372 ELECTROSTATICS AND MAGNETISM. [PT. II. CH. IX. 



and the polarization is 



T= F- FQ F = 30.-/O F 



1 47T ' 47T/J! 47T 47TO 



* 3 /a-/4j 3 

 The self-demagnetizing force is 



If /A be infinite this becomes equal to F , so that the total 

 force inside the sphere is zero. This is the case for a conducting 

 sphere in an electric field, and is nearly the case for soft iron in 

 a magnetic field. 



Outside the sphere we have a different form for H, 



so that 



^_ 8ft 4-rrffi/ cos 

 ' 8/T ~3~ ~7 



The field due to the polarization is accordingly, by 123 (7), 

 the same as the field of a doublet of moment 4>7rR s II^=R 3 Fi, and 

 the total field outside the sphere is obtained by superposing this 

 upon the uniform field F . If p = oo the moment of the sphere is 



. 



The lines of force due to a uniform field disturbed by a doublet 



FIG. 74. 



