156 



EEPOET — 1892. 



The other two, Nos. 12 and 29, were H cells of the pattern described 

 by Lord Rayleigh. 



These cells were compared with the standard at tbe Cavendish 

 Laboratory with the results shown in Table XVII., which gives the 

 differences between the four cells and the standard in hundred thou- 

 sandths of a volt. 



Table XVII. 



On July 29 cell No. 71 had been taken away. Dr. Kahle kindly 

 determined the differences between No. 69 and each of the other cells 

 before they left Berlin. Values for these same differences can be obtained 

 from Table XVII. 



We thus get Table XVIII. 



Table XVIII. 



Thus the relative values of the cells as found at Cambridge are 

 practically the same as those found at Berlin. Moreover, taking the B.M.F. 

 of the Cambridge standard as 1'4<342 volt at 15° C, that of the Berlin 

 cells, with porous pots, is 1'43405, and of the Berlin H cells about 

 1-4338. 



The value actually found by Dr. Kahle for the B.M.F. of the porous 

 pot cells is 1'4336 volt, so that the agreement is satisfactory. In all the 

 above it has been assumed that the resistance of 106"30 centimetres of 

 mercury is 1 ohm, and that the amount of silver deposited per second by 

 a current of 1 ampere is 001118 gramme. 



The H form of cell in all cases examined at Berlin has a slightly 

 lower B.M.F. than those with the porous pots, the difference being about 

 •0003 volt. 



