98 ON DIELECTRICS. 



give the equation 



i 



tan /= tan /', 



which expresses what may be called the law of refraction of the 

 force, or of the flow at the moment at which the force passes from 

 air into a liquid or solid dielectric. 



114. More generally, let us suppose that the surface S separates 

 two dielectrics, solids or liquids, whose specific inductive capacities 

 are respectively equal to /^ and /* 2 . If the surface is replaced by 

 an infinitely thin layer of air, then if F, F 1? and F 2 are the forces in 

 air, in the first, and in the second medium, we shall have 



11/1 



from which is deduced 



(F n ) 

 and 



The fictive layer is determined by the equation 

 ( F J2 ~ ( F )i = 



putting <r = Oj + <r 2 . Lastly, the law of refraction gives for the angles 

 t\ and /g of the forces, with the perpendicular on both sides of the 

 surface, the ratio 



tan t\ tan / 



115. TUBES AND FLOW OF INDUCTION. Let us agree to apply 

 the term induction at a point, to the product of the force F by the 

 specific inductive capacity p of the substance, and the term quantity 



