IMPROVEMENTS IN AND APPERTAINING TO TRANSMITTERS 'for the Invention of FOR TELEPHONES.”
Year: 1878

page_text: LETTERS PATENT to Henry Hunnings, of Bolton Percy, in the County of York,
IMPROVEMENTS IN AND APPERTAINING TO TRANSMITTERS
'for the Invention of
FOR TELEPHONES.”
PROVISIONAL SPECIFICATION left by the said Henry Hunnings at the
Office of the Commissioners of Patents on the 16th September 1878.
HENRY HUNNINGS, of Bolton Percy, in the County of York.
IN AND APPERTAINING TO TRANSMITTERS FOR TELEPHONES."
"IMPROVEMENTS
In transmitting sound by the ordinary telephone the power of the voice is much
reduced. Now my Invention is designed to take the place of the transmitting
telephone, and consists in a compact apparatus that can be freely handed about
without liability to be injured. It consists of one or two vibrating diaphragms
composed wholely or in part of suitable metal, such as, preferably, platinum, silver,
ferrotype iron, 'tinned iron, et cetera, placed in close proximity to each other, and
connected respectively with the opposite poles of a galvanic battery, the receiving,
telephone being in circuit. The intervening space is filled with carbon or other
suitable conducting substance, preferably in the form of powder, and about of an
inch in depth. The whole is secured in a box of suitable non-conducting material
with a mouth-piece.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Henry Hunnings in the Great Seal Patent Office on the 14th March
1879.
HENRY HUNNINGS, of Bolton Perey, in the County of York.
AND APPERTAINING TO TRANSMITTERS FOR TELEPHONES.'
"
"IMPROVEMENTS IN
In transmitting sound by the ordinary telephone the power of the voice is much
reduced at the receiving end. Now my Invention is designed to take the place of
the transmitting telephone, and consists in a compact apparatus that can be freely
handed about without liability to be injured. It consists of a front vibrating
diaphragm composed wholly or in part of suitable metal, such as, preferably,
platinum, silver, ferrotype iron, tinned iron, et cetera. In close proximity to the
aforesaid vibrating diaphragm is fixed a disc of brass or other suitable metal, the
intervening space being filled with carbon in the form of powder to the depth of
about of an inch. The aforesaid vibrating diaphragm and the fixed disc of brass
are connected respectively with the opposite poles of a voltaic battery. The whole
may be secured in a box of suitable non-conducting material, with a mouth-piece if
desired.
The way in which I prefer to construct my Invention is shown in the accom-
panying Drawing, shewing an enlarged section of the telephone transmitter. The
details can be indefinitely varied, the great feature being in the use of carbon used
in a state of fine loose powder not in any way compressed or consolidated, as I find
the loose particles of conducting matter to be most delicately sensitive to sonorous
vibrations.
Referring to the Drawing, A is the vibrating diaphragm, which I make very thin,
preferably of platinum foil, though thin ferrotype iron, silver, or other material may
be used, being fixed as shown, or in other suitable manner so as to vibrate freely;
it is kept in place by ring F. B is the fixed disc or diaphragm of brass or suitable
metal, the intervening space being filled with the loose finely-divided conducting
material C. I find the most advantageous result to proceed from the use of oven-
made engine coke crushed very finely, not ground, so as to pulverize (not to shear
or tear) the particles, as I find the best results proceed from this. I may, however,
use metallized carbon powder, prepared with mercury or other suitable metal, if
desired. E, E, are the binding screws placed in connection with the plates A and B.
The above is placed in circuit with a voltaic battery and receiving telephone of
suitable construction, such as Bell's, and the words or other sounds made close or
otherwise to the instrument will be found to be distinctly and loudly reproduced at
the receiving instrument. The diaphragms and case D might be altered in form,
and made oval or square, or other suitable shape, if desired, but the best results are
produced if the instrument is made as described.
Having now described my Invention, and the best mode known to me of carrying
it into effect, I wish it to be understood that I do not claim the principle of using
carbon in the solid or consolidated form to increase or diminish the resistance of a
telephonic circuit, for the purpose of transmitting sounds, as this is exemplified in
the well-known "Hughes microphone" and the "Edison carbon telephone," nor do
I claim the coating of fibrous or similar surfaces with carbon to produce the same
result, but what I believe to be new and desire to claim as my Invention under the
herein-before in part recited Letters Patent is,―
1st. The use of finely powdered carbon or like conductor (preferably oven-made
engine coke prepared as described) in a loose and free state (not compressed or
consolidated in any way, or combined with foreign material), as a means of varying
the resistance of a telephonic circuit by the vibrations of a thin metallic or metal-
covered diaphragm enclosing it, controlled by the sound waves impinging upon it.

page_text: 2nd. A telephone transmitter consisting of a layer of finely divided carbon or
similar conducting material C, preferably oven-made engine coke placed in a loose
and free state between the thin metallic or metal-covered diaphragms A, B, in a
suitable case, such as D, as and for the purposes described.
In witness whereof, I, the said Henry Hunnings, have hereunto set my hand
and seal, this Twenty-fourth day of February, in the year of our Lord One
thousand eight hundred and seventy-nine.
HENRY HUNNINGS. (L.S.)