NATURE 



^2,7 



THURSDAY, JUNE i6, 1881 



THE STORAGE OF ELECTRIC ENERGY 



I AM continuing my experiments on the Faure accumu- 

 lator with every-day increasing interest. I find M. 

 Reynier's statement, that a Faure accumulator, weighing 

 75 kilograms (165 lbs.) can store and give out again 

 energy to the extent of an hour's work of one-horse 

 power (2,000,000 foot-pounds) amply confirmed. I have 

 not yet succeeded in making the complete measurements 

 necessary to say exactly what proportion of the energy 

 used in the charging is lost in the process of charging and 

 discharging. If the processes are pushed on too fast 

 there is necessarily a great loss of energy, just as there is 

 in driving a small steam-engine so fast that energy is 

 wasted by "wire-drawing" of the steam through the 

 steam pipes and ports. If the processes are carried on 

 too slowly there is inevitably some loss through local 

 action, the spongy lead becoming oxidised, and the 

 peroxide losing some of its oxygen viciously, that is to 

 say, without doing the proper proportion of electric work 

 in the circuit. I have seen enough however to male me 

 feel very confident that in any mode of working the accu- 

 mulator not uselessly slow, the loss from local action 

 will be very small. I think it most probable that 

 at rates of working which would be perfectly convenient 

 for the ordinary use of fixed accumulators in connection 

 with electric lighting and electric transmission of power 

 for driving machinery, large and small, the loss of energy 

 in charging the accumulator and taking out the charge 

 again for use will be less than 10 per cent, of the whole 

 that is spent in charging the accumulator : but to realise 

 such dynamical economy as this prime cost in lead must 

 not be stinted. I have quite ascertained thataccumulators 

 amounting in weight to three-quarters of a ton will suffice 

 to work for six hours from one charge, doing work during 

 the six hours at the uniform rate of one-horse-power, and 

 with very high economy. I think it probable that the 

 economy will be so high that as much as 90 per cent, of 

 the energy spent in the charge will be given out 

 in the circuit external to the accumulator. When, 

 as in the proposed application to driving tramcars, 

 economy of weight is very important, much less per- 

 fect economy of energy must be looked for. Thus, 

 though an eighth of a ton of accumulators would 

 work very economically for six hours at one-sixth of a 

 horse-power, it would work much less economically for 

 one hour at one horse-power ; but not so uneconomically 

 as to be practically fatal to the proposed use. It seems 

 indeed very probable that a tramcar arranged to take in, 

 say 7i cwt. of freshly-charged accumulators, on leaving 

 head-quarters for an hour's run, may be driven more 

 economically by the electric energy operating through a 

 dynamo-electric machine than by horses. The question 

 of economy between accumulators carried in the tramcar, 

 as in M. Faure's proposal, and electricity transmitted 

 by an insulated conductor, as in the electric railway at 

 present being tried at Berlin by the Messrs. Siemens, is 

 one that can only be practically settled by experience. 

 In circumstances in which the insulated conductor can 

 be laid, Messrs. Siemens' plan will undoubtedly be the 

 Vol. XXIV. — No. 607 



most economical, as it will save the carriage of the weight 

 of the accumulators. But there are many cases in which 

 the insulated conductor is impracticable, and in which 

 M. Faure's plan may prove useful. Whether it be the 

 electric railway or the lead-driven tramcar, there is one 

 feature of peculiar scientific interest belonging to electro- 

 dynamic propulsion of road carriages. W'hatever work 

 is done by gravity on the carriage going down hill will be 

 laid up in store ready to assist afterwards in drawing the 

 carriage up the hill, provided electric accumulators be 

 used, whether at a fixed driving station or in the carriage 

 itself. WiLLiA.M Thomson 



University, Glasgow, June 13 



THE LIFE OF WHEWELL 



The Life, and Selections from the Correspondence, of 

 William Whewell, D.D., late Master of Trinity 

 College, Cambridge. By Mrs. Stair Douglas. (C. 

 Kegan Paul and Co., 188 1.) 



IT is now about four years since the first instalment of 

 a biography of the late Dr. Whewell was published- 

 These volumes, admirably edited by Mr. Todhunter, give 

 us a brief outline of his history, but consist chiefly of a 

 most valuable analytical account of his writings and a 

 selection from his literary and scientific correspondence. 

 In the preface a more complete memoir of Dr. Whewell's 

 personal and domestic history is announced as in pre- 

 paration. The present volume, edited by Dr. Whewell's 

 niece, Mrs. Stair Douglas, fulfils the promise then given. 

 The preface explains the long interval — fourteen years — 

 which has elapsed since Dr. Whewell's death. A series 

 of untoward events have continued to retard publication. 

 From various causes much delay occurred before the 

 exact plan of the work was determined and the subjects 

 apportioned. At first it was hoped that what may be 

 called the academic life of Dr. Whewell would be under- 

 taken by Mr. Aldis Wright, the present Bursar of Trinity 

 College. But the pressure of heavy and unavoidable 

 engagements has precluded him from proceeding with 

 the task. Mrs. Douglas then endeavoured to work the 

 materials into the selections from Dr. Whewell's personal 

 correspondence which she had nearly completed, with 

 the assistance of Mr. J. Lempriere Hammond, Fellow of 

 Trinity, and one of Dr. Whewell's executors. Before this 

 was accomplished she was deprived of his invaluable aid 

 by his lamented and untimely death. Thus some portions 

 of the present work are a little incomplete. Still, as these 

 are generally of a rather technical nature, and more interest- 

 ing to members of the University than to the general reader, 

 their absence probably will not be very widely felt. We 

 may be allowed to express our admiration at the tact and 

 good taste with which Mrs. Douglas has executed her 

 task. She allows Dr. Whewell as far as possible to speak 

 for himself, connecting his letters generally with only 

 such brief biographical paragraphs as are necessary for a 

 connected and intelligible narrative. There is little com- 

 ment and no attempt at the fulsome praise with which 

 biographies are often disfigured. Her descriptions, though 

 brief, are often graphic, while the letters enable us to see 

 the Master of Trinity as he appeared to the inner circle 

 of intimate friends and loved relations. 



Of his vast and varied knowledge it is almost needless 



