568 



NA TURE "^ 



\Oct. 9, 1879 



ELECTRICITY AS A MOTIVE POWERS 



THE lecturer commenced by referring to the stagnation of 

 trade, to the various remedies that had been proposed to 

 relieve it, and to the fact that while some were maintaining and 

 others stoutly denying that commercial depression could be cured 

 by legislation, we were too apt to forget that there existed a 

 means by which, without lessening the wage of the workman or 

 the profit of the master, the cost of production could be dimi- 

 nished, prices lowered, and the failing trade of England resusci- 

 tated. He next considered the consumption of coal for various 

 purposes yearly in Sheffield, and showed that, although the price 

 of coal in that town %\a3 very low, being only five shillings per 

 ton for steam coal, the total annual cost for Sheffield alone must 

 be something like 790,000/. Actual instances were then given 

 of great saving being effected by water-power being employed 

 on a large scale for doing mechanical work. Contrasted with 

 this, calculation showed that at the Falls of Niagara as much power 

 was wasted as could be produced by the total present annual con- 

 sumption of coal throughout the whole world. And when it 

 was remembered that there existed in the world other waterfalls 

 besides Niagara, that we had also innumerable rapidly-flowing 

 rivers, the important fact, well known to scientific men, but one 

 which it was so difficult to induce the world at large to grasp, 

 stared us in the face — that we oljtained in a laborious w-ay from 

 the depths of the earth the power we employed, and we let run 

 to waste, every hour of our lives, many, many times as much as 

 we used. 



Again, even in a perfectly flat country, where waterfalls were 

 unknown, the question of the economic transmission of energy 

 had no less interest, for large steam-engines could be worked 

 much more economically than small ones, large steam-engines 

 requiring a consumption of only two, or two and a half, pounds, of 

 coal per horse-power per hour, whereas small steam-engines burned 

 eight or ten pounds, or even more. And even where large econo- 

 mical engines were employed there was often, as in the gigantic 

 cotton-spinning mills in Manchester, an enormous waste of 

 power in the shafting used in transmitting it from the engine at 

 the base of the factory to all the different floors, and parts of 

 each floor, a waste so great that, in spite of the extreme ineffi- 

 ciency of small engines, it had been proposed, as an economical 

 measure, to replace the one large steam-engine by many small 

 ones, each driving two or three machines direct. 



The lecturer then proved numerically that (contrary to the 

 views expressed by some people) it was impossible to use econo- 

 mically in a town, for motive power, the water already brought 

 in pipes to the houses for drinking purposes, since in most towns 

 power so produced would cost about one shilling per horse-power 

 per hour, and although in Sheffield the great head of the water 

 would diminish this to about fivepence per horse- power per hour, 

 still this had to be compared with considerably less than one 

 farthing per hour the low cost in Sheffield of producing each 

 horse-power with a very large good steam-engine. 



Experience was leading us to see that it was to electricity that 

 we must resort to obtain a carrier that would, at a small cost, 

 transport our motive power over long distances, and as an illus- 

 tration that the electric transference of energy on a large enough 

 scale to be of practicable value was possible, knives were ground 

 on the platform by power conveyed about a quarter of a mile 

 through wires carried over the houses, a Siemens's dynamo 

 machine being employed at the one end to convert into electricity 

 the motive power supplied by a steam-engine, and a similar but 

 smaller Siemens's dynamo machine being used on the platform at 

 the other end to reconvert into motive power the electric current 

 conveyed by the wires. 



The principles on which dynamo-electric inachines and 

 electro-motors act were then entered into fully experimentally, 

 and reference was made to the first electro-motor ever made — 

 that constructed by Salvator del Negro in 183 1 — as well as to the 

 improvements introduced into it by Jacobi, who replaced the 

 oscillating motion by a rotatory one ; different forms of modern 

 electro-motors were then shown in action driving sewing- 

 machines, &c. It was mentioned that although Jacobi abandoned 

 his electro-motor u-ed to propel a boat on the Neva because the 

 fuel cost too much, still, that the subject of electro-motors was 

 none the less practically important because we had since learnt 

 why the old form was such an expensive producer of power, and 

 what was the proper duty to be performed by electro-motor.-. 



* Abstract (by the author) of the British Association lecture delivered to 4,000 

 of the working-men of Sheffield, August 23, 1879, by Prof. W. E. Ayrton. 



It was this very question : — Can an electric engine be made to 

 work more economically than a steam engine? that first attracted 

 Joule, of Manchester, in 1843, to commence that all-important 

 investigation, which lasted for six years, the determination of the 

 mechanical equivalent of heat. 



Formerly, electric currents were almost entirely produced by 

 galvanic batteries, in which zinc was burnt juft as in the furnace of 

 a steam engine coke was burnt. The amount of heat that could 

 be got from burning a pound of zinc could be ascertained in the 

 same way as the amount of heat produced by the burning of a 

 pound of coal, but the fact that the latter was about seven times 

 the former was of little value in the science of electro-motors, 

 until Joule had proved that a certain quantity of heat was always 

 equivalent to exactly the same quantity of work, no matter how 

 the heat be produced ; had proved in fact that energy was as 

 indestructible as matter, a law which had for one of its proofs 

 the long unsuccessful search for a perpetual motion. 



As a result of this law of the conservation of energy Prof. 

 Ayrton went on to show that since a pound of ordinary coal 

 burning gave out seven times as much heat as the burning of a 

 pound of zinc, we might say at once, that a steam engine would 

 give seven times as much work as an electric engine for equal 

 weights consumed, if in both cases all the heat could be turned 

 into work ; or, fince zinc was about twenty-four times as dear as 

 coal, that a steam engine would be about 1 50 times as economical 

 as an electro motor, worked by a battery, if in both cases all the 

 heat were converted into work. 



But so far, he said, "we have only considered the law of 'Con- 

 servation of Energy.' There is, however, another, and no less 

 important, principle called the ' Dissipation of Energy ; ' and 

 this law tells us that although the energy of a system cannot by 

 itself increase or diminish, yet our power to convert one form o( 

 energy into another is continually growing less, our stock of 

 available energy is gradually failing. Our mountain lakes, our 

 vast store of coal, are practically useless until either the water is 

 set in motion rolling down the hillside, or until the particles of 

 the coal are set in rapid vibration as it slowly bums ; energy of 

 position, energy of chemical affinity, are of no use to the manu- 

 facturer until turned into kinetic energy or energy of motion. 

 But from friction of various kinds, whenever energy exists in the 

 kinetic form, some portion of it is being continually converted 

 into heat. Whenever man or nature utilises energy it must be 

 first turned into some kinetic form, and whatever be the aini of 

 the special machinery employed some of this energy passes into 

 heat. We cannot make even a clock go without regular winding 

 up, although the only useful work done by the clock is to turn 

 its hands at regular speeds ; the earth's energy of rotation is 

 now, like the moon's in past ages, gradually growing less, and 

 is being converted into heat on account of tidal retardation ; the 

 earth, moon, and sun, and all the planets are losing their energies 

 of motion and relative positions, to be all ultimately turned into 

 heat. 



" But at any rate, it will be said, there will still remain the heat, 

 and since heat can be converted back into other forms of energy, 

 we shall be none the worse off. But it must not be forgotten 

 that whenever heat is produced some passes off by conductipn 

 through even our best nonconducting substances, and by radia- 

 tion into space from even our best non-radiating surfaces ; and 

 this conducted and radiated heat, although it m.ay impart some 

 trifling warmth to unseen worlds, is for the greater part entirely 

 lost to our universe. And even were it not so, even had we 

 perfectly nonconducting coatings, and perfectly non-radiating 

 surfaces — had we, in fact, the most perfect heat engine that out 

 study of the science of heat would lead us to believe theoretically 

 possible, one with no friction, no loss of heat by conduction 

 through the sides of our cylinders, and no radiation from their 

 surfaces — still our power to convert heat into other forms of 

 energy would be very limited. For if there are two bodies, one 

 hotter than the other, we can employ an engine, like a steam- 

 engine, to convert part of the heat in the hotter one into some 

 other form of energy ; but the amount of heat converted, with even 

 this ideal perfect engine, will, with such temperatures as are met 

 with in practice, only be a fraction of what necessarily passes 

 through the engine from the hot body to the cold, and warms up 

 the latter ; and as our whole power of conversion of heat into 

 work depends on the difference of temperature, we lose it alto- 

 gether when we have brought all parts of a system to the same 

 temperature, no matter how high this temperature may be. 



" It is not, therefore sufficient to say that the burning of a pound 

 of coal produces seven times as much heat as the burning of a 



