328 HENRY A. KOWLAND 



being very accurate, as will be seen later, great care had to be used to 

 eliminate all sources of error, as for example, electrostatic action. In 

 the first trial of the method small differences were noticed in the ratio 

 of two self-inductances, depending both on the resistances used, and 

 also on the connections of the coils, whether the leads were double, 

 single, long or short. The same variation was noticed when several 

 coils were joined in series and compared with another coil, and when 

 these coils were compared separately and their sum taken. 



This irregularity led to an investigation of the effects of various 

 resistances and connections in one of the circuits, the other circuit 

 being unaltered. A little farther on, the variation in the deduced value 

 of the self -inductance of one of the coils, when different resistances and 

 leads were used, will be given, which variation was caused by the 

 electrostatic action of the connections, etc. (Page 316.) 



The necessity of eliminating electrostatic action made obligatory the 

 use of open resistances which had small self-inductances. These re- 

 sistances were of three kinds resistances in the form of spirals, resist- 

 ances wound on thin strips of micanite or paper, and those wound on 

 open frames; see page 316. 



The self-inductance of the first and second classes of resistances was 

 very small, as in one case there were only a few turns, and in the other 

 the cross-section was very small. 



The third class were those wound on frames whose self-inductances 

 were calculated. There were several resistances of 2000 ohms each, 

 whose self -inductances were -0000436 henry, which would hardly affect 

 the phase of the current or the impedance of the circuit. 



These coils were subdivided into resistances of various amounts. 

 Another frame resistance used was of 7463 ohms divided into parts of 

 about 250 ohms each. The self-inductance of the entire 7463 ohms 

 was -000105 henry. 



As the open resistances were not divided into small amounts it was 

 necessary to use resistance boxes for adjustment; as few ohms as possi- 

 ble were used in each case. 



From the fact that the coils of the electrodynamometer had self- 

 inductance a correction was introduced in order that the ratio of the 

 resistances should give the ratio of the self-inductances of the coils 

 direct. 



The value of this correction in ohms was calculated as follows: 



