CLARK CELL AS A STANDARD OF ELECTROMOTIVE FORCE. 
025 
Rayleigh. The cells had been compared with each other and with other standards 
before leaving Berlin, the differences being determined in hundred-thousandths of 
a volt. 
Table XXI. gives the differences between these cells and our standards in hundred- 
thousandths of a volt. 
Table XXI. 
Date .... 
July 26. 
July 27. 
July 29. 
Temperature 
16°-1 
15°'9 
15°-9 
N umber. 
69 
- 15 
- 18 
- 14 
71 
- 11 
- 15 
Taken away 
29 
- 36 
- 35 
- 36 
12 
- 39 
- 38 
- 39 
In comparing these results with the numbers given in other tables, it must be borne 
in mind that the unit here is only one-twenty-fifth of that previously employed. 
It appears then that the standard form in use at Berlin has a slightly lower E.M.F. 
than that of our standard, while the H-cells are distinctly lower, differing by nearly 
•0004 volt. 
Dr. Kahle has made an important series of observations, ‘ Zeitschrift fur Instru- 
mentenkunde/ April, 1892, on the effect of impurities on the E.M.F. of an H cell, 
and has determined absolutely their E.M.F., and that of Dr. Feussner’s form of cell. 
On reducing his numbers to the units employed by us, we find for the E.M.F. of 
the Feussner cell the value 1’4339 volt, and for that of the H-cell 1’4337 volt. 
The value obtained by us for the E.M.F. of our standard is F4342 volt. Thus 
Dr. Kahle’s experiments agree with our own in making the E.M.F. of our cells rather 
higher than those constructed by him, though the difference is small. 
As we have already mentioned, the differences between the Cell No. 69 and the 
others were found at Berlin ; the same differences can be obtained from our experi¬ 
ments. They are shown in the following :— 
4 L 
MDCCCXCII.-A. 
