125 
1921-22.] On Models of Ferromagnetic Induction. 
This point received a curious development at the hands of Mr James 
Swinburne, who remarked that according to the theory there should be 
no dissipation of energy if a cylinder of iron were caused to turn slowly 
in a constant magnetic field of great strength, for then the Weber elements 
would remain always parallel to the field with no unstable phase in the 
course of their turning.* The result was unexpected, but it was experi- 
mentally confirmed by Professor F. G. Baily.f 
In all probability the Weber element is part of the electron system of 
the atom, deriving its magnetic moment from the motion of electricity, 
and the control under which it turns is electromagnetic. My theory of 
1890 ascribed that control solely to the mutual magnetic forces between 
each Weber element and its neighbours. For reasons which have been 
explained in this paper, though the mutual forces between neighbouring 
Weber elements must not be overlooked, I now ascribe the control 
mainly to magnetic forces which are exerted on the Weber element by 
other portions of its own atom. When this action is taken into account 
we find the Weber element to be capable of a narrow range of reversible 
deflection, followed by unstable movement into another position of stability, 
without unduly strong control. Thus a quantitative correspondence 
becomes possible between the magnetic field which is required to upset the 
element and those fields which are known to produce strong magnetisation 
in iron and other ferromagnetic metals. The modified theory accordingly 
escapes a fundamental objection to which the original theory was open; at 
the same time it retains all the features in which that theory was found 
to agree with the observed facts of magnetic induction. 
A basic feature in the modified theory is that it recognises two parts 
of the atom : a part which turns in response to an applied field, and a 
part which does not turn — which is fixed in relation to neighbouring 
atoms, but exerts control on the turning of the other part. This idea 
harmonises so well with the behaviour of ferromagnetic substances that 
it is offered for acceptance with considerable confidence. But in suggesting 
any apportionment of the electron system of the atom into these two 
parts we enter a region of speculation. The models which are described 
here claim no more than an illustrative value. They show how, on that 
basis, one may imagine groupings by which the observed phenomena can 
be closely reproduced, whether the electron structure is assumed to be 
that suggested by Rutherford and Bohr or that suggested by Lewis and 
Langmuir. They imitate the form of the magnetisation curve in a 
cyclic process : they hint at explanation of the known effects of strain, 
* Industries, Sept. 19, 1890. t Phil. Trans., vol. clxxxvii, A, p, 715, 1896. 
