362 MAGNETIC INDUCTION. 



equation, both inside and outside the surface. If we denote by 12' its 

 value on the outside, for two infinitely near points on opposite sides 

 of the surface, we shall have the condition 



379. EQUATION OF CONTINUITY. COEFFICIENT OF INDUCTION. 

 The principle of the conservation of the flow of induction (323) 

 enables us to establish in a very simple manner the conditions 

 of continuity V, U, and 12, at the surface of the magnetised 

 body. 



Consider two infinitely near points on the perpendicular on each 

 side of the surface ; let F : be the value of the induction at the point 

 n the interior, F\ the value of the magnetic force at the external 

 point. If (F 1 ) n and F n denote the normal components of these two 

 forces calculated in the same direction, then in virtue of the theorem 

 of the conservation of flow, we have the condition 



The magnetisation being parallel to the magnetising force, the 

 induction in the present case becomes 



it is proportional to the magnetising force. 

 If we put 



we have 



and the equation relative to the surface becomes then 



() fF.-F.. or M-l* 



Thus, for two infinitely near points on either side of the surface, the 

 ratio of the perpendicular components of the magnetic force is constant. 

 This is a fundamental deduction from Poisson's theory, which we 

 have already used (111) in defining dielectrics. The coefficient /* 



