SUPERFICIAL INDUCED MAGNETISATION. 361 



This conclusion presupposes that the parenthesis i + 4^ is not 

 zero ; but this latter case never occurs, the absolute value of k for 



diamagnetic bodies being far from attaining . 



4?r 



377. The surface density a- of the induced layer is 



cr = l COS0, 



6 being the angle of the magnetisation with the perpendicular to the 

 surface (Fig 84). 



Fig. 84. 



Let this perpendicular be called n when it is drawn inwards, 

 and n' when it is drawn outwards, and let a be the perpendicular 

 to the surface for which the function 3> has a constant value, 

 we have 



o- = I cos 6 = ; = - . 

 on un 



378. The value of the potential due to the induced masses that 

 is to say, to the surface layer is 



-//=? 



The function 12 is finite and continuous, and satisfies Laplace's 



