312 Hoy al Society, 



5 I 



.'. 2' = 208Ml,-82; = 3™-90,2 = 2085-01,error + 0™-55 = — ^. 



M. Poisson's formula gives 



2;' = 2077-98, 1 8 s = 3-98, 2=2081-96, error-2'5 = —. 



Supposing the observations to be exact, the only cause of 

 variation is the hygrometrical state of the air, which in the 



extreme case may cause a difference of '0012508 = : and 



800 



consequently my error shows the atmosphere to be nearly in 

 its mean state, whilst M. Poisson's must suppose the air to be 

 excessively humid. 



I am. Gentlemen, your most obedient, 

 London, June 4, 1839. S. M. Drach. 



XL VI II. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from vol. xiv. p. 502.] 



May 30,— npHE reading of a paper entitled, " Fifth letter on Vol- 

 X taic Combinations ; with some account of the effects 

 of a large Constant Battery : addressed to Michael Faraday, Esq., 

 D.C.L., F.R.S., Fullerian Professor of Chemistry in the Royal In- 

 stitution of Great Britain. By John Frederic Daniell, Esq., F.R.S., 

 Professor of Chemistry in King's College, London," was resumed 

 and concluded. 



The author, pursuing the train of reasoning detailed in his pre- 

 ceding letters*, enters into the further investigation of the variable 

 conditions in a voltaic combination on which its efficiency depends ; 

 and the determination of the proper proportions of its elements for 

 the economical application of its power to useful purposes. He 

 finds that the action of the battery is by no means proportioned to 

 the surfaces of the conducting hemispheres, but approximates to the 

 simple ratio of their diameters ; and hence concludes that the cir- 

 culating force of both simple and compound voltaic circuits in- 

 creases with the surface of the conducting plates surrounding the 

 active centres. On these principles he constructed a constant bat- 

 tery consisting of seventy cells in a single series, which gave, be- 

 tween charcoal points separated to a distance of three-quarters of 

 an inch, a flame of considerably volume, forming a continuous arch, 

 and emitting radiant heat and light of the greatest intensity. The 

 latter, indeed, proved highly injurious to the eyes of the spectators, 

 in which, although they were protected by grey glasses of double 



• Al)stracts of Prof. Daniell's preceding letters have appeared in Lond. 

 and Edinb. Phil. Mag., vol. viii. p. 431 ; vol. ix. p. 376; and vol. xii. p. 364. 



