THREE DIELECTRICS SEPARATED BY PARALLEL PLANES. 131 



The perpendicular components of the force are, at the same 

 points, 



COS 0) 



In order to satisfy the equation of continuity of the dielectrics, the 

 product of the perpendicular component by the specific inductive 

 capacity, must be the same on both sides of the surface of separation, 

 which gives 



whence 



The density at every point in the plane is 



, _ 



2m a i 



47T 



2ma i zma i 



47T ' p 3 



47T ' /O 3 ' 



150. THREE DIELECTRICS SEPARATED BY PARALLEL PLANES. 

 Let us imagine three different media, whose specific inductive capa- 



Fig. 38. 



cities are respectively equal to ^ lf p 2 and yn 3 , separated by parallel 

 planes Q and Q', and let the acting mass m be situate in the first 

 medium, at A (Fig. 38). 



K 2 



