" This
apparatus comprised groups of coils and condensers by means of which
he obtained, as we cannot now doubt, effects due to true electric
waves.
Place should also be made for a well-known inventor, D.E. Hughes, who
from 1879 to 1886 followed up some very curious experiments in which
also these oscillations certainly played a considerable part. It was
this physicist who invented the microphone, and thus, in another way,
drew attention to the variations of contact resistance, a phenomenon
not far from that produced in the radio-conductors of Branly, which
are important organs in the Marconi system. Unfortunately, fatigued
and in ill-health, Hughes ceased his researches at the moment perhaps
when they would have given him final results.
In an order of ideas different in appearance, but closely linked at
bottom with the one just mentioned, must be recalled the discovery of
radiophony in 1880 by Graham Bell, which was foreshadowed in 1875 by
C.A. Brown. A luminous ray falling on a selenium cell produces a
variation of electric resistance, thanks to which a sound signal can
be transmitted by light.
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