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 wave; while if the electron stops suddenly, a kind of pulsation is transmitted through the ether, and thus we obtain Roentgen rays.

Sec. 4.  NEW VIEWS ON THE CONSTITUTION OF THE ETHER AND OF MATTER

New and valuable information is thus afforded us regarding the properties of the ether, but will this enable us to construct a material representation of this medium which fills the universe, and so to solve a problem which has baffled, as we have seen, the prolonged efforts of our predecessors?

Certain scholars seem to have cherished this hope.  Dr. Larmor in particular, as we have seen, has proposed a most ingenious image, but one which is manifestly insufficient.  The present tendency of physicists rather tends to the opposite view; since they consider matter as a very complex object, regarding which we wrongly imagine ourselves to be well informed because we are so much accustomed to it, and its singular properties end by seeming natural to us.  But in all probability the ether is, in its objective reality, much more simple, and has a better right to be considered as fundamental.

We cannot therefore, without being very illogical, define the ether by material properties, and it is useless labour, condemned beforehand to sterility, to endeavour to determine it by other qualities than those of which experiment gives us direct and exact knowledge.

The ether is defined when we know, in all its points, and in magnitude and in direction, the two fields, electric and magnetic, which may exist in it.  These two fields may vary; we speak from habit of a movement propagated in the ether, but the phenomenon within the reach of experiment is the propagation of these variations.

Since the electrons, considered as a modification of the ether symmetrically distributed round a point, perfectly counterfeit that inertia which is the fundamental property of matter, it becomes very tempting to suppose that matter itself is composed of a more or less complex assemblage of electrified centres in motion.