Oct. 5 1888.] 



SCIENTIFIC NEWS. 



567 



mechanism by means of which the electric power is 

 transmitted, 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 predicted with marvel- 

 lous 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 hap-hazard. As well might the determination 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 distance 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 transmitting 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. 



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 elec- 

 tric power consumed for sending the telegraph messages 

 was so small, the amount of power lost en route compara- 

 tively so valueless, that the telegraph engineer had no 

 need to trouble himself with these 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 Telegraph Office, London, which costs some 

 thousands annually to keep in order, what is that com- 

 pared with the salaries of all the 3,089 superintendents, 

 assistants, telegraph clerks, and the maintenance of 1,150 

 telegraph lines that start from the Central Office ? 



In all the last three systems on 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 utilised. This power is given to some form of air, 

 water, or electric pump which transfers the power to the 

 air, water, or electricity by which it is conveyed to the 

 other end of the system. There it is re-converted 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 elec- 

 tricity 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 

 possessed by rushing water. But what I particularly 

 wish to impress on you by classing air, water, and elec- 

 tricity together is that electricity 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. Electricity 

 is no more a source of power than a bell wire is ; elec- 

 tricity is a marvellously convenient agent for conveying a 

 pash Dr a pull to a great distance but is not by the using 



up of the electricity that electric lights burn or that electro 

 motors revolve. It is by the electricity losing pressure, 

 exactly as water loses head when turning the miller's 

 wheel as it flows downhill, 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. The working stuff, which- 

 ever of the three it may be, is first raised in pres- 

 sure and endowed with energy, symbolised 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 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 corres- 

 ponding 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 initially 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 ex- 

 pensive. A very perfect fireplace in which there was 

 very complete combustion, and a 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 com- 

 mercially work electric motors has been known for the 

 last half-century, and the matter was very clearly put in 

 an extremely interesting paper " On Electric Magnetism 

 as a Motive Power," read in 1857, by Mr. Hunt, before 

 the Institution of Civil Engineers, a copy of which 

 has been kindly lent me by Dr. Silvanus Thomp- 

 son. Professor William Thompson, of Glasgow, 

 I quote from the discussion on the paper, put 

 the matter very pithily by showing that even if it were 

 possible to construct a theoretically perfect electro- 

 motor, 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 lbs. of zinc per 

 hour, whereas with a good actual steam engine of even 

 thirty years ago, one horse power cculd be produced by 

 the combustion of exactly the same weight of the much 

 cheaper fuel, coal. This argument against the com- 

 mercial employment of zinc to produce electric currents 



