PRODUCED BY ALTERNATING ELECTRIC CURRENTS. 
The bracket will be negative when a = +45°. 
(8.) In confirmation it 
symmetrical to OY), and 
The couples are then 
may be noticed that if y = -a — y (i,e., when the system is 
a — 0° or 90°, the couples are equal and opposite. 
TK 3 
'12ir~]ra i a' i cra' 
A 'i 
sin 2 y, 
and are negative and positive on the a, b and a', b' shells respectively, for all possible 
values of y, for which the a, b shell is to the right of a', b'. 
Fig. 45. 
The Couples 
on Two Spherical Shells in the presence of a Magnetic Pole of 
strength H cos pt. 
26. Take OX through the centres of the spheres and OY through the pole, whose 
distance from 0 is c. 
Fig. 46. 
2 t 2 
