s more
concerned in discovering whether it is possible to give an explanation
of electrical and magnetic phenomena which shall be founded on the
mechanical properties of a single medium, than in stating this
explanation in precise terms. He is aware that if we could succeed in
constructing such an interpretation, it would be easy to propose an
infinity of others, entirely equivalent from the point of view of the
experimentally verifiable consequences; and his especial ambition is
therefore to extract from the premises a general view, and to place in
evidence something which would remain the common property of all the
theories.

He succeeded in showing that if the electrostatic energy of an
electromagnetic field be considered to represent potential energy, and
its electrodynamic the kinetic energy, it becomes possible to satisfy
both the principle of least action and that of the conservation of
energy; from that moment--if we eliminate a few difficulties which
exist regarding the stability of the solutions--the possibility of
finding mechanical explanations of electromagnetic phenomena must be
considered as demonstrated. He thus succeeded, moreover, in stating
precisely the notion of two electric and magnetic fields which
are produced in all points of space, and which are strictly
inter-connected, since the variation of the one immediately and
compulsorily gives birth to the other.

From this hypothesis he deduced that, in the medium where this energy
is localized, an electromagnetic wave is propagated with a velocity
equal to the relation of the units of electric mass in the
electromagnetic and electrostatic systems. Now, experiments made known
since his time have proved that this relation is numerically equal to
the speed of light, and the more precise experiments made in
consequence--among which should be cited the particularly careful ones
of M. Max Abraham--have only rendered the coincidence still more
complete.

It is natural henceforth to suppose that this medium is identical with
the luminous ether, and that a luminous wave is an electromagnetic
wave--that is to say, a succession of alternating currents, which
exist in the dielectric and even in the void, and possess an enormous
frequency, inasmuch as they change their direction thousands of
billions of times per second, and by reason of this frequency produce
considerable induction effects. Maxwell did not admit the existence of
open currents. To his mind,