May 5, 1881] 



NATURE 



21 



among other things, as well as to give everybody an electric 

 light. 



"Probably you think it very strange that I should show you 

 the iuelTiciency of electric transmission of energy, and then make 

 this very bold assertion. Well, the fact is that the ordinary 

 electrical machines in use have not been constructed with a view 

 to economy. They have been constructed to show that brilliant 

 lights and considerable power may be produced from small 

 machines. They have, at a comparatively small cost, attracted 

 attention to the fact that electricity is an im]5ortant agency. In 

 so far they have done well ; but on the other hand they gave 

 rise to the well-known assumption that Jo per cent, of the 

 mechanical power i^iven to the generator was the maximum 

 amount which could be taken from the motor. The true solu- 

 tion of the problem of transmission of power was, I believe, 

 first given by Prof. Ayrton in his Shefiield British Association 

 lecture. It had been suppjsed that to transmit the power of 

 Niagara Falls to New York a copper cable of enormous thick- 

 ness would be needed. Mr. Ayrton showed that the whole 

 power might be transmitted by a fine copper wire, if it could 

 only be sutificiently well insulated. He also sho« ed that instead 

 of a limiting efficiency of 50 per cent., the one thing preventing 

 our receiving the whole of our power, is the mechanical fric- 

 tion which occurs in the machines. He showed, in fact, how 

 to get rid of electrical friction. I will briefly give you our 

 reasons. A machine at Niagara receives mechanical power, 

 and generates electricity. Call this the generator, and remember 

 that Wall-sheet III. teaches us that the mechanical power is 

 proportional to the electromotive force produced in the gener- 

 ator, multiplied into the current which is actually allowed 

 to flow. Let there be wires to another electric machine 

 in New York, which will receive electricity, and give out 

 mechanical work, as this machine does here. Now I showed 

 you a little while ago that this machine, which may be called the 

 motor, produces a back electromotive force, and tlie mechanical 

 power given out is proportional to the back electromotive force 

 multiplied into the current. The current, which is of course the 

 same at Niagara as at New York, is proportional to the differ- 

 ence of the two electromotive forces, and the heat wasted is 

 proportional to the square of the current. You see then, from 

 Wall-sheet III., that we have the simple proportion — power 

 utilised is to power wasted, as the back electromotive force of 

 the motor is to the difference between electromotive forces of 

 generator and motor. This reason is very shortly and yet very 

 exactly given in Wall-sheet IV., a printed copy of which you all 

 hold in your hands." 



Wall-sheet IV. 



Let electromotive force of generator be E ; of motor F. Let 

 total resistance of circuit be R. Then if we call P the horse- 

 power received by the generator at Niagara. Q the horse-power 

 given out by motor at New York, that is, utilised. H the 

 horse-power wasted as heat in machines and circuit. C the 

 current flowing through the circuit. 



p _ E (E - F) 



Q = 



746R 

 F(E - F) 



H 



746 R 

 (E - F)= 



746 R 

 Q : H : : F : E - F. 

 "To put it more shortly still, the power wasted is proportional 

 to the square of the current flowing, whereas the power utilised 

 is proportional to the current, and also to the electromotive 

 force ol the motor. The greater, then, we make the electro- 

 motive forces, the less is the loss of power in the whole opera- 

 tion. Perhaps you will see this better from the water analogy. 

 A small quantity of water flowing through a water-main may 

 convey a large amount of energy, if it only has sufhcient head. 

 The frictional loss of power is independent of the head, but 

 depends very much on the quantity of water. In the model 

 before you is the water analogy. Here is a reservoir, which 

 I shall call A, kept filled w ith water by a steam pump, which 

 draws the water from the sea-level, which I shall call K. Water 

 flows from reservoir A to distant reservoir B, where it drives a 

 turbine giving out work due to its head B K. The current from 

 A to B, through the communicating pipe, is the same always, so 



long as A and B are at the same difference of level, and therefore 

 the frictional loss of energy is alw ays the same, whereas the work 

 utilised from b, by driving the turbine, increases proportionally 

 to the height of B above sea-level. The result, then, to which 

 the above laws led us was that for the future development of the 

 transmission and distribution of electric energy it will be necessary 

 to use electric machines of great electromotive force. Indeed 

 so important must this principle become that we believe there 

 is a future in this direction for the employment of even plate 

 electrical machines, such as that of Holtz." 



Then followed a discussion of methods of obtaining great 

 electromotive force. Mr. Perry's own ways of carrying out 

 these ideas are shown in his own dynamo-machine, which is 

 large, has great speed, has no iron in its movable part, and has 

 a commutator of small frictional resistance. Electric lighting 

 and heating, telephones, and electric railways of the future were 

 all spoken of as illustrations of the transmission of energy 

 by electrical means, and as such they must be governed by the 

 above principle. 



It was then shown experimentally that electrical energy may 

 be stored up in considerable quantities in an available form for 

 future use, and the bearing of this fact on the future utilisation 

 of great but variable natural sources of power, such as the wind 

 and tide, was dwelt upon. 



The remainder of the lecture was devoted to the importance 

 of the principle of recurrent effects ; one illustration was given 

 as follows: — "If I very much alter the magnetic field in this 

 telephone, by bringing a powerful magnet near it, with great 

 care in listening I hear the faintest sigh, due to the diaphragm 

 settling itself into a new position, its vibrations dying away 

 as it does so ; and if I brought a small magnet near, I 

 should hear nothing. And yet the change of magnetism which 

 produces the loud telephonic effects which we listen to is almost 

 infinitely smaller. Why is this ? It is due to the rapid recur- 

 rence of the effects. Now you are all aware of the importance 

 of the telephone as a method of communication ; I believe that a 

 much greater importance is in store for it as a laboratory 

 appliance." 



The photophone and the method by means of which Messrs. 

 Ayrton and Perry determined the index of refraction of ebonite, 

 finding its sqnare to be roughly the same as the mean value of 

 its measured specific inductive capacities : the use of a power- 

 ful sub marine source of musical sound as a coast-warning, 

 which might be heard in a ship well above all other sounds, and 

 the experiments which have been made by the lecturer and his 

 colleague in this direction : these and other matters were 

 discussed as examples of the use of the principle of recurrent 

 effects. The lecture concluded by an account illustrated by 

 experiments of Mr. Edward Bright's method of de-electrifying 

 woollen yarn, and of Messrs. Ayrton and Perry's plan for seeing 

 by electricity what is occurring at a distant place. A selenium 

 cell moving over an image at, say, York, gave corresponding 

 light and shade to corresponding parts of a screen at, say, 

 London. Mr. Perry's \'ork image was very simple, being a 

 series of black, grey, and white squares, which were faithfully 

 reproduced on the distant screen. 



MECHANICAL RESEARCH 

 TT will be remembered that some time ago the Institution of 

 Mechanical Engineers appointed a Committee to examine 

 into three selected questions of research in matters pertaining to 

 their profession. These researches are still in progi'ess, but pre- 

 liminary reports have been Issued by the Committee, of which 

 we propose to give a brief account. 



T7ie Hardening and Tempering of Steel. — One or two letters on 

 this subject have lately appeared in our columns, and allusion 

 has been made to the report by Mr. Wm. Anderson, presented 

 to the Committee who were appointed specially to investigate 

 this difficult question. Mr. Anderson's report, which contains 

 much useful information in a comparatively small compass,_ is 

 itself too long for our pages. We therefore give the following 

 rhwni of the question, taking Mr. Anderson's report as our 

 basis ; — 



WhUst the theory of this subject is in a very vague and un- 

 certain condition, the facts are exceedingly well known, and are 

 daily applied in almost every department of arts and manufac- 

 tures. Wherever steel tools are used it is necessary that they 

 should be hardened and tempered ; since the ordinary tool-steel, 

 as supplied chiefly from Sheffield, is too soft for cutting and 



