Electron Theory of Matter. 
Hence the sphere has a specific moment given by 
e' 2 V 
193 
Pz ■ 
2dc 2 1 
(33) 
which is diamagnetic and in general of the order of 
magnitude o£ p 2 . 
§25. In the diagram E is the position of the ith. electron of 
Z7H 
the ring at time t ; its azimuth is <j> = c0t + 8-\- - — . The 
direction of the external field, h, which by (32) is also that 
of 12, lies in the plane xQz, and makes the angle 6 with Oz. 
Ffe. 1. 
z 
E 
O 
s^< ^ 
The component angular velocities of the sphere therefore are 
Ocos 9 along Oz, and Q sin along O.i*. Since we require 
only the change in p 2 we require only that component of the 
magnetic force due to the sphere, which gives an axial 
mechanical force, that is, we require only the radial magnetic 
force. Since the angle between the radius OE and the angular 
velocity 12 sin is (£>, while O cos 6 is perpendicular to OE, 
the outward radial magnetic force is entirely due to 12 sin 6 
and is equal to 
^(l-^Wsin0cosA*. 
cb \ 5/W 
Therefore the axial mechanical force is the real part of 
+ 5$i( i -ssy< 7,sin ' «*■•(.««+*+ v) (34) 
It must be added to the right-hand side of the third of 
equations (24) and is of the opposite sign, as is to be expected 
from Lenz's Law. 
♦ A. H. Bucherer, Phys. Ztsch. vol. vi. p. 269. 
Phil Mag. S. G. Vol. 15. No. 85. Jan. 1908. 

