PRODUCED BY ALTERNATING ELECTRIC CURRENTS. 
287 
Their magnitudes are 
727r 2 p 2 aVW' . 
^ K " 'p* p ' 3 AiA'i d 3 Sm 2y ’ 
and are negative and positive on the a, b and a, b' shells as long as the former is to 
the right of the latter. 
Fig. 16. 
We now consider the couples on two spherical shells in the presence of a magnetic 
pole of strength H cos jpt. 
We take the same axes as before with the magnetic pole at (o, c, o). 
The couple on the a, b shell proves to be 
and that on the a, V shell 
_ TT2 ko-Q- II | q7 /\ 
11 p s p ri A X A\ d* ^ + Z0 
_ hs 36^WW 
p*p 6 AjA j d* v ' 
Hence 
(a.) The couples vanish* as they should, when c = 0, or cr = 0, or a — 0. 
(/ 3 .) When b = — b' and a == ct, the figure is symmetrical to the plane YOZ, 
and the couples are equal and opposite : that on the a, b shell to the right is 
positive. 
Fig. 17. 
M 
(y.) For other cases the discussion is similar to that for the cylinders with parallel 
current T cos pb 
