Improvements relating to Telephonic Switching Apparatus.
Year: 1892

page_text: Date of Application, 8th Sept., 1892
Complete Specification Left. 29th May, 1893-Accepted, 8th July, 1893.
PROVISIONAL SPECIFICATION.
Improvements relating to Telephonic Switching Apparatus.
I, ALFRED ROSLING BENNETT, 22 St. Alban's Road, Harlesden, in the County
of Middlesex, 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.
One part of my invention refers chiefly to improvements in the system described
in my Specification of Letters Patent, No. 19,020, dated 4th November 1891, by
which any subscriber is enabled to signal to the operator at the exchange, either
before or after the establishment of a connection at the exchange between himself
and some other subscriber.
The chief feature of this part of my invention consists in joining the signal
apparatus used for notifying to the operator the termination of a conversation
to only one of the conductors of the flexible connecting cords used at the
exchange for joining subscribers' loops, whereas in the aforesaid Specification
I describe an arrangement wherein the two conductors of the flexible connecting
cord are joined by a bridge wire, the middle point of which is joined to the said
signal apparatus.
A second part of my invention refers chiefly to improvements in the system
described in the Specification of Letters Patent No. 20,545 dated 26th November
1891, wherein an operator's telephone is described as being connected to both con-
ductors of the flexible connecting cords, for the purpose of receiving notifications
of the termination of conversations from the subscribers. In my present invention
I connect the operator's telephone used for this purpose to only one of the conductors
of the said flexible cord.
Another part of my invention relates in reference to multiple switch-boards
to an improved arrangement of operator's test apparatus and is designed so
that the flexible connecting cords used for coupling two subscribers' metallic
loops, shall themselves form the cords which the operator uses to test whether
any one of the said loops is engaged or in use on a different section of the
board.
By my invention.I also provide a registering device which will automatically
register or record the number of connections which have been made to a subscriber's
line and thereby afford a basis for making charges and statistics.
I will now proceed to indicate more clearly the nature of the. improvements
hereinabove mentioned.
In the said Specification No. 19,020 of 1891, suitable apparatus at the sub-
scribers' stations for joining the subscriber's metallic loop to the earth, or to a
third or return wire, and at the exchange triple-contact spring jacks connected to
an annunciator or indicating device, are shewn and described, together with a
second indicating device joined between both conductors of a connecting cord and
earth.
By my present invention I provide a relay or indicating device which is included
in a wire which joins one conductor only of each of the flexible connecting cords.
used for coupling subscribers' metallic loops together to the earth. I thus dispense
with the bridge wire joining the two conductors of the flexible connecting cords
which I have hitherto employed.
According to another part of my present invention I provide an operator's
telephone which takes the place of the relay, annunciator. or other indicator, one
terminal of the said telephone being joined, direct to earth. or to, the return wire

page_text: while the other terminal is joined to one contact of each of the spring jacks on a
section, and also to one of the conductors of each of the flexible connecting cords,
provided for use at the section..
When I provide an operator's telephone I prefer to arrange that a subscriber
instead of merely connecting his metallic loop to earth shall be able to place his
telephone in a branch between the earth and either or both of the wires of his
metallic loop, as described in the aforesaid Specification No. 20,545 of 1891.
I then
If desired I may provide a registering device for automatically recording the
number of calls or connections, that have becu made to any subscriber.
introduce such a registering device into the earth or return circuit at the exchange,
so that whenever a subscriber rings "up" or calls to the operator in order to be
connected to another subscriber or rings "off" to be disconnected at the close of a
conversation, the registering device will make a record. I may place the said
registering device, which may be of any suitable design, in the earth wire at a
subscriber's station so that a current flows through the same and makes a record
whenever the subscriber connects his metallic loop to the earth for the purpose of
calling the operator or ringing "off."
My improved system of operator's test apparatus according to my present inven-
tion is substantially as follows, 1 join the conductors of each flexible connecting
cord by a bridge wire which includes two equal resistances as explained in my
Specification No. 18,451 dated 27th October 1891 and join the middle of the bridge
wire of one connecting cord through a relay to one pole of a battery the second
pole of said battery being joined through a second relay to the middle point of the
bridge wire of another connecting cord and to the first pole of a second battery,
the second pole of which is joined through a third relay to the bridge wire of a
third connecting cord and to the first pole of a third battery, and so on through the
switch-board. It is evident that the total number of batteries required will be one
less than the number of connecting cords in the exchange, and also that every con-
necting cord will have its own particular relay. Or I may arrange that the bridge
wires of each flexible connecting cord shall be connected through a relay and
battery to a common return or lead running through the exchange. The batteries
will then be connected in parallel.
In a modification of this part of my invention I join one conductor of one of
the flexible connecting cords through a relay to one pole of a battery the second
pole of said battery being joined through a second relay to the conductor of the
next connecting cord and to the pole of another battery, the second pole of which
is joined through a third relay to the third connecting cord and to another battery
and so on through the exchange thus dispensing with the bridge wires, or I may
join the batteries in parallel one conductor of each flexible connecting cord being
joined through a relay and battery to a common return or lead.
It is easily understood that if two metallic loops be connected by one of the
connecting cords in any part of the exchange, and an operator touches one of the
contact blocks on another section of a multiple switch board of either of the said
loops with the plug of any other flexible connecting cord, a circuit will be estab-
lished through the loop which the operator attempted to join up, the two flexible
connecting cords and their relays, and the battery included between the said
flexible connecting cords. The relays of both cords therefore will indicate by the
deflection of their armatures that the loop is already in use, and by closing the
circuit of a local battery a bell may be made to sound a loud or continued
alarm should a second connection to an engaged loop be accidently or designedly
made:
In a further modification of this part of my invention, I insert in one of the
conductors of each of the flexible connecting cords a battery and relay. The
battery is small so that when a flexible cord is employed for the purpose of con-
necting two subscribers' metallic loops no indication will be afforded by the relay
since the battery will not have power to deflect it through the resistance offered
by the subscribers' loops and telephones, but when another flexible connecting

page_text: cord is used to connect one of the said loops which is already in use with another
loop the resistance between the two cords will be small and the combined electro-
motive force of the two batteries which are included in the said flexible connecting
cords will give an indication on the relays of the said cords.
I may if desirable use electric bells or other suitable indicators instead of the
relays herein mentioned.
I wish it understood that all my improvements hereinabove mentioned are
applicable to systems of telephony in which multiple switch boards provided with
contact blocks joined to the subscribers' metallic loops either in series or in
parallel are used and in which complete metallic circuits are employed for the
subscribers' line wires.
Dated this 8th day of September 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements relating to Telephonic Switching Apparatus.
I, ALFRED ROSLING BENNETT, 22 St. Alban's Road, Harlesden, in the County
of Middlesex, Electrical Engineer, 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 relates to telephonic switching apparatus and comprises the.
improvements hereinafter indicated.
One part of my invention refers chiefly to improvements in the system described
in my Specification of Letters Patent No. 19,020 dated 4th November 1891, by
which any subscriber is enabled to signal to the operator at the exchange, either
before or after the establishment of a connection at the exchange between himself
and some other subscriber.
The chief feature of this part of my invention consists in joining the signal
apparatus used for notifying to the operator the termination of a conversation to
only one of the conductors of the flexible connecting cords used at the exchange
for joining subscriber's loops, whereas in the aforesaid Specification I describe an
arrangement wherein the two conductors of the flexible connecting cord are joined
by a bridge wire, the middle point of which is joined to the said signal
apparatus.
A second part of my invention refers chiefly to improvements in the system
described in the Specification of Letters Patent No. 20,545 dated 26th November.
1891, wherein an operator's telephone is described as being connected to both
conductors of the flexible connecting cords for the purpose of receiving notifica-
tions of the termination of conversations from the subscribers. In my present
invention I connect the operator's telephone used for this purpose to only one of
the conductors of the said flexible cord.
Another part of my invention relates, in reference to multiple switch-boards, to
an improved arrangement of operator's test apparatus and is designed so that the
flexible connecting cords used for coupling two subscribers' metallic loops, shall
themselves form the cords which the operator uses to test whether any one of the
said loops is engaged or in use on a different section of the board.
I will now proceed to indicate more clearly the nature of the improvements
hereinabove mentioned, by the aid of the accompanying drawings, in which
Figure 1 is a diagram shewing one method of carrying out my invention.
Figure 2 is a diagram shewing a modification wherein triple contact spring jacks
are used on the switch board..
Figures 3 and 4 are diagrams shewing the devices for enabling the ordinary
flexible connecting cords to be used as operator's testing cords.

page_text: In the said Specification No. 19,020 of 1891, suitable apparatus at the subscribers
stations for joining the subscriber's metallic loop to the earth, or to a third or
return wire, and at the exchange triple-contact spring jacks connected to an
annunciator or indicating device, are shewn and described, together with a second
indicating device joined between both conductors of a connecting cord and earth.
By my present invention I provide a relay or indicating device which is included.
in a wire which joins one conductor only of each of the flexible connecting cords
used for coupling subscribers' metallic loops together, to the earth. I thus dispense
with the bridge wire joining the two conductors of the flexible connecting cords
which I have hitherto employed.
Referring now to Figure 1, five subscribers' metallic circuits M¹ to M³ are.
shown each joined through a multiple switch-board having contacts at S' S² and S³.
The subscribers' instruments are marked by P¹ to P, and E' to E' represent the
earth wires and switches by means of which the subscribers are enabled to connect
their metallic loops temporarily to earth or to a third or return wire when such is
provided. Three connecting cords are shown two of which are in use for the
purpose of coupling metallic circuits M', M2 and M³, M' together, while the third
is idle. Each connecting cord is furnished with two insulated conductors C², C³,
one of which has a branch wire W leading from it through a relay or other suitable
indicating instrument to earth or to a third or return wire. Between the branch
wires W and earth is connected a voltaic battery or other suitable source of
electricity V. The circuit is only completed through this battery and one of the
relays or indicators when a subscriber whose line is connected at the switch-board
temporarily earths his metallic loop by means of the wire and switch provided at
his instrument for the purpose.
On such an earth connection being established by the subscriber at P¹ for
instance, a current flows from the battery V through the indicating instrument R¹,
the branch wire W, the conductor of connecting cord C³, over one wire of the
metallic loop M¹ to the subscriber's station and to earth. The subscriber is thus
enabled to actuate the indicating instrument R at will and so notify the operator
at the switch-board that he desires disconnection from the person with whom he:
has been in communication.
According to another part of my present invention I provide at each operator's
section of the switch-board an operator's telephone which takes the place of the
relay or other indicating instrument, one terminal of the said telephone being
joined direct to earth or to the return wire while the other terminal is joined to one.
contact of each of the spring-jacks on an operator's section, and. also to one of the
conductors of each of the flexible connecting cords provided for use at the section.
In this case I arrange that a subscriber instead of merely connecting his metallic
loop to earth shall be able to place his telephone in a branch between either or both
of the wires of his metallic loop and earth or a third or return wire if such be
used.
Figure 2 is a diagram which shews an arrangement of this kind. M', M²
represent two subscribers' metallic circuits; P1, P2 the subscribers instruments
which by the operation of a finger key or.switch may be cut out of the circuit of
the metallic loop and included in the circuit of the earth wire E or E. At the
switch-board each subscriber's loop is furnished with a spring-jack S, having
contacts at 1, 2 and 3. When no connecting plug is in a spring-jack contacts 1
and 2 are normally together while contact 3 is insulated. Contact 2 is in
permanent connection with one terminal of the operator's telephone 0, so that when
Do plug is in the spring-jack a subscriber by pressing his switch and thereby placing
his telephone between his metallic loop and earth can establish communication at
will with the telephone O, at which the operator is continually listening. The
telephonic current flowing through one wire of his loop and contacts 1 and 2 of the
spring-jack S. But when a connecting plug is in the spring-jack, as shown in
Figure 2, contact 2 is separated from contact 1 and insulated so that the normal
connection with telephone O is destroyed. So far the connections are the same as

page_text: 4
The several inventions hereinbefore set forth may be adapted to multiple
switch-boards having contacts either in series or in parallel.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
:—
1. The combination with a telephone system having complete metallic circuits
and switch-boards with flexible connecting cords, of a switch at the subscriber's
station adapted to connect the subscriber's metallic loop to earth or to a third or
return wire, and a circuit at the exchange for each connecting cord joined as a
branch or deviation from one of the conductors of cach of the said flexible
connecting cords to earth or to the aforesaid return wire, and including a battery
and indicator, for the purpose specified.
2. A. telephone system arranged substantially as described with reference to
Figure 1 of the accompanying drawings and operating as specified.
L
3. In a metallic circuit telephone system the means for calling up during the
existence of a connection, of the operator by a subscriber, said means comprising
special circuit including the subscriber's telephone, one or both wires of the metallic
loop, the operator's telephone placed in a branch or derivation from one of the
conductors of the connecting cord, and the earth or a third wire, which special
circuit is established by the subscriber when required.
4. In a telephone system worked with complete metallic circuits, the combination
with the subscribers metallic loops, of the spring jacks, connecting cords and
operators' telephones, substantially as described with reference to Figure 2 of the
accompanying drawings, for the purpose specified.
5. In a telephone system worked with complete metallic circuits for the
subscribers lines and multiple switch boards, testing apparatus wherein the flexible
connecting cords used for coupling two subscribers" metallic loops, themselves
form the operator's testing cords, substantially as described.
6. The combination with a telephone system worked with complete metallic
circuits, of testing apparatus substantially as described with reference to Figure 3
or to Figure 4 of the accompanying drawings.
Dated this 20th da£ M 1002
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.

page_text: previously described in the Specification of Letters Patent No. 20,545 of 1891.
According to my present invention for the purpose of enabling the subscriber to
notify the termination of a conversation to the operator a new connection with
telephone is established when a plug is in by means of a branch wire W
which is joined permanently to one of the two conductors C1, C2 of the double-
conductor connecting cord which joins the contacts of the connecting plugs. So a
subscriber by placing his telephone between his metallic circuit and earth can
always open up communication with the operator whether a connection is on or not.
I therefore dispense with the bridge wire and resistances which I hitherto used for
connecting the two conductors of the flexible connecting cord.
My improved system of operator's test is shown in Figures 3 and 4 in which M'
to M are metallic loops joining three subscribers PI to P³ to a multiple switch-
board on which each loop is provided with three contacts S' to S³. Referring now
to Figure 3 three flexible connecting cords are shown for example, each having
two insulated conductors C1, C2, which are bridged by a wire including two equal
resistances R', R2 which may each be of 3000 ohms resistance as explained in my
Specification of Letters Patent No. 18,451 of 1891. From between the resistances
of the first cord a wire W' is taken off and led through an indicating instrument It
to one pole of a battery V₁ the other pole of which is in connection with the centre
of the bridge of the second cord through the indicating instrument I2 and wire W
and also with the centre of the bridge of the third cord through the battery V2,
the instrument I³ and wire W³. The batteries must be connected so as to assist
and not to oppose cach other.
If the loop M² is connected to the loop M³ by means of the first flexible
connecting cord as shown by the dotted lines in the said Figure 3 it is plain that
none of the indicating instruments will be affected so long as none of the other
contacts of these loops are untouched by any other connecting cord. But should it
be attempted to make a second connection to either of these loops, say by applying
the third connecting cord to contact S³ of loop M², the instruments I and I would
immediately sound since a circuit will have been established via the two connecting
cords, the part of the loop M' intervening between contacts S2 and S³, the
instruments 1 and 13, and the batteries V1, V2. But should the third connecting
cord be applied to say contact S³ of loop M' none of the indicating instruments will
work, for M' not being connected elsewhere cannot provide a circuit. The operator
will then know from the absence of a signal that M' is not engaged and may be
safely connected.
It is evident that the total number of batteries required in this arrangement will
be one less than the number of connecting cords on the switch-board and also that
every connecting cord will have its own particular indicating instrument. But in
practice it is more convenient to assign one indicating instrument to each operator
which instrument is connected on the one side to all the connecting cords assigned
for the use of that operator and on the other side to the battery.
It is easily understood that if two metallic loops be connected by one of the
connecting cords in any part of the switch-board and an operator touches one of the
contact blocks of either of these loops on another section of a multiple switch-board
with the plug of any other flexible connecting cord a circuit will be established
through the loop which the operator has touched, the two flexible connecting cords
and their indicating instruments and the battery or batteries included between the
said flexible connecting cords. The instruments of both cords will therefore indicate
that the loop is already in use. If the indicating instruments employed are relays
the deflection of their armatures may close the circuit of a local battery and bell
and so to sound a loud or continued alarm should a second connection to an engaged
loop be accidentally or designedly made.
In Figure 4 a modification of this improved operator's test system is shown
wherein the bridges and resistances between the conductors of the connecting cords
are omitted and the branch wires W¹, W, W³ joined direct to one of the conductors
say C, of the respective cords.