366 Prof. J. A. McClelland on the Comparison 
about 60 scale-divisions for 1 volt, and about 30 grams of 
uranium nitrate were placed on the central part of the plate A; 
observations were taken alternately with the capacity C joined 
up to c, and with the capacity ‘001 microfarad joined up to e,. 
giving results as follows :— 
001+. C+e. 
dU divisions in 52°6 seconds 
50 divisions in 52°5 
50 divisions in 52°2 
Mean... 52-43. ;, Mean... 89:1 
Therefore C+e 2 8910 
“G01 ¢ 67 S245" 
50 divisions in 89 
‘D> seconds 
”? 50 divisions in 88°7 
9 
yD] 
) 

A smaller quantity of uranium was then used to determine 
the ratio between c and ‘001 microfarad, as with the quantity 
used above the movement of the spot of light would have been 
too rapid when only the capacity c wasin use. The following 
are the numbers in this determination :— 
e+001. c. és 
100 divisions in 21°9 seeonds. 
50. divisions in 7)5°8 seconds ae Ye ay 
10 divisions in 21°8 
50 divisions in 75°7 
99 
‘4 100 divisions in 22°2 __,, 
Meany. i ter os - Mean... 21°30 
Therefore e+ 001 _ 15150 
c DOG 
These equations give 
e¢ ='000169 microfarad ; 
C='001817 microfarad. 
To give somewhat of a test of the reliability of the method, 
the same capacity was determined on another occasion, taking 
no care to use the same quantity of uranium, and, in fact, 
having very different ionization-currents from those used in 
the first case. The following numbers were obtained, only 
one observation being taken in each case :— o4: 
C+e, “O01 +e. ‘ 
50 divisions.in 48°2 seconds 50 divisions in 28*6 seconds. 
c+ -001, : 3 | 
50 divisions in 56°5 __,, 100 divisions in 16°D «4, ° 
