Professor Wiener obtained stationary waves some little while before M.
Lippmann's discovery, in a layer of a sensitive substance having a
grain sufficiently small in relation to the length of wave. His aim
was to solve a question of great importance to a complete knowledge of
the ether. Fresnel founded his theory of double refraction and
reflexion by transparent surfaces, on the hypothesis that the
vibration of a ray of polarized light is perpendicular to the plane of
polarization. But Neumann has proposed, on the contrary, a theory in
which he recognizes that the luminous vibration is in this very plane.
He rather supposes, in opposition to Fresnel's idea, that the density
of the ether remains the same in all media, while its coefficient of
elasticity is variable.
Very remarkable experiments on dispersion by M. Carvallo prove indeed
that the idea of Fresnel was, if not necessary for us to adopt, at
least the more probable of the two; but apart from this indication,
and contrary to the hypothesis of Neumann, the two theories, from the
point of view of the explanation of all known facts, really appear to
be equivalent.
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