570 



NATURE 



\Oct. 9 1879 



" It would be impossible to increase indefinitely the speed of 

 revolution of the cylinder of an induction machine, since apart 

 from mere mechanical friction the iron constituting the core of 

 the revolving part has to be magnetised and demagnetised very 

 rapidly as it revolves. Now, there is a physical limit to the 

 speed with which thii can be done, and in addition this rapid 

 change of magnetism heats the iron very much. But experiment 

 shows that at the ordinary speed of revolution of dynamo-electro 

 machines, 700 turns per minute, the electromotive force is pro- 

 portional to the speed. We are, therefore, very far yet from the 

 limit of speed. Consequently it would be well for the transmis- 

 sion of power to attempt first, a considerable increase of speed in 

 the generator, combined with so light a load on the motor, that 

 its speed is also very high. When this begins to fail as larger 

 and larger amounts of power are transmitted, then we might 

 begin increasing the amount of wire on the revolving coils of 

 each ; but this, of course, has the objection that the loss of power 

 from a given current would then become somewhat larger. 



" In some of the dynamo-electric machines, the current that is 

 sent through the external wires is the same as that which circu- 

 lates round the fixed electro-magnets to create the magnetic field 

 in which the movable coils revolve. Now, the small current 

 which I am here advocating should pass between the generator 

 at the one end of the line, and the electro-motor at the other, 

 would be too smalt to properly magnetise the fixed electro- 

 magnets of the two machines, so that even a high speed of the 

 bobbin will not produce a high electromotive force. But this 

 difficulty is easily overcome by the plan already employed, for 

 totally different reasons, by Gramme, Lontin and Wilde, in their 

 generator for producing currents for electric lighting, viz., that 

 of using either a separate exciter, or a- separate portion of the 

 revolving bobbin in the generator, to produce the current to 

 magnetise the fixed eleetro-magnets. In connection with this 

 current for exciting the fixed magnets, it is worthy of notice in 

 passing, to observe that since experience shows that the electro- 

 motive force of a dynamo-electric machine is proportional to the 

 velocity, I conclude that the magnets are saturated, and that the 

 exciting current is already too strong, so that it may be with 

 advantage reduced, or many fewer coils of wire employed in this 

 portion of the machine. 



" We have then been led to this most important result which I 

 hope is clear to you all, and which I trust you may all carry 

 away with you — that a dynamo-electric machine, with a separate 

 exciter, driven very fast tvith a steam engine, or with a stream 

 of water, at high or loiv pressure, and sending, by even quite a 

 fine wire, a small current to a distant electro-motor, also .running 

 very fast and magnetised by a separate exciter, is an economic 

 arrangement for the transmission of power," 



An examination was then made of the way this result was 

 affected by increasing the length of the connecting wires, and it 

 was proved that the electric transmission of power was not only 

 practical, but also very economical, both for short and long dis- 

 tances, if the generator of the electric current at one end of the 

 line and the motor, worked by this electric current, at the other 

 end of the line, were both run fast enough, and if only we 

 required to transmit a sufficiently large quantity of power. 



The lecturer then went on to say, "We have been considering 

 the transport of power derived more especially from natural 

 sources ; but since we have seen that by the use of electricity, 

 properly employed, the waste of power in transmission can be 

 reduced for any distance to about 30 per cent, of the whole 

 power absorbed at the generator, it follows that the employment 

 of steam-engines of vast size at points outside Sheffield would 

 be by far the most economical mode of extracting the energy out 

 of coal. For it is at least four times as expensive to produce 

 power with a small steam-engine as with a large one ; therefore, 

 including the waste of power in electric transmission, the cost 

 of production of power in small workshops would be little more 

 than one-third as dear as if small steam-engines were used, and 

 similarly the waste of power in any large mill or factory in its 

 transmission from the large steam-engine at its base to all the 

 floors and machines on each floor would be very much 

 diminished. 



' ' Consequently it would be much more economical to work this 

 lathe on the platform, as I will now proceed to do, by a big 

 steam-engine in Howard-street, several hundred yards away, than 

 to use a small steam-engine here for this purpose." 



He then reminded them that not only can electricity produce 

 motive power, but also light and heat, and electric heating and 

 lighting had this great advantage, that no chimneys were 



required. Experiments were then made of boiling water and; 

 lighting the Albert Hall by an electric current generated a 

 quarter of a mile away. 



Reference was then made to the great money-saving of some- 

 thing like 30J-. an hour, that Dr. Siemens had been able to effect 

 at the Albert Hall, London, by replacing the old gas jets by 

 electric lamps giving even more light, and to the unexpected 

 advantage attained by the present stillness of the air arising from 

 the use of the electric light, and which enabled the singing and 

 music there to be better heard now. Great weight was attached" 

 to the fact that at the Albert Hall the science of hanging a 

 brilliant light high up had been luckily allowed to ride over the 

 precedent of putting a number of feeble glimmers all over n 

 building, and in connection with this it was explained that the 

 reason why electric lighting for streets had been economically 

 much less successful, was because English con-ervatism had 

 prevented the authorities from realising the possibility of usin"- 

 for street electric illumination anything differing from an ordinary 

 iron lamp-post. Attention was then drawn to the fact bearin" 

 most closely on the economy of electric lighting on a large scale, 

 and which had been obtained as the result of experiments, that 

 the larger were the dynamo machines used for producing the- 

 electric light, the more light was produced per horse-power. 

 Taking all this into consideration, Prof Ayrton arrived at the 

 result that "at any rate we may be absolutely safe in saying that the 

 cost of using gas in Sheffield for lighting large halls, such as the 

 one we are now in, factories, and the streets could be halved if 

 electric currents, generated by water engines worked by hill 

 streams, as well as by very large steam engines, were substituted 

 for gas. 



" But can this be'quite right,for I have proved that to transfer 

 energy economically we must use a large pressure and a small 

 flow. Now, how can we produce a very bright electric liTht 

 with a small current ? Why, by not using the current that comes 

 along the wire to produce the light at all, but merely to drive an 

 electro-motor, which motor, at the place where any large amount 

 of light was required, would be employed in giving motion to a 

 second dynamo-electric machine, which would produce the 

 currents for lighting purposes. 



" This experiment I might show you, but as we have used 

 already several times during the evening electric lights fed from 

 a distance, we will vary the experiment and try an analogous one. 

 Messrs. Walker and Hall will now, at their works, give rapid 

 motion to a dynamo-machine, and the current which, when 

 properly arranged, as I have explained to you, may be small, will 

 set in motion this electro-motor. This in its turn will cause this 

 other dynamo machine to rotate rapidly and produce a current 

 which I will use for rapidly gilding this piece of plate." 



Calculation showed that if electric currents generated by very 

 large steam engines at certain points, and by turbines driven by 

 the falling water on the hillsides round Sheffield, were substituted 

 for the use of coal for motive power, smelting, heating, and 

 lighting buildings, that a saving of something like 400,000/. a 

 year might be anticipated for that town ; and as an argument to 

 prove that although such a reform was startling in its economical 

 bearing, it might nevertheless be sound, the following was 

 adduced: — Imagine the cost of cutlery and plated goods to remain 

 as at present, but all machinery to be removed from Sheffield, 

 then what an enormous loss would accrue to the town from 

 everything having to be done by hand labour. The saving 

 then which the lecturer was showing the audience how to obtain, 

 enormous though it might be, was still small compared with the 

 gain that the introduction of machinery during the last hundred 

 years had effected for that town. 



Next was considered whether the Sheffield Water Company 

 had any water in their reservoirs that could be spared for pro- 

 ducing motive power, since of course the water which did work 

 at its source would lose head and so be unable to come to the 

 tops of the houses in the town as at present, and it vi as shown 

 that there was a considerable surplus supply. As an illustration 

 of such a use of the %vater power, a two inch board was sawn on 

 the platform by a circular saw, driven by an electric current 

 generated by a water engine in the yard of the Water Works, 

 and conveyed to the Hall by wires crossing the streets. 



As a practical illustration of what had been done the lecturer 

 said: — "Last year two French engineers, MM, Chretien and 

 Felix, at Sermaize (Marne), actually ploughed fields by electricity, 

 the electric current being produced by two dynamo-electric 

 machines, of a form invented by M. Gramme, and shown in the 

 diagrams on the walls. These machines^ were usually worked 



