VION April 27, 1877, Edison filed in the United States Patent
Office an application for a patent on a telephone, and on May 3, 1892, more than fifteen years afterward, Patent No.
474,230 was granted thereon. Numerous other patents have
been issued to him for improvements in telephones, but the
one above specified may be considered as the most important
of them, since it is the one that first discloses the principle
of the carbon transmitter.This patent embodies but two claims, which are as follows:
|"1. In a speaking-telegraph transmitter, the combination
of a metallic diaphragm and disk of plumbago or equivalent
material, the contiguous faces of said disk and diaphragm
being in contact, substantially as described.|
|"2. As a means for effecting a varying surface contact
in the circuit of a speaking-telegraph transmitter, the combination of two electrodes, one of plumbago or similar material, and both having broad surfaces in vibratory contact
with each other, substantially as described."|
The advance that was brought about by Edison's carbon
transmitter will be more apparent if we glance first at the
state of the art of telephony prior to his invention.
Bell was undoubtedly the first inventor of the art of transmitting speech over an electric circuit, but, with his particular form of telephone, the field was circumscribed. Bell's
telephone is shown in the diagrammatic sectional sketch
In the drawing M is a bar magnet contained in the rubber
case, L. A bobbin, or coil of wire, B, surrounds one end of
the magnet. A diaphragm of soft iron is shown at D, and
Questia, a part of Gale, Cengage Learning. www.questia.com
Book title: Edison:His Life and Inventions.
Contributors: Frank Lewis Dyer - Author, Thomas Commerford Martin - Author.
Publisher: Harper & Brothers.
Place of publication: New York.
Publication year: 1910.
Page number: 839.
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