These
extremely rapid radiations have been shown by that eminent physicist
to occur in the light of the electric sparks which flash between two
metal points, and which are produced by a large induction coil with
condenser and a Wehnelt break. Professor Schumann has succeeded in
photographing them by depositing bromide of silver directly on glass
plates without fixing it with gelatine; and he has, by the same
process, photographed in the spectrum of hydrogen a ray with a
wave-length of only 0.1 micron.
The spectroscope was formed entirely of fluor-spar, and a vacuum had
been created in it, for these radiations are extremely absorbable by
the air.
Notwithstanding the extreme smallness of the luminous wave-lengths, it
has been possible, after numerous fruitless trials, to obtain
stationary waves analogous to those which, in the case of sound, are
produced in organ pipes. The marvellous application M. Lippmann has
made of these waves to completely solve the problem of photography in
colours is well known. This discovery, so important in itself and so
instructive, since it shows us how the most delicate anticipations of
theory may be verified in all their consequences, and lead the
physicist to the solution of the problems occurring in practice, has
justly become popular, and there is, therefore, no need to describe it
here in detail.
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