Edison, recognising it as a rival to his
carbon-transmitter, then a valuable property, claimed it as an
infringement of his patents and charged him with plagiarism. A spirited
controversy arose, and several bitter lawsuits were the consequence, in
none of which, however, Professor Hughes took part, as they were only
commercial trials. It was clearly shown that Clerac, and not Edison,
had been the first to utilise the variable resistance of powdered
carbon or plumbage under pressure, a property on which the Edison
transmitter was founded, and that Hughes had discovered a much wider
principle, which embraced not only the so-called 'semi-conducting'
bodies, such as carbon; but even the best conductors, such as gold,
silver, and other metals. This principle was not a mere variation of
electrical conductivity in a mass of material brought about by
compression, but a mysterious variation in some unknown way of the
strength of an electric current in traversing a loose joint or contact
between two conductors. This discovery of Hughes really shed a light on
the behaviour of Edison's own transmitter, whose action he had until
then misunderstood. It was now seen that the particles of carbon dust
in contact which formed the button were a congeries of minute micro-
phones.
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