IMPROVEMENTS IN TELEPHONE TRANSMITTERS
Year: 1885

page_text: I THOMAS JOHN HANDFORD of 42 Southampton Buildings in the County of
Middlesex, Patent Agent do hereby declare the nature of this invention for
"IMPROVEMENTS IN TELEPHONE TRANSMITTERS a communication to me from
abroad by Edward Hibberd Johnson of New York City in the County and State
of New York, United States of America Electrician, to be as follows:-
The object of the invention is more especially to produce, for the transmission
of articulate speech, a practical and efficient telephone transmitter, employing
electrodes of platinum or other suitable metal, at which the circuit in which the
said electrodes are situated is opened and closed by the movement thereat, but the
principal features of the invention can also be used to advantage in telephone
transmitters operating by variations in contact such for example as the carbon
transmitter, and the invention extends to this latter class of instruments as well
as to all other forms of telephone transmitters, in which the principles and devices
herein described are capable of being employed, although the following description
for clearness and simplicity is limited to the form of instrument first above
mentioned.
It has been found by the experiments resulting in this invention, that in order
to get perfect articulation with a transmitter having electrodes of platinum, or a
similar metal, it is necessary that the movable electrode should be capable of
moving in perfect unison with the condensations and rarefactions of the atmosphere
caused by the vocal organs in speaking. This requires that the movable electrode
and the part upon which it is mounted should be without weight and hence have
neither inertia nor momentum, should not be subjected to any external force, so as
to be absolutely free to respond to the sound waves, and should have no elasticity
and be incapable of independent vibration-in fact should be a part of the air
whose movements form the sound waves.
But, since the movable electrode and the sound recurring body by which it is
carried, necessarily have weight, inertia, momentum and elasticity, proper means
must be provided for balancing or counteracting these forces, for permitting the

page_text: free movement of the movable electrode from the normal position of contact and
yet so limiting and controlling its movement that there can be no abnorinal
separation of the electrodes in excess of the movement due to the condensations
and rarefactions of the atmosphere. It is evident also, that since the margin for
adjustment with platinum electrodes is necessarily small, means should be provided
for maintaining a constant adjustment of the electrodes.
Diaphragins or bodies having within themselves vibrating movements, have been
found unsuitable for the sound receivers when the best results are desired.
This invention makes it possible to dispense with diaphragms entirely, the sound
receiving body here employed being one which is moved bodily back and forth by
the sound waves and has within itself no capacity for independent vibration.
The sound receiving body is in fact a piston, which receives the sound waves
directly upon one end, and it is guided by an enclosing cylinder, or is itself tubular
and works upon an internal cylindrical support, or both these methods of guiding
the piston may be employed. This piston is made as light as possible, it being a
thin shell of aluminum or hard rubber, or it may be made of paper, felt, cork, wood
or other light material.
It carries the movable electrode and when made to slide over an internal
support is open at one end and closed at the other; but when not internally
supported it may be closed at one or at each end.
The enclosing cylinder of the instrument is closed at one end, that opposite the
mouth piece and the piston is made to fit quite accurately the walls of this enclosing
cylinder or the internal cylindrical support or both. The effect of this construction
is to form an air cushion preventing abnormal movements of the piston. The
space between the piston and the closed end of the cylinder or that within the
piston, between its closed end and the internal cylindrical support, is a closed space
the air passage to and from which is formed only by the limited space around the
piston. Hence for all but movements of limited extent the speed of the piston
must be slow. It seems true, however, that the elasticity of the confined body of
the air permits, by its compression and expansion an infinitely rapid movement
back and forth of the piston within a small limit, which limit is sufficiently great
for all movements that may be required in the proper transmission. of articulate
speech, but any greater or abnormal movement is checked by the air cushion,
which in this way serves to limit and control the movement of the movable
electrode by balancing or counteracting the elasticity and momentum of the
parts which cause a rebound at the electrodes and an abnormal separation
thereof.
This air cushion, it will be understood, does not practically detract from the
perfect freedom of contact at the electrodes and of movement of the movable
electrode within the exceedingly small limit required for its separation from the
stationary electrode.
For maintaining a constant adjustment of the electrodes, a device is provided
which automatically brings the electrodes into the proper relative position.
In order that the free contact of the electrodes may be preserved, this automatic
adjusting device is arranged to be inert and inactive when the electrodes are in
contact, but so as to be brought instantly into action by the separation of the
electrodes and then acting with an excess of power to bring them together again
and into the proper adjustment. For this purpose an electrically operated device
is used, such as an electro-magnet or solenoid the coils of which bear a shunt
relation to the electrodes, so that the contact of the electrodes will short circuit the
magnet or solenoid coils. The magnet armature or solenoid core which is made as
light as possible, is carried by the piston.
This automatic adjusting device also assists to prevent the abnormal separation
of the electrodes. A. limiting stop of any suitable character is employed to prevent
the piston from dropping out of reach of the attractive force of the magnet or
solenoid as it might otherwise do when the instrument is cut out of circuit, but
when the position of the instrument is fixed, this stop is not required.

page_text: The magnet or solenoid hence will always bring the electrodes into the proper
relative position, when the instrument is thrown into circuit, and no hand adjust-
ment of any kind will be required.
A further feature of the invention is the use of a definite resistance arranged to
be thrown into circuit by the separation of the electrodes, and to be short circuited
by the contact of such electrodes. This resistance may be located in a shunt
circuit around the electrodes forming a constantly closed shunt circuit around such
electrodes. It is an important element in a a transmitter employing electrodes of
platinum or other suitable metal.
When the automatic adjusting device is employed in the same instrument, the
resistance may be formed by the coils of the magnet or solenoid, although
additional resistance may be used.
The use of a magnet or solenoid in the shunt circuit around the electrodes,
which magnet or solenoid is thrown into circuit when the electrodes separate, has
advantages not possessed by a simple resistance and of considerable importance in
the instrument. At the instant of separating the electrodes, the magnet or solenoid
sets up a counter electromotive force opposing the current charging it, and this has
the effect of reducing the flow of current to a much greater extent than would be
due simply to the introduction into the circuit of the resistance of the magnet or
solenoid coils. It also partially or wholly neutralizes the static charge in the
circuit and sharpens the current pulsations. The best result is probably obtained
when the power of the magnet or solenoid is such, and the other elements of the
circuit are so proportioned that at the instant of separating the electrodes, the
counter force of the magnet or solenoid will completely neutralize the battery
current and the static charge, so that the operation of the instrument will be
equivalent to the opening and closing of the entire circuit.
The instrument may be provided with openings in the sides of the cylinder cap
to relieve the pressure of "air rushes" from the piston sound wave receiver.
Frictional terminal connections are made between the section of the circuit located
in the parts of the instrument, so that the act of putting the parts together will
complete the connections within the instrument.
As has been already intimated the features of the invention are applicable also
to instruments, like the carbon transmitter which operate by variations in contact
pressure rather than by an actual separation of the electrodes.
The instrument described may be connected with the line through an induction
coil, or it may be placed directly in the line and a line battery be employed.
In embodying the several features of Invention herein before described in a
telephone transmitter the Invention may be carried out in the following manuer :-
The inclosing cylinder is closed at one end by a plug or cap upon which is
centrally mounted the magnet. For compactness, this magnet is preferably made
of cylindrical form, a shell forming one leg of the magnet, while a core within this
shell forms the other magnet leg. The winding is upon the core within the shell.
This magnet does not fill the space within the cylinder, but upon it works the
piston sound-wave receiver, carrying the armature. The magnet shell is preferably
covered with a sleeve of hard rubber or other suitable material upon which the
piston slides it having a long bearing thereon so as to move without danger of
binding. The piston fits this sleeve closely and also fits closely the walls of the
enclosing cylinder, but it is evident that the piston may work clear of either the
internal or the external cylinders.
"
The armature may be perforated, for lightness, and if not against the end wall
of the piston, to give a greater body of air for the cushion before explained. A cap,
screws upon the end of the enclosing cylinder, and forms the mouth piece. It has
openings in its sides to relieve the pressure of "air rushes" upou the piston. This
cap also limits the movement of the piston, preventing it from moving out of
reach of the force of the magnet, but as before mentioned, no such limitation would
be required if the instrument were given a fixed position in which there would be
no tendency for the piston to drop away from the magnet. The electrodes of the

page_text: instrument are of platinum, or other suitable metal, one being mounted upon the
core of the magnet and the other upon the centre of the armature, although as
before explained the electrodes may be like those of a carbon transmitter, or of any
other suitable construction. The plug, has two binding screws for connecting the
instrument in circuit. The plates into which these screws turn are connected
with the two ends of the magnet coils. The plate of one screw is also connected
with the shell of the magnet, and hence with one electrode. The plate of the other
screw is connected with a ring plate on the shoulder of the plug and this makes
frictional contact with a corresponding plate on the end of the enclosing cylinder.
A pin-passes from the last mentioned plate through to the other end of the
cylinder where it is bored out and split to form a socket for a removable pin the
latter being connected by a fine wire with the armature and forming a circuit
connection which can be readily accomplished.
By these connections it will be seen, the magnet coils and the electrodes are given
a shunt relation to each other, the contact of the electrodes short-circuiting the
magnet coils.
According to another mode of carrying out the Invention the piston does not
work over the magnet, but is located wholly beyond it and is guided entirely by
the enclosing cylinder. When a solenoid is used instead of the magnet, the piston
carries the solenoid core, which is tipped with platinum to form one electrode while
the other electrode is carried by a stud to which runs one connection from one of
the binding screws for connecting the instrument in circuit.
It should be understood that the details of the instrument may be modified
whilst retaining the essential features of invention first hereinbefore described.
TH J. HANDFORD,
42, Southampton Buildings,
London, W.C.

page_text: I THOMAS JOHN HANDFORD of 42 Southampton Buildings in the County of
Middlesex, Patent Agent do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement :-
The object of the invention is more especially to produce for the transmission
of articulate speech a practical and efficient telephone transmitter, employing
electrodes of platinum or other suitable metal, at which the circuit in which the
said electrodes are situated is opened and closed by the movement thereat, but the
principal features of the invention can also be used to advantage in telephone
transmitters operating by variations in contact such for example as the carbon
transmitter, and the invention extends to this latter class of instruments as well as
to all other forms of telephone transmitters, in which the principles and devices
herein described are capable of being employed, although the following description
for clearness and simplicity is limited to the form of instrument first above
mentioned.
It has been found by the experiments resulting in this invention, that in order
to get perfect articulation with a transmitter having electrodes of platinum, or a
similar metal, it is necessary that the movable electrode should be capable of
moving in perfect unison with the condensations and rarefactions of the atmosphere
caused by the vocal organs in speaking This requires that the movable electrode
and the part upon which it is mounted should be without weight and hence have
neither inertia nor momentum should not be subjected to any external force, so as.
to be absolutely free to respond to the sound waves, and should have no elasticity
and be incapable of independent vibration-in fact should be a part of the air
whose movements form the sound waves.
But since the movable electrode and the sound recurring body by which it is
carried, necessarily have weight, inertia, momentum and elasticity, proper means
must be provided for balancing or counteracting these forces for permitting the
free movement of the movable electrode from the normal position of contact and
yet so limiting and controlling its movement that there can be no abnormal
separation of the electrodes in excess of the movement due to the condensations
and rarefactions of the atmosphere. It is evident, also, that since the margin for
adjustment with platinum electrodes is necessarily small, means should be provided
for maintaining a constant adjustment of the electrodes.
Diaphragms or bodies having within themselves vibrating movements, have
been found unsuitable for the sound receivers when the best results are desired.
This invention makes it possible to dispense with diaphragms entirely, the
sound receiving body here employed being one which is moved bodily back and
forth by the sound waves and has within itself no capacity for independent
vibration.
The sound receiving body is in a fact a piston, which receives the sound waves
directly upon one end, and it is guided by an enclosing cylinder, or is itself tubular
and works upon an internal cylindrical support, or both these methods of guiding
the piston may be employed. This piston is made as light as possible it being

page_text: a thin shell of aluminum or hard rubber, or it may be made of paper, felt, cork,
wood or other light material.
It carries the movable electrode and when made to slide over an internal support
is open at one end and closed at the other; but when not internally supported it
may be closed at one or at each end.
The enclosing cylinder of the instrument is closed at one end, that opposite the
mouth piece, and the piston is made to fit quite accurately the walls of this enclosing
cylinder or the internal cylindrical support or both. The effect of this construction
is to form an air cushion preventing abnormal movements of the piston. The
space between the piston and the closed end of the cylinder, or that within the
piston between its closed end and the internal cylindrical support, is a closed space
the air passage to and from which is formed only by the limited space around the
piston. Hence for all but movements of limited extent the speed of the piston
must be slow. It seems true, however, that the elasticity of the confined body of
the air permits, by its compression and expansion an infinitely rapid movement
back and forth of the piston within a small limit, which limit is sufficiently great
for all movements that may be required in the proper transmission of articulate
speech, but any greater or abnormal movement is checked by the air cushion,
which in this way serves to limit and control the movement of the movable
electrode by balancing or counteracting the elasticity and momentum of the parts
which cause a rebound at the electrodes and an abnormal separation thereof.
This air cushion, it will be-understood, does not practically detract from the
perfect freedom of contact at the electrodes and of movement of the movable
electrode within the exceedingly small limit required for its separation from the
stationary electrode.
For maintaining a constant adjustment of the electrodes, a device is provided
which automatically brings the electrodes into the proper relative position.
In order that the free contact of the electrodes may be preserved, this automatic
adjusting device is arranged to be inert and inactive when the electrodes are in
contact, but so as to be brought instantly into action by the separation of the
electrodes and then acting with an excess of power to bring them together again,
and into the proper adjustment. For this purpose an electrically operated device
is used, such as an electro-magnet or solenoid, the coils of which bear a shunt
relation to the electrodes, so that the contact of the electrodes will short circuit the
magnet or solenoid coils. The magnet armature or solenoid core which is made as
light as possible, is carried by the piston.
This automatic adjusting device also assists to prevent the abnormal separation
of the electrodes. A limiting stop of any suitable character is employed to prevent
the piston from dropping out of reach of the attractive force of the magnet or
solenoid as it might otherwise do when the instrument is cut out of circuit, but
when the position of the instrument is fixed, this stop is not required.
The magnet or solenoid hence will always bring the electrodes into the proper
relative position, when the instrument is thrown into circuit, and no hand adjust-
ment of any kind will be required.
A further feature of the invention is the use of a definite resistance arranged to
be thrown into circuit by the separation of the electrodes, and to be short circuited
by the contact of such electrodes. This resistance may be located in a shunt
circuit around the electrodes forming a constantly closed shunt circuit around such
electrodes. It is an important element in a transmitter employing electrodes of
platinum or other suitable metal.
When the automatic adjusting device is employed in the same instrument, the
resistance may be formed by the coils of the magnet or solenoid, although
additional resistance may be used.
The use of a magnet or solenoid in the shunt circuit around the electrodes, which
magnet or solenoid is thrown into circuit when the electrodes separate, has
advantages not possessed by a simple resistance and of considerable importance in
the instrument. At the instant of separating the electrodes, the magnet or solenoid

page_text: sets up a counter-electromotive force opposing the current charging it, and this has
the effect of reducing the flow of current to a much greater extent than would be
due simply to the introduction into the circuit of the resistance of the magnet or
solenoid coils. It also partially or wholly neutralizes the static charge in the
circuit and sharpens the current pulsations. The best result is probably obtained
when the power of the magnet or solenoid is such, and the other -elements of the
circuit are so proportioned, that at the instant of separating the electrodes, the
counter force of the magnet or solenoid will completely neutralize the battery
current and the static charge, so that the operation of the instrument will be
equivalent to the opening and closing of the entire circuit.
The instrument may be provided with openings in the sides of the cylinder cap
to relieve the pressure of "air rushes" from the piston sound wave receiver.
Frictional terminal connections are made between the section of the circuit
located in the parts of the instrument, so that the act of putting the parts together
will complete the connections within the instrument.
The instrument described may be connected with the line through an induction
coil, or it may be placed directly in the line and a line battery be employed.
And in order that the said Invention may be perfectly understood I shall now
proceed more particularly to describe the same and for that purpose shall refer to
the several figures on the accompanying sheet of drawings, the same letters of
reference indicating corresponding parts in all the figures.
Figure 1 of the accompanying drawings represents a vertical section of a
telephone transmitter constructed according to this Invention the magnet being in
elevation.
Figure 2 is a separate vertical section of the magnet and piston of this
instrument.
Figure 3 is a view, similar to figure 1, of an instrument with a modified form of
piston.
Figure 4 is a vertical section of the principal parts of an instrument employing a
solenoid.
Figure 5 is a separate view of the frictional circuit connection for the movable
electrode.
The
A, is the enclosing cylinder, which is closed at one end by a plug or cap B,
centrally upon which is mounted the magnet C. For compactness this magnet is
preferably made as shewn in figure 2, of cylindrical form, a shell forming one leg
of the magnet while a core within this shell forms the other magnet leg. The
winding is upon the core within the shell. This magnet does not fill the space
within the cylinder A, but upon it works the piston sound-wave receiver D,
carrying the armature E. The magnet shell is preferably covered with a sleeve
of hard rubber, or other suitable material as shewn at n, upon which the piston
slides, it having a long bearing thereon so as to move without danger of binding.
The piston fits this sleeve closely and also fits closely the walls of the enclosing
cylinder A, but it is evident that the piston may work clear of either the internal
or the external cylinders. The space o forms an air cushion for limiting and
controlling the movement at the electrodes as herein before explained.
armature E may be perforated as shewn for lightness, and if, as in the example
illustrated, not against the end wall of the piston, to give a greater body of air for
the cushion. A cap F, screws upon the end of the cylinder A, and forms the
mouth piece. It has openings a in its sides to relieve the pressure of "air rushes
upon the piston. This cap also limits the movement of the piston, preventing it
from moving out of reach of the force of the magnet, but, as before mentioned, no
such limitation would be required if the instrument were given a fixed position in
which there would be no tendency for the piston to drop away from the magnet.
The electrodes bc of the instrument are of platinum, or other suitable metal, one
being mounted upon the centre of the armature and the other upon the core of the
magnet, although, as before explained, the electrodes may be like those of a carbon
transmitter, or of any other suitable construction. The plug B, has two binding
"

page_text: screws de for connecting the instrument in circuit. The plates into which these
screws turn are connected with the two ends of the magnet coils. The plate of
the screw e is also connected with the core of the magnet, and hence with the
electrode c. The plate of the screw d is connected with a ring plate ƒ on the
shoulder of the plug B and this makes frictional contact with a corresponding
plate g on the end of the cylinder A. A pin h passes from the plate g through to
the other end of the cylinder where it is bored out and split to form a socket 7 (see
detail Figure 5) for a removable pin k, the latter being connected by a fine wire i
with the armature and forming a circuit connection which can be readily accom-
plished. By these connections, it will be seen, the magnet coils and the electrodes
are given a shunt relation to each other, the contact of the electrodes short-
circuiting the magnet coils.
In figure 3, the piston does not work over the magnet, but is located wholly
beyond it and is guided entirely by the enclosing cylinder. In figure 4, a
solenoid G, is used instead of the magnet. The piston carries the solenoid core E¹
which is tipped with platinum to form the electrode b, while the electrode c is
carried by a stud to which runs one connection from the binding screw e.
As has been already intimated the features of the invention are also applicable
to instruments, like the carbon transmitter, which operate by variations in contact
pressure rather than by an actual separation of the electrodes as in the examples
given; but as the mode of applying the Invention to transmitters of other types
will be obvious to those skilled in this particular art from the description herein-
before given of the principles and features of the Invention I have not thought it
necessary to illustrate it in my drawings.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that
what I claim is
1st A telephone transmitter having electrodes in free contact and permitted a
free movement in the act of separating but controlled and limited in that movement
by devices which are brought into action by the movement at the electrodes,
substantially as herein before described.
2nd A telephone transmitter having an air cushion for limiting and controlling
the movement at the electrodes, substantially as hereinbefore described.
3rd A telephone transmitter having an automatically acting, electrical adjusting,
controlling and limiting device, which is brought into and thrown out of action
by the movement at the electrodes, substantially as hereinbefore described.
4th A telephone transmitter having a sound-wave receiver adapted to move
bodily like a piston, substantially as hereinbefore described.
5th A telephone transmitter, having a definite resistance, or a device for producing
counter electro-motive force, or both, located in a shunt around the electrodes,
substantially as hereinbefore described.
6th The single instrument having combined therein the several essential elements
specified, and constructed substantially as herein before described.
TH J. HANDFORD,
50, Bedford Row,
(Late of 42, Southampton Buildings),
London, W.C.
Dated Gifs yun day or October 1885.
TH J. HANDFORD,
50, Bedford Row,
(Late of 42, Southampton Buildings),
London, W.C.