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THE QUANTUM [ xn . 5 
relation to the quantum mechanism in the atom described by 
Whittaker. For the magnetic wheel in rotation, which he uses 
as an illustrative model, is equivalent to a set of rotating magnetic 
tubes, and the structure is essentially a mechanism by which 
an electrostatic field is produced by the motion of these tubes. 
Stress may be laid on Whittaker’s argument that when a charged 
particle is approaching an atom, the electric field about the atom 
is not permanent, but is evoked by the approach of the particle. 
The approaching charge induces within the atom a “ magnetic 
current,” i.e. the magnetic analogue of an electric current. 
Also it is worthy of special note that in this mechanism the 
electric separation in the atom, which is caused by the collision 
with the bombarding particle (carrying an electron charge), is 
precisely a separation of two electronic charges + e and — e. 
The process might be described as the manufacture of a positive 
and negative electron, or at least as a stage in such manufacture. 
Again, the emission of radiation by the mechanism may be 
regarded as the liberation of a magnetic tube from the structure. 
Although the models we have described are admittedly 
speculative, they do possess the advantage of emphasizing the 
magnetic nature and the periodic character of all fundamental 
physical processes and systems. “ Until fuller certainty comes, 
it is well that every hypothetically possible fine of advance should 
be explored.” * The suggestions of this chapter are put forward 
in the conviction that these words are in a special sense true at 
the present stage in the development of physical theory. 
* W. Peddie, Proc. Roy. Soc. Edin., voi. 42, p. 223, 1922.