364 MAGNETIC INDUCTION. 



that is to say 



or 



The functions 12 and ft' which determine the surface layer are 

 defined by the same conditions as the preceding, with this single 

 difference, that the equation of continuity (4) contains the co- 

 efficients of induction of the two media. 



The surface density is still given by the perpendicular components 



If we put 

 that is to say 



4717* 



the expression for the density becomes 



47TO- = F n (/x 1 - i), or o- = kf n . 



It is this surface layer which determines the motion of the body 

 A in the medium. It is the same as if the external medium were 

 suppressed, or more exactly replaced by air, and the coefficient 

 of induction of the body replaced by another value /*j, or the 

 coefficient of magnetisation k by a different value k v The apparent 

 magnetisation I v of the body would thus have for its perpendicular 

 projection 



382. The discussion of this problem gives rise to some con- 

 clusions analogous to those which are deduced from the principle of 

 Archimedes for bodies immersed in liquids. 



