408 Dr. 0. Y. Drysdale on the Use of the 



the possibilities of the method. An ordinary Crompton 

 potentiometer was used with a Weston dynamometer volt- 

 meter in series with it, and the connexions were made as in 

 fig. 3. A Rubens vibration galvanometer was at first used, 



Fiff. 3. 



CRCnPTOw POTEN 



but was replaced by a Campbell bifilar instrument, which 

 was found much more sensitive and convenient. A check 

 with direct current and a Cadmium cell showed that the 

 normal current was obtained when the dynamometer indicated 

 82 " volts," and this reading was reproduced in all the 

 ■alternate-current measurements. 



The first test was a comparison of the readings of a 

 Kelvin Deka-ampere-balance, with the current as given by 

 the P.D. across a Crompton *04 o> manoanin resistance. 

 The following results were obtained : — 



Current bj 

 Kelvin. 



Current by 

 Potentiometer. 



Frequency of supply 



