COEFFICIENT OF INDUCTION. 363 



represented the specific inductive capacity of electricity; we shall 

 here call it the coefficient of magnetic induction. It must not be 

 confounded with the coefficient of induced magnetism which has 

 been represented by k. 



380. Expressing equation (2) as a function of the potentials, 

 we get 



or 



To determine the magnetisation of a body placed in a magnetic 

 field, and bounded by a surface S, we must find two conditions 12 

 and 12' which satisfy the following conditions 



i st The function is finite and continuous in the interior of the 

 surface, and satisfies Laplace's equation A12 = 0. 



2nd. The function 12' is finite and continuous on the exterior, zero 

 at an infinite distance, and also satisfies Laplace's equation. 



3rd. The functions 12 and 12' are equal to each other on the 

 surface, and their differentials satisfy the equation of continuity (3). 



These functions represent the potential of a magnetic layer 

 distributed on the surface of the body. The density of this layer at 

 every point is determined by the variation of the normal components, 

 which gives 



from which is deduced 





381. CASE OF Two DIFFERENT MAGNETIC MEDIA. RELATIVE 

 MAGNETISATION. Let us suppose that the body A, bounded by the 

 surface S, is situated in a magnetic medium whose coefficient of 

 induction is //; the theorem of the conservation of the flow of 

 induction gives still 



