n6 THE QUANTUM [vm. 5 
mechanism in the atom, viz. that it implies the existence of 
unipolar magnets, is valid only in the particular case considered 
in which the electron moves along the axis of the magnetic wheel. 
In this case the electron has to pass through two rings of poles 
of contrary sign, and the angular impulse arising from the inner 
ring is exactly equal and opposite to the angular impulse from 
the outer ring. 
There appears to be a possible way out of the difficulty if 
we suppose that the electron, instead of moving along the axis, 
is projected in such a manner that it passes through the ring 
composed of poles of one name, but not through the ring formed 
of poles of contrary name. 
As illustrating the possibility of obtaining such rotations 
with ordinary bar magnets, we may recall the classical experi 
ment of Faraday who produced the continued revolution of one 
of the poles of a magnet round a vertical conducting wire. In 
this experiment the whole magnet, with the exception of one 
extremity, was immersed in mercury, and the action of the 
wire carrying the current was limited almost entirely to the 
exposed pole. In modifications of the experiment,* frequently 
used for lecture demonstration, the magnet is suspended on a 
pivot and by means of mercury contacts the vertical current is 
made to pass near the upper pole only, the current being led off 
horizontally about the centre of the magnet. It was a model of 
this kind which suggested the possibility of meeting the difficulty 
raised by Eldridge in the manner described above. 
In our previous work some physical significance has been 
attached to tubes of magnetic induction, and it is interesting to 
trace the distribution of the tubes in the case presented by Prof. 
Whittaker’s magneton. Regarding the model as a wheel with a 
S-pole at the hub and N-poles distributed round the rim, the 
lines of force starting from the rim would curve round and enter 
the wheel at its centre. The number of tubes N, is 4?r times the 
total pole strength, i.e. N = 4^M, where M denotes the sum of 
the poles (of one sign) of the different bar magnets which form 
the spokes of the wheel. 
Now equation 8:7 gives Aco — 2eM, i.e., the angular 
momentum = 2eM. = — N0. 
271 
According to Nicholson’s hypothesis angular momentum 
can be expressed as nh/2n. Equating these expressions, 
~Ne = nh/2n, and thus we get N = n(h/e). That is, the total 
number of magnetic tubes associated with the magneton is an 
* Francis Watkins, A Popular Sketch of Electro-magnetism and Electro 
dynamics, 1828 ; P. M. Roget, Treatise on Electro-magnetism, 1832.