5>o 



NA TURE 



{Sept. 20, 1 8 88 



which I have excluded from my list, fulfils this condition, but so 

 also does the transmission of power by a loaded coal-waggon. 

 In both these cases, however, it is fuel itself that is transmitted, 

 and not the power obtained by burning the fuel at a distant 

 place. 



Let us study this electric transmission a little in detail. I pull 

 this handle, and the bell at the other end of the room rings; but 

 in this case there is no visible motion of anything between the 

 handle and the bell. [Electric bell rung by an electric current 

 produced by pulling the handle of a very small magneto-electric 

 machine.] Whether I ring the bell by pulling a wire, or by 

 sending an air puff, or by generating an electric current by the 

 exertion of my hand, the work necessary for ringing the bell is 

 done by my hand exactly as if I took up a hand-bell and rang it. 

 In each of the three cases I put in the power at one end of the 

 arrangement, and it produces its effect at the other. In the 

 electric transmission how does this power travel ? Well, we do 

 not know.' It may go through the wires, or through the space 

 outside them. But although we are really quite in the dark as 

 to the mechanism by means of which the electric power is trans- 

 mitted, one thing we do know from experience, and that is this : 

 given any arrangement of familiar electrical combinations, then 

 we can foretell the result. 



Our knowledge of electrical action in this respect resembles 

 our knowledge of gravitation action. The only thing quite 

 certain about the reason why a body falls to the ground is that 

 we do not know it ; and yet astronomical phenomena can be pre- 

 dicted with marvellous accuracy. I mention the analogy, since 

 some people fancy because the answer to that oft-repeated 

 question, "What is electricity?" not only cannot be given 

 exactly, but can only be guessed at in the haziest way, even by 

 the most able, that therefore all electric action is haphazard. As 

 well might the determinations of a ship's latitude at sea be 

 regarded as a mere game of chance because we have not even a 

 mental picture of the ropes that pull the earth and sun together. 



This power of producing an action at a ditance of many yards, 

 or it may be many miles, by the aid of electricity without the 

 visible motion of any substance in the intervening space is by no 

 means new. It is the essence of the electric telegraph ; and 

 electric transmission of power was employed by Gauss and 

 Weber when they sent the first electric message. I am trans- 

 mitting power electrically whether I now work this small model 

 needle telegraph instrument, or whether I turn this handle and 

 set in motion that little electric fan. [Experiment shown.] 



But until about ten years ago the facility that electricity gave 

 for producing signals almost instantaneously at a great distance 

 was the main thing thought of. The electric power consumed 

 for sending the telegraph messages was so small, the amount of 

 power lost en rotite comparatively so valueless, that the telegraph 

 engineer had no need to trouble himself with those considerations 

 that govern us to-day when we are transmitting power large 

 enough to work a factory or an electric tramway. Although 

 there are as many as 22,560 galvanic cells at the Central Tele- 

 graph Office, London, which cost some thousands annually to 

 keep in order, what is that compared with the salaries of all the 

 3089 superintendents, assistants, telegraph-clerks, messengers, 

 and the maintenance of the 1150 telegraph lines that start from 

 the Central Office ? 



In all the last three systems in my list some form of power, 

 such as flowing water, or the potential energy stored up in coal, 

 wood, zinc, or other fuel, has initially to be utilized. This power 

 is given to some form of air, water, or electric pump, which trans- 

 fers the air power to the air, water, or electricity, by which it is 

 conveyed to the other end of the system. There it is re-con- 

 verted into useful mechanical power by means of an air, water, 

 or electric motor. 



You will observe that I class together air, water, and electricity ; 

 by that I do not mean to imply that electricity is a fluid, although 

 in many respects it acts like a fluid — like a fluid of very little 

 mass, however ; or, odd as it may seem, like a fluid moving 

 extremely slowly, for electricity goes round sharp corners with 

 perfect ease, and without any of the phenomena of momentum pos- 

 sessed by rushing water. But what I particularly wish to impress 

 on you by classing air, water, and electricity together is that electri- 

 city is not, as some people seem to think, a something that can be 

 burnt or in some way used up and so work got out of it. Elec- 

 tricity is no more a source of power than a bell-wire is, electricity 

 is a marvellously convenient agent for conveying a push or a pull 

 to a great distance, but it is not by the using up of the electricity 

 that electric lights burn or that electromotors revolve. It is by 



the electricity losing pressure, exactly as water loses head when 

 turning the miller's wheel as it flows down hill, that work is done 

 electrically. 



This model shows, in a rough, symbolical way, what takes 

 place in the transmission of power whether by air, water, or 

 electricity. [Model shown.] The working stuff, whichever of the 

 three it may be, is first raise d in pressure and endowed with 

 energy, symbolized by this ball being raised up in the model ; 

 it then gradually loses pressure as it proceeds along the tube or 

 wire which conveys it to the other end of the system, the loss of 

 pressure being accompanied by an increase of speed or by its 

 giving up power to the tube or wire and heating it. This is 

 shown in the model by the ball gradually falling in its course. 

 At the other end there is a great drop of pressure corresponding 

 with a great transference of power from the working stuff to the 

 motor, and finally it comes back along the return pipe or wire, 

 losing, as it returns, all that remains of the pressure given to it 

 inkially by the pump. The ball has, in fact, come back to its 

 original level. 



The problem of economically transmitting power by air, 

 water, or electricity is the problem of causing one or other of 

 these working stuffs— air, water, or electricity — to economically 

 perform the cycle I have described. 



In each of the four stages of the process — (1) transference of 

 power to the working substance at the pump ; (2) conveyance 

 of power to the distant place ; (3) transference of power from 

 the working substance to the motor at the distant place ; 

 (4) bringing back the working substance — there is a loss of 

 power, and the efficiency of the arrangement depends on the 

 amount of these four losses. The losses may be shortly called 

 (1) loss at the pump ; (2 and 4) loss on the road; (3) loss at 

 the motor. 



Until 1870 the pump most generally employed for pumping 

 up electricity and giving it pressure was the galvanic battery — 

 scientifically an extremely efficient converter of the energy in 

 fuel into electric energy, only unfortunately the only fuel a 

 battery will burn is so expensive. A very perfect fire-place, in 

 which there was very complete combustion, and very little loss 

 of heat, but which had the misfortune that it would only burn 

 the very best wax candles, would be analogous with a battery. 

 The impossibility of using zinc as fuel to commercially work 

 electromotors has been known for the last half-century, and the 

 matter was. very clearly put in an extremely interesting paper 

 "On Electro-magnetism as a Motive Power," read in 1857 by 

 Mr. Hunt befpre the Institution of Civil Engineers, a copy of 

 which has been kindly lent me by Dr. Silvanus Thompson. 

 Prof. William Thomson (Glasgow) — I quote from the dis- 

 cussion on the paper— -put the matter very pithily by show- 

 ing that, even if it were possible to construct a theoretically 

 perfect electromotor, the best that could be hoped for, if it 

 worked with a Daniell's battery, would be the production of 

 a one horse-power by the combustion of 2 pounds of zinc 

 per hour, whereas with a good actual steam-engine of even 

 thirty years ago, one horse-power could be produced by the 

 combustion of exactly the same weight of the much cheaper 

 fuel coal. This argument against the commercial employment 

 of zinc to produce electric currents is irresistible, unless — and 

 this is a very important consideration, which is only beginning to 

 receive the attention it deserves — unless, I say, the compound of 

 zinc formed by the action of the battery can be reduced again 

 to metallic zinc by a comparatively inexpensive process, and 

 the zinc used over and over again in the battery. If the com- 

 pound of zinc obtained from the battery be regarded as a waste 

 product, then it would be much too expensive to work even 

 theoretically perfect electromotors, if they were existent, by 

 consuming zinc. Suppose, however, a process be devised by 

 means of which burnt zinc can be unburnt with an expenditure 

 comparable with the burning of the same weight of coal, then it 

 might be that, although coal would still form the basis of our 

 supply of energy, the consumption of zinc batteries might be an 

 important intermediary in transforming the energy of coal, 

 economically, into mechanical energy. 



While, then, some experimenters are aiming at possibly increas- 

 ing the working power of a ton of coal to eight times its pres 

 value by earnestly seeking for a method of converting the ener 

 it contains directly into electric energy without the interventi 

 of a wasteful heat engine, it should not be forgotten that in 

 cheap unburning of oxidized metal may lie another solution. 



The solution of this latter problem is quite consistent with ti 

 principles of the conservation and dissipation of energy, sir 



