131 
1921-22.] On the Quantum Mechanism in the Atom. 
that the fields thus set up are always such as to attract the charge towards 
the conductor : whereas we have to explain the setting up of a field which 
repels the charge away from the atom. 
As a second attempt at an explanation, we might suppose that there 
are in the atom a number of permanent electric dipoles pivoted at their 
centres, which, when the atom is isolated, take up positions of equilibrium 
in various directions so as to neutralise each other’s fields externally, but 
which, when an electron approaches the atom, are drawn out in parallelism 
to each other, and thus set up an electric field. This explanation must, 
however, be rejected for the same reason as the foregoing, namely, that 
such an arrangement would cause an attraction instead of a repulsion 
between the electron and the atom. 
Now this latter attempt at an explanation is really an electric analogue 
of the arrangement of small magnets within the atom by which the facts 
of induced magnetisation are accounted for in paramagnetic bodies : and 
this remark leads at once to an observation which supplies the key to the 
difficulty : namely, that what is wanted in our case is an electric analogue 
of the mechanism of induced magnetisation in diamagnetic bodies. 
Induced magnetisation in a diamagnetic body is, however, accounted for 
by supposing that the inducing magnet, as it approaches the body, induces 
electric currents in the atoms of the body. We are driven to conclude that 
a corresponding explanation, or at least a corresponding set of mathe- 
matical equations, applies in our case, and thus infer that the electron, as 
it approaches the atom, induces ivithin the atom a '' magnetic current^’ i.e. 
the magnetic analogue of an electric current : or at any rate induces some- 
thing which behaves like a magnetic current. 
In order to show how this can he done, we shall now describe a model 
in which the process can be seen at work. 
§ 3. The Mode of Absorption of Energy by the Atom 
FROM THE Electron. 
Our task is now to describe a mechanism within the atom which will 
respond to the approach of an electron by setting up a “ magnetic current.” 
If the model corresponds to nature, we ought to find that the field thus 
set up by the mechanism will drive the electron away from the atom, 
without any loss of energy, unless the kinetic energy of the electron 
comes up to a certain standard, so that there is a “ perfectly elastic 
impact ” : while if the kinetic energy of the electron exceeds this standard, 
the electron penetrates the structure and loses precisely this standard 
