1921-22.] Note on Professor Whittaker’s Paper. 
145 
displacement. The mutual magnetic forces between wheel and ring tend 
to restore the whole to its original configuration. Thus oscillations are 
set up which expend their energy in the emitted radiation. 
In this form, therefore, the model furnishes a mechanism not only for 
extracting a quantum of energy from the passing electron, but for convert- 
ing that into alternating magnetic currents and thereby into radiation. 
From the structure of the model it will be apparent that the period is 
sensibly constant for any moderate amplitude of oscillation. 
In the note added under date March 15 to my recent paper ‘‘ On 
Models of Ferromagnetic Induction” (Proc. R.S.E., vol. xlii, p. 97, 
February 20, 1922) — a note which was written after a conversation with 
Professor Whittaker — it was suggested that the quantum of radiation might 
be determined by the definite amount of work (say U') which would have 
to be expended in causing what is here called the wheel to break away 
from one position of stable equilibrium and fall into another. But in the 
theory which he has now developed Professor Whittaker finds his quantum 
in quite another — and as it seems a more convincing — way, namely, as the 
amount of work U which the electron does in passing clear through the 
system. Accepting this later view, I conceive U' to be probably greater, 
and possibly much greater, than U ; with the result that the passing 
electron simply produces oscillation about the original position of stable 
equilibrium, without causing the system to pass from one stable con- 
figuration to another. 
Two other points suggest themselves. The electron, in Professor 
Whittaker’s theory, gives angular momentum to the atom, or part of the 
atom, and itself loses only linear momentum in the direction of the axis. 
The principle of conservation would seem to require the assistance of the 
ether. The electron is in general emitted from some other atom, and in 
leaving it will give an angular impulse to that atom. The changes of 
angular momentum, on the part of the two atoms, will be opposite in sign, 
and may under certain conditions be equal. Taking both atoms together 
there may be conservation, but even then it appears necessary to think 
of the angular momentum as stored in the ether during the transit of 
the electron. 
That the ejection of an electron from an atom gives the atom an 
angular impulse follows from Professor Whittaker’s equations. It will be 
at once apparent if one considers the particular case of an encounter in 
which the bombarding electron has just enough velocity not to be reflected 
back. The bombarding electron then stops dead, remaining in the atom, 
and it gives the atom an angular impulse. The emission of an electron 
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