ARE EMPLOYED IN THE THEORY OF TERRESTRIAL MAGNETISM. 253 

 From these equations we get 



}" 1 /7"'+ 2 P m _i_i 



_ * ^ +1 





the differential equation for 



<g 



equation (12) gives 





Hence if we have a function of /A and X of the form R = Q% cos (m\ + a) 

 where m is a positive integer, we shall have 



but 



