Prof. Daniell on the Constant Voltaic Battery. 297 



quid of one of the exti'eme compartments. A plate of zinc 

 was immersed in one and a plate of copper in the other, and 

 the two were placed in metallic communication by means of 

 the wires of a galvanometer. 



Under these circumstances, when all the compartments were 

 charged with dilute sulphuric acid (joth acid), a deviation of 

 the galvanometer needle was produced, which, as with an or- 

 dinary couple, gradually decreased. Upon consulting M. 

 Becquerel's original memoir {Ann. de Phys. et de Ckim., tome 

 xli. p. 21), I find the following tabular record of the results : — • 

 Time of Immersion. Deviation of Needle. 



0' 63° 



15' 53 



30' 46 



Upon re-commencing the experiment with the addition of 

 3?jith nitric acid to the dilute sulphuric acid in the copper com- 

 partment, the intensity of the current changed, but gradually 

 diminished as in the following table : — 



Time of Immersion. Deviation of Needle. 



0' 81° 



15' 73 



30' 65 



Upon the substitution of nitrate of copper for the nitric acid, 

 the results were sensibly the same. M. Becquerel varied these 

 experiments in many ways, and with the aid of this apparatus 

 arrived at the following conclusions: — 



" The maximum of intensity is obtained by immersing the 

 copper plate in a solution of nitrate of copper, and the zinc in 

 a solution of sulphate of zinc, but there is also a diminution with 

 time ; a little less rapid however than with an ordinary couple." 

 The following is the table of the last results : — 

 Time of Immersion. Deviation of Needle. 



0' 84° 



15' 72 



30' 68 



The next paragraph of M. E. Becquerel's 'Notice' I will 

 give in his own words for fear of mistakes : — 



" Si Ton met de I'acide nitrique etendu dans la case zinc, 

 un peu d'eau et d'acide sulfurique dans la case cuivre, et que 

 dans la caisse A A' on n'emploie qu'un diaphragme, ou que 

 Ton rapproche les deux diaphragmes de telle sorte que I'acide 

 nitrique de la case zinc puisse passer lentement dans la case 

 cuivre, afin d'augmenter la conductibilitc, alors on peut, au 

 lieu de rendre les intensites decroissantes, les rendre croissantes 

 pendant la premiere demi-heure ; cela depend de la quantite 

 Phil. Mag. S. 3. VoK 20. No. 131. April 184-2. X 



