ANISOTRpPIC BODIES. 375 



392. ANISOTROPIC BODIES. Consider an anisotropic body in a 

 uniform field. Let , ', k" be the three principal coefficients of 

 magnetisation, and A, A', A" the cosines of the angles of the strength 

 of the field with the axes ; the coefficients of magnetisation being 

 supposed to be very small, the values of the intensities of the three 

 partial magnetisations will be 



and the corresponding magnetic moments 



=ul = u< 

 1 =ul' =u<i>k'\', 



From this we deduce, for the resultant magnetic moment, 

 M 2 = 



The resultant magnetic axis of the sphere makes with the axes of 

 the co-ordinates, angles whose cosines a, a', a" are defined by the 

 equations 



and this axis makes, with the direction of the field, an angle 6 defined 

 by the equation 



COS C/ = aA-faA+aA = 



H 



Denoting by M' the moment of the couple produced by the action 

 of the field on the sphere, we have 



