NA TURE 



[November 5, 1891 



small contact-piece of soft iron, and of measuring by 

 means of a graduated spring that gradually extended, the 

 force requisite to detach the iron," and given a description 

 of the much more satisfactory method adopted by Row- 

 land and others. 



After a chapter on methods of magnetization, in which 

 all the ancient and now discarded methods of " touch " 

 are described, we have an excellent popular discussion of 

 terrestrial magnetism, ending with a splendidly illustrated 

 account of aurorae. The introduction of the subject of 

 aurorae at this point is justified on the ground that they 

 are electrical phenomena connected with the magnetism 

 of the earth, and a sketch is given of the various theories 

 which have been proposed. 



Passing now to the subject of electricity, we have 

 the same wealth of illustration, though many of the 

 smaller cuts, like some of those in the section on mag- 

 netism, are old familiar friends. Electrical machines 

 are described, from Otto Guericke's down to Wimshurst's. 

 Nothing impresses us as more indicative of the enormous 

 advance of electrical science in recent times than a com- 

 parison of Plates V. and XI II. of this book. The former, 

 a well-known picture, represents an electrical machine 

 "according to the model in fashion about 1754"; the 

 latter, a large Edison steam-dynamo. In the former a 

 bevy of ladies and gentlemen in the costume of last 

 century are grouped round a sulphur ball machine, which 

 a gentleman in powdered wig and ruffles is vigorously 

 turning by means of a crank attached to a large and much 

 ornamented driving-wheel of wood. Evidently we have 

 here " electricity in the drawing-room," as practised 

 in the middle of last century. On the other plate 

 we see a large modern steam-engine, in all its 

 array of steam-pipes, balanced cranks, and connect- 

 ing-rods, resting on a massive bed-plate of iron 

 bolted to a base of masonry, and driving an enormous 

 dynamo. The somewhat dilettante group of men and 

 women have disappeared, and in their place stands a 

 typical Yankee engineer, oil-can in hand, and coatless, 

 intently regarding the bearings of the engine. Here there 

 is no unnecessary ornamentation, no suggestion of elegant 

 trifling, everything is sternly suggestive of work and 

 nothing else. Nevertheless, in the contrast, the real 

 dignity and beauty is with the present, not with the past ; 

 with modern science in the laboratory, the workshop, or 

 the factory ; with work carried on in the deepest earnest, 

 with plain duty-doing, irrespective of sensation or ap- 

 plause. 



Next comes an account of batteries, which (like several 

 other parts of the book) we think might very well have 

 been lightened by ignoring old and obsolete pieces of 

 apparatus ; after that, we have a discussion of the pro- 

 duction of electric currents. In a book of this size, in 

 which a considerable amount of space is devoted to things 

 relatively unimportant, the subject of electrolysis might 

 have been more fully treated ; for example, there are 

 matters connected with electrolytic theories to which, 

 since such a theory as that of Clausius is introduced, 

 a few pages might very well have been devoted. The 

 absolute measurement of currents by means of electrolysis 

 from the known electro-chemical equivalents of different 

 substances is not referred to ; indeed, an electro-chemical 

 equivalent does not seem to be anywhere defined. But 

 NO. I 149, VOL. 45] 



what strikes one as strange indeed is that in the chapter 

 on thermo-electricity Peltier's name is only mentioned in 

 connection with an illustration showing what is called 

 his " thermo-electric pince." Not a word is said on the 

 subject of the Peltier effect, or the Thomson effect, not to 

 speak of the bearing of these on thermo-electric theory ! 

 Again, no mention appears to be made of any form of 

 secondary cell except that of Plants : surely some of the 

 modern forms now so largely in use in practice for electric 

 lighting, traction, &c., might have been figured and 

 described. 



The next section of theory, electro-magnetism, has three 

 chapters devoted to it. The main phenomena are well 

 described, and excellently illustrated by diagrams. Here 

 the only forms of tangent and sine galvanometer figured 

 are those of Pouillet (one of these (p. 337) has an 

 enormous needle). Some of the splendid instruments 

 which have been made for absolute measurements (for 

 example, Fitzgerald's tangent galvanometer) ought surely 

 to find a place in a work like the present, published as it 

 is at a time when currents, &c., are no longer measured 

 in arbitrary units, and their determinations are as far as 

 possible divested of errors arising from instrumental 

 peculiarities and accidents of place. A definition might 

 also have been given here of the electro-magnetic unit of 

 current, with some indication, where the constant of a 

 galvanometer is referred to, of how it is possible to 

 measure currents in absolute units, and the importance 

 in this respect of electro-magnetic instruments, the con- 

 stants of which can be determined from their dimensions 

 and arrangement. At p. 333 a current of so many amperes 

 is referred to as producing a certain force at the needle, 

 but we have not anywhere, so far as we have been able 

 to discover, a definition of an ampere. 



The following passage (p. 369) apparently quoted from 

 Faraday's " Researches," was at first sight rather startling : 

 " In this state of circumstance(s) the force of the electro- 

 magnet was developed by sending an electric current 

 through its coils, and immediately the image of the lamp- 

 flame continued magnetic.'" It is almost needless to say 

 that a reference to the " Researches " showed that the 

 copyist had dropped out a line from Faraday's account 

 of the actual phenomenon, which was not exactly that 

 asserted in the quotation. After "flame" supply the 

 words " became visible, and continued so as long as the 

 arrangement." 



The second part of the book is most excellent. All 

 applications of electricity of any importance are fully 

 described, and magnificent cuts, without stint, illustrate 

 in the clearest manner the marvellous and complex con- 

 trivances and arrangements now in use in the various 

 systems of telegraphy and telephony, electric lighting, 

 &c., &c. Full-page plates of the illumination of Tunis 

 by the search-lights of the French fleet, the electric light 

 in use in the erection of a great Parisian magasin, the 

 head-light of a locomotive illuminating the track, the 

 interior of one of the Paris forts during the siege, and 

 other subjects, serve to show the great part now played 

 by electricity in all branches of industry and the arts, 

 even including warfare, slow as that is in some respects 

 to profit by the latest results of scientific invention. No 

 book could form a more attractive and useful present for 

 a boy with a taste for mechanics and practical electrical 



