W. H. Preece, who had visited Edison at Menlo Park, with
having 'stolen his thunder.' The imputation was indignantly denied, and
it was obvious to all impartial electricians that Professor Hughes had
arrived at his results by a path quite independent of the carbon
transmitter, and discovered a great deal more than Edison had done. For
one thing, Edison believed the action of his transmitter as due to a
property of certain poor or 'semi-conductors,' whereby their electric
resistance varied under pressure. Hughes taught us to understand that it
was owing to a property of loose electrical contact between any two
conductors.
The soft and springy button of lamp-black became no longer necessary,
since it was not so much the resistance of the material which varied as
the resistance at the contacts of its parts and the platinum
electrodes. Two metals, or two pieces of hard carbon, or a piece of
metal and a piece of hard carbon, were found to regulate the current in
accordance with the vibrations of the voice. Edison therefore discarded
the soft and fragile button, replacing it by contacts of hard carbon and
metal, in short, by a form of microphone. The carbon, or microphone
transmitter, was found superior to the magneto-electric transmitter of
Bell; but the latter was preferable as a receiver to the louder but less
convenient chemical receiver of Edison, and the most successful
telephonic system of the day is a combination of the microphone, or new
carbon transmitter, with the Bell receiver.
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