M'Clelland — Comparison of Capacities in Electrical Work. 171 

 Time taken to move over 50 scale-divisions : — 



Mean, 



The agreement between these numbers is no better than that 

 usually observed in other experiments ; in fact, not as good as in 

 many other cases. 



(b) We shall now give the numbers observed in a comparison 

 of a condenser with a standard condenser, marked *001 micro- 

 forad. We shall denote the capacity of the condenser to be 

 measured by C, and the capacity of the electrometer and other 

 parts of the system, by c. 



The electrometer in this experiment gave a deflection of 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 c, giving results 

 as follows : — 



•001 + e 



50 divisions in 52'6" 



50 divisions in 52 , 5 // 



50 divisions in 52*2" 

 Mean, 52-43' 



C+e 



50 divisions in 89-5" 

 50 divisions in 88-7' 



Mean, 89 1' 



Therefore, 



C+c 



8910 



•001 + c 5243 



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 



