394 



NATURE 



[August 15, 1907 



mover, the battery, which was the source of power. At 

 present the only available use for this power must be 

 confined to special purposes where the danger of steam 

 and the creation of vapour were sought to be avoided, or 

 where economy of space was a great consideration. Prof. 

 Tyndall agreed with the last speaker, but suggested that 

 there might be some way of mitigating the apparent 

 diminution of power due to the induction of opposing 

 electromotive forces in the machine itself. Mr. C. Cowpcr 

 spoke of some experiments, made by himself and Mr. 

 E. A. Cowper, showing the advantage gained by properly 

 laminating the iron cores used in the molor. He put the 

 cost of electric power at 4/. per horse-power per hour. 

 He deprecated building electric motors with reciprocating 

 movements and cranks ; described the use of silver com- 

 mutators : and mentioned the need of adjusting the lead 

 given to the contacts. There was, he said, no reason to 

 suppose that electric motors could be made as light as 

 steam-engines. Even in the case of small motors of one- 

 tenth or one-hundredth of a horse-power, for light work, 

 where the cost of power was of small consequence, a 

 boy or a man turning a winch would probably furnish 

 power at a cheaper rate. .\Ir. Alfred Smee agreed that 

 the cost would be enormous for heavy work. .Although 

 motive power could not at present be produced at the 

 same expense on a large scale by the battery as by coal, 

 still they were enabled readily to apply the power at any 

 distance from its source ; the telegraph might be regarded 

 as an application of motive power transmitted by elec- 

 tricity. Mr. G. P. Bidder considered that there had been 

 a lamentable waste of ingenuity in attempting to bring 

 electromagnetism into use on a large scale. Mr. Joule 

 wrote to say that it was to be regretted that in France 

 the delusion as to the possibility of electromagnetic engines 

 superseding steam still prevailed. He pointed out, as a 

 result of his calorimeter experiments, that if it were 

 possible so to make the electric engine work as to reduce 

 the amount to a small fraction of the strength which it 

 had when (he engine was standing still, nearly the whole 

 of the heat (energy) due to the chemical action of the 

 battery might be evolved as work. The less the heat 

 evolved, as heat, in the battery, the more perfect the 

 economy of the engine. It was the lower intensity of 

 chemical action of zinc as compared with carbon, and the 

 relative cost of zinc and coal, which decided so completely 

 in favour of the steam-engine. Mr. Hunt, replying to the 

 speakers in (he discussion, said that his endeavour had 

 been to show that the impossibility of employing electro- 

 magnetism as a motive power lay with the present voltaic 

 battery. Before a steam-engine could be considered, the 

 boiler and furnace must be considered. So likewise must 

 the battery if electric power were to become economical. 

 Then the President, Mr. Robert Stephenson, wound up 

 the discussion by remarking that there could be no doubt 

 that the application of voltaic electricity, in whatever 

 shape it might be developed, was entirely out cf the ques- 

 tion, commercially speaking. The mechanical application 

 seemed to involve almost insuperable difnculties. The 

 force exhibited by electromagnetism, though very great, 

 e.xtended through so small a space as to be practically 

 useless. A powerful magnet might be compared to a 

 steam-engine with an enormous piston, but with exceed- 

 ingly short stroke ; an arrangement well known to be very 

 undesirable. 



In short, the most eminent engineers in 1S57 one and 

 all condemned the idea of electric motive power as un- 

 practical and commercially impossible. Even Faraday, in 

 his lecture on " Mental Education " in 1854, had set 

 down the magneto-electric engine along with mesmerism, 

 homoeopathy, odylism, the caloric engine, the electric light, 

 the sympathetic compass, and perpetual motion as coming 

 in different degrees amongst " subjects uniting more or 

 less of the most sure and valuable investigations cf science 

 with the most imaginary and unprofitable speculation, that 

 are continually passing through their various phases of 

 intellectual, experimental, or commercial development, 

 some to be established, some to disappear, and some to 

 recur again and again, like ill weeds that cannot be 

 extirpated, yet can be cultivated to no result as wholesome 

 food for the mind." 



NO. 1972, VOL 76] 



fi/(y Wars Later. 



Fifty years h.ive fled, and Hunt, Grove, Smee, Tyndall, 

 Cowper, Jtjule, Bidder, and Stephenson have long passed 

 away. Lord Kelvin remains the sole and honoured 

 survivor of that remarkable symposium. But the electric 

 motor is a gigantic practical success, and the electric 

 motor industry has become a very large one, employing 

 thousands of hands. Hundreds of factories have discarded 

 iheir steam-engines to adopt electric-motor driving. All 

 travelling cranes, nearly all tramcars, are driven by 

 electric motors. In the Navy and in much of the merchant 

 service the donkey-engines have been replaced by electric 

 motors. Electric motors of all sizes and outputs, from 

 one-twentieth of a horse-power to 8000 horse-power, are 

 in commercial use. One may well ask : What has 

 wrought this astonishing revolution in the face of the 

 unanimous verdict of the engineers of 1857? 



The answer may be given in terms of the action and 

 reaction of pure and applied science. Pure science 

 furnished a discovery; industrial applications forced ii' 

 development ; that development demanded further abstract 

 investigation, which in turn brought about new appli- 

 cations. It was beyond all question the development tl 

 the dynamo for the purposes of electrotyping and electrii 

 light which brought about the commercial advent of the 

 electric n-.otor. For about that very time Holmes and 

 Siemens and Wilde and Wheatstone were at work develop- 

 ing Faraday's magneto-electric apparatus into an apparatus 

 of more practical shape; and the electric lighthouse lamp 

 was becoming a reality which Faraday lived to see before 

 his death in 1867. That eventful year witnessed the intro- 

 duction of the more powerful type cf generator which 

 excited its own magnets. And even before that date a 

 young Italian had made a pronouncement which, though 

 it was lost sight of for a time, was none the less of 

 importance. .Antonio Pacinotti in 1S64 described a 

 machine of his own devising, having a specially wound 

 revolving ring-magnet placed between the poles of a 

 stationary magnet, which, while it would serve as an 

 admirable generator of electric currents if mechanically 

 driven, would also serve as an excellent electric motor if 

 supplied with electric currents from a battery. He there- 

 upon laid down the principle of reversibility of action, a 

 principle more or less dimly foreseen by others, but never 

 before so clearly enunciated as by him. .And so it turned 

 out in the years from 1S60 to 18S0, when the commercial 

 dynamo was being perfected by Gramme, Wilde, Siemens, 

 Crompton, and others, that the machines designed specially 

 to be good and economical generators of currents proved 

 themselves to be far better and more efficient motors than 

 any of the earlier machines which had been devised 

 specially to work as electromagnetic engines. Moreover, 

 with the perfection of the dynamo came that cheap source 

 of electric currents which was destined to supersede the 

 battery. That a dynamo driven by a steam engine furnish- 

 ing currents on a large scale should be a more economical 

 source of current than a battery in which zinc was con- 

 sumed, does not appear to have ever occurred to the 

 engineers who, in 1857, discussed the feasibility of electric 

 motive power. Indeed, had any of them thought of it, 

 they would have condemned the suguestion as chimerical. 

 There was a notion abroad — and it persisted into the 

 'eighties — that no electric motor could possibly have an 

 efficiency higher than 50 per cent. This notion, based 

 on an erroneous understanding of the theoretical investi- 

 gations cf Jacobi, certainly delayed the progress of events. 

 Yet the clearest heads of the time understood the matter 

 more truly. The true law of efficiency was succinctly 

 stated by Lord Kelvin in 1S51, and was recognised by 

 Joule in a paper written about the satne date. In 1S77 

 Mascart pointed out how the efificiency of a given magneto- 

 electric machine rises with its soeed up to a limiting value. 

 In 1870 Lord Kelvin and ■ Sir William Siemens gave 

 evidence before a Parliamentary Committee as to the 

 possible high eflKiency cf an electric transmission of 

 power ; and in .August of the same year, at the British 

 .Association meeting at Sheffield, the essential theory of 

 the efficiency of electric motors was well and admirably 

 put in a lecture by Prof. .Ayrlon. In 1882 the present 

 author designed, in illustration cf the theory, a graphic 



