298 Prof. Daniell mi the Constant Voltaic Battery. 



d'acide nitrique versee dans la case zinc : si Von en met avec pre- 

 caution, on pent arriver a ohtenir un courant constant pendant 

 jmc demi-heure ou une heure. Cette disposition dii couple X'ea- 

 lise done pendant un certain temps le resultat que nous avons 

 annonce, c'est-a-dire detruit le courant secondaire; car Vacide 

 nitrique qui se trouvc dans la case zinc s'empare constamment du 

 cuivre de la solution, qui, apres avoir traverse les diaphragmes, 

 se depose sur le zinc. 



" Ainsi ces experiences montrent la possibilite d'obtenir un 

 coui'ant constant en detruisantle courant secondaire." (P.4'40.) 



Now, most assuredl}', the principles and results derived 

 from these experiments are not the principles and results of 

 " the constant battery : " they are not the principles and re- 

 sults of my battery, which M. Becquerel has nevertheless de- 

 scribed as — " construit d'apres les principes exposes precedem- 

 ment," and, as one amongst other similar ones, " d'un usage 

 plus facile et dont Taction est constante pendant un temps plus 

 long." (P. 444.) 



The amount oi constancy which M. E. Becquerel obtained, 

 and the certainty with which he obtained it, are thus described 

 in his original memoir : — 



" II m'est arrivee plusieurs Jbis d'obtenir une compensation 

 telle que les deviations de I'aiguille aimantee etaient constants 

 pendant une heure, avantage que Ton n'a jamais avec les piles 

 ordinaires ;" and M. E. Becquerel, as we have just seen, says 

 that " by adding nitric acid with precaution one may manage 

 to obtain a constant current for half an hour or an hour." 



With my constant battery, constructed with siphon tubes, 

 as described by M. E. Becquerel, a steady current might be 

 kept up, if necessary, for a week together, provided a proper 

 supply of materials were furnished; and the amount of force 

 set in action by it would be measured not by some 60° of the 

 galvanometer, but by the number of yards of platinum wire 

 which it would fuse or render red-hot. 



Even in the use of the diaphragm*, which might at first 

 sight appear to be similar in the two constructions, there is 

 direct opposition ; for my object is to keep the two electro-, 

 lytes which 1 employ perfectly separate, so that no portion 

 of one may penetrate to the other, except in the process of 

 electrolysis, while, according to M. Becquerel's principles, it 



* The passage of the voltaic current through diaphragms of bladder was 

 well Known to experimentalists before the publication of M. Becquerel's 

 researches. 'J'he late Dr. Ritchie, amongst others, made frequent use of 

 them ; and in the Phil. Trans, for 1829, p. 363, there is a paper by that gen- 

 tleman, in which " a small rectangular box divided into two compartments 

 by a diaplu'agm of bladder " is described, which was used for the purpose 

 of exposing the plates of a galvanic circle to two diiferent liquids. 



