Improvements in and relating to Telephonic Apparatus.
Year: 1892

page_text: Date of Application, 3rd Nov., 1892
Complete Specification Left, 2nd Aug., 1893-Accepted, 2nd Sept., 1893
PROVISIONAL SPECIFICATION.
Improvements in and relating to Telephonic Apparatus.
I, ALFRED ROSLING BENNETT, of 22 St. Albans Road, Harlesden, in the
County of London, Electrical Engineer do hereby declare the nature of this
invention to be as follows:-
My invention relates to telephonic switching apparatus and comprises the
improvements hereinafter indicated.
My invention refers chiefly to improvements in the apparatus and systems
described in the Specifications of British Letters Patent No. 12484 of 1891;
No. 18451 of 1891; No. 19020 of 1891; No. 20545 of 1891; and No. 15238
of 1892.
The objects of my invention may be briefly enunciated under the following
headings, Firstly, I provide, a method by means of which the operator at any
section of a multiple switch oard can by applying a test discover whether any
particular subscriber's metallic circuit is connected at any other section; Secondly
I provide means whereby any subscriber can signal to another subscriber with
whom he is connected, without attracting the attention of the operator at the
exchange, or, when required, can signal the operator or ring off" without
disturbing the other subscriber; my invention also comprises other improvements
hereinafter indicated.
"
In carrying out the first parts of my invention I provide a pair of flexible con-
necting wires, made into one cord furnished with a suitable contact peg adapted
for metallic circuit switching and permanently joined to each subscriber's metallic
loop in shunt or in parallel. The contact holes or spring-jacks may be joined
either in parallel or in series.
The flexible cords so provided are, as is usual in telephonic switch-rooms, fitted
with pulleys and weights, so that a cord on being released from a contact by the
operator will automatically resume the position in the set which it occupies when
out of use. I make the taking of a cord from its usual place by an operator for the
purpose of establishing a connection and its automatic return to a fixed situation
actuate contact levers which thereby establish or break contact when a cord is pulled
from, or returned to, its position of rest.
In adapting this method of making and breaking contact to the system of
operator's test described in the aforesaid prior Specifications the two conductors of
cach connecting cord are bridged by resistance coils and from between these coils an
insulated wire is led to one contact of a lever switch. The other contact of the
switch is connected to earth or to one pole of the testing battery from the other
pole of which another wire leads to the operator's testing apparatus.
I arrange as aforesaid that when the cord is out of use the lever and its contact
are separated and when the cord is in use for the purpose of making a connection
on the switch-board the lever and its contact are brought together and electrical
connection is established between them. Or the results of the motion may be
reversed, that is to say, contact may be established when the cord is at rest and
broken when in use.
According to this system two of the subscribers' loops are switched together by.
drawing a cord permanently joined to one of the loops from its normal position and
inserting its peg in the contact hole or block of the other loop. If the lever
and contact are arranged to be brought together by the drawing of a cord from rest
it will be understood that the test battery will now be in connection with both of
the loops and that an operator on another section of the switch-board testing either

page_text: Toup will
close the circuit or the battery and obtain an engaged signal on the
apparatus.
In a modification of this part of my invention a wire is led from one only of the
conductors of the cord through the lever and its contact to earth or to one pole of
the testing battery and the bridge wire containing the two resistance coils is
omitted.
In a further modification I provide a wire leading from a point intermediate
between the resistance coils of a wire which bridges a flexible connecting cord to
the first contact of an automatic switch operated as before described. The other
contact of the automatic switch is then joined through a relay to one pole, for instance
the zinc pole, of a suitable battery, the copper pole of said battery being joined
through a second relay to the second contact of a second automatic switch and to
the zinc pole of another battery, the copper pole of the second battery being joined
in like manner through a third relay to the second contact of a third automatic
switch and to the zinc pole of a third battery and so on throughout the
exchange.
The movement of the cord may be made to operate the lever switch in several
ways, for instance the weight which draws back the cord to its position of rest
after use may be guided to fall on one end of a pivoted arm or lever which it will
drive against, or away from, a suitable contact or pair of contacts; the haft of the
switch-peg may make or break the contact of a spring switch fixed to a board
against which the switch-peg is drawn when out of use by the pulley weight; or a
projection on the switch-cord itself may be employed to make or break the necessary
connection.
In Specification No. 19020 of 1891 hereinbefore mentioned I describe a telephonic
switching system in which electro-magnetic indicators are provided for the purpose
of attracting the operator's attention and also for notifying the termination of
a conversation. By this system one subscriber is enabled after connection to ring
the bell of his correspondent without disturbing the operator. According to my
present invention I modify this switching system in several ways.
For instance I may dispense with the triple-contact spring-jack therein described
and substitute simple contact holes or sockets adapted for metallic circuit switching.
In parallel with these contact holes a flexible connecting cord having two conductors
with resistances bridged between them is permanently joined. From between the
resistances a wire is led to one side or contact of a lever switch operated by the
motion of the connecting cord being drawn from, or returned to, its position of rest
as hereinbefore described. To the other contact of the lever switch is attached a
wire leading through an electro-magnetic indicator to earth or to a return wire to
the subscriber's station. In the earth circuit or return wire I include a battery
or other source of electricity which may be either at the exchange or at the
subscriber's station. The subscriber, as is described in the aforesaid Specification
No. 19020 of 1891, on pressing a key or lever switch temporarily connects his
metallic loop to earth or to a return wire. According to my present invention the
subscriber in order to call the exchange depresses this lever, thereby causing a
battery current to circulate through the earth or return wire, one or both wires of
his metallic loop, one or both of the resistances which bridge his connecting cord,
the automatic spring lever switch and the electro-magnetic indicator. The
operator's attention being thus attracted may open communication with the
subscriber in two ways. A spring jack may be provided in the indicator circuit
into which a switch-plug having two contacts is placed. The operator's telephone
is thereby looped into the circuit. In this case the subscriber keeps his key
depressed when speaking to the operator. Or the operator's telephone may be
plugged direct into the subscriber's metallic loop. In this case the subscriber must
allow the key to rise in order to speak. To connect two of the metallic circuits
the operator draws the cord of one subscriber from its position of rest and inserts
the plug into the contact hole or socket of the other. When thus connected the
subscribers can ring to each other without disturbing the exchange. To notify the

page_text: termination of a conversation one or both subscribers depress their keys establishing
an earth circuit through the lever switch of that cord which has not been drawn
from its position of rest and causing the indicator connected therewith to fall. In
a modification of this system the resistance bridge across the cord conductors
may be dispensed with and the wire to the lever switch taken off one of the
conductors.
When this system is used with multiple switch-boards the automatic lever switch
operated by the motion of the cord may be provided with a pair of contacts, one
making connection with the lever when the cord is at rest for the purpose of the
indicator circuit just described; the other making connection with the lever when
the cord is in use for the purpose of establishing communication between the
metallic loop and the operator's test battery: The lever is in this case joined to
the wire taken off from between the bridge resistances or direct from one of the
conductors of the cord.
In a further modification of this part of my invention I arrange the automatic
lever switch so that each conductor of a cord may possess a metallic connection
with an insulated contact attached to the cord and projecting slightly from its
circumference. In the position of rest these two contacts connect by pressure
caused by the pulley weight with two fixed contact stops or springs which have
looped between them an electro-inagnetic indicator which is thereby brought into
circuit with the subscriber's metallic loop and can be dropped by him when he sends
a ringing current round his loop. In the position of use, that is to say when the
cord has been pegged into the contact hole of another metallic loop, the contacts
are separated and the indicator is cut out of circuit. But the indicator of the
other connected subscriber is still in, since its cord has not been disturbed and the
dropping of this indicator notifies the termination of a conversation.
This system
requires no key or earth connection at the subscribers' stations, but the subscribers
cannot ring each other without disturbing the exchange.
In those switching systems which require electro-magnetic indicators the
operators have usually to replace the shutters or flags of the indicators after they
have been dropped or deflected by the subscribers' calling or ringing-off signals.
According to a modification of my invention a lever switch attached to, or worked
by the motion of, a connecting cord, substantially as is herein before described, may
be used to automatically restore the shutters or flags to their normal positions if
the indicators are of the polarized type or otherwise constructed in such a way
that they are deflected by the circulation through their coils of a current in one
direction and restored by a current flowing in the other direction, or deflected by a
vibratory or alternating current and restored by a constant voltaic current.
effect this I arrange the lever switch and its contacts in such a way that when the
cord is out of use and at rest the indicator coils are in connection with the
subscriber's metallic loop ready to respond to any calling current, and that when
the cord is drawn from its position for the purpose of making a connection the
indicator is first automatically cut off from the metallic loop and then temporarily
connected to a reversing battery which restores the deflected shutter or flag to its
normal position.
To
Another modification of this part of my invention consists in permanently joining
a connecting cord in parallel with a subscriber's metallic loop and with its contact
holes or sockets, as already described, and in taking a wire either direct from one
of the conductors or from between the resistances of a bridge across the conductors
to a telephone at which the operator is continually listening and the other terminal
of which is connected to earth by a return wire to the subscriber's station. Any
suitable number of metallic circuits can be so connected to one telephone. The
subscriber obtains communication with the operator both for demanding connection
and disconnection, by depressing a key or lever the effect of which is to place his
telephone between his metallic circuit and earth or a return wire. The connection
being made by the operator pegging the cord of one subscriber into the contact hole
of the other, the subscriber allows his key to rise and can then talk or ring his.

page_text: correspondent through the metallic circuit without being overheard by, or
disturbing the operator. With this modification no automatic lever switch is
required unless multiple switch-boards are used when one may conveniently be
employed for the purposes of the operator's test as hereinbefore indicated.
Another part of my invention refers exclusively to those methods in which
resistances bridged across the conductors of a connecting cord or metallic circuit
are dispensed with and the necessary deviation or shunt is taken direct from one of
the conductors of the said flexible connecting cords. When this plan is followed
the equilibrium of the metallic circuit is not so perfect as when a bridge having
branches of equal resistance, self-induction, magnetic inertia and static capacity is
employed. The attachment of the wire and apparatus to one side only of the loop
tends to disturb the balance, especially in respect of capacity. To counteract this
I attach to the other conductor of the flexible cord a condenser, an insulated coil
of wire or a mass of insulated metal so as to increase the capacity of that side of
the loop proportionally with that of the other. An adjustable condenser may be
employed for the purpose.
.
This method of compensating for a preponderance of capacity on one side of the
loop is also applicable to the case in which, with multiple switch-boards arranged
with the spring-jacks in series, an insulated tail of wire is left in connection with
one side of a loop when a communication is proceeding.
Another part of my invention relates to the transmitter induction coils provided
at subscribers' stations for the purpose of transforming the microphonic vibrations.
The secondaries of these induction coils are usually joined in series with the
receiving telephone in such a way that currents arriving from the line pass first
through the coil and then through the receiver, or vice versa. This plan is satis-
factory when the lines are single with an earth return but when metallic circuits
are used the electrical balance which it is so desirable to maintain between the two
wires of a loop is disturbed when two subscribers are connected, so that their
secondaries are both on one side of the loop and their receivers on the other. To
obviate this I divide the secondary of the induction coil into two parts of equal
resistance aud capacity and connect the receiving telephone between them. This
plan ensures perfect balance in the apparatus at the subscribers' stations under all
conditions.
Dated ho
1
T
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the. Applicant.
COMPLETE SPECIFICATION.
Improvements in and relating to Telephonic Apparatus.
1, ALFRED ROSLING BENNETT, 22 St. Albans Road, Harlesden in the County
of Middlesex, 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 :-
My invention refers chiefly to improvements in the apparatus and systems
described in the Specifications of British Letters Patents No. 12484 of 1891;
No. 18451 of 1891; No. 19020 of 1891; No. 20545 of 1891; and No. 15238
of 1892.
The objects of my invention may be briefly enunciated under the following
headings, Firstly, I so provide that the operator at any section of a multiple switch-
board can by applying a test discover whether any particular subscriber's metallic
circuit is connected at any other section; Secondly I provide means whereby any
subscriber can signal to another subscriber with whom he is connected, without
attracting the attention of the operator at the exchange or, when required, cau
signal the operator or "ring off" without disturbing the other subscriber; my
invention also comprises other improvements hereinafter indicated.

page_text: In carrying out the first parts of my invention provide a pair of flexible
connecting wires, made into one cord furnished with a suitable contact peg adapted
for metallic circuit switching and permanently joined to each subscriber's metallic
loop in shunt or in parallel. The contact holes or spring-jacks may be joined either
in parallel or in series. The flexible cords so provided are, as is usual in telephonic
switch-rooms, fitted with pulleys and weights, so that a cord on being released from
a contact by the operator will automatically resume the position in the set which it
occupies when out of use. I make the taking of a cord from its usual place by an
operator for the purpose of establishing a connection and its automatic return to a
fixed situation actuate contact levers which thereby establish or break contact when
a cord is pulled from, or returned to, its position of rest.
In adapting this method of making and breaking contact to the system of
operator's test described in the aforesaid prior Specifications the two conductors of
each connecting cord are bridged by resistance coils and from between these coils
an insulated wire as set forth in 12484 of 1891 is led to one contact of a lever
switch. The other contact of the switch is connected to earth or to one pole of the
testing battery from the other pole of which another wire leads to the operator's
testing apparatus.
I arrange as aforesaid that when the cord is out of use, the lever and its contact
are separated and when the cord is in use for the purpose of making a connection
on the switch-board the lever and its contact are brought together and electrical
connection is established between them. Or the results of the motion may be
reversed, that is to say, contact may be established when the cord is at rest and
broken when in use.
According to this system two of the subscribers' loops are switched together by
drawing a cord permanently joined to one of the loops from its normal position and
inserting its peg in the contact hole or block of the other loop. If the lever and
contact are arranged to be brought together by the drawing of a cord from rest it
will be understood that the test battery will now be in connection with both of the
loops and that an operator on another section of the switch-board testing either
loop will close the circuit of the battery and obtain an engaged signal on the
apparatus.
In the accompanying drawings,
Figure 1 is a diagram shewing a portion of a multiple switch-board provided with
operators' test apparatus the circuit of which is made and broken by means of the
flexible connecting cord as hereinafter explained.
Figure 2, shews the application of the same principle to another forin of
operator's test apparatus, and
Figures 3, 4 and 5 shew the application of the same principle to various forms of
subscriber's call apparatus.
Like letters of reference denote similar parts in all the drawings.
Referring now to Figure 1, S1, S2, S3, signify three sections of a multiple switch
board, T, T2, T3, represent three subscribers' telephonic instruments which are
connected to their respective contacts on the multiple switch-board by three
metallic loops marked M', M³, M³. The flexible connecting cords F1, F2, F3, one
of which is provided for each metallic loop on the switch-board contain two
insulated conductors CC which are permanently connected to and consequently
form part of the two wires of its metallic loop. The two wires of the metallic loop
or the two conductors of the connecting cord are connected by a bridge wire which
contains in its circuit two coils of equal resistance and other electrical properties as
fully described in the Specification of Letters Patent No. 12484 of 1891 aforesaid.
From a point between these coils R1, R2 is led a branch wire W permanently joined
in connection with the switch lever L which is kept from making contact with the
contact-stop B by the flexible cord F. The said flexible cord engages in such a
manner with the switch L that when the cord is out of use and in its allotted
position of rest under the influence of the weight X acting by means of the
pulleys P, the switch lever L is lifted clear of the contact stop B and is electrically

page_text: insulated from it. But when the flexible cord is pulled down by an operator for
the purpose of establishing a connection the lever Ĺ ceases to be influenced by the
cord and weight and falls on the contact-stop B with which it maintains electrical
connection so long as the cord is away from its position of rest. The contact
stops B1, B2, B3 are all connected to a common wire attached to one pole of the
battery V, the other pole of which is connected to the operators' testing
instruments I, 12, 13 and the operators' testing cords J, J, J³. It will be under-
stood from this description that whenever a cord is down and its lever L and contact-
stop B are thereby in connection, the metallic loop of that particular cord will be
charged from the battery V and the application of any of the operators' testing
cords J to any of the contacts or spring-jacks S of the metallic loop will cause a
current to flow and the operator's testing instrument 1 to be actuated notifying that
the loop is engaged and must not be used. On the other hand the absence of a
signal due to the lever L and contact stop B being separated will show that the
loop is out of use.
In a modification of this part of my invention a wire is led from one only of the
conductors of the cord through the lever and its contact to earth or to one pole of
the testing battery and the bridge wire containing the two resistance coils is
omitted.
In a further modification which is shown in Figure 2 of the accompanying
drawings I provide a wire leading from a point intermediate between the resistance
coils R, R of a wire W which bridges the two conductors of a flexible connecting
cord to the lever of an automatic switch as L' operated as before described. In
this modification the contact stop B₁ of the automatic switch is joined through a
relay or other suitable indicating instrument I' to one pole, for instance the zinc
pole, of a suitable battery V₁, the copper pole of said battery being joined through
a second relay 12 to the contact-stop B2 of a second automatic switch L, and to
the zinc pole of another battery V2, the copper pole of the second battery being
joined in like manner through a third relay 13 to the contact stop B³ of a third
automatic switch L³ and to the zinc pole of a third battery and so on throughout
the exchange. It is clear that the insertion of a connecting cord such as F' in
the contact or spring-jack of another metallic loop as S2 of the loop M² will
cause the battery VI to charge both the metallic loops M¹ and M². M¹ will be
charged through the relay I, the contact stop B' the lever L' the wire W and the
coils R', R. M2 will be charged through the relay I' the contact-stop B¹, the
lever L', the wire W, the coils R1, R2, the conductors C C of the flexible cord F1
and the contacts A. A of the switch-peg with which the cord is necessarily fitted
and the contact or spring-jack S. Now if the flexible cord of a third metallic
loop as F3 of M³ is applied to any of the contacts or spring-jacks of either M¹
or M³, for instance contact Ss of loop M2, for the purpose of establishing a
connection or as a test it is clear that the circuit of the batteries V', V' will be
closed by the act, via contact S³ of loop M³, contacts A, A and conductors C¹, C'
of flexible cord F³, resistance coils R¹, R and wire W of F³, lever L³, contact
stop B3, and relay 13, and that an alarm signal will be given on both the relays I'
and I³. A connection cannot consequently be established with a loop. which is
already engaged without an alarm being given, which alarm if the relay is arranged
to actuate a local circuit containing a battery and bell, may be made to continue
so long as the attempt to effect a connection is not desisted from. In the operators'
testing systems ordinarily in use a forgetful or careless operator may effect a
connection with an already engaged line notwithstanding that it has been shewn to
be engaged by the test, as the test signal is only transitory. My present invention
however renders it necessary to persist deliberately in the face of a continuous
alarm in order to bring about a duplicate connection. This alarm moreover
continues after such a connection is made and as long as it is kept on.
The operator's test circuit may be extended with advantage to the testing room
of a telephonic exchange in which room electricians are present for the purpose of
attending to and localising faults. As at present arranged it is within the power

page_text: of such electricians to switch an instrument into circuit with any subscriber's line
and listen to all that is said thereon without detection. But if the operators'
testing circuit is extended to the electricians' room and all connecting cords used
by the electricians are joined to it and fitted with balanced resistances and indicating
relays preferably placed under lock and key, any attempt to tap or listen on an
engaged circuit would result in an alarm which might be made to sound in the
superintendent's office at the chief operator's table or any other desired spot.
Secrecy of telephonic communication would thereby be greatly enhanced.
It will be understood that when the two loops M and M' are connected as
already described by the employment of flexible cord Fl inserted in contact S' of
loop M, any attempt to use the cord F of the second loop would be frustrated
for as soon as it is pulled from its position of rest the lever L³ would touch the contact
stop B and close the circuit of the battery V₁, via relay 12, stop B2, lever L³,
wire W, coils R, R of cord F, contact S' of loop M², contacts A, A and
conductors C¹, C of cord F¹, coils R', R of cord F', wire W, lever L', stop B',
and relay I', thus causing both the relays I and 12 to sound. Instead of each
connecting cord being provided with an indicating instrument one instrument will
suffice for each operator's section all the cords allotted to one section being
connected to one instrument, and the different groups of cords thus formed being
connected with each other through batteries as shown.
I do not confine myself to the device shown for operating the lever switch
automatically by means of the connecting cord inasmuch as the movement of the
cord may be made to operate the lever switch in several ways, for instance the
weight which draws back the cord to its position of rest after use may be guided
to fall on one end of a pivoted arm or lever which it will drive against, or away
from, a suitable contact or pair of contacts the haft of the switch-peg may make
or break the contact of a spring switch fixed to a board against which the switch-
peg is drawn when out of use by the pulley weight; or a projection on the switch-
cord itself may be employed to make or break the necessary connection.
In Specification No. 19020 of 1891 herein before mentioned I describe a tele-
phonic switching system in which electro-magnetic indicators are provided for the
purpose of attracting the operator's attention and also for notifying the termination
of a conversation. By this system one subscriber is enabled after connection to
ring the bell of his correspondent without disturbing the operator. According to
my present invention I modify this switching system in several ways.
For instance I may dispense with the triple-contact spring-jack therein described,
and substitute simple contact holes or sockets adapted for metallic circuit switching
as shown at S¹, S in Figure 3 of the accompanying drawings. In parallel with
these contact holes flexible connecting cords F1, F' having two conductors C, C³
with resistances R', R' bridged between them, are permanently joined. From
between the resistances a wire W is led to a lever switch such as L' operated by
the motion of the connecting cord being drawn from, or returned to, its position of
rest as herein before described. To the contact stop H' of the lever switch is
attached a wire leading through an electro-magnetic indicator O₁ to earth or to a
return wire to the subscriber's station. In the earth circuit or return wire, I
include a battery V or other source of electricity which may be either at the
exchange or at the subscriber's station. A subscriber, as T', as is described in
the aforesaid Specification No. 19020 of 1891, on pressing a key or lever switch
provided for the purpose at his station temporarily connects his metallic loop to
earth or to a return wire by means of the wire E. According to my present
invention the subscriber in order to call the exchange depresses this lever, thereby
causing a current from the battery V to circulate through the earth or return wire,
one or both wires of his metallic loop, one or both of the resistances which bridge
his connecting cord, the automatic lever switch and the electro-magnetic indicator.
The operator's attention being thus attracted may open communication with the
subscriber in two ways. A spring jack shewn at J', J' or some equivalent device.

page_text: may be provided in the indicator circuit into which a switch-plug having two
contacts is placed. The operator's telephone is thereby looped or cut into the
circuit. In this case the subscriber keeps his key depressed when speaking to the
operator. Or the operator's telephone may be plugged direct into the subscriber's
metallic loop as at St. In this case the subscriber must allow the key to rise in
order to speak. To connect two of the metallic circuits the operator draws the
cord of one subscriber as F¹ from its position of rest and inserts the plug A, A
into the contact hole or socket of the other as S2. When thus connected the
subscribers can ring to each other on their metallic loop without disturbing the
exchange. To notify the termination of a conversation one or both subscribers
depress their keys establishing an earth circuit through the lever switch of that
cord which has not been drawn from its position of rest and causing the
indicator O' connected therewith to fall. In a modification of this system the
resistance bridge across the cord conductors may be dispensed with and the wire
to the lever switch taken off one of the conductors.
When this system is used with multiple switch-boards the automatic lever switch
operated by the motion of the cord may be provided with a pair of contact stops,.
one as at H' making connection with the lever when the cord is at rest for the
purpose of the indicator circuit just described; the other which is below the level
making connection with the lever when the cord is in use for the purpose of.
establishing communication between the metallic loop and the operator's test
battery. The lever is in this case joined to the wire taken off from between the,
bridge resistances or direct from oue of the conductors of the cord.
In a further modification of this part of my invention shown in Figure 4 of the
accompanying drawings I arrange the automatic lever switch so that each
conductor C1, C2 of a cord as F¹ may possess a metallic connection with an insulated
contact H1, H2 attached to the cord and projecting slightly from its circumference.
In the position of rest these two contacts connect by pressure caused by the pulley
weight X, with two fixed contact stops or springs B1, B2 which have looped between
them an electro-magnet indicator O'. This indicator is thereby brought into
circuit with the subscriber's metallic loop M¹ and can be dropped by him when he
sends a ringing current round his loop. In the position of use, that is to say when.
the cord has been pegged into the contact hole of another metallic loop as at S2, M³
the contacts 13', B2 and H1, H2 of F are separated and the indicator O' is cut out
of circuit. But the indicator 02 of the other connected subscriber M' is still in
circuit since the cord F2 has not been disturbed and the dropping of this indicator
notifies the termination of a conversation. This system requires no key or earth
connection at the subscribers' stations, but the subscribers cannot ring each other
without disturbing the exchange.
Another modification of this part of my invention shown in Figure 5 of the
accompanying drawings, consists in permanently joining a connecting cord as F1, F2
in parallel with a subscriber's metallic loops M', M2 and with their contact holes or
sockets S1, S2 as already described, and in taking a wire W either direct from one
of the conductors C, C or from between the resistances R', R² of a bridge across
the conductors to a telephone O at which the operator is continually listening and
the other terminal of which is connected to earth or by a return wire to the
subscribers' stations. Any suitable number of metallic circuits can be so connected
to one telephone. The subscriber obtains communication with the operator both for
demanding connection and disconnection, by depressing a key or lever the effect of
which is to place his telephone between his metallic circuit and earth or a return
wire by means of the line E, as set forth in Specification No. 20545 of 1891. The
connection being made by the operator pegging the cord of one subscriber as F¹
of M¹ into the contact hole of another as S2 of M2, the subscriber allows his key to
rise and can then talk or ring his correspondent through the metallic circuit without
being overheard by, or disturbing the operator. With this modification no auto-
matic lever switches are required in connection with the cords, unless multiple

page_text: switch boards are used when one may conveniently be employed for the purposes of
the operators' test as hereinbefore indicated.
Another part of my invention refers exclusively to those methods in which
resistance bridges across the conductors of a connecting cord or metallic circuit are
dispensed with and the necessary deviation or shunt is taken direct from one of the
conductors of the said flexible connecting cords. When this plan is followed the
equilibrium of the metallic circuit is not so perfect as when a bridge having
branches of equal resistance, self-induction, magnetic inertia and static capacity is
employed. The attachment of the wire and apparatus to one side only of the loop
tends to disturb the balance especially in respect of capacity. To counteract this I
attach to the other conductor of the flexible cord a condenser, an insulated coil of
wire or a mass of insulated metal so as to increase the capacity of that side of the
loop proportionally with that of the other. An adjustable condenser may be
employed for the purpose.
This method of compensating for a preponderance of capacity on one side of the
loop is also applicable to the case in which, with multiple switch-boards arranged
with the spring-jacks in series, an insulated tail of wire is left in connection with
one side of a loop when a communication is proceeding.
Another part of my invention relates to the transmitter induction coils provided
at subscribers' stations for the purpose of transforming the microphonic vibrations.
The secondaries of these induction coils are usually joined in series with the
receiving telephones in such a way that currents arriving from the line pass first
through the coil and then through the receiver or vice versa. This plan is
satisfactory when the lines are single with an earth return but when metallic
circuits are used the electrical balance which it is so desirable to maintain between
the two wires of a loop is disturbed when two subscribers are connected, as must
frequently happen in practice with the ordinary coils, so that their secondaries are
both on one side of the loop and their receivers on the other. To obviate this I
divide the secondary of the induction coil into two parts of equal resistance and
capacity and connect the receiving telephone between them. This plan ensures
perfect balance in the apparatus at the subscribers stations under all conditions,
and as both secondaries are superimposed on one primary of the usual construction
no injury results to the transmitting circuit.
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 :-
1. In telephone exchange systems worked with complete metallic circuits and
multiple switch-boards, the employment of flexible connecting cords one of which is
permanently joined to each subscriber's loop and is adapted to make or break the
operator's testing circuit when pulled by the operator from its normal position,
substantially as, and for the purpose, specified.
2. In a telephone exchange system worked with complete metallic circuits and
multiple switch boards, the combination of flexible connecting cords one of which is
permanently connected to each subscriber's metallic loop with the operator's testing
systems such as described in the Specification of British Letters Patent Nos. 12484
and 18451 of 1891 and No. 16124 of 1892, or with the call apparatus such as
described in either of the Specifications of British Letters Patent No. 19020 or
No. 20545 of 1891 substantially as and for the purpose specified.
3. In telephone exchange systems worked with complete metallic circuits, the
apparatus for enabling the subscriber to signal direct to the operator when a con-
nection is desired, arranged substantially as described with reference to Figure 4 of
the drawings.
4. In telephone exchange systems worked with complete metallic circuits,
attaching to the unconnected wire of each flexible cord a coil of wire or condenser
or the like, substantially as described for the purpose specified.
B

page_text: 5. In telephone systems, whether exchange or private, an induction coil having
its secondary divided into two parts with the receiving telephone connected between
the said parts, substantially as described.
Dated this 2nd day of August 1893.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.