548 THE POPULAR SCIENCE MONTHLY, 



Sir William Thomson early in this month wrote to the "Times," 

 pointing out the great advance which this invention had made in the 

 practical and economical storage of energy. His letter was answered 

 by Professor Osborne Reynolds, who, with the intention of preventing 

 the public from being astonished at the storing of so much energy as 

 one million foot-pounds in apparatus occupying a cubic foot of space 

 and weighing about seventy-two pounds, proceeded somewhat irrele- 

 vantly as w^e think to discuss the energy contained in a pound of coal, 

 and also to complicate the now inevitable controversy by referring to 

 a totally different problem, the transmission of energy by electrical 

 means. The controversy thus started has gone on. Sir William Thom- 

 son, Professor Osborne Reynolds, Professor Ayrton, and Professor 

 Tyndall, taking part in it. 



The question, as far as the public are concerned, is a purely com- 

 mercial one. As yet, of course, the data of the cost of the battery and 

 its durability are not yet ascertained ; but, in any future discussion on 

 the subject, the question of convenience, as well as that of absolute 

 expense, wall have to be taken into consideration. At joresent we 

 know that, at some expense, probably not too great, w^e can utilize a 

 source of energy of feeble power for many purposes by allowing it to 

 act for a long time, collecting its energy, and using it quickly, and 

 that the loss in the process wall be but small ; and that, further, if it 

 be desired to use the electric light temporarily, it can be produced 

 conveniently, if not economically, by the use of M. Faure's invention. 

 Sir William Thomson in his first letter points out many practical uses 

 for the new invention ; we may supplement them by pointing out how 

 the new secondary battery may be applied conveniently for many pur- 

 poses. Three ordinary Daniell's cells will charge an element of the 

 new battery easily, so that, if there be plenty of time for preparation, 

 we can, by the aid of Faure's batteries, use this cleanly apparatus, 

 which gives off no noxious fumes and needs but little attention, for all 

 the purposes for which, up to the present time, we were obliged to em- 

 ploy the costly and troublesome Grove's or Bunsen's batteries, which 

 contain violent caustic poisons, and give off irritating and unwhole- 

 some fumes. 



The whole discussion about the mechanical value of coal seems to 

 us mistaken ; neither Sir AVilliam Thomson nor any other physicist 

 proposes to use the new battery universally, and, at present, our 

 cheapest way of charging it is by the use of a dynamo-electric ma- 

 chine, driven by a steam- or gas-engine i. e., by making use of the 

 mechanical power of coal and the oxygen of the air ; setting aside, of 

 course, the exceptional cases where Avater-power is to be obtained. 

 Sir William Thomson himself gave, we think, the coiqj de grace to any 

 attempt at comparing the relative values of transmitting electric cur- 

 rents through conductors from the source of energy to a distant sta- 

 tion where energy is wanted, and conveying energy by exciting Faure's 



