IMPROVEMENTS IN FRICTION TELEPHONES OR ELECTROMOTOGRAPHS
Year: 1879

page_text: LETTERS PATENT to John Imray, of No. 28, Southampton Buildings, in the
County of Middlesex, for the Invention of "IMPROVEMENTS IN FRICTION
TELEPHONES OR ELECTROMOTOGRAPHS." A communication from abroad by
Joshua Franklin Bailey, of New York, United States of America.
COMPLETE SPECIFICATION filed by the said John Imray at the Office of the
Commissioners of Patents on the 6th December 1879.
JOHN IMRAY, of No. 28, Southampton Buildings, in the County of Middlesex.
"IMPROVEMENTS IN FRICTION TELEPHONES OR ELECTROMOTOGRAPHS." A. com-
munication from abroad by Joshua Franklin Bailey, of New York, United States
of America.
This Invention relates to telephones of the kind sometimes known as electro-
motographs, founded on the principle applied by Edison, according to which an arm
connected to a resonant diaphragm and pressed against a moving surface of
chemically prepared paper has its friction on the surface varied by passage of
electrical currents, and so produces vibrations of the diaphragm, giving out sounds
corresponding with those which acting on a transmitting telephone occasion the
variations in the electrical impulses. The object of this Invention is to increase the
efficiency of instruments of the kind referred to, so as to render them capable of
being practically applied for the transmission of sounds over considerable distances.
The accompanying Drawings represent the improved construction of receiving
telephone and its connections with a distant transmitter. Fig. 1 is a vertical
section, Fig. 2 a back view, and Fig. 3 is a plan of the receiving telephone according
to this Invention; and Fig. 4 is a diagram shewing the mode of arranging the
circuit for communication. a is a cylinder of compressed chalk soaked in an
electrolytic solution, such for example as caustic alkali, to give conductivity. The
axis b of the cylinder is connected by gearing c, d, to an axis e having a bandle f, by
turning which the cylinder a is caused to rotate. The movement might be derived
from clock-work or other convenient motor. On the periphery of the cylinder a
a blade g which is attached to the diaphragm d' is pressed by a piece of wire k
acted on by a spring h, the pressure of which can be regulated by the screw m. The
line wire is attached to g, and the axis b of the cylinder is connected to earth. On
causing the cylinder a to revolve in the direction of the arrow, if no electrical

page_text: current passes the friction of the blade g on the cylinder will be considerable and
such as to drag the diaphragm d' inwards, but if an electrical current passes of such
sign that hydrogen is evolved on the surface of the cylinder under the blade, tho
friction will be reduced to an extent corresponding with the strength of the current,
permitting the diaphragm to spring more or less outwards. Variations in the
current will therefore by effecting variations in the friction produce vibrations of
the diaphragm. When a current of opposite sign is transmitted, causing evolution
of oxygen, the friction is not sensibly reduced, but on the contrary it is generally
somewhat increased. For this reason the line current is maintained of constant
sign, but varied in potential, so as to vary the friction by greater or less evolution
of hydrogen; and whilst the same sign is maintained in the line current, its
potential is varied by the augmentations resulting from added currents of the same
sign, and by the diminutions resulting from partly neutralising currents of the
opposite sign., n is a reservoir of water in which dips a roller r of absorbent
material such as sponge or felt which can be moved from time to time by a lever l
so as to moisten the cylinder a. Practically, when the instrument is cased in metal
a fow turns of the cylinder a in contact with r will give the former sufficient
moisture to last a week, consequently the moistening part of the apparatus might
be dispensed with, the cylinder being occasionally moistened by hand. Referring
to the diagram Fig. 4, T is a carbon transmitting telephone, such as that known
as Edison's, placed in a local circuit with an induction coil I and a local battery x.
When the transmitting key L makes contact with n the current from a passes by
the wire 1, the principal coil of I, the wires 2 and 3, the key L, wire 4, through the
transmitting telephone T, and thence by wire 5 to the junction g and the battery a.
The sound pulses being transformed into positive and negative electrical undulations
in the circuit from the secondary coil of I in the known manner, these undulations
are made to act on the distant receiving telephone by means of the following
connections-The line from the distant station being connected to 8, the curront
thence passes by the wire 9 to the call bell j, by the wire 10 to the key t, by the
wire 6 to the contact p, by the wire 7 to the blade g of the receiving telephone,
through the chalk cylinder a to wire 8 of the secondary circuit, and thence by the
wire 3 to the contact u and tho key L which is making contact therewith, whence
it passes by the wire 4, through the transmitter T, the wire 5 to q, and by 12 and v
'to earth. The connection v may be to line whilst s is to earth. As the principal
line passes through the transmitter which is connected to the local battery part of
the current goes to line constituting the constant current above referred to availablo
for comparatively short lines. In long lines, or lines of considerable resistance, this
current would be so weakened as to be unable to produce sensible reduction of
friction at the receiver, and consequently in such cases several cells are connected
with the line.
While the key L makes contact with u as above described, the telephonic com-
imunications can be made. On moving the key I to the contact p the telephonic
circuit is broken, and the circuit for the call bell is completed, the line at a being
connected by 9, the bell j and wire 10 to the key t, thence by 6 to p, by L, 3, and 2
to the principal coil of I, and thence by 1 to the local battery, thence by q, 12,
and v to earth. By depressing the koy & the circuit is opened. The two recoivors
and transmitters might all be connected to one line, and might act without induction
coils, but with less efficiency. Moreover, the receiving instrument above described
might be employed for transmitting, this being a result of changes of electrical
resistance between the blade g and the cylinder a when g is caused to move by
vibrations of the diaphragm to which it is attached. When the blade is at rest the
resistance is usually about 2500 ohms, but by the least movement, such as will be
produced by sound pulses acting on the diaphragm, the resistance is immediately
reduced to about 200 ohms.; this receiver can therefore transmit almost as well as
the usual carbon transmitter. In preparing the chalk cylinder a it is of advantages
to mix a solution of a salt of mercury, such as acetate, with caustic soda in any
proportions. The moistening of the cylinder might be effected automatically by

page_text: connecting to the moistening roller r a spring bearing on the cylinder with pressure
so adjusted that the increased friction as the cylinder becomes dry would cause the
roller to be lifted so as to moisten the cylinder, and on the friction becoming thus
reduced the moistening roller would again descend. In the apparatus shewn in
Figs. 1, 2, and 3 the transmitter T, the call bell j, and induction coil I are compactly
arranged along with the receiver. These parts might however be arranged
separately, as in the diagram, Fig. 4.
Having thus described the nature of this Invention, and in what manner the
same is to be performed, as communicated to me by my foreign correspondent, I
claim,―
The construction and arrangement_of telephonic apparatus as herein described
with reference to the accompanying Drawings.
In witness whereof, I, the said John Imray, have hereunto set my hand and
seal, this Sixth day of December, in the year of our Lord One thousand
eight hundred and seventy nine.
JOHN IMRAY. (L.S.)