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Proceedings of the Royal Society of Edinburgh. [Sess. 
of temperature, of vibration, and of what is found when magnetic atoms 
are mixed or compounded with non-magnetic atoms. To the exact form 
of the models, however, no special importance should be attached : they 
will have served their purpose if they make the general ideas which they 
illustrate more intelligible and more widely known. 
Note added March 15, 1922. 
Since the reading of the paper, Professor Whittaker has made to me 
the interesting suggestion that these models, apart from their bearing on 
the theory of ferromagnetic induction, may be applied to elucidate a point 
in quantum theory. This is because, in the model, a definite amount of 
energy is absorbed when the part that turns is displaced irreversibly from 
any one of its various positions of stable equilibrium, and a definite amount 
of energy is given out when that part settles again into a position of stable 
equilibrium. 
To appreciate the significance of this property of the model, from the 
point of view of quantum theory, it should be recalled that (as was pointed 
out in § 30) the part that is capable of turning need not necessarily possess 
magnetic moment. When used to represent an atom of a substance which 
is not ferromagnetic, the model may contain an inner part which, although 
it does not possess magnetic moment, is capable of turning relatively to 
the outer part, but is held in relation to the outer part by forces between 
its poles and those of the outer part.* A model satisfying this condition is 
easily made, for example as in fig. 22 (PI. II), by having the part W present 
nothing but like poles to the operative poles of the surrounding portions 
of the atom. When the atom is placed in a homogeneous magnetic field, 
the part W will have no tendency to turn. But imagine it to be exposed 
to a transient deflecting action such as might be caused by an encounter 
with another atom or with a free electron. Assume, for example, that an 
electron has an encounter with one side. In that event W will be 
deflected, and, if the transient deflecting action be sufficiently strong, 
W will be pulled away from its first position of stability and will fall, 
after the encounter, into one or another of the possible positions. It will 
therefore oscillate until the energy of the oscillation is dissipated by the 
radiation which is thereby given out. 
* The words “inner ’’and “outer” are retained only as a convenient means of fixing 
the ideas. We are concerned here simply with relative motion between parts of the atom, 
with elastic relative displacements through a limited range, with the breaking away from 
a stable configuration, and with the dissipation of energy that attends the settling again 
into a stable configuration. 
