Improvement in Telephony.
Year: 1892

page_text: Date of Application, 2nd Aug., 1892-Accepted, 5th Nov., 1852
COMPLETE SPECIFICATION.
Improvement in Telephony.
We JOHN WESLEY GIBBONEY a citizen of the United States residing at
Lynn, County of Essex State of Massachusetts United States of America,
Electrician, and ELIHU THOMSON a citizen of the United States residing at
Swamps-cott County of Essex State of Massachusetts United States of America
Electrician, 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 present invention relates to a method of setting up waves in an electric
circuit in response to vocal sounds or other mechanical impulses transmitted to
the apparatus which corresponds to the ordinary transmitters in telephone systems.
It consists, briefly, in putting on the line a set of pulsations or alternations of
current from a suitable source which are made to pass through the turns of a coil
in inductive relation, as in transformers or induction coils, to another coil or coils,
the current in which latter coil or coils is made to vary by a change in inductive
capacity or change of resistance or self-induction, or changes of these effects jointly,
to a greater or less extent brought about by the vibrations of the voice as in speech
transmission, or other mechanical impulses imparted to the transmitter or diaphragm
provided therefor.
The changes of capacity, self-induction, resistance, or both, or all, act inductively
to vary the primary currents traversing the line and may therefore effect distant
instruments placed in series therewith, or placed in such connection that they
may respond to the variations. Such an instrument is an ordinary telephone
receiver.
Our present invention also relates to a telephonic system in which an alternating
current of such low rate of alternation as will not seriously interfere with speech is
used upon the line for transmission in place of a continuous or battery current, and
the invention is applicable to telephonic exchange work, whereby an alternating
current generator may be placed at an exchange or station to which a large
number of subscriber's lines pass, which alternating current generator may be a
dynamo driven at the requisite speed to produce the alternations required. The
alternations are divided or induced into the subscriber's lines and form the means
for transmission from the subscriber's lines to other subscriber's lines to which they
may for the time being be connected through the exchange or otherwise. The
preferred rate of alternations is low, and as low as 32 vibrations per second or even
below 16 vibrations are available. These rates of vibration or alternation are so
low that although the instruments are subjected to them they do not seriously
interfere with speech as the tone that they produce is almost inaudible on account
of the small volume of air set in motion by the diaphragms of the instruments.
With our system there is dispensed with all local batteries at the subscriber's
end of the linc and the system is, as it were, a closed circuit system possessing
great flexibility. Our invention also permits the working of the annunciators at
the exchange by the subscriber momentarily opening the line by a switch, or
better, by the simple act of lifting the telephone from the hook, while the replacing
of the telephone on the hook again signals the exchange that the use of the line is
discontinued.
The system also provides circuits, if found desirable, so that there shall not
be any circuits actually grounded, as connections to earth through condensers may
be made instead of returning through a continuous conductor or a metallic circuit
connected to earth such as is ordinarily employed.

page_text: Our invention will be understood by reference to the accompanying drawings, in
which
Figs. 1 and 2 illustrate diagrammatically the main principle of our invention.
Fig. 3 is a diagram illustrating the invention as applied to the exchange or
central station of a telephone system to which the subscriber's lines are led.
Fig. 4 shows the preferred character of current used in operating our system.
Fig. 5 and Fig. 6 are diagrams showing the arrangement at the subscribers'
end of the system.
Fig. 7 is a modified type of transmitter which may be employed in some cases.
Fig. 8 shows a preferred arrangement of circuit which may be used in connection
with the system.
In Fig. 1 is shown a line L connecting a telephone receiver as at R with
apparatus consisting of a receiver R¹ in circuit with a coil P, and an alternating
current generator or generator of alternating or varying impulses, as at A. The
earth plates E E serve to return current or complete the circuit, but may manifestly
be replaced by a metallic wire. The alternating current generator A. may produce
impulses of such high period as to be above the limit of audition, or it may
produce waves of such low period as not to give loudly audible sounds in the
receiver R or R, or in either case may make an audible sound of so feeble a
character as not to interfere with the speech waves in the receivers. In inductive
relation to the coil P, as when wound upon a common core or wound parallel to
the coil P, is a secondary coil S which is combined with an arrangement for
receiving the waves of the voice and increasing or diminishing, in accordance with
the vibrations of the voice, the inductive effect of the coil P in the magnetic
circuit of the coil S. If the coil S be of very fine wire so that the currents flowing
in it are of considerable potential, two plates forming the surfaces of a condenser
or static telephone transmitter, as at B, may be used, one of them being a diaphragm
to receive the vocal waves, or to be talked against, and the other being fixed so
that as the diaphragm flexes or moves it approaches more or less closely to the
other plate and changes the static capacity of the dielectric layer between. These
changes result in varying, in accordance with the changes of the waves of the
voice, the induction between the coils S and P so as to modify the original wave
by the superposition of the vocal waves. If, as stated, the original waves are but
slightly audible, or inaudible waves, the vocal waves retain their characteristic of
audibility and may be transmitted to the line and carried to a receiver or
receivers R R¹ in the same circuit, or a circuit in inductive relation thereto.
There are other ways of accomplishing the result than by the use of the static
transmitter B. For example, in Fig. 2 the arrangements are the same as in Fig. 1
with the exception that the secondary coil S is of quite low resistance, or consists
of but few turns of insulated conductor, and has in its circuit an ordinary carbon
transmitter T for receiving the vocal waves, or in case the secondary circuit S is of
still lower resistance the transmitter T may have a conducting diaphragm, forming
one pole, and a metallic button of good conductivity resting thereon, forming the
other pole. In fact with sufficiently few turns in this coil electrodes of pure silver
may be used in the transmitter, or, again, electrodes of silver amalgamated with
mercury may be used, the variation of resistance in the circuit of the coil S being
due to the variations of section in the mercury, or the variation in the contact.
resistance between the two surfaces one moved by the diaphragm and the other
resting against the first. It is evident that any well known form of transmitter
which varies the resistance of the circuit by the sound of the voice may be inserted
into the circuit of the coil S and subserve the purpose of the invention, it only
being necessary to adapt the number of turns of the coil S to the normal resistance
of the transmitter itself. Instead of varying resistance of course the movement of
an iron core in a coil or the movement of a coil over an iron core accomplished by
the voice might be used to vary the self-induction in the circuit of the coil S and
thus modify the waves of current induced in it from the primary P, which induced

page_text: waves react upon the priniary P and cause the transmission of corresponding waves
to the line and to the receivers on the line.
It will be understood that our invention permits the use of any potential in the
coil P and the line, and permits, also, the use of current of any desired potential on
the secondary or transmitter circuit, and this is in fact one of the main features of
our invention. It also dispenses with batteries feeding current through the
transmitter, and the generator A feeding the alternating impulses or other impulses
may of course be located at any convenient point, far away from the transmitters, if
need be. The field magnets of the alternating current, or varying current,
generator A may also be excited in any suitable manner, such, for instance, as by a
separate winding upon its armature, as shown in Fig. 1, in which the field magnet M
is shown connected to brushes on a commutator for delivering currents suitable for
such purpose, or by a battery, as indicated at J, Fig. 2,
In Fig. 3 at G is indicated a generator of alternating currents which may consist
simply of a coil of wire wound upon a laminated iron core of iron and which is
driven by suitable power, or, preferably, around which is driven a set of
magnets N S.
The generator A has a coil in which alternating currents are
generated, and the preferred form of wave is indicated in Fig. 4,-something like a
sawtooth, or pointed wave. The construction of the field and armature will require
to be modified to approximate this form of wave. These are principles now well
understood in the art and the result may be achieved in a number of different
ways.
Connections are led from the coil A in which the alternating currents are
generated to a set of secondary coils or transformers indicated at B¹ B³ B³ B*, as
many as there are subscribers' lines entering the exchange. These transformers
may be connected in multiple or series or in any other arrangement, but are shown
connected in multiple from the terminals leading from the coil A. The primary
coils therefore receive the same alternating current impulses, or pulsating impulses,
as are generated in the coil' A. These primary coils work inductively on secondary
coils wound upon the same core, or in inductive relation to the primary coils, and
the secondary coils are in the subscribers' lines or arranged to be in the subscribers'
lines when communication is desired to be had. The subscribers' lines leading from
these secondaries are shown as four in number a, b, c, d, and may, as usual be led off
to considerable distances. The terminals of the secondary coils not connected to
the lines a, b, c, d, are arranged to be connected to earth at E through a
condenser K, or directly to earth, as desired, and in the lines a, b, c, d, as
at e, f, g, h, are arranged annunciators which so long as current flows in the lines
retain their drops in position, but on a momentary interruption of current occurring
allow their drops to fall and indicate that the subscriber desires to use the line or
call the exchange. Arrangements should exist, but they are not shown in the
figure, for plugging into the subscribers' lines as usual, the exchange instruments
whereby the operator can communicate with the subscriber. The transmitter and
receiver used in the exchange will be similar in pattern to that which the subscriber
uses.
On a call being indicated by the dropping of an annunciator, say at e, the operator
plugs or switches line in the ordinary way to the other subscribers' line and at the
same time disconnects the earth at E¹. This may be done by the insertion of
plug switches or by the ordinary exchange switchboards. Assuming then that the
lines a, b, c, d, have been connected through the exchange in response to a call
from either bor c, communication can now be had between the subscribers' on those
lines.
In Figs. 5 and 6 is shown the subscribers' equipment which consists of a call-
bell H consisting of an electromagnetic arrangement responsive to an alternating
current of low frequency and considerable intensity. It also consists of the
transmitter transformer T a coil of which, as P, is connected into the line when in
use, while the secondary Sis connected locally through the transmitter T whereby

page_text: variations of the amount of closure of the circuit through the coil S may be
obtained, and the secondary S may have a current of low potential when metallic
electrodes are used in the transmitter, or when the variations of resistance in that
circuit are obtained by a diaphragm acting on a mercury globule. It would be of
higher resistance, but still of comparatively coarse wire, if a carbon transmitter
were used; and in the case of a static transmitter, such as shown in Fig. 7,
consisting of a condenser whose plates are brought near together and capable of
being moved by the waves of sound of the voice, it would be a very high resistance
coil of very many turns. R represents the receiver introduced into the line in
series with the coil P, and they may be connected through a transformer as is the
transmitter, and wound accordingly. The receiver is of the ordinary type such as
is used in common telephone practice, consisting of a magnetized core, or a fine soft
iron core, subjected to the action of the coil through which the line currents flow,
with a diaphragm in front of the end of the core for receiving the vibratory action
and translating them into corresponding sound waves. An earth connection should
be made as at E. This earth connection may however, may not be a complete
conducting connection but may be made through a condenser of suitable capacity
so that the line remains insulated while still capable of transmitting the waves of
current. At R is shown in dotted lines the position of the receiver when hung
upon its supporting hook, or rather its position in the act of being hung upon its
hook. When unhung contact 1, is closed and would form, if it is desired to use the
connection, a shunt to the bell magnet H. As, however, the bell magnet does not
respond to the normal impulses during speech it is not necessary to so connect it
except to avoid the self-induction or resistance. At j, k, are contacts which are
operated as follows.
When the telephone receiver R₁ is unhung the circuit is closed at by the
movable lever on which the telephone is supported, indicated at L, always tending
upward and depressed during the hanging of the telephone receiver. This completes
the line through to the transmitting instruments. When the receiver R' is hung
on the lever L, contact is closed at j, and the connection is made which cuts out
the transmitter and receiver and keeps only the bell H in the subscribers' line b.
This set of switching actions is not essential to the operation of the system, as is
manifest, but we find it is quite useful in the following particular.
In taking the receiver R¹ from the hook, contact at j, is opened before contact k,
is closed, or in other words there is a momentary opening of the line. This
momentary opening of the line may be the means of signalling to the exchange
or dropping the exchange annunciator, the system operating like a closed circuit
system. When the annunciator drop is lifted it is held in its lifted position
so long as the line from earth plate E to earth E2 is intact, whether the
condensers are used in the line or not. During this time the secondary of the
transformer B' is sending impulses at a low rate, say 16 or 20 vibrations per
second, but not of sufficient force or potential to ring the bell H. The lifting of
the receiver R¹ and lever L, opens contact j, a slight time before closing it at k,
and the annunciator of e drops indicating that the subscriber has lifted the telephone
from the hook and desires to communicate. The exchange now answers the call
by plugging in the telephone at the exchange using a telephone set similar to
that which the subscriber has. The subscriber speaking into the transmitter T
varies in any suitable manner the resistance of the circuit S which is in inductive
relation to the coil P in the line. The circuit of the transmitter T forms a closed
circuit secondary to the primary coil P in the line through which alternating
currents are constantly flowing when such coil is in circuit. The variations of
resistance of this closed circuit secondary circuit set up variations of counter
electromotive force in the coil P' which react throughout the connected lines and
at a rate corresponding with speech vibrations, and these smaller superposed
waves on the low rate alternating current or pulsating current impulses are
carried to the other subscriber on the line at say c, where they may be heard
'

page_text: in a receiver R² if lifted from the hook, as whereby contact A² is closed.
The subscriber on the line c, has a similar set of instruments to those just
described, and the connections are substantially the same. It may be mentioned
that the back contact of the lever 1, and indicated at 2, may either be con-
nected to earth directly or it may be connected by a wire to earth as shown in
dotted lines w, instead of the earth connection to the line leading through the
instruments.
Since alternating currents or impulses flow equally in both lines b, and c, when,
connected, speech may be had back and forth from one end to the other by the
use of the transmitters and receivers provided, and although there is an alternating
current traversing the line simultaneously it is a low period current which hardly
produces any effect in the receiver on account of its low rate, and in fact in any
case could only produce a very low hun upon which the waves of the voice are
superimposed.
With the form of wave shown in Fig. 4 in which there is a quick change of the
current at all times there are no dead points of communication which would stop
the action of the transmitter except at the tops of the waves, but these are so small
a portion of the general wave that they do not affect the speech transmission
perceptibly.
It remains to describe the arrangement by which the exchange calls the subscriber.
For this purpose a transformer, as at B5, may be provided which is capable of
being connected into the subscribers' lines by proper switch appliances, as at V,
and which transformer B³ may be made to produce currents of great vigor or
higher potertial which add themselves to the currents already found upon the
lines and due to the transformers B1, B2, B3, and B. With this added
current the bell magnets H may easily be made to respond to the alternations,
their adjustment being such that during the transmission of speech alternations they
are incapable of operating the bell and require the added current to actuate them.
The rate of alternations impressed upon the lines may be just rapid enough to
produce a low hum and may serve, therefore, as an indication of the line.
If the
subscriber in listening at his receiver does not detect the low hum he will know at
once that the line is interrupted. If, however, it be heard with the normal strength
and rate, it is an indication that the line is complete.
In our system the subscribers' apparatus becomes practically a fixed apparatus,
not requiring attention such as is demanded in the keeping up of a battery, and the
electrical energy which is at the command of the subscriber is as unlimited as the
resources of the exchange permit. If it is desired, no part of the system need be
grounded.
Fig. 7 shows a transmitter in which the closed secondary S is of a very fine wire
and connected to two parallel plates which form a transmitter condenser, the
movements to and fro of the plates during speech varying the condensing capacity.
and therefore the amount of flow of current in S and inductively the action of the
coil P. This arrangement to be effective should have as much condenser surface
as possible or a higher rate of alternations be used than with the other type of
transmitter.
It is important in the operation of our system to introduce a condenser of
moderate capacity in a shunt around the secondary coil of the trans-
formers B1 B2 B3 B. The capacity of these condensers should be so small
that no interference is produced with the operation of the transformer, or in
other words, do not short circuit the secondary of the same, but that for quick
impulses they shall practically be a shunt around the secondary of the trans-
former B. The waves of speech may pass through the condenser, Fig. 8, with
perfect freedom whereas the alternating waves supplied to the line would not find
sufficient capacity in the condenser to be much affected thereby. In this way the
self-induction of the secondaries of the transformers may be in a large measure
eliminated.
"

page_text: In order to insure that the circuit of each subscribers' line shall be opened for a
moment during the removal of the receiver and the replacing of the same, it is
advisable to provide the sustaining hooks or levers with dash pots, or other retarding
mechanism, whereby an appreciable interval elapses in the change of position of
the lever from its upward to its downward position, or the reverse. Such devices
are indicated at D D as dash pots filled with fluid for checking the motion.
Of course it is not essential that in signalling from the exchange outward to the
lines that the same frequency of alternations be used, or that alternating currents be
employed at all, as by making the subscribers bell sensitive to interrupted currents,
or by making them sensitive to particular periods of currents the signals may be
effected by different currents from those which are used normally upon the line.
The signal arrangements do not form an essential feature of the invention and may
be replaced by the ordinary magneto and a proper signalling system used in con-
nection therewith, but it is preferred to combine the features which have been
described in the complete system of this character as it gives economy of operation
and economy in the plant.
:
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
1. The method of transmitting speech consisting in passing over the line waves
of alternating current, or varying current, of slight audibility in the receivers, and
superposing thereon waves of current corresponding to vocal waves, substantially as
described.
2. The method of transmitting speech consisting in putting upon the line alter-
nating or pulsating waves of current, inaudible or nearly so in receivers, and
inductively superposing waves of current corresponding to the vocal waves received
by a transmitter.
3. The method of transmitting speech, consisting in passing over a line or circuit,
including the receivers and transmitting devices, waves of electric current incapable
or nearly incapable of producing audible tones in the receivers, and modifying. the
induction between the line transmitter coil and a local coil in inductive relation
thereto through the agency of voice waves.
4. The method of transmitting speech along a line having receivers and trans-
mitters, consisting in producing induction between a pulsating or alternating current
in the line, of such rate as not to produce strongly audible tones or sounds in the
receiver, and a local circuit in inductive relation to a coil in the line, and modifying
the resistance, capacity, or self-induction of such local circuit by the local waves
received by the transmitter.
5. In combination with a telephone line having receivers thereon of means for
producing in said line varying or alternating current impulses of such period as not
to produce strongly audible tones or sounds in receivers, and means, such as a local
coil in inductive relation to a coil in the line, for superimposing undulations induc-
tively transferred from the local coil to the line coil, the local coil being provided
with a telephone transmitter in the circuit whereby the capacity of the resistance of
its circuit may be varied by the waves of the voice communicated to said transmitter.
6. In a telephone system in which alternating or varying impulses are passed
over the line, un induction coil the primary of which is in the line and the secondary
of which is local to the transmitter and connected to the said transmitter, whereby
the variations of resistance, capacity, or self-induction set up in the transmitter by
the voice waves are inductively transferred to the primary coil in the line to vary
its current, or superimposing the vocal undulatory current on the alternating or
varying line current.
7. The combination in a telephone system of an induction coil provided with a
primary coil of many turns traversed by alternating or varying impulses of current,
and also provided with a secondary coil of few turns locally connected through a

page_text: transmitter, whereby the resistance of said local coil circuit is varied as described
and for the purpose specified.
8. The combination in a telephone apparatus, of a source of alternating or
varying electric current, a line circuit connected to said current source, a trans-
former or inductorium the primary coil of which is in said line circuit or inductively
related thereto, and a secondary circuit for said transformer whose resistance,.
capacity, or self-induction is adapted to be modified by sound waves, as set forth.
9. In a system of telephonic transmission, a generator of alternating or varying
currents of little or no audible effect in the receiving instruments, inductive devices
or induction coils operated by said currents whereby similar induced currents are
supplied to the separate lines, means, such as switches, for connecting such separate
lines, receivers in said lines, and transmitters also in said lines having induction
coils, one in the line and one in the local circuit including a resistance varying or
current varying device responsive to sound waves.
•
10. In a system of telephonic transmission, a set of transformers inductive devices
the primaries of which are fed by alternating or varying currents of low period, and
the secondaries of which are connected into the circuit upon which speech is to be
conveyed, receivers in said lines, devices or induction coils with primaries connected
to the line and secondaries connected to current varying transmitters responsive to
sound waves.
11. In a system of telephonic transmission, a set of transformers or inductive
devices the primaries of which are fed by alternating or varying currents of low
period, and the secondaries of which are to be connected into the circuit upon which
speech is to be conveyed, condensers in shunt relation to such secondaries, receivers
in said lines, devices or induction coils with primaries connected to line and
secondaries connected to current varying devices or transmitters responsive to sound
waves.
12. In a system of telephonic transmission comprising a number of lines, means
for generating and transmitting alternating or varying current impulses of com--
paratively low period through the lines, and means for modifying such waves of
current consisting of an induction coil, one of the coils of which is in the line and
the other of which is in a local circuit including the transmitter, substantially as
described.
13. In a system of telephonic transmission comprising a system of lines normally
fed by alternating or varying impulses of current, signalling devices in said lines
responsive to calling currents and unresponsive to the normal pulsations or
alternations, telephone receivers for said lines, and transmitting mechanism con--
sisting of a line coil in inductive relation to a local coil in the circuit of which latter
is placed a current varying device, such as a variable resistance, said current varying
device or transmitter being responsive to vocal or other sounds.
14. In a system of telephonic transmission a system of lines normally fed by
alternating or varying impulses of current, signalling devices in said lines responsive
to calling currents, switch stations or exchanges, annunciators at said stations
individually responsive to the opening of their respective lines, receivers adapted
to be connected into said lines by the operation of suitable switch mechanism, and
transmitters likewise adapted to be connected to such lines, said transmitters having
a local circuit including resistance or current varying device responsive to sounds,
said local circuit being in inductive relation to a coil in the line circuit while the
transmitter is in use.
15. In a system of telephonic transmission, such as described, hooks or supports
for the receivers, switch mechanism adapted to open the line by the removal of the
receiver from its hook and to maintain the line closed while the receiver is in use,
and to again open the line on the replacing of the receiver upon the hook or
support.
16. A support for telephone receivers adapted to open the line during the taking
off and replacing of the receiver and to maintain the line closed at other times.

page_text: 17. In a closed circuit system of telephonic transmission, lines on closed circuit
or through condensers, means in each of said lines for generating or conveying to it
alternating or varying impulses of current of low period, transmitters and mechanism
for keeping said transmitters in circuit in said lines when in use, comprising a coil
in the line with a local coil in inductive relation thereto, and resistance or current
varying devices responsive to vocal or other sounds.
18. A telephone exchange system, comprising a generator of alternating current
impulses, means for conveying individually such impulses of varying current to the
individual lines leading from the exchange, annunciators or signal devices in said
lines, signal apparatus in said lines at the subscribers' or users part of the line
responsive to currents sent out from the exchange, switching devices for inter-
connecting the lines at the exchange, transmitters and receivers connected into the
lines when in use, said transmitters consisting substantially of induction coils, -one
coil being in the line and another in inductive relation thereto when connected 'to
mechanism for varying current or resistance in the circuit of said coil in
correspondence with sound waves reaching the transmitter.
:
19. The method of telephoning consisting in maintaining on the line circuit an
electric current periodically varying in character, passing the said current through
the primary winding of an induction coil having a secondary circuit including a
telephone transmitter, and varying the resistance, capacity, or self-induction, of said
secondary circuit by the agency of sound vibrations.
20. The method of telephoning consisting in feeding the line circuit with an
electric current of changing value, operat ng an electro-responsive device by said
current, and varying said current by a cal induction modifier actuated by sound
vibrations and in operative relation to saiu electro-responsive device.
21. The method of telephoning, consisting in passing over a circuit an alternating
current, or a current periodically changing in value, and inductively modifying said
current in correspondence with sound vibrations.
22. The method of telephoning, consisting in passing over a circuit an alternating
current, or a current of changing value, passing said current through a coil of an
inductorium, and varying the counter-induction of said inductorium by the agency
of sound vibrations.
23. The method of telephoning, consisting in feeding the line with an electric
current of periodically rising and falling potential, passing said current through a
counter-inductive device included in the line circuit, and varying the counter-
induction of said device by the agency of sound vibrations, whereby the said
current is made to flow over said line in impulses or waves corresponding to the
sound vibrations.
T1
:
1 1000
Witnesses:
ROBERT SHAND.
JOHN W. GIBBONEY.
ELIHU THOMSON.
CHARLES E. HATTHAN.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, Agents for the Applicants.