POWER LOSSES IN INSULATING MAIERLILS 



113 



TABLE II. 



Variation with Temperature of Dielectric Constant, Phase Difference and Their Product 

 for Some Commercial Insulating Materials {Frequency 500,000 C. P. S.) * 



The above data were obtained by the resistance variation method,* 

 Fig. 1. Each value of phase difference and of dielectric constant 

 represents the average of at least five readings on a single sample 

 using not less than three different values of the known resistance R. 

 A condenser, the dielectric of which consists of the material to be 

 tested, is connected in series with a suitable inductance, a known re- 



* The measurements on each sample were made in the order in which they are 

 given in the table. 



' Bureau of Standard Circular No. 74, p. 180. 



