IMPROVEMENTS IN TRANSMITTERS FOR TELEPHONES.
Year: 1879

page_text: LETTERS PATENT to Alexander Marr, of the City of Manchester, in the County
of Lancaster, for the Invention of "IMPROVEMENTS IN TRANSMITTERS FOR
TELEPHONES.'
"
Sealed the 19th September 1879, and dated the 21st June 1879.
PROVISIONAL SPECIFICATION left by the said Alexander Marr at the
Office of the Commissioners of Patents on the 21st June 1879.
ALEXANDER MARR, of Manchester, in the County of Lancaster.
IN TRANSMITTERS FOR TELEPHONES."
"IMPROVEMENTS
In transmitters for telephones the vibrating diaphragms are usually made of thin
sheets of metal with solid or powdered carbon between.
Now my Invention consists in making the diaphragins of wood, preferably pine,
inside which diaphragms and near the centre I attach discs of solid carbon placed
in close proximity to each other, and connected respectively with the opposite poles.
of a voltaic battery or a magnetic current, the receiving telephone being in the
circuit. The outer edges of the diaphragms are joined together by an annular
piece of wood, and the space between, about one-eighth of an inch, the carbon discs
being about one-sixteenth of an inch apart, I fill with powdered carbon.
By means of my improvements sound is more fully transmitted than by any
instrument in which solid carbon or powdered carbon only is used in combination
with metal diaphragms, and the wooden diaphragms being much thicker and
stronger than the metal diaphragms now in use are not easily injured.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Marr in the Great Seal Patent Office on the 20th
December 1879.
ALEXANDER MARR, of the City of Manchester, in the County of Lancaster.
"IMPROVEMENTS IN TRANSMITTERS FOR TELEPHONES."
In transmitters for telephones the vibrating diaphragms are usually made of thin
sheets of metal with solid or powdered carbon between. In performing my Inven-
tion I make the diaphragms of wood, preferably pine, inside which diaphragms
and near the centre I attach a disc or discs of solid carbon, placed in close
proximity to each other, and connected respectively with the opposite poles of a
voltaic battery or a magnetic current, the receiving telephone being in the circuit.
The outer edge of the diaphragm is attached to the body of the instrument by
screws, or two diaphragms are joined together by an annular piece of wood, and the
space between, about one eighth of an inch (the carbon discs being about one
sixteenth of an inch apart), I fill with powdered carbon.
And in order that my Invention may be fully understood I will describe the
accompanying Sheet of Drawings. Fig. 1 is a plan of a transmitter with the mouth-
piece removed, and Fig. 2 is an elevation in section of a transmitter to which my
improvements are applied. a is the body of the transmitter; b is a wooden
diaphragm; c and d are carbon discs; e is the powdered carbon which fills the
space between the carbon discs; f is a wire connecting the top carbon disc to the
battery pole; g is the wire connecting the bottom carbon disc to the telephone,
which must be used in conjunction with a transmitter at each end of the circuit;
h is the mouthpiece screwed on to the body of the transmitter; and i is a cap for
the purpose of protecting the connections.
The mode of operation is as follows:-The mouthpiece is held to the mouth of
the speaker and the voice causes the diaphragm to vibrate, which in its turn by
compression or disturbance of the particles of carbon strengthens or weakens the
battery current passing along the wires fand g, thus influencing sympathetically
the telephone at the other end of the circuit; by this means it is not necessary to
have battery power at both ends of the circuit, and the regulating screws commonly
used are dispensed with.
Having thus stated the nature of my Invention, and described the manner of
performing the same, I wish it to be understood that I do not limit myself to the
exact details given; but that what I do claim is the improved combination and
arrangement of the wooden or other diaphragm with the carbon discs and powdered
carbon, substantially as shewn and described.
In witness whereof, I, the said Alexander Marr, havo hereunto set my hand
and seal, this Nineteenth day of December, One thousand eight hundred
and seventy nine.