ELECTKICAL MEASUREMENT BY ALTERNATING CURRENTS 301 



the wire almost independent of the current period, and does not, of 

 itself, introduce harmonics. The harmonics are due to the variation 

 of the magnetic permeability with the amount of magnetization. 



Electric absorption in a condenser acts as a resistance varying with 

 the square of the period, the capacity also varying, as I have shown 

 above. 



In general any circuit containing resistances, inductances and capaci- 

 ties combined acts as a resistance and inductance or capacity, both of 

 which vary with the current period, the square of the current period 

 alone entering. For symmetry the square of the current period can 

 alone enter in all these cases and those above. 



Hence only inductances containing no iron or not near any closed 

 metallic circuits have a fixed value. The same may be said of con- 

 densers, as they must be free from electric absorption or electrolytic 

 action to have constants independent of the period. There is no ap- 

 parent hysteresis in condensers and the constants do not apparently 

 vary with the electrostatic force. 



The following numbers indicate both the number of the method and 

 the figures in the plate, p. 302. 



Method 1. 



L' _ [r (R. + R' 

 ~c 



Method 2. 



-R.R"} \_R, (r+R"} + R u (r + fl,)] 



Method 3. 

 In (1) make R' = R" = R, t = Q or in (2) make R" = R t = 0, R,, = <x> , 



^ = rR 



c 



In case the circuit r contains some self inductance, I, we can correct 

 for it by the equation 



