nt in
a wire a perturbation which afterwards is propagated along the wire,
and how a resonator enabled him to detect the effect produced.

The most important point made evident by the observation of
interference phenomena and subsequently verified directly by M.
Blondlot, is that the electromagnetic perturbation is propagated with
the speed of light, and this result condemns for ever all the
hypotheses which fail to attribute any part to the intervening media
in the propagation of an induction phenomenon.

If the inducing action were, in fact, to operate directly between the
inducing and the induced circuits, the propagation should be
instantaneous; for if an interval were to occur between the moment
when the cause acted and the one when the effect was produced, during
this interval there would no longer be anything anywhere, since the
intervening medium does not come into play, and the phenomenon would
then disappear.

Leaving on one side the manifold but purely electrical consequences of
this and the numerous researches relating to the production or to the
properties of the waves--some of which, those of MM. Sarrazin and de
la Rive, Righi, Turpain, Lebedeff, Decombe, Barbillon, Drude, Gutton,
Lamotte, Lecher, etc., are, however, of the highest order--I shall
only mention here the studies more particularly directed to the
establishment of the identity of the electromagnetic and the luminous
waves.

The only differences which subsist are necessarily those due to the
considerable discrepancy which exists between the durations of the
periods of these two categories of waves. The length of wave
corresponding to the first spark-gap of Hertz was about 6 metres, and
the longest waves perceptible by the retina are 7/10 of a micron.[24]

[Footnote 24: See footnote 3.]

These radiations are so far apart that it is not astonishing that
their properties have not a perfect similitude. Thus phenomena like
those of diffraction, which are negligible in the ordinary conditions
under which light is observed, may here assume a preponderating
importance. To play the part, for example, with the Hertzian waves,
which a mirror 1 millimetre square plays with regard to light, would
require a colossal mirror which would attain the size of a
myriametre[25] square.

[Footnote 25: I.e., 10,000 metres.--ED.]

The efforts of physicists have to-day, however, filled up, in great
part, this interval, and from both banks at once they have lab