to about twenty miles a second, which motion, there is reason
to believe, is chiefly due to a proper movement of Sirius. These deduc-
tions from prismatic observations are of the highest value astronomically,
since they will eventually enable the real motions of the stars to be deter-
mined, for ordinary observation could only show us that component of the
motion which is at right angles to the visual ray, while this gives the com-
ponent along the visual ray. In the same manner, it is inferred that Arc-
_
'
FIG. 231. Solar Prominences, No. 2.
turus, a bright star in the constellation Bootes, is approaching us with a
velocity of fifty-five miles per second.
When the solar spots are examined with the spectroscope, the dark image
of the slit produced by the hydrogen line, F, is observed to show a strange
crookedness when it is formed by rays from different parts of the spot.
This distortion is due to the same cause as the displacement of the stellar
lines, namely, motions of approach or recession of the masses of glowing
hydrogen. Mr. Norman Lockyer, to whom we are indebted for the most
elaborate investigations of the solar surface, has calculated, from the posi-
tion of the lines, the velocities with which masses of heated hydrogen are
seen bursting upwards, and those which belong to the down-rushes of cooler
gas. Velocities as great as 100 miles per second were, in this way, inferred
to occur in some of the storms which agitate the solar surface. Two draw-
ings of a solar storm, given by Mr. Lockyer, are shown in Figs. 230 and
231. These are representations of one of the so-called red prominences,
the first giving its appearance at five minutes past eleven on the morning
of March I4th, 1869, and the last showing the same ten minutes after-
330 THE SPECTROSCOPE.
wards. The enormous velocity which these rapid changes imply will be
understood when it is stated that this prominence was 27,000 miles high.
"This will give you some idea," says Mr. Lockyer, " of the indications which
the spectroscope reveals to us, of the enormous forces at work in the sun,
merely as representing the stars, for everything we have to say about the
sun the prism tells us and it was the first to tell us we must assume to
be said about the stars. I have little doubt that, as time rolls on, the spec-
troscope will become, in fact, almost the pocket companion of every one
amongst us ; and it is utterly impossible to foresee what depths of space
will not in time be gauged and completely investigated by this new method
of research."
The light of comets has also been examined by the spectroscope, and
many interesting results arrived at. Our limits do not, however, permit
us to enter into a discussion of these interesting subjects.
Fig. 232 is a section of another of Mr. Browning's popular instruments,
which is named by him the " Amateur's Star Spectroscope." It exhibits
very distinctly the different spectra of the various stars, nebulae, comets, &c.
FIG. 232. Section of Amateur's Star Spectroscope.
The reader who is desirous of learning more of this fascinating subject
is referred to Dr. Roscoe's elegant volume, entitled, " Lectures on Spectrum
Analysis." This work, which is embellished with handsome engravings
and illustrated by coloured maps and spectra, gives a clear and full account
of every department of the subject, and in the form of appendices, abstracts
of the more important original papers are supplied, while a complete list
is given of all the memoirs and publications relating to the spectroscope
which have been published.
This brief account of the spectroscope and its revelations, which is all
that our space permits us to give, will not fail to awaken new thoughts in
the mind of a reader who has obtained even a glimpse of the nature of the
subject, especially in relation to that branch of which we have last treated,
for in every age and in every region the stars have attracted the gaze and
excited the imagination of men. The belief in their influence over human
affairs was profound, universal, and enduring ; for it survived the dawn of
rising science, being among the last shades of the long night of supersti-
tion which melted away in the morning of true knowledge. Even Francis
Bacon, the father of the inductive philosophy, and old Sir Thomas Browne,
the exposer of " Vulgar Errors," believed in the influences of the stars ; for
while recognizing the impostures practised by its professors, they still re-
garded astrology as a science not altogether vain. It was reserved for the
mighty genius of Newton to prove that in very truth there are invisible
ties connecting our earth with those remote and brilliant bodies ties more
potent than ever astrology divined ; for he showed that even the most dis-
tant orb is bound to its companions and to our planet by the same power
THE SPECTROSCOPE.
that draws the projected stone to the ground. And now the spectroscope
is revealing other lines of connection, and showing that not gravitation alone
is the sympathetic bond which unites our globe to the celestial orbs, but
that there exists the closer tie of a common constitution, for they are all
made of the same matter, obeying the same physical and chemical laws
which belong to it on the earth. We learn that hydrogen, and magnesium,
and iron, and other familiar substances, exist in these inconceivably distant
suns, and there exhibit the identical properties which characterize them
here. We confirm, by the spectroscope, the fact partially revealed by other
lines of research, that the stars which appear so fixed, are, in reality, career-
ing through space, each with its proper motion. We learn also that the
stars are the theatres of vast chemical and physical changes and trans-
formations, the rapidity and extent of which we can hardly conceive. There
is, for example, the case of that wonderful star in the constellation of the
Crown, which, in 1866, suddenly blazed out, from a scarcely descernible
telescopic star, to become one of the most conspicuous in the heavens, and
the bright lines its beams produced in the spectroscope revealed the fact
that this abrupt splendour was due to masses who can imagine how vast ?
of incandescent hydrogen. This brightness soon waned, and r Cor ones
Borealis reverted once more to all but telescopic invisibility. The seeming
fixity of the stars is an illusion of the same nature as that which prevents
a casual observer from recognizing their apparent diurnal motion, and now
we have also ample evidence that permanence of physical condition, even
in the stars, is impossible. Everywhere in the universe there is motion and
change ; there is no pause, no rest, but a continual unfolding, an endles
progression.
And emulate, vaulted,
" Know the stars yonder,
The stars everlasting,
Are fugitive also,
The lambent heat-lightning,
And fire-fly's flight."
FIG. 233. Portrait of Professor Helmholtz.
SIGHT.
THE investigations of modern science have borne rich fruit, not only by
vastly extending our knowledge of the universe of things around us,
but also making us acquainted with the mode in which certain agents act
upon our bodily organs, and by revealing, up to a certain point, what may
be termed the mechanism of that most wonderful thing the human mind
or, at least, that part which is immediately concerned in the perceptions
of an external world. Of all the physical influences which affect the human
mind, those due to light are the most powerful and the most agreeable.
One of the most ancient of philosophers says, in the simple words which
are appropriate to the expression of an undeniable truth, " Truly the light
is sweet, and a pleasant thing it is for the eyes to behold the sun." The
impression produced by light alone is a source of pleasure a cheering in-
fluence of the highest order ; and there is a special character in the pleasing
effects of light, from the circumstance that they do not exhaust the sense
so quickly as do even pleasurable impressions on other organs such as
sweet tastes, fragrant odours, or agreeable sounds. Sight is not liable
to that satiety which soon overtakes the enjoyment of sensations arising
332
SIGHT. 333
from the other senses ; it possesses, therefore, a refinement of quality of
which the rest are devoid. Sight converses with its objects at a greater
distance than does any other sense, and it furnishes our minds with a
greater variety of ideas. Indeed, our mental imagery is most largely made
up of reminiscences of visual impressions ; for when the idea of anything
is brought up in our minds by a word, for example, there arises, in most
cases, a more or less vivid presentation of some visible appearance. Our
visual impressions are also longer retained in memory or idea than any
other class of sensations.
The nature of the impressions we receive through the eye is extremely
varied ; for we thus perceive not only the difference between light and
darkness, but in the sensations of colour we have quite another class ol
effects, while the lustre and sparkle of polished and brilliant objects add
new elements of beauty and variety. We find examples of the latter
qualities in the verdant sheen of the smooth leaf, in the splendid reflec-
tions of burnished gold, in the bright radiance of glittering gems, and " in
gloss of satin and glimmer of pearls." The eye is also the organ which
conveys to our minds the impressions of visible motion, with all those plea-
sures of exciting spectacle which enter so largely into our enjoyment of
life. It likewise discriminates the forms, sizes, and distances of objects ;
but by a process long misunderstood, and dependent upon a set of percep-
tions which, although precisely those whence we derive our most funda-
mental notions of the objects around us, have been completely overlooked
in that time-honoured enumeration of the senses which recognizes only five.
If such be the extent to which our minds are dependent upon the wonder-
ful apparatus of the eye, it may easily be imagined what must be the com-
parative narrowness of mental development in those who have never en-
joyed this precious sense, and the feeling of deprivation in those, who,
having enjoyed it, have unfortunately lost it. Well may our sublime poet
despairingly ask
Since light so necessary is to life,
And almost life itself if it be true
That light is in the soul
The all in every part : why was the sight
To such a tender ball as the eye confined,
So obvious and so easy to be quenched ? "
for he himself, in his own person, experienced this deprivation, and he
thus touchingly, in his great work, laments his loss :
" Thus with the year
Seasons return ; but not to me returns
Day, or the sweet approach of even or morn,
Or sight of vernal bloom, or summer's rose,
Or flocks, or herds, or human face divine ;
But cloud instead, and ever-during dark
Surround me ; from the cheerful ways of men
Cut off; and for the book of knowledge fair
Presented with a universal blank
Of Nature's works to me expunged and rased,
And wisdom at one entrance quite shut out."
An organ which is the instrument of so many nice discriminations as is
the eye must, of course, present the most delicate adjustment in its parts.
So much has in recent times been learnt of the nature of its mechanism ;
of the relation between the impressions made upon it and the judgments
formed by the mind therefrom ; of the illusions which its very structure
produces ; of the defects to which it is liable ; and of its wonderfully
334
SIGHT.
refined physiological elements that a branch of science sufficiently exten-
sive to require a large part of a studious lifetime for its complete mastery
has grown up under the hands of modern physiologists, physicists, and
psychologists. To some of the results of their labour we would invite the
reader's attention ; and in order to render the account of them intelligible,
we must, to a certain extent, describe " things new and old."
THE EYE.
FIG. 234. Vertical Section of the Eye.
/ T* HE form of the human eye and the general arrangement of its parts may
* be understood by referring to Fig. 234, which is a section of the eye-
ball. It has a form nearly globular, and is covered on the outside by a tough
firm case, A, named the sclerotic coat, which is, for the most part, white
and opaque. This covering it is which forms what is commonly termed
the " white of the eye ; " but in the front part of the eyeball it loses its
STGHT. 335
opacity, and merges into a transparent substance, termed the cornea, B.
The cornea has a greater convexity than the rest of the exterior of the eye-
ball, so that it causes the front part of the eye to have a somewhat greater
projection than would result from its general globular form. This sclerotic
coat with its continuation, the cornea serves to support and protect the
more delicate parts within, and is itself kept in shape by the humours,
which fill the whole of the interior. The greater space is occupied by the
vitreous humour ', C ; but the space immediately behind the transparent
cornea is filled with the aqueous humour, D. The latter is little else than
pure water, and the former is like thin transparent jelly. The cavities con-
taining these two humours are separated by the transparent double convex
lens, E, called the crystalline lens, which, in consistence, resembles very
thick jelly or soft gristle. The outward surface of this lens has a flatter
curvature than the inner surface. Immediately in front of the crystalline
lens is found the iris, F, which may be described as a curtain having in the
middle a round hole. The iris is the part which varies in colour from one
individual to another being blue, brown, grey, &c. ; and the aperture in
its centre is the dark circular spot termed the pupil.
The general disposition of the parts of the eye with regard to light will
be most easily understood by comparing it with an optical instrument, to
which it bears no little resemblance, namely, the camera obscura, so well
known in connection with photography. We may picture to ourselves a
still more complete resemblance, by imagining that the lens of the camera
is single, that we have fixed in front of it a watch-glass, with the convex side
outwards, and that we have filled with water the whole of the interior of
the camera, including the space between the watch-glass and the lens. The
focussing-screen of the camera corresponds with the inner surface of the
back of the eyeball, about which we shall presently ha^e more to say. Now,
even if the camera had no lens, but were simply a box filled with water,
and having in front the watch-glass, fixed in the manner just mentioned,
we could obtain the images of objects on the screen, as a consequence 01
the curvature of the watch-glass. It would, however, in this case, be neces-
sary to have the camera much longer, or, in other words, the rays would
be brought to a focus at a greater distance than if we put in the glass lens,
which would, thus placed in the water, cause the rays to converge to a
focus at a much shorter distance, although its effect when surrounded by
water would be less powerful than in the air. There we see the effect of
the crystalline lens of the eye in bringing the rays to a focus within a much
shorter distance than that which would be required had there been present
only the curved cornea, and the aqueous and vitreous humours of the eye,
which are but little different from pure water in their optical properties.
If vfQ focus the camera by adjusting the distance between the lens and
the screen so as to get a distinct image of a near object, we should find, on
directing the instrument to a distant one, that the image would be blurred
and indistinct, and the lens would have to be moved nearer to the screen ;
or we could get the image of the distant object distinct by replacing the
lens by another lens in the same position, but having some flatter curva-
ture. It is plain that the same object would be gained if our lens could be
made of some elastic material, which, on being pulled out radially at its
edges, could be made to assume the required degree of flatness without
losing its lenticular form. Now, it is precisely with an automatic adjust-
ment of this kind that the crystalline lens of the eye is provided, for the
lens is suspended by an elastic ligament, G, by the tension of which its sur-
336
SIGHT.
faces are more flattened than they would otherwise be ; but when the ten-
sion of this ligament is relaxed, by the action of certain delicate muscles
which draw it down, the elasticity of the lens causes it to assume a more
convex form.
These optical adjustments give, on the inner surface of the coats of the
eye, a more or less perfect real image of the objects to which the eye is
directed, and it is on the back part of this inner surface that the network
of nerves, called the retina^ H, is spread out. The sclerotic coat, already
spoken of, is lined internally with another, named the choroid, which is
composed of delicate blood-vessels, inter-
mingled with a tissue of cells filled with
a substance of an intensely black colour.
It is upon this last layer that the delicate
membrane of the retina is spread out be-
tween the choroid and the vitreous humour.
The retina is, in part, an expansion of the
fibres of the optic nerve over the back part
of the eyeball. If we suppose the globe of
this cut vertically into two portions, and so
divide the front from the back part of the
eye, the retina would be seen spread out on
the concave surface of the back part, and in
the middle of this part, opposite the crys-
talline lens, would be seen a spot in which
the retina assumes a yellowish colour, and
in the centre of this, a little round pit or
depression. The spot is called the macula
lutea, or yellow spot, and the little central
pit, which is of the highest importance in
vision, is termed the fovea centralis. A
little way from the yellow spot, and nearer
the nose, is a point from which a number
of fibres are seen to radiate, and this is, in
fact, the part at which the optic nerve enters
the eyeball, and from which it sends out its
ramifications over the retina. This part,
for a reason which will shortly appear, is
called the blind spot.
When the minute structure of the retina
is examined by the microscope, its physio-
logical elements are found to undergo very
remarkable modifications at the yellow
spot. In the retina, although the total
thickness does not exceed the g^th part of
an inch, no fewer than eight or ten different
essential or nervous layers have been distinguished. Fig. 235 rudely repre-
sents a section. The lowest stratum, A, which is next the choroid, and forms
about a quarter of the total thickness, is formed of a multitude of little
rod-shaped bodies, a, ranged side by side, and among these are the conical
or bottle-shaped bodies, b. This lowest stratum of the retina is called the
layer of rods and cones. At their front extremities the rods and cones pass
into very delicate fibres, which, going through an extremely fine layer of
fibres, B, are connected with a series of small rounded bodies, which form
FIG. 235.
Section of Retina.
SIGHT. 337
the layer of nuclei, C, separated by a layer of nervous fibres, D, from a
granular layer, E, in front of which is a stratum of still finer granules, F,
underlying a layer of ganglionic nerve-cells, G, of a larger size than any of
the other elements, and these ganglionic cells send out numerous branching
nerve-fibres, forming the layer H. Finally, on the front surface of the retina
there is a thin stratum formed of fibres, which issue from the optic nerve, K,
Fig. 234, and in fact constitute the expansion of this nerve on the inner
surface of the eyeball. The terminations of some, at least, of these nerve-
fibres have been traced, and have been found to form junctions with those
branching from the ganglionic cells.
Of the part played by each of these delicate structures in exciting visual
impressions little is yet known. How light, or the pulsations of ether, if
such there be, is ultimately converted into sensation will probably for ever
remain a mystery, although it is quite likely that the kind of visual impres-
sion which is conveyed by each part of the elaborate structure of the retina
FIG. 236.
may ultimately be distinguished. One curious result of modern investiga-
tion is that light falling directly upon fibres of the optic nerve is quite
incapable of exciting any sensation whatever. Light has no more effect on
this nerve and its fibres than it would have on any other nerve of the body
if exposed to its action. The apparatus of rods, cones, and other structures
are absolutely essential to enable light to give that stimulus to the optic
nerve which, conveyed to the brain, is converted into visual sensations. So
if this apparatus were absent in our organs of vision, in vain would the
optic nerve proper be spread out over the interior of the eyeball : we should
be no more able to see with such eyes than we are able to see with our
hands.
We now invite the reader's careful consideration to the diagram, Fig. 236,
which is a section of the retina through the yellow spot. The upper part
of the figure is the front, and the deep depression is the little pit already
spoken of ihefovea centralis. The lowest dark line represents the base-
ment membrane of the retina, and immediately above is seen the layer of
rods and cones, and the various strata already spoken of are represented
in their due order in the marginal parts of the diagram. Now observe the
remarkable modifications of the nervous structures in the neighbourhood
of the fovea centralis, some of which are visible in the diagram. In the
first place, the cones are there much longer, more slender, and more closely
set, so that there is a far greater number of them on a given surface ; but
22
33 8 SIGHT.
the rods are comparatively few, and are, in fact, not found at all under the
floor of the little pit. The layer of nuclei, into which the cones extend, is
thinner, and is found almost immediately below the anterior surface, for
all the other layers thin out in the fovea in a very curious manner. It is,
however on the margin of the fovea that the stratum of ganglionic cells, G,
Fig. 235, attains its greatest thickness, for there it is formed by the super-
position of eight or ten cells, being here thicker than any other layer, while
it is so thinned off towards the margin of the retina that it no longer forms
even a continuous stratum. This layer, however, becomes much thinner
in the fo^ea^ which contains, in fact, but few superposed cells. The tint of
the yellow spot is said to be derived from a colouring matter, which affects
all the layers except that of the cones. The centre of the yellow spot,
where the fovea centralis is situated, is extremely transparent, and is so
delicate that it is very easily ruptured, and has frequently been taken for
an aperture.
We should not have risked wearying the reader with these details con-
cerning the little pit in the centre of the retina had it not possessed an
extreme importance in the mechanism of the eye, a fact which he will at
once appreciate when we say that of the whole surface of the retina, the only
spot where the image of an object can produce distinct vision is the fovea
centralis. Since this is undoubtedly true, it follows that the physiological
elements which we there find are precisely those which are most essential
for producing this effect. The case may be exemplified by recurring to
the comparison of the eye with a photographer's camera, by supposing his
screen to be of such a nature that only on one very small spot near its
centre could a distinct image be possibly obtained of just one point of an
object. Such a defect in his camera would render the photographer's art
impossible, and this defect (if it may be so called) in the eye would render
it almost equally useless, had not an adjustment, which more than com-
pensates for it, been afforded in the extreme mobility of our organs of vision.
This adjustment is so perfect that people in general do not even suspect that
the image of each point of an object which they distinctly see must be formed
on one particular spot on the retina a spot about one-tenth of the diameter
of an ordinary pin-head ! We may venture, without any disrespect to the
reader, to assume that the chances are that it is new to him to learn how each
letter in the lines beneath his eye must successively, but momentarily, form
its image in the very little pit in the centre of his retina; and the chances are
at least a hundred to one that, even if aware of this, he has passively received
the statement, and that he has not made the least attempt to realise the truth
for himself. Yet nothing is easier. Let him request a friend to slowly peruse
some printed page, while he meanwhile intently watches his friend's eyes.
He will then perceive that before a single word can be read there is a move-
ment of the eyeballs, which are, quite unconsciously to the person reading,
so directed that the image of each letter (for the area of distinct vision is
incapable of receiving more than this at once) shall fall upon the only parts
of the retinae from which a distinct impression can be conveyed along the
optic nerve. Thus it is that the eye, without any conscious effort of the
observer, is directed in succession to the various points of an object, and
it is only by an effort of will in fixing the eyes upon one spot that one be-
comes aware of the blurred and confused forms of all the rest of the visual
picture. Yet so readily do the eyeballs turn to any part of the indistinct
picture on which the attention is fixed, that it is not improbable a person
unversed in such experiments, wishing to verify our conclusions by looking,
SIGHT.
339
say, at one spot on the opposite wall, will be very apt, in thinking of the
features of the rest of the picture, to direct his eyes there, and then declare
that he, at least, sees no such vague forms. If such be his experience,
the correction is easy. He has only to ask some one to watch closely his
eyes while he repeats the experiment, and after a few trials he will suc-
ceed in maintaining the requisite immobility of the eyeballs a condition
upon which the success of many such experiments depends.
This extreme mobility of the eyeballs more than compensates for the
loss of the clear and well-defined picture, for it calls into action one of
the most sensitive of all the impressions of which we are capable, and
one which possesses in so high a degree the power of uniting with our
FIG. 237 '.Muscles of Eyes.
The muscles of the eyeballs viewed from above : B, the internal rectus ; E, the external rectus ;
s, the superior rectus ; T, the superior oblique, passing through a. loop of ligament at u, and
turning outwards and downwards to its insertion at c. The inferior rectus and the inferior
oblique are not visible in the figure : the superior rectus is removed from the right eyeball in
order to show the optic nerve N.
other sensations, that this sixth sense has been, as already stated, utterly
overlooked, except by the more modern students of the nature of our
sensations. It is usually termed the muscular sense, and to it are due
some of the nicest distinctions of impressions of which we are capable. The
muscles of every part of our frame take their part in producing impressions
in our minds, and those of the eyeballs have a very large share in furnish-
ing us with ideas of forms and motions. Fig. 237 is a diagram showing
the general arrangement of these muscles ; and their anatomical designa-
tions, which need not much concern us at present, are given beneath the
figure. The wonder is, that the sensations arising from the relative con-
ditions of parts so few, should afford us the immense variety of notions re-
ferrible for their origin to these muscles only. We take one example in
222
340
SIGHT.
illustration. Suppose we watch the flight of a bird, at such an elevation
that no part of the landscape comes into the field of view at all ; and that,
again, we follow with the eye, under similar circumstances, the path of a
rocket. We can unhesitatingly pronounce the motions unlike, and yet in
each case there was no visual impression present but that of the object
focussed upon the yellow spot. But the movement of the muscles in one
case was different from that in the other. Nay more, we can form such a
judgment of the motion as to pronounce that the object followed such and
such a curve we may recognize the parabola in one path, and the circle,
perhaps, in the other. And this kind of discrimination arises from the fact,
that when we have, maybe times without number, previously looked at
parabolas and circles, in diagrams perhaps, the muscles of the eyeballs
have performed just the same series of movements, as point after point of
the line was made to form its image on the yellow spot. This is not the
only class of impressions that these muscles are capable of affording ; there
Is, for example, little doubt that they aid us in estimating distance. But
space will not permit further discussion of this subject.
Although the blurred and indefinite retinal picture may be compen-
sated, and perhaps more than compensated, by the readiness with which
the eyes move, it is, of course, possible that greater precision and delicacy
of visual impression over the whole surface of the retina might be consis-
tent with a still greater increase of our powers of perception. There are
instances in which the absence of finish, as it may be termed, in all but one
little spot in the picture, proves a real inconvenience and a sensible depri-
vation. Perhaps a friend calls our attention to the fact that a balloon is
sailing through the air, or some fine morning, hearing in the fields the
blithe song of the sky-lark, we look up and vainly try to bring the small
image upon the place of distinct vision. Now, if an image which falls upon
any other part of the retina is perceived, even indistinctly, an instant suffices
to direct the eyes into the exact position requisite for clear vision an ex-
ample of the marvellous precision with which impressions are put in rela-
tion to each other by the unconscious action of the brain. But while an
image on the fovea, only ^nfe^th of an inch diameter, produces a distinct
sensation, it is found that if the image falls on the retina at a point some
distance from the yellow spot, the image must be 1 50 times larger in order
to produce any impression ; and it is in consequence of the image of balloon
or bird not having the requisite size to give any impression to the less sen-
sitive portion of the retina, that we grope blindly, as it were, until by chance
the image falls near the yellow spot, when the tentative motion of the eye-
balls is instantly arrested, and the image fixed. On the other hand, the
field of indistinct vision which the eye takes in is extremely wide, for bright
objects are thus perceived, even when their direction forms an angle laterally
of nearly 90 with the axis of the eye ; and, if the object be not only bright,
but in motion, its presence is noticed under such circumstances with still
greater ease. Thus, an observer scanning the heavens would have a per-
ception of a shooting star anywhere within nearly half the hemisphere. The
range is, however, less than 90 in a vertical direction.
We have said that the fibres of the optic nerve, entering the back part
of the eyeball, at K, Fig. 234, ramify over the anterior surface of the retina
in fibres which form a layer of considerable relative thickness. The light,
therefore, first encounters these nerves, and only after traversing their
transparent substance does it reach the deeper seated layer of rods and
tones, where it excites some action that is capable of stimulating the optic
SIGHT.
nerve. These rods and cones might naturally be supposed to be merely
accessory to the fibres of the optic nerve, had we not the following conclu-
sive evidence that the cones play a necessary part in the action, and that
it is only through them that light acts upon the optic nerve :
1. The cones are more developed and more numerous in the spot where
vision is most distinct
2. The " blind spot " is full of fibres of
the optic nerve, but is absolutely insen-
sible to light, and is without rods or cones.
3. We can distinguish an image on the
fovea, having only guWh of an inch dia-
meter ; but on the other parts of the retina
the images must have larger dimensions.
It is found that the size of the smallest
distinguishable images agrees nearly with
the diameters of the cones at the respec-
tive parts.
To some readers the fact will doubt-
less be new, that a considerable por-
tion of the eye is quite insensible to
light, namely, that portion already de-
signated as the " blind spot." A simple
experiment, made by help of Fig. 238,
will prove this. Place the book so that
the length of the figure may be parallel
to the line joining the eyes, and let the
right eye be exactly opposite the white
cross, and at a distance from it of about
1 1 in. If the left eye be now closed, while
with the right the cross is steadily viewed
so that it is always clear and distinct,
the white circle will completely disappear,
and the ground will appear of a uniform
black colour. In order to insure success,
the observer must be careful not to look
at the white circle, but at the cross, and
some persons find this more difficult than
others. The position of the blind spot in
the eye has been already mentioned, and
its significance in showing the insensi-
bility to light of the fibres of the optic
nerve has been pointed out. In the table
of the dimensions of some parts of the
eye, which, for convenience of reference,
is given together below, it will be seen that
the diameter of the blind spot is consider-
able compared with the size of the retina,
its greatest diameter being about =, D in.
The length on the retina of the image of a man at a distance of 6 ft. or 7 ft.
is not greater than this, so that in a certain position with regard to the eye
a person would, like the white circle, be quite invisible. In like manner,
by looking steadily in a certain direction with one eye, the image of the
full moon maybe made to fall upon the blind spot, and the luminary then
FlG. 238.
342 SIGHT.
becomes invisible, and would be so even if its apparent diameter were
eleven times greater ; so that if we suppose eleven full moons ranged in a
line, the whole would be quite invisible to a person looking towards a cer-
tain point of the sky at no great angular distance from them.
The following are the dimensions in English inches of some parts of the
eye:
In.
Diameter of the entrance of the optic nerve 0*08
Distance of centre of optic nerve from centre of yellow
spot 0-138
Diameter Qifovea centralis '. 0*008
Diameter of the nerve-cells of the retina 0*0005
Diameter of the nuclei o f oooc>3
Diameter of the rods o'oooo4
Diameter of the cones in yellow spot 0*00018
Length of rods 0*0016
Length of cones in yellow spot 0*0008
Thickness of retina at the back of the eye 0*0058
By means of an instrument to be presently described, the ophthalmoscope,
it is possible to view directly the whole surface of the retina, and to observe
the inverted images of the objects there depicted. It is thus observed that
it is only on the parts near the yellow spot that the images are formed with
clear and sharp definition. Away from this the definition is less perfect ;
and besides the diminished sensitiveness of the retina, this circumstance
contributes to the vagueness of the visual picture, although the falling off
in clearness of vision at a very little distance from the yellow spot is far
more marked than the loss of definition in the image there formed.
Until within the last few years it has been most confidently asserted by
many authors that the eye, considered as an optical instrument, is abso-
lutely perfect, and entirely free from certain defects to which artificial in-
struments are liable. Thus Dr. W. B. Carpenter states, in his " Animal
Physiology" (1859) : "The eye is much more remarkable for its perfection
as an optical instrument than we might be led to suppose from the cursory
view we have hitherto taken of its functions ; for, by the peculiarities of its
construction, certain faults and defects are avoided, to which all ordinary
optical instruments are liable." Among the imperfections which are com-
pletely corrected in the eye, he names u spherical aberration " and " chro-
matic aberration" both of which give rise to certain defects in optical
instruments. But by recent careful investigations it has been conclusively
shown that the eye is not free from chromatic aberration ; that it has
defects analogous to spherical aberration ; and that there are, besides,
certain optical imperfections in its structure, which are avoided in the
artificial instruments. Professor Helmholtz, one of the most distinguished
of German mathematicians, physicists, and physiologists, whose great work
on " Physiological Optics " is the most complete treatise on the subject
which has ever appeared, is so far from considering the eye as possessed
of all optical perfections that he remarks that, should an optician send him
an instrument having like optical defects, he would feel justified in sending
it back. The defects which may be traced in the eye, considered as an
optical instrument, do not, however, he admits, detract from the excellence
of the eye considered as the organ of vision.
When we find that Sir Isaac Newton pointed out the chromatic aberra-
SIGHT. 343
tion of the eye two centuries ago when we find that D'Alembert, in 1767,
proved that the lenses of the eye might have as great a dispersive power
as glass without the want of achromatism necessarily becoming noticeable
when we find that the celebrated optician Dolland, the inventor of the
achromatic lens, showed that the refractions which take place in the eye
all tend to bring the violet rays towards the axis more than the red when
we find that Maskelyne the astronomer, Wollaston the physicist, Fraun-
hofer the optician, and other scarcely less distinguished men of science,,
have made actual measurements of the distances of the fact in the human
eye for the different rays of the spectrum when we find how these defects
have so long ago been observed, examined, and measured as to their amount
the persistence with which writer after writer has asserted the achroma-
tism of the human eye appears so extraordinary, that it can only be accounted
for by the prevalence of the preconceived notion that the eye is absolutely
perfect a notion not without its reason and grounds, in the fact of the
exquisite adaptation of the organ of sight to the needs of humanity.
Although the want of achromatism in the eye thus escapes ordinary-
notice, it is, on the other hand, easy to render it evident by simple experi-
ments. If, for example, we view from a certain distance the solar spectrum
projected on a white screen, it will be found that, when we see the red end
quite distinctly, the violet end will, at the same time, appear vague and
confused, and vice versa. The author believes that the following very
simple experiment will at once convince any person that the fact is as
stated. Procure a small piece of blue or violet stained glass, and another
piece of red glass, and, having cut out of an opaque screen a rectangular
opening, say | in. long and \ in. wide, place the glasses close to it, so that
one-half the opening is covered by the red glass and the other half by the
violet glass, the two being placed so that, on looking through the screen, a
violet square and a red square are visible. The opaque screen may be
made of black paper, cardboard, or tinfoil, and the edges of the opening
must be cut perfectly even. On looking through this arrangement, held at
a distance of about two feet from the eye, both squares may be seen dis-
tinctly by a person of ordinary vision ; but, at a distance of five inches from
the eye, he will find it impossible to see the squares otherwise than with
vague and ill-defined edges. This is because the crystalline lens cannot
adapt its curvature so as to bring the rays from the object to a focus on the
retina. Now, by trial, the nearest distance at which each of the coloured
squares becomes visible may be found, and it will be observed, that the
violet square is first sharply defined at a less distance than the red, where-
as, if the eye brought the red and violet rays to a focus at the same point,
the smallest distance of distinct vision would coincide in both cases.
The reader may observe the same fact for himself, in even a still simpler
manner, by turning to Fig. 238, page 341. When the white circle is viewed
by one eye, at a distance of about a foot, and an opaque screen, such as a
coin, is held close to the eye, so that the pupil is half covered by it, the
one side of the white circle will appear bordered by a narrow fringe of blue,
and the other side by a narrow fringe of orange. If the opaque screen be
shifted from one side of the pupil to the other, the colours will change
places, the orange appearing always on the same side of the white circle
as the screen is held before the eye. The same appearances are presented
in a still more marked degree when the full moon is made the subject of
the experiment.
The diagram, Fig. 239, shows the course of the red and violet rays from
344
SIGHT.
aluminous point, A, the refraction being supposed to take place at E l B ? .
The violet rays after refraction form the cone, B lt E, Bo, and E is their
focus ; the red rays form the cone, B 1? F, B 2 , and have a focus at F. The posi-
tion of the retina would be intermediate between E and F, and is indicated
by c x , C 2 . It will be noticed that the violet rays cross, and are received on
the retina in the same circle, G G, so tha*- the colours, then blended, would
be separately imperceptible ; but the point would produce a diffused cir-
cular image of the blended colours.
In viewing an object the moon, for example the accommodation of
the eye is like that indicated in the diagram. The distinct image due to
the red rays would be formed behind the retina, and that due to the violet
rays would be in front of it. In the image on the retina the most intense
rays such as the orange, yellow, and green are those which are blended
by the adjustment of the eye, and the red and violet form images more
out of focus (to use a common expression), and a very little larger than the
more intense image. We might expect that a white disc would therefore
appear with a fringe of colour, resulting from a mixture of red and violet ;
but the fringe is too narrow, and the colour itself too feeble, to become
perceptible. When, however, the pupil of the eye is half covered, the red
and violet images are displaced in different directions, the position of the
retina being too far forward for the one, and too far back for the other. The
coincidence therefore ceasing, the colours show themselves at the margins
of the image.
The non-perception under ordinary circumstances of the chromatic aber-
ration of the eye is largely due to the greater intensity of the colours which
differ least in their refrangibilities. The clearness of our vision does not,
therefore, practically suffer from this defect of the eye. Professor Helm-
holtz constructed lenses which rendered his eyes really achromatic, and
looking through these when the pupil was half covered, no coloured fringes
were seen at the edges of dark or light objects, or when the objects were
looked at with an imperfect accommodation of the eye. He was, however,
unable to detect any increase of clearness or distinctness of vision by the
correction.
The eye is also subject to other aberrations and irregular refractions,
which are special to itself; for example, with moderately illuminated objects
the crystalline lens produces images apparently well defined, and nothing
is visible to suggest the absence of uniformity in its structure. But when
the light is intense, and concentrated in a small object surrounded by a dark
field, the irregular structure of the crystalline lens shows itself in the most
marked manner. Eveiy one must have noticed the appearance presented
by the distant street-lamps on a dark night, and by the stars. The latter
SIGHT. 345
we know to be for us mere points of light, and their images produced by
perfect lenses would also be mere points ; instead of which we see what
seem to be rays issuing from the star, an appearance which has given rise
to the ordinary representation of a star as a figure having several rays.
That no such rays actually do emanate from the real star may be easily
proved: first, by concealing the luminous point from view, by means of a
small object held up as a screen. If the rays had any existence outside of
the eye, they would still be seen ; instead of which, the whole of them dis-
appear when the luminous point, or, in the case of the street-lamp, when
the flame, is covered by the screen. A second proof that the origin of
the phenomenon is in the eye, and not in the object, is afforded by the fact
that if, while attentively observing the rays, we incline the head, the rays
turn with the eyes, so that when the head is resting on the shoulder
the ray which appeared vertical
becomes horizontal. The cause
of these divergences from the
regular image lies in the fact of
the crystalline lens being built
Up of fibres which have refrac-
tive powers somewhat different
from that of the intermediate sub-
stance. These fibres are arranged
in layers parallel to the surfaces
of the crystalline lens, and the di-
rection of the fibres in each layer
is generally from the centre to the
tircumference ; but towards the
axis they form, by bending, a kind
of six-rayed figure, as shown in
Fig. 240, which represents the FlG. 240.
arrangement of the fibres of the
external layers of the lens. In the outermost layers the branches of the
star-shaped figure are subdivided into secondary branches, which give
rise to more complicated figures. When we view by night a very brilliant
but small light, even these subdivisions may be traced in the radiating
figure.
The light which enters the eye is partly absorbed by the black pigment
of the choroid, and partly sent back by diffused reflection from the retina
through the crystalline lens and pupil. The image of a luminous body as
depicted on the retina of another person cannot be seen by us under ordinary
circumstances, because, by the principle of reversibility already mentioned
as of universal application in optics, the rays which issue from the retinal
images are refracted on leaving the eye, and follow the same paths by
Which they entered it, so that they are sent back to the object. An ob-
server cannot see the retinal image of a candle in another person's eye,
unless he allows the rays to enter his own, and this cannot be done directly,
because the head of the observer would be interposed between the candle
and the eye observed, and the light would then be intercepted. By hold-
ing a piece of unsilvered plate glass vertically, we may reflect the light of
a candle into the eye of another person, and then the light thrown out
from the retinal image of the candle will, on again meeting the surface of
the glass, be in part reflected to its source, and in part pass through the
glass, on the other side of which it may be received into the eye of an
346
SIGHT.
observer. The positions of the observed and observing eye may be de-
scribed as exactly opposite to and near each other, while the candle is
placed to one side in the plane separating the two ayes, and the glass is
held so that it forms an angle of 45 with the line Jo inm g the P u P lls - Und er
these circumstances the observer may see the light at the back of the eye,
but he will not be able to distinguish anything clearly, because his own eye
cannot accommodate itself so as to bring to a focus the rays coming from
the retina of the other, since these rays are refracted by the media through
which they emerge. But, by means of suitable lenses interposed between
the two eyes, the retina and all its details may be distinctly seen and
examined. Such an arrangement of lenses and a reflecting surface con-
FlG. 241. Ruefe's Ophthalmoscope.
stitute the instrument called the ophthalmoscope (o^daX^os, the eye) of which
there are many forms, but all constructed on the principle just indicated.
This principle was first pointed out by Helmholtz, who described the first
ophthalmoscope in 1851.
Ruete's ophthalmoscope is represented in Fig. 241. The parts of the in-
strument are supported on a stand, c, and about the vertical axis of this the
column, D, and the arms, H and K, can turn freely and independently ; E is
a concave metallic mirror, about 3 in. in diameter, and having an aperture in
its centre through which the observer, B, looks. The arm, H, merely carries
a black opaque screen, which serves to shield the eye of B from the light of
the lamp, and to reduce, if required, the amount of light passing through the
aperture in the mirror. The arm, K, which is about a foot in length,
carries two uprights which slide along it, and in each of these slides a rod
bearing a lens, which can thus be adjusted into any required position. The
instrument is used in an apartment where all light but that of the lamp can
be excluded. In the instrument just described an inverted image is obtained,
which is sufficient for ordinary medical purposes, but this construction does
SIGHT. 347
not allow of the examination of retinal images, which is best performed with
an instrument having a plane mirror.
The appearance presented by the back of the eye when viewed in the
ophthalmoscope is represented in Fig. 242. The retina appears red, except
at the place where the optic nerve enters, which is white. On the reddish
ground the retinal blood-vessels can be distinguished ; A, A, A, branches
of the retinal artery, have a brighter red colour, and more strongly reflect
the light than the branches, B, B, B, of the retinal vein. Among these, and
especially towards the margin, are seen, more or less distinctly, the broader
vessels of the choroid. Above the optic nerve and a little to the right may
be observed the fovea centralis.
FIG. 242.
During the last twenty years the ophthalmoscope has been the chief
means of extending the knowledge of oculists regarding the diseased and
healthy conditions of the eye. In this way the substance of the lens and
the state of the humours can be directly seen, the causes of impaired
vision can be discovered, and the nature of many maladies made out with
certainty. This modern invention, by which the interesting spectacle of
the interior of the living eye can be observed, has therefore been far from
proving a barren triumph of science. Many insidious maladies can thus
be detected, and may be successfully treated before the organ has become
hopelessly diseased. In some cases the ophthalmoscope gives the most
certain evidence of the existence of obscure and unsuspected diseases of
other parts of the body.
34 8 SIGHT.
VISUAL IMPRESSIONS.
EVERYBODY knows that, however well the flat picture of an object
may imitate the colours and forms of nature, we are never deceived into
supposing that we have the real object before us. There must, therefore, be
something different in the conditions under which we see real objects from
those under which we view their pictures. The most favourable circum-
stances for receiving an illusive impression of solidity from a flat picture, is
when we view it from a fixed position and with one eye. This is because
one means by which we unconsciously estimate distances depends upon the
changes in the perspective appearances of objects caused by changes in
our point of view. In many cases these changes in the perspective are the
only means we have of judging of the relative distances of objects. But
there is another circumstance which is still more intimately connected with
our perception of solidity. Each eye receives a slightly different image of
the objects before us (unless these be extremely remote), inasmuch as they
are viewed from a different point. When the objects are very near, the two
retinal images may differ considerably, as the reader may convince himself
by viewing with each eye, alternately, objects immediately before him,
while the other eye is closed, and the head all the while motionless. The
nearer objects will plainly appear to shift their positions as seen against
the background of the more distant objects ; and a somewhat more care-
ful observation will reveal changes of perspective, or apparent form, in
every one of these objects. An extreme case is presented in that of a play-
ing card, or ihin book, held in the plane which divides the eyes. The back
or the face, the one side or the other, will be seen, according as the right
or the left eye is opened. If we close the left eye, the displacement and
change of apparent form produced by a slight movement of the head are
sufficiently obvious ; a movement of the head T\ in. to the left causes a
decided change in the relative positions of adjacent objects. It is plain,
however, that it is precisely from a point 2| in. to the left that the left eye
views these objects, and hence the perspective appearance seen by the
left eye must have the difference due to this shifting of the point of view.
On the other hand, if one looks at a picture, or flat surface, placed imme-
diately in front, no change in the relative positions of its parts is discernible
by viewing it with either eye alternately. Not but that there is a difference
in the retinal images in the two cases, but there is an absence of any point
of comparison by which the change may be judged. If we take a photo-
graph of a statue, it will, when viewed by one or the other eye, present the
difference of the retinal images which is due to a flat surface ; the parts of
the photographic image will be of slightly different proportions as seen by
each eye. If, instead of the photograph we have before our eyes a statuette,
each eye will see a quite different view : the right eye will see a portion
which is invisible to the left eye, and vice versd, and, in fact, we shall see
more than half round the object. Here, then, we have certain differences
of the retinal pictures when solid objects are viewed, and these differences
by innumerable repetitions have, unconsciously to ourselves, become asso-
ciated with notions of solidity, of something having length, breadth, and
depth, or thickness. The marvellous delicacy of these perceptions will be
alluded to hereafter.
SIGHT.
349
Let us suppose that the lenses of two cameras are fixed in the positions
occupied by the two eyes, and that a photograph is taken in each camera,
the subject being, for example, a statuette. It is obvious that the diffe-
rences of the two photographs would correspond with the differences of the
two retinal images, and that, if a person could view with the right eye only
the photograph taken in the right-hand camera, and with the left eye the
left-hand photograph only, there would be formed on the retinae of his eyes
images very nearly corresponding with those which the actual object would
produce, and the result would be, if these retinal pictures occupied the
proper position on the eyes, that the impression of solidity would be pro-
duced, which is called the stereoscopic effect.
This may be done without the aid of any instrument, as almost any per-
son may discover after some trials with nothing but a stereoscopic slide, if
he can succeed in maintaining the optic axis of his eyes quite parallel. In
such a case he will observe the stereoscopic effect by the fusing together, as
it were, into one sensation, of the impression received by the right eye from
the right photograph, with that received by the left eye from the left photo-
graph. But as each eye will, at the same time, have the photograph in-
tended for the other in the field of view, the observer will be conscious of
a non-stereoscopic image on each side of the central stereoscopic one.
FIG. 243. WheatstonJs Reflecting Stereoscope.
These outside images are, however, very distracting, for the moment the
attention is in the least directed to them, the optic axes converge to the
one side or the other, losing their parallelism, and the stereoscopic effect
vanishes, because the images no longer fall in the usual positions on the
retinae. It is, in consequence, only after some practice that one succeeds
in readily viewing stereoscopic slides in this manner, but the acquirement
is a convenient one when a person has rapidly to inspect a number of such
slides, for he can see them stereoscopically without putting them in the
instrument. Many persons, however, find great difficulty in acquiring this
power. In such cases it is well to begin by separating the two photographs
by means of a piece of cardboard, covered with black paper on both sides.
When this is held in the plane between the eyes, each eye sees only its
own photograph, and the observer is not troubled with the two exterior
images. After a little practice in this way, the cardboard may usually be
dispensed with, and the observer will insensibly have acquired the habit
of viewing the slides stereoscopically, without any aid whatever.
Instruments have, however, been contrived which enable one to obtain
the desired result without effort ; and one form of these is now tolerably
35
SIGHT.
well known to everybody. The first stereoscope was the invention of
Wheatstone. The reflecting stereoscope is represented in Fig. 243, and
consists essentially of two plane metallic mirrors inclined to the front of the
instrument at angles of 45, so that in each of them the observer sees only
the design which belongs to it. The rays reach the eyes as if they came
from images placed in front of the observer ; and the two images having
the proper differences, produce together the impression of solid objects.
Brewster's stereoscope -which is far more widely known than Wheat-
stone's has two acute prisms, or, more usually, two portions of a convex
lens are cut out, and placed with their margins or thin parts inwards, and
they thus produce the same effect as would be obtained by combinations
of a prism with a convex lens. Another very common form of the stereo-
scope has merely two convex lenses. The
effect of the convex lenses is to increase the
apparent size of the images by diminishing the
divergence of the rays emitted by each point,
producing the appearance of larger designs
seen at a greater distance. The effect of the
prism is to give the rays the direction which
they would have if they proceeded from an
object placed in a position immediately be-
tween the two designs, and an additional ele-
ment by which we estimate distance, namely,
the convergence of the optic axes, is made to
aid in the illusion, when the rays proceeding
from the two different pictures have approxi-
mately the inclination that they would have if
they emanated from real objects at the place
where the image is apparently formed. The
box or case in which the lenses or lenticular
prisms are placed takes various forms. One
of the most common is represented in Fig.
244, but the stand on which it is mounted is not
a necessary part of the instrument, although
it is sometimes convenient. A handsome
form is met with as a square case, enclosing a number of photographic
stereoscopic views mounted on an endless chain in such a manner that
they are brought successively into view by turning a knob on the outside.
When an instrument of this kind is fitted up with a series of the beautiful
landscape transparencies, which are produced by certain continental pho-
tographers, a more perfect reproduction of the impressions derived from
nature, exclusive of colour, cannot be conceived. We seem to be present
on the very spots which are so truthfully depicted by the subtile pencil of
the sunbeam ; we feel that we have but to advance a foot in order to mix
with the passengers in the streets of Paris or of Rome, and that a single
step will bring us on the mountain -side, or place us on the slippery
glacier ; at our own fireside we can feel the forty centuries looking down
upon us from the heights of those grand Egyptian pyramids, and find our-
selves bodily confronted with the mysterious Sphinx, still asking the solu-
tion of her enigma. The truth and force with which these stereoscopic
photographs reproduce the relief of buildings are such, that when one sees
for the first time the real edifice of which he has once examined the stereo-
scopic images, it no longer strikes him as new or unknown ; for he derives
FIG. 244.
SIGHT.
351
from the actual scene no impression of form that he has not already received
from the image.
But of all subjects of stereoscopic photography the glaciers are, perhaps,
those which best show the
power of the instrument as
far surpassing all other re-
sources of graphic presen-
tation. The most careful
painting fails to convey
a notion of the strange
glimmer of light which fills
the clefts of the ice, seen
through the transparent
substance itself. The
simple photograph com-
monly presents nothing
but a confused mass of
grey patches ; but com-
bine in the stereoscope
two such photographs,
each formed of nothing
but slightly different grey
patches, and a surprising
effect is at once produced :
the masses of ice assume
a palpable form, and the
beautiful effects of light
transmitted or reflected
by the translucent solid
reveal themselves. An-
other very beautiful class
of subjects for stereoscopic
slides is found in those
marvellous instantaneous
photographs, which seize
and fix the images of the
waves as they dash upon
the shore. Here a scene
which has tasked the
power of the greatest
painter is brought home
to us with such force and
vividness that *we all but
hear the wild uproar of
the breakers.
But for the art of pho-
tography the stereoscope ia 2 45-
would not thus be ready
to minister to our enjoyment, for no pictures wrought by man's handiwork
could approach the requisite accuracy which the two stereoscopic pictures
must possess. All attempts to produce such pictures by engraving or litho-
graphy have failed, except only in the case of linear geometrical designs,
such as representations of crystals. A very useful and suggestive applica*
352 SIGHT.
tion of the stereoscope has been made to the illustration of a treatise on
solid geometry, where the lines representing the planes, being drawn in
proper perspective, the reader by placing a simple stereoscope over the
plates sees the planes stand out in relief before him, and the multitude of
lines, angles, &c., which in a simple drawing might be distracting even for
a practised geometrician, assume a clear and definite form. The difference
between the two retinal pictures of objects is so slight, that when the objects
are at a little distance, ordinary observation fails to discover it without the
aid of special instruments ; and an inspection of the pair of photographs in
a stereoscopic slide will convince any one that, even in these, close and
careful observation is required to perceive the difference.
Some of the principles of stereoscopic drawings may be seen exemplified
by the pair we give in Fig. 245. With this figure the reader may attempt
the experiment of seeing the stereoscopic effect without the stereoscope.
When he has succeeded in doing this, or when he fuses the images together
by placing a simple stereoscope over the page, he will find the result very
singular ; for he will receive the impression of a solid crystal of seme dark
polished substance black lead, for instance placed on a surface of the
same material. The edges of the solid will appear to have a certain lustre,
such as one sees on the edges of a real crystal. The reason of this impres-
sion being produced by two drawings, one of which is formed by black
lines on a white ground, while the other has white lines on a black ground,
is probably due to the circumstance that we very often see in nature the
lustrous edges of an object with one eye only. That is, one eye is in the
path of the rays which are regularly reflected from the object, while the
other is not, a fact which may be verified in an instant by looking first with
one eye and then with the other, at a polished pencil, or similar object,
when placed in a certain position.
There is a kind of modification of the reflecting stereoscope, known under
the name of the pseudoscope, which is highly instructive, as showing how
much our notions of the solidity of objects are due to the differences of
the retinal images. In the pseudoscope the rays reach the eyes after pass-
ing through rectangular prisms in such a manner that objects on the right
appear on the left, and objects on the left appear on the right ; but the
images agree by reason of the symmetry of the reflection, although the
image of the objects that without the instrument would be formed in the
right eye is, by the action of the prisms, formed in the left eye, and vice
versa. The impressions produced are very curious : convex bodies appear
concave a coin, for example, seems to have the image hollowed out, a
pencil appears a cylindrical cavity, a globe seems a concave hemisphere,
and objects near at hand appear distant, and so on. These illusions are,
however, easily dispelled by any circumstance which brings before the
mind our knowledge of the actual forms, and by a mental effort it is pos-
sible to perceive the actual forms even with the pseudoscope, and indeed
to revert alternately, with the same object, from convexity to concavity.
This last effect is very curious, for the object appears to abruptly change
its form, becoming alternately hollow and projecting, according as the mind
dwells upon the one notion or the other ; but the experiment is attended
with a feeling of effort, which is very fatiguing to the eyes.
Professor Helmholtz has contrived another very curious instrument,
depending on the same principles as the stereoscope. He terms it the
telestereo scope, and while the effect of the pseudoscope is to reverse the
relief of objects, the telestereoscope merely exaggerates this relief ; hence
SIGHT.
353
this instrument is well adapted for making those objects which from their
distance present no stereoscopic effect, stand out in relief. The distance
between our eyes is not sufficiently great to give us sensibly different views
of very distant objects, and what the telestereoscope does is virtually to sepa-
rate our eyes to a greater distance. Fig. 246 is a horizontal section of the
instrument. L and R represent the position of the eyes of the spectator ;
a, d, are two plane mirrors at 45 to his line of sight ; A, B, are two larger
plane mirrors, respectively nearly parallel to the former. cda'L and/> R
show the paths of rays from distant objects, and it is obvious that the right
eye will obtain a view of the objects identical with that which would be
presented to an eye at R', while the left eye has similarly the picture of the
FIG. 246. 7 he Telestereoscope.
objects as seen from the point I/. The four mirrors are mounted in a box,
and means are provided for adjusting the positions of the larger mirrors,
as may be required. With this instrument the distant objects in a land-
scapea range of mountains, for example which present to the naked eye
little or no appearance of relief, have their projections and hollows revealed
in the most curious manner.
It is upon a similiar principle that stereoscopic views of some of the
celestial bodies have been obtained. Admirable stereoscopic slides of
the moon have been produced by photographing her at different times,
when the illumination of the surface is the same, but when, in consequence
of her libration, somewhat different views of our satellite are presented
to us. Two such photographs, properly combined in the stereoscope, give
not only the spherical form in full relief, but all the details of the surface :
the mountains, craters, valleys, and plains are seen in their true relative
projection.
The telestereoscope may be inverted, so to speak, and its effect reversed;
for an arrangement of mirrors similarly disposed, but on such a scale as
will permit the eyes to be respectively in the lines c d and/^-, would reflect
from objects in the direction L R rays which would have but little of the
difference of direction to which the stereoscopic effect is due. Hence solid
objects viewed with such an instrument appear exactly like flat pictures, the
effect being far more marked than in simply viewing them with one eye.
An ingenious method of exhibiting a stereoscopic effect to an audience
23
354 SIGHT.
has been contrived by Rollmann. He draws on a black ground two linear
stereoscopic designs that for the left eye with red lines, that for the right
eye with blue. Each individual in the audience is provided with a piece
of blue glass and a piece of red : he places the red glass before the left eye,
the blue glass before the right : each eye thus receives only the picture
intended for it, for the blue lines cannot be seen through the red glass, or
the red lines through the blue glass. The diagrams may, of course, be
projected on a screen by a magic lantern, in which case the circumstances
are even more favourable. Duboscq has arranged a kind of opera-glass,
so that a person may view appropriate designs on the large scale, and
arrangements have been also contrived by which the stereoscopic effect
may be seen in moving figures.
Every student of this interesting subject should examine a few stereo-
scopic images produced by simple lines representing geometrical figures,
or the photographs of the model of a crystal, as these exhibit in the most
striking manner the conditions requisite for the production of stereoscopic
effects. A person having a little skill in perspective and geometry might
construct the two stereoscopic images of a body defined by straight lines,
but the drawings must be executed with extreme exactitude, for the least
deviation would produce the most marked effect in the stereoscopic appear-
ance. The production of stereoscopic photographs now forms a'consider-
able branch of* industrial art. At first, these photographs were made by
taking the two different views with the same camera at two operations.
But there were difficulties in obtaining uniformity of depth in the impres-
sions, and the change in the shadows produced by the earth's rotation
showed itself although the interval between the two exposures might not
exceed thre or four minutes. The increased shadows in such cases show
themselves in the stereoscope, like dark screens suspended in the air. It
was Sir David Brewster who, in 1849, first proposed the plan now univer-
sally adopted, of producing the views simultaneously by twin cameras form-
ing their images on different parts of the same sensitive plate, the centres
of the lenses being placed at the same distance apart as a man's eyes, that
is, from i\ to 3 in. This is, of course, the only manner in which instan-
taneous views can be secured. Helmholtz, however, advocates the photo-
graphs of remote objects being taken at a much greater distance apart, for
they otherwise present little appearance of relief. By selecting from an
assortment of slides, two views of the Wetterhorn, taken from different
points in the Grindelwald valley, and combining these in the stereoscope,
he found that a far more distinct idea of the modelling of the mountain
could be thus obtained than even a spectator of the actual scene would
receive by viewing the mountain from any one point. Such a mode of com-
bining the photographs would produce in the stereoscope the same effect as
the telestereoscope would in the landscape, but the effect would be caused
to a proportionately far higher degree.
The date of Wheatstone's first publication regarding the stereoscope was
J 833 ; but a complete description and theory of the instrument was not
published until five years afterwards. Brewster first made public, in 1843,
his invention of the stereoscope with lenses, which is now sc familiar to us,
and few scientific instruments have become so quickly and extensively
popular ; certainly no other simple and inexpensive instrument has con-
tributed so largely to the amusement and instruction of our domestic circles.
And, to the philosopher who studies the nature of our perceptions, the
stereoscope has been even more instructive, for, instead of vague surmises,
SIGHT.
355
it provided him with the solid ground of experiment on which to found his
theories. The literature of this one subject stereoscopic effect is exten-
sive enough to occupy a tolerably long book-shelf. It dates from 300 B.C.,
when Euclid touched upon the subject in his Optics ; and after a lapse o<
more than eighteen centuries it was taken up by Baptista Porta, in 1583 ;
but the whole development of this subject belongs almost entirely to the
last half-century.
The part which the muscles of the eyes take in our perceptions of form
has been already alluded to, and it may be interesting to illustrate this
point by a curious example or two of illusions arising from their move-
ments. If our reader will glance at Fig. 247, he will see that the lines, a b
and c d, appear to be farther apart towards the centre than at the ends,
while fg and h z, on the other hand, appear nearest together in the middle.
He will hardly be convinced that in each case the lines are quite parallel
FIG. 247.
until he has actually measured the distances. A still more striking example
of the same kind of illusion is shown by Fig. 248, due to Zollner. This
appears a sort of pattern, in which the broad bands are not upright, but
sloping alternately to the right and left, and with the spaces between the
lines wider at one end than the other. The lines in the figure are, how-
ever, strictly parallel. The illusion by which they appear divergent and
convergent is still more strongly felt when the book is held so that the
wider bands are inclined at an angle of 45 to the horizon. There is another
illusion here with reference to the short lines, which will appear to be oppo-
site to the white spaces on the other side of the long lines to which they are
attached. That these illusions are really due to movements of the eyes
may be proved by viewing the designs in any manner which entirely pre-
vents the movement, as by fixing the gaze on one spot in the case of
Fig. 247, when the illusion will vanish ; but this, plan is not so easily applied
to Fig. 248. A convincing proof, however, will be found in the appearance
of these figures when they are viewed by the instantaneous light of the
electric spark, as when a Leyden jar is discharged in a dark room. The
reader viewing the figures, held near the place where the spark appears,
232
356
SIGHT.
FIG. 248.
will see them distinctly without the illusions as to the non-parallelism of the
Jines. In the absence of an electrical machine, or coil and jar, the reader
may have an opportunity of seeing the figures by flashes of lightning at
night, when the result will be the same.
There is a property of the eye which
has led to the production of many amus-
ing and curious illusions. This property
in itself is no new discovery, for its pre-
sence and effects must have been noticed
ages ago. The property in question is
illustrated when we twirl round a stick
or cord, burning with a red glow at the
end. We seem to trace a circle of fire;
but as the glowing spark cannot be in
more than one point of the circle at once,
it is plain that the impression produced
on the eye must remain until the spark
has completed its journey round the
circle, and reaching each point succes-
sively renews the luminous impression.
Like other subjects relating to vision,
this phenomenon has been carefully ex-
amined in recent times, and its laws
accurately determined.
The fact which is obvious from such an experiment, may be thus stated:
Visual impressions repeated with sufficient rapidity produce the effect of
objects continually present. This persistence of the visual impressions is
easily made the subject of experiment by means of rapidly rotating discs ;
and in the common toy called a " colour top " we have a ready means of
verifying some of the conclusions of science on this subject. Some very
interesting results may be> obtained by an apparatus as simple as this, re-
garding the laws of the phenomenon we are considering, and the effects of
various mixtures of tints and colours.
The well-known toy, the thaumatrope,
depends on the same principle. In this
a piece of cardboard is painted on one
side, with a bird, for example, and on
the other side with a cage : when the
cardboard is twirled round very rapidly
by means of a cord fixed at opposite
points of its length, both bird and cage
become visible at once, and the bird
appears in the cage.
A still more ingenious application of
this principle we owe to Plateau, who
described it in 1833, under the title of
FIG. 249.
\\\ephenakistiscope; and also to Stamp-
fer,who independent
lently devised the same
arrangement about the same time, and
named it the stroboscopic disc. The
teader may, at almost any toy-shop, purchase one of them, provided with
a number of amusing figures ; or he may easily construct for himself one
which will exemplify the principle. He requires no other materials than
SIGHT.
357
a piece of cardboard, and his only tools may be a sharp penknife, a pair
of compasses, and a flat ruler. Let him draw on his cardboard a circle of
8 in. diameter, and divide its circumference by eight equidistant points.
From, these radii should be drawn with the point of the compasses, and
equal distances from the centre marked off upon them, to fix the centres of
the small circles, which must all have exactly the same size (say, I in. in
diameter) and be marked by a distinct line. In these are to be marked the
hand of a clock-face in the positions shown in
Fig. 249 ; and finally, in the direction of the
radii, narrow slips are to be cut out of the
cardboard as shown. If a pin be put through
the centre of the disc, attaching it thus to the
flat end of a cork, so that it can freely rotate
in its own plane,, and the disc be turned rapidly
round, as in Fig. 250, in front of a looking-
glass, while the spectator looks through the
slits, he will see the hand on the little dial ap-
parently turning round, with rather a jerky
movement it is true, somewhat like the dead-
beat seconds-hand that is sometimes seen on
clocks. The illusion is best when the slits are
so narrow that only one of the several images
is visible by reflection, namely, that which is
adjacent to the slit. Thus, as the disc rotates,
each little circle is visible for an instant as the slit passes in front of the
spectator's eye ; and if the rotation be sufficiently rapid, the impression of
the disc is permanent, as it is constantly being renewed by the successive
circles, while, on the contrary, the hands, having different positions, pro-
FIG. 250.
FIG. 251.
tfoce images in different positions, giving the appearance of a jerky rotation.
The instruments sold in the shops have sometimes a thin metallic disc
with the slits in it, and a series of designs printed in smaller paper discs.
The paper discs may be screwed on the other disc as required, and a
button on a pulley with an endless band is provided for producing the
358
SIGHT.
rotation more conveniently. Fig. 251 shows one of the pictures for a disc
with twelve slits, and the effect produced by it is that of a dancing figure.
Another arrangement for showing the same illusion has lately become a
very popular toy, and quite deservedly so, for it has the advantages of re-
quiring no looking-glass, and of making the effect visible to a number of
persons at the same time. This apparatus, which has been termed the
Zoetrope, consists simply of a cylindrical box, like a drum with the upper end
cut off. It is mounted on a pivot, which permits its revolving rapidly about
its vertical axis when touched by the finger. The cylinder has a number of
equidistant vertical slits round the upper part of its circumference. The
figures which produce the illusion are printed on a slip of paper, which is
placed in the lower part of the drum, and when this is in rapid rotation,
and the figures are viewed through the slits, the illusion is produced in
exactly the same manner as in the revolving disc.
FIG. 252. Portrait of Sir W. Thompson.
ELECTRICITY.
ABOUT forty years ago a popular book was published having for its
theme the advantages which would flow from the general diffusion
of scientific knowledge. Great prominence was, of course, given to the
utility of science in its direct application to useful arts, and many scientific
inventions conducing to the general well-being of society were duly enume-
rated. Under the head of electricity, however, the writer of that book men-
tioned but few cases in which this mysterious agent aided in the accom-
plishment of any useful end. The meagre list he gives of the instances in
which he says " even electricity and galvanism might be rendered subser-
vient to the operations of art," comprises only orreries and models of corn-
mills and pumps turned by electricity, the designed splitting of a stone by
lightning, and the suggestion of Davy that the upper sheathing of ships
should be fastened with copper instead of iron nails, with a hint that the
same principle might be extended in its application. At the present day
the applications of electricity are so numerous and important, that even a
brief account of them would more than fill the present volume. Electricity
is the moving power of the most remarkable and distinguishing invention
of the age the telegraph ; it is the energy employed for ingeniously mea-
suring small intervals of time in chronoscopes, for controlling time-pieces,
359
360 ELECTRICITY.
and for firing mines and torpedoes ; it is the handmaid of art in electro-
plating and in the reproduction of engraved plates, blocks, letterpress, and
metal work ; it is the familiar spirit invoked by the chemist to effect mar-
vellous transformations, combinations, and decompositions ; it is a thera-
Deutic agent of the greatest value in the hands of the skilful physician,
.a'uch an extension of the practical applications of electricity as we have
indicated implies a corresponding development of the science itself ; and,
indeed, the history of electricity during the present century is a continuous
record of brilliant discoveries made by men of rare and commanding genius
such as Davy, Ampere, and Faraday. To give a complete account of
these discoveries would be to write a treatise on the science ; and although
the subject is extremely attractive, we must pass over many discoveries
which have a high scientific interest, and present to the reader so much of
this recently developed science as will enable him to comprehend the
principles of a few of its more striking applications.
The science of electricity presents some features which mark it with
special characters as distinguished from other branches of knowledge. In
mechanics and pneumatics and acoustics we have little difficulty in pic-
turing in our minds the nature of the actions which are concerned in the
phenomena. We can also extend ideas derived from ordinary experience
to embrace the more recondite operations to which heat and light may be
due, and, by conceptions of vibrating particles and undulatory ether, obtain
a mental grasp of these subtile agents. But with regard to electricity no
such conceptions have yet been framed no hypothesis has yet been ad-
vanced which satisfactorily explains the inner nature of electrical action,
or gives us a mental picture of any pulsations, rotations, or other motions
of particles, material or ethereal, that may represent all the phenomena.
Incapable as we are of framing a distinct conception of the real nature of
electricity, there are few natural agents with whose ways we are so well
acquainted as electricity. The laws of its action are as well known as
those of gravitation, and they are far better known than those which govern
chemical phenomena or the still more complex processes of organic life.
Definite as are the laws of electricity, there is no branch of natural or
physical science on which the ideas of people in general are so vague.
Spectators of the effects of this wonderful energy as seen violently and
destructively in the thunderstorm, and silently and harmlessly in the Aurora
knowing vaguely something of its powers in traversing the densest mate-
rials, in giving convulsive shocks, and in affecting substances of all kinds
the multitude regard electricity with a certain awe, and are always ready
to attribute to its agency any effect which appears mysterious or inex-
plicable. The popular ignorance on this subject is largely taken advantage
of by impostors and charlatans of every kind. Electric and magnetic
nostrums of every form, electric elixirs, galvanic hair-washes, magnetized
flannels, polarized tooth-brushes, and voltaic nightcaps appear to find a
ready sale, which speaks unmistakably of the less than half-knowledge
which is possessed by the public concerning even the elements of electrical
science.
^ Electricity has also a special position with regard to its intimate connec-
tion with almost every other form of natural energy. Evolved by mechani-
cal actions, by heat, by movements of magnets, and by chemical actions, it
is capable in its turn of reproducing any of these. It plays an important,
but as yet an undefined, part in the physiological actions constantly going
on in the organized body, and is, in fact, all-pervading in its influence over
ELECTRICITY. 361
all matter, organic and inorganic a secret power strangely but universally
concerned in all the operations of nature. We are compelled to regard
electricity not as a kind of force acting upon otherwise inert matter, but
rather as an affection or condition of which every kind of matter is capable,
although we are still unable to form a conjecture of the precise nature of
the action.
We have now to address ourselves to the task of unfolding so much of
the science as will enable the reader to understand the leading principles
of such important applications as electro-plating, illumination, and the
telegraph ; and this will necessarily include an account of the grand dis-
covery of the identity, or at least intimate connection, of magnetism and
electricity.
ELEMENTARY PHENOMENA OF MAGNETISM
AND ELECTRICITY.
THE distinctive property of a magnet is, as everybody knows, to
pieces of iron, and this property having been observed by the a:
attract
ic ancients
in a certain ore of iron which was found near the city of Magnesia, in Asia
Minor, the property itself came to be called Magnetism. A bar of steel, if
rubbed with the natural magnet or loadstone, acquires the same property,
and if the bar be suspended horizontally or poised on a pivot, it will settle
only in one definite direction, which in this country is nearly north and
south. If a narrow magnetized bar be plunged into iron filings, it will be
found that these are attracted chiefly by the ends of the bar, and not at all
by the centre. It appears as if the magnetic power were concentrated in
the extremities of the bar, and these are termed its poles, the pole at the
end of the bar which points to the north is called the north pole of the
magnet, and the other is named the south pole. If a north pole of one
magnet be presented to the north pole of another, they will repel each other,
and the same repulsion will take place between the south poles, whereas
the north pole of one magnet attracts the south pole of another. In other
words, poles of the same name repel each other, but poles of opposite names
attract each other, or still more concisely, like poles repel, ur.like poles
attract each other.
Magnetism acts through intervening non-magnetic matter with undi-
minished energy. Thus, the attractions and repulsions of magnetic poles
manifest themselves just as strongly when the poles are separated by a
stratum of wood or stone as when merely air intervenes, and the attraction
of small pieces of iron by a magnet takes place through the interposed
palm of one's hand without diminution. A delicately suspended needle in
even a remote apartment of a large building moves whenever a cart passes
in the street. It is almost too well known to require mention here, that
iron and steel are the only common substances which are capable of plainly
exhibiting magnetic forces, and, indeed, there are no known substances
capable of so powerful a magnetization as these. But the difference in the
magnetic behaviour of iron and steel is not so well understood, and it is a
point of importance for our subject, and connected with a fundamental law
which governs all magnetic manifestations. A piece of pure iron is very
readily cut with a file, whereas a piece of steel may be so hard that the file
362 ELECTRICITY.
makes no impression upon it whatever ; and hence a piece of pure iron, or
rather iron holding no carbon in combination, and possessed of no steely
quality, is often spoken of as soft iron. When a piece of soft iron is placed
near the pole of a magnet, the iron becomes, for the time, a magnet. If iron
filings be sprinkled over it, they will arrange themselves about the parts of
the iron respectively nearest and farthest from the magnet, thus showing
that the piece of soft iron has acquired magnetic poles. It will be found
on examining these poles that the one nearest the magnet is of the contrary
name to the pole of the magnet, and the farthest is of the same name. The
conversion of the soft iron into a magnet by the influence of a magnetic
pole is termed induction. It need hardly be said that the inductive effect
is more powerful in proportion to the shortness of the distance separating
the piece of soft iron from the magnetic pole, and, of course, the effect is
at its maximum when there is actual contact. Induction thus explains, by
aid of the law of the poles, the attraction which a magnet exercises over
pieces of iron, for it is plain that the inductive influence is accompanied
by attraction between the two contiguous oppositely-named poles of the
magnet, and of the piece of iron. But attraction is not the only force, for
the pole developed at the farthest portion of the piece of iron being of the
same name as the inducing pole, these will be mutually repulsive. The
attractive force will, however, be more powerful on account of the shorter
distance at which it is exerted, and will predominate over the repulsive
force, particularly at short distances, because then the difference will be
relatively greater. At distances from the inducing pole relatively great to
the distance between the two poles of the piece of iron, the difference may
be so small that its effect in attracting the piece of soft iron will be imper-
ceptible, and then the piece of iroa acted on by two (nearly) equal parallel
forces, will be subject to what is termed in mechanics a couple, the only
effect of which is to turn the body into such a position that the opposing
forces act along the same line. The definite direction assumed by a freely
suspended needle may be explained by supposing that the earth itself is a
magnet having a south pole in the northern hemisphere, and a north pole
in the southern hemisphere, the line joining these poles being shorter than
the axis of the earth, and not quite coinciding with it in position ; and the
fact of the needle being turned round but not bodily attracted is then easily
accounted for, the attractive and repulsive forces being reduced to a couple
in the manner just explained.
If the attempt be made to turn a piece of steel into a magnet, by the
induction of a magnetic pole, the same results will be obtained as in the
case of soft iron, but in a much feebler degree, and with this difference :
the piece of steel does not lose its magnetism when the inducing magnet
is withdrawn, whereas in the case of the soft iron every trace of mag-
netism vanishes the instant the inducing pole is removed. And if the
pole of the magnet be not only put in contact with one end of the piece of
steel, but rubbed on it, the piece will acquire permanent and powerful
magnetism. Hence it will be noticed that a piece of soft iron can by the
mere approximation of a magnetic pole be converted in an instant into a
magnet, and by the removal of the magnet can as instantly be deprived of
its magnetism, and made to revert into its ordinary condition ; while steel
is not so readily magnetized, but retains its magnetism permanently.
The elementary phenomena of electricity are extremely simple and easy .
of demonstration, and as the whole science rests upon inferences derived
from these, the reader would do well to perform the following simple expe-
ELECTRICITY.
363
riments for himself. Apparatus is represented in Fig. 253, but the only
essential portion is a straw, B, suspended from any convenient support by
a very fine filament of white silk. To one or both ends of the straw a little
disc of gilt paper, or a small ball of elder-pith or of cork, should be attached,
so that the straw may be balanced horizontally. Now rub on a piece of
woollen cloth a bit of sealing-wax, or a stick of sulphur, or a piece of amber,
or a penholder, paper-knife, or comb made of ebonite, and immediately
present the substance to the ball at the end of the straw. It will be first
attracted to the rubbed surface, but after coming into contact with it, repul-
sion will be manifested and the ball will se-
parate, and may be chased round the circle
by following it with the excited body. The
attraction of light bodies by amber after it
has been rubbed appears to be the one soli-
tary electrical observation recorded by the
ancients, but it has given its name to the
science, eXeKrpo*/ being the Greek name for
amber. The cause, then, of this property
is named electricity, and bodies which ex-
hibit it are said to be electrified. The reader
will remark that these words explain no-
thing : they are used merely to express a
certain state of matter and the entirely un-
known cause of that state. Let the pith
or cork ball at the end of the straw be again
charged with electricity, by bringing it into
contact with a piece of sealing-wax or ebo-
nite which has just been electrified by fric-
tion. In this condition it will, as we have
just seen, be repelled by the substance which
charged it, and on trial it will be found to be
repelled also by all the substances we have
named, after they have been excited by fric-
tion. But if, while still charged with the
electricity communicated to it by contact
with sealing-wax, sulphur, ebonite, or amber, we present to it a warm and
dry glass tube which has just been rubbed with dry silk, we shall find that
the ball will be strongly attracted. After contact with the glass, repulsion
will take place, and the ball will refuse again to come into contact with the
excited glass. In this condition, however, it will be immediately attracted
by rubbed sealing-wax or ebonite, and so on alternately : the ball when
repelled by the wax is attracted by the glass, and when repelled by the
glass is attracted by the wax.
These simple experiments prove that, whatever electricity may be, there
are two kinds of it, or, at least, it manifests two opposite sets of forces.
The electricity evolved by the friction of glass with silk was formerly called
vitreous electricity, and that shown by excited resin, sealing-wax, amber,
&c., was named resinous electricity. These names have now been respec-
tively replaced by the terms positive and negative. It must be understood
that these terms imply no actual excess or defect, but are purely distin-
guishing terms, just as we speak of the up and down line of a railway, with-
out implying an inclination in one direction or the other. A fact of great
importance in electrical theory is discovered when the substances in which
FIG. 253. A simple Electro-
scope.
364 ELECTRICITY.
electricity is developed are carefully examined : it is found that one kind
is never produced without the other simultaneously appearing. Thus, the
silk which has been used for rubbing the glass in the above experiments
will be found to exhibit the same electricity as sealing-wax or ebonite.
And, further, the quantities of positive and negative electricity evolved are
always found to be equal, or equivalent to each other ; that is, if they are
put together they completely neutralize or destroy each other's effects. We
have used the word " quantity," implying that electricity can be measured.
No doubt, whatever electricity may be, there may be more or less of it ; but
can we measure an imponderable, invisible, impalpable thing, incapable of
isolation ? What we really measure when we say that we measure elec-
tricity is the attractive or repulsive force : we balance this against some
other force (that of gravitation, for example), and we say, so much weight
lifted represents so much electricity.
If we try to electrify a piece of metal by holding it in the hand and rub-
bing it against woollen cloth, silk, or other substance, we shall fail in the
attempt : no signs of electricity will thus be shown by the metal. Hence
bodies were formerly divided into two classes those which could be elec-
trified by friction, and those which could not. It was afterwards found,
however, that there was no real ground for this division, but that, on the
contrary, no two bodies can be rubbed together, even if they are made of the
same substances, without positive electricity appearing in one, and an equi-
valent quantity of negative electricity in the other. The real difference be-
tween bodies which prevents the manifestation of electricity in many cases
depends upon the fact that electricity is able to traverse some substances
with great facility, while others prevent its passage. Thus, if we suspend
horizontally a hempen cord by white silk attached to the ceiling, so that
the hempen cord comes in contact with nothing but the silk, we shall find,
on presenting a piece of excited ebonite to one end of the cord, that electric
attraction of light bodies will be manifested at the other. If a silk cord be
substituted for the hempen one, no such effect will be observed. The hemp
is, therefore, said to be a conductor, and the silk a non-conductor. Again,
if we substitute for one of the silk threads suspending the cord a piece of
twine, or a wire, we shall fail to obtain any electric manifestations at the
remote end, because the electricity will be carried off into the earth by the
conducting powers of these substances. On the other hand, filaments of
glass or ebonite may be used, instead of the silk, with the same effect : they
do not allow the electricity to run through them to the ground, and are
therefore termed, like the silk, insulators of electricity. The distinction of
bodies into conductors on the one hand, arid into non-conductors or insu-
lators on the other, is of paramount importance in the science and in all
its applications. This distinction, however, is not an absolute one : there
is no substance so perfect an insulator that it will not permit any electricity
to pass, and there is no conductor so perfect that it does not offer resistance
to the passage. Substances may be arranged in a list which presents a
gradation from the best conductor to the best insulator. The metals are
by far the best conductors, but there is great relative diversity in their con-
ductive power. Silver, copper, and gold are much the best conductors
among the metals, iron offering eight times, and quicksilver fifty times, the
resistance of silver. Coke, charcoal, aqueous solutions, water, vegetables,
animals, and steam are all more or less conductors, while among the sub-
stances called insulators may be named, in order of increasing insulating
.power, india-rubber, porcelain, leather, paper, wool, silk, mica, glass, wax,
ELECTRICITY. 365
sulphur, resins, amber, gum-lac, gutta-percha, and ebonite. It will now be
obvious why the electricity developed by the friction of a piece of metal
fails to manifest itself under ordinary circumstances, as, for instance, when
held in the hand : the metal and the body being both conductors, the elec-
tricity escapes. But if the piece of metal be held by an insulating handle
of glass or ebonite, the electrified condition may easily be observed.
THEORY OF ELECTRICITY.
*"F*HE few elementary facts which have been pointed out are absolutely
* necessary for the foundation of what is sometimes termed the theory
of electricity, but which is properly no theory, at least, not a theory in the
same sense as gravitation is a theory explaining the motions of the planets,
or even in the sense in which the hypothesis of the ether and its movements
explains the phenomena of light. It is absolutely necessary to have a con-
ception of some kind which may serve to connect in our minds the various
phenomena of electricity, if it were only to enable us the more easily to talk
about them. In default of any supposition which will shadow forth what
actually occurs in these phenomena, we have recourse to what has been
aptly termed a representative fiction : we picture to ourselves the actions
as due to imaginary fluids fluids which we know do not exist, but are as
much creations of the mind as Macbeth's air-drawn dagger ; not, however,
like his " false creation," proceeding from " the heat-oppressed brain," but
intellectual fictions, consciously and designedly adopted for the purpose of
enabling us the better to think of the facts, to readily co-ordinate them,
and to express them in simple and convenient language. Non-scientific
persons hearing this language usually mistake its purport, and imagine that
the actual existence of an " electric fluid " is acknowledged. The accounts
which appear in the newspapers of the damage done by thunder-storms
are often amusing from the objectivity which the reporter attributes to the
" electric fluid." It is described, perhaps, as " entering the building,"
" passing down the chimney," then " proceeding across the floor," " rushing
down the gas-pipes," " forcing its way through a crevice, and then stream-
ing down the wall," &c., in terms which imply the utmost confidence of
belief in the existence of the " fluid." With this intimation that the hypo-
thesis of electric fluids is merely, then, a "fa<;on de parler" the reader will
not be misled by the following brief explanation of the elementary facts in
the language of the theory.
In the natural state all bodies contain an indefinite quantity of an im-
ponderable subtile matter, which may be called " neutral electric fluid."
This fluid is formed by a combination of two different kinds of particles,
positive and negative, which are present in equal quantities in bodies not
electrified ; but when there is in any body an excess of one kind of particles,
that body is charged accordingly with positive or negative electricity. Both
fluids traverse with the greatest rapidity certain substances termed con-
ductors; but they are retained amongst the molecules of insulating sub-
stances, which prevent their movement from point to point. When one body
is rubbed against another, the neutral electric fluid is decomposed the
positive particles go to one body, the negative with which these positive
3 66 ELECTRICITY.
particles were before united pass to the other body. The particles of the
same name repel each other, but particles of opposite names attract each
other ; and it is this attraction which is overcome when the electricities
are separated by friction or in any other manner.
It will be observed that the above is nothing but the statement of the
elementary facts in the language of the hypothesis. This system of the
two fluids readily lends itself to the explanation of nearly all the pheno-
mena presented in what is termed static electricity that is, in those phe-
nomena where the actions are conceivably due to a more or less permanent
separation of the fluids. The grand discoveries in electricity turn, how-
ever, upon quite another condition, namely, one in which the two hypothe-
tical fluids must be imagined as constantly combining, and here the utility
of the hypothesis is less marked. Inasmuch, however, as there can be no
doubt regarding the identity of the agent operating in the two sets of cir-
cumstances, the facts of dynamical electricity must still be expressed in the
same language, with the aid of any additional conceptions which may give
us more grasp of the subject
ELECTRIC INDUCTION.
IN all electrical phenomena an inductive action occurs, which resembles
that which we have already indicated with regard to magnetism. Thus,
if we take an insulated metallic conductor in the uncharged state, and bring
it near an electrified body, we shall find that the conductor, while still at a
considerable distance, will give signs of an electrical charge. Suppose
we have a cylindrical conductor, and that we present one end of it to the
electrified body, but at such a distance that no spark shall pass, we shall
find, if the charge on the electrified body be strong and the conductor be
brought sufficiently near, that on bringing the finger near the insulated
cylinder, a spark passes. While the cylinder continues in the same position
with regard to the electrified body, no further sparks can be drawn from
it ; but if the distance between the two bodies be increased, the insulated
cylinder will be found to have another charge of electricity, which will again
produce a spark. And by repeating these movements we may obtain as
many sparks as we desire by these mechanical actions, without in the
least drawing upon the charge on the original electrified body. The elec-
trophorus is a device for obtaining electricity by this plan, and several
rotatory electrical machines have lately been invented which yield large
supplies of electricity by a similar inductive action.
It is found that in such a case as that we have above supposed, if the
electrified body is charged with positive electricity, the uncharged conductor
brought near it has its electricities separated the negative attracted and
held by the attraction of the positive charge in the parts of the cylinder
nearest the inducing body ; while the corresponding quantity of positive
electricity is driven towards the most remote parts of the insulated conduc-
tor. It is this last which gives the spark in the first case, and if it be not thus
withdrawn from the conductor, it re-combines with the negative electricity
when the conductor is withdrawn from the neighbourhood of the electrified
body, and the conductor then reverts to the natural or unelectrified state.
ELECTRICITY.
367
But the contact of a conducting body with the conductor while it is under
the influence of the electrified body withdraws only positive electricity, the
negative being held, as it were, by the attraction of the positive electricity
of the charged body is not thus removed, and in this condition it is some-
times called disguised or dissimulated electricity a term the propriety of
which is doubtful. The excess of negative "fluid" which the conductor
thus acquires shows itself, however, only when the inducing body has been
withdrawn. Precisely similar effects will take place, mutatis mutandis, if
the electrified body has a negative charge. A demonstration of inductive
effects is readily afforded in the action of the gold-leaf electroscope, Fig.
254, in which two strips of gold-leaf are suspended within a glass case from
wire passing through the top, and terminated in a metal plate. This instru-
ment isoftenused forshowing the existence of very
small electric charges. Let a stick of sealing-wax
be rubbed and held, say, a foot or more from the
plate of the electroscope, the leaves will diverge
with negative electricity. The sealing-wax being
retained in the same position, touch the plate for
an instant with the finger. This will remove the
negative charge, but the positive electricity will be
retained on the plate by the attraction of the nega-
tive of the sealing-wax. Now remove the sealing-
wax, when the dissimulated charge will spread
itself over the whole insulated metallic portion of
the electroscope, and the leaves will diverge with
a strong charge of positive electricity. If an
excited glass tube is brought near the electro-
scope, the leaves will now diverge still more ; if
the sealing-wax is replaced in its former position,
the leaves will collapse. In all these cases the
electrified body parts with none of its own elec-
tricity by developing electrical effects in the neigh-
bouring bodies.
The inductive actions we have described take
place through the air, which is a non-conductor,
and such actions may be made to take place
through any other non-conductor. With solid
non-conductors, such as glass, gutta-percha, &c.,
the inducing body may be brought very near to
the conductor on which it is to act ; for the intervening solid substance, or
dielectric, as it has been appropriately called, opposes a resistance to the
combination of the opposite electricities, and the inductive effects are
greatly intensified by the approximation. Faraday discovered that the
amount of inductive action with a given charge is also dependent upon the
nature of the dielectric, and that the electric forces act upon the particles
of the dielectric, circumstances which are of the greatest importance, as
we shall presently find, in practical telegraphy. The most familiar instance
of induction is probably well known to the reader in the Leyden jar, Fig. 255,
which is simply a wide-mouthed bottle of thin glass, covered internally and
externally with tin-foil to within a few inches of the neck. The inner coat-
ing communicates by means of a rod and chain with a brass knob. Such a
jar admits of the accumulation of a larger quantity of electricity than the
conductor of a machine will retain. A very few turns of the machine will
FIG. 254.
The Gold-leaf Electro-
scope.
3 68
ELECTRICITY.
suffice usually to charge the conductor to the fullest extent ; but if it be
put in communication with the knob of a jar, a great many more turns will
be required to attain the same charge in the conductor, and the excess of
electricity represented by these additional turns will have accumulated
within the jar an effect due to the "dissimulated" electricity of its exterior.
Everybody knows the result when a
metallic communication is established
between the exterior and the interior
of a charged Leyden jar. There is a
very bright spark, a snap, and the jar
is "discharged." Everybody knows,
also, the sensation experienced when
his body takes the place of the metallic
communication, or forms part of the
circuit through which the communi-
cation takes place. Everybody knows
that the shock then felt may also be ex-
perienced at the same moment by any
number of persons who join hands,
under such conditions that they also
form a part of the line of communi-
cation. Such facts irresistibly sug-
gest the notion of something passing
through the whole chain, and this
notion is in perfect harmony with the
hypothesis of the " fluids," for we have only to suppose that it is one or
both of these which rush through the circuit the instant the line of com-
munication is complete. As the discharge is instantaneous, so the flow
or current of electric fluid must be regarded as instantaneous also. And
all the effects which such discharges produce concur to lead us to the con-
clusion that, in the discharge of a Leyden jar, an instantaneous action of
a kind which other dispositions of apparatus enable us to produce con-
tinuously takes place.
FIG. 255. The Leyden Jar.
DYNAMICAL ELECTRICITY.
T ET us take a vessel containing water, to which some sulphuric acid
*rf has been added, Fig. 256, and in the liquid plunge a plate of copper,
C, and a plate of pure zinc, z, keeping the plates apart from each other.
As it is not easy to obtain zinc perfectly free from admixture of other
metals, an artifice is commonly resorted to for obtaining a surface of pure
metal, by rubbing a plate of the ordinary metal with quicksilver, which
readily dissolves pure zinc, but is without action on the iron and other
metals with which the zinc is contaminated, while the quicksilver is not
acted upon by the diluted acid, but is merely the vehicle by which the pure
zinc is presented to the liquid. Under the conditions we have described,
no action will be perceived, no gas will be given off, nor will the zinc dis-
solve in the acid. If the electrical condition of the portion of the copper-
plate which is out of the liquid be examined by means of a delicate electro-
ELECTRICITY.
3 6 9
scope, it will be found to possess a very weak charge o>i positive electricity,
and a similar examination of the zinc plate will show the existence on it of
a feeble charge of negative electricity. If the two plates be made to touch
FlG. 256. A Voltaic Element.
each other, or if a wire be attached to each plate, as shown in the figure,
and the wires be brought into contact outside of the vessel, an action in
the liquid is immediately perceptible at the surface of the copper plate,
when a multitude of small bubbles of hydrogen gas will at once make their
appearance, and the gas will be given off continuously from the copper
plate so long as there is metallic contact through the wires, or otherwise,
between the two plates, or until the acid is saturated with zinc for in this
action the zinc is dissolving, and, in consequence, liberating hydrogen,
which strangely makes it appearance, not at the place where the chemical
action really occurs, namely, at the surface of the zinc which is in contact
with the acid, but at the surface of the copper which is not acted upon by
the acid.
It is known that when we establish a metallic communication between
two bodies charged with equivalent quantities of positive and negative
electricities respectively, these combine and neutralize each other, and all
signs of electricity vanish. It is obvious that the contact of the two wires
has this effect, as the signs of electric charge which were before discover-
able in each of the plates are no longer found while the wires are in con-
tact. But the charges reappear the instant the contact is broken, the
chemical action ceasing at the same time. If the wire connecting the two
plates outside of the vessel be carefully examined, it will be found, so long
as the chemical action is going on, to be endowed with new and very re-
markable properties. If this wire be stretched horizontally over a freely
suspended magnetic needle, and parallel to it, the needle will be deflected
from its position, and, if the wire be placed very near it, will point nearly
east and west, instead of north and south. Now, this effect is produced
by any part whatever of the wire, and it instantly ceases if the wire be cut
at any point. These facts at once suggest the idea of its being due to
something flowing through the wire, so long as metallic continuity is pre-
served. This idea is much strengthened when we find that the action of
the connecting wire upon the magnetic needle is quite definite or, in
other words, there are indications which correspond with the notion of
direction. For when the wire, which we shall still suppose 'to be stretched
24;
370
ELECTRICITY.
horizontally above the needle and parallel to its direction, is so connected
with the plates immersed in the acid that the portion which approaches
the south-pointing pole of the needle proceeds from the copper plate, while
the portion above the north pole is in connection with the zinc plate, then
the north end of the needle will always be deflected towards the west
whereas, if the connections be made in the contrary manner, the deflection
will be in the opposite direction ; and if the wire be below the needle, the
contrary deflections will be observed with the same connections. The dis-
covery of the action of such a wire on the magnetic needle was made by
CErsted in 1819, and it is a discovery remarkable for the wonderful extent
of the field which it opened out, both in the region of pure science and in
that of practical utility.
Since by such experiments as those just mentioned the notion of a current
is arrived at, the mind recurs to the fiction of the " fluids," and pictures the
" positive fluid " as rushing in one direction, and the " negative fluid " in
the other, to seek a re-combination into " neutral fluid." But we must never
lose sight of the fact that these ideas are consciously adopted as repre-
sentative fictions to help our thoughts just as John Doe and Richard Roe,
imaginary parties to an imaginary lawsuit, used to be named in legal docu-
ments, in order to explain the nature of the proceedings. Failing, then, to
I i *r
V
FiG. 257. Amperes Rule.
find anything really flowing along our wire, it is still absolutely necessary,
seeing there is something definite in its action, to assign a direction to the
supposed current ; and it has been agreed that we shall represent the cur-
rent as flowing from the positively charged body to the negatively charged
body that is, in the case we have been considering, from the copper to
the zinc through the wire. When this conventional representation has
been adopted, the action on a magnetic needle can easily be defined and
remembered by an artifice proposed by Ampere. In Fig. 257, let N s re-
present the magnetized needle, N being the pole which points towards the
north, and s the south pole. Let c be the end of the wire connected with
the copper plate, and z that connected with the zinc. The current is there-
fore supposed to flow in the direction indicated by the arrows in a wire
above the needle and in the wire placed below. Now, suppose that a man
is swimming in the current in the same direction it is flowing, and with his
face towards the needle, then the north pole of the needle will always be
deflected towards his left. With the direction of current represented in the
figure, the pole, N, will be thrown forward from the plane of the paper, or
towards the spectator.
The reader who desires to study the mutual action of currents and mag-
nets will find it necessary to fix this idea in his mind. He will now be able
to see that if the wire be coiled round the needle, as shown by the lines and
arrows, Fig. 257, so that the same current may circulate in reverse direc-
ELECTRICITY. 371
tions above and below the magnet, its effects in deviating the needle will
everywhere concur that is, the action of each part will be to turn the north
pole towards the left. It is, therefore, plain that if the wire conveying the
current be passed several times round the magnetic needle, the deflecting
force will be increased ; and a current, which would, by merely passing
above or below the magnet, produce no marked deflection, might be made
to produce a considerable effect if carried many times round it. The ar-
rangement for this purpose is shown in Fig. 258, where it will be perceived
that the needle is surrounded by a coil of wire, so that the current circu-
lates many times about it, and the effects of each part of the circuit concur
in deflecting the needle. Such an arrangement of the wire and needle
constitutes what is called the galvanometer,^ instrument used to discover
the existence and direction of electric currents.
1
FlG. 258. Galvanometer.
The arrangement of metals and acid which we have described is termed
a voltaic couple, element, or cell; and a great controversy has long been
carried on among men of science as to the place at which the develop-
ment of electricity has its origin. Three-quarters of a century ago, the
effect was attributed by Volta to the mere contact of the two dissimilar
metals. In the experiment we have described this contact, supposing the
wires to be of copper, would occur at the junction of the wire and the zinc
plate. Now, by joining the copper plate of such a cell to the zinc plate of
another cell, the copper of that to the zinc of a third, and so on, it is evident
that the number of dissimilar contacts might be indefinitely increased, and
the electric power should be proportionately augmented. It is found that
this is really the case, but Volta's explanation has been opposed by another
which regards the chemical action in the cells as the real origin of the
electric manifestations. This last explanation, supported by many appa-
rently conclusive experiments of Faraday and others, has been generally
accepted. Galvanic batteries as a series of cells joined together in a cer-
tain manner are termed have been constructed, in which there is no con-
tact of dissimilar metals ; and no electric current can be obtained from an
apparatus in which no chemical action takes place. The contact theory
in a modified form has recently been revived by Sir W. Thompson and
others. In this it is now maintained that some separation of electri-
cities really does take place by contact of dissimilar substances, but that a
current can be produced only when this separation is continually renewed
by chemical actions. Be the true explanation what it may, the fact is
imdoubted that by joining cell to cell, we can really obtain vastly more
powerful effects. If we take a single cell, such as that represented in
r ig. 256, and connect the plates with a long and thin wire, we shall find
24 2
372 ELECTRICITY.
that the current flowing through each part of the circuit is much weaker
than when we connect the plates with a short and thick wire. In other
words, the action in the latter case, when the wire is stretched over a
magnetic needle, will be more powerful than in the former. By using a
long and thin wire the current may be so weakened that it becomes neces-
sary to surround the needle with many coils of the wire to produce a
marked deflection. Again, much depends upon the material ; thus a
copper wire conveys a much more powerful current than a German silver
one of the same dimensions. There thus appears to be a certain analogy
between the flow of electricity along conductors to that of water through
pipes. The longer and narrower are the pipes, the less is the quantity of
water forced through them by a given head ; and similarly, the resistance
to the passage of a current increases with the length and narrowness of
the conducting wire. When all other circumstances are the same, the
electrical resistance of a conductor varies directly as its length and inversely
as its sectional area. Hence the current flowing in the apparatus repre-
sented in Fig. 256 would be increased by making the wire thicker, and by
making it shorter by bringing z and C nearer together, and by making the
area they expose to the liquid larger ; for in the liquid also the current
flows as indicated by the arrow, a fact which may be proved by the deflec-
tion of a magnetized needle suspended above the vessel. The magnitude
of the current depends, then, upon two opposing forces, namely, that which
continuously separates the electricities, or drives them apart to recombine
through the circuit, and that which opposes their passage. The former,
which is termed the electromotive force, originates, according to some, from
the mere contact of dissimilar materials, according to others from the
chemical action. Now, we may increase the strength of the current in a
given arrangement, either by increasing the electromotive force, or by
diminishing the resistance. The increase of the strength of the current,
produced by merely pouring more acid into the vessel, Fig. 256, is due,
according to the chemical theory, to the former cause ; according to the
contact theory, to the latter. By multiplying the cells we increase the
electromotive forces : the current receives, so to speak, an onward shove
in each cell, but with each cell we introduce an additional resistance.
Hence, it follows, that when the resistance of the circuit outside of the
cells is extremely small, the current produced by a single cell is as power-
ful as that produced by a thousand. But when the external resistance is
great, as when long thin wires are used, the united electromotive forces of
a number of cells are needed to drive the current through the circuit. The
strength of a current, c, is therefore expressible by the following simple
formula, in which r stands for the internal resistance, and e for the electro-
motive force in each cell ; n represents the number of cells in the battery,
these being supposed exactly similar in every respect ; R is the sum of
the resistances in the circuit outside of the battery.
lie
It is easily seen that the smaller R is made, the more nearly does the
strength of the current become independent of the number of cells.
But many modifications have been made in the materials and form of the
cells, by which greater power and duration of action have been attained.
Our space permits a description of only two forms, and these must be de-
scribed without a discussion of the principles upon which their increased
ELECTRICITY.
efficiency depends. Daniell's constant cell is represented in Fig. 259, where
D is a battery of ten such cells, A is a cylindrical vessel of copper, C is a
tube of porous earthenware, closed at the bottom, and within it is suspended
the solid rod of amalgamated zinc, B. The copper vessel and the zinc rod
FIG. 2^.Danieirs Cell and Battery.
are provided with screws by which wires may be attached. In the copper
vessel is placed a saturated solution of sulphate of copper, and some crystals
of the same substance are placed on the perforated shelf within the vessel.
The porous tube is filled with diluted sulphuric acid. When the battery
FIG. 260. Grove's Cell and Battery.
is in action the zinc is dissolved by the sulphuric acid, and metallic copper
is continually deposited upon the internal surface of the copper vessel.
Daniell's battery, in some form or other, is much used for telegraphs and
for electrotyping. Grove's cell is shown in section in Fig. 260. The
external vessel is made of a rectangular form in glazed earthenware or
374
ELECTRICITY.
glass. It contains a thick plate of amalgamated zinc, A, A, bent upwards,
and between the two portions a flat porous cell, C, C, is placed, filled with
strong nitric acid, in which is immersed a thin sheet of platinum. The
outside vessel is charged with water, mixed with about ^th of sulphuric
acid. D represents a battery of four such cells, in which the mode of con-
necting the platinum of one to the zinc of the next may be noticed. The
terminal platinum and zinc form \htpoles of the battery, and to them the
wires are attached which convey the current. The substitution of plates
of coke for the platinum gives the form of battery known as Bunsen's, which
is also sometimes made with circular cells. Cover's and Bunsen's are much
more powerful arrangements than Daniell's, but the latter has the advan-
tage as regards the duration and uniformity of its action.
When the current produced by a battery of a dozen or more such cells
is conveyed by a wire, it is observed that this wire becomes sensibly hot,
and, if the wire be thin enough, the heat may be sufficiently great to heat
FIG. 261. Wire ignited by Electricity.
the wire to redness. By stretching a piece of platinum wire between two
separate rods which convey the current, as represented in Fig. 261, the
length of wire through which the current passes may be adjusted so as to
give any required amount of light, and the wire may even be heated to the
fusing-point of platinum. This property of electricity has some interesting
applications, as, for example, in firing mines and other explosive charges,
and in some surgical operations. A still more interesting exhibition of
heating and luminous effects is observed when the terminals of a battery
of many cells are connected with two rods of coke, or gas-retort carbon.
When the pointed ends of the rods are brought into contact, the current
passes, and the points begin to glow with an intensely bright light, and if
they are then separated from each other by an interval of ^th of an inch
or more, according to the power of the battery, a luminous arc extends
between them, emitting so intense a light that the unprotected eye can
hardly support it. This luminous arc is called the voltaic arc, and it excels
all other artificial lights in brilliancy, a fact due to the extremely high
temperature to which the carbon particles are heated, the temperature
being, perhaps, the highest we can attain. It must not be supposed that
in this brilliant light we see electricity : the light is due to the same cause
as the light of a candle or gas flame, namely, incandescent particles of
solid carbcn. These particles are carried from one carbon point to the
ELECTRICITY.
375
other, and it is found that the positive pole rapidly loses its substance,
which is partly deposited on the negative pole. But in order to obtain a
steady light, it is requisite to keep the pieces of carbon at one invariable
distance ; and therefore the transference of the material from one pole to
the other, and the loss by combustion, must be compensated by a slow
movement of the carbons towards each other. Several kinds of apparatus
are used for this purpose, but they all depend upon the principle of regu-
lating the motions by the action of an electro-magnet, formed by the current
itself, which becomes weaker as the carbons are farther apart. The move-
ment is communicated to the apparatus by clockwork. Duboscq's electric
FIG. 262. Duboscq's Electric Lantern and Regulator.
lantern is shown in Fig. 262, with enlarged images of the carbon points
projected on a screen. The mechanism of the regulator is contained with-
in the cylindrical box immediately below the lantern. The supports of
both carbons are moved ; that which bears the positive carbon pole being
advanced twice as fast as the other, and thus the light is maintained at the
same level, for the positive carbon wears away twice as fast as the other.
The light is more brilliant when charcoal is used instead of coke, but then
it is necessary to operate in a vacuum, to avoid the combustion of the char-
coal. The voltaic arc has recently been applied to illuminate lighthouses,
and for other purposes, and will probably soon be more widely employed,
for a cheap and convenient mode of producing a uniform current of elec-
tricity has recently been discovered and will be presently described.
The current which is maintained by the chemical action taking place in
the cells of the battery can also be made to do chemical work outside of
the battery. When the poles of the battery are terminated by wires or plates
of platinum, and these are plunged into water acidulated with sulphuric
acid, bubbles of gas are seen to rise rapidly from each wire, or electrode^
376
ELECTRICITY.
as it is termed. Fig. 263 shows an arrangement by which these gases may
be collected separately, and examined, by simply placing over each elec-
trode an inverted glass tube, filled also with the acidulated water. The
gases collect at the tops of the tubes, displacing the water, and it is found
that from the wire connected with the zinc end of the battery, or negative
electrode, hydrogen gas is given off, while at the positive electrode oxygen
gas is liberated, in volume precisely equal to half that of the hydrogen.
This being the proportion in which these two substances combine to pro-
duce water, it appears that in the passage of the current a certain quantity
of water is decomposed ; and the quantity thus decomposed is in reality a
H
21
FlG. 263. Decomposition of Water.
measure of the current, all the other effects of which are found to be pro-
portional to this. When the electricity in a current is said to be measured,
it is simply the power of the current to deflect a magnet, or the quantity
of gas it can liberate, or some other such effect, which is in fact measured.
The discharge of a Leyden jar through such an apparatus as that repre-
sented in Fig. 263 would present no perceptible decomposition of the
water; yet such a discharge passed through the arms and body produces,
as everybody knov/s, a painful shock, and is accompanied by a bright spark
and a noise, while the simultaneous contact of the fingers with the positive
and negative poles of the galvanic battery occasions neither shock nor
spark. Thousands of discharges from large jars must be passed through
acidulated water to liberate the amount of gas which a battery current of a
second's duration will produce. The electricity of the jar is often spoken
about as having a higher tension than that of the battery, but the latter sets
an immensely greater quantity of electricity in motion. The idea may be
illustrated thus : Suppose we have a small cistern of water placed at a great
height, and that this water could fall to the ground in one mass. The fall
of the small quantity from a great height would be capable of producing
very marked instantaneous effects, such as smashing, as with a blow, any
ELECTRICITY.
377
structure upon which it might fall. This would correspond with the small
quantity of electricity which passes in the discharge of a Leyden jar. Con-
trast this with the case in which we allow a very large quantity of water to
descend from a very small height as when the water of a reservoir is flow-
ing down a. gently inclined channel. It is plain that a different kind of
effect might be produced in this case ; the current might be made, for in-
stance, to turn a water-wheel, which the more forcible impact of the small
quantity of water in the case first supposed would have broken into pieces.
It is probable that the apparent decomposition of water by the electric
current is in reality a secondary effect, and that it is the sulphuric acid
which is decomposed. When, instead of acidulated water, we place in the
apparatus a solution of sulphate of copper, it is found that metallic copper
is deposited on the negative electrode, and sulphuric acid collects at the
positive electrode. The metal is deposited in a firm and coherent state, and
the useful applications of this deposition of metals are of great interest and
importance. For, in a similar manner, gold, silver, lead, zinc, and other
metals may be made to form thin uniform layers over any properly pre-
pared surface. The immense advantages which the arts have derived from
electro-plating illustrate in a convincing manner the benefits which physical
science can confer on society at large.
The process of electro-plating may be practised by the aid of apparatus
of very simple character. Fig. 264 shows all that is necessary for obtaining
perfect casts in copper of seals, small medals,
&c. A A is a section of a common tumbler ;
B B is a tube, made by rolling some brown
paper round a ruler, uniting the edge with
sealing-wax, and closing the bottom by a
plug of cork, round which the paper may be
tied by a string, or in any other convenient
manner. The tumbler contains a solution of
sulphate of copper, and the tube is filled with
water, to which about one-twentieth of its
bulk of sulphuric acid has been added. A
strip of amalgamated zinc, or a piece of thick
amalgamated zinc wire, is placed in the tube,
and a piece of copper bell-wire is twisted
round the top of it, and has attached to its
other extremity, and immersed in the copper
solution, the article which is to be covered
with copper. We may suppose that this is
to be a cast in white wax or in plaster of
one side of a medal. The cast is carefully
covered with black lead by means of a soft
brush, and the copper wire is inserted in such
a manner as to be in contact with the black
lead at some part. When the apparatus has been left for some hours in
the position represented, a deposit of copper will be found over the black-
leaded surface, and it will be a perfect impression of the wax cast.
Such a copper cast, or any article in copper having a perfectly clean
surface, can be readily covered by a film of silver by means of a similar
arrangement, where a solution of cyanide of potassium, in which some
chloride of silver has been dissolved, is made to take the place of the sul-
phate of copper. Electro-plating with the precious metals has become a
FIG. 264. Electro-plating.
378 ELECTRICITY.
commercial industry of great importance ; and this process has completely
superseded the old plan of covering the metallic article to be plated with
an amalgam of silver or of gold, and then exposing it to heat, which vola-
tized the mercury, leaving a thin film of gold or of silver adhering to the
baser metal. On the large scale a battery of several cells is used for electro-
plating, and the articles are immersed in the metallic solutions as the
negative poles of the battery; any required thickness of deposit being given
according to the length of the time they remain. At the works of Messrs.
Elkington, of Birmingham, these operations are conducted on a grand
scale. The liquid there employed for silvering is a solution of cyanide of
silver in cyanide of potassium, and the positive pole is formed of a plate of
silver, which dissolves in proportion as the metal is deposited on the nega-
tive pole. As the charging of batteries is a troublesome operation, and
their action is liable to variations which affect the strength of the currents,
the more uniform, more convenient, and more economical mode of pro-
ducing currents by magneto-electricity, which will presently be described,
has been to a great extent substituted for the voltaic battery.
The wire conveying a current not only affects a magnetic needle in the
FlG. 265. A Current producing a Magnet.
manner already described, but itself possesses magnetic properties, of
which, indeed, its action on the needle is the result and the indication. If
such a wire be plunged into iron filings, it will be found that the filings are
attracted by it : they cling in a layer of uniform thickness round its whole
circumference and along its whole length, and the moment the connection
with the battery is broken they drop off. This experiment shows that every
part of the wire conveying a current is magnetic, and it may be proved that
the action is not intercepted by the interposition of any non-magnetic
material. Thus the action of the wire upon the magnetic needle takes
place equally well through glass, copper, lead, or wood. Consequently, if
we cover the wire with a layer of gutta-percha, or over-spin it with silk or
cotton, we shall obtain like results on our filings, and if we coil the covered
wire round a bar of iron, while the non-conducting covering of the wire will
compel the current to circulate through all the turns of the coil, it will not
interfere with the magnetic action on each particle of the bar. Whenever
this is done it is found that the iron is converted into a powerful magnet
so long as the current passes. Fig. 265 represents in a striking manner
the result when the current is made to circulate through numerous convo-
lutions of the wire ; and as each turn adds its effect to that of the rest,
magnets of enormous strength may be formed by sufficiently increasing the
ELECTRICITY.
379
number of the turns. The end of the iron bar is shown projecting from
the axis of the coil, and below it is placed a shallow wooden bowl, con-
taining a number of small iron nails. The instant the battery connection
is completed these nails leap up to the magnetic pole, and group them-
selves round it in the manner shown in the cut ; and again, when the cur-
rent is interrupted, the iron reverts to its ordinary condition, the magnetism
vanishes, and the nails drop down in an instant. These effects may be
produced again and again, as often as the current flows and is broken. A
magnet so produced is called an electro-magnet, to distinguish it from the
ordinary permanent steel magnets. By coiling the conducting wire round
FIG. 266. An Electro-magnet.
a bar of iron which has been bent into the form of a horse-shoe r very
powerful magnets may be produced, and enormous weights may be sup-
ported by the force of the magnetic attraction so evoked. Fig. 266 repre-
sents the apparatus for experiments of this kind, in which weights exceeding
a ton can be sustained.
Here, then, we have a striking instance of the subtile agent electricity,
evoked by the contact of a few pieces of zinc with dilute acid, showing it-
self capable of exerting an enormous mechanical force. Engines have
been constructed in which this force is turned to account to produce rota-
tory motion as a source of power. Such engines have certain advantages
for special purposes ; but the money cost for expenditure of material for
power so obtained is, at least, sixty times greater than in the case of the
steam engine. It is, however, in producing mechanical effects at a dis-
3 So ELECTRICITY.
tance that the electric current finds the most interesting practical applica-
tion of its magnetic properties. These are the actions which are so exten-
sively utilized in the construction of telegraphic instruments, of clocks
regulated by electric communication with a standard time-keeper, and
of many ingenious self-registering instruments. The telegraph will be
described in the next article, and we shall also have occasion in subse-
quent articles to describe some of the other applications of electro-magnetic
and electro-chemical force.
INDUCED CURRENTS.
'""PHESE very remarkable phenomena were discovered by the illustrious
* Faraday, in 1830, and this discovery, and that of magneto-electricity,
may be ranked among the most memorable of his many brilliant contribu-
tions to electric science. Let two wires be stretched parallel and very near
to each other, but not in contact. Let the extremities of one wire, which
we shall term A, be connected with a galvanometer (page 371), so that the
existence of any current through the wire may be instantly indicated. Let
the two extremities of the other wire, B, be put into connection with the
poles of a battery. The moment the connection is complete, and the
battery current begins to rush through B, a deflection of the galvanometer
needle will be observed, indicating a current of very short duration through
A in the opposite direction to the battery current through B. This induced
current, which is called the secondary current, does not continue to flow
through A : it occurs merely at the time the primary or battery current is
established ; and though the latter continues to flow through the wire, B, no
further effect is produced in the other wire. When, however, the battery
connection is broken, and the primary current ceases to flow, at that instant
there is set up in the wire, A, another momentary secondary current, but
this one is in the same direction as the battery current. This is termed the
direct secondary current, in opposition to the former, which is called the
inverse current.
These effects are much more powerful when, instead of lengths of straight
wire, or single circles of wires, we use two coils of wire, one of which,
namely, that which conveys the primary currents, is placed in the axis of
the other. It must be distinctly understood that the secondary currents
are of momentary duration only ; they are not produced at all while the
battery is flowing, but only at the time of its commencement and cessation.
If, however, we make the primary coil so that it can be slid in and out of
the axis of the other, then while the primary current is continuously flow-
ing, we can produce secondary currents in the other coil, by causing the
coils to approach or recede from each other. As we bring the coils near
each other, and slide the primary into the secondary, the current in the
latter is inverse j when the one coil is receding from the other, it is direct.
These mechanical actions are not produced without expenditure of force,
for the approaching coils repel each other and the receding coils attract
each other. The setting up of the battery current in the primary coil when
placed within the other is equivalent to bringing it, with the current flow-
ing, from an immense distance in an extremelv small time. Similarly,
ELECTRICITY. 381
when the battery current is broken, it is equivalent to an instantaneous
recession. The effects, therefore, are proportionately powerful. It is found,
also, and this we shall presently refer to more fully, that when, instead of
the primary coil, a magnet is similarly moved into, or removed from, the
axis of the secondary coil, currents in opposite directions are set up in the
latter without any battery being used at all. The direction of these currents
is the same as would be produced by a primary current that would form,
in a piece of iron placed in the axis of the coil, an electro-magnet with
poles similarly situated to those of the magnet so introduced or withdrawn.
Hence, by placing a bar of soft iron in the axis of the primary coil, the
secondary currents will be produced with increased force. When a long
secondary coil, having the turns of its wire well insulated from each other,
surrounds a primary coil provided with a core of soft iron, or still better,
with a bundle of annealed iron wires, a series of powerful discharges, like
those of a Leyden jar, may be obtained between the terminals of the
secondary coil, when the battery contact is made and broken in rapid
succession.
Such induction coils have been very carefully and skilfully constructed by
FIG. i&j.Rtthmkorjf's Coil.
Ruhmkorff,and are therefore often called " RuhmkorfFs Coils." One of these
is represented in Fig. 267. A B is the coil, and the apparatus is provided
with what is termed a condenser, which consists of layers of tin-foil placed
between sheets of thick paper, and alternately connected so that one set
communicates with one extremity of the primary coil, and the other with
the other. This condenser is conveniently contained in the wooden base
of the instrument. Its introduction has greatly increased the intensity of
the secondary current, and sparks of 18 in. or 20 in. in length have been
obtained in the place of very short ones.
It should be stated that of the two secondary currents, only one has
sufficient intensity to traverse the secondary circuit when there is any break
in its continuity. This is the direct secondary current, or that which is
produced on breaking the primary circuit. The reason is that the com-
mencing current in the primary circuit induces in the spires of its own coil
an inverse current, and the battery current therefore -attains its full strength
.gradually, but still in a very short time ; while, on the cessation of the
battery current, the same induction sends a wave of electricity through the
primary coil in the same direction, and then the current ceases abruptly.
Consequently, in the latter case, the induced electricity of the secondary
coil is set in motion in much less time, and therefore possesses much greater
intensity.
3 82
ELECTRICITY.
The magnetism of the iron core is usually made use of to break and
make the current, by the attraction of a piece of iron attached to a spring,
which, by moving towards the end of the core, separates from a point in
connection with the battery, and, the current no longer flowing, the mag-
netism ceases, and the spring again brings back the iron and renews the
contact.
By means of such coils many surprising effects have been produced.
Perhaps one of the most beautiful experiments in the whole range of physi-
cal science is made by causing the discharges of the secondary coil to take
FIG. 268. Discharge through Rarefied Air.
place through an exhausted vessel in the manner represented in Fig. 268.
A beautiful light fills the interior of the vessel, and the terminals appear
to glow with a strange radiance one being surrounded with a kind of blue
halo and another with a red. On reversing the direction of the currents,
which is done by the little apparatus at the right-hand end of the coil in
Fig. 267, the blue and the red radiance change places. Beautiful flashes of
light may also be made to appear in the vessel, having the most marked re-
semblance to the streamers of the Aurora Borealis. When, instead of vessel^
almost free from common air, we repeat the experiment with tubes con-
taining an extremely small residue of some other gas, such as hydrogen,
carbonic acid, &c., the colour of the light and other appearances change.
ELECTRICITY. 383
Geissler's tubes have already been spoken of in connection with the spec-
troscope ; but, independently of that, the various beautiful appearances
which such tubes have been made to present, by the introduction of fluores-
cent substances and other devices, render the induction coil an instrument
of the highest interest to the scientific amateur. Then there are striking
physiological and other effects which the coil is capable of producing. For
instance, we are able by its instrumentality to produce from atmospheric
air unlimited quantities of that singular modification of oxygen which is
called ozone. The electricity of the coil has been used for firing mines,
torpedoes and cannons, and for lighting the gas-burners of large buildings.
Mr. Apps has devoted much attention to improving the insulation of
induction coils, and he recently made for the Polytechnic Institution one of
astonishing power, being perhaps the largest yet constructed. This is repre-
sented in Plate VII., surrounded by the somewhat scenic accompaniments
which are supposed necessary to render science attractive to the multitude.
Externally the coil appears an ebonite tube, about 20 in. in diameter and
between 4^ ft. and 5 ft. in length. From each end smaller cylinders pro-
ject, covered by ebonite, and the whole is mounted upon supports also
covered with ebonite. The soft iron core 5 ft. long and 4 in. in diameter
is formed of a bundle of wires. The primary coil is of pure copper wire,
nearly Jjjth of an inch thick, and in length 3,770 yards, over-spun with
cotton, and making about 6,000 turns round the iron core. The primary
wire is covered by an ebonite tube \ in. thick, and outside of this is the
secondary coil, 4 ft. 2 in. long, surrounding the ebonite tube to the depth
of 6 in., and containing 150 miles of silk-covered wire, "oi^in. in diameter.
The weight of this secondary wire is 606 Ibs., and so carefully have the
spires been arranged that the insulation is everywhere more than ten times
greater than the tension of the electricity when the coil is in action, and
altogether the construction of this instrument is highly creditable to the
skill and scientific knowledge of Mr. Apps. The external diameter of the
secondary coil is I ft. 7 in. The condenser contains 750 square feet of tin-
foil. The battery current for the primary coil is furnished by forty Bunsen
cells. A contact-breaker of the ordinary kind, but detached from the coil,
was first provided ; but this was soon deranged by the sparks destroying
the contact points, and finally a contact-breaker on Foucault's plan was
adopted, in which the contacts are made with mercury in the midst of
alcohol. A large and very strong glass vessel in fact, the inverted glass
cell of a bichromate battery was bored through, and the neck fitted into
a cap with cement, a thick wire covered with platinum being inserted in
the cap ; the platinum amalgam was poured on this, and over it a pint of
alcohol ; the contact-wire was also very large, and pointed with a thick stud
of platinum, and, being attached to a spring, contact was easily made and
broken. Flashes of light could be seen between the amalgam and the
alcohol ; but explosions did not occur, and the height of the column of
the latter prevented the forcible ejection of the spirit, which no longer
took fire. This break was used for eight hours in a continuous series of
experiments.
It was found that this great coil would give a spark 29 in. in length, and
its discharge would perforate a certain thickness of plate glass. A Leyden
battery of 40 square feet could be charged by three contacts of the break,
and by its discharge considerable lengths of wire could be deflagrated.
The appearance of the spark, with this as with other large induction coils,
may be described as a thick line of light surrounded by a reddish halo of
384 ELECTRICITY.
or
less brilliancy, which last has an appreciable duration, while the line
spark proper is instantaneous. The reddish glow may be blown aside by
a current of air when a series of discharges is taking place, and separated
from the denser-looking line of light. The latter is formed by intensely-
heated particles of the metals between which the discharge occurs, while
the former is probably due to the incandescence of the gases of the air.
When one of the discharging-wires of the coils was brought to the centre of
a large swing looking-glass, and the other wire connected with the amalgam
at the back, the sparks were thin and wiry, arborescent, and very bright,
and the crackling noise of the discharge was quite different from that of
FlG. 269. Appearance of the Spark on the Looking-glass.
the heavy thud or blow produced by the flaming spark. The peculiar
appearance presented by these sparks is shown in Fig. 269. Some expecta-
tions appear to have been formed that a source of electricity of so much
power would lead to some scientific discoveries at the Polytechnic ; but
these expectations have not been realized, and the coil has served merely
for the occasional instruction or amusement of the marvel-seeking audiences
of that popular institution.
MAGNETO-ELECTRICITY.
it had been shown that an electric current was capable of
evoking magnetism, it seemed reasonable to expect that the reverse
operation of obtaining electric currents by means of magnets should be
possible. Faraday succeeded in solving this interesting problem in Novem-
ber, 1831. and one of his earliest, simplest, and most convincing experi-
ELECTRICITY. 385
ments for the demonstration of the production of electricity by a magnet
is represented in Fig. 270. A B is a strong horse-shoe magnet, C is a
cylinder of soft iron, round which a few feet of silk-covered copper wire are
wound ; one end of the wire terminates in a little copper disc, and the other
FIG. 270. Magneto-electric Spark.
end is bent, as shown at D, so that it is in contact with the disc, but press-
ing so lightly against it that any abrupt movement of the bar causes the
point of the wire and the disc to separate. When the bar is allowed to
fall upon the poles of the magnet, the separation occurs, and again when
it is suddenly pulled off ; and on each occasion a very small but brilliant
spark is observed where the contact of the wire and disc is broken. It
was in allusion to this experiment that a contributor to " Blackwood's
Magazine" wrote:
Around the magnet, Faraday
Is sure that Volta's lightnings play ;
But how to draw them from the wire ?
He took a lesson from the heart ;
'Tis when we meet, 'tis when we part,
Breaks forth the electric fire.
If a coil of fine insulated wire 'be passed many times round a hollow
cylinder, open at the ends, and the extremities of the wire connected with
a galvanometer at some distance, then if into the axis of the coil, A B,
Fig. 271, a steel magnet be suddenly introduced, an immediate deflection
of the needle takes place ; but after a few oscillations it returns to its former
position. When the magnet is quickly withdrawn, the needle receives a
momentary impulse in the opposite direction. The magnetization and de-
magnetization of the iron core in the induction coil would, therefore, of
itself cause the induced currents already described, for these actions are
equivalent to sudden insertion and withdrawal of a magnet. If we suppose
25
3 86
ELECTRICITY.
C, in Fig. 271, to represent, not a magnet, but a piece of soft iron the
reader will remember that this soft iron can be, as often as required, mag-
FIG. 271. A Magnet producing a Current.
netized and demagnetized by simply bringing near one end of it the pole
of a permanent magnet (see page 362). Upon this principle many ingenious
FIG. 272. Clarke's Magneto- electric Machine.
machines have been constructed for producing electric currents by. the
relative motions of magnets and of soft iron cores surrounded by wires.
ELECTRICITY.
387
Clarke's machine is shown in Fig. 272. A is a powerful steel magnet
fixed to the upright. A brass spindle passing between the poles can be
made to rotate very rapidly by the multiplying-wheel, E, on which a handle
is fixed. There are two short cylinders of soft iron, parallel to the spindle,
united together by the transverse piece of iron, D, which turns with the
spindle. Each bar is surrounded by a great length of insulated copper
wire, and the ends of the wires are so connected with springs which press
against a portion of the spindle, which is here partly formed of a non-
conducting material, that the currents generated in the coils, although in
different directions as they approach a pole and recede from it, are never-
theless made to flow in one direction in the external circuit. R R in the
figure represent two brass handles, which are grasped by a person wish-
ing to experience the shocks the machine can give when the wheel is
turned. When the terminals of the coil are provided with insulating
handles and connected with pointed pencils of charcoal, the electric light
FIG. 273. Magneto-electric Light.
can readily be produced by expenditure of mechanical effort in turning the
handle. The arrangement of the points for this purpose is shown in Fig.
273, and we shall presently see what ac v intage has been drawn from this
experiment on a great scale as a source of light.
It will be observed that during the revolution of the armatures, as the
wire-covered iron cores are termed, there are two maximum and two
minimum points at which the currents are strongest and weakest. These
variations may be lessened by increasing the number of armatures and
of magnets, and Mr. Holmes arranged a machine with eighty-eight coils
and sixty-six magnets, and the connections were so contrived that the
currents always flowed in the same direction in the external circuit. This
machine required i horse-power to drive it when the currents were flowing,
but much less when the circuit was interrupted, and it was designed for,
and successfully applied to, the production of the electric light for light-
house illumination. Instead of steel magnets which gradually lose their
strength, it is obvious that electro-magnets might be employed, but this
source of electricity is costly, troublesome, and inconstant. Mr. Wilde" hit
upon the idea of using a small magneto-electric machine with permanent
steel magnets, to generate the current for exciting a larger electro-magnet,
and the current from this produced a still more powerful electro-magnet,
252
3 88 ELECTRICITY.
from which a magneto-electric current could be collected and applied.
The same idea was subsequently applied in other forms, as by shunting off
a portion of the current produced from the mere residual magnetism of an
electro-magnet, to pass through its own coils and evoke a stronger magnet-
ism, which again reacts by producing a more powerful current, and so on
continually ; the limit being dependent only on the mechanical force em-
ployed, and on the power of the wires to convey the electricity, for they
become very hot, and, unless artificially cooled, the insulating material
would be destroyed. The armatures used in Wilde's, Ladd's. and other
machines of this kind, are quite different in arrangement from those of
Clarke's machine, and are far superior. They are formed of a long bar of
soft iron, of a section like this, M, and the wire is wound longitudinally
between the flanges from end to end of the bar, up one side and down the
other. This armature rotates about its longitudinal axis between the pairs
oi the poles of a file of horse-shoe magnets, either permanent, or electro-
magnets excited by the magneto-electric currents. In this case opposite
poles are induced along the edges of the bar, and these poles are reversed
at each half-turn. The intensity of the induced currents increases with
the velocity with which the armature is made to revolve up to a certain
point ; but because the magnetization of the soft iron requires a sensible
time to be effected, and the poles are reversed at every half-turn, it is
found that a speed increasing beyond the limit is attended by decrease of
the intensity of the current. The intensity in such machines has, therefore,
a definite limit. But in a modification of the magneto-electric machine,
which has quite recently been invented by M. Gramme, the limit is vastly
extended by the ingenious disposition of the iron core and armatures, and
his machines appear to solve the problem of the cheap production of steady
and powerful electric currents, so that electricity will soon be applied in
processes of manufacture where the cost of electrical power has hitherto
placed it out of the question. We shall now endeavour to explain the
principle on which the Gramme machine depends, and describe some forms
in which it is constructed.
THE GRAMME MAGNETO-ELECTRIC MACHINE.
T ET x, Fig. 274, be a coil of covered wire ; then while a bar magnet, B A,
- 1 ' is advancing towards it and passing through it, as at M, a current will
FIG. 274.
flow through the coil and along a wire connecting its ends, s s. The cur-
rent will change its direction as the centre of the magnet is leaving the coil
ELECTRICITY.
389
to advance in the direction, B A. If A A' be a bar of soft iron, with the coil
fixed upon it, we can still excite currents in the coil by magnetizing the bar
inductively. If the pole of a permanent magnet be carried along from A'
to M in a direction parallel to the bar, but not touching it, the part of the
bar immediately opposite will be a pole of opposite name, and the advance
of this induced pole towards M will be attended with a current in the coil,
and its recession by an opposite current. It need hardly be mentioned
that the same result is attained if the magnetic pole is stationary, and the
bar with the coil upon it moved in proximity to it. Now imagine that the
FIG. 2/5- Gramme Machine for the Laboratory or Lecture Table.
bar is bent into a ring, the ends, A A', being united. If the ring be made to
turn round its centre in its own plane, and near a magnetic pole, it is plain
that when the coil is approaching this pole a current will be produced in it,
and when it is receding, an opposite current. Let the number of coils be
increased, and each coil in turn will be the seat of a current, or of the elec-
trical state which tends to produce a current. In Fig. 275 the reader may
see how this disposition is realized. The figure shows a form of the Gramme
Machine adapted for the lecture-table or laboratory. A M' B M is the soft
iron ring, covered with a series of separate coils placed radially, o is a com-
pound horse-shoe steel magnet, s its south pole, N its north pole, each pole
being armed with a block of soft iron hollowed into the segment of a circle
and almost completely embracing the circle of coils. The magnetism of each
pole is strongly developed in the interior faces of these armatures. The induc-
tive action tends to produce two equal and opposite currents, which, like the
currents of two similar voltaic batteries joined by their like poles, neutralize
39
ELECTRICITY.
each other in the connected coils, but flow together through an external
circuit. Fig. 276 will make clear
the manner in which the coils,
B B, are placed on the ring, A.
The length of wire in each coil
is the same, and the extremi-
ties are attached to strips of
copper, R R, which are fixed
on the spindle of the machine.
The two ends of each wire are
connected with two consecu-
tive strips, while the coils are
insulated from each other, and
thus each coil, like the element
of a battery, contributes to the
aggregate current. The cur-
rents are drawn off, as it were,
from these axial conductors at
FIG. 276. Insulated Coils surrounding two opposite points of the ring,
an Anmdus of Iron Wires. by springs very lightly touch-
ing them on each side of the
spindle, as may be seen in Fig. 275. In Fig. 277 is another arrangement of
FIG. 277. Hand Gramme Machine, with Jamirts Magnet.
the table apparatus with the magnet vertical, and formed according to the
new plan suggested by M. Jamin, who finds the best magnets are made by
tying together thin strips of steel.
ELECTRICITY.
But the importance of this invention consists in the facility which it
affords for cheaply producing electricity on a scale adapted for industrial
operations, for the deposition of metals, for artificial light, and for chemical
purposes. The great importance of a cheap electric light for lighthouses
prompted the British Government to permit the inventor to exhibit the light
thus produced from the Clock Tower of the Houses of Parliament; for the
signal light during the sittings of the House had previously been produced
by a gas-light This electric light was produced by a powerful Gramme
machine, such as that shown in Fig. 278, driven by a small steam engine
in the vaults of the Houses of Parliament, and the ordinary carbon points,
reflectors, &c., were used in the Clock Tower, where the light was exhibited ;
copper wire - inch diameter being used to convey the current from the
machine to the carbons. The result of these experiments may be gathered
from the following extract from an official report made by the engineers of
the Trinity House :
" Pursuant to the instructions received from the Deputy Master to fur-
nish you with my opinion on the relative merits of the electric and gas
lights under trial at the Clock Tower, Westminster, I beg to submit the
following report: On the evening of the ist ultimo I was accompanied
by Sir F. Arrow (who kindly undertook to check my observations by his
experience) to the Westminster Palace, where we met Captain Galton, R.E.,
Dr. Percy, and some gentlemen connected with the electric and gas appa-
ratus under trial. I was informed that the stipulations under which the
lights were arranged were, that they be fixed white to illuminate a sector
of the town surface of 180, having a radius of three miles. I first exa-
mined the Gramme magneto-electric machine, in use for producing the
currents of electricity. This machine we found attached by a leather
driving-belt to the steam engine belonging to the establishment. We then
proceeded to the Clock Tower, where we found the electric lamp, at an
elevation of 250 ft. The Wigham gas apparatus was placed at the same
elevation, within a semi-lantern of twelve sides, about 8| ft. in diameter,
and 10 ft. 3 in. high in the glazing. Near the centre of the lantern were
three large Wigham burners, each composed of 108 jets. After the exa-
mination of the apparatus, we proceeded to Primrose Hill, for the purpose
of comparing the electric and gas lights at a distance of three miles. The
evening, which was wet and rather misty, was admirably suited to our
purpose, ordinary gas-lights being barely visible at a distance of one
inile "
The results of a photometric comparison of the electric and gas lights
were as under, the machine making 389 revolutions per minute, and ab-
sorbing 2 '66 horse-power; the illuminating power of the gas used being 25
candles, and the quantity consumed 300 cubic ft. per hour.
Electric Light.
Wigham
Gas Burner.
108 jets.
Relative intensity of
lights
Q4.C-C6
37crc6
Or as
IOO
3Q'IQ
Illuminating power i
n standard sperm candles
^066
jy l y
I I GO 1
.1,1 v^y
392
ELECTRICITY.
"Electric Light. Total cost per session ^174 $s. od., being equal to
5-T. yd. per hour of exhibition of the light. Details shown in the full report.
Gas Light. Total cost per session of one burner of 108 jets, i 59 I %s. ^d.,
equal to 5-r. J'4^. per hour of exhibition of light, and 296 3^. 4
?^
G
1
more resorted to. During this process the cable parted, and Fig. 300
shows the scene on board the Great Eastern produced by this occurrence,
as represented by an artist of the" Illustrated London News" who accom-
panied the expedition. The broken cable was caught several times by
grapnels, and raised a mile or more from the bottom, but the tackle proved
428 THE ELECTRIC TELEGRAPH.
unable to resist the strain, and four times it broke ; and after the spot had
been marked by buoys, the Great Eastern steamed home to announce the
failure of the great enterprise. For this 5,500 miles of cable had altogether
been made, and 4,000 miles of it lay uselessly at the bottom of the ocean,
after a million and a quarter sterling had been swallowed up in these
attempts.
FIG. 299. The Instrument-Room at Valentia.
But these disasters did not crush the hopes of the promoters of the great
enterprise, and in the following year the Great Eastern again sailed with
a new cable, the construction of which is shown of the actual size, in
Fig. 301. In this there is a strand of seven twisted copper wires, as before,
forming the electric conductor; round this are four coatings of gutta-percha;
and surrounding these is a layer of jute, which is protected by ten iron
wires (No 10, B.W.G ) of Webster and Horsfall's homogeneous metal,
twisted spirally about the cable ; and each wire is enveloped in spiral
strands of Manilla hemp. The Great Eastern sailed on the I3th of July,
and on the 28th the American end of the cable was spliced to the shore
section in Newfoundland, and the two continents were again electrically
.connected. They have since been even more so, for the cable of 1865 was
eventually fished up. and its electrical condition was found to be improved
rather than injured by its sojourn at the bottom of the Atlantic. It was
spliced to a new length of cable, which was successfully laid by the Great
Eastern, and was soon joined to a Newfoundland shore cable. There
were now two cables connecting England and America, and one connect-
ing America and France has since been laid. At the present time up-
wards of 20,000 miles ot submerged wires are in constant use in various
parts of the world.
Certain interesting phenomena have been observed in connection with
submarine cables, and some of the notions which were formerly entertained
THE ELECTRIC TELEGRAPH.
429
FIG. yx>. The Breaking of the Cable.
as to the speed of electricity have been abandoned, for it has been ascer-
tained that electricity cannot properly be said to have a velocity, since the
same quantity of electricity can be made to traverse the same distance with
extremely different speeds. No effect can be perceived in the most deli-
cate instruments in Newfoundland for one-fifth of a second after contact
has been made at Valentia ; after the lapse of another fifth of a second the
received current has attained about seven per cent, of its greatest perma-
nent strength, and in three seconds will have reached it. During the
whole of this time the current is flowing into the cable at Valentia with its
maximum intensity. Fig. 302 expresses these facts by a mode of repre-
sentation which is extremely convenient. Along the line O X the regular
intervals of time in tenths of seconds are marked, commencing from O, and
the intensity of the current at each instant is expressed by the length of
the upright line which can be drawn between O x and the curve. The curve
therefore exhibits to the eye the state of the current throughout the whole
time. If after nearly a second's contact with the battery the cable be con-
nected with the earth at the distant end, the rising intensity of the current
will be checked, and then immediately begin to decline somewhat more
gradually than it rose, as indicated by the descending branch of the curve
in Fig. 302. A little reflection will show the unsuitability for such currents of
430
THE ELECTRIC TELEGRAPH.
instruments which require a fixed strength to work them. We may remark
that, supposing a receiving instrument were in connection with the Atlantic
Cable which required the maximum strength of the received current to
work it, the sending clerk would have to maintain contact for three seconds
FIG. 301. Atlantic Telegraph Cable, 1866.
before this intensity would be reached, and then, after putting the cable to
earth, he would have to wait some seconds before the current had flowed
out. Several seconds would, therefore, be taken up in the transmission of
IN SECONDS.
FIG. 302.
one signal, whereas by means of the mirror galvanometer about one-four-
teenth of this time suffices, and the syphon recorder will write the messages
twelve times as fast as the Morse instrument. The cause of the gradual
rise of the current at the distant end of a submarine cable must be sought
for in the fact that the coated wire plays the part of a Leyden jar, and the
electricity which pours into it is partly held by an inductive action in the
surrounding water. The importance of Sir W. Thompson's inventions as
THE ELECTRIC TELEGRAPH.
regards rapidity of signalling, upon which the commercial success of the
Atlantic Cable greatly depends, will now be understood.
By furnishing the means of almost instantaneous communication be-
tween distant places, the electric telegraph has enabled feats to be per-
formed which appear strangely paradoxical when expressed in ordinary
language. When it is mentioned as a sober fact that intelligence of an
event may actually reach a place before the time of its occurrence, a' very
extraordinary and startling statement appears to be made, on account of
the ambiguous sense of the word time. Thus it appears very marvellous
that details of events which may happen in England in 1876 can be known
in America in 1875, but it is certainly true ; for, on account of the difference
of longitude between London and New York, the hour of the day at the
latter place is about six hours behind the time at the former. It might,
therefore, well happen that an event occurring in London on the morning
of the ist of January, 1876, might be discussed in New York on the night
of the 3 ist of December, 1875. There are on record many wonderful in-
stances of the celerity with which, thanks to electricity, important speeches
delivered at a distant place are placed before the public by the newspapers.
And there are stories in circulation concerning incidents of a more ro-
mantic character in connection with the telegraph. The American journals
not long ago reported that a wealthy Boston merchant, having urged his
daughter to marry an unwelcome suitor, the young lady resolved upon at
once uniting herself to the man of her choice, who was then in New York,
en route for England. The electric wires were put in requisition ; she took
her place in the telegraph office in Boston, and he in the office in New
York, each accompanied by a magistrate; consent was exchanged by
electric currents, and the pair were married by telegraph ! It is said that
the merchant threatened to dispute the validity of the marriage, but he did
not carry this threat into execution. The following jeu d' esprit appeared
a short time ago in " Nature," and, we strongly suspect, has been penned
by the same hand as the lines quoted from " Blackwood," on page 385.
ELECTRIC VALENTINE,
(Telegraph Cterk r the small weights used by the analytical chemist. 1 1 would make
admirable utensils for the more delicate operations of cooking replacing
the copper ones, which render pickles and soups so poisonous. It is ex-
tremely sonorous, and would make capital bells."
Some difficulty in working the metal has occurred from the want of any
suitable solder. This difficulty has been overcome by electrolytically coat-
ing the metal with copper at the place where it has to be united with others,
and then soldering the copper in the ordinary manner. Aluminium readily
forms alloys with copper, silver, and iron. The alloys with copper vary in
colour from white to golden yellow, according to the proportion of the
metals. Some of these alloys are very hard and possess excellent working
qualities. The alloy of copper with 10 per cent, of aluminium, which is
called aluminium bronze, has been manufactured by Messrs. Bell in con-
siderable quantities. It is made by melting a quantity of very pure copper
in a plumbago crucible, and when the crucible has been removed from the
furnace, the solid aluminium is dropped in. An extraordinary increase of
temperature then occurs : the whole mass becomes white hot, and unless
the crucible be made of a highly refractory material, it is fused by the heat
developed in the combination of the two metals, although it may have
stood the heat necessary for the fusion of copper.
The qualities of aluminium bronze have been investigated by Lieut.-
Col. Strange, who finds that the alloy possesses a very high degree of ten-
sile strength, and also great power of resisting compression. Its rigidity,
or power of resisting cross strains, is also very great ; in other words, a bar
of the alloy, fixed at one end and acted on at the other by a transverse
force tending to bend it, offers great resistance, namely, three times as
much as gun-metal. An advantage attending the use of the alloy for many
delicate purposes is found in its small expansibility by heat ; it is therefore
well adapted for all finely-graduated instruments. It is very malleable, has
excellent sounding properties, and resists the action of the atmosphere. It
works admirably with cutting tools, turns well in the lathe, and does not
clog the files or other tools. It is readily made into tubes, or wires, or
other desired forms. The elasticity it possesses is very remarkable ; for
wires made of it are found to answer better for Foucault's pendulum expe-
.riment than even those of steel. These admirable qualities would seem
to recommend the alloy for many applications in which it might be expected
to excel other metals. It appears, however, that the demand for it has not
met the expectations of the manufacturers, and the production has been
somewhat diminished of late, although it is used to some extent for chains,
pencil-cases, toothpicks, and other trinkets. When more than 10 per cent,
of aluminium is added to the copper, the alloy produced is weaker ; and if
the proportion is increased beyond a certain extent, the bronze becomes so
brittle that it may be pulverized in a mortar.
The metal magnesium was first prepared, in 1830, by the French chemist
Bussy, by a process similar to that by which Deville obtained aluminium.
NEW METALS. 511
rcelain
ad been
Bussy heated anhydrous magnesium chloride with potassium in a po
crucible ; and when the vessel had cooled, and the soluble residue ha
dissolved out by water, the metal was found as a grey powder, which could be
melted into globules. The recognition of the metal as the base of magnesia
is, however, due to Davy. About a quarter of a century after Bussy's dis-
covery Ueville having shown that sodium could be substituted for potassium
in such reductions, the metal became more cheaply producible, and soon
afterwards Bunsen and Roscoe pointed out its value as a source of light.
Mr. Sonstadt devoted himself to the elaboration of a method of working
Deville's process on the large scale, and he succeeded in establishing a
company in Manchester for the manufacture. The process as carried on
at the company's works in Salford is thus described in the " Mechanics'
Magazine," 3Oth August, 1867 :
" Lumps of rock magnesia (magnesium- carbonate) are placed in large
jars, into which hydrochloric acid in aqueous solution is poured. Chemical
action at once ensues : the chlorine and the magnesium embrace, and the
oxygen and carbon pass off in the form of carbonic acid. The result is
magnesium in combination with chlorine, and the problem now is how to
dissolve this new alliance to get rid of the chlorine and so cbtain the mag-
nesium. First, the water must be evaporated, which would be easy enough
if not attended with a peculiar danger. To get the magnesium chloride
perfectly dry it is necessary to bring it to a red heat ; but this would result
in the metal dropping its novel acquaintance with chlorine and resuming
its ancient union with oxygen. To avert this re-combination, the magne-
sium chloride whilst yet in solution is mixed with sodium chloride (/.., com-
mon salt), and thus fortified, the aggressions of oxygen whilst drying are
kept off. The mixture is exposed in broad open pans over stoves, and when
sufficiently dry, the double salt is scraped together and placed in an iron
crucible, in which it is heated until melted, whereby the last traces of water
are driven off. It is then stowed away until required in air-tight vessels,
to prevent deliquescence. Here comes in that curious metal, sodium, also
discovered by Davy. Five parts of the mixed magnesium and sodium
chlorides, mingled with one part of sodium, are placed in a strong iron
crucible with a closely-fitting lid, which is then screwed down. The crucible
is heated to redness in a furnace, and its contents being fused, the sodium
takes the chlorine from the magnesium. When the crucible has been lifted
from the fire and allowed to cool, the lid is removed and a solid mass is
discovered, which, when tumbled out and broken up, reveals magnesium
in nuggets of various sizes and shapes, bright as silver."
The crude metal also presents itself in the crucible as small grains, and
even as a black powder. The whole is carefully separated from the refuse ;
it is purified by distillation in a current of hydrogen gas ; and it is after-
wards melted and cast into ingots. Magnesium is a very light metal, its
specific gravity being only 1 743 ; that is, it is only one and three-quarter
times heavier than water. When heated in the air it takes fire, and is
rapidly converted into the oxide, magnesia. In the form of wire or of
narrow ribbon, it burns easily in the air, producing a light of dazzling bril-
liancy, which among artificial modes of illumination is rivalled only by the
electric light. This is the chief use at present made of the metal. Lamps
have been contrived for burning the wire in such a manner as to obtain a
steady light, the wire being pushed forward at a regulated rate by clock-
work. The magnesium light is rich in the rays which act upon sensitive
photographic plates, and it has been successfully employed in obtaining
5 i2 NEW METALS.
photographs of dark interiors, such as vaults or caverns, and for the explo-
ration of mines and other dark places. The brilliancy of the firework dis*
plays which can be produced by magnesium far surpasses that obtainable
by any other material used by the pyrotechnist. In such exhibitions
balloons are sent up having burning magnesium attached to them ; and the
metal in the state of filings is also mixed with other materials. But mag-
nesium is still a very costly metal, and while the firework-makers find it too
expensive for common use, they complain that its brilliancy in occasional
displays dulls by contrast the effect of the ordinary fireworks, with which
the spectators are no longer satisfied.
Magnesium wire is not produced by drawing, as the metal is not ductile.
The wire is formed by a method identical with that used in the fabrication
of the leaden rope for making bullets (p. 226) ; that is to say, the metal is
forced in a heated and softened state through a small opening in an iron
cylinder. The intensity of the magnesium light has been measured by
Bunsen and Roscoe. They say that 72 grains of magnesium, when properly
burnt, evolve as much light as 74 stearine candles burning for ten hours,
and consuming 20 Ibs. of stearine. Lamps in which magnesium may be
steadily burnt are made by Mr. F. W. Hart, of London. In the more
elaborate forms of these lamps, there are springs and wheels for pushing
forward the magnesium ribbon, or a strand of magnesium wire, into the
flame of a spirit-lamp ; while at the same time the magnesium wire is made
to revolve on its axis, in order to overcome its tendency to bend down,
which would be a great disadvantage when the light is used for optical
apparatus. But for ordinary purposes a much simpler arrangement suffices :
the magnesium ribbon or wire is coiled on a drum, from which it is drawn
off by passing between two little rollers, which are turned by hand. The
wire or ribbon is drawn off the drum by the rollers, and pushed forward
through a guiding tube, which brings it into the apex of the flame of a
spirit-lamp. In this simpler form of lamp the rate is, of course, directly
dependent on the person who turns the winch of the feeding-rollers ; but
in the automatic lamp there are appliances for adjusting the rate ; the
suitable speed must be first found by trial, and then the apparatus is to be
regulated accordingly. By means of these lamps photographs can be taken
as quickly as with sun-light, on account of the abundance of chemically-
active rays given out by the burning magnesium. It has been found that
an equivalent of magnesium, in combining with oxygen, liberates a larger
amount of heat than the equivalent quantity of any other metal, not ex-
cluding even potassium. Magnesium forms alloys with several other metals,
such as lead, tin, mercury, gold, silver, platinum. All these alloys are
brittle, and have a granular or crystalline fracture. They are too readily
acted on by air and moisture to be of any service in the arts. The alloy
of 85 parts of tin with 15 of magnesium is hard and brittle ; its colour is
lavender, although both constituents are white, or nearly so ; and it de-
composes water at ordinary temperatures. Both metallic magnesium and
aluminium furnish useful re-agents to the scientific chemist. The latter
metal, when fused, dissolves boron, silicon, and titanium, and on cooling
deposits these elements in the crystalline form, this being the only known
process for artificially preparing them in the crystalline state.
FIG. 337. Portrait of Mr. Thomas Hancock*
INDIAN-RUBBER AND GUTTA-PERCHA,
INDIAN-R UBBER.
"D ESEARCHES into the history of the human race in remote ages have
" revealed the fact, that before man knew how to extract metals from
their ores, his only implements were formed of stone ; and before he be-
came acquainted with iron, there was an intermediate period in which the
more easily obtained metal, copper, had to serve as the material for all
tools and weapons. Hence archaeologists speak of the stone age, the
bronze age, and the age of iron. If we were obliged to name the nineteenth
century after the material which distinctively serves in it for the most ex-
tensive and varied uses, surely we should call it the Age of Indian-rubber!
The industrial application of Indian-rubber is entirely modern. The
substance itself appears, however, to have been known to the natives of
Peru from time immemorial, and to have been used for the preparation of
some kind of garments. Although the first specimens were sent to Europe
so long ago as 1736, and the substance was from that time submitted to
513 33
5 i4 INDIAN-RUBBER AND GUTTA-PERCHA.
many investigations, no other use was found for it up to the year 1 820 than
to efface from paper the marks made by pencils. From this it derives the
name by which it is commonly known. It has also been called "gum elastic,"
and caoutchouc from the Indian name. Crude caoutchouc is the product
obtained by the spontaneous solidifying of the milky juice of certain tropical
plants such as the Hcevea elastica, 'Jatropha elastica, and the Siphonia
cautshu. The first grows chiefly in South America, and in the basin of the
Amazon forms immense forests. At a certain season each year bands of
persons, called " seringarios? armed with hatchets, visit these forests for the
purpose of extracting the caoutchouc. They make incisions into the trunk,
and the milky juice immediately runs out, and drops into a vessel placed
to receive it, and attached to the tree by means of a lump of clay. In about
three hours the juice ceases to flow, and the seringario collects the pro-
ducts of the incisions in one large vessel. By dipping a board into this
vessel, it becomes covered with the juice; and when this is allowed to dry,
the caoutchouc remains as a thin brownish yellow layer. The caoutchouc
is not dissolved in the juice, but is merely suspended in it ; and to hasten
the drying and coagulation of the liquid, the board is warmed over a smoky
fire made with green wood. When alternate immersions and drying have
covered the board with a sufficient thickness of caoutchouc, the layer is
slit open with a knife, and the board is withdrawn. This is the best kind
of crude caoutchouc, because it is free from all admixture of foreign bodies
except the carbon derived from the smoky flame. The bottle Indian-
rubber is moulded on pear-shaped lumps of clay, which are covered with
successive layers of the milky juice ; when a sufficient thickness has been
attained, the clay is removed by soaking in water.
Up to 1820, as already mentioned, Indian-rubber was used only for
effacing pencil-marks, and about that time a piece half an inch square sold
for two shillings and sixpence. But the extreme elasticity and extensibility
of this singular substance was attracting the attention of practical men in
England, Scotland, and France. One of the earliest patents obtained in
this country for applications of caoutchouc was taken out by Mr. Thomas
Hancock, of Newington, in 1820. This gentleman has written an account
of the Indian-rubber manufacture from the commencement, and the book
is extremely interesting from the clear and simple manner in which the
inventor describes how he effected one improvement after another in his
processes and machinery. Mr. Hancock had, previous to his turning his
attention to Indian-rubber, no acquaintance with chemistry ; but he was
skilled in mechanical engineering and the use of tools, and this knowledge
proved to be precisely the kind most valuable for dealing with the first
stages of caoutchouc manufacture. His first patent was for the use of
Indian-rubber for the wrists of gloves, for braces, for garters, for boots and
shoes instead of laces, and for other similar purposes. The rings for the
wrists of gloves, &c., were simply cut from the bottle Indian-rubber by
machinery the patentee himself contrived for that purpose. Mr. Hancock
next arranged an apparatus for flattening the raw Indian-rubber by warmth
and pressure, so as to make it available for the soles of boots, &c. He
relates the practical difficulties he had to encounter in his operations, and
the manner in which he overcame them. He soon noticed and utilized
the fact that two clean freshly-cut surfaces of caoutchouc, when pressed
together, cohere and unite perfectly. This further led him to devising a
macame by which all the waste cuttings and parings might be worked up.
This machine consisted of a cylinder revolving within a cover, both being
INDIAN-RUBBER AND GUTTA-PERCHA. 515
provided with steel teeth, by which the pieces of caoutchouc placed be-
tween them were torn into shreds, and then kneaded into a solid coherent
mass of homogeneous texture. The first machine of this kind made by
Mr. Hancock would work up about I Ib. of Indian-rubber ; but now ma-
chines on the same principle are in use operating on more than 200 Ibs. of
material at once, and turning it out on a roll 6 ft. long, and 10 in. or 12 in. in
diameter.
While Hancock was thus successful in mechanically working Indian-
rubber, Macintosh, of Glasgow, found means of effecting its solution by
coal-naphtha, and he obtained, in 1823, a patent for the application of his
discovery to the fabrication of waterproof garments. Waterproof cloth, or
" Macintosh," is prepared by varnishing one side of a suitable fabric with
a solution of caoutchouc, or by covering one side of a cloth with a thin
film, and then bringing it into contact with a second piece similarly pre-
pared the two caoutchouc layers becoming incorporated when the double
cloth is passed between rollers. Other solvents for Indian-rubber have
been discovered in ether, chloroform, sulphide of carbon, and rectified
turpentine. By treatment with these liquids it swells up, and eventually
dissolves, producing a viscid ropy mass, which, by evaporation of the
solvent, leaves the caoutchouc with all its original elasticity. By the use
of these last-named solvents the persistent and diagreeable odour occa-
sioned by coal-oil is avoided. Mr. Hancock relates that when the manu-
facturers had overcome all obstacles, and had succeeded in producing
thin, light, pliable, and perfectly waterproof fabrics, they had to encounter
another quite unexpected difficulty the tailors set their faces against the
new material, and could not be induced to make it up ! The manufac-
turers were, the/efore, obliged themselves to fashion waterproof garments,
and retail them to the public. This, however, turned out to be a benefit,
for the seams were made waterproof, so as to exclude even the little water
which would otherwise pass in by capillary attraction at the stitches.
It will now be observed that there are two distinct modes of working
caoutchouc : by dealing, viz., with the solid material, or with the solutions.
Thus, from a solid disc of caoutchouc long ribbons of the material may be
cut, and these ribbons, by being passed between a set of circular knives,
may be divided into a number of square threads. These threads may then
be drawn out to six or ten times their length ; and, if wound and main-
tained in this state of tension for forty-eight hours in a warm place, they
will lose their condition of tension, and their elongated form will become
their natural or unstrained one. In this manner are the Indian-rubber
threads prepared, which, covered with silk or other material, form elastic
fabrics such as those used in the sides of boots. The circumstance of
caoutchouc, when heated for some hours at a temperature a little above
the boiling-point of water, retaining whatever form it has during the heat-
ing, is the basis of methods of obtaining thin sheets and other forms of the
material. Tubes are made by forcing the heated caoutchouc through an
annular opening by application of great pressure ; it sets in cooling, pre-
serving a section corresponding with the orifice through which it issues.
In another mode of forming tubes, a paste composed of cauotchouc, oxide
of zinc, and lime, is formed into sheets, which are cut into strips. The strips
are folded longitudinally, and the edges are cut together at an angle of
45 with the surface, so that the cut surfaces may meet each other when
the strip is rolled on a mandril to give it a cylindrical form. A slight
pressure suffices to solder together the cut surfaces, and the tube is then
" vulcanized " by a process to be presently described. 33 2
5i6 INDIAN-RUBBER AND GUTTA-PERCHA.
The dissolved caoutchouc serves to prepare waterproof garments, round
threads, sheets of Indian-rubber, &c. Fabrics are coated with the solution
by pouring it on the material as it is passing horizontally from a roller. A
straight- edge, under which the charged cloth passes, distributes the caout-
chouc in a uniform layer, the thickness of which is regulated by the space
between the knife-edge and the fabric. When sulphide of carbon is the sol-
vent used, its evaporation is complete in about ten minutes, but with other
solvents two or three hours are required. The caoutchouc is usually mixed
with lampblack before being spread on the cloth, and the article is finished
by giving the Indian-rubber layer a coat of gum-lac varnish. Sheets of
Indian-rubber are obtained by spreading fifteen or twenty layers over a
cloth, which is afterwards detached by wetting it with a solvent
Threads of circular section are manufactured from a paste of caoutchouc,
made by dissolving that substance in sulphide of carbon mixed with 8
per cent, of alcohol. This paste is placed in a cylinder, out of which it is
forced by a piston through a number of circular holes, whence it issues in
the form of filaments. These are received upon a stretched cloth, which
moves along, carrying the parallel threads, until the sulphide of carbon
has evaporated.
A modification of caoutchouc, possessing very valuable qualities for many
purposes, was discovered by Mr. Charles Goodyear, and largely applied by
him in the United States to the fabrication of waterproof boots. In 1842
these boots were imported into Europe, and it was seen that this form of
the material had the advantages of not sticking to other bodies at any
ordinary temperatures, and of preserving its elasticity even in the coldest
weather, whereas ordinary Indian-rubber becomes rigid by cold. The cut
edges of this variety of caoutchouc do not cohere by pressure. Mr. Good-
year attempted to keep his process a secret ; but Mr. Hancock, having soon
detected the presence of sulphur in the American preparations, set to work
to discover how that substance was made to combine with the caoutchouc.
He succeeded, and he obtained a patent for sulphurizing Indian-rubber
before the original inventor had applied for one. Mr. Hancock found
that a sheet of caoutchouc immersed in melted sulphur at 250 F., gradu-
ally absorbed from 12 to 15 per cent, of its weight of sulphur ; and,
further, that this does not in any way alter its properties. When, however,
the sulphurated substance was for a few minutes exposed to a temperature
of 300, it acquired new qualities, which were precisely those of the modi-
fication employed by Mr. Goodyear for his impervious boots. This trans-
formation effected by sulphur Mr. Hancock called vulcanization; and
vulcanized Indian-rubber is now employed in nearly all the innumerable
applications of caoutchouc, provided the presence of sulphur is not abso-
lutely objectionable. Goodyear's process consists in mixing the sulphur
with the caoutchouc, the suitable proportion (7 to 10 per cent.) having
been determined beforehand, and the sulphur ground up with the Indian-
rubber in the masticating machine, or disseminated through the viscid liquid
if a solution is used, or dissolved in the solvent employed. This gives better
results than Hancock's process, because the sulphurization is more uniform,
and this method is therefore more largely employed. When the various
articles have been fabricated in the ordinary manner from the mixture of
caoutchouc and sulphur, they are enclosed in vessels, where they are sub-
mitted for two or three hours to the action of steam under a pressure of
nearly 4 atmospheres, so that the steam may have a temperature of about
280 F. A still easier method, due to Mr. Parkes, consists in steeping the
INDIAN-RUBBER AND GUTTA-PERCHA. 517
articles (which in this case should be thin) in a solution of one part of chloride
of sulphur in sixty of bisulphide of carbon. The object becomes vulcanized
by simple exposure to the air, without the aid of heat. But this process is
said to be liable to cause the article afterwards to become brittle. The
addition of oxide of zinc, carbonate of lead, and other substances, is found
to yield a product better adapted for certain purposes than one in which
only sulphur is used.
The list of applications of vulcanized Indian-rubber would be a very long
one ; but as a great number of these applications must be known to every-
body, it will be unnecessary to specify them. It has lately been used for
carriage-springs, for the tires of wheels, and for the rollers of mangles. Its
employment in the construction of portable boats, pontoons, life-buoys,
dresses for divers and for the preservation of life at sea, air-tight bags and
cushions, air and water beds, cushions of billiard-tables, are a few of the
thousand instances of its utility which might be quoted.
When the proportion of sulphur mixed with the caoutchouc is increased
to 25 or 35 per cent., another product having qualities entirely different
from those of vulcanized Indian-rubber is obtained when the mixture is
heated. This is the jet-black substance termed ebonite or vulcanite, which
is made into such articles as combs, paper-knives, buttons, canes, portions
of ornamental furniture, and plates of electrical machines. It is in many
cases an excellent substitute for horn and for whalebone, while for insula-
ting supports, &c., in electric apparatus, it is unrivalled. It has a full
black colour and takes a bright polish ; and it may be cut, or filed, or
moulded. It is very tough, hard, and durable. In the transformation of
Indian-rubber into vulcanite, the temperature must be somewhat higher
than that required for the production of the vulcanized Indian-rubber. The
caoutchouc used is very carefully purified before it is incorporated with the
sulphur ; and the yellow paste formed by the mixture is subjected to the
contact of steam at a temperature of about 310*
GUTTA-PERCHA.
C* UTTA-PERCH A is a substance very like Indian-rubber in its chemical
^-* properties, having the same composition, although in outward appear-
ance very different. It was first sent to Europe in 1822, but did not become
an article of commerce until 1 844. It is the solidified juice of a tree (Isonan-
dra percha) which abounds in Borneo and Malacca. The trunk of the
tree grows to a diameter of 6 ft., but as timber it is valueless . When an in-
cision is made through the bark and into the wood, a milky juice flows out,
which speedily solidifies. Gutta-percha is a very tough substance, but is
without the elasticity of Indian-rubber. It differs from the latter, too, in
becoming softened by a gentle heat, and it will then readily take and
retain any impressions with great sharpness and fidelity. Thus beautiful
mouldings and other ornamental objects are easily made. It also has the
valuable quality of welding when softened by heat. It is a non-conductor
of electricity, and it is largely used for covering telegraph-wires, and espe-
cially for forming an insulating coating in submarine cables. It seems to
have become known precisely at the time it was required for this purpose,
518 INDIAN-RUBBER AND GUTTA-PERCHA.
and the success of ocean telegraphy is largely owing to its valuable pro-
perties. It is employed as a substitute for leather in soling shoes and boots,
and in forming straps and bands for driving machinery ; also in the pre-
paration of tubes used for conveying liquids, and for speaking-tubes. Dilute
mineral acids have no action upon it, and hence it is especially valuable for
making bottles to contain hydrofluoric acid, which attacks glass. A draw-
back to the use of gutta-percha is its tendency to become oxidized when
exposed to light and air, by which it entirely loses its power of becoming
plastic by heat, and is converted into a brittle substance. But in the dark,
or under water, it may, however, be preserved for an indefinite period
without change.
Mr. Charles Hancock, in 1847, patented a machine for cutting the gutta-
percha into slices. In this machine there is a circular iron plate, with three
radial slots, in which knives are fixed somewhat in the manner of the cut-
ting tool of a spokeshave. The lumps of gutta-percha drop against these
knives as the plate is driven round, and the material is cut into slices, which
have a thickness determined by the projection which has been given to the
blades. Sometimes an upright chopper is used, with straight or curved
blades. These slices are immersed in hot water, until they are softened,
and they are then subjected to the action of rollers armed with toothed
blades, called " breakers," and also to the action of the mincing cylinder,
which is furnished with radiating blades, and revolves partly immersed in
the water. The material is carried out of the hot water to these machines
by endless webs mounted on rollers. The breakers and mincing cylinders
make about 800 revolutions per minute. The gutta-percha, thus reduced
to fragments, is carried forward again by endless webs into cold water, where
it is thoroughly washed and separated from the impurities, which fall to the
bottom, while the lighter gutta-percha floats on the surface of the water.
Gutta-percha, like caoutchouc, can be combined with sulphur. The
best product is obtained when a small proportion of sulphur is used along
with some metallic sulphide. Mr. C. Hancock uses 48 parts of gutta-
percha, i of sulphur, and 6 of antimony sulphide. These ingredients are
thoroughly mixed and put into a boiler, where they are heated under pres-
sure for an hour or two. Another method of treating gutta-percha was also
devised by Mr. C. Hancock, who found that when this strange substance
was exposed to nitric oxide gas (which is given off when nitric acid acts
on copper) it became quite smooth, and acquired an almost metallic lustre,
losing also all its stickiness. Another modification is formed by treating
gutta-percha with chloride of zinc ; and yet another by the action of a sol-
vent, such as turpentine, a sulphide, sulphur, and carbonate of ammonia,
employed simultaneously. Mr. Hancock mixes all these materials together
in a " masticator," and then applies heat to them while confined in a vessel
under pressure. The product of these operations is a very singular modifi-
cation of gutta-percha, in which the material assumes a spongy, elastic con-
dition, and in this form it is used to form the stuffing of sofas, easy chairs,
&c. Among the purposes to which gutta-percha has been applied besides
the general one of w iterproof tissues and fabrics, may be named the for-
mation of straps, belts, bandages, cups, and other vessels, rollers for cotton-
spinning machinery, hammers of pianofortes, cards for wool-carding,
hammercloths, life-preservers, and trusses.
Gutta-percha is made into strips, bands, cords, or threads of any required
section, by passing sheets of suitable thickness between rollers provided
with grooves and cutting-edges. For strips and bands the sheets are passed
INDIAN-RUBBER AND GUTTA-PERCHA. 519
through the machine cold, and divided by the cutting-edges. But for round
cords or threads sheets are supplied to the rollers from a receptacle in which
they acquire a temperature of about 200 F. The material is forced to take
the form of the grooves, the operation in this case being analogous to that
of rolling iron bars. The gutta-percha cords are received as they issue
from the rollers in a tank of cold water, from which they pass on, to be
wound on reels or drums. It is obvious that cords of any section may be
formed by making use of grooves of suitable shape. Tubes of gutta-
percha are made by forcing the softened substance out of an annular ori-
fice : it is received into vessels filled with cold water. Telegraph-wires
are covered by a similar process the copper wire being made to pass
through the centre of a circular opening with the gutta-percha surround-
ing it. .Picture-frames, &c., are made by forcibly pressing warm gutta-
percha into the warmed moulds. Gutta-percha tubing is largely used
everywhere for the speaking-tubes by which persons in remote apartments
of even the largest building can converse. This is one of the labour-
saving inventions of our day. It must have struck every one who has seen
these speaking-tubes in operation in a large establishment, what a vast
amount of running to and fro they save, and how much they expedite
business by the convenient means they afford of giving orders and direc-
tions to persons in distant apartments. This tubing is also used for the
conveyance of liquids, and it has been proposed to employ it instead of the
ordinary leaden piping used for carrying water. It may seem to the reader
that gutta-percha is too fragile a material to resist the pressure to. which
water-pipes are exposed. But, judging from some experiments made by
the engineer of the Birmingham Waterworks, the power of gutta-percha
tubing to resist pressure is quite extraordinary, and far beyond what would
be supposed. The tubes experimented on had diameters of f and |th of
an inch respectively. The water from the main, where the pressure was
that caused by a head of 200 ft., was in communication with these pipes for
several weeks, and they were found unaltered in any way. In order to test
the strength of the tubes, and find the greatest pressure they would bear,
the engineer then had them connected with a hydraulic proving-pump ;
and here, when exposed to the highest pressure at which the ordinary
water-pipes were tested, namely, to 250 Ibs. on the square inch, they also
remained intact. The pressure was afterwards increased to 337 Ibs., but
without any damage to the tubes.
The increasing importance of gutta-percha maybe inferred from the con-
tinually augmented importation of the crude "substance into this country.
In 1850 only n,ooocwt. were imported, but the quantity has increased
year by year ; and in 1872 we received nearly 46,000 cwt. The demand
is still increasing ; but there is reason to apprehend that under the stimulus
of a rising market, the producers have collected the gutta-percha wastefully
and with great destruction of the trees, so that it is not improbable that if
the demand still increases, there may be a gutta-percha famine. The
concreted juices of certain other trees have been proposed as substitutes
for gutta-percha. None of these have as yet come into practical use. The
increase in a few years of the quantity of Indian-rubber imported into the
United Kingdom is perhaps more extraordinary. From the tables given
in Mr. Hancock's book, it appears that our imports of caoutchouc were
853,000 Ibs. in 1850, but by 1855 they had amounted to 5,000,000 Ibs.
FlG. 338. Portrait of Sir James Soung Simpson, M.D.
ANESTHETICS.
THE discover)' which is indicated by the somewhat unfamiliar word *
which heads this article is perhaps the greatest which has ever been
made in connection with the science of medicine. At least, there is no
other discovery of modern times which has so largely and directly contri-
buted to the assuagement of human suffering. Nay, in this respect there
is perhaps in the whole annals of the healing art no other which can rival
it, if we except that famous one of Jenner's which has arrested the ravages
of small-pox. During the last thirty years, all the more formidable opera-
tions of the surgeon have been, in almost every case, performed with a happy
unconsciousness on the part of the patient. In unconsciousness, induced
by the same means, has relief also been found for severe suffering arising
from other causes. The substances which are denoted by the word "anaes-
thetics" differ from the drugs which the older surgeons sometimes ad-
ministered before an operation, in order to lull the patient's sense of pain.
They differ in their nature and in the mode of their administration ; by
the certainty and completeness of their action ; by the entirely transient
effects they produce, which pass off without leaving a trace.
To the great chemist whose name has already been mentioned as the
* From a (Q.V), privative, and aivdrjTtKOS, capable of perceiving or feeling.
520
ANESTHETICS.
521
discoverer of the metals of the alkalies and alkaline earths we are in-
debted for the first of the remarkable class of bodies we are about to dis-
cuss. The first work that Davy published had for its title " Researches,
Chemical and Philosophical, chiefly concerning Nitrous Oxide and its
Respiration." This was in the year 1800, when the philosopher had hardly
completed his twenty-first year. The work caused no little sensation in
the scientific world, and it was in consequence of the reputation he acquired
by these researches that Davy was appointed to the chemical professorship
at the Royal Institution. Davy was not the original discoverer of nitrous
oxide, but he first entered upon a full investigation of its properties, and
announced the singular effect produced by its inhalation. The kind of
transient intoxication and propensity to laughter which it exites have ob-
tained for this compound the familiar name of laughing gas. Davy had
by experiment on his own person proved the anaesthetic properties of this
gas, for he had a tooth painlessly extracted when under its influence,
and he says in the work above named that " as nitrous acid gas seems
capable of destroying pain, it could probably be used with advantage in sur-
gical operations where there is no effusion of blood." Davy's observations
and suggestions were destined to lie barren for nearly half a century, but
they nevertheless formed the basis of the great results which have since
been attained.
Before proceeding farther, it will perhaps be well to make the unscientific
reader acquainted with the chemistry of nitrous oxide. We may presume
that he knows that atmospheric air is a mixture of the two invisible gases,
nitrogen and oxygen (the small quantity of carbonic acid also present need
not now be considered). When a known quantity of air is passed over red-
hot copper turnings, contained in a tube, the whole of the oxygen is seized
upon by the copper, and only the nitrogen issues from the tube, and may
be collected. Some of the copper is thus converted into oxide, and the
increase of the weight of the tube's contents shows the weight of oxygen
contained in the air, while the weight of nitrogen may be known from the
volume collected. In this way the chemist analyses atmospheric air, and
determines that 100 parts by weight of dry air contain about 79 of nitrogen
and 21 of oxygen ; or, by measure, about four times as much of the former
as of the latter. Now, chemists are acquainted with no fewer than five
different substances which contain nothing but nitrogen and oxygen. These
substances are either gases, or can be changed into the gaseous form by
heat, and they can all be analysed in the same manner as air. The results
of such analyses show in 100 parts by weight of each substance the fol-
lowing proportions of its constituents :
No. i.
No. 2.
No. 3.
No. 4.
No. 5.
Nitrogen
Oxygen
63-64
36-36
46-67
53*33
36-84
63-16
30-44
69-56
25'93
74-07
In casting the eye over this table, no relation will probably be detected
between the five cases. But if we write down, not the quantities of nitro-
gen and oxygen contained in 100 parts of each compound, but the quan-
tity of oxygen which in each compound is united to some fixed quantity
of nitrogen, we shall at once detect a remarkable law : thus, taking 28 as
the fixed weight of nitrogen, for reasons which need not be here explained :
5 22
ANESTHETICS.
No. i.
No. 2.
No. 3.
No. 4.
No. 5.
Nitrogen .
28
28
28
28
28
( Oxvgren .
16
32
48
64
80
( or
16x1
16x2
16X3
16X4
16X5
Chemists have a sort of shorthand method of expressing the composition
of substances, which may be conveniently illustrated by the case before us.
Let it be agreed that the letter N shall not only represent nitrogen, but
always fourteen parts by weight grains, ounces, &c., &c., of nitrogen ;
and that, similarly, O shall stand for sixteen parts by weight of oxygen. It
is plain that the composition of the compound No. 2 may be represented
by simply writing down "NO ;" and that of No. 4, in which there is just
double the proportion of oxygen, by " NOO." But to avoid an unnecessary
repetition of the same symbol, when it has to be taken more than once, a
small figure is written after and a little below it. Thus, for OO, " O 2 " is
written. The proportional composition of each of the five compounds will
now be obvious from the following symbols :
No. i.
No. 2.
No. 3.
No. 4.
No. 5.
N 2 O
NO
N 2 3
NO 2
N 2 5
These symbols may be regarded as merely a compendious expression of
the composition of each substance as a shorthand statement of (he facts
of analysis. But to the majority of chemists the symbols have a deeper
significance ; for they are taken as representing the atoms of each element
which enter into each smallest possible particle of a compound ; they ex-
press a certain theory of the ultimate constitution of matter. Thus, if we
suppose that there exist indivisible particles of nitrogen and of oxygen,
and that each smallest particle, or molecule, of the compounds under
consideration is constituted of a certain definite and invariable number of
each kind of atoms ; and, further, if we suppose that an atom of oxygen is
heavier than one of nitrogen in the proportion of 16 to 14, or 8 to 7, we
shall have a simple theoretical explanation of the relations in the propor-
tions already pointed out. In fact, these would result from the simplest
combinations of the two kinds of atoms ; and we can picture each one of
the smallest particles of the several bodies as thus constituted :
No. i.
No. 2.
No. 3.
No. 4.
No. 5.
O
00
ooo
00
0:0
00
N 2 O
NO
N 2 3
NO 2
N 2 6
The black circles represent nitrogen atoms, and the open ones oxygen
ANESTHETICS. 523
atoms ; the symbols are placed below in order that their relation to the
supposed atomic constitution may be obvious at a glance. While the
symbol of a compound must always accord with its percentage composi-
tion, the latter does of itself determine the symbol or formula. A number
of other circumstances, which cannot here be discussed, are taken into
account as evidence of the constitution of the molecule.
This digression on chemical formulae will, it is hoped, enable the general
reader, who may not previously have been acquainted with them, to per-
ceive their significance, instead of passing them over as unintelligible
cabalistic letters when they occur in the following pages. With this ob-
ject, it may be added that the elements, hydrogen, carbon, and chlorine,
are respectively represented by H, C, and Cl ; and that the proportional
quantities, which are also implied in the symbols, and are those by which
H, C, and Cl combine with other bodies, are 1,12, and 35*5 respectively.
Another point which should be understood is that the properties and be-
haviour of a chemical compound are different, and usually extremely dif-
ferent, from those of any of its constituents. This is well illustrated in the
subject we are considering. Atmospheric air is a mixture (not a compound)
of nitrogen and oxygen gases, and all its properties are intermediate be-
tween those of its ingredients taken separately. Nitrous oxide, N.jO,has
properties not possessed by either constituent separately. For example, it
is very soluble in water, whereas oxygen is very slightly so, and nitrogen
still less. The other compounds we have referred to differ widely from
nitrous oxide and from each other in their properties.
Nitrous oxide is an invisible gas, having a slightly sweetish taste and
smell. It is dissolved by water, which, at ordinary temperatures, takes up
about three-fourths of its volume of the gas. By cold and great pressure
the gas may be condensed into a colourless liquid. The gas is obtained
in a pure state by gently heating the salt called ammonium nitrate, which
is formed by neutralizing pure nitric acid with carbonate of ammonia. The
action which occurs may be explained thus : the hydrogen of the ammo-
nium unites with a portion of the oxygen of the nitric acid, forming water,
whilst the remainder of the oxygen combines with the nitrogen. As che-
mical actions are regarded as either separations or unions of atoms, they
can be expressed by what is called a chemical equation, the left-hand side of
which shows the arrangement of the atoms before the action, and the
right-hand side the arrangement after it, the sign of equality being read as
" produce" or " produces." But the validity ol the equations, like that of
the symbolic formulae, is quite independent of the existence of atoms ; for
the equation always rests on certain facts, namely, the relations between
the quantities of the substances which enter into, and those which are pro-
duced by, a chemical action. Thus, in the present case the action may be
symbolically expressed as follows :
H 4 NN0 3 = 2 H 2 + N 2
Ammonium nitrate. Water Nitrous oxide.
The equation expresses the fact that every 80 parts by weight of ammonium
nitrate, which are used in this reaction, split up into 36 of water and 44 of
nitrous oxide.
No attempt seems to have been made to turn Davy's suggestion to prac-
tical account ; but in courses of chemical lectures at the hospitals and else-
where the peculiar physiological properties of nitrous oxide have, since
Davy's announcement, always been demonstrated by some person inhaling
524
ANESTHETICS.
the gas. In the medical schools the students often operated on a comrade
who was under the influence of nitrous oxide to the extent of bestowing
sundry pinches and cuffs, which fully proved the anaethestic qualities of
the nitrous oxide. In 1818 Faraday pointed out the similarity between the
effects of ether and of nitrous oxide, and from that time Professor Turner
regularly included among the experiments of his course of chemistry the
inhalation of the vapour of ether by one of the students. This was done
by simply pouring a little ether into a bladder of air, and by means of a
tube drawing the mixed air and vapour into the mouth. Until 1844 the
effects of nitrous oxide and of ether vapour remained without application,
although thus continually demonstrated in lectures. At the close of that
year, Mr. Horace Wells, a dentist, of Hartford, Connecticut, U.S.A., wit-
nessed the usual experiments with nitrous oxide at a public lecture. At his
request the lecturer attended at Mr. Wells's residence the following day, to
administer to him the nitrous oxide, in order that he might try its efficacy
in annulling pain, for he was himself to have a tooth extracted by a brother
dentist. His exclamation on finding the operation painlessly over was,
" A new era in tooth-pulling !" Mr. Wells continued his experiments on the
use of nitrous oxide in dental operations, but he did not apparently obtain
uniform results, for he pronounced its effects uncertain, and he gave it up.
On the occasion when Mr. Wells's tooth was extracted, Dr. W. T. G. Morton
was present, and he soon afterwards found that under the influence of
ether vapour, teeth might be painlessly extracted and surgical operations
performed. Dr. Morton attempted to conceal the substance he used under
the name of " letheon," for which he obtained a patent. But the well-known
and characteristic odour of ether declared the nature of the "letheon ;" and
Dr. BigeloNv having in consequence tried ether, found it to produce all the
effects of "letheon." So the matter was no longer a secret. Dr. Morton
was, therefore, the person who first applied ether vapour, and the extrac-
tion of a tooth was the occasion of its first application. This was in 1 846.
It was used for the first time in England on the iQth of December, 1846,
also for the extraction of a tooth ; and two days afterwards Mr. Listen, the
eminent surgeon, performed the operation of amputating the thigh while
his patient was under the influence of ether. The employment of ether
in surgical operations quickly spread, and its administration in hospitals
became general throughout Europe and America.
The chemical constitution of ether, and its relation to alcohol, may be
indicated by the following formulae :
HOH HO(C 2 H 5 ) (C 2 H & )0(C 2 H 5 )
Water. Alcohol. Ether.
If we suppose one of the hydrogen atoms in the molecule of water to
be removed and replaced by the group (C 2 H 5 ), the result is alcohol. If,
now, (C 2 H 5 ) be substituted in the alcohol for the remaining atom of hydro-
gen, we get a particle of ether. Ether was discovered in 1 540, and de-
scribed as sweet oil of vitriol, but its real nature was first pointed out by
Liebig. It is prepared by distilling a mixture of sulphuric acid and alcohol.
It is a colourless transparent liquid, extremely volatile, and possessing a
peculiar and powerful odour. It evaporates so rapidly that a drop allowed
to fall from a bottle on a warm day may be converted into vapour before
it reaches the ground. When its vapour is inhaled in sufficient proportion
mixed with air, it soon produces a complete insensibility to pain. In the
case of a full-grown man who inhales air containing 45 per cent, of the
ANAESTHETICS. 525
vapour, about 2 drams per minute of the liquid are consumed. The air is
allowed to stream over the surface of the liquid in a proper apparatus,
where it takes up the vapour, and the two pass through a flexible tube to a
piece fitting over the mouth and nostrils of the patient. The effects pro-
duced are progressive, and may be thus described :
For about two minutes after the beginning of the inhalation, the patient
retains his mental faculties, and has some power of controlling his move-
ments, but in a confused and disordered manner. At the end of the third
minute he is unconscious ; there are no voluntary movements, but muscular
contractions may agitate the frame. At the end of the fourth minute, the
only perceptible movements are the motions of the chest in respiration. If
the inhalation be discontinued at the end of the fourth minute, when I oz.
of ether will have evaporated, similar stages are passed through in reverse
order during recovery. The condition reached at the end of the fourth
minute continues about two minutes ; the intermediate state lasts three
or four minutes ; the condition of confused intellect and will, about five
minutes. This is succeeded by a feeling of intoxication and exhilaration,
which continues for ten or fifteen minutes. It was probably this excite-
ment of the system produced by ether which has caused it to be super-
seded in Britain, at least in about twelve months after its adoption, by
chloroform.
Chloroform appears to have been independently discovered in 1831, by
Soubeiran, and by an American chemist, Guthrie. It is usually procured by
distilling a mixture of bleaching powder, spirits of wine, and water. Chloro-
form is a colourless volatile liquid, of an odour much more agreeable than
that of ether. Its composition is represented by CHC1 3 . The merit of
having first applied the singular properties of this substance to the allevia-
tion of human suffering belongs to the late Sir J. Y. Simpson, of Edinburgh.
Its use as an anaesthetic was apparently suggested to this eminent professor
by Mr. Waldie, of Liverpool. It was first applied at Edinburgh on the
1 5th November, 1847 ; and when its efficacy had been proved, it was soon
extensively used, and in Europe, at least, almost entirely superseded ether,
as being more rapid and certain in its action, not producing injurious ex-
citement, and being pleasanter to inhale. A notion prevailed that chloro-
form was not only more powerful in its operation than ether, but also more
safe. In January, 1 848, its administration, however, proved fatal to a patient ;
and since then a certain number of casualties of this kind have occurred
with chloroform, ether, and other anaesthetics.
The patient is often made to inhale the vapour of chloroform by merely
holding before his mouth and nostrils a sponge or handkerchief, on which
a small quantity of the liquid has been poured. Dr. Snow contrived an
apparatus for administering the vapour with more regularity. A metal box
adapted to the shape of the face is made to cover the mouth and nostrils.
This piece has two valves, one of which admits the air and vapour from an
elastic tube connected with the apparatus containing the chloroform, and
prevents its return ; the other valve is a flap opening outwards, which
allows the expired air to escape. There is also an adjustment for admit-
ting directly into the mouthpiece more or less atmospheric air.
The sensations first experienced when chloroform is inhaled are said to
be agreeable. Many persons have described the feeling as resembling rapid
travelling in a railway carriage ; there is a singing in the ears, and when
the power of vision ceases, and the person is no longer conscious of light,
the sensation is that of entering a tunnel. After this there is a lessened
526 ANESTHETICS.
sensibility to pain ; and in the next stage the unconsciousness to outward
impressions is deeper, but the mental faculties, though impaired, are not
wholly suspended, for the patient may speak, and usually dreams some-
thing which he afterwards remembers. When the person is still more
under the influence of the chloroform, no voluntary motions take place,
although there may be some inarticulate muttering. Dr. Snow describes
several conditions which may be observed in patients undergoing opera-
tions under the influence of chloroform. First, the patient may preserve
the most perfect quietude without a sign of consciousness or sensation ;
this is the most usual condition. Second, he may moan, or cry, or flinch
under the operation, without, however, having the least memory of any paiit>
when he recovers. Third, the patient may talk, laugh, or sing during the
operation ; but what he says is altogether devoid of reference to what is
done. Fourth, he may be conscious of what is taking place, and may look
on while some minor operation is proceeding, without feeling it, or with-
out feeling it painfully. This is often the condition of the patient as the
effect is passing off, while some smaller.operation is still proceeding. Fifth,
the patient may complain he is being hurt ; but afterwards, when the effect
of the chloroform has passed off, he will assert that he felt no pain what-
ever. When the chloroform has been inhaled for but a short time, the
patient becomes conscious in about five minutes after its discontinuance ;
but with a longer inhalation the period of unconsciousness may last for
perhaps ten minutes. The return of consciousness takes place with tran-
quillity : not unfrequently the patient's first speech, even after a serious
operation, often being an assertion that the chloroform has not taken
effect.
In the strongest degree of ether and chloroform effects, all the muscles
of the body are relaxed ; the limbs hang down, or rest in any position in
which they are placed ; the eyelids droop over the eyes, or remain as they
are placed by the finger ; the breathing is deep, regular, and automatic ;
there is often snoring, and this is, indeed, characteristic of the deepest
degree of unconsciousness ; the relaxation of the muscles renders the face
devoid of expression, and with a placid appearance, as if the person were
in a sound natural sleep. He is perfectly passive under every kind of opera-
tion. The breathing and the action of the heart proceed all the while with
unimpaired regularity. It is, however, known by experiments on animals
that if the inhalation be prolonged beyond the period necessary to produce
these effects, the respiratory functions are interfered with by the insensi-
bility extending to the nerves on which they depend. The breathing of an
animal thus treated becomes irregular, feeble, or laborious, and death en-
sues. However nearly dead from inhalation of ether vapour the animal
may be, provided respiration has not actually ceased, it always recovers
when allowed to breathe fresh air. Of course, the etherization is never
carried to this stage with human beings.
Air containing 2 grs. of chloroform in 100 cubic inches suffices to induce
insensibility ; but 5 grs. in 100 cubic inches is found a more suitable pro-
portion. Dr. Snow, who strongly disapproved of the uncertain and irre-
gular mode of administering chloroform on a handkerchief or sponge,
contrived the inhaling apparatus already described. The air before reach-
ing the mouth and nostrils of the patient passes through a vessel containing
bibulous paper moistened with chloroform. This vessel he surrounds with
water at the ordinary temperature of the air, in order to supply the heat
absorbed by the conversion of the liquid into vapour, so that the formation
ANAESTHETICS. 527
of the latter may go on regularly. The same thoughtful arrangement
formed part of the ether-inhaler he had previously contrived.
The extraordinary effects of ether and chloroform have introduced new
and important facts into psychological science, and have illustrated and
extended some of the most interesting results of physiological research.
Let us trace the action of these substances, and explain it as far as may
be. Nitrous oxide, ether vapour, and chloroform vapour are all soluble in
watery fluids. The lungs present a vast surface bathed by watery fluids,
and therefore these gases are largely absorbed ; and by a well-known pro-
cess, they pass directly into the blood, through the delicate walls of the
capillary vessels. The odour of ether can be detected in any blood, drawn
from persons under its influence. Ether, or chloroform, thus brought into
the general current of the circulation, is quickly carried to all parts of the
body, and thus reaches the nerve-centres. , On these it produces character-
istic effects by suspending or paralysing nervous action : why or how this
effect takes place is unknown. The nervous centres are not all acted upon in
an equal degree some require a larger quantity of the drug to affect them at
all. The parts of the nervous system first affected are the cerebral lobes,
which are known to be the seat of the intellectual powers. The cerebellum
the function of which there is reason to believe is the regulation and co-
ordination of movements is the next to yield to the influence. Then follow
the spinal nerves, which are the seat of sensibility and motive power. This
is as far as the action can safely be carried : the nervous centre called the
medulla oblongata, which is placed at the junction of the brain and the
spinal cord, still performs its functions one of the most important of which
is to produce the muscular contractions that keep the respiratory organs
in action. We have seen, by the effects of further etherization in animals,
that when this part of the system is affected, the animal dies from a stop-
page of the respiration.
But, unfortunately, there have been instances in which death has been
caused by the administration of ether and chloroform even under the most
skilful management. But these occurrences were not the result of the inha-
lation having been carried so far as to stop respiration : in some cases the
patient has died before the first stage of insensibility. These fatal cases have
all been marked by a sudden paralysis of the heart that organ has abruptly
ceased to act. Why in these, certainly a very small percentage of patients,
the action of the drug should at once take effect on the heart has not yet
been explained. The rhythmic action of the heart depends upon nervous
centres enclosed within its own substance, so that this organ is to a certain
extent independent ; but it is connected with the other nervous centres by
the branches of a remarkable nerve which proceeds from the medulla oblon-
gata^ and also by another set of nerves which come from the chain of
ganglia called the sympathetic nerve. The nerve connecting the heart with
the medulla is a branch of that called the pneumo-gastric, and it is a well-
established fact that the action of the heart may be arrested by irritation
of this nerve. The comparatively few fatalities which have attended the
use of anaesthetics may, therefore, be due either to an immediate action on
the nerve-centres of the heart, or possibly to a mediate action through the
medulla and the pneumo-gastric nerve.
Soon after the introduction of ether the use of nitrous oxide was discon-
tinued by the dentists, on account of the apparent uncertainty of its action.
Within the last few years, however, its employment in the extraction of
teeth has been revived by Dr. Evans, of Paris, who found that to insure
'528 ANAESTHETICS.
certainty in its action, the great point is the inhalation of the gas in a pure
state and without admixture of air. Nitrous oxide seems now to be exten-
sively used by dentists, and thus Davy's experiment of 1800 is repeated
and verified daily in thousands of cases, and to the great relief of hundreds
who probably never heard his name.
Other bodies, such as amylene (C 5 H 10 ), carbon tetrachloride (CC1 4 ), &c.,
have been tried as substitutes for ether and chloroform ; but having been
found less efficacious or more dangerous, their use has been abandoned.
It might be instructive to reflect how much unnecessary pain would have
been spared to mankind had ether and chloroform been known and ap-
plied at an earlier age. We know not what other beneficent gifts chemistry
may yet have in store for the alleviation of suffering, but it is unlikely that
even ether and chloroform are her derniers mots. It should be remembered
that the chemists who discovered and examined these bodies were attracted
to the work by nothing but the love of their science. They had no idea
how invaluable these substances would afterwards prove. The chemist of
the present day, whose labour is often its own reward, may be cheered and
stimulated in his toil by the thought that while no discovery is ever lost,
but goes to fill its appropriate place in the great edifice of science, even
the most apparently insignificant truth may directly lead to invaluable re-
sults for humanity at large.
What strange things the ancient thaumaturgists might have done had
they been possessed of the secret of chloroform or of nitrous oxide ! What
miracles they would have wrought what dogmas they would have sanc-
tioned by its aid ! But the remarkable effects produced by the inhalation
of certain gases or vapours were not altogether unknown to the ancients
although these effects were then attributed to anything but their real
cause. It is related that a number of goats feeding on Mount Parnassus
came near a place where there was a deep fissure in the earth, and there-
upon began to caper and frisk about in the most extraordinary manner.
The goatherd observing this, was tempted to look down into the hole, to
see what could have caused so extraordinary an effect. He was himself
immediately seized with a fit of delirium, and uttered wild and extravagant
words, which were supposed to be prophecies. The knowledge of the pre-
sumed divine inspiration spread abroad, and at length a temple in honour
of Apollo was erected on the spot. Such was the origin of the famous
Oracle of Delphi, where the Pythoness, the priestess of Apollo, seated on
a tripod placed over the mysterious opening, delivered the response of the
god to such as came to consult the oracle. It is stated by the ancient
writers, that when she had inhaled the vapour, her eyes sparkled, convul-
sive shudders ran through her frame, and then she uttered with loud cries
the words of the oracle, while the priests who attended took down her in-
coherent expressions, and set them in order. These possessions by the
spirit of divination were sometimes violent. Plutarch mentions a priestess
whose frenzy was so furious, that the priests and the inquirers alike fled
terrified from the temple ; and the fit was so protracted that the unfortu-
nate priestess herself died a few days afterwards.
FlG. 339. A Railway Cuffing.
EXPLOSIVES.
T^HE illustration above will serve to remind the reader of the great im-
portance of explosive agents in the operations of civil industry. By
reason of the more impressive and exciting spectacles which attend the
use of such agents in warfare, we are rather apt to lose sight of their far
more extensive utility as the giant forces whose aid man invokes when he
wishes to rend the rock in order to make a road for his steam horse, or in
order to penetrate into the bowels of the earth in search of the precious
ore. A little reflection will show that if such work had to be done with
only the pickaxe, the chisel, and the crowbar, the progress would be pain-
fully slow ; and railway cuttings through masses of compact limestone,
like that represented in Fig. 339, for example, would be well-nigh impos-
sible. The formation of cuttings and tunnels, and the removal of rocks in
mining operations, are not the only service which explosive agents render
to the industrial arts ; there is, besides other uses which might be enume-
rated, the preparation of foundations for buildings, bridges, harbours, and
lighthouses. The use of gunpowder in all such operations as those which
have been referred to is too well known to require description. But of late
years gunpowder has been to a great extent superseded for such purposes
by two remarkable products of modern chemistry, called gun-cotton and
nitro-glycerine. Military art has also benefited by at least one of these
529 34
530
EXPLOSIVES.
products ; and the use of charges of gun-cotton for torpedoes has already
been described and illustrated in these pages.
It is not a little curious that the two most terribly powerful explosives
known to science should be prepared from two most harmless and familiar
substances. The nice, soft, clean, gentle cotton-wool, in which ladies wrap
their most delicate trinkets, becomes, by a simple chemical transformation,
a tremendously powerful explosive ; and the clear, sweet, bland liquid,
glycerine, which they value as a cosmetic for its emollient properties, be-
comes, by a like transformation, a still more terrifically powerful explosive
than the former. It is, perhaps, even more curious that having undergone
the transformation which confers upon it these formidable qualities, neither
cotton-wool nor glycerine is changed in appearance. The former remains
white and fleecy ; the latter is still a colourless syrupy-looking liquid.
The fibres which form cotton, linen, paper, and wood, are composed almost
entirely of a substance which is known to the chemist as cellulose or cellu-
lin. That this substance, as it exists in the fibres of linen and in sawdust,
could be converted into an explosive body by the action of nitric acid, ap-
pears to have been first observed by the French chemist, Pelouze, in 1838.
The action with cellulose in the form of cotton-wool was more fully examined
by Professor Schonbein, of Basle, who, in 1846, first described the method
of preparing gun-cotton, and suggested some uses for it. He directs that
one part of finely-carded cotton-wool should be immersed in fifteen parts of
a mixture of equal measures of strong sulphuric and nitric acids ; that after
the cotton has remained in the mixture for a few minutes, it should be re-
moved, plunged in cold water, and washed until every trace of acid has
been removed, and then carefully dried at a temperature not exceeding the
boiling-point of water.
After Professor Schonbein had demonstrated the power of the new agent
in blasting, and its projectile force in fire-arms, its manufacture on a large
scale was undertaken at several places. Messrs. Hall commenced to make
it at their gunpowder works at Faversham, and a manufactory was also
established near Paris. In July, 1847, a fearful explosion of gun-cotton
occurred at the Faversham works, which was believed to have been
caused by the spontaneous detonation of that substance. This induced
Messrs. Hall to discontinue the manufacture as too dangerous ; and they
even destroyed a large quantity of the product which they had in hand by
burying it in the ground. The making of gun-cotton was soon afterwards
discontinued also by the French, who did not find the substance to possess
all the qualities fitting it for military use. The Prussian Government also
began to make gun-cotton ; but the experiments were put a stop to by the
explosion of their factory. An eminent artillery officer in the Austrian
service, General von Lenk, undertook a thorough examination of the manu-
facture and properties of gun-cotton for military purposes. He introduced
several improvements into the processes of the manufacture ; and the
Austrian Government established works at Hirtenberg, with a view to .the
adoption of gun-cotton as a substitute for gunpowder in fire-arms. It has
some undoubted advantages over powder, for it neither heats the gun nor
fouls it. and it produces no smoke. Notwithstanding this the Austrians
have not abandoned the use of gunpowder in favour of gun-cotton.
Gun-cotton, as a military agent, has a strenuous advocate in Professor
Abel, who presides over the Chemical Department of the British War
Office. To this gentleman we are indebted for great improvements in the
manufacture of gun-cotton, and for a more complete investigation of its
EXPLOSIVES. 531
properties. Professor Abel's processes were put in practice at a manufac-
tory which the Government established at Waltham Abbey ; and Messrs.
Prentice also set up works at Stowmarket.
Some details of the mode in which the manufacture of gun-cotton was
carried on at Stowmarket may be of interest. The cotton was first tho-
roughly cleansed and carefully dried ; and these operations are of great
importance, for unless they are well performed, the product is liable to
explode spontaneously. The cotton was then weighed out in charges of
i lb., and each charge was completely immersed in a separate vessel, con-
taining a cold mixture of sulphuric and nitric acids. After a short immer-
sion the cotton was removed from the liquid, and with about ten times its
own weight of acids adhering to it, each charge was placed in a separate
jar, where it was allowed to remain for forty eight hours. The vessels were
kept cool during the whole period by being placed in a trough through
which cold water was flowing. On removal from the jars, the cotton was
freed from adhering acid by being placed in a centrifugal drying machine.
It was then drenched with a large quantity of cold water, and dried, washed
again in a stream of cold water for forty-eight hours, and the operations
of alternately washing for forty-eight hours and drying were repeated eight
times. The drying was effected by placing the material in cylinders of
wire-gauze, which were whirled round by a steam engine at the rate of 800
revolutions per minute, so that the water was expelled by centrifugal force.
The cotton was next reduced to a pulp by a process similar to that which
is employed in paper-making, and the moist pulp was rammed into me-
tallic cylinders by hydraulic pressure, in order that it might be brought into
forms suitable for use in blasting, &c. The pulp was put into these moulds
while wet, but the water was nearly all expelled by the compression. The
cylinders of gun-cotton thus obtained were then covered with paper-parch-
ment, and finally dried at a steam temperature, with many precautions.
The compression of the cotton pulp, by bringing a large quantity of the
material into a smaller bulk, causes a greater concentration of the explo-
sive energy, and this is a matter of great importance in blasting.
We may now consider what chemistry has to teach concerning the nature
of the action by which cotton-wool is converted into gun-cotton. Cotton
itself is nearly pure cellulose. The chemical composition of cellulose may
be represented most simply by the formula C ft H 10 O 5 . Nitric acid is a
powerful oxidizing agent, and is constantly used in chemistry to fix oxygen
in various substances ; but another kind of action exerted by nitric acid in
certain cases consists in the substitution of a portion of its atoms for hy-
drogen, by which the residue of the particle of nitric acid is converted
into water. The formula for nitric acid may be written HO NO 2 , and it
will be seen that by changing NO 2 for H, water, HOH, would be pro-
duced. This is precisely the kind of action which occurs when cellulose
is converted into nitro-cellulose. Two or three, or more, atoms of hydrogen
may be taken out of cellulose, and replaced by two or three, or more, groups
NO 2 , and the result will be a different kind of nitro-cellulose, according to
the number of atoms in the molecule replaced by NO 2 . Several varieties
of gun-cotton are known, these being doubtless the result of the differences
here alluded to. The action producing di-nitro-cellulose is represented by
this equation :
CH 10 5 + 2HN0 3 = C 6 H 8 (N0 2 ) 2 5 + 2 H 2 O.
Cellulose. Nitric acid. Di-nitro-cellulose. Water.
34 2
53 2 EXPLOSIVES.
The equation shows that water is produced by the reaction, and the sul-
phuric acid which is used in the preparation performs no further part than
to take up this water, which would otherwise go to dilute the rest of the
nitric acid. The union of sulDnuric acid and water is attended with great
heat, hence the necessity of cooling the vessels in making the gun-cotton.
Quite other products would be formed if the mixture became heated.
The action of nitric acid on glycerine is of the same kind as that on
cellulose. When glycerine is allowed to drop into a cooled mixture of nitric
acid and sulphuric acid, the eye can detect little or no difference between
the appearance of the liquid which collects in the bottom of the vessel and
the glycerine dropped in. The product of the action is, however, the ter-
rible nitto- glycerine, a heavy, oily-looking liquid, which explodes with fearful
violence. Even a single drop placed on a piece of paper, and struck on
an anvil, detonates violently and with a deafening report. The chemical
change which is effected in the glycerine (C 3 H 8 O 3 ), is the substitution of
three NO 2 groups for three of hydrogen, producing C 3 H 5 (NO 2 )3O 3 , or
tri-nitro-gfycerine. The general reader may perhaps marvel that the che-
mist should be able not only to count the number of atoms which go to
make up the particles of a compound body, but to say that they are arranged
so and so : that the atoms do not form an indiscriminate heap, but that they
are connected in an assignable manner. The reader is no doubt aware
that these compound particles are extremely small, and he may reasonably
wonder how science can pronounce upon the structure of things so small.
He may be more perplexed to learn that a calculation made by Sir W.
Thompson shows that the particles of water, for instance, cannot possibly
be more than the 250000000^ of an inch in diameter, and may be only i-2Oth
of that size. The truth is that the very existence of atoms and molecules
is an assumption. Like the undulatory ether, it is an hypothesis which is
adopted to simplify and connect our ideas, and not a demonstrated reality.
But the atomic hypothesis has so wide a scope that some philosophers hold
the existence of atoms and molecules as almost a known fact Be that as
it may, the chemist in assigning to a body a certain molecular formula
really does nothing but express the results of certain experiments he has
made upon it. With one re-agent it is decomposed in this manner, with
another in that. By certain treatment it yields an acid, a salt ; so much
carbonic acid, such a weight of water, is acted on or remains unaltered ;
gives a precipitate or refuses to do so. Such are the facts which the che-
mist conceives are co-ordinated and expressed by the formula he gives to
a substance. The best formula is that which accords with the greatest
number of the properties of the body which includes as many of the facts
as possible. It follows, therefore, that a formula which aims at expressing
more than the mere percentage composition of the body which, in the
language of the atom hypothesis, seeks to represent the mode in which the
atoms are grouped in the molecule, but which in reality represents only
reactions, is written according as the chemist considers this or that group
of reactions more important. These remarks might be illustrated by filling
this page with the different formulae (a score or more) which have been
proposed as representing the constitution (reactions ?} of one of the best-
known of organic compounds, namely, acetic acid.
Whether atoms really exist, and their arrangement in the particles of
bodies can be deduced from the phenomena, or not, the fact is undeniable
that these ideas have given chemists a wonderful grasp of the facts of their
science. The consistency and completeness of the explanation afforded
EXPLOSIVES. 533
by these theories are ever being extended by modifications which enable
them to embrace more and more facts. Some of the properties of the
substance we are now considering confirm in a remarkable manner the
theoretical views which are expressed in its constitutional formula. We
may first consider the nature of gunpowder, and by comparing it with nitro-
glycerine, endeavour to explain the greater power of the latter substance.
Gunpowder is a mixture of charcoal, sulphur, and nitre, the latter consti-
tuting three-fourths of its weight. Nitre supplies oxygen for the combus-
tion of the charcoal, which is thus converted into carbonic acid, and the
sulphur, which is added to increase the rapidity of the combustion, is also
oxidized. The products of the action are, however, numerous and compli-
cated, but the important result is the sudden generation of a quantity of
carbonic acid, nitrogen, carbonic oxide, hydrogen, and other gases, which
at the oxidizing temperature and pressure of the air would occupy a space
300 times greater than the powder from which they are set free ; but the
intense heat attending the chemical action dilates the gases, so that at
the moment of explosion they would occupy a space at least 1,500 times
greater than the gunpowder. The materials of which gunpowder is com-
posed are finely powdered, in order that each portion shall be in immediate
contact with others, which shall act upon it. Plainly, the more thorough
the incorporation of the materials that is, the more finely ground and
intimately mixed they are the more rapid will be the inflammation of the
powder.
Looking now at the crude formula of nitro-glycerine, C 3 H 5 N 3 O tt , the
reader will remark that the molecule contains more than sufficient oxygen
to form carbonic acid with all the carbon atoms, and water with all the
hydrogen atoms ; for the C 6 in two molecules of nitro-glycerine would take
only O 12 to form 6CO 2 ; and the H 10 , to be converted into 5H 2 O, would
only need O 5 ; thus there would be an excess of oxygen. Now, it may
occur to the reflective reader that in every molecule of nitro-glycerine the
carbon and hydrogen are already associated with as much oxygen as they
can take up : that they are, in fact, already burnt, and that no further union
is possible. But from chemical considerations it has been deduced that
in the nitro-glycerine molecule the oxygen atoms, except only three, which
are partially and imperfectly joined to carbon, are united to nitrogen atoms
only. The constitution of the molecule may be represented by arranging,
as below, the letters which stand for the atoms, and by joining them with
lines, which shall stand for the bonds by which the atoms are united.
O H H H O
II III II
N- O C C C O N
II III II
O H O H O
0-N-O
We see here that the hydrogen atoms are completely, and the carbon
atoms partially, detached from the oxygen atoms; and therefore these
atoms are in the condition of the separated carbon and oxygen atoms in
gunpowder. Only the pieces of matter which lie side by side in gunpowder
are in size to the molecules of nitro-glycerine as mountains to grains of
sand. The mixture of the materials is then so much more intimate in
nitro-glycerine, since atoms which can rush together are actually within
534
EXPLOSIVES.
the limits of the molecules ; and these molecules have such a degree of
minuteness, that 25 millions, at least, could be placed in a row within the
length of an inch. We know that the finer the grains and the more inti-
mate the mixture, the quicker will gunpowder inflame ; but here we have a
mixture far surpassing in minute subdivision anything we can imagine as
existing in gunpowder. Hence the combination in the case of nitro-glycerine
must be instantaneous, whereas that in gunpowder, quick though it be,
must still require a certain interval. If it take a thousandth of a second
for the gases to be completely liberated from a mass of gunpowder, and
only one-millionth of a second for a vast quantity of carbonic acid, nitro-
gen, and steam to be set free from nitro-glycerine, the destructive effect
will be much greater in the latter case. Again, the volume of the gases
liberated from nitro-glycerine in its detonation have at least 5,000 times
the bulk of the substance. We have entered into these chemical conside-
rations, at some risk of wearying the reader, with the desire of affording
him a clue to the singular properties of nitro-glycerine and gun-cotton,
which we are about to describe.
The nature of the chemical changes which maybe set up in an explosive
substance, and the rapidity with which these changes proceed throughout
a mass of the material, are greatly modified by the conditions under which
the action takes place. If a red-hot wire be applied to a small loose tuft
of gun-cotton, it goes off with a bright flash without leaving any smoke or
any other residue. Thus, when the substance is quite unconfined, no ex-
plosion occurs. If the cotton-wool be made into a thread, and laid along
the ground, it will burn at the rate of about 6 in. per second ; if it be twisted
into a yarn, the combustion will run along at the rate of 6 ft. per second ;
but if the yarn be enclosed in an Indian-rubber tube, the ignition proceeds
at the rate of 30 ft. in a second. If to a limited surface of gun-cotton, such
as one end of a length of gun-cotton yarn, a source of heat is applied the
temperature of which is high enough to set up a chemical change, but not
high enough to inflame the resulting gases (carbonic oxide, hydrogen, &c.)
the cotton burns comparatively slowly, rather smouldering than inflam-
ing. If, however, aflame be applied, the gun-cotton flashes off with great
rapidity, because the heat applied sets fire to the gaseous products of the
chemical action. But if the gun-cotton be confined so that the gases can-
not escape, the combustion becomes rapid however set up. The reason is
that if the gases escape into the air, they carry off so much of the heat pro-
duced by the smouldering gun-cotton, that the temperature does not rise
to the extent required to produce the flaming ignition, in which the pro-
ducts are completely oxidized. If a mass of gun-cotton be enclosed in a
capacious vessel from which the air has been removed, and the gun-cotton
be ignited by means of a wire made hot by electricity, the cotton will at
first only burn in the slow way without flame ; but as the gases accumulate
and exert a pressure which retards the abstraction of heat accompanying
their formation, the temperature will rise and attain the degree necessary
for the complete and rapid chemical changes involved in the flaming com-
bustion. Thus, the more resistance is offered to the escape of the gases,
the more rapid and perfect is the combustion and explosive force produced
by the ignition. Now, the explosion of gun-cotton has been found to be
too rapid when it is packed into the powder-chamber of a gun, for its ten-
dency is to burst the gun before the ball has been fairly started. Hence
a material like gunpowder, in which the combustion is more gradual, is
better suited for artillery. The ignition of gunpowder, though rapid, is not
EXPLOSIVES. 535
instantaneous, and therefore we can speak of it as more or less gradual.
Indeed, in even the most violent explosives, some time is doubtless re-
quired for the propagation of the action from particle to particle. This
extreme rapidity of combustion, and consequent rending power, which is
so objectionable in a gun-chamber, makes gun-cotton a most powerful
bursting charge for shells, and, when it is enclosed in strong receptacles,
for torpedoes also.
But by the researches of Nobel, Professor Abel, and others, it has been
discovered and this is, perhaps, the most remarkable discovery in con-
nection with explosives that gun-cotton, nitro-glycerine, and other explo-
sive bodies, are capable of producing explosions in a manner quite different
from that which attends their ignition by heat. The violence of this kind
of explosion is far greater than that due to ordinary ignition, for the action
takes place with far greater rapidity throughout the mass, and is, indeed,
practically instantaneous. It appears to be produced by the mere mechani-
cal agitation or vibrations which are communicated to the particles of the
substance. Turning back to the representation of the molecule of nitro-
glycerine on page 533, it will not be difficult to imagine that this may be
an unstable kind of structure ; that the atoms of oxygen are prevented from
rushing into union with those of hydrogen and carbon only by the inter-
position of the nitrogen ; and that an agitation of the structure might shake
all the atoms loose, and leave them free to re-combine according to their
strongest affinities. Nitro-glycerine is by no means so ready to itiflame as
is gun-cotton : it is said that the flame of a match may be safely extin-
guished by plunging it into the liquid ; and when a sufficient heat is applied
to a quantity of the liquid in the open air, it will burn quietly and without
explosion. Even when nitro-glycerine is confined, the application of heat
cannot always be made to produce its explosion ; or, at least, the circum-
stances under which it can do scare not accurately known, and the opera-
tion is difficult and uncertain. On the other hand, nitro-glycerine explodes
violently even when freely exposed to the air if there be exploded in con-
tact with it a confined charge of gunpowder, or a detonating compound
such as fulminating powder. Gun-cotton possesses the same property of
exploding by concussion, which appears indeed to be a general one belong-
ing to all explosive bodies. According to recent researches, even gunpowder
is capable of a detonative explosion. A mass of gunpowder confined with
a certain proportion of gun-cotton, which is itself set off by fulminate of
mercury, is said to exert an explosive force four t.mes greater than that
developed by the ignition of the gunpowder in the ordinary manner. It
has also been found that wet gun-cotton can be exploded by concussion,
and the force of the explosion is unimpaired even when the material is
saturated with water. This makes it possible to use gun-cotton with greater
safety, as it may be transported and handled in the wet condition without
risk, and it preserves its properties for an indefinite period without being
deteriorated by the water. Some experiments illustrating the extraordinary
force of the detonative explosions of gun-cotton and nitro-glycerine will
give the reader an idea of their power.
A palisade, constructed by sinking 4 ft. into the ground trunks of trees
1 8 in. in diameter, was completely destroyed in some experiments at Stow-
market by the explosion of only 15 Ibs. of gun-cotton. Huge logs were
sent bounding across the field to great distances, and some of the trees
were literally reduced to match-wood. The gun-cotton, be it observed, was
simply laid on the ground exposed to the air. The destructive powers of
53 6 EXPLOSIVES.
nitro-glycerine are even greater. A tin canister, containing only a few
ounces of nitro-glycerine, is placed, without being in any way confined, on
the top of a smooth boulder stone of several tons weight ; it is exploded
by a fuse containing fulminating powder, which is fired from a distance by
electricity. There is a report, and the stone is found in a thousand frag-
ments. The last experiment shows one of the advantages of nitro-glycerine
over gunpowder as a blasting material, beyond its far greater power, which
is about ten times that of gunpowder. A charge of gunpowder inserted in
a vertical hole tends to force out a conical mass, the apex of which is at
the space occupied by the charge. With nitro-glycerine, and also with
gun-cotton, which last has almost six times the force of gunpowder, a
powerful rending action is exerted below as well as above the charge.
Again, in blasting with gunpowder the charge must be confined, and the
hole is filled in above the charge with tightly rammed materials, forming
what is termed the tamping. But nitro-glycerine requires no tamping : a
small, thin metallic core containing the charge is simply placed in the
drill-hole, or the liquid itself is poured in, and a little water placed above
it. The effect of the explosion of nitro-glycerine in " striking down," when
apparently no resistance is offered, will seem very strange to the reader
who is oblivious of certain fundamental principles of mechanics. The
force of the explosion is due entirely to the sudden production of an enor-
mous volume of gas, which at the ordinary pressure would occupy several
thousand times the bulk of the material from which it is produced. This
gas, by the law of the equality of action and reaction, presses down upon
the stone with the same force that it exerts to raise the superincumbent
atmosphere. The pressure of the gas at the moment of its liberation is
enormous ; but the atmosphere cannot instantaneously yield to this, for
time is required to set the mass of air in motion, and the wave of com-
pression advances slowly compared with the rapidity of the explosion.
Hence the air acts, practically, like a mass of solid matter, against which
the gases press, and which yields less readily than the rock, so that the
blow which is struck takes visible effect on the latter. Now, with gun-
powder, the evolution of gas is less rapid, the atmosphere has time to yield,
and the reaction has not the same violence. The rapidity of the evolution
of gas from the exploding nitro-glycerine is so great, that the gases, though
apparently unconfmed, are not so in reality ; for the atmosphere acts as a
real and very efficient tamping.
When nitro-glycerine first came into use for blasting purposes, it was
used in the liquid form under the name of " blasting oil;" but the dangers
attending the handling of the substance in this state are so great, that it
is now usual to mix the liquid with some powdered substance which is itself
without action, and merely serves as a vehicle for containing the nitro-
glycerine. To mixtures of this kind the names " dynamite" " dualine?
" lithojracteur? &c., have been given.
It is now hardly necessary to point out that the discovery of these new
explosives has largely extended our power over the rocks, enabling works
to be executed which would have been considered impracticable with less
powerful agents. It is true that the most fearful disasters have been acci-
dentally produced by the new explosives ; but such occasional devastation
is the price exacted for the possession of powerful agents. And just as in
other cases steam, for example where great forces are dealt with, so
these new powers must be managed with unceasing care, and placed in
the ha*nds of only skilful and intelligent men.
FIG. 340. View on the Tyne.
MINERAL COMBUSTIBLES.
/CERTAIN mineral combustibles may fairly claim attention in a work
^-^ treating of the discoveries of the nineteenth century, not because these
bodies have been known and used only in recent times, but for other rea-
sons. The true nature of coal that most important of all combustibles
its relation to the past history of the earth, and to the present and future
interests of mankind ; the work it will do ; the extent of the supply still
existing in the bowels of the earth ; the innumerable chemical products
which it yields are subjects on which the knowledge gained during the
present century forms a body of discovery of the most interesting and
important kind. Another substance we have to mention, though not a
modern discovery, has lately been found in far greater abundance, and is
now so largely used for various purposes, that it has become an important
article of commerce.
COAL.
TV/TOST persons know, or at least have been told, that coal is fossil
1Y1 vegetable matter, the long-buried remains of ancient forests. But
537
538
MINERAL COMBUSTIBLES.
probably many receive the statement, not perhaps with incredulity, but
with a certain vague notion that it is, after all, merely a daring surmise.
And, indaed, nothing is at first sight more unlike stems, or leaves, or roots
of plants than a lump of coal. Then everybody knows that coal is found
thousands of feet beneath the surface of the earth, whereas plants can
grow only in the light of the sun. One begins to understand the matter
only when the teachings of geology have shown him that, so far from the
crust of the earth being, as he is apt to suppose, fixed and unchangeable,
it is in a state of constant fluctuation. Changes in the levels of the ground
are always going on : in one place it is rising, in another sinking ; here a
FlG. 341. Fossil Trees in a Railway Cutting.
tract of land is emerging from the ocean, there a continent is subsiding
beneath the water. The extreme slowness with which these changes pro-
ceed causes them to escape all ordinary observation. The case may be
compared to the hour-hand on the dial, which a casual spectator might
pronounce quite stationary, since the observation of a few seconds fails to
detect its movement. As the whole period comprehended in human annals
counts but as a second of geological time, it cannot be wondered at that
it required a vast accumulation of facts, and much careful and patient
deduction from them, before a conclusion was reached so apparently con-
tradictory of experience. It is, indeed, startling to learn that u the sure
and firm-set earth " is in a state of flow and change. Even the " everlast-
ing hills" give evidence that their materials were collected at the bottom
MINERAL COMBUSTIBLES.
539
of the sea, and we know that the water which runs down their sides is
slowly but surely carrying them back particle by particle. Of the magni-
tude of the changes which the surface of the earth has undergone m times
past, and which are still imperceptibly but constantly proceeding, the ordi-
nary experience of mankind can of itself give no example. But such changes
have sufficed to entomb a vast quantity of relics of the innumerable forms
of vegetation which flourished and waved their branches in the sun, ages
upon ages before the advent of man.
It may be thought impossible that vegetable matter should have so
changed as to become a dense, black, glistening, brittle mass, showing no
obvious forms of leaves or texture of wood. But no one who has seen
how a quantity of damp hay closely pressed together will, after a time,
become heated and change in colour to black, can have any difficulty in
comprehending how chemical and mechanical actions may completely
alter the aspect of vegetable
matter. We have, however,
the most direct evidence of
the vegetable origin of coal in
the numberless unquestion-
able forms of trees and plants
met with in all coal strata.
Sometimes the trunks of the
trees fossilized into stony mat-
ter are found upright in the
very situation in which they
grew. Thus in Fig. 341 is re-
presented the appearance ex-
hibited by the trunks and roots
of some fossil trees, which
were exposed to view in the
formation of a railway cut-
ting between Manchester and
Bolton. In every coal-field
also beautiful impressions of
the stems and leaves of plants
are met with one common
form of which is shown in Fig.
342. Most of the plants so
found belong to the flowerless
division of the vegetable
kingdom. Some are closely
allied to the ferns of the pre-
sent day to the common " mare's-tail " (Eqmsetinri}, to the club-moss, and
to other well-known plants. The firs and pines of the coal age are scarcely
distinguishable from existing species. If a fragment of ordinary coal be
ground to a very thin slice so thin as to be transparent and placed
under the microscope, it will show a number of minute rounded bodies,
which are, there is good reason to believe, nothing else than the spores or
seeds of plants, closely resembling the existing club-mosses. The spores
of the* club-moss (Lycopodiitm) are so full of resinous matter, that they
are used for making fireworks and the flashes of lightning at theatres. It
is, therefore, extremely probable that the bitumen of coal is due to the
resin of similar spores, altered by the effects of subterranean heat. The
FlG. 342. Impression of Leaf found in
Coal Measures (Pecopteris).
540
MINERAL COMBUSTIBLES.
FIG. 343. Possible Aspect of the Forests of the Coal Age.
immense abundance of these little spores in the coal is a proof that they
accumulated in the ancient forests as the mosses grew, and therefore the
matter of coal was not accumulated under water or washed down into the
sea ; for these little spores are extremely light, and they cannot be wetted
by water, and therefore they would have floated on the surface, and would
not have been found so diffused throughout the coal. Fig. 343 is a picture
of the possible aspect of the ancient forests of the coal age. In the humid
atmosphere which probably prevailed at that period, the large tree-ferns
and gigantic club-mosses, which are conspicuous in the picture, must have
flourished luxuriantly.
The immense importance of coal for domestic purposes will be obvious
MINERAL COMBUSTIBLES.
54i
from the fact that it is estimated that in the United Kingdom alone no less
than 30,000,000 tons are annually consumed in house fires. Another great
use of coal is in the smelting, puddling, and working of iron, and this pro-
bably consumes as much as our domestic fireplaces. Then there is the
vast consumption by steam engines, by locomotives, and by steamboats*
Another purpose for which coal is largely used is the making of illumina-
ting gas ; and to the foregoing must also be added the quantity which goes
to feed the furnaces necessary in so many of the arts such as in the
manufacturing of glass, porcelain, salt, chemicals, &c. The quantity of
coal raised in Great Britain was not accurately known until 1854, when it
was ordered that a register should be kept, and an annual return made.
The following figures in round numbers represent the returns which have
been published since that date :
Year. Coal raised, in Tons.
1854 64,661,000
1855 64,453,000
1856 66,645,000
1857 65,395,000
1858 65,008,000
1859 71,979,000
1860 83,208,000
1861 85,635,000
1862 83,638,000
1863 88,292,000
Year. Coals raised, in Tons.
1864 92,787,000
1865 98,150,000
1866 101,630,000
1867 104,500,000
1868 103,141,000
1869 107,427,000
1870 110,289,000
1871 117,352,000
1872 123,497,000
1873 127,017,000
The first return showed our annual produce to be 64,661,000 tons. The
amount did not greatly vary until 1859, when there was an increased
production of nearly seven millions of tons ; in 1860 a further increase of
eleven millions of tons more. Since then the quantity annually raised has
been increasing. Comparing the quantity which has been raised in any
year after 1 863 with that raised ten years before, we see that the increase
in ten years is nearly half as much again ; or, that at the present rate of
increase the amount annually raised doubles itself at least every twenty
years. Now, the question arises, How long can this go on ? However
great may be the store of coal, it must sooner or later come to an end. Is
it possible to calculate how long our coals will last ? and what are the
results of such calculations ? These calculations have been made ; but
there are great discrepancies in the results, for the estimates of the amount
of available coal still remaining vary greatly, and different views are held
regarding the rate of consumption in ihe future. A very liberal estimate,
by an excellent authority, of the quantity of coal remaining under British
soil, makes it 147,000 millions of tons. With a consumption stationary at
the present rate, this will last 1,200 years ; with an increase of consumption
of 3,000,000 tons a year, 276 years ; but if the consumption continues to
increase in the same geometrical ratio it has hitherto followed, the supply
will scarcely last 100 years. It cannot be conceived, however, that this
last will be the real case, for the increasing depth to which it will be neces-
sary to go will soon cause a great increase in the cost, and thus effectually
check the consumption. Great Britain will, however, be compelled to
retire from the coal trade altogether, by the cheaper supplies which other
countries will yield, long before the absolute exhaustion of her own coal-
fields. It is calculated that the coal-fields of North America contain thirteen
times as much as those of all Europe put together. Coal is also found
542
MINERAL COMBUSTIBLES.
abundantly in India, China, Borneo, Eastern Australia, and South Africa;
and it is believed that these stores will supply the world for many thousand
years.
Seeing, then, that our supply of coal has a limit, and that at the present
increasing rate of consumption, the chief source of the wealth of Great
Britain must necessarily be exhausted in a few more centuries, it behoves
us to turn our mineral treasures to the best account, and to adopt every
possible means of obtaining from our coal its whole available heat and
force. The amount of avoidable waste of which we are guilty in the con-
FIG. 344. The Fireside.
sumption of coal is enormous. This is especially the case in its domestic
use, where probably nine teen- twentieths of the heat produced is absolutely
thrown away sent off from the earth to warm the stars. In England
people look upon the wide open fireplace as the image and type of home
comfort. No doubt there are, from long use and habit, many pleasing as-
sociations which cluster round the domestic hearth ; but we, to whom it is
given to " look before and after," must think what it takes to feed that wide-
throated chimney. All but a very small fraction of the heat thus escapes,
and is lost to man and the world for ever ; and surely we shall deserve the
curses of our descendants if we continue recklessly to throw away a treasure
which, unlike the oil in the widow's cruse, is never renewed for there is
no contemporaneous formation of coal. Thanks to the enhanced price of
coal during the last few years, some attention has been directed to con-
MINERAL COMBUSTIBLES. 543
trivances for the economical consumption of coal in its domestic, as well
as in its manufacturing, applications.
A time, however, will sooner or later come, when the whole available
coal shall have been consumed. What will then be the fuel of the engines,
and steamboats, and locomotives of the future ? The reader may think
that then it will only be necessary to burn wood. But wood is already
being consumed from the face of the earth much more rapidly than it is
produced. How, then, can it be available when coal fails? The truth is,
we are now consuming not merely the wood which the sun-rays are build-
ing up in our own time, but in hewing down the forests we are using the
sun-work of a century, while in coal we have the forests of untold ages at
our disposal the accumulated combustible capital stored up during an
immense period of the earth's existence. Upon this stored-up capital we
are now living, our current receipts of sun-force being wholly inadequate
to meet our expenditure. The coal is the sun-force of former ages ; and it
is from this we are now deriving the energy which performs most of our
work. George Stephenson long ago declared that his loc omotives were
driven by sunshine by the sunshine of former ages bottled up in the coal.
And he was right. The mechanical energy of our steam engines, and the
chemical energy of our blast furnaces, are derived from the combustion of
vegetable matter, in which the heat and light of the sun our present sun
or that of the coal ages are in someway stored up. The burning of wood
or coal is, chemically, the reverse action to that performed by the sun-
light : by the former carbon and oxygen are united, by the latter they are
separated.
We foresee, then, a future period however distant may be that future
in which the world's capital shall have been exhausted, and the energies
which are now employed in doing the world's work will no longer be avail-
able. But the reader will perhaps think that by improvements in the steam
engine, and in other ways, means will be found of getting more and more
work out of coal. It is true that we obtain from coal only a fraction of its
available energy ; but the whole work which could, by any possible pro-
cess, be done by the combustion of coal is definite and limited, although its
amount is large. A pound of coal burnt in one minute sets free an amount
of energy which would, if it could all be made available, do as much as
300 horses working in the same time. But, again, the reader may think,
even if at some distant future the supplies of fuel for the steam engines of
our remote posterity should fail, that before that time some other form of
force than steam or heat engines will have been discovered some applica-
tion of elect' icity, for example. Now, it will appear, from principles which
will be discussed in a subsequent article, that not only is there no proba-
bility of such a discovery, but that now, when the relations of the whole
available energies of the globe have been traced and defined, Science can
find no ground for admitting such a possibility under the present condition
of the universe.
PETROLEUM.
V\7HEN coal is heated in closed vessels, there are given off, as we shall
* * presently see, a number of gaseous and volatile products many
being compounds of carbon and hydrogen which condense to liquids or
544
MINERAL COMBUSTIBLES.
solids at ordinary temperatures. Carbon is by far the largest constituent
of coal, which commonly contains only about 10 per cent, of other sub-
stances, although the proportions vary very widely. Another important
constituent of coal is its hydrogen, and the value of coal as a source of
heat depends almost entirely upon the carbon and hydrogen it contains.
Carbon is one of the most remarkable of all the elements of the globe for
its power of entering into an enormous number of compounds. Thus, for
example, the compounds of carbon with only hydrogen are innumerable ;
but they are all definite, and their composition is expressible by the admir-
able system of chemical symbols, of which the reader has now, it is hoped,
some definite notion. Perhaps these hydro-carbons are among the best
evidences which could be adduced that modern science has obtained a
grasp of certain conceptions which have a real correspondence with the
actual facts of nature, even as regards the intimate constitution of matter.
This is not the place to enter into a complete exposition of this subject.
We may, however, irvite the reader's attention to a few simple facts. A
very large number of compounds of carbon and hydrogen are known. If
the percentage compositions of these be compared together, it is only the
eye of a most expert arithmetician which can detect any relation between
the proportions of the constituents in the various compounds. The che-
mist, however, by associating such of these compounds as resemble each
other in their general properties, finds that they can be arranged in series,
in which the composition is accurately expressed by multiples of the pro-
portions: C=i2, H i. And not only so, the different series themselves
form a series of series, having a simple relation to each other. Thus, con-
fining ourselves to some of the known hydro-carbons, we have the following :
A
B
C
D
E
F
C H 4
C H 2
C 2 H 6
C 2 H 4
C 2 H 2
C 3 H 8
C 3 H 6
cX
C 3 H 2
4^10
C 4 H 8
cX
cX
C 4 H 2
^5^12
C 5 H 10
C 5 H 8
C 5 H 6
C 5 H 4
C 5 H 2
C 6 H 14
C 6 H 12
C 6 H 10
C 6 H 8
C 6 H 6
ClHj
&c.
&c.
&c.
&c.
&c.
&c.
C H 2 -j-2
CH 2
CH 2 _ 2
C H 2 4
C H 2 6
C H 2 s
This table might be indefinitely extended, but enough is given to enable
the intelligent reader to discover the laws connecting these formulas. The
series headed B, it will be observed, have all the same percentage compo-
sition. Why, then, one formula rather than another ? The answer to this
question is the statement of a theoretical law upon which the whole science
of modern chemistry is based; for it has the same relation to that science
as gravitation has to astronomy. It is a matter of fact that all gases, what-
ever their chemical nature, expand alike with the same application of heat,
and all obey the same law, which connects volumes and pressures. These
are very remarkable uniformities, for gases in this respect exhibit the most
decided contrast to liquids and solids. The volume of each solid and of
each liquid has its own special relations to temperature and pressure : here
MINERAL COMBUSTIBLES. 545
there is endless diversity. The volumes of all gases have one and the same
relation to temperature and pressure : here there is absolute uniformity.
As an explanation of these and other facts relating to gases, Amedeo
Avogadro, in 1811, put forward this hypothesis Equal volumes of all
gases, under like circumstances of temperature and pressure, contain the
same number of molecules. This hypothesis was revived by Ampere a few
years later, and sometimes is called his. A necessary consequence of this
law is that the weights of the molecules of gases are proportional to their
densities or specific gravities. Hence when the percentage composition of
a hydro-carbon has been determined, by burning or oxidizing it in such a
manner as to obtain and weigh the products, carbonic acid and water, the
next thing the chemist does is to obtain the weight of a volume of the gas.
The number of times this exceeds the weight of hydrogen gas, under the
same conditions, expresses how many times the molecule is heavier than
the hydrogen molecule. Now, the chemist's unit of weight in these inquiries
is the weight of a single atom of hydrogen ; and, as there are grounds for
believing that the molecule of hydrogen consists of two atoms of that sub-
stance, its weight = 2. Now, if the molecule of marsh gas, the first hydro-
carbon in the above list, has the composition assigned, it will be 12+4=16
times heavier than the atom of hydrogen, and *-=8 times heavier than
the molecule of hydrogen. Hence, if Avogadro's law be correct, marsh gas
should be just eight times heavier than hydrogen gas ; which is really the fact.
The formula expressing the composition of the molecule of a hydro-carbon,
or of any chemical compound whatever, is always so fixed that the same
relations may hold ; and almost the first thing a chemist does in examining
a new body is to endeavour to obtain it in the state of gas.
The first four members of the series headed A are gases at ordinary
temperatures, the fifth is a gas at temperatures above the freezing-point,
and a liquid at lower temperatures ; the next following members are liquids
which boil (that is, are converted into gases) at temperatures rising with
each additional carbon atom about 20 F. The specific gravities and boiling-
points of these liquids augment as we pass from one hydro-carbon to the
next, and the lower members of the series are solids, fusing at tempera-
tures higher and higher as the number of carbon atoms is greater. Similar
gradations of properties are exhibited by the other series of hydro-carbons.
Petroleum or rock-oil is the name given to liquid hydro-carbons found in
nature, and consisting chiefly of compounds belonging to the series marked
A in the above list. Some varieties of petroleum hold in solution other
hydro-carbons, and in some cases paraffin is extracted from the oils by
exposing the liquid to cold, when the solid crystallizes out. Paraffin is a
solid belonging to the B series, and it is for the most part obtained by
heating certain minerals.
Deposits of liquid hydro-carbons, perhaps formed by a kind of natural
subterranean distillation from coal or other fossil organic matter, exist in
various localities. These deposits have long been known and utilized at
Rangoon, in Burmah, and on the shores of the Caspian Sea. At Rangoon
the mineral oil is obtained by sinking wells about 60 ft. deep in a kind of
clay soil, which is saturated with it. The oily clay rests upon a bed of slate
also containing oil, and underneath this is coal. It may be supposed that
subterranean heat, acting upon the coal, has distilled off the petroleum,
which has condensed in the upper strata. This petroleum, when distilled
in a current of steam, leaves about 4 per cent of residue, and the volatile
portion contains about one-tenth of its weight of a substance (paraffin)
35
54 6 MINERAL COMBUSTIBLES.
which is solid at ordinary temperatures. After an agitation with oil of
vitriol, and another distillation, rock oil or naphtha is obtained, which,
however, is still a mixture of several distinct chemical compounds. Mineral
oils have also been found in China, Japan, Hindostan, Persia, the West
India Islands, France, Italy, Bavaria, and England. In one of the Ionian
Islands there are oil-springs which have flowed, it is said, over 2,000 years.
But it is the recently discovered and extremely copious springs and wells
in Pennsylvania and Canada which have given a vastly extended import-
ance to the trade in mineral oiL Rock oil is now used in enormous quan-
tities as the cheapest illuminating oil, and that which furnishes the most
intense light. Its consumption as a lubricating oil for machines has also
been very large. Mineral oil was occasionally found at various places in
the United States, and sometimes used by the inhabitants of the locality
before the recent discoveries; but it was not until August, 1859, that it was
met with in large quantities. About this time a boring which was made at
Oil Creek, Pennsylvania, reached an abundant source, for 1,000 gallons a
day were drawn from it for many weeks. The news of the discovery of this
copious oil-spring spread rapidly: thousands of persons flocked to the
neighbourhood in hopes of easily making a fortune by " striking oil." Be-
fore the end of 1 860 more than a thousand wells had been bored, and some
of these had yielded largely. The regions of North America in which
petroleum has been found cover a large part of the States, and comprise
Pennsylvania, New York, Ohio, Michigan, Kentucky, Tennessee, Kansas,
Illinois, Texas, and California. In the vicinity of Oil Creek the bore-holes
are usually about 3 in. or 4 in. in diameter, and are often 500 ft. deep, and
even 800 ft. is not uncommon. To make a bore-hole 900 ft. deep, and pro-
cure all the requisites steam engines, barrels, &c., for pumping the oil
costs about $5,000. In 1869 many of these wells still yielded regularly
300 barrels a day, but the supply has not continued with the same abun-
dance. One of the luckiest wells flowed at its first opening at the rate
of about 25,000 barrels a day. The apparatus used for working the oil-
wells is very simple a rude derrick, a small steam engine, a pump, and
some barrels and tubs being all that is necessary. Fig. 345 will give the
reader an idea of the scene presented by a cluster of oil-wells in the Oil
Creek region. Oil Creek received its name before the petroleum trade was
established, from the oil found floating on the surface of the water. It is on
the Alleghany River, about 150 miles above Pittsburg, and here at its mouth
is situated Oil City. There is a wharf in Pittsburg for the oil traffic, and
the barrels are brought down the river in flats, or the oil is poured into
very large flat boxes, divided into compartments, which are then closed,
ancl the boxes floated down in groups of twenty or more. The refining
process consists in placing the crude oil into a large iron retort, connected
with a condenser formed of a coil of iron pipes, surrounded by cold water.
Heat is applied, and the lighter hydro-carbons (naphtha) come over first.
After the naphtha, the oils which are used for illuminating purposes distil
off. A current of steam is then forced into the retort, and this brings over
the heavy oils which are used for greasing machinery. A black tarry oil
yet remains ; and, finally, after the separation of this, a quantity of coke.
The products are subjected to certain processes of purification, which need
not here be described. The magnitude of the American oil trade may be
inferred from the fact that in the second year of its existence, from January
to June, 1862, more than 4,500,000 gallons were exported from four sea-
ports. This can hardly be wondered at, considering the extremely low
MINERAL COMBUSTIBLES.
547
FIG. 345. View on Hyde and Egbert's Farm, Oil Creek.
price at which this excellent illuminating and lubricating agent can be pro-
duced. Refined petroleum can be bought at Pittsburg for 16 cents, per
gallon. It is believed by some that the supplies of petroleum which exist
in various localities are so abundant that they will furnish illuminating oils
to the whole world for centuries.
PARAFFIN.
T N the course of some researches on the substances contained in the tar,
* which is obtained by heating wood in close vessels, Reichenbach found
a white translucent substance, to which he gave the above name, because
it was not acted upon by any of the ordinary chemical reagents, such as
sulphuric acid, nitric acid, &c. This substance, which is composed of
carbon and hydrogen only, is not unlike spermaceti ; it is colourless, trans-
lucent, and without smell or taste. But when slightly warmed, it becomes
very plastic, and may then be moulded with the greatest ease and in this
respect it differs from spermaceti. Paraffin melts at from 88 to 150 F.,
to a colourless liquid, which is so fluid that it may be filtered through paper
like water, and at a higher temperature it can be distilled unchanged.
Paraffin does not dissolve in water, and is but slightly soluble in alcohol.
In ether, naphtha, turpentine, benzol, and sulphide of carbon, it dissolves
very readily. When heated with sulphur, it is decomposed : the sulphur
seizes upon its hydrogen, sulphuretted hydrogen is given off, and the
carbon is separated ; and this action has been proposed as a ready means
of obtaining pure sulphuretted hydrogen for laboratory use. It is probable
35 2
54 8 MINERAL COMBUSTIBLES.
that paraffin is a mixture of various hydro-carbons, having a composi-
tion expressible by the formula, C H 2 ; for different specimens fuse at
different temperatures, according as the paraffin has been obtained from
one or the other source.
In the year 1847, Dr. Lyon Playfair directed the attention of Mr. James
Young, then of Manchester, to a dense petroleum which issued from the
crevices of the coal in a Derbyshire mine It was soon found that this
substance yielded a distillation a pale yellow oil which, on cooling, de-
posited solid paraffin. Mr. Young, recognizing the importance of this dis-
covery, had an establishment at once erected on the spot, and the work of
extracting paraffin was carried on until the supply of the petroleum had
become nearly exhausted. Forced to seek for other sources of paraffin,
Mr. Young was fortunate enough, after many trials, to discover that a
species of bituminous coal, which occurs at Boghead, near Bathgate, in
the county of Linlithgow, yielded by distillation annually large quantities
of paraffin. In 1850 he procured a patent for " treating bituminous coals
to obtain paraffin, and oil containing paraffin, therefrom." This method
consisted in distilling the coal in an iron retort, gradually heated up to low
redness, and kept at that temperature until the volatile products ceased
to come off. Under this patent, Mr. Young developed the manufacture of
paraffin into a new and important branch of industry. The oil which first
comes over in the distillation of the Boghead mineral is largely used for
illuminating purposes under a variety of names besides that of paraffin oil,
which term is, we believe, chiefly applied to a less volatile portion, exten-
sively used for lubricating machinery, and consisting ofliquid hydro-carbons
of the same percentage composition as solid paraffin, which substance it
also holds in solution. Mr. Young's process consisted in placing the mineral
in a retort encased in brickwork an arrangement which caused the tem-
perature of the retort to be more uniform than if the heat of the furnace
had been applied to it directly. The retorts were placed vertically, and they
were fed with the mineral by a hopper at the top. The products of the
distillation passed through a worm tube surrounded by cold water into a
cooled receiver. The result of the first distillation was a crude oily matter,
differing from tar in being lighter than water, and in not drying-up when
exposed to the air. This crude oil was then several times alternately treated
with sulphuric acid and caustic potash, and distilled ; and when about two-
thirds of the oil had been separated from the rest, as an oil for burning
and lubricating purposes, the residue yielded paraffin, or " paraffin wax,"
as it is sometimes called. It is estimated that in Scotland no less than
800,000 tons of shale are annually distilled for mineral hydro-carbons, with
a consumption of 500,000 tons of fuel. It is believed that about 25,000,000
gallons of crude oil are thus obtained, and from this 350,000 gallons of
illuminating oil, 10,000 tons of lubricating oil, and 5,800 tons of solid
paraffin are produced. Among the products exhibited in the International
Exhibition of 1 862, was a block of beautifully translucent paraffin, of nearly
half a ton weight.
Paraffin is also obtained on the continent by distilling a variety of coal
termed lignite. The tar which comes over is distilled, until nothing but
coke remains. The condensed products are then treated with caustic soda,
, in order to remove carbolic acid and other substances. After washing with
water, the oils are treated with sulphuric acid, in order to remove basic
substances. The oil is again washed, and is then rectified by another dis-
tillation. The products which successively come over are, if necessary,
MINERAL COMBUSTIBLES. 549
separated by being collected in different vessels ; but sometimes they are
mixed together, and sent into the market as illuminating oils under various
names, such as " photogen," " solar oil," &c. Oils having a specific gravity
about 0-9 are collected apart, and are placed in tanks in a very cool place.
In the course of a few weeks the solid paraffin, which is dissolved in the
other hydro-carbons, crystallizes out. The liquid oils are drawn off, and the
crude paraffin, which is of a dark colour, is freed from adhering oil by a
centrifugal machine, and afterwards by pressure applied by hydraulic
power. It then undergoes several other processes of purification before it
is obtained as a colourless translucent solid.
Several thousand tons of paraffin are annually consumed for making
candles, which is the most important application of the material. The
variation in the fusing-points of different specimens is doubtless due to
admixtures in greater or less proportion of other more easily fusible hydro-
carbons. It was on account of the imperfect separation of these that the
candles first made from paraffin were so liable to soften and bend, and felt
greasy to the touch. Paraffin for candle-making is sometimes mixed with
a certain proportion of other substances, such as palmitic acid, &c. Among
the patented applications of paraffin are the lining of beer-barrels, and the
preserving of fruits, jams, and meat. Some kinds of paraffin are also used
in the manufacture of matches.
Liebig once expressed a wish that coal-gas might be obtained in a solid
form : " It would certainly be esteemed one of the greatest discoveries of
the age if any one could succeed in condensing coal-gas into a white, dry,
odourless substance, portable and capable of being placed in a candlestick
or burned in a lamp." Now, it is curious that paraffin has nearly the same
composition as good coal-gas : it burns with a bright and smokeless flame,
and beautiful candles are formed of it, which burn like those made of the
finest wax. When the fused paraffin first assumes the solid form, it is trans-
parent like glass ; and if it could be retained in that condition, we might
have the pleasing novelty of transparent candles. But the particles seek
to arrange themselves in crystalline forms, and the substance soon takes
on its white semi-opaque appearance.
The great richness of the Boghead mineral in paraffin, which appears
to exist in it ready formed, prevented for many years any successful com-
petition by the working of other sources of supply. But paraffin is an
abundant constituent of Rangoon petroleum, and considerable quantities
may be obtained by distilling peat, and other fossil substances. All petro-
leums and paraffins are, in fact, mixtures of a number of hydro-carbons,
whicli in many cases cannot be entirely separated from each other. The
accidents which have from time to time occurred with some of these com-
bustibles, and have caused legislative enactments with regard to them, are
due to the imperfect removal by distillation of the more volatile bodies,
which rise in vapour at ordinary temperatures. Explosions of the hydro-
carbons can occur only under the same circumstances as with coal-gas ;
that is to say, the application of a flame to a mixture of the vapour with
atmospheric air.
FIG. 346. View of the City of London Gas-works.
COAL-GAS.
WHEN coal is burning in a common fire, we may see jets of smoky
gas issuing from the pieces of coal before they become red hot. This
vapour, coming in contact with flame in another part of the fire, may often
be observed to ignite, thus supplying an instance of gas-lighting in its most
elementary form. In the ordinary fire the air has free access, and the
inflammable gases and vapours continue to burn with flames more or less
bright, and when these have ceased the cabonaceous portion continues
afterward to glow until nearly the whole has been consumed, except the
solid residue which we call the ashes. These ashes in general contain a
portion of unconsumed carbon, mixed with what is chemically the ash,
namely, certain incombustible salts, constituting the white part of the
ashes. If, however, we heat the coal in a vessel which prevents access of
air, and allows the gases to escape, the coal is decomposed much in the
same way as when it is burnt in the open fire ; but the products formed are
no longer burnt, the supply of oxygen being cut off. Every one knows the
familiar experiment of filling the bowl of a common clay tobacco-pipe with
powdered coal, then covering it with a dab of clay, and placing it in a fire.
The gas which soon comes from the stem of the pipe does not take fire
unless a light be applied, when it may be seen to burn with a bright flame,
and after the flow of gas has ceased, nearly the whole of the carbon of the
coal will be found unconsumed in the bowl of the pipe. This simple expe-
riment illustrates perfectly the first step in the manufacture of coal-gas,
namely, the process of heating coal to redness in closed vessels, by which
operation the substances originally contained in coal are destroyed, and
their elements enter into new combinations.
550
COAL-GAS. 551
These elements are few in number ; for, except the very small portion
which remains as incombustible white ash, coal is constituted of carbon,
hydrogen, oxygen, nitrogen, and a little sulphur. All the varied and inte-
resting products obtained by the destructive distillation of coal are com-
binations of two or more of these four or five elements. Illuminating gas
is far from being the only product when coal is heated without access of
air ; for of the numerous substances volatized at the red heat of the gas-
retort a great number are not only incapable of affording light, but liable
to generate noxious compounds when burnt Besides this there are nume-
rous bodies which, though leaving the retort in the gaseous form, imme-
diately assume the liquid or solid state at ordinary temperatures. All such
substances must be separated before permanent gases are obtained fit for
illuminating purposes and capable of being carried through pipes to dis-
tant places. Thus an important part of the apparatus for gas manufacture
consists in arrangements for separating the condensible bodies, and for
removing useless or injurious gases from the remainder.
FIG. 347. Section of Gas-making Apparatus.
The products resulting from the destructive distillation of the coal may,
therefore, be classified as a> solids left behind in the retort ; b, solids and
liquids condensed by cooling the vapours which issue from the retort ; c,
coal-gas a mixture of gases from which certain useless and noxious con-
stituents must be removed. Fig. 347 is intended to give a diagrammatic
view of the apparatus employed in the generation, purification, and storage
of gas, the various parts being shown in section. A is the furnace contain-
ing several retorts, of which B is one. From each retort a tube, d, rises
vertically, and curving downward like an inverted Uj it enters a long hori-
zontal cylinder, yj half filled with water, beneath the surface of which the
open end of the recurved tube dips. The cylinder containing water passes
horizontally along the whole range of furnaces in the gas-works, and is
known as the hydraulic main. It is here, then, the tar and the moisture
first condense, and the pipe is always kept half full of these liquids, so that
the ends of the pipes, d, from the retorts, dipping beneath its surface, form
552
COAL-GAS.
traps or water-valves, which allow any retort to be opened without per-
mitting the gas to escape. As the tar accumulates in the hydraulic main,
it flows over through a pipe, g, leading downwards into the tar-well, H.
The gases take the same course ; but while the tar flows down the vertical
tube, R, ths gases pass on through/ into the condensers or refrigerators.
Gas cannot escape from the open end of the tube, for it is always closed by
the liquids tar and ammoniacal liquor which accumulate and flow over
the top of the open inner vessel into the cistern, s, from which they are
drawn off from time to time by the stop-cock, i. Although when the gas
has arrived at this cistern much of its tar and ammoniacal vapours have
been condensed, a portion is still retained by reason of the high tempera-
ture of the gas ; and this has to be removed before it is permitted to enter
the purifier. This is the object of passing the gas through the series of
pipes, //, forming the condenser. These are kept cool by the large surface
they expose to the air, and, when necessary, cold water from the cistern,
K, may be made to flow over them. The tar and other liquids condense
in the iron chest, T, which is so divided by partitions as to compel the gas
to pass through the whole series of tubes ; and as the liquid accumulates,
it also overflows into the tar-well. The cooled gas then enters the purifier,
L L, in which are layers of slaked lime placed on a number of shelves. By
contact with the extensive surface of slaked lime the gas has its sulphur-
etted hydrogen, carbonic acid, and some other impurities, removed ; and
it then, through the tube , enters the gasholder, in which it is stored up
for use.
Hydrated oxide of iron is now much used for purifying coal-gas. The
oxide is mixed with sawdust, and placed in layers 10 in. thick. Sulphide
of iron and water is formed ; and when the mixture has ceased to absorb
any more, it is removed and exposed to a current of air ; the hydrated
oxide is thus reproduced and sulphur set free. The process may be re-
peated many times in succession, until the absorbent power is impaired by
the accumulation of sulphur.
The gasholder or " gasometer," as it is often improperly named is an
immense cylindrical bell, made of wrought iron plates, and inverted in a tank
of water, in which it rises or falls. It is counterpoised by weights attached
to chains passing over pulleys, so as to press the gas with a small force in
order to drive it along the main, which communicates with the pipes sup-
plying it to the various consumers. The pressure impelling the gas through
the mains does not in general exceed that of a column of water two or
three inches high.
It will be necessary, after this slight outline describing the essential
parts of the apparatus, to enter more fully into the details of the several
parts.
The retorts are constructed of wrought iron, cast iron, or earthenware,
and in shape are cylindrical, with a diameter of 12 in. to 18 in., or more,
and a length of 6 ft. to 10 ft. Though sometimes circular in section, other
forms are commonly used such as the elliptical, and especially the Q-
shaped. The retorts are closed except at the mouth-end, Fig. 348, from the
top of which rises the stand-pipe, A, which has usually a diameter of about
5 in. When the charge has been introduced, the mouth is closed by a
plate of iron, B, closely and securely applied by means of a screw, c, as shown
in the figure a perfectly tight joint being obtained by a luting of lime mortar
spread on the part of the lid which comes into contact with the mouth of
the retort. The retorts are always set horizontally in the furnace each
COAL-GAS.
553
furnace usually including a set of five retorts. The charge of coals is in-
troduced on a tray of sheet iron adapted to the size of the retort, which,
when properly pushed in, is inverted so as turn out the contents, and then
withdrawn.
The time required to completely expel the volatile constituents from the
charge in a gas retort varies very much, because there are great diversities
in the composition of the different kinds of coal employed. Some varieties
of coal, such as cannel, are easily decomposed, and the operation may be
complete in about three hours ; while other kinds may require double that
time. The quantity of gas procurable from a given weight of coal also varies
according to the kind of coal made use of. Thus, while a hundredweight
of cannel may give 430 cubic feet
of gas, the same weight of New-
castle coals will yield but 370 cu-
bic feet. The nature of the gases
given off from a retort will be
different at the different stages
of the operation.
The scene presented by the
retort-house of a large gas manu-
factory, when viewed at night, is
a singular spectacle. The strange
lurid gleams which shoot out
amid the general darkness as the
retorts are opened to withdraw
the coke, and the black forms
of the workmen partially illumi-
nated by the glare, or flitting like
dark shadows across it, form a
picture which might engage the
pencil of a Rembrandt. In Plate
IX. is depicted the retort-house at
the Imperial Gas Works, King's
Cross. Here the retorts are ar-
ranged in several tiers the coal
being brought, and the cokewith-
drawn, by the aid of an iron car-
riage running on rails parallel to
the line of furnaces.
In the process of heating, a proper regulation of the temperature is of
the highest importance. It is found that when the retorts are heated to
bright cherry-red, the best results are obtained. At a lower temperature
a larger quantity of condensable vapours are given off, which collect in the
gasholders and distributing pipes as solid or liquid, and occasion much
inconvenience, while the quantity of gas obtained is decreased. On the
other hand, if the temperature be too high, some of the gases are decom-
posed, and the quantity of carbon contained in the product is so much
diminished as seriously to impair the illuminating power. Again, every
second the gases after their production remain in the red-hot retort dimi-
nishes their light-giving value ; for those hydro-carbons on which the
luminiferous power of the gas depends, are then liable to partial decom-
position ; a portion of their carbon is deposited on the walls of the retort
in a dense layer, gradually choking it up, while the liberated hydrogen does
FIG. 348.- The Retort.
554 COAL-GAS.
not add to the illuminating but to the heating constituents of the gas. A
plan has been patented by Mr. White, of Manchester, for rapidly removing
the illuminating gases from the retort by sweeping them out by means of
a current of what has been termed " water gas." This water gas is pro-
duced by causing steam to pass over heated coke, and is a mixture of car-
bonic acid, carbonic oxide, and hydrogen. Though only two of these are
combustible gases and even they do not yield light by their combustion,
and, by adding to the bulk of the gas, serve rather to dilute it yet it has
been found that in some cases twice the amount of light is obtainable by
White's process than the same weight of coal supplies when treated in the
ordinary manner.
The hydraulic main, as already mentioned, being kept half full of tar
into which the lower ends of the dip-pipes descend, prevents the gas from
escaping through the stand-pipes when the lid of a retort is removed for
the introduction of a fresh charge. The hydraulic main is from 12 to 18
in. diameter, and the dip-pipes pass into it by gas-tight joints. Various
forms of purifiers are in use besides the simple one already mentioned.
Some of these have arrangements for agitating the gas with a purifying
liquid by mechanical means, the motion being supplied by a steam engine.
The gasholder, as it sinks in the water of the cistern, presses with less
force on the contained gas, and unless this inequality of pressure were
counteracted there would be very unequal velocities in the flow of gas
from the burner. The equality of pressure is obtained by making the
weight of the chains by which the gasholder is suspended equal to half
the weight the gasholder loses in the same length of its motion. Gas-
holders are also constructed without chains or counterpoises, as these are
found to be unnecessary where the height of the gasholder does not exceed
half its width. In such cases, especially when the vessel is very large, the
difference of pressure at the highest and lowest position is quite incon-
siderable, and nothing more is necessary than that upright guides or pillars
be placed to preserve the vertical motion of the vessel. Another improve-
ment, which enables a lofty gasholder to be used without increasing the
depth of the tank, consists in forming the gasholder of several cylinders,
which slide in and out of one another like the draw-tubes of a telescope.
Each cylinder has a groove formed by turning up the iron inside the rim,
and at the top of the next cylinder the edge is turned outwards so as to drop
in the groove or channel, which thus forms a gas-tight joint, for it is of
course filled with water as it rises. The pressure is, however, more accu-
rately regulated by an apparatus called the governor, through which the
gas passes in before it enters the mains. The construction and action of
the regulator will be understood from Fig. 349, where A represents a kind
of miniature gasholder, inverted in the cistern, B. From the centre of the
interior of the bell hangs a cone, C, within the contracted orifice of the
inlet-pipe. If this cone be drawn up, the size of the orifice, D, is reduced,
and, on the other hand, by its descent it enlarges the opening through
which the gas passes outward. By properly adjusting the weights of the
counterpoise, E, such a position of the cone may be found that the gas passes
into the mains at an assigned pressure. Suppose, now, that from any
cause the pressure of gas in F increases, that pressure acting upon the
inverted bell, A, causes it to rise and carry with it the cone, which, by
narrowing the orifice of the outlet, checks the flow of gas. Similarly, a
decrease of pressure in the mains would be followed by the descent of the
cone, and consequently freer egress of gas. In hilly towns it is necessary
PLATE IX.
RETORT HOUSE CF THE IMPERIAL GAS-WORKS, KINGS CROSS, LONDON.
COAL-GAS.
555
to fix regulators of this kind at certain heights in order to equalize the
pressure. It is found that a difference of 30 ft. in level affects the pres-
sure of gas in the same main to about the same amount as would a column
FIG. 349. The Gas Governor.
of water one-fifth of an inch high, the pressure being least at the lowest
point.
Coal-gas is a mixture of several gases, and these may be classified as,
first, the light-giving gases, or those which burn with a luminous flame ;
secondly, gases which burn with a non-luminous flame, and which there-
fore contribute to the heat, and not to the light, of a gas-flame, and have
the effect of diluting the gas ; third, gases and vapours which are properly
termed impurities, as they are either incombustible or by their combustion
give rise to injurious products. Of the first kind the principal is olefiant
gas, a gas which burns with a brilliant white flame without smoke. It is
a compound of hydrogen and carbon, six parts by weight of carbon being
combined with one part by weight of hydrogen. Besides olefiant gas other
gaseous hydrocarbons are found in smaller quantities. These contain a
larger proportion of carbon than olefiant gas. The second class contains
hydrogen, light carburetted hydrogen, and carbonic oxide. Hydrogen is
one element of water, of which it forms one-ninth of the weight. It burns
with a flame giving singularly little light, but having intensely heating
power ; in fact, one of the brightest lights we can produce is obtained by
allowing the flame of burning hydrogen to heat a piece of lime. Light
carburetted hydrogen, like olefiant gas, is a compound of hydrogen and
carbon, but the proportion of carbon to hydrogen is only half what it is in
olefiant gas, namely, three parts to one. This gas enters largely into the
55 6 COAL-GAS.
composition of coal-gas, and occurs naturally in the coal seams, being, in
fact, the dreaded fire-damp of the miner. It is much lighter than defiant
gas, for while that gas is of nearly the same specific gravity as atmospheric
air, light carburetted hydrogen is only a little more than half that specific
gravity. It is this ingredient of coal-gas which renders it so light as to be
available for inflating balloons. It burns with either a bluish or a slightly
yellow flame, yielding hardly any light. Olefiant gas and the other lumi-
niferous hydro-carbons, when exposed to a bright red heat, split up for the
most part into this gas and carbon. This explains the importance of rapidly
removing the gas from the retort in which it is generated, a point which
has been referred to above. Carbonic oxide is a gas which one may often
see burning with a pale blue flame above the glowing embers of a common
fire, the flame giving, however, little light. It is a compound of carbon and
oxygen, containing only one-half the quantity of oxygen which its carbon
is capable of uniting with, and therefore ready to unite with another pro-
portion, which it does in burning, carbonic acid being the product.
The third class of constituents of coal-gas the impurities are those
which the manufacturer strives to remove by passing the gas over lime,
milk of lime, oxide of iron, &c. Sulphuretted hydrogen, a compound of
sulphur and hydrogen, has an extremely nauseous odour resembling that
of rotten eggs. It is always formed in the distillation of coal, and if not
removed from the gas in the process of purification, it has a very objection-
able effect ; for one product of its combustion is sulphurous acid, and in a
room where such gas is burnt much damage may be done by the acid
vapours; for example, the bindings of books, &c., soon become deteriorated
from this cause. The detection of sulphuretted hydrogen in coal-gas is
quite easy, for it is only necessary to hold in a current of the gas a piece
of paper dipped in a solution of the acetate of lead. If in a few minutes
the paper becomes discoloured the presence of sulphuretted hydrogen is
indicated.
But the bete noire of the gas-maker is a substance called " sulphide of
carbon," which is formed whenever sulphur and carbonaceous matters are
brought together at an elevated temperature* Sulphide of carbon is, in
the pure state, a colourless liquid, of an intensely offensive odour, resem-
bling the disagreeable effluvia of putrefying cabbages. The liquid is ex-
tremely volatile, and coal-gas usually contains some of its vapour. When
too high a temperature is used in the generation of the gas, it contains
a large quantity of this deleterious ingredient, especially if the amount of
sulphur contained in the coal is at all considerable. This sulphide of
carbon vapour is very inflammable, and one product of its combustion is
a large quantity of sulphurous acid. This substance cannot be removed
from coal-gas by any process sufficiently cheap to admit of its application
on the large scale. It is said, however, that by passing the gas over a
solution of potash in methylated spirit, the sulphide of carbon vapour can
be completely got rid of. The price of these materials renders the process
available in special cases only, where the damage done by the sulphurous
acid would be serious, as in libraries, &c. Besides the impurities we have
already enumerated, many others are present in greater or less quantity.
Carbonic acid the gas resulting from the complete combustion of carbon
should be entirely removed by the lime purifiers, as the presence of even
a small percentage detracts materially from the illuminating power. This
gas is not inflammable and cannot support combustion. It has decided
acid properties, and readily unites with alkaline bases forming carbonates :
COAL-GAS. 557
it is upon this behaviour that its removal by lime depends. The illumi-
nating power of coal-gas containing only I per cent, of carbonic acid is
reduced thereby by about one-fifteenth of its whole amount.
The proper mode of burning the gas so as to obtain the maximum
amount of light it is capable of yielding requires a compliance with certain
physical and chemical conditions. The artificial production of light de-
pends upon the fact that by sufficiently heating any substance, it becomes
luminous, and the higher the temperature the greater the luminosity. The
light emitted by solid bodies moderately heated is at first red in colour ; as
the teniperature rises it becomes yellow, which gradually changes to white
when the heat becomes very intense. The widest difference exists, how-
ever, in the temperature required to render solids or liquids luminous, and
that needed to cause gases to give off light. In all luminous flames the
light is emitted by solid particles highly heated. Every luminous gas-
flame contains solid particles of carbon, as may be easily shown by the
soot deposited on any cold body such as a piece of metal introduced into
the flame. On the other hand, the flame of burning hydrogen, which pro-
duces only aqueous vapour, furnishes no light, but a heat so intense, that
a piece of lime introduced into the jet becomes luminous to a degree hardly
supportable by the eye. The conditions requisite, therefore, for burning
illuminating gas are, first, just such a supply of air as will prevent particles
of carbon from escaping unconsumed in the form of smoke, and yet not
enough to burn up the carbon before it has separated from the hydrogen,
and passed through the flame in the solid state ; second, the attainment of
the highest possible temperature in the flame, compatible with the former
condition. When the supply of oxygen is not in excess, the hydrogen of
the gaseous hydro-carbon appears to burn first ; the carbon is set free, and
its solid particles immersed in the flame of the burning hydrogen are there
intensely heated ; but ultimately reaching the outer part of the flame, they
enter into combination with the oxygen of the air, producing carbonic acid ;
or if present in excessive quantity, they are thrown off as smoke. If the pur-
pose of burning the gas is to obtain heating effects only, this is accomplished
by supplying air in such quantities, that the carbon enters into combination
with oxygen in the body of the flame, with-
out a previous separation from the hydro-
gen with which it is combined. In this
case a higher temperature is attained^ and
the flame is wholly free from smoke; so that
vessels of any kind placed over it remain
perfectly clean and free from the least de-
posit of soot. The last result is of great ad-
vantage in chemical processes, especially
where glass vessels require to be heated,
for the chemist retains an uninterrupted
view of the actions taking place in his
flasks and retorts.
No better illustration of the nature of
the combustion in a gas-flame can be found
FIG. QQBunserts Burner. than is furnished by Bunsen's burner, Fig.
350, now universally employed as a source
of heat in chemical laboratories. In this
burner the gas issues from a small orifice at the level of a, near the bottom of
the tube, b, which is open at the top, and is in free communication at the bot-
558
COAL-GAS.
torn with openings through which air enters and mixes with the gas, as they
rise together in the tube and are ignited at the top. If the pressure of the
gas be properly regulated, the flame does not descend in the tube, but the
mixture burns at the top of the tube, producing a pale blue flame incapable
of emitting light, but much hotter than an ordinary flame, for the combus-
tion is much quicker. If the openings at a be stopped, the supply of air
to the interior of the tube is cut off, and then the gas burns at the top of
the tube, ^, in the ordinary manner, giving a luminous flame. Ordinary
gas-jets burning in the streets, at open stalls or shops, may be seen on a
windy night to have their light almost extinguished by the increased
supply of oxygen, carried mechanically into the body of the flame, the
white light instantly changing to pale blue. The disappearance of the
light in such cases is due, as in Bunsen's burner, to the supply of oxygen
in sufficient quantity to combine at once with the carbon as well as the
hydrogen of the hydro-carbons.
FIG. 351. Faraday 's Ventilating Gas-burner.
The burners now chiefly used for the consumption of coal-gas for illu-
minating purposes are the bat's-wing, the fish-tail, and various forms of
Argahd. The bat's-wing burner is simply a fine slit cut in an iron nipple,
and it produces a flat fan-like flame. The fish-tail is formed by boring
two holes so that two jets of gas inclined at an angle of about 60 infringe
on each other and produce a flat sheet of flame. The Argand, in its
simplest form, consists of a tubular ring perforated with a number of small
holes from which the gas issues. Many modifications of this kind of
burner have been devised, in all of which a glass chimney is requisite to
obtain a current of air sufficient to consume the gas without smoke, and
it is important that the height of the chimney should be adapted to the
amount of light required if the gas is to be used economically. Argand
COAL-GAS. 559
burners are specially advantageous where a concentrated light is required.
Fig. 351 represents a ventilating gas-burner, contrived by Faraday, the
object being to remove from the apartment the whole of the products of
the combustion of the gas. A is the pipe conveying the gas to the
Argand burner, B, the flame of which is enclosed in the usual cylindrical
glass chimney, c c, open at the top. This is enclosed in a wider glass
cylinder closed at the top by a double disc of talc, D D, and opening at its
base into the ventilating tube, E E. The direction of the currents produced
by the heat of the flame is shown by the arrows. The whole is entirely
enclosed by a globe of ground glass. Means are provided for regulating
the draught in the pipe, E E, which, when heated, creates of itself a strong
current of air through the apparatus.
The illuminating power of coal-gas may be measured directly by com-
paring the intensity of the light emitted by a gas-flame consuming a known
quantity of gas per hour with the light yielded by some standard source.
The standard usually employed is a spermaceti candle burning at the rate
of 120 grains of sperm per hour. It is not necessary that the candle actu-
ally used should consume exactly this amount, but the consumption of
sperm by the candle during the course of each experiment is ascertained
by the loss of weight, and the results obtained are easily reduced to the
standard of 120 grains per hour. An instrument is used for determining
the relative intensities of the illumination, called Bunsen's photometer. It
consists of a graduated rule, or bar of wood or metal, about 10 ft. long. At
one end of this bar is placed the standard candle, at the other is the gas-
flame. A stand slides along the rule supporting a circular paper screen at
the level of the two flames, and at right angles to the line joining them.
This paper screen is made of thin writing-paper, which has been brushed
over with a solution of spermaceti, except a spot in the centre, or, more
simply, a grease-spot is made in the middle of a piece of paper. In conse-
quence the paper surrounding the spot is much more transparent; yet when
it is placed so that both sides are equally illuminated, a spectator will not
perceive the spot in the centre when viewing the screen on either side.
When the screen has been placed by trial in such a position between the
two sources of light, it is only necessary to measure its distance from each
flame in order to compute the number of times the illuminating power of
the gas-flame exceeds that of the candle. This computation is based on
the fact that the intensity of the light from any source diminishes as the
square of the distance from the source. Thus, if a sheet of paper be illu-
minated by a candle at 2 ft. distance, it will receive only one-fourth of the
light that would fall upon it were its distance but I ft., and if removed to
3 ft. distance it has only one-ninth of the light. In the instrument used
for measuring the illuminating power of gas the rule is graduated in accord-
ance with this law, so that the relative intensities may be read off at once.
The gas passes through a meter for measuring accurately the quantity per
minute which is consumed by the burner, and there is also a gauge for
ascertaining the pressure. Another mode of estimating the illuminating
power of coal-gas is by determining the quantity of carbon contained in a
given volume. For, in general, the richness of the gas in carbon is a fair
index of the quantity of its luminiferous constituents. This may be readily
effected by exploding the gas with oxygen, and measuring the amount of
carbonic acid produced. Still more accurate determinations of the illu-
minating value of gas may be obtained by a detailed chemical analysis.
The illuminating power of any gas is so calculated that it represents the
560
COAL-GAS.
number of times that the light emitted by a jet of the gas, burning at the
rate of 5 cubic feet per hour, exceeds the light given off by the standard
sperm candle burning 1 20 grains of sperm per hour. For example, when
it is said that the illuminating power of London gas is 13, it is meant that
when the gas is burnt in an ordinary burner at the rate of 5 cubic feet per
hour, the light is equal to that given by thirteen sperm candles burning
together 13 X 120 grains per hour. The quality of gas varies very much,
as it depends upon the kind of coal employed, and upon the mode in which
the manufacture is conducted. The following are the results of experi-
ments made to determine the illuminating power of the gas supplied to
several large towns :
Candles.
London 12*1
Paris 12*3
Birmingham 15*0
Berlin 15-5
Candles.
Carlisle 16*0
Liverpool 22*0
Manchester 22-*o
Glasgow 28*0
The relative quantities of tar, ammonia water, and coke yielded in vari-
ous gas manufactories also vary very considerably for the same reasons.
In the early days of gas illumination the consumers were charged accord-
ing to the number of burners ; but this arrangement proved so unsatisfac-
tory that the gas-meter became a necessity, and already in 1817 meters had
been devised, which were not essentially different from those now in use.
Although gas is used in so many houses, there are few persons who have
any notion of the mechanism of the gas-meter. Our space will not allow
full details of the construction, but the following particulars may be men-
tioned. In the ordinary " wet " meter there is a drum divided into four
compartments by radiating partitions ; this drum revolves on a horizontal
axis, and the lower half of the drum, or rather more, is beneath the surface
of water contained in the case, the water being at the same level inside and
outside the drum. The gas enters one of the closed chambers formed
between the surface of the water and a partition of the drum. Its pressure
tends to increase the size of the chamber, hence the drum revolves. The
preceding division of the drum being filled with gas, this is driven into the
exit pipe by the motion of the drum, as it is included in a space comprised
between the water and a partition. Each division in turn comes into com-
munication with the gas-main, and as it is filled passes on towards the posi-
tion in which a passage is opened for it to the exit-pipe. Each turn of the
drum, therefore, carries forward a definite quantity of gas, and the only
thing necessary is a train of wheels, to register the number of revolutions
made by the drum. The " wet " meter is much inferior in almost every
respect to the " dry " meter, in which no water is used. The principle of the
" dry" meter is very simple. The gas pours into an expanding chamber,
partly constructed of a flexible material, and which may be compared to
the bellows of a circular accordion. The expansion is made to compress
another similar chamber, already filled with gas, which is thus forced
through the exit-pipe. When the first chamber has expanded to a definite
volume, it moves a lever, and this reverses the communications. The ex-
panded chamber is now opened to the exit-pipe, and the other to the
entrance-pipe, and so on alternately. A train of wheels registers the number
of movements on a set of dials.
FIG. 352. Apparatus for making Magenta.
COAL-TAR COLOURS.
COAL-TAR is an exceedingly complex material, being a mixture of a
great number of different substances. The following table shows the
chemical name of many of the substances obtainable from the coal-tar. It
must not be supposed that these substances exist ready formed in the coal,
and that they are merely expelled by the heat. We can understand better
how heat, acting upon an apparently simple substance like coal, and one
containing so few elements, is able to produce so large a variety of different
bodies, if we remember that heat is the agent most often employed to effect
chemical changes, and that from even two elements, variously combined,
bodies differing entirely from each other are producible.
SUBSTANCES FOUND IN COAL-TAR.
a. COMPOUNDS OF CARBON AND HYDROGEN.
Hydrides of amyl, hexyl, heptyl, nonyl, and decyl.
Amylene, hexylene, heptylene, octylene, nonylene, decylene ; (paraffin).
Benzol, toluol, xylol, cumol, cymol.
Naphthalene.
Anthracene.
Pyrene.
Chrysene.
561 36
COAL-TAR COLOURS.
b. COMPOUNDS OF CARBON, HYDROGEN, AND OXYGEN.
Phenol, cresol, phlorol.
Rosolic acid, brunolic acid.
C. COMPOUNDS OF CARBON, HYDROGEN, AND NITROGEN.
Aniline, toluidine.
Pyridine, picoline, lutidine, collidine, parvoline, coridine, rubidine, viridine.
Leucoline, lepidine, cryptidine.
Cespitine, pyrrol.
This list contains only the names of substances which have actually been
found in the coal-tar, and it is certain that a number of products must have
escaped notice. It is obvious, too, that by using coal of different kinds, and
by varying the temperature and pressure at which the operation of dis-
tilling the coal is effected, we shall probably be able to increase the number
of possible constituents of coal-tar almost indefinitely. The list above pre-
sents to the non-chemical reader a string of quite unfamiliar names ; but,
though the system of nomenclature in chemistry is far from perfect, yet
each of these names has a meaning for the chemist beyond the mere de-
signation of a substance. The chemical name aims at showing, or at least
suggesting, the composition of a body and the general class to which it
belongs. This may be illustrated by the names of hydro-carbons in the
above list. The five compounds headed by benzol have many properties
in common, and each one is entirely different in its chemical behaviour to
those which follow amylene. The Greek numerals enter into the names of
the latter, in order to express, in this case, the number of atoms of carbon
which are supposed to be contained in each ultimate particle of the body.
We write down in parallel columns the names of these two classes of bodies,
together with the symbols which represent their composition, reminding the
reader that the letter C represents carbon ; the letter alone indicating one
atom of that element, but, when followed by a small figure, it implies that
number of carbon atoms ; in like manner H, N,and O represent atoms of
hydrogen, nitrogen, and oxygen respectively.
Benzol C 6 H 6
Toluol C 7 H 8
Xylol C 8 H 10
Cumol C Q H 12
Cymol C 10 H 14
Hexylene C 6 H 12
Heptylene C 7 H 14
Octylene C 8 H 16
Nonylene C Q H 18
Decylene C 10 H 20
If these lists be carefully examined, it will be observed that there is a
regular progression in the constituent atoms, so that each set of substances
forms a series, the differences being always the same. The various bodies
contained in the coal-tar are separated from each other by taking advan-
tage of the fact that each substance has its own boiling-point ; that is, there
is a certain temperature, different for each body, at which it will rise into
vapour quickly and continuously. Benzol, for example, boils at 82 C.,
toluol at 1 14 C., and phenol at 188 C. ; so that, if we apply heat to a mix-
ture of these three substances, the benzol will boil when the temperature
reaches 82, and will pass away in vapour, carrying off heat, so that the
temperature will not rise until all the benzol has been driven off ; then, when
the temperature reaches 114, the toluol will begin to come off, but not
COAL-TAR COLOURS. 563
until that has all passed over into the receiver will the temperature rise
above 114; and the phenol remaining will distil, only at 188.
Another mode of separating bodies when mixed together is by treating
them with a liquid which acts on, or dissolves out, some of the constituents,
but not the rest. The coal-tar, as it is received from the gas-works, is
placed in large stills, capable, perhaps, of holding several thousand gallons,
and usually made of wrought iron. Stills sufficiently good for the purpose
are commonly constructed from the worn-out boilers of steam engines.
The application of heat, of course, causes the more volatile substances to
come over first. These are condensed and collected apart until products
begin to come off which are heavier than water. The first portion of the
distillate, containing the lighter liquids, is termed " coal naphtha." The pro-
cess is continued, and heavier liquids come over, forming what is called in
the trade the " dead oil." Pitch remains behind in the retort, from which
it is usually run out while hot, but sometimes the distillation is carried a
step further.
The chief colour-producing substances contained in coal-tar are benzol,
toluol, phenol, naphthalene, and anthracene. The aniline which is present
in the tar is very small in amount, and if this ready-formed aniline were
our only supply, it would be impossible to make colours from it on an
industrial scale. The first of the above-named substances, benzol, was
discovered by Faraday, in 1825, in liquid produced by strongly compressing
gas obtained from oil. He called it bicarburet of hydrogen ; but afterwards
another chemist, having procured the same body by distilling benzoic acid
with lime, termed it benzine. It readily dissolves fats and oils ; and is used
domestically for removing grease-spots, cleaning gloves, &c, and in the arts
as a solvent of india-rubber and gutta-percha. It is a very limpid, colour-
less liquid, very volatile, and, when pure, is of a peculiar but not disagree-
able odour. It boils at 82 C, and, cooled to the freezing-point of water, it
solidifies into beautiful transparent crystals, a property which is sometimes
taken advantage of to separate it in a state of purity from other liquids
which do not so solidify.
Benzol is very inflammable, and its vapour produces an explosive mix-
ture with air. The vapour, which is invisible, will run out of any leak in
the apparatus, like water, and flow along the ground. Accidents have
occurred from this cause, and a case is on record in which the vapour
having crept along the floor of the works, was set on fire by a furnace
forty feet away from the apparatus, the flame, of course, running back to
the spot from which the vapour was issuing. Benzol is a dreadful sub-
stance for spreading fire should it become ignited, for, being lighter than
water, it floats upon its surface, and therefore the flames cannot be extin-
guished in the ordinary way. The discovery of the presence of benzol in
coal-tar was made by Hofman in 1845. ^ * s obtained from the light oil of
coal-tar by first purifying this liquid by alternately distilling it with steam
and treating with sulphuric acid several times. The product so obtained
is a colourless liquid, sold as " rectified coal naphtha," which, however, has
again to be several times re-distilled with a careful regulation of the tem-
peratvwe, so that the benzol may be distilled off from other substances, boil-
ing at a somewhat higher temperature, with which it is mixed. Even then
the resulting liquid (commercial benzol) contains notable quantities of
toluol. If benzol be added in small quantities at a time to very strong and
warm nitric acid, a brisk action takes place, and when after some time water
is added, a yellow oily-looking liquid falls to the bottom of the vessel. The
363
564
COAL-TAR COLOURS.
FIG. 353. Iron Pots for making Nitro-Benzol.
benzol will have disappeared, for nitric acid under such circumstances acts
upon it by taking out of each particle an atom of hydrogen, which it re-
places by a group of atoms of nitrogen and oxygen, and, instead of benzol,
we have the yellow oil, nitro-benzol. Chemists are accustomed to repre-
sent actions of this kind by what is called a chemical equation, the left-hand
side showing the symbols representing the constitution of the bodies which
are placed together, and the right hand the symbols of the bodies which
result from the chemical action. Here is the equation representing the
action we have described :
C 6 H 6
Benzol.
N0 2 OH
Nitric acid.
Nitro-benzol.
HOH
Water.
Nitro-benzol has a sweet taste and a fragrant odour. It is known in
commerce under the names of artificial oil of bitter almonds and essence
of mirbane, and it has been used for perfuming soap. The chemical action
between benzol and concentrated nitric acid is so violent that, when nitro-
benzol first had to be manufactured on the large scale, great difficulty was
experienced on account of the serious explosions which occurred. The
apparatus now used in making nitro-benzol on the large scale is represented
COAL-TAJt COLOURS.
565
in Fig. 353, which shows some of the cast-iron pots, of which there is usu-
ally a long row. These pots are about 4! ft. in diameter, and the same in
depth. Each is provided with a stirrer, which is made to revolve by a
bevil-wheel, c, on its spindle, working with a pinion on a shaft, b, driven by a
steam engine. A layer of water is kept on the tops of the lids, the water
being constantly passed in and drawn off through the pipes, d, in order
to keep it cool. For the chemical action is, as usual, attended with heat,
which vaporizes some of the benzol, but the cold lid re-condenses the
FIG. 354. Section of Apparatus for making Nitro-Benzol.
vapour, which would otherwise escape with the nitrous fumes that pass off
by the pipe, a. There is at e an opening, through which the material may
be introduced, and in the bottom of the vessel is an aperture through which
the products may be drawn off. Fig. 354 shows a section of one of the
cast-iron vessels, and exhibits the mode in which the spindle of the stirrer
passes through the lid. In the cup, rt, filled with a liquid, a kind of in-
verted cup, which is attached to the spindle, turns round freely. It would
not do to choose water for the liquid in this cup, for water would, by absorb-
ing the nitrous fumes, form an acid capable of attacking and destroying
the spindle. Nothing has been found to answer better for this purpose than
nitre-benzol itself. The charge introduced into these vessels is a mixture
566
COAL-TAR COLOURS.
of nitric and sulphuric acids together with the benzol. During the action,
which may last twelve or fourteen days, no heat is applied, for the mixture
becomes hot spontaneously, and in fact care must be taken that it does
355. Apparatus for making Aniline.
not become too hot. The nitro-benzol thus obtained is purified by washing
with water and solution of soda.
If nitro-benzol were brought into contact with ordinary hydrogen gas, no
action whatever would take place. But it is well known to chemists that
gases which are just being liberated from a compound have at the instant
of their generation much more powerful chemical properties than they pos-
sess afterwards. Gases in this condition are said to be in the nascent state.
COAL-TAR COLOURS.
567
If we submit nitro-benzol to the action of nascent hydrogen we find a
remarkable change is produced. This change consists, first, in the hydro-
gen robbing the nitro-benzol of all its oxygen atoms ; second, in the addi-
tion of hydrogen to the remainder ; third, in some re-arrangement of the
atoms, by which a new body is formed. Not that these changes are suc-
cessive, or that we actually know the movement of atoms, but we are thus
able to form ideas which correspond with the final result. The new sub-
stance is named aniline. It is regarded by chemists as a base ; that is,
a substance capable of neutralizing and combining with an acid to form a
salt. Its composition is represented by the symbols C 6 H 5 H 2 N. Aniline
was found in coal-tar in 1834, and even its colour-producing power was
noticed, for its discoverer named it kyanol, in allusion to the blue colour
it produced with chloride of lime. Later it was obtained by distilling indigo
with potash, and hence received its present name from anil, the Portu-
guese for indigo. The quantity of aniline contained in the tar is quite
insignificant.
Aniline is prepared from nitro-benzol on the large scale by heating it
with acetic acid and iron filings or iron borings, a process which rapidly
changes the nitro-benzol into aniline. The equation representing the
change is
QH 5 N0 2
Nitro-benzol.
H 6 =
Hydrogen.
Aniline.
2H 2 0.
Water.
The operation is effected in the apparatus represented in Fig. 355. It
consists of a large iron cylinder, within which works a paddle on a vertical
revolving spindle, which, being hollow, is also a pipe to convey high pres-
sure steam within the apparatus.
Fig. 356 is a section of the hollow
spindle, in which / is the pivot at
the bottom of the cylinder on
which it turns ; d is the stirring
paddle; e is an aperture admitting
the steam from the pipe, c, form-
ing the shaft of the paddle, which
is made to revolve by the bevil-
wheel. The steams enters by the
elbow-pipe, which has a nozzle
ground to fit the head of the ver-
tical revolving pipe, upon which
it is pressed down by the screw.
When the materials have been
introduced into the cylinder, the
stirrer is set in motion, and super-
heated steam is sent down the
pipe ; the aniline is volatilized and
FIG. 356. Section of Hollow Spindle,
Aniline Apparatus.
passes with the steam through the
pipe, which is connected with a worm surrounded by cold water. The aniline
is purified by another distillation over lime or soda. When pure, aniline
is a colourless, somewhat oily-looking liquid, of a feeble aromatic odour.
Under the influence of light and air it becomes of a brownish tint, in which
condition it usually presents itself in commerce. It scarcely dissolves in
water, but is readily soluble in alcohol, ether, &c.
It was Mr. Perkin who, in 1856, first obtained from aniline a substance
568 COAL-TAR COLOURS.
practically available for dyeing. Let it be noticed that when Mr. Perkin
discovered aniline purple, he was not engaged in searching for dye-stuffs,
but was carrying on a purely scientific investigation as to the possibility of
artificially preparing quinine. With this view, having selected a substance
into the composition of which nitrogen, hydrogen, and carbon enter in
exactly the same proportions -as they occur in quinine, but differing from it
by containing no oxygen, he thought it not improbable that by oxidizing
this body he might obtain quinine. In this he was disappointed, for the
result was a dirty reddish-brown powder. Being desirous, however, of
understanding more fully the nature of this reddish powder, he proceeded
to try the effects of oxidation on other similarly constituted but more
simple bodies. For this purpose he fortunately selected aniline, which,
when treated with sulphuric acid and bichromate of potash, he found to
yield a perfectly black product. Persevering in his experiments by exami-
ning this black substance, he obtained, by digesting it with spirits of wine,
the now well-known " aniline purple." Mr. Perkin, having determined to
make the aniline purple on the large scale, patented his process, and suc-
ceeded in overcoming the many obstacles incident to the establishment of
a new manufacture requiring as its raw material products not at that time
met with as commercial articles. The process is now carried on on the
large scale by mixing sulphuric acid and aniline in the proportions in which
they combine to form the sulphate of aniline, and dissolving by boiling with
water in a large vat. Bichromate of potash is dissolved in water in another
large vat. When both solutions are cold, they are mixed together in a
still larger vessel and allowed to stand a day or two. A fine black powder
settles on the bottom of the vessel in large quantities ; this is collected
in filters, washed with water, and dried. This powder is not aniline purple
alone, but a mixture of this with other products, presenting a very unpro-
mising appearance; but when it has been digested for some time with
diluted methylated spirit, all the colouring matter is dissolved out, and is
obtained from the solution by placing the latter in a still, where the spirit
is distilled off and collected for future use, while all the colouring matter
remains behind, held in solution by the water. From this aqueous solution
the mauve is thrown down by adding caustic soda. It is collected, washed,
and drained until of a pasty consistence, in which condition it is sent into the
market. It can be obtained in crystals, but the commercial article is seldom
required in this form, as the additional expense is not compensated by any
superiority in the practical applications of the colour. Mauve is readily
soluble in spirits of wine, but not very soluble in water. Its tinctorial power
is so great that one-tenth of a grain suffices to impart quite a deep colour
to a gallon of water. Silk and woollen fabrics have an extraordinary
attraction for this colouring matter, which attaches itself very firmly to their
fibres. If some white wool is dipped into even a very dilute solution, the
colour is quickly absorbed. Mauve is more permanent than any other coal-
tar colour, being little affected by the prolonged action of light.
Mauve is chemically a salt of a base which has been termed " mauve-
ine." Mauveine itself is a nearly black crystalline powder, which forms
solutions of a dull blue-violet tint, but when an acid is added to such a
solution the tint is at once changed to purple. Mauveine is a powerful
base, displacing ammonia from its compounds. The commercial crys-
tallized mauve is the acetate of mauveine.
The process by which Mr. Perkin orginally obtained mauve from aniline
evidently depends upon the well-known oxidizing property of bichromate
COAL-TAR COLOURS.
569
of potash, and experiments were accordingly made with other oxidizing
bodies and aniline ; in fact, patents were taken out for the use of nearly
every known oxidizing chemical. Three years after Mr. Perkin's discovery
of mauve, M. Verguin, of Lyons, obtained, by treating crude aniline with
chloride of tin, the bright red colouring matter now known as magenta.
It was found also that crude > aniline, when treated with other metallic
chlorides, nitrates, or other salts, which are oxidizing agents less powerful
than bichromate of potash, yields this bright red colouring matter. A
process patented by Medlock, in 1860, in which arsenic acid is the oxi-
dizing agent, has almost entirely superseded, in England at least, all the
others yet proposed for the manufacture of magenta. It is not a little
remarkable that magenta would not have been discovered had M. Verguin
and others operated on pure aniline instead of on the ordinary commercial
article. For it was found subsequently by Dr. Hofman that pure aniline can-
not be made to yield magenta : the presence of another body is necessary.
A reference to the table of coal-tar constituents will show that there is
a hydro-carbon named " toluol." This substance is of a similar nature to
benzol, and has a boiling-point so little above that of benzol, that in the
rough methods of separation usually employed, a notable quantity of toluol
is carried over with the benzol, and is always present in the commercial
article. In the processes which benzol undergoes for conversion into ani-
line, the toluol accompanies it in a series of parallel transformations, re-
sulting in the production of a base termed " toluidine " similar to aniline
being, however, in its pure state a solid at ordinary temperatures. We
write down the symbols representing the composition of the bodies formed
in the two cases in order to clearly show this :
Benzol C 6 H 6
Nitro-benzol C 6 H 5 (NO 2 )
Aniline C 6 .H 5 NH 2
Toluol C 7 H 8
Nitro-toluol C 7 H 7 (NO 2 )
Toluidine C 7 H 7 NH 2
This aniline prepared from commercial benzol always contains some
toluidine ; and it is essential for the production of magenta that this sub-
stance should be operated on along with the aniline. Whether the presence
of some toluidine is also necessary for the production of mauve and other
colours is not yet known, but they are always prepared from commercial
benzol. It is certain that pure aniline yields no magenta, neither does pure
toluidine ; but a mixture supplies it in abundance. For the preparation of
magenta the best proportions for this mixture would be about three parts
of aniline to one of toluidine ; but, in practice, it is not necessary to obtain
the two substances separately, as benzol, mixed with a sufficient quantity
of toluol, may be obtained by regulating the distillation. The apparatus
used in the production of magenta is shown in Fig. 352. It consists of a
large iron pot set over a furnace in brickwork, and having a lid with a stuff-
ing-box, through which passes a spindle carrying a stirrer. A bent tube rises
from the lid, and is connected with a worm surrounded by cold water, for
the purpose of condensing the aniline which is vapourized in the process.
The aniline, containing a due amount of toluidine, is mixed in this apparatus
with about one and a half times its weight of a saturated solution of arsenic
acid (H 3 AsO 4 ). The fire is lighted and kept up for several hours : water
first, and lastly aniline, distil over. When the operation is ended, steam is
blown through the apparatus, thus carrying off an additional portion of
aniline. The crude product is then boiled with water, the solution filtered,
570
COAL-TAR COLOURS.
and common salt added, which precipitates an impure magenta. This is
afterwards dissolved and recrystallized several times. The crystals of this
magenta like those of many of the coal-colour products have a peculiar
greenish metallic lustre ; they dissolve in warm water, forming a deep
purplish-red solution. The chemical composition of magenta has been in-
vestigated by Dr. Hofman, who found it to be a salt of an organic base,
to which he gave the name of " rosaniline." This rosaniline is easily ob-
tained from magenta by addition to its solution of an alkali. While all its
salts are intensely coloured, rosaniline itself is a perfectly colourless sub-
stance, becoming reddened by exposure to the air, as it absorbs carbonic
acid, thus passing to the condition of a salt. Rosaniline, then, displays
its chromatic powers only when it is combined with an acid. This pro-
perty is sometimes shown at lectures in a striking manner by dipping a
piece of paper into a colourless solution of rosaniline, and exposing it to
the air, when, as the rosaniline absorbs carbonic acid, the paper changes
from white to red. A more elegant form of the same experiment is to dip
a white rose into a solution of rosaniline containing a little ammonia. As
the ammonia escapes, or is expelled by a current of warm air, the same
kind of action occurs, and the white rose changes to red as if by magic,
the emblem of the House of York is transformed into the badge of Lan-
caster ! The chemical nature of rosaniline is regarded as analogous to
that of ammonia it is, in fact, looked upon by chemists as a sort of am-
monia, in each particle of which some atoms of hydrogen have been replaced
by certain groiips of carbon and hydrogen atoms some of these groups be-
ing derived from the aniline and others from the toluidine. The particular
salt of rosaniline which constitutes the crude product of the action on the
aniline and toluidine, depends on the substance employed to effect the
oxidation. If a chloride, the resulting product is chloride of rosaniline ; if
a nitrate, it is the nitrate ; and so on. The magenta which is formed in the
first instance by the process we have described is an arseniate of rosani-
line ; but in the subsequent processes, it is converted into the chloride
the salt usually sold as magenta. Other salts of rosaniline are made on
the large scale especially the acetate, the beautiful crystals of which have
the advantage of being very soluble.
Magenta attaches itself strongly to animal fibres, but the colour is some-
what fugacious under the action of sunlight. It is used not only as a dye,
but more largely as the raw material from which a number of other beauti-
ful colours are obtained. For this reason it is manufactured on an enormous
scale, thousands of tons being produced annually, and the money value of
the colour produced from it must be reckoned by thousands of pounds.
Yet aniline was a few years ago merely a curiosity never met with out of
the laboratory of the scientific chemist. It is stated that a single firm now
makes more than twelve tons of aniline weekly, and on its premises may
be seen tanks, in each of which 30,000 gallons of magenta solution is
depositing its crystals. If a salt of rosaniline be heated with aniline, the
colour changes gradually through purple to blue, while ammonia is at the
same time given off. This is the colour known as aniline blue, " bleu du
Lyons," &c. In its preparation it has been found that the best results are
obtained by employing the salt of some weak acid acetate of rosaniline,
for example and pure aniline, that is, aniline free from toluidine. The
operation is conducted in iron pots very similar to those used in making
magenta, but smaller. These pots are not set over a fire, but a number of
them are placed in a large vessel containing oil, by which they can be
COAL-TAR COLOURS. 57 1
maintained at a regulated temperature when the oil is heated. The crude
product undergoes several purifications, and the aniline blue is supplied
in commerce in powder, or dissolved in spirits of wine. It is insoluble in
water, and this has been an obstacle to its employment ; but recently a
similar substance has been obtained in a soluble form, and is extensively
used for dyeing wool, under the name of " Nicholson's blue." Other blues
have been similarly prepared, and from the same two substances, magenta
and aniline, a colour known as " violet imperial " was formerly made in
very large quantities, but it has been superseded by the colours about to
be described. It may be well to mention that these blues and violets have
been found to contain bases formed of rosaniline, in which one, two, or
three atoms of hydrogen are replaced by the group C 6 H 5 . This group
of atoms will be noticed to belong to aniline, and chemists have named
it phenyl, and, therefore, bases of these coloured salts are respectively
named phenyl-rosaniline, di-phenyl-rosaniline, tri-phenyl-rosaniline. But
Dr. Hofman found that other groups of atoms besides C 6 H 5 may be made
to take the place of H in rosaniline. By acting on rosaniline or its salts
with iodides of ethyl, C 2 H 5 I, or iodide of methyl, CH 3 I, he obtained a
beautiful series of violets, of which many shades could be produced,. vary-
ing from red-purple to blue. These are the colours so well known as
Hofman's violets, and are prepared on the large scale by heating a solu-
tion of magenta (chloride of rosaniline) in alcohol or wood spirit, with the
iodide of ethyl or the iodide of methyl. The nature and proportions of
the ingredients are regulated according to the tint required. The vessels
are hermetically closed during the heating, which is accomplished by steam
admitted into a steam-jacket surrounding the vessel. The crude product
has to be separated from the substances with which it is mixed, and the
colouring matter is finally obtained, presenting in the solid state the
peculiar semi-metallic lustre so characteristic of these products. Like the
other colours, Hofman's violets are salts of colourless bases, which, as
indicated above, are substitution products of rosaniline. The tints they
produce incline to red, violet, or blue, according as one, two, or three
hydrogen atoms are replaced by the ethyl or methyl groups. Colours have
also been obtained from mauve and iodide of ethyl for example, the
dye known in commerce as " dahlia." Other colours are procured from
magenta by treating it with various compounds : one such is the " Britan-
nia violet," discovered also by Mr. Perkin, who procures it from magenta
and a hydrocarbon-bromide derived from the action of bromine or common
turpentine. This is a very useful colour, and is largely used in dyeing and
printing violets, of which any shades may be obtained.
Another derivative of rosaniline is the aniline green. It is obtained by
dissolving the rosaniline salt in dilute sulphuric acid, adding crude alde-
hyde (a substance obtained by acting with oxidizing agents on alcohol).
The mixture is heated until a sample dissolves in acidulated water with a
blue tint ; it is poured out into boiling water containing in solution hypo-
sulphite of sodium, boiled, the liquid filtered ; and the green dye, if required
in the solid state, is precipitated by carbonate of sodium. Aniline green
dyes wool and silk, the latter especially, of a magnificent green ; perhaps as
beautiful a colour as any of the coal-tar series, and one which has the sin-
gular advantage among greens of looking as beautiful in artificial light as
in daylight. The manner in which this dye was discovered is somewhat
curious. It is related by Mr. Perkin of a dyer, named Chirpin, that he was
trying to render permanent a blue colouring matter, which had been found
572 COAL-TAX COLOURS.
could be produced from rosaniline by the action of aldehyde and sulphuric
acid. After a number of fruitless attempts at fixing it, he confided his
perplexities to a photographic friend, who evidently thought that if it was
possible to fix a photograph, anything else might be fixed in like manner,
for he recommended his confidant to try hyposulphite of sodium. On
making the experiment, however, the dyer did not succeed in fixing his
blue, but converted it into the splendid aldehyde green. Like other colour-
ing matters we have described, this is a salt of a colourless base containing
sulphur. Like rosaniline, the colourless base takes on the characteristic
colour of its salts by merely absorbing, carbonic acid from the air.
Again, by a modification of the process for producing the Hofman violets,
another green of an entirely different constitution may be obtained. It is
bluer in tint than the former, and is much used for cotton and silks, under
the name of " iodine green."
In' the manufacture of magenta there is formed a residuum or bye-product,
consisting of a resinous, feebly basic substance, from which Nicholson ob-
tained a dye, imparting to silk and wool a gorgeous golden yellow colour.
This dye cannot be obtained directly, but is always produced in greater or
less quantity when magenta is made on the large scale, and is separated
during the purification. By first dyeing the silk or wool with magenta, and
then with this dye, which is commercially known as " phosphine," brilliant
scarlet tints are obtained. The yellow colours have been found to be salts
of a base termed chrysaniline, a sort of chemical relative of rosaniline, as
may be seen in comparing the formulas which represent their constitution,
with which we place also the symbol for another substance obtained by
submitting rosaniline to the influence of nascent hydrogen. This body,
leucaniline, again yields rosaniline very readily when the hydrogen is re-
moved by oxidizing agents. It will be noticed that the three bodies form
a series the members of which differ only by H 2 , thus indicating their close
relationship.
C 20 H 17 N 3 Chrysaniline.
C 20 H 1Q N 3 Rosaniline.
C 20 H 21 N 3 Leucaniline.
Some idea will have been obtained from the foregoing particulars of
the great colour-supplying capabilities of aniline ; but we have not yet
exhausted the utility of this interesting substance. It is probable that the
letters on the page now under the reader's eye owe their blackness to an
aniline product. For after all the salts furnishing the lovely tints we have
mentioned have been extracted, there is in their manufacture a final
residuum, and from this an intense black is obtained, which is largely used
in the manufacture of printing-ink.
We have mentioned phenol as a substance yielding colours. Phenol is
the body now so well known as a disinfectant under the name of " carbolic
acid," a name given to it by its discoverer, Runge, who prepared it from
coal-tar, in 1834. Phenol forms colourless crystals, which dissolve to some
extent in water, and very readily in alcohol. It is a powerful antiseptic,
that is, it arrests the process of pul refaction in animal or vegetable bodies,
and it is also highly poisonous. The constitution of phenol is given by
the formula C 6 Hg OH, in which the reader will recognize the same group
of atoms already indicated as entering into the aniline derivatives. From
some of these phenol may in fact be obtained, and although it cannot be
formed directly from benzol, phenol can be made to furnish benzol. When
COAL-TAR COLOURS. 573
crude phenol is treated with a sulphuric acid and oxalic acid, a substance
is obtained which presents itself as a brittle resinous mass of a brown
colour, with greenish metallic lustre. This substance is called rosolic acid
by chemists, but in commerce it is known as aurine, and is used for dyeing
silk of an orange colour, which, however, is not very permanent. But by
heating rosolic acid with liquid ammonia, a permanent red dye is procured
which has been termed peonine, and has been much used for woollen goods.
But it lately had the reputation of exerting a poisonous action, producing
blistering and sores when stockings or other articles dyed with it were
worn in contact with the skin. It is now, therefore, less extensively em-
ployed. Coralline, another body identical with or very similar to the
former, is similarly prepared from rosolic acid by heating it with ammonia
under pressure.
Again, by heating coralline with aniline, a blue dye, known as " azurine,"
or "azuline," was formerly made in large quantities ; but it has been sup-
planted by the aniline blues already described.
When phenol is acted upon by nitric acid new compounds are produced,
standing in the same relation to phenol as nitro-benzol does to benzol. The
final result of the action of nitric acid on phenol is picric acid, called also
" carbazotic acid," and, more systematically, " tri-nitro-phenol ; " for it is
regarded as phenol in which three of the hydrogen atoms have been re-
placed by the group NO 2 thus, C 6 H 2 (NO a )3 OH. It forms bright yellow-
coloured crystals, and its solution readily imparts a bright pure yellow
colour to wool, silk, &c. It received the name of picric acid (iriKpos, bitter)
from the exceedingly bitter taste of even an extremely diluted solution. It
is said that picric acid is employed as an adulterant in bitter ale instead of
hops. Now, the colouring power of picric acid is so great, that even the
minute quantity which could be used to impart bitterness to beer is recog-
nizable by dipping a piece of white wool into the beer, when, if picric acid
be present, the wool acquires a clear yellow tint. Besides its employment
as a yellow, it is useful for procuring green tints by combination with the
blues. Picric acid again furnishes, by treatment with cyanide of potassium, a
deep red colour, consisting of an acid which, when combined with ammonia,
furnishes a magnificent colouring material which is, in fact, murexide, a
dye identical with the famous Tyrian purple of the ancients, and formerly
obtainable only from certain kinds of shell-fish.
Naphthaline another of the colour-yielding substances of coal-tar is,
like benzol, a hydro-carbon, but one belonging to quite another chemical
series. Its formula is C 10 H 8 , and it has an interest to chemists altogether
apart from its industrial uses, from having been the subject of the classic
researches of the French chemist, Laurent researches which resulted
in the introduction of new and fertile ideas into chemical science, con-
tributing largely to its rapid progress. Naphthaline forms colourless
crystals, which, like camphor, slowly volatilize at ordinary temperatures,
and are readily distilled in a current of steam. It is thus sufficiently vola-
tile to escape complete deposition in the condensers of the gas-works, and
to be partly carried over into the mains, where its collection occasions
some trouble. Nitric acid acts upon naphthaline in a manner analogous
to that in which it acts on benzol, forming nitro-naphthaline, which, in its
turn, submitted to the action of iron filings and acetic acid, is transformed
into a base called " naphthylamine." The salts of naphthylamine are
coloured products which, in some cases, have been found available as dyes.
There is a crimson colour, and a yellow largely used under the name of
574 COAL-TAR COLOURS.
"Manchester yellow," for imparting to silk and wool a gorgeous golden
yellow colour. Another coloured derivative of naphthaline, called " carmi-
naphtha," was discovered by Laurent in the course of his researches.
It would be easy to fill this volume with descriptions of the properties,
and modes of preparing the numerous colouring matters that have been
obtained from coal-tar products. In order to give the reader an idea of
the extent to which the tar products have been made to minister to our
sense of the beautiful, a list is here given of the principal colouring matters
from these sources that have been employed in the arts. The various
names under which a product has been commercially known are in most
cases given. It must be understood that the same name is frequently
applied to products chemically distinct, and some of the names which
appear as synonyms may also in reality indicate different substances.
. LIST OF COAL-TAR COLOURS.
I. COLOURS DERIVED FROM ANILINE AND TOLUIDINE.
Blues and Violets.
Mauve, aniline purple, Perkin's violet, violine, mauve, rosaniline, indisine,
&c.
Aniline blue, rosaniline blue, Hofman's blue, bleu de Paris, bleu de Lyons,
bleu de Mulhouse, bleu de Mexique, bleu de nuit, bleu lumiere, night
blue.
Hofman's blue.
Nicholson's blue, soluble blue.
Hofman's violet, rosaniline violet.
A long series of red and blue violets, bearing Hofman's name and distin-
guished in commerce by adding R or B, according to the redness or the
blueness of the tint, ranging from RRRR to BBBB.
Dahlia.
Toluidine blue.
Violet de Paris.
Mauvaniline.
Violaniline.
Regina blue, opal blue, bleu de Fayolle, violet de Mulhouse.
Britannia violet
Violet imperial.
And many others.
Reds.
Aniline red, new red, magenta, solferino, anileine, rouge", roseine, azaline.
Rubine, rubine imperial.
Chrysaniline red.
(The above are all salts of rosaniline.)
Xylidine, tar red, soluble red.
Yellows.
Chrysaniline, phosphine, aniline yellow, yellow fuschine.
Chrysotoluidine.
Dinaline.
Field's orange.
COAL-TAR COLOURS. 575
Greens.
Aldehyde green, aniline green, viridine, emeraldine.
Iodine green, iodide of methyl green, iodide of ethyl green.
Perkin's green.
Browns.
Havanna brown.
Bismarck brown, aniline brown, Napoleon brown, aniline maroon.
Greys and Blacks.
Aniline grey, argentine.
Argentine black.
II. COLOURS DERIVED FROM PHENOL.
Blues and Violets.
Isopurpuric acid, Grdnat
Azuline, azurine.
Reds.
Picramic acid.
Coralline, peonine.
Red coralline.
Yellows.
Picric acid, carbazotic acid.
Aurine, rosolic acid.
Green.
Chloropicrine.
Browns.
Picrate of ammonia.
Isopurpurate of potash.
Phenyl brown, phenicienne.
III. COLOURS DERIVED FROM NAPHTHALENE.
Reds.
Pseudoalizarine, naphthalic red.
Roseonaphthaline, carminaphtha.
Yellows.
Binitronaphthaline, naphthaline yellow, golden yellow, Manchester yellow.
And others.
The introduction of aniline colours into dyeing and calico-printing has
caused quite a revolution in these arts, the processes having become much
more simple, and the facilities for obtaining every variety of tint largely
increased. The arts of lithography, type-printing, paper-staining, &c.,
have also profited by the coal-tar colours. For such purposes the colour
57 6 COAL-TAR COLOURS.
is prepared by fixing it on alumina, a process in which much difficulty
was at first experienced, for the colours are themselves almost all of a
basic nature. The desired result is now attained by fixing them on the
alumina with tannic or benzoic acid. These lakes produce brilliant printing-
inks, which are extensively used. The aniline colours are also employed
for coloured writing-inks, tinted soaps, imitations of bronzed surfaces, and
for a variety of other purposes.
Not many years ago coal-tar was a valueless substance : it was actually
given away by gas-makers to any one who chose to fetch it from the
works. It was then " matter in the wrong place;" but Mr. Perkin's dis-
covery led to its -being put in the right place, and it has become the raw
material of a manufacture creating an absolutely new industry, which has
developed with amazing rapidity. This industry dates from only 1856,
and in 1862 the annual value of its products was more than ,400,000.
Dr. Hofman, in reporting on the coal-tar colours shown at the Paris Exhi-
bition of 1867, computed the value at that time at about ^1,250,000, al-
though the products were much cheaper than before. Large manufactories
have been established in Great Britain, in France, Germany, Switzerland,
America, and other countries. The possibility of such an industry is an
interesting illustration of the manner in which the progress made in any
one branch of practical science may lead to unexpected developments in
other quarters. The quantity of aniline obtained from coal-tar is very
small compared to the amount of coal used, as may be seen from the
following table, in which the respective weights of the various products
required in the manufacture of mauve are arranged as given by Mr.
Perkin for the produce of 100 Ibs. of coal.
Ibs. oz.
Coal loo o
Coal-tar 10 12
Coal-tar naphtha o 8|-
Benzol o 2|
Nitro-benzol o 4^
Aniline o 'z\
Mauve o oj
From this we may perceive that had not the manufacture of gas been
greatly extended, so as to yield a large aggregate produce of tar, the re-
quisite supply for the manufacture of aniline would not have been attain-
able ; and the industrial application of the previously worthless bye-product
reacts upon gas manufacture by cheapening the price of that commodity,
thus tending still more to extend its use.
Although anthracene has already been named as one of the colour-
producing substances found in coal-tar, we have not in the list of coal-tar
colours included the colouring matter which anthracene is capable of yield-
ing. The reason is that this case stands apart in some respects from the
rest. The colours derived from aniline and the other substances already
enumerated are instances of the production of bodies not found in nature
mauve, magenta, &c., do not, so far as we know, exist in nature. Their
artificial formation was a production of substances absolutely new. The
colour of which we have now to treat is, on the other hand, found in nature,
and from its occurrence in the rubia tinctoria^ the roots of that plant have
for ages been employed as a source of colour, and are well known in this
country as "madder." The plant is grown largely in Holland, in France,
COAL-TAR COLOURS. 577
in the Levant, and in the south of Russia.* Madder is used in enormous,
quantities for dyeing reds and purples : the well-known " Turkey red " is
due to the colouring matter of this root. The total annual value of the
madder grown is calculated to reach nearly 2| million pounds sterling.
More than forty years ago it was discovered that the madder- root yielded
a colouring substance, to which the name of " alizarine " was bestowed, from
alizari, the commercial designation of madder in the Levant. The aliza-
rine does not exist in the fresh root, but is produced in the ordinary pro-
cesses of preparing the root and dyeing with it, in consequence of a peculiar
decomposition or fermentation. Alizarine may be procured from dried
madder by simply submitting it to sublimation, when beautiful orange
needle-shaped crystals of alizarine may be obtained. It is nearly insoluble
in water, but readily dissolves in hot spirits of wine. Acids do not dissolve
it, but potash dissolves it freely, striking a beautiful colour ; with lime,
barytes, and oxide of iron, it forms purple lake, and with alumina a beauti-
ful red lake. According to Dr. Schunck, of Manchester, to whose investi-
gations we are indebted for much of our knowledge of madder, the root
contains a bitter uncrystallizable substance called " rubian," which, under
the action of certain ferments, and of acids and alkalies, is decomposed
into a kind of sugar, and into alizarine and other colouring matters. The
ferment, which in the process of extracting the colouring matter from the
roots causes the formation of alizarine, is contained in the root itself.
We have already seen how an investigation relating to a question of
pure chemical science accidentally led Mr. Perkin to the discovery of
mauve the precursor of the long range of beautiful colours already de-
scribed. The mode of artificially preparing alizarine, so far from being an
accidental discovery, was sought for and found in 1869 by two German
chemists, Graebe and Liebermann. The researches of these chemists were
conducted in a highly scientific spirit. Instead of making attempts to pro-
duce alizarine by trying various processes on first one body, then another,
to see if they could hit upon some tar product, or other substance, which
would yield the desired product, they began by operating analytically on
alizarine itself. Just as a mechanic ignorant of horology, required to make
a watch, would be more likely quickly to succeed in his task by taking a
watch to pieces to see how it is put together, than if he had tried all man-
ner of arranging springs and wheels until he hit upon the right way ; so
these chemists set themselves to take alizarine to pieces, in order to see
from what materials they might be able to put it together. They decom-
posed alizarine, and among the products found a hydro-carbon identical in
all its properties with anthracene.
Anthracene was discovered in coal-tar by Laurent in 1832, and its
properties were investigated by Anderson in 1862. It may be remarked
that such investigations were not conducted with a view to any industrial
uses of anthracene, but merely for the sake of chemistry as a science.
Certainly no one could have supposed at that time that the slightest rela-
tion existed between anthracene and madder. Anthracene is a white
solid hydro-carbon, which comes over only in the last stages of the distil-
lation of coal-tar, accompanied by naphthaline, from which it is easily
separated by means of spirits of wine, by which the naphthaline is readily
* The natural Order to which the madder plant belongs is interesting from the number of its
members which supply us with useful products. That valuable medicine, quinine, is obtained
from plants belonging to this family, as is also ipecacuanha, and other articles of the materia
medtca. Coffea arabica, which furnishes the coffee-berry, is another member.
37
57 8 COAL-TAR COLOURS.
dissolved, but the anthracene scarcely. Anderson, in 1861, discovered,
among other results, that anthracene, C 14 H 10 , by treatment with nitric
acid became changed into oxy-anthracene, C 14 H 8 O2 ; an d this reaction
we shall see is a step in the process of procuring alizarine from anthracene.
Phenol, as already mentioned, can be made to yield benzol, by a process
of deoxidization. With a view to similarly obtaining a hydro-carbon from
alizarine, Graebe and Liebermann passed its vapours over heated zinc
filings, and thus produced anthracene from alizarine. It now remained to
find a means of reversing this process, that is, so to act on anthracene as
to produce alizarine, and this was effected by treating anthracene with
bromine, forming a substance which, on fusing with caustic potash,
yielded alizarate of potash, from which pure alizarine resulted by treat-
ment with hydrochloric acid. A much cheaper method was, however,
necessary for manufacturing purposes, and it was found in a process by
which oxy-anthracene, C 14 O 8 H 2 , is treated at a high temperature with
strong sulphuric acid, and the product so formed heated with a strong
solution of potash, yielding alizarate of potassium as before. Many other
interesting substances appear to be formed in the reactions, but the nature
of these bodies has as yet been imperfectly investigated. No doubt what-
ever can be entertained of the identity of natural with artificial alizarine ;
and the production of this substance, the first instance of a natural colour-
ing matter made artificially, may be regarded as a great triumph of
chemical science. It was not long ago supposed that the chemical bodies
found in plants or animals, or produced by vital actions, could not possibly
be formed by any artificial process from their elements. The laws which
presided at their formation were, it was conceived, wholly different from
those which governed the chemicals of the laboratory, for they were held
to act exclusively under the influence of a mysterious agent, namely, " vital
force." It was supposed, for example, that from pure carbon, oxygen, and
hydrogen, no chemist would ever be able to produce such a compound as
acetic acid. Accordingly the domain of chemical science, previous to the
end of the first quarter of the present century, was divided by an impass-
able barrier into the two regions of organic and inorganic chemistry. Now,
however, the chemist is able to build up in his laboratory from their very
elements a great number of the so-called organic bodies. And it is quite
possible to do this in the case of alizarine ; that is, a chemist having in
his laboratory the elements, hydrogen, carbon, oxygen, &c., could actually
build up the substance which gives its value to madder.
The quantity of anthracene procurable from coal-tar is, unfortunately,
comparatively small, for it is found that from the distillation of 2,000 tons
of coal only one ton of anthracene can be obtained. The use of artificial
alizarine would doubtless entirely supplant the employment of madder-
root if anthracene could be obtained in larger quantities ; and the change
would be highly advantageous to this country, for as no madder is grown
in Great Britain, and we consume nearly half the whole annual growth, it
follows that every year a million pounds sterling go out of the country for
this commodity. When anthracene is produced from coal in sufficient
abundance, this sum will be available for the support of our own popula-
tion. In the meantime, the manufacture of artificial alizarine is restricted
only by the supply of its raw material.
FIG. is?. James Prescott "Joule, F.R.S.
THE GREATEST DISCOVERY OF
THE AGE.
THE indulgent reader who may have followed the course of the fore-
going pages, will perhaps peruse the title of this article with some
little bewilderment. His attention has been drawn to one after another
of a series of remarkable and important discoveries, and he will naturally
wonder what can be the discovery which is greater than any of these.
Now, a discovery is great in proportion to the extent and importance of
the results that flow from it. These results may be immediate and practical,
as in the case of vaccination ; or they may be scientific and intellectual, as
in Newton's discovery of the identity of the force which draws a stone to
the ground with that which holds the planets in their orbits. Such dis-
coveries as most enlarge our knowledge of the world in which we live, by
embracing in simple laws a vast field of phenomena, are precisely those
which are most prolific in useful applications. If we admit, as we must,
the truth of Bacon's aphorism, which declares that " Man, as the minister
and interpreter of nature, is limited in act and understanding bv his obser-
579
580 THE GREATEST DISCOVERY OF THE AGE.
vation of the order of nature ; neither his understanding nor his power
extends farther,"* then it would be easy to show that the discovery of which
we have to treat, more than any other, must be of immense practical service
to mankind in every one of the ways in which a knowledge of the order of
nature can be of use, viz. : " First, In showing in how to avoid attempting
impossibilities. Second, In securing us from important mistakes in at-
tempting what is, in itself, possible, by means either inadequate or actually
opposed to the end in view. Third, In enabling us to accomplish our
ends in the easiest, shortest, most economical, and most effectual manner.
Fourth, In inducing us to attempt, and enabling us to accomplish, objects
which, but for such knowledge, we should never have thought of under-
taking." t
A great principle, like that which we are about to explain to the reader,
is too vast in its bearings for its discovery and elaboration. to have been
the work of an individual. This truth, and indeed the whole of our know-
ledge, is but the result of the development and growth of pre-existing
knowledge. In fact, every discovery, however brilliant every invention,
however ingenious, is but the expansion or improvement of an antecedent
discovery or invention. In strictness, therefore, it is impossible to say
where the first germ of even our newest notions may be found. Our latest
philosophy can be shown to be the result of progressive modifications of
ideas of remote ages. Hence every great truth, every grand invention,
has in reality been the offspring of many minds ; but we record as the
discoverers and inventors those men who have made the longest strides
in the path of progress, and whose genius and labours have overcome
obstacles defying ordinary efforts.
The extent of the field which is covered by the principle we have in view
is so vast embracing, as it does, the whole phenomena of the universe
that it will not be possible to do more within our limits than give the reader
a general notion of the principle itself. It may be useful to instance a
truth which has a similar generality and significance, and which has also
acquired the force of an axiom, because it is verified every hour. It is
that greatest generalization of chemistry, affirming that in all its transfor-
mations matter is indestructible, and can no more be destroyed than it can
be called into being at will. This truth is so well established, that some
philosophers have asserted that an opposite state of things is inconceivable.
But it was not always known ; and there are at the present day untutored
minds which not only believe that a substance destroyed by fire is utterly
annihilated, but what they find inconceivable is the continued existence of
the substance in an invisible form. The candle burns away, its matter
vanishes from our view; but if we collect the invisible products of the com-
bustion, we find in them the whole substance of the candle in union with
the atmospheric oxygen. We may, in imagination, follow the indestructible
atoms of carbon in their migrations, from the atmosphere to the plant,
which is eaten by the animal and goes to form its fat, and from the tallow,
by combustion, back into the atmosphere again. The notion of the real
identity of matter under changing forms has been expressed by our great
dramatist in a well-known passage, which is remarkable for its philosophic
insight, when we consider the age in which it was written :
" Homo naturae minister et interpres, tantum facit et intelligit quantum de naturae ordine re
vel mente observaverit : nee amplius scit aut potest." Novum Organum, Afihor. i.
1Sir J. Hersche'.
THE ORE A TEST DISCO VER Y OF THE AGE. 581
HAMLET. To what base uses we may return, Horatio ! Why may not imagination trace the
noble dust of Alexander, till he find it stopping a bung-hole ?
HORATIO. 'Twere to consider too curiously to consider so.
HAMLET. No, faith, not a jot; but to follow him thither with modesty enough, and likelihood
to lead it. As thus : Alexander died, Alexander was buried, Alexander returneth to dust ; the
dust is earth ; of earth we make loam ; and why of that loam, whereto he was converted, might
they not stop a beer-barrel ?
Imperial Caesar, dead, and turned to clay,
Might stop a hole to keep the wind away ;
O, that the earth, which kept the world in awe,
Should patch a wall to expel the winter's flaw !
Now the greatest discovery of our age is that force, like matter, is inde-
structible, and that it can no more be created than can matter. The
reader may perhaps think the statement that we cannot create force is in
contradiction to experience. He will be disposed to ask, What is the steam
engine for but to create force ? Do we not gain force by the pulley, the
lever, the hydraulic press ? And are not tremendous forces produced when
we explode gunpowder or nitro-glycerine ? When the principle with which
we are here concerned has been developed and stated in accurate terms, it
is hoped the reader will see the real nature of these contrivances. We are,
however, aware that it is quite impossible within the limits of a short article
to do much more than indicate a region of discovery abounding with results
which may be yet unfamiliar to some. Into this, if so minded, they should
seek for further guidance, which they will pleasantly find in the pages of
Dr. Tyndall's " Heat considered as a Mode of Motion," and in a little work
by Professor Balfour Stewart, entitled " The Conservation of Energy," and
quite fascinating from the clearness and simplicity of its style. We may
continue our humble task of merely illustrating the general nature of this,
in reality the most important, subject which we have had occasion to bring
under the reader's notice.
Perhaps the first step should be to point out the fact of the various
forces of nature mechanical action, heat, light, electricity, magnetism,
chemical action being so related that any one can be made to produce
all the rest directly or indirectly. Some examples of the conversion of
one form of force into another occur in the foregoing pages. Thus, on
page 363 an experiment is described in which electricity produces a mecha-
nical action ; electricity is also shown, on page 374, to produce heat ; on
page 376 chemical action ; on page 378 magnetism. Then, as instances of
the inverse actions, there is on page 366, in the first paragraph on " Electric
Induction," an account of the mode in which mechanical movements may
give rise to electricity; and in the experiments in pages 385, 386, and
particularly in the account of the Gramme machine, page 388, it is shown
how mechanical movements can, through magnetism, produce electricity.
The voltaic element, page 369, and the galvanic batteries, are instances of
chemical action supplying electricity. On page 325 a striking instance is
mentioned of changes in the forms of force. Every lighted candle is a
case of chemical action giving rise to light ; and interesting examples of the
inverse relation are referred to on page 447. On page 116 is represented
the conversion of arrested motion into heat and light. We have, indeed,
sufficient examples to arrange a series of these conversions of forces in a
circle. Thus, chemical action (oxidation in the animal system) supplies
muscular power, this sets in motion a Gramme machine, the motion is con-
verted into electricity, the electricity produces the electric light, and light
causes chemical action, and with this the cycle is complete. In the steam
engine heat is converted into mechanical force, and many cases will pre-
582 THE GREATEST DISCOVERY OF THE AGE.
sent themselves to the reader's mind in which mechanical actions give rise
to heat. The doctrine of a mutual dependence and convertibility among
all the forms of force was first definitively taught in England by Mr. (now
Justice) Grove, in 1842 ; and almost simultaneously Dr. Meyer promulgated
similar views in Germany. Mr. Grove subsequently embodied his doctrine
in a treatise, called " The Correlation of the Physical Forces," which has
seen several editions.
But this teaching included much more than a mere connection between
the various forces, for it extended to quantitative relations. It declared
that a given amount of one force always produced a definite amount or
another . that a certain quantity of heat, for example, would give rise to
a certain amount of mechanical action, and that this amount of mechanical
action was the equivalent of the heat which produced it, and would in its turn
reproduce all that heat. These last doctrines, however, rested on a specula-
tive basis, until Mr. James Prescott Joule, of Manchester, carried out a most
patient, laborious, and elaborate experimental investigation of the subject.
His labours placed the truth of the numerical equivalence of forces on a
foundation which cannot be shaken ; and he accomplished for the principle
of the indestructibility of force what Lavoisier did for that of the inde-
structibility of matter he established it on tha incontrovertible basis of
accurate and conclusive experiment. His determination of the value of
the mechanical equivalent of heat especially is a model of experimental
research ; and subsequent investigators have, by diversified methods, con-
firmed the accuracy of his results. A great part of his work consisted in
finding what quantity of heat would be produced by a given quantity of
work.
Before we proceed to give an indication of one of Dr. Joule's methods of
making this determination, we may point out that if a weight be raised a
certain height, the work which is done in raising it will be given out by the
weight in its descent. If you carry a I Ib. weight to the top of the London
Monument, which is 200 ft. high, you perform 200 units of work. When the
weight is at the top, the work is not lost ; for let the weight be attached
to a cord passing over a pulley, and it will, as it descends, draw up to the
top another i Ib. weight. If you drop the weight so that it falls freely, it
descends with a continually increasing velocity, strikes the pavement, and
comes to rest. Still your work is not lost. The collision of the weight and
the pavement develops heat, just as in the case of the experiment depicted
on page 116, but to a less degree the increase of temperature might not
be sensible to the touch, but could be recognized by delicate instruments.
Your work, then, has now changed into the form of heat the weight and
the pavement are hotter than before. This heat is carried off by contigu-
ous substances. But still your work is not lost, for it has made the earth
warmer. The heat, however, soon flows away by radiation from the earth,
and is diffused into space. The final result of your work is, then, that a
certain measurable quantity of heat has been sent off into space. Is your
work now finally lost ? Not so : in reality, it is only diffused throughout
the universe in the form of radiant heat of low intensity. Yet it is lost for
ever for useful purposes ; for from this final form of diffused heat there is
no known or conceivable process by which heat can be gathered up again.
Dr. Joule arranged paddles of brass or iron, so that they could turn freely
in a circular box containing water or quicksilver. From the sides of the
box partitions projected inwards, which contained openings that permitted
the divided arms of the paddle to pass, and preventing the liquid from,
7 HE GREATEST DISCOVERY OF THE AGE. 583
moving en masse, thus caused a churning action when the paddle was
turned. Now, every one who has worked a rotatory churn knows that a
considerable resistance is offered to this action ; but every one does not
know that under these circumstances the liquid becomes warmer. It was
Dr. Joule's object to discover how much the temperature of his liquid was
raised by a measured quantity of work. He used very delicate thermo-
meters, and had to take a number of precautions which need not here be
described ; and he obtained the definite quantity of work by the descent of
a known weight through a known distance, a cord attached to the weight
being wound on a drum, which communicated motion to the paddle. The
experiments were conducted with varying circumstances, to avoid chances
of error, and were repeated very many times until uniform and consistent
indications were always obtained. The result of the experiments showed
that 772 units of work (foot-pounds) furnished heat which would raise the
temperature of I Ib. of water from 32 to 33 F., which is the unit of heat.
This number, 772, is a constant of the greatest importance in scientific and
practical calculations, and is called " the mechanical equivalent of heat"
The amount of work it represents is sometimes called a " Joule," and is
always represented in algebraical formulas by " J." Mr. Joule's first paper
appeared in 1843, an d soon afterwards various branches of the subject of
" The Equivalence and Persistence of Forces " were taken up by a number
of able men, who have advanced its principles along various lines of inquiry.
Among the most noted contributors to this question we find the names of
Sir William Thompson, Helmholtz, James Thomson, Rankin, Clausius,
Tait, Andrews, and Maxwell.
In the steam engine the case is the inverse of that presented by the above-
named experiment of Dr. Joule's. Here we have heat producing work.
Now, the quantity of steam which enters the cylinder of a steam engine
may be found, and the temperature of the steam can be determined, and
from these the amount of heat which passes into the cylinder per minute,
say, can be calculated. A large portion of this heat is, in an ordinary
engine, yielded up to the condensing water, and another part is lost by
conduction and radiation from the cylinder, condenser, pipes, &c. But
both these quantities can be estimated. When the amount is compared
with that entering the cylinder in the steam, a difference is always found,
which leaves a quantity of heat unaccounted for. When this quantity is
compared with the work done by the engine in the same interval (which
work can be measured as described on page 10), it is always found that for
every 772 units of work a unit of heat has disappeared from the cylinder.
The numerical relation between work and heat which is established in
these two cases has been tested in many quite different ways ; and, within
the limits of experimental errors, always with the same numerical result.
But equally definite quantitative relations are known to exist among all
the other forms of force ; and the manner in which these are convertible
into each other has already been indicated, although want of space prevents
full illustration of this part of the subject. It may, however, be seen that
each form of force can be mediately or immediately converted into mecha-
nical effect, hence each is expressible in terms of work. That is to say, we
can assign to a unit of electricity, for example, a number expressing the
work which it would do if entirely converted into work ; and the same
number also expresses the work which would be required to produce the
unit of electricity. An ounce of hydrogen in combining with 8 oz. of oxy-
gen produces a certain measurable quantity of heat. If that heat, say = H,
584 THE GREATEST DISCOVERY OF THE AGE.
were all converted into work, we now know that the work would = H J.
Hence we can express a definite chemical action in terms of work. The
same is generally true of all physical forces, though in some cases, such as
light, vital action, &c, the quantitative relations have not yet been defi-
nitely determined.
Since, then, all the forces with which we are acquainted are expressible
(though the exact relations of some have yet to be discovered) in terms of
work, it is found of great advantage to consider the power of doing work
as the common measure of doing all these. Thus, if we define energy as
that which does, or that which is capable of doing, work, we have a term
extremely convenient in the description of some aspects of our subject.
Thus we can now speak of the energies of nature, instead of the forces.
And all forces, active or passive, may be summed up in one word energy.
And, further, the great discovery of the conservation of forces under definite
equivalents, may be summed up very briefly in this statement THE AMOUNT
OF ENERGY IN THE UNIVERSE IS CONSTANT. To make this statement
clear requires that a distinction between two forms of every kind of energy
be pointed out To recur to the example before imagined : if you carry the
i Ib. weight up the Monument, and deposit it on the ledge at the top, it
might lie there for a thousand years before it was made to give back the
work you had performed upon it. That work has been, in a'manner, stored
up by the position you have given to your weight. Now, in taking up the
weight, you expended energy you really performed work : that is an in-
stance of energy in operation, and may be termed " actual energy." In
what form does the energy exist during the thousand years we may suppose
your weight to lie at the top of the Monument ? It is ready to yield up
your work again at any moment it is permitted to descend, and it possesses
therefore during the whole period a potential energy equal in amount to
the actual energy you bestowed upon it. A similar distinction between
actual and potential energy exists with regard to every form of force. If
by any means you separate an atom of carbon from an atom of oxygen,
you exert actual energy. The process is analogous to carrying up the
weight. The atoms when separated possess potential energy, they can
rush together again, like the weight of the earth, and in doing so will give
out the work which was expended on their separation. A parallel illustra-
tion might be drawn from electrical force.
A typical example of the storing up of energy is furnished by a cross-
bow. The moment a man begins to bend the bow he is doing work, be-
cause he pulls the string in opposition to the bow's resistance to a change
in its form ; and it is plain that the amount of energy thus expended is
measurable. Suppose, now, the bow has been bent and the string caught
in the notch, from which it is released by drawing the trigger when the
discharge of the bow is desired. The bow may be retained for an indefi-
nite period in the bent condition, and in this state it possesses, in the form
of potential energy, all the work which has been expended in bending it,
and which it will, in fact, give out, in some way or other, whenever the
trigger is drawn. To fix our ideas, let us suppose that to draw the string
over the notch required a pull of 50 Ibs. over a space of 6 in. ; that is equi-
valent to 50X^ = 25 units of work. Now let the bow be used to shoot an
arrow weighing \ Ib. vertically upwards. The height in feet to which the
arrow will rise multiplied into its weight in pounds will be the work done
upon it by the bow. Now, we say that experiment proves that in the case
supposed the arrow would rise just 100 ft., so that the work done by the
THE GREATEST DISCOVERY OF THE AGE. 585
bow (f X 100= 25) would be precisely that done upon it. For the sake of
simplicity, we keep this illustration free from the mention of interfering
causes, which have to be considered and allowed for when the matter is
put to the real test of quantitative experiment. The instance of the cross-
bow brings into notice a highly instructive circumstance, which is this :
the bow, which it may have taken the strength of a Hercules to bend, will
shoot its bolt by the mere touch of a child on the trigger. In the same
way, when a man fires a gun, he merely permits the potential energy con-
tained in the charge to convert itself into actual, or kinetic, energy. The
real source of the energy, in the case of the child discharging the cross-
bow, is the muscular power of the man who drew it ; the real source of the
energy in exploding gunpowder is the separation of carbon atoms from
oxygen atoms, and that has been done by the sun's rays, as truly as the
string was pulled away from the bow by muscular power. If we turn our
attention to nitro-glycerine or to nitro-cellulose, we can, by following the
chemical actions giving rise to these substances, in like manner trace their
energies to our great luminary. The unstable union by which oxygen and
nitrogen atoms are locked up in the solid and liquid forms of nitro-cellu-
lose and nitro-glycerine is also the work of the sun ; for nitrogen acids, or
rather nitrates, are produced naturally under certain electrical and other
conditions of the atmosphere, which are due, directly or indirectly, to the
sun's action ; and they cannot be formed artificially, except by imitating
the natural conditions, as by passing electric sparks through air, &c.
It will now be understood, as regards the wonderful relations between
animal and vegetable life, which have already been alluded to more than
once, how the sun, by expending actual energy, separates atoms of carbon
from atoms of oxygen in the leaves of plants, and confers upon these a posi-
tion of advantage, i.e., potential energy; and how animals, absorbing the
separated carbon in the form of food, and inhaling the separated oxygen
in the air they breathe, cause the conversion of the potential into actual
energy, which appears in the heat, movements, and vital functions of the
animal body. In coal we have the energy which plants absorbed from the
sun ages ago, stored up in a potential form. The carbon atoms are ready
to rush into union with oxygen atoms, and convert their energy of position
into the energies developed by chemical action, viz., heat, light, &c.
Energy is thus constantly shifting its form from actual to potential, and vice
versa, and exhibiting itself under the various transformations of force, as
when sun-force changes to chemical action, chemical action to heat, heat
to electricity, &c. Energy is, indeed, the real modern PROTEUS constantly
assuming different shapes, difficult to grasp if not held in fetters; now
taking on the form of a lion, now of a flame of fire, a whirlwind, a rushing
stream. As sober, literal matter of fact we catch glimpses of energy under
these very forms.
The greatest discovery of the age has, as already indicated, immediate
and important practical bearings. The amount of thought which, even in
the present day, is devoted by unscientific mechanics to the old problem
of perpetual motion is far greater than is generally supposed. The principle
of the conservation of energy shows that this is an impossibility ; that the
inventor who seeks to create force might just as well try to create matter ;
that the production of a perpetually moving self-sustaining machine is as
far removed from human power as the bringing into existence of a new
planet. In force, as in matter, the law is inexorable ex nihilo nihil fit.
Again, knowing the definite amount of energy obtainable from the combus-
586 THE GREA TEST DISCO VER Y OF THE A GE.
tion of a pound of coal, we can compare the amount we actually procure
from it in our steam engines with this theoretical quantity as the limit to-
wards which our improvements should bring us continually nearer, but
which we can never exceed, or, indeed, even reach. The schemers of
perpetual motion are not the only class of speculators who pursue objects
which are incompatible with our principle. There are many who seek to
accomplish desirable ends by inadequate means : who, for example, are
aiming perhaps to accomplish the reduction of ores by a quantity of fuel
less than that mechanically equivalent to the work, or who conceive that
by adding to coal some substance which itself is unchanged, an indefinitely
greater amount of heat may be liberated by the combustion.
Enough has been said to show that the energies of animal life can be
traced to the sun as their source. The sun builds up the plant, separating
oxygen from carbon. The animal directly or mediately by devouring other
animals takes the carbonaceous matter of the plant, and reunites it with
oxygen. In" the plant the sun winds up the spring which gives life to the
animal mechanism ; for the winding-up of a spring and the separation of
the atoms having chemical affinities are alike instances of supplying poten-
tial energy. In the animal there is a running-down of the potential into
actual energy. It is plain also that of the total energy radiated from the sun
in every direction, the earth receives but a very small part (^^oogbooou)'
By far the larger part is diffused into space, where, for all such purposes
as those with which we are concerned, it is lost. The heat which the sun
sends out in a year is calculated to be equal to that which would be pro-
duced by the combustion of a layer of coal 17 miles thick over the whole
surface of the luminary. Is the sun, then, a flaming fire? By no means.
Combustion is not possible at its temperature ; and as we know the sub-
stances which enter into its composition are the same as those we find in
the earth, we know that the chemical energies of such substances could not
supply the sun's expenditure. Passing over as unsatisfactory an explana-
tion which might occur to some minds namely, that the sun was created
hot at the beginning, and has so continued there are two theories which
attempt to account for the sun's heat. One is that of Meyer, who supposes
the heat is due to the continual impact of meteorites drawn to the sun by
its gravity ; and the other is that of Helmholtz, who attributes the heat to
the continual condensation of the substance of the sun. Helmholtz calcu-
lates that a shrinking of the sun's diameter by only T ooTjth of its present
amount, would supply heat to last for two thousand years ; while the con-
densation of the substance of the sun to the density of the earth would
cover the sun's expenditure for 17,000,000 of years. There is great proba-
bility that both theories may be correct, and that the cause of the sun's
heat may be considered as due in general terms to aggregation of matter,
by which the original potential energy of position is converted into the
actual energy of heat and light. Now, however immense may be our plane-
tary system, the sun being continually throwing off this energy into space,
there must come a time when the supplies of meteorites will fail, and when
the great globe of the sun will have shrunk to its smallest dimensions. We
see, then, that heat and light are produced by the aggregation of matter ;
the heat and light are radiated into space ; the small fraction intercepted
by our globe is the source of almost every movement the original stuff, so
to speak, out of which all terrestrial forces are made. The sun produces
the winds, the thunderstorms, the electric currents of the Aurora, the phe-
nomena of terrestrial magnetism, and is the source of vegetable and animal
THE GREATEST DISCOVERY OF THE AGE. 587
life. The waves, the rains, the mountain torrents, the flowing rivers, are
the work of the sun's emanations.
In the illustration of the energy expended on raising a weight afterwards
dropped, we traced that energy into the final form of heat of a low tempera-
ture radiated into space. It would be easy to show that all energy ultimately
takes the same form. Now, although it is easy to convert work into heat,
there is no conceivable process by which uniformly-diffused heat can again
be made to do any kind of work. The case may be compared to water,
which in moving down from a higher to a lower level may be made to per-
form any variety of work. But when all the water has passed down from the
higher level to the lower, it can no longer do any work. Whenever work is
done by the agency of heat, there is always a passing from a higher tempera-
ture to a lower a transference of heat from a hotter body to a colder. If
the condenser of the steam engine had the same temperature as the stea'm,
the machine would not work. Not only do all the energies in operation on
the face of the earth continually run down into the form of radiant heat
sent off by the earth into space ; but our sun's energy, and that of the suns
of other systems, are also continually passing off into space ; and the final
effect must be a uniform diffusion of heat in a universe in which none of
the varied forms of energy we now behold in operation will be possible,
because all will have run down to the same dead level of uniformly-diffused
heat. This startling corollary from the principle of the conservation of
energy has been worked out by Sir W. Thompson under the title of " The
Dissipation of Energy." It leads us to contemplate a state of things in
which all light and life will have passed away from the universe a con-
dition which the poet's terrible dream of darkness, " which was not all a
dream," seems to shadow forth
" The bright sun was extinguished, and the stars
Did wander darkling in the eternal space,
Rayless and pathless ; and the icy earth
Swung blind and blackening in the moonless air.
******
The world was void,
The populous and the powerful was a lump,
Seasonless, herbless, treeless, manless, lifeless
A lump of death a chaos of hard clay.
The rivers, lakes, and ocean all stood still,
And nothing stirred within their silent depths.
* * * * * *
The waves were dead ; the tides were in their grave,
The Moon, their mistress, had expired before ;
The winds were withered in the stagnant air,
And the clouds perished ; Darkness had no need
Of aid from them She was the Universe."
The doctrine of this persistence and dissipation of energy completely
harmonizes with the grand speculation termed the " nebular hypothesis,"
which regards the universe as having originally consisted of uniformly dif-
fused matter, which, being endowed with the power of gravitation, aggregated
round certain centres. This process is still going on ; and, according to
modern speculations, light and life and motion are but manifestations of
this primaeval potential energy being converted into actual energy, and
degrading ultimately into the form of universally-diffused heat. To quote
the closing sentences of the eloquent passage in which Professor Tyndall
concludes the work mentioned above, " To nature nothing can be added,
from nature nothing can be taken away ; the sum of her energies is con-
stant, and the utmost man can do in the pursuit of physical truth, or in the
586 THE GREATEST DISCOVERY OF THE AGE.
tion of a pound of coal, we can compare the amount we actually procure
from it in our steam engines with this theoretical quantity as the limit to-
wards which our improvements should bring us continually nearer, but
which we can never exceed, or, indeed, even reach. The schemers of
perpetual motion are not the only class of speculators who pursue objects
which are incompatible with our principle. There are many who seek to
accomplish desirable ends by inadequate means : who, for example, are
aiming perhaps to accomplish the reduction of ores by a quantity of fuel
less than that mechanically equivalent to the work, or who conceive that
by adding to coal some substance which itself is unchanged, an indefinitely
greater amount of heat may be liberated by the combustion.
Enough has been said to show that the energies of animal life can be
traced to the sun as their source. The sun builds up the plant, separating
oxygen from carbon. The animal directly or mediately by devouring other
animals takes the carbonaceous matter of the plant, and reunites it with
oxygen. Iri the plant the sun winds up the spring which gives life to the
animal mechanism ; for the winding-up of a spring and the separation of
the atoms having chemical affinities are alike instances of supplying poten-
tial energy. In the animal there is a running-down of the potential into
actual energy. It is plain also that of the total energy radiated from the sun
in every direction, the earth receives but a very small part (^oooVoorra)'
By far the larger part is diffused into space, where, for all such purposes
as those with which we are concerned, it is lost. The heat which the sun
sends out in a year is calculated to be equal to that which would be pro-
duced by the combustion of a layer of coal 17 miles thick over the whole
surface of the luminary. Is the sun, then, a flaming fire? By no means.
Combustion is not possible at its temperature ; and as we know the sub-
stances which enter into its composition are the same as those we find in
the earth, we know that the chemical energies of such substances could not
supply the sun's expenditure. Passing over as unsatisfactory an explana-
tion which might occur to some minds namely, that the sun was created
hot at the beginning, and has so continued there are two theories which
attempt to account for the sun's heat. One is that of Meyer, who supposes
the heat is due to the continual impact of meteorites drawn to the sun by
its gravity ; and the other is that of Helmholtz, who attributes the heat to
the continual condensation of the substance of the sun. Helmholtz calcu-
lates that a shrinking of the sun's diameter by only T7 njut)th of its present
amount, would supply heat to last for two thousand years ; while the con-
densation of the substance of the sun to the density of the earth would
cover the sun's expenditure for 17,000,000 of years. There is great proba-
bility that both theories may be correct, and that the cause of the sun's
heat may be considered as due in general terms to aggregation of matter,
by which the original potential energy of position is converted into the
actual energy of heat and light. Now, however immense may be our plane-
tary system, the sun being continually throwing off this energy into space,
there must come a time when the supplies of meteorites will fail, and when
the great globe of the sun will have shrunk to its smallest dimensions. We
see, then, that heat and light are produced by the aggregation of matter ;
the heat and light are radiated into space ; the small fraction intercepted
by our globe is the source of almost every movement the original stuff, so
to speak, out of which all terrestrial forces are made. The sun produces
the winds, the thunderstorms, the electric currents of the Aurora, the phe-
nomena of terrestrial magnetism, and is the source of vegetable and animal
THE GREATEST DISCOVERY OF THE AGE. 587
life. The waves, the rains, the mountain torrents, the flowing rivers, are
the work of the sun's emanations.
In the illustration of the energy expended on raising a weight afterwards
dropped, we traced that energy into the final form of heat of a low tempera-
ture radiated into space. It would be easy to show that all energy ultimately
takes the same form. Now, although it is easy to convert work into heat,
there is no conceivable process by which uniformly-diffused heat can again
be made to do any kind of work. The case may be compared to water,
which in moving down from a higher to a lower level may be made to per-
form any variety of work. But when all the water has passed down from the
higher level to the lower, it can no longer do any work. Whenever work is
done by the agency of heat, there is always a passing from a higher tempera-
ture to a lower a transference of heat from a hotter body to a colder. If
the condenser of the steam engine had the same temperature as the stea'm,
the machine would not work. Not only do all the energies in operation on
the face of the earth continually run down into the form of radiant heat
sent off by the earth into space ; but our sun's energy, and that of the suns
of other systems, are also continually passing off into space ; and the final
effect must be a uniform diffusion of heat in a universe in which none of
the varied forms of energy we now behold in operation will be possible,
because all will have run down to the same dead level of uniformly-diffused
heat. This startling corollary from the principle of the conservation of
energy has been worked out by Sir W. Thompson under the title of " The
Dissipation of Energy." It leads us to contemplate a state of things in
which all light and life will have passed away from the universe a con-
dition which the poet's terrible dream of darkness, " which was not all a
dream," seems to shadow forth
" The bright sun was extinguished, and the stars
Did wander darkling in the eternal space,
Rayless and pathless ; and the icy earth
Swung blind and blackening in the moonless air.
****
The world was void,
The populous and the powerful was a lump,
Seasonless, herbless, treeless, manless, lifeless
A lump of death a chaos of hard clay.
The rivers, lakes, and ocean all stood still,
And nothing stirred within their silent depths.
* * * * *
The waves were dead ; the tides were in their grave,
The Moon, their mistress, had expired before ;
The winds were withered in the stagnant air,
And the elouds perished ; Darkness had no need
Of aid from them She was the Universe. "
The doctrine of this persistence and dissipation of energy completely
harmonizes with the grand speculation termed the " nebular hypothesis,"
which regards the universe as having originally consisted of uniformly dif-
fused matter, which, being endowed with the power of gravitation, aggregated
round certain centres. This process is still going on ; and, according to
modern speculations, light and life and motion are but manifestations of
this primaeval potential energy being converted into actual energy, and
degrading ultimately into the form of universally-diffused heat. To quote
the closing sentences of the eloquent passage in which Professor Tyndall
concludes the work mentioned above, " To nature nothing can be added,
from nature nothing can be taken away ; the sum of her energies is con-
stant, and the utmost man can do in the pursuit of physical truth, or in the
5 88 THE GREATEST DISCOVERY OF 7 HE AGE.
applications of physical knowledge, is to shift the constituents of the never-
varying total. The law of conservation rigidly excludes both creation and
annihilation. Waves may change to ripples, and ripples to waves ; mag-
nitude may be substituted for number, and number for magnitude ; aste-
roids may aggregate to suns, suns may resolve themselves into florae and
faunae, and florae and faunae melt in air : the flux of power is eternally the
same. It rolls in music through the ages, and all terrestrial energy the
manifestations of life as well as the display of phenomena are but the
modulations of its rhythm."
The discoveries to which we have here endeavoured to attract the reader's
attention thus give rise to conceptions of the utmost grandeur and interest.
We see that the sum of Nature's energies is constant ; that all the mani-
festations of force are but the transference of power from one position to
another. And we have recognized the material source of all our terrestrial
energies in the sun. It is but the small fraction of the total energy pour-
ing from our luminary that reaches us, yet it suffices to maintain the life of
the globe. It is the energy indirectly derived from the sun which drives
our steam engines, impels the missiles from our guns, wafts our ships over
the ocean, and blasts the rocks for our roads and mines.
INDEX.
Abel, Professor, 530, 535
Adhesion of locomotive, 18
Advantages of present age, 2
Air, 523
Albert Bridge, Saltash, 194
Alizarine, 577
Aluminium, 507
bronze, 510
Ampere's hypothesis, 545
Ampere's rule, 370, 399
Amphioxus 490
Anaesthetics, 520
Anemometer, 475
Angle, limiting, or critical, 285
Aniline, 567
black, 572
blue, 570
green, 571
purple, 568
Anthea cereus, 489
Anthracene, 576, 577
Applegath printing machine, 208
and Cowper, ditto, 204
Apps's anemometer, 475
induction coil, 383
Aquaria, 484
Arago, 440
Argand gas-burners, 558
lamps, 436
Armour, ships', strengths of, no
Armstrong's, Sir W., guns, 118
- hydraulic crane, 229
Atoms, 522, 532
Aurora, 382
Australian gold, 497
Austrian torpedoes, 149
Axolotl, 495
Bacon, Francis, 579
Baxter House experiments, 36
Bell Rock lighthouse, 434
Bells, electro-magnetic, 404
Benzol, 563
Bessemer, 22, 25
Channel steimer, 93
converter, 38
iron, 36
steel, 37
Blanchard lathe, 54
Blast furnace, 28
Blind spot in eye, 341
Blood spectra, 318
Blowing apparatus, 31
Boilers of steam engines, 13
Boring for coals, &c., 257
Bourdon's pressure gauge, 12
Box girders, 191
Breech-loading rifles, 131
Brewster, Sir D., 291, 306, 350, 354
Brighton Aquarium. 491
Britannia Bridge, 191
. raising tubes. 232
Browning microspectroscopes, 320
spectroscope, 308, 318
Brunei, 194
Bullets, explosive, 145
, machinery for making, 226
Bunsen and Kirchhoff, 308
and Roscoe, 512
Bunsen's battery, 374
burner, 307, 557
Caesium, 312
Calico printing machines, 217
California, discovery of gold in. 497
"Cape Horn," 78
Captain, H.M.S., 106
Carbonic oxide, 29, 31
Carcel lamp, 436
Carpenter. Dr. W. B., 342
Carriages, railway, 69
for rock drills, 254
Carriers in pneumatic tubes, 240
Cars, Pullman, 70
Castalia, steamship, 96
Cast iron, composition of, 30
Catoptric lighthouse apparatus, 438
Cause of light and colour, 294
Celestial Chemistry and Physics 322
Central Telegraph Office, London, 424
Centres of gravity and buoyancy, 109
Centrifugal force, 65
Chains, 226
Chain-testing machine, 225
Channel Tunnel, the, 260
Chassepot rifle, 135
Chemical action ot' light, 447
equations, 523
nomenclature, 562
symbols, 522
work of electricity, 375
Chloroform, 525
Chromatic aberration of eye, 342
Chromo-lithography, 465
Chronograph) _ Wfr ,v ...
Chronoscope j electnc 475
Cincinnati Suspension Bridge, 198
Clarke, hydraulic lift graving dock, 227
Clay process, stereotyping by, 460
Clifton Suspension Bridge, near Bristol, 196
, Niagara, 198
Coal, 537
Coal-gas, 550
Coal-tar colours, 561
Code, telegraphic, of American War Dept., 407
, Morse's, 410
-, Wheatstone's dot, 415
Colesberg, 503
Cold-short iron, 35
Collodion process, 457
589
59
INDEX.
Colours not in the objects, 290
Colour printing, 466
Comets, spectra of, 330
Composition, rollers, 292
Condie's steam-hammer, 24
Copying principle, 44
Corona, 324
Couple, mechanical, 109
Cramp gauge, 63
Crystalline lens, 335
Crystal Palace, an example of use of iron in
architecture. Plate II.
Crystal Palace Aquarium, 486
Cup and cone, 31
Current, electric, 370
, induced, 380
Currents in submarine cables, 429
Daguerre, 448
Daguerreotype, 449
Dallmeyer, 456
Daniell's battery, 373
Delphi, oracle at, 528
Dial telegraphs, 416
Diamondiferous, 504
Diamond rock drill, 255
Diamonds, 501
Dioptric lighthouse apparatus, 439
D lines of sodium spectrum, 311, 322
Discoveries, progressive, 580
Dissipation of Energy, 586
Distinct vision, 338
Domestic consumption of coal, 541, 542
Double refraction and polarization, 285
Dowlais (Iron-works), 31, 34
Dredges, Suez Canal, 169
Drilling machine. 48
Dry digging, 503
Duboscq's electric lamp, 375
Dynamical electricity, 368
Earth circuit, 424
Ebonite, 517
Eccentric, 9
Eclipse of sun, 324
Eddystone lighthouse, 433
Electricity. 359
Electric current, 570
induction. 366
- light, cost of, 392
in lighthouses, 437
telegraph, 397
torpedo, 149
Electro-magnet, 378
Electromotive force, 372
Electro-plating, 377. 395
Electrode, 375
Electrotyping. 461
Elementary bodies, 507
' phenomena of Magnetism and Elec-
tricity, 302
Energy, 584
Ether, 524
. the luminiferous, 294
Exhaustion of coal, 541, 542, 543
Expansive working of steam, 6/17
Explosion by concussion, 534
~ of locomotive, 18
~' of torpedoes, 149
Explosives, 529
Explosive bullets, 145
Eye, 334
, dimensions of some parts of, 342
not optically perfect, 342
Eyeballs, muscles of, 340
Fairbairn, Sir W., 234
Faraday, 384, 385, 524
Faraday's ventilating gas-burner, 558
Field telegraphs, 405
Fizeau. 273
Fire-arms, 117
Fish-plates. 63
Fly-wheel, 7, 34
Fluids, electric, 365
Force, conservation of. 584
, electromotive. 372
Foucault, 274
Fovea centralis, 336, 337
Fraunhofer's lines, 306. 322
Fresnel's mirrors, 205
measurement of velocity of light, 439
Fribourg Suspension Bridges, 197
Froment's dial telegraph, 417
Galvanic batteries. 371, 372
Galvanometer, 371
, mirror, 420
Gas governor, 554
holder, 552
making apparatus, 551
meters, 560
pressure. 554
retorts, 552
Gases of blast furnace, 31
Gatling battery gun, or mitrailleur, 137
Gauges, broad and narrow, 64
Bourdon's pressure, 12
Geissler's tubes. 383
Ghost, Pepper's, 278
Giffard's injector, n
Girder Bridges, 191
Glass, strains in, 293
Glatton, H.M.S., in
Gold and Diamonds, 496
Gold. 496
Gold-mining operations, 409
Goodyear, Mr., 516
Governor of steam engines, 6
Gower Street Station, 72
Gramme Magneto-Electric Machine. 388
Graphotype, 471
Grove, Sir W. R.. 582
's battery, 373
oun-cotton, 536
torpedoes, 153
Great Eastern, 87, 102, 226, 426, 428
Greatest Discovery of the Age, 579.
Gunpowder, 533
Guns, submarine, 160
Gutta-percha, 517
Hancock, Mr. Charle, 518
Mr. Thomas, 514
INDEX.
59*
Harvey's torpedoes, 154
Heat produced by electric current, 380
Heat spectrum, 452
Helmholtz, 342, 344, 352, 354
Hercules, H.M.S., 100
Hippocampus, 493
Hoe's printing machines, 212, 214
Holophotal light, 443
Holyhead and Kingston steamers, 90
Horse-power, 10
Hot blast. 30
Hough's meteorograph, 473
Hughes's printing telegraph, 410
Hydraulic power. 220
Iceland spar, 285
Illuminating power of gas 559
Illusion by movement of eye, 355
by persistence of vision, 356
, stage, 200
Images formed by lenses, 285. 455
Inconstant, H.M.S., 102
Indian-rubber and gutta-percha, 513
Indian-rubber, 513
Indicator, 9
Induced currents, 513
J nduction coils, 381
Injector, n
Iron, 25
bridges, 187
cast, 29
lighthouses, 435
ores, 26
ships, 87
, smelting, 27
, wrought, 34
Jackson, 401
Jamin's magnet, 390
Joule, 582, 583
Jupiter, 271
Kaleidoscope, 276
Kirchhoff, 322
Konig's printing machine, 204
Kb'nig m Kaiser Willielm ironclad, 114
Krupp's guns, 127
steel, 42
works, 126
Lathe at Woolwich, 121
, B Ian chard, 54
, screw-cutting, 45
Lap of slide-valve, 9
Lens, formation of image by a, 455
in steps, 439
, photographic, 455
Lepidosiren, 494
Letterpress printing, 202
Leydenjar, 368
Light, 267
.electric, 374
Light, invisible, 270
Lighthouses, 432
Limiting angle, 285
Link motion, 16
Lithium, 311
Lithography, 463
Liverpool and Manchester Railway. 14
Madder, 576
Magnesium, 511
Magnetism produced by current. 378
Magneto-electricity, 384
Magneto-electric machines, 387, 388
I Malus, 291
I Manufacturing ~v. making, 43
!Map, Channel Tunnel, 260
, Pacific Railway, 75
I , Suez Canal, 167
i Martini-Henry rifle. 132
i Matter indestructible, "588
I Measuring machines. 46
Menai Straits bridges, 191, 19;
I Meteorites. 26
Meteorographs, 473
Meteorology, importance of, 483
Mirror galvanometer, 420
Mirrors, plane, 275
.illusions by, 279
Meters, gas, 560
Mitrailleurs, or machine guns, 136
Monarch, H.M.S., 106
Molecules, 522, 532
Moncrieff's gun-carriages, 129
Mont Cenis Tunnel, 247
Montigny mitrailleur, 140
Morse's code, 410
instruments, 408
telegraphic line, 406
transmitting key, 411
plate, 412
Napier's platen machine, 217
Naphthaline, 573
Nasmyth's steam-hammer, 22
Nature knowledge, i
- printing, 467
Needle telegraphs, 403
Negretti and Zambra's recording thermometer,
478
New metals, 505
Newton's prism experiment. 304
Niagara Suspension Bridges, 198
Nicol's prism, 289
Niepce, J. N.,448
de Saint- Victor, 450. 454
Nitro-benzol, 564
Nitrogen and oxygen compounds, 521
Nitro-glycerine, 533
CErsted's experiments, 399
Oil springs, 546
Ophthalmoscope, 346
Optical apparatus of lighthouses, 437
Orders of lighthouse apparatus, 441
Organic bodies, 578
Oscillating engines, 14
592
INDEX.
Paddle-wheels. 84
Papier-mache stereotype process, 460
Paraffin, 547
oils, 548, 549
Parallel motion, 8
Pascal principle, 221
Pattern printing, 217
Pepper, J. H., 179, 278, 279
Petroleum, 543
Phenakistiscope, 356
Photograph engraved on glass, 185
Photographic camera, 454
Photography, 446
in colours, 453
in the daik, 452
Photolithography, 471
Photozincography, 471
Planes, Whitworth's, 52
Planing machines, 50
Plants in coal measures, 539
Plaster of Paris, stereotype process, 460
Pneumatic dispatch, 236
force, 243
Pniel, 502
Points, railway, 66
Polariscope, 291
Polarizer, 289
Polytechnic, Regent Street. 184. 383
Portable telegraphic instruments, 406
Portrait, Davy, 505
, Helmholtz, 332
, Joule, 569
, Kirchhoff, 302
, Lesseps, 162
, Morse. 397
, Senefelder, 459
, Simpson, 520
, Thompson, 359
, Watt, 3
, Whitworth, 43
Port Said, 164
Post-office railway van, 69
Potassium, 506
Power, horse, ip
, hydraulic. 220
Powers, mechanical, 222
Power of a steam-engine, 9
of locomotive, 18
Pressure gauge, 12
transmitted in fluids, 220
Printing machines, 201
processes, 459
telegraphs, 420
Progress of mankind, 2
Projectiles, 116, 125
, deviation of, 122
, long range of Whitworth, 124
, speed of, measured, 478
Prospecting, 257
Proteus anguinus, 493
, the modern, 585
Pseudpscope, 353
Puddling, 32
Railways, 59
Great Western, 64
, Metropolitan, 72
, Midland, 70
> London and Manchester, 60, 82
Railways. London and Woolwich, 62
, Pacific. 74
, Stockton and Darlington, 59
Rangoon petroleum, 545
Rays polarized, 287
Recording instruments, 314
Red-short iron, 35
Reflection in water, 282
of light, 275
, total, 285
Refraction, 283
, double, 285
Resistance, electrical, 372
Retina, 336
Rifled cannon, 118
Rifling guns, 122
Rifle, Chassepot, 135
, Martini-Henry, 132
, Snider-Enfield, 131
Rock boring, 245
"Rocket." 14
Rock drilling machines, 251
Rolling iron, 33
mill, accident at a, 34
Ronalds' telegraph, 398
Roscje, 311, 323, 330
and Bumen, 512
Royal Gun Factory, Woolwich, 23
Ruete's ophthalmoscope, 346
Ruhmkorff's coil, 381
Saltash Bridge, 194
Sand, 179
blast, 1 8