100 ON DIELECTRICS. 



At the bounding surface of two media we shall always have to 

 distinguish two densities ; the density a- of the fictive layer, which 

 must be assumed at the bounding surface of the dielectrics in order 

 that opposite any point, outside this surface, there may be the effect 

 equivalent to their internal polarization ; there is also the density </ 

 of the true layer, which might have been developed, by friction for 

 instance, on this same surface. 



We shall thus have for the bounding surface of the two media 

 the equations 



Agreeing to count in each medium the perpendiculars from the 

 surface, and calling V 1 and V 2 the values of the potential on the 

 two dielectrics respectively, these equations may be written 



0.OORY. + S + 



3V, SV 2 



^ +/+4 = 



The inductive capacity //. is always positive and greater than 

 unity ; in conductors it may be regarded as equal to infinity. 



117. In the case in which the dielectrics have not received 

 electricity either in the interior or on the surface, these equations 

 reduce to 



<>v 2 



from which we have 



4*7*! 



