ELECTEOMOTIVE FORCES OF THE ELECTRIC ARC. 



311 



The two quantities, the impedance and power- factor, are therefore determined in 

 terms of a resistance R and three R.M.S. voltages quite independent of any 



--v- 



Fig. 2. 



assumptions as to the wave-form of the alternating testing current. If the same 

 voltmeter is used to measure each of these voltages, then it will be noticed that the 

 results only depend on the relative calibration of one instrument, a consideration of 

 great importance owing to the difficulties in the way of accurate absolute calibration 

 with the very high frequencies used. 



Circuit and Apparatus Used. 



In order to measure the impedance and power-factor by the method just considered, 

 several different arrangements of the circuit were tried ; that finally adopted for the 



I/ '. 



Fig. 3 



experiments is shown diagrammatically in fig. 3. The main direct-current circuit 

 consisted of: 



