148 



REPOBT 1892. 



Table IX. 



The mean value of the temperature-coefficient, therefore, would be 

 0-000796 + 0-000014 (i-15). 



Lord Rayleigh has given the following values for the two different 

 cells he investigated : — 



+ 0-000827 + 0-000018 (t-lb) 



+ 0-000740 + 0-000016 {t-16) 

 the mean being 



+ 0-000783 + 0-000017 (t-U). 



I suppose, for practical purposes, the values found by Lord Rayleigh 

 and by me are identical. 



The most important matter is to obtain the absolute term of the 

 E.M.F. For the purpose I used a measuring arrangement similar to 

 Lord Rayleigh's. The current, which produces on the terminals of a 

 known resistance a pressure equal to that of the Clark cell, was obtained 

 by the silver voltameter. It was found that the same current deposits 

 the more silver the more oxide of silver is dissolved in the solution of the 

 nitrate. I made a solution of nitrate crystals, and boiled a part of it a 

 long time with oxide of silver ; the deposit obtained with this basic solution 

 was about ^ Q^p^ ths greater than that with the original solution. There- 

 fore, using a certain number for the equivalent of silver, there will be a 

 little uncertainty of some parts in 10,000 in measuring currents by the 

 deposit of silver. Now, as first shown by Professor Schuster, and also 

 proved by me by a good deal of experimenting, the deposit, when the 

 voltameter is in vacuo, is about four parts of 10,000 greater than in 

 ordinary air. But the absolute value of the E.M.F. is not touched by 



