190 Mr. G. A. Schott on the 
We notice at once that np is precisely of the order 
of p b as given by (26) or (27), unless ™ 1 ^ 1 be very large. 
On account of damping fa is probably many times yjr, but cf>i 
is of the order ^, unless we suppose the potential energy to 
be much increased by the shock. This, however, can hardly 
be the case, since a shock does not instantaneously change 
the position of the electron, but merely its velocity. It follows 
that while (28) can account for a much larger diamagnetic 
moment than is actually found, it can hardly account for a 
sufficiently large paramagnetic moment. 
Voigt gives a formula (134) (I. c. p. 134) for the magnetic 
moment due to rotating electrons, which is equivalent to 
*— B6 ^ 
for a single electron, where k is the radius of gyration, and 
for simplicity the densities of both electric charge and mass 
have been supposed uniform. If we assume the mass to be 
3 e 2 . a 2 
wholly electromagnetic, so that m= —^ 5 while k 2 = -=, we get 
3 OC~CC 
The moment due to a negative electron is thus far too small 
to account even for diamagnetism ; but that due to a rotating 
positive sphere of atomic radius would, with the same assump- 
tion as to its mass, give a diamagnetic moment comparable 
with the paramagnetic moment due to a ring as given by (26) 
or (27). This will be of importance to us in § 23. 
A third formula (103) (I. c. p. 143) may be written 
eP/^~ eh 
m = 
ek*/— eh \ 
where k is the radius of gyration of a rotating electron and 
h its mean initial angular velocity of rotation. The formula 
gives the mean magnetic moment due to an assemblage of 
rotating electrons, whose rotation round the axis of symmetry 
is unresisted, whilst that about other axes is strongly resisted, 
the stationary state being supposed to have been reached. 
Apart from theoretical difficulties due to the term 7i , this 
term is not sufficiently well defined to render the formula 
amenable to calculation, so that a comparison with experiment 
is impossible. 
