11
117
INDUCTION IN ROTATING SPHERES
currents
therefore assume that the perpendicular distance of the wires Rectilinear
conveying the currents is at a distance from the centre large and limited
compared with the radius of the disc, so as to simplify the disc.
calculations.
FIG. 12 d.-Rotating disc and rectilinear currents.
In the first place, suppose again
If we develop
c = c',
a = - a'.
in powers of the
the expression
we get
=
-
=
W
x log
k
T
coordinates, and neglect higher powers of
2axy
c² + a²+
= _ ap²sin 2w
y2
c² + a²'
2ay³x(3c² - a²)
3(c²+a²)3
+
c² + a²
(3c2- a²)a
+.
6(c² + a²)s* (sin 2w - † sin 4w).