IMPROVEMENTS IN ELECTRIC TELEPHONY AND APPARATUS THEREFOR
Year: 1878

page_text: LETTERS PATENT to Joshua Franklin Bailey, of New York City, in the.
United States of America, at present residing at the Grand Hotel, Paris, in
the Republic of France, for the Invention of "IMPROVEMENTS IN ELECTRIC
TELEPHONY AND APPARATUS THEREFOR." A communication from Frank
Leonard Pope, of Elizabeth, New Jersey, United States of America, Electrical
Engineer.
Sealed the 28th December 1878, and dated the 29th October 1878.
"
PROVISIONAL SPECIFICATION left by the said Joshua Franklin Bailey at
the Office of the Commissioners of Patents on the 29th October 1878.
JOSHUA FRANKLIN BAILEY, of New York City, in the United States of
America, at present residing at the Grand Hotel, Paris, in the Republic of France.
IMPROVEMENTS IN ELECTRIC TELEPHONY AND APPARATUS THEREFOR." [A com-
munication from Frank Leonard Pope, of Elizabeth, New Jersey, United States of
America, Electrical Engineer.]
It has long been known that sounds of all kinds are produced by vibrations,
and that when vibrations of a suitable character are communicated to an elastic
medium like the atmosphere, they cause alternate expansions and condensations of
its constituent particles, which alternate expansions and condensations are in turn
communicated to any elastic or resilient body with which the atmosphere is in
contact. It has also been heretofore known that when an electric current traverses
two separate conducting bodies placed in contact with each other under slight
pressure, that the resistance which opposes itself to the flow of the said current at
the point of contact is within certain limits in an inverse ratio to the pressure of
one of the said conducting bodies against the other.
The present Invention relates to a method of and apparatus for transmitting oral
communications over telegraphic circuits, in which a device is made use of that is
acted upon by sonorous vibrations traversing the atmosphere in such a manner as
to produce corresponding variations or fluctuation of strength (technically termed
undulations) in a continuous electric current, which variations are accurately

page_text: reproduced in the electro-magnet at the receiving station, notwithstanding the
inductive interference of other telegraphic circuits running parallel to the circuit
-through_which the herein-before mentioned apparatus is being operated.
For these purposes two conducting bodies, one of which is constructed in a proper
form to be readily thrown into vibration by atmospheric sound waves, are placed-
directly in contact with each other under slight pressure, and an electric circuit
is caused to traverse the point of contact. Such an apparatus constitutes a
telephonic transmitter of extreme simplicity and efficiency, which is well adapted
to be used in connection-with-any of the well-known forms of receiving telephones,
and is especially useful upon circuits which are subject to inductive interference
from adjacent or parallel telegraphic conductors upon the same supports or in the
same cable, whether aerial or submarine.-
In the accompanying Drawings Figure 1 is a sectional view of a telephonic-
transmitter embodying the herein-before mentioned improvements; Figure 2 is a
face, and Figure 3 an edge view of the transmitting plate.
Referring to Figure 1, C and C¹ represent two circular plates which should be
composed of some substance which is elastic or resilient, and is at the same time a
conductor of electricity. It is preferred to make these of hard gas carbon for
reasons which will be herein-after set forth, but it may be here stated that they
may be made of either one of several different metals, although the best results are
obtained by the use of carbon. The plates C and C¹ are preferably alike, and they
are placed with their flat surfaces in immediate contact with each other in a
circular chamber formed within the box or case A, as shown in Figure 1.
The chamber may be lined at the bottom and sides with a layer of woollen cloth,
felt, or some similar semi-elastic material c. The plates C and C' fit somewhat
loosely into the chamber thus lined, but not so much so but that the lining serves
to retain them in their proper place by friction irrespective of the position of the
A conical mouth-piece a is formed in the top of the case A, and serves to
concentrate the atmospheric sound vibrations upon the upper or transmitting
plate C.
case A.
The plate C is connected by a wire with the binding screw d, and the plate C¹ in
like manner with the binding screw d'. The connection between the wire and the
carbon plate is preferably effected in the manner shown in Figure 3. A groove is
turned in the edge of the plate, and the wire is wrapped one or more times around
the plate in the groove, and twisted upon itself as seen at b.
Thus a considerable length of wire is brought in contact with the carbon, and
the connection offers very little resistance to the passage of the current.
In order to make use of the improved transmitter which has been described,
it' is placed in the circuit with a receiving telephone of any of the well-known
forms consisting of an electro-magnet and a plate or diaphragm, and a voltaic
battery of say three or four elements. When the apparatus is at rest a constant
current will traverse the circuit passing through the plates C and C¹. When for
example a person speaks into the mouth-piece a, sonorous vibrations are set up in
tho atmosphere, and these are communicated to the transmitting plate C and cause
corresponding vibrations in the pressure or area of contact, or both, between the
the vibrating plate C and the stationary plate C¹. The resistance at the point of
contact being thus varied, the strength of the constant current traversing the circuit
is varied in like ratio, and a corresponding effect is produced in the action of the
electro-magnet of the receiving telephone upon its armature, whence it results that
the vibrations of the transmitting plate C¹ are reproduced by the diaphragm of the
receiving telephone.
The arrangement of the circuit which has been described is only suitable for
moderate distances. When the distances are greater, the proportion of the variable
resistance between the plates C, C³, to the total resistance of the circuit becomes too
small to effect the desired result.
In such cases it will be found preferable to arrange the apparatus in the manner
shown in Figure 4. The plate C and C¹ of the telephonic transmitter are placed in

page_text: a local circuit 1, 2, 3, which includes a battery E, and the primary wire of an
electro-magnetic induction coil 1 of well-known construction. The secondary wire
of the said induction coil is included in the circuit 4, 5, 6, which extends to the
distant station, and at that point passes through a receiving telephone T of any of
the ordinary forms. The length of wire and number of convolutions in the
secondary coil of the induction apparatus I should be increased in proportion to the
length of the wire 5 in order to produce the best results. It will be understood
that the action of this apparatus does not depend in the least upon the variation of
the specific resistance of a mass of carbon under pressure, but solely upon the
application of the well-known fact that the resistanco encountered by an electric
the
current in passing from one conducting body to another depends upon pressure
at the point of contact.
It is preferred to construct these plates of carbon, for the reason that its surface
is not easily oxidised by the passage of a current, while on the other hand most
metals when exposed to similar conditions soon become coated at the point of
contact with a non-conducting oxide, which increases the resistance to an extent
that renders the apparatus after a little time wholly inoperative.
In order to assist the operation of the apparatus herein-before described when
employed on circuits which are subject to the inductive interference of other
parallel circuits on which ordinary telegraphic systems, such as the Morse, are in
operation, a very large resistance R is inserted in the telephone wire at or near
the receiving instrument, and if necessary also at or near the transmitting station
as at R¹. By properly proportioning the length of the primary, to that of the
secondary wire of the induction coil, the telephonic currents may be made of such
intensity as to readily pass through a resistance so large as to practically exclude
all induced currents from the circuit on account of their comparatively low.
intensity.

page_text: SPECIFICATION_in_pursuance of the conditions of the Letters Patent filed by
the said Joshua Franklin Bailey in the-Great-Scal_Patent Office on the
29th April 1879.
=
A com-
JOSHUA FRANKLIN BAILEY, of New York City, in the United States of
America, at present residing at the Grand Hotel, Paris, in the Republic of France.
"IMPROVEMENTS IN ELECTRIC TELEPHONY AND APPARATUS THEREFOR."
munication from Frank Leonard Pope, of-Elizabeth, New Jersey, United States of
America, Electrical Engineer.
It has long been known-that-sounds of all kinds are produced by vibrations, and
that when vibrations of a suitable character are communicated-to-an-elastic_medium
like the atmosphere, they cause alternate expansions and condensations of its
constituent particles, which alternate expansions and condensations are in turn
communicated to any elastic or resilient body with which the atmosphere is in
contact. It has also been heretofore known that when an electric current traverses
two separate conducting bodies placed in contact with each other under slight
pressure, that the resistance which opposes itself to the flow of the said current at
the point of contact is within certain limits in an inverse ratio to the pressure of
one of the said conducting bodies against the other.
The present Invention relates to a method of and apparatus for transmitting oral
communications over telegraphic circuits in which a device is made use of, that is,
acted upon by sonorous vibrations traversing the atmosphere in such a manner as
to produce corresponding variations or fluctuation of strength (technically termed
undulations) in a continuous electric current, which variations are accurately
reproduced in the electro-magnet at the receiving station, notwithstanding the
inductive interference of other telegraphic circuits running parallel to the circuit
through which the herein-before mentioned apparatus is being operated.
The first part of the Invention consists in placing two conducting plates or
bodies, one of which is constructed in a proper form, to be readily thrown into
vibration by atmospheric sound waves directly in contact with each other under
slight pressure, and in causing an electric circuit to traverse the point of contact.
Such an apparatus constitutes a telephonic transmitter of extreme simplicity and
efficiency, which is well adapted to be used in connection with any of the well-
known forms of receiving telephones, and is especially useful upon circuits which
are subject to inductive interference from adjacent or parallel telegraphic con-
ductors upon the same supports, or in the same cable whether aerial or submarine.
The second part of the present Invention relates more especially to a method of
and apparatus for excluding interfering inductive currents from telephonic circuits,
and is intended to be used in most cases in cerubrication with the apparatus and
method forming the first part of the Invention. In the accompanying Drawings
Figure 1 is a sectional view of a telephonic transmitter embodying the herein-before
mentioned improvements; Figure 2 is a face, and Figure 3 an edge view of the
transmitting plate, and Figure 4 shows the method of arranging the apparatus upon
a circuit for operation.
Referring to Figure 1, C and C¹ represent two circular plates which should be
composed of some substance which is elastic or resilient, and is at the same time a
conductor of electricity. It is preferred to make these of hard gas carbon for
reasons which will be herein-after set forth, but it may be here stated that they
may be made of either one of several different metals, although the best results are
obtained by the use of carbon. The plates C and C¹ are preferably alike, and they
are placed with their flat surfaces in immediate contact with each other in a
circular chamber formed within the box or case A, as shown in Figure 1.
The chamber may be lined at the bottom and sides with a layer of woollen cloth,
felt, or some similar semi-elastic material c. The plates C and C¹ fit somewhat
loosely into the chamber thus lined, but not so much so but that the lining serves

page_text: |to retain them in their proper place by friction irrespective of the position of the
case A. A conical mouth-piece a is formed in the top of the case A, and serves to
concentrate the atmospheric sound vibrations upon the upper or transmitting
plate C.
The plate C is connected by a wire with the binding screw d, and the plate C
in like manner with the binding screw d. The connection between the wire and
the carbon plate is preferably effected in the manner shown in Figure 3; a groove
is turned in the edge of the plate, and the wire is wrapped one or more times
around the plate in the groove, and twisted upon itself as seen at b.
Thus a considerable length of wire is brought in contact with the carbon, and the
connection offers very little resistance to the passage of the current.
In order to make use of the improved transmitter which has been described, it is
placed in the circuit with a receiving telephone of any of the well-known forms,
consisting of an electro-magnet and a plate or diaphragm, and a voltaic battery of
say three or four elements. When the apparatus is at rest a constant current will
traverse the circuit passing through the plates C and C. When for example a
person speaks into the mouth-piece a sonorous vibrations are set up in the
atmosphere, and these are communicated to the transmitting plate C, and cause
corresponding variations in the pressure or area of contact, or both, between the
vibrating plate C and the stationary plate C. The resistance at the point of
contact being thus varied, the strength of the constant current traversing the
circuit is varied in like ratio, and a corresponding effect is produced in the action of
the electro-magnet of the receiving telephone upon its armature, whence it results
that the vibrations of the transmitting plate C¹ are reproduced by the diaphragm
of the receiving telephone.
The arrangement of the circuit which has been described is only suitable for
moderate distances. When the distances are greater, the proportion of the variable
resistance between the plates C, C¹, to the total resistance of the circuit becomes too
small to effect the desired result.
It such cases it will be found preferable to arrange the apparatus in the manner
shown in Figure 4. The plates C and C' of the telephonic transmitter are placed
in a local circuit 1, 2, 3, which includes a battery E, and the primary wire of an
electro-magnetic induction coil I of well-known construction. The secondary wire
of the said induction coil is included in the circuit 4, 5, 6, which extends to the
distant station, and at that point passes through a receiving telephone T of any of
the ordinary forms. The length of wire and number of convolutions in the
secondary coil of the induction apparatus I should be increased in proportion to the
length of the wire 5, in order to produce the best results. It will be understood
that the action of this apparatus does not depend in the least upon the variation of
the specific resistance of a mass of carbon under pressure, but solely upon the
application of the well-known fact that the resistance encountered by an electric
current in passing from one conducting body to another depends upon the pressure
at the point of contact. It is preferred to construct these plates of carbon for the
reason that its surface is not easily oxydized by the passage of a current, while on
the other hand most metals when exposed to similar conditions soon become coated
at the point of contact with a non-conducting oxide, which increases the resistance
to an extent that renders the apparatus after a little time wholly inoperative.
The second part of the Invention relates to a method of and devices for assisting
the operation of the apparatus herein-before described when employed on circuits
which are subject to the inductive interference of other parallel circuits on which
ordinary telegraphic systems, such as the Morse, are in operation.
The effect of the alternate opening and closing of the electric circuit on these
parallel wires is to induce currents or pulsations in the telephone circuit, which
however are of less intensity than the currents which give rise to them. In order
to exclude these extraneous currents, a very large resistance R is inserted in the
telephone wire at or near the receiving instrument, and if necessary also at or near
the transmitting station as at R¹. By properly proportioning the length of the

page_text: secondary wire of the induction coil, the telephonic currents may be made of such
intensity as to readily pass through a resistance so large as to practically exclude
_all_induced currents from the circuit on account of their comparatively low
intensity.
Having thus described the nature of the said Invention-and-the_manner_of
performing the same, I would have it understood that I claim,―
First. The construction of telephones consisting of two conducting plates or
bodies in contact with each other under slight pressure, and with an electric
current traversing the points of contact, one of such bodies being capable of being
thrown into vibration by atmospheric sound waves, substantially as described.
Second. The construction of telephones, substantially as described and repre-
sented in the annexed-Drawings.
Third. The means of preventing inductive interference-by inserting a large
resistance in the telephone circuit at the receiving station, or both at the trans-
mitting and receiving stations, substantially as described.
Fourth. The method of arranging the telephone and its adjuncts in circuit,
substantially as described and shown in respect to Figure 4 of the Drawings.
In witness whereof, I, the said Joshua Franklin Bailey, have hereunto set my
hand and seal, this Fifth day of March, in the year of our Lord One
thousand cight. hundred and seventy-nine.
J. F. BAILEY.
(L.S.)