353 
1921-22.] Sir Alfred Ewing’s Magnetic Atom. 
and that in the atoms containing many electrons we have an inner stable 
group with a few electrons on the outer shell which are active in pro- 
ducing chemical change ; and we shall, further, assume that each electron 
has also magnetic properties in addition to electrostatic properties, either 
because it is moving in an orbit which is small as compared to the atom, 
or is itself a rotating ring as supposed by Parson ; and we shall also assume 
that it is able to turn on an imaginary axis under the influence of its 
magnetic polarity. If we make these assumptions with regard to the 
structure and properties of the atom, the researches of Sir Alfred Ewing 
into the hysteresis of iron become of profound significance to the 
chemist. Sir Alfred Ewing’s first researches into the hysteresis of iron 
were published in 1890, and he has recently further developed his theory 
of the structure of the iron atom in a paper read to the Royal Society 
of Edinburgh.* He has demonstrated that if we take a group of tiny 
magnets, representing Weber’s magnetic particles, each able to rotate on 
a centre, they will arrange themselves into a stable position ; and if we 
then bring them under the influence of an increasing magnetic force, 
they will at first oscillate about their position of stability, but when the 
magnetic force becomes sufficiently strong they will break away and will 
then fall into a new stable position. When the magnetic force is merely 
sufficient to set up oscillations through angles less than the angle of 
rupture, the whole system behaves like an elastic body and no work is 
done on the system ; but if the units are rotated until the angle of rupture 
is reached, they then swing irreversibly into a new stable position and a 
deffnite amount of work has been done on the system to induce the break 
away, and this work is entirely converted into radiation, vibration, or heat 
when the magnets swing into the new stable position. Moreover, if a still 
stronger magnetic force is applied to the system of magnetic units than is 
necessary to produce the break away, the work done and the final dissipa- 
tion of energy remains the same. We have here, then, a system which 
when acted upon by an external magnetic force either absorbs no energy 
at all, or absorbs a definite quantity of energy which is then dissipated. 
The significance of these results in helping to explain the phenomena 
associated with chemical combination, and enabling us to get a dynamic 
statement of what happens when atoms unite, is obvious. 
In his recent researches Sir Alfred Ewing has found that the quantita- 
tive data of the hysteresis of iron are best explained by assuming a central 
magnetic unit able to rotate, controlled by fixed magnetic poles with like 
* Proc. Roy. Soc., vol. xlviii, p. 342 ; Phil. Mag.., Sept. 1890 ; PhiL Mag., Sept. 1890; 
Proc. Roy. Soc., Feb. 1922 ; Phil. Mag., March 1922 ; Proc. Roy. Soc. Edin., vol. xlii, p. 97. 
VOL. XLTI. 23 
