of Capacities in Electrical Work. 367 
Calculating as before, we get 
ce =°000170 microfarad, 
C=:001802 microfarad. 
The agreement with the preceding numbers is very good, 
especially when we consider that only one observation was 
taken in each case. 
(c) To show that this method is suitable for much larger 
capacities than those used in the preceding examples, we 
shall give an example in which a capacity known to be about 
*5 microfarad was determined by comparing it with a standard 
capacity of ‘1 microfarad. For this purpose, an electrometer 
of the Dolezalek type was used, giving a deflexion equal to 
5300 scale-divisions for 1 volt. 
Observations were taken as before, first with the unknown 
capacity C joined up to the electrometer and the plate A, and 
then with the capacity *1 microfarad joined up. 
About 100 grams of uranium nitrate were placed on A 
(fig. 1), and the following numbers noted; ¢ denotes the 
capacity of the Dolezalek electrometer, and some apparatus 
that was in connexion with it :— 


C+e. ‘Ite. 
50 divisions in 104°5 seconds 100 divisions in 41°8 seconds 
50 divisions in 1044 _,, 100 divisions in 41°8 __,, 
Mean... 104°45__ Mean... 41°8 
Therefore C+e_ 2089 
‘lt+e 41-3” 
Less than 1 gram of uranium nitrate was now used te 
determine the ratio of c to a known capacity of ‘001 micro- 
farad, giving as follows :— 
c. e+:001. 
100 divisions in 21°0 seconds 100 divisions in 30°5 seconds 
100 divisions in 21:2 __,, 100 divisions in 30°0 __,, 
Therefore e+ 001 te 605 
C 422 
These equations give— 
=°0023 microfarad, 
C =*5089 microfarad. 
A repetition of this determination gave as before, with 
smaller capacities, an equally consistent result. 
2C2 Ta 

