326 
MR. G. T. WALKER OK REPULSION AND ROTATION 
III. When ^ {b + b') is negative, and is numerically greater than d/6, the couples 
are both positive. 
Pig - . 51. 
Pig. 52. 
The Couples on two Spherical Shells in the presence of a small Magnet of Moment 
K cos pt, whose Axis cuts the Line joining the Centres of the Spheres at an 
angle cl. 
28. We regard the magnetic particle as having a pole of strength (K/k) cos pt at 
a? = 0 , y = c, and a pole of strength — (K/k) cos pt at 
x = — k sin cl , y = c + k cos cl , where cl = ( 77 / 2 ) — a. 
Fig. 53. 
If a coefficient of magnetic potential due to a single pole at (0, c ) of strength 
H cos pt, be 
H f(b, b\ c) 
that due to the magnet will be the limit when k is small of 
(K /k) f(b, b' } c ) — (K/k) f(b-\-K sin cl, b' + k sin a, c + k cos a'), 
i.e., will be 
-K 
S/.SA • ,,3/ 
» + ad sm “ + a; cos “ 
