142 HEXRY A. KOWLAND 



It is to be noted that the cases of electric absorption which we 

 observe are mostly those of condensers formed of two planes, or of one 

 cylinder inside another, as in a telegraph cable. Our theory shows 

 that different explanations can be given of these two cases. 



The case of parallel plates does not admit of being explained, except 

 on the supposition that m varies in the first manner above given, or in 

 this manner in combination with the others, for we can only conceive 

 of the conductivity and the specific inductive capacity as being func- 

 tions of the ordinate or of the electric force. As the latter is constant 

 for all points between the plates, m would still be constant although it 

 were a function of the electric force, and thus electric absorption would 

 not take place. 



We may then conclude that in the case of parallel plates, omitting 

 explanations based on electrolysis or thermo-electric currents, the only 

 explanation that we can give at present is that which depends on the 

 non-homogeneity of the body, and is the case which Maxwell has given 

 in the form of two different materials. Our equations show that the 

 form of layers is not necessary, but that any departure from homo- 

 geneity is sufficient. It is to be noted that the homogeneity, which we 

 speak of, is electrical homogeneity, and that a mass of crystals with 

 their axes in different directions would evidently not be electrically 

 homogeneous and would thus possess the property in question. In the 

 case of glass it is very possible that this may be the case and it would 

 certainly be so for ice or any other crystalline substance which had 

 been melted and cooled. 



In the case of hard india rubber, the black color is due to the particles 

 of carbon, and as other materials are incorporated into it during the 

 process of manufacture, it is certainly not electrically homogeneous. 



As to the ordinary explanation that the electricity penetrates a little 

 below the surface and then reappears again to form the residual charge, 

 we see that it is in general entirely false. We could, indeed, form a 

 condenser in which the surface of the dielectric would be a better con- 

 ductor than the interior and which would act thus. But in general, 

 the theory shows that the action takes place throughout the mass of 

 the dielectric, where that is of a fine grained structure and apparently 

 homogeneous, as in the case of glass, and consists of a polarization of 

 every part of the dielectric. 



To consider more fully the case of a condenser made of parallel 

 plates, let us resume our original equations. Without much loss of 

 generality we can assume a laminated structure of the substance in 



