297 



these results we see that we are always able to reduce mutual to self 

 inductance. Measuring the self inductance of a coil connected in 

 different ways, we can always determine the mutual inductances in 

 terms of the self inductances. 



Thus we need not search for methods of directly comparing mutual 

 inductances with each other, although I have given two of these, but 

 we can content ourselves with measuring self inductances and capaci- 

 ties. Fortunately most of the methods are specially adapted to the 

 latter, the ratio of self inductance to capacity being capable of great 

 exactness by many methods. 



In the use of condensers I have met with great difficulty from the 

 presence of electric absorption. I have found that this can be repre- 

 sented by a resistance placed in the circuit of the condenser, which 

 resistance is a function of current period. 



I have developed MaxwelPs theory of electric absorption in this 

 manner. Correcting his equations for a small error, I have developed 

 the resistance and capacity of a condenser as follows: 



Let a condenser be made of strata of thicknesses a x a 2 , etc., and 

 specific induction capacities fc x Jc 2) etc., and resistances p^ p 2 , etc. Then 

 we have 



where 



etc. 



etc. 



Mr. Penniman has experimented in the Johns Hopkins University 

 laboratory with condensers by method 25 and found some interesting 

 results. With a mica standard condenser of microfarad he was not 



