156 



NATURE 



[ymte 1 6, 1 88 1 



of gas produced, 61-50 cubic metres of illuminating gas, and 

 38-50 cubic metres of heating and motive-power gas. 



This result would be obtained by receiving into separate 

 reservoirs the gas produced during the first fifteen minutes, and 

 durinc the last ih. 45m. of the distillation, and in reserving for 

 illuminating purposes the gas made in the interval of oh. I5ni. 

 to 2h. 15m. of the charge from the coiumencement of the 

 distillation. 



STORAGE OF ELECTRIC ENERGY 



THE following correspondence on this subject has appeared in 

 the Times. By help of this and the communication in 

 our issue of to-day from Sir W. Thom-on, the reader will be 

 able to understand the present position of this important 

 question. 



The marvellous " box of electricity " described in a letter to 

 you, which was published in the Times off.May 16, has been 

 subjected to a variety of trials and measurements in my labora- 

 tory for now three weeks, and I think it may interest your readers 

 to learn that the results show your correspondent to have been 

 by no means too enthusiastic as to its great practical value. I 

 am continuing my experiments to learn the behaviour of the 

 Faure batteiy in varied circumstances, and to do what I can 

 towards finding the best way of arranging it for the different 

 kinds of service to which it is to be applied. At the request of 

 the Conseil d'Administration of the Societe de la Force et la 

 Lumiere, I have gladly undertaken this work, because the 

 subject is one in which I feel intensely interested, seeing in it a 

 realisation of the most ardently and unceasingly felt scientific 

 aspiration of my life — an aspiration which I scarcely dared to 

 expect or to hope to live to see realised. 



The problem of converting energy into apreservable and stor- 

 able form, and of laying it up in store conveniently for allowing 

 it to be used at any time when wanted, is one of the most 

 interesting and important in the whole range of science. It is 

 solved on a small scale in winding up a watch, in drawing a bow, 

 in compressing air into the receiver of an air-gun or of a White- 

 head torpedo, in winding up the weights of a clock or other 

 machine driven by weights, and in pumping up water to a height 

 by a windmill (or otherwise, as in Sir William Armstrong's 

 hydraulic accumulator) for the purpo- e of using it afterwards to 

 do work by a waterwheel or water pressure on a piston. It is 

 solved on a large scale by the application of burning fuel to smelt 

 zinc, to be afterwards used to give electric light or to drive .an 

 electro-magnetic engine by becoming, as it were unsmeited in a 

 voltaic battery. Ever since Joule, forty years ago, founded the 

 thermodynamic theory of the voltaic battery and the electro- 

 magnetic engine, the idea of applying the engine to work the 

 battery backwards and thus restore the chemical energy to the 

 materials so that they may again act voltaically, and again and 

 again, has been familiar in science. But with all ordinary forms 

 of voltaic battery the realisation of the idea to any purpose 

 seemed hopelessly distant. By Plante's admirable disco veiy of 

 the lead and peroxide of kad voltaic ba.tery, alluded to by your 

 correspondent, an important advance towards the desired object 

 was made twenty years ago ; and now by M. Faure's improve- 

 ment practical fiuition is attained. 



The " mdlion of foot pounds " kept in the box during its 

 seventy-two hours' journey from Paris to Glasgow was no ex- 

 aggeration. One of the four cell^, after being discharged, was 

 recharged again by my own laboratory battery, and then left to 

 itself absolutely undisturbed for ten days. After that it yielded 

 to me 260,000 foot pounds (or a little more than a quarter of a 

 million). This not only confirms M. Reynier's measurements, 

 on the faith of which your correspondent's statement was made ; 

 it seems further to show that the waste of the stored energy by 

 time is not great, and that for days or weeks, at all events, it 

 may not be of practical moment. This, however, is a question 

 which can only be answered by careful observations and measure- 

 ments car ied on for a much longer time than I have hitherto 

 had for investigating the Faure battery. I have already ascer- 

 tained enough regarding its qualities to make it quite certain that 

 it solves the problem ( f storing ele:;tric energy in a manner and 

 on a scale useful for many impor'.ant practical applications. It 

 has already had in this country one interesting application, of 

 the smallest in respect to dynamical energy used, but not of the 

 smallest in respect to ber.eficei.ce, of all that may be expected of 



it. A few days ago my colleague, Prof. George Buchanan, car- 

 ried away from my laboratory one of the lead cells (weighing about 

 18 lbs.) in his carriage, and by it ignited the thick platinum wire 

 of a galvanic ccraseur and bloodlessly removed a nevoid tumour 

 frc'ni the tongue of a young boy in about a minute of time. The 

 operation would have occupied over ten minutes if performed 

 by the ordinary chain icraseur, as it must have been had the 

 Faure cell not been available, because in the circumstances the 

 surgical electrician, with his pharaphernalia of voltaic battery to 

 be set up beforehand, would not have been practically admissible. 



The largest useful application waiting ju^t now for the Faure 

 battery — and it is to be hoped that the very iniHimum of time 

 will be allowed to pass till the battery is supplied for this appli- 

 cation — is to do for the electric light what a water cistern in a 

 house does for an inconstant water supply. A little battery of 

 seven of the boxes described by your correspondent suffices to 

 give the incandescence in Swan or Edison lights to the extent of 

 100 canoles for six hours, without any perceptible diminution of 

 brilliancy. Thus, instead of needing a gas engine or steam 

 engine to be kept at work as long as the light is wanted, with 

 the liability of the light failing at any moment through the 

 flipping of a belt — an accident of too frequent occurrence— or 

 any other breakdown or stoppage of the machinery, and instead 

 of the wasteful inactivity during the hours of day or night when 

 the light is not required, the engine may be kept going all day 

 and stopped at night, or it may be kept going day and night, 

 w hich will undoubtedly be the most economical plan when the 

 electric light comes into general enough use. The Faure 

 accumulator, always kept charged from the engine by the house 

 supply wiie, with a proper automatic stop to check the supply 

 w hen the accumulator is full, will be always ready at any hour 

 of the day or night to give whatever light is required. Precisely 

 the same advantages in respect of force will be gained by the 

 accumulator when the electric town sujply i^, as it surely will 

 be before many years pass, regularly used for turning lathes and 

 other machinery in workshops and sewing-machines in private 

 houses. 



Another very important application of the accumulator is for 

 the electric lighting of steam-ships. A dynamo-electric machine 

 of very moderate magnitude and expense, driven by a belt from 

 a drum on the main shaft, working through the twenty-four 

 lioure, will keep a Faure accumulator full, and thus, notwith- 

 standing irregularilies of the speed of the engine at sea or occa- 

 sional stoppages, the supply of electricity will always be ready 

 to feed Swan or Edison lamps in the engine-room and cabins, 

 or arc lights for mast-head and red and green side lamps, wiih 

 mere certainty and regularity than have yet been achieved in the 

 gas supply for any house on terra firma. 



I must apol'gise for trespassing so largely on your space. 

 My apology is that the subject is exciting great interest among 

 the public, and that even so slight an instahijent of information 

 and suggestions as I venture to offer in this letter may be 

 acceptable to some of your readers. William Thomson. 



The University, Glasgow, June 6. 



Although agreeing with every word of Sir William Thom- 

 son's letter in the Times of to-day, and ei.tirely sympathising 

 with his enthusiasm as regards the n arvellous box of electricit)', 

 still I feel that it would have been desirable if in pointing 

 out the importance of this new discovery Sir William Thomson 

 had guarded against a very probable misconslniction of the 

 purport of his letter. 



The means of storing and re-storing mechanical energy form 

 the aspiratirrn not only of Sir William, but of every educated 

 mechanic. It is, however, a question of degree — of the amount 

 of energy stored as compared with the weight of the reservoir, 

 the standard of d mparison being coal and corn. Looked at in 

 this w ay one cannot but ask whether, if this form of storage is 

 to be the realisation of our aspirations, it is not completely 

 disappointing. Large numbers are apt to create a wrong im- 

 pression until we inquire what is the unit. Eleven million foot 

 pounds of energy is what is stored in I lb. of ordinary coal. So 

 that in this box, weighing 75 lb., there was just as much energy 

 as in I .^ oz. of coal, which might have been brought from Paris 

 or anywhere eLe in a waistcoat pocket, or have been sent by 

 letter. 



When we come to the question of the actual conveyance of 

 energy for mechanical purposes, this view is of fundamental 

 importance. The weight of the same amount of energy in the 

 new form is Soo times greater than the equivalent amount of 

 coal; and as a matter of economy, supposing that energy in this 



