y tends
towards that of light.

All the earlier experiments have led us to consider that the electric
charge was the same for all electrons, and it can hardly be conceived
that this charge can vary with the velocity. For in order that the
relation, of which one of the terms remains fixed, should vary, the
other term necessarily cannot remain constant. The experiments of
Professor Kaufmann, therefore, confirm the previsions of Max Abraham's
theory: the mass depends on the velocity, and increases indefinitely
in proportion as this velocity approaches that of light. These
experiments, moreover, allow the numerical results of the calculation
to be compared with the values measured. This very satisfactory
comparison shows that the apparent total mass is sensibly equal to the
electromagnetic mass; the material mass of the electron is therefore
nil, and the whole of its mass is electromagnetic.

Thus the electron must be looked upon as a simple electric charge
devoid of matter. Previous examination has led us to attribute to it a
mass a thousand times less that that of the atom of hydrogen, and a
more attentive study shows that this mass was fictitious. The
electromagnetic phenomena which are produced when the electron is set
in motion or a change effected in its velocity, simply have the
effect, as it were, of simulating inertia, and it is the inertia due
to the charge which has caused us to be thus deluded.

The electron is therefore simply a small volume determined at a point
in the ether, and possessing special properties;[49] this point is
propagated with a velocity which cannot exceed that of light. When
this velocity is constant, the electron creates around it in its
passage an electric and a magnetic field; round this electrified
centre there exists a kind of wake, which follows it through the ether
and does not become modified so long as the velocity remains
invariable. If other electrons follow the first within a wire, their
passage along the wire will be what is called an electric current.

[Footnote 49: This cannot be said to be yet completely proved. _Cf_.
Sir Oliver Lodge, _Electrons_, London, 1906, p. 200.--ED.]

When the electron is subjected to an acceleration, a transverse wave
is produced, and an electromagnetic radiation is generated, of which
the character may naturally change with the manner in which the speed
varies. If the electron has a sufficiently rapid periodical movement,
this wave is a light