IMPROVEMENTS IN TELEPHONIC SWITCHING APPARATUS
Year: 1884

page_text: I, ALFRED ROSLING BENNETT, Telegraphic Engineer, of 8A Royal Exchange
Buildings, Glasgow, in the County of Lanark, do hereby declare the nature of my
said Invention for "IMPROVEMENTS IN TELEPHONIC SWITCHING APPARATUS" to be
as follows:
The object of my improved telephonic switching apparatus is to increase the
speed with which the wires converging in a telephonic Exchange or switch-room
may be joined together and separated according to the requirements of the
subscribers.
I divide the wires converging in the Exchange into groups. A group may
consist of any convenient number of wires up to 150. Each group is provided
with a separate switch-board or switch-table; has a separate transmitting and
receiving set of telephonic apparatus, and should be under the charge of a separate
operator.
A general plan of the invention, without the plugs and cords used for coupling
the subscriber's wires, together and the apparatus connected with them, is shown
in Figure 1, in the accompanying drawings.
L1, L2, L³, LA, are four subscribers' lines forming a group or part of a group.
J1, J, J, J, are spring-jacks of any efficient pattern. X1, X2, X³, X*, are annun-
ciators or indicators of any efficient pattern. Z' Z Z³ Z' are resistance bobbins.
R is a receiving telephone of any efficient pattern. T is a telephonic transmitter
of any efficient pattern. G is a voltaic or a secondary battery, in connection with
the telephonic transmitter. I is the primary circuit of an induction coil such as is
ordinarily used with telephonic transmitters. I is the secondary circuit of the
same coil. U is a point at which all the subscriber's lines unite after passing
through their respective annunciators and resistance bobbins.
The course of a current arriving at the Exchange from a subscriber's line, for
example L³, is consequently through the spring-jack J; the annunciator X²; and
the resistance bobbin Z' to the point U. Here the current divides between the
receiving telephone R, the secondary circuit I of the induction coil and all the
other subscriber's lines of the same group, proportionally to their several resistances,
in accordance with the law of derived circuits.
A current from the telephonic transmitter T divides at U between all the
subscribers lines of the same group.
Variations in the mode of connecting the receiving telephone are shown in
Figures 14, 18, 10, and 1º, K in Figures 1B, 1C, and 1º, denoting a switch to be
worked by the hand or foot of the operator.

page_text: When the receiving telephone has two electro-magnets these may advantageously
be joined in parallel branches instead of in series as is generally done. This mode
of joining is shown in Figure 1.
The function of the resistance bobbins Z1, Z2, Z3, &c., is to compel a greater
portion of the current to traverse the receiving telephone R. If the bobbins
were omitted, too much of the in-coming current dividing at U, would go back over
the other subscribers' lines, especially over the shorter ones, so that the speaking
would not be sufficiently audible in the receiving telephone R. When the number
of short lines in a group of subscribers' lines is small, it will suffice to place
resistance bobbins in circuit with them only, especially if a receiving telephone of
low resistance is used at R. But I prefer, as a general rule, to place resistance
bobbins in circuit with all the lines. If this is not done, a leakage to earth
ocurring on a long line near the Exchange will cause too great a proportion of
current to pass over that line, which then practically becomes a very short one.
The placing of resistance bobbins in all the lines prevents such a fault having any
marked effect on the currents traversing the receiving telephone R or proceeding
from the telephonic transmitter T. The resistance of the bobbins may vary greatly
according to the number of subscribers' lines in a group, and their length and
resistance. 600 ohms each is a proper resistance when 60 lines are connected in a
group. The fewer the lines the smaller is the resistance of the bobbins required.
The resistance bobbins may be furnished with iron cores, and being thus con-
verted into electro-magnets, may be made to actuate alarms or indicators; or, if
furnished singly or in groups with thin iron diaphragms, or collectively with one
large iron diaphragms, may be made to act as receiving telephones, or a receiving
telephone, in lieu of the receiving telephone R.
Instead of separate resistance bobbins being employed, the coils of the electro-
magnets of the annunciators X1, X2, X³, &c., may be made of specially high
resistance. The coils of annunciators ordinarily used are generally about
100 ohms in resistance, and rarely exceed 150 ohms. When intended to take the
place of the resistance bobbins the coils may be made of any resistance from 150
to 2000 ohms, the most suitable resistance being determined by the number of lines
in a group and their length and resistance.
The plugs and cords for coupling the subscribers' lines together, with the
apparatus connected with them, are shown in Figure 2.
P and P¹ are metallic plugs made to fit the spring-jacks J, J, &c., shown in
Figure 1.
S and S¹ are metallic strips attached to the surface of the operating table.
C and C¹ are flexible insulated conductors attached to the plugs P, P', and to
the annunciator A, in such a manner that an electrical current applied at the
metallic strip S will traverse the plug P, the conductor C, the annunciator A, the
conductor C¹, the plug P¹, and the Strip S'.
W, Ware weights attached to pulleys arranged so as to bring the flexible
conductors C, C, back to their normal positions (in which the plugs P P¹ are in
metallic contact with the strips S, S¹) after being moved.
G is a battery, pole-changer, magnetic machine, or any other source of electrical
energy, driven by hand or by power, in permanent electrical connection with the
strips S S. By preference, I use a pole-changer driven by clockwork arranged to
run several hours without requiring re-winding, and a voltaic battery connected as
shown in Figure 2.
This system of switching may be employed in two different ways, one method
being adapted for the busy hours of the day, for example from 9 a.m. to p.m.,
when communications are frequent, and the other for use in the early morning,
evening and night.
The mode of operating during the busy hours of the day is as follows:
An operator listens continually at the receiving telephone R (Figure 1.). When
a subscriber wishes to communicate with the Exchange he has consequently
nothing to do but to lift the telephone of his instrument off its hook, apply it to

page_text: his ear and say what he
subscriber is thus avoided.
speak to subscriber N° 50.
ear, and says "14 to 50."
wants. All preliminary ringing on the part of the
Let it be assumed that subscriber N° 14 wishes to
No 14 lifts his telephone off its hook, applies it to his
The operator listening at the receiving telephone R (Figure 1.) hears, and while
acknowledging the receipt of the message by repeating the numbers, takes one of
the plugs, say P, (Figure 2) and inserts it in the spring-jack connected to sub-
scriber's line No 50.
The plug P being in communication through the strip S, the conductor C,
annunciator A, conductor C, strip S¹ and plug P1 with G (Figure 2), the source of
electrical power, its insertion in the spring-jack immediately causes the alarm bell
of subscriber N° 50 to ring.
After leaving P in the spring-jack No 50 for two or three seconds, the operator
lifts the corresponding plug P1 from its position in contact with the strip S¹ and
inserts it in spring-jack No 14.
Subscribers No 14 and No 50 are now in direct communication, as shown in
Figure 3, the course of the speaking current being spring-jack Nº 14, P, C, A, C¹, P¹
and spring-jack N° 50.
"
Subscriber N° 50, hearing his alarm bell ring, knows that some other subscriber
is wishing to speak to him, and lifts his telephone off its hook and asks Who is
there"?
Subscriber N° 14, who has been waiting with his telephone to his ear, hears,
and the conversation commences.
At its termination, one of the subscribers presses his battery button or turns the
crank of his magneto-generator. The current sent into the line by this act, causes
the shutter of the annunciator A to drop.
On perceiving this the operator immediately withdraws the plugs P and P¹ from
the spring-jacks, and allows them to resume their normal positions on the
strips S, S
The subscribers N° 14 and N° 50 are instantly disconnected from each other and
are once more in communication with the receiving telephone R, (Figure 1.) at the
Exchange.
During the slack hours of the day, and the night, or when the business of the
Exchange does not require an operator to be always listening for_communications
at the receiving telephone R, a subscriber wishing to speak to the Exchange presses
his battery-button or turns the crank of his magneto-generator, an act which
causes the shutter of the annunciator in connnction with his line, for example X¹
(Figure 1), to fall. The attention of the operator being thus attracted he places the
receiving telephone R (Figure 1) to his ear and enquires what is wanted. Before
speaking, the operator may ring the alarm bell of the subscriber whose annunciator
shutter has fallen by inserting one of the plugs P, P¹ (Figure 2) in his spring-jack,
but this should be unnecessary.
The operator having opened communication with the calling subscriber, the
subsequent proceedings are precisely as already described.
The annunciators, X, X, X³, (Figure 1) in circuit with the subscribers' lines
may be entirely dispensed with by inserting in the earth wire common to a group
of subscribers' lines a sensitive relay of very low resistance. Half an ohm is found
a suitable resistance. The currents from the batteries or magneto-generators of
subscribers calling during the night or slack hours of the day will actuate the relay
and cause an alarm bell to ring in the Exchange. This arrangement is shown in
Figure 4.
When this plan is adopted the operator must be careful to enquire the number
of the subscriber calling as no indication is afforded by the relay..
The temporary cutting out of circuit of the resistance bobbin in any subscriber's
line will increase the loudness of the speaking between that subscriber and the
operator at the Exchange, as a greater proportion of the current will traverse that
particular line. To meet a reduction in the loudness of speaking caused by a fault

page_text: in the line or in the subscribers instrument, each resistance bobbin may be fitted
with a switch or spring-key, the depressing of which by the operator will short
circuit the resistance bobbin. This modification is shown in Figure 5.
The invention, although forming in itself a complete system of switching, may be
divided into two parts, each of which parts may be applied as an auxiliary to
other systems. For example, the part of the invention comprised in Figures 1, 14,
1B, 10, 10, 1, and Figures 4 and 5 may be used with advantage in conjunction
with other systems of ringing and other arrangements of cords and indicators
than are shown in Figures 2 and 3. On the other hand the system of ringing,
cords and indicators shown in Figures 2 and 3 may be used with advantage in
conjunction with other modes of connecting the receiving and transmitting
apparatus and of arranging the subscribers' lines than that shown by Figures 1, 14,
13, 1°, 1º, 1 and Figures 4 and 5.

page_text: I, ALFRED ROSLING BENNETT, of 8A Royal Exchange Buildings, Glasgow, in
the County of Lanark Telegraph 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:
-
The object of my improved telephonic switching apparatus is to increase the
speed with which the wires converging in a telephonic Exchange or switch-room
may be joined together and separated according to the requirements of the
subscribers.
I divide the wires converging in the Exchange into groups. A group may consist
of any convenient number of wires up to 150. Each group is provided with a
separate switch-board or switch-table; has a separate transmitting and receiving
set of telephonic apparatus, and should be under the charge of a separate
operator.
A general plan of the invention, without the plugs and cords used for coupling
the subscribers wires together and the apparatus connected with them, is shown in
Figure 1 in the accompanying drawings.
L, L, L, L, are four subscribers' lines forming a group or part of a group.
J, J, J, J, are spring-jacks of any efficient pattern. X1, X2, X³, X+, are
annunciators or indicators of any efficient pattern. Z1, Z2, Z3, Z, are resistance
bobbins. R is a receiving telephone of any efficient pattern. T is a telephonic
transmitter of any efficient pattern. G is a voltaic or a secondary battery, in
connection with the telephonic transmitter. I is the primary circuit of an
induction coil such as is ordinarily used with telephonic transmitters. I' is the
secondary circuit of the same coil U is a point at which all the subscribers' lines
unite after passing through their respective annunciators and resistance bobbins.
The course of a current arriving at the exchange from a subscriber's line, for
example L³, is consequently through the spring-jack J; the annunciator X'; and
the resistance bobbin Z to the point U. Here the current divides between the
receiving telephone R, the secondary circuit 1' of the induction coil and all the
other subscribers' lines of the same group, proportionally to their several resistances
in accordance with the law of derived circuits.
A current from the telephonic transmitter T divides at U between all the
subscribers' lines of the same group.
Variations in the mode of connecting the receiving telephone are shown in
Figures 14, 1, 1º, and 1º, K in Figures 1B, 1C and 1º, denoting a switch to be
worked by the hand or foot of the operator.
When the receiving telephone has two electro-magnets these may advantageously
be joined in parallel branches instead of in series as is generally done. This mode
of joining is shown in Figure 1B.
The function of the resistance bobbins Z1, Z2, Z3, &, is to compel a greater
portion of the current to traverse the receiving telephone R. If the bobbins were
omitted, too much of the in-coming current dividing at U, would go back over
the shorter ones, so that the speaking would not be sufficiently audible in the

page_text: receiving telephone R. When the number of short lines in a group of subscribers'
lines is small, it will suffice to place resistance bobbins in circuit with them only,
especially if a receiving telephone of low resistance is used at R. But I prefer as
a general rule, to place resistance bobbins in circuit with all the lines. If this is
not done, a leakage to earth occuring on a long line near the Exchange will cause
too great a proportion of current to pass over that line, which then practically
becomes a very short one. The placing of resistance bobbins in all the lines
prevents such a fault having any marked effect on the currents traversing the
receiving telephone R or proceeding from the telephonic transmitter T. The
resistance of the bobbins may vary greatly according to the number of subscribers'
lines in a group, and their length and resistance, 600 ohms each is a proper
resistance when 60 lines are connected in a group, but this resistance may be very
greatly increased, even to the extent of 10,000 ohms or more. My system may be
made to work with much smaller resistances than 600 ohms, especially if the
subscribers' lines are divided into groups containing fewer lines than 60, but not
satisfactorily. The interposition of some resistance is absolutely necessary to
prevent the working of a whole group of lines from being fatally affected by the
occurrence of an earth fault near the Exchange on one or more of them. The
fewer the lines the smaller is the resistance of the bobbins required.
The resistance bobbins may be furnished with iron cores, and being thus converted
into electro-magnets, may be made to actuate alarms or indicators; or, if furnished
singly or in groups with thin iron diaphragms, or collectively with one large iron
diaphragm, may be made to act as receiving telephones, or a receiving telephone,
in lieu of the receiving telephone R.
Instead of separate resistance bobbins being employed, the coils of the electro-
magnets of the annunciators X, X, X³, &, may be made of specially high
resistance. The coils of annunciators ordinarily used are generally about 100 ohms
in resistance, and rarely exceed 150 ohms. When intended to take the place of
the resistances which form an essential part of this invention the coils may be
made of any resistance from 150 to 2000 ohms, the most suitable resistance being
determined by the number of lines in a group and their length and resistance.
The plugs and cords for coupling the subscribers' lines together with the
apparatus connected with them, are shown in Figure 2.
P and P are metallic plugs made to fit the spring-jacks J, J², &c, shown in
Figure 1.
S and S¹ are metallic strips attached to the surface of the operating table.
C and C are flexible insulated conductors attached to the plugs P, P¹, and to
the annunciator A, in such a manner that an electrical current applied at the
metallic strip S will traverse the plug P, the conductor C, the annunciator A, the
conductor C, the plug P¹, and the strip S¹.
W, W¹ are weights attached to pulleys arranged so as to bring the flexible
conductors C, C¹ back to their normal positions (in which the plugs P, P' are in
metallic contact with the strips S S¹) after being moved.
G is a battery, pole-changer, magneto machine, or any other source of electrical
energy, driven by hand or by power, in permanent electrical connection with the
strips S, S¹. By preference I use a pole-changer driven by clockwork arranged to
run several hours without requiring re-winding, and a voltaic battery connected as
shown in Figure 2.
This system of switching may be employed in two different ways, one method
being adapted for the busy hours of the day, for example 9 am to 6 p.m. when
communications are frequent, and the other for use in the early morning, evening,
and night.
The mode of operating during the busy hours of the day is as follows:-
An operator listens continually at the receiving telephone R (Figure 1.). When
a subscriber wishes to communicate with the Exchange he has consequently
nothing to do but to lift the telephone of his instrument off its hook, apply it
to his ear and say what he wants. All preliminary ringing on the part of the

page_text: Bubscriber is thus avoided.
speak to subscriber No 50.
ear, and says " 14 to 50."
Let it be assumed that subscriber N° 14, wishes to
No 14 lifts his telephone off its hook, applies it to his
The operator listening at the receiving telephone R (Figure 1.) hears and while
acknowledging the receipt of the message by repeating the numbers, takes one of
the plugs, say P, (Figure 2.) and inserts it in the spring-jack connected to
subscriber's line No 50.
The plug
being in communication through the strip S, the conductor C,
annunciator A, conductor C¹, strip S¹, and plug P¹ with G (Figure 2), the source of
electrical power, its insertion in the spring-jack immediately causes the alarm bell
of subscriber N° 50 to ring.
After leaving P in the spring-jack N° 50 for two or three seconds, the operator
lifts the corresponding plug P¹ from its position in contact with the strip S¹ and
inserts it in spring-jack N° 14.
Subscriber's No 14 and N° 50 are now in direct communication, as shown in
Figure 3, the course of the speaking current being spring-jack N° 14 P, C, A, C¹ P¹
and spring-jack N° 50.
"
Subscriber N° 50 hearing his alarm bell ring, knows that some other subscriber
is wishing to speak to him, and lifts his telephone off its hook and asks who
is there "?
Subscriber N° 14, who has been waiting with his telephone to his ear, hears,
and the conversation commences.
At its termination, one of the subscribers presses his battery button or turns the
crank of his magneto-generator. The current sent into the line by this act,
causes the shutter of the annunciator A to drop.
On perceiving this the operator immediately withdraws the plugs P and P¹
from the spring-jacks, and allows them to resume their normal positions on the
strips S, S¹.
The subscribers N° 14 and N° 50 are instantly disconnected from each other and
are once more in communication with the receiving telephone R (Figure 1) at the
Exchange.
During the slack hours of the day, and the night, or when the business of the
Exchange does not require an operator to be always listening for communications
at the receiving telephone R, a subscriber wishing to speak to the Exchange
presses his battery button or turns the crank of his magneto-generator, an act
which causes the shutter of the annunciator in conconection with his line, for
example X (Figure 1) to fall. The attention of the operator being thus attracted
he places the receiving telephone R (Figure 1) to his ear and enquires what is
wanted. Before speaking the operator may ring the alarm bell of the subscriber
whose annunciator shutter has fallen by inserting one of the plugs P, P' (Figure 2)
in his spring-jack, but this should be unnecessary.
The operator having opened communication with the calling subscriber, the
subsequent proceedings are precisely as already described.
The annunciators, X1, X2, X³, (Figure 1) in circuit with the subscribers' lines
may be entirely dispensed with by inserting in the earth wire common to a group
of subscribers' lines a sensitive relay preferably of low resistance.
Half an ohm is found a suitable resistance for the relay, but it may be made
much more. The currents from the batteries, or magneto-generators of subscribers
calling during the night or slack hours of the day will actuate the relay and cause
an alarm bell to ring in the Exchange. This arrangement is shown in Figure 4.
When this plan is adopted the operator must be careful to enquire the number
of the subscriber calling as no indication is afforded by the relay.
The temporary cutting out of circuit of the resistance bobbin in any subscribers'
line will increase the loudness of the speaking between that subscriber and the
operator at the Exchange, as a greater proportion of the current will traverse that
particular line. To meet a reduction in the loudness of speaking caused by a
fault in the line or in the subscribers' instrument, each resistance bobbin may be

page_text: fitted with a switch or spring-key, the depressing of which by the operator will
short circuit the resistance bobbin. The same end may be achieved by arranging
each indicator so that the fall of its shutter in response to the ringing of a
subscriber shall short-circuit the resistance bobbin in connection with it.
These modifications are shown in Figures 5 and 5ª.
The invention although forming in itself a complete system of switching, may
be divided into two parts, each of which parts may be applied as an auxiliary to
other systems.
For example the part of the invention comprised in Figures 1. 1A, 1B, 1C, 1D,
and Figures 4 and 5 may be used with advantage in conjunction with other
systems of ringing and other arrangements of cords and indicators than are shown
in Figures 2 and 3.
On the other hand the system of ringing cords and indicators shown in
Figures 2 and 3 may be used with advantage in conjunction with other modes of
connecting the receiving and transmitting apparatus and of arranging the sub-
scribers' lines than that shown by Figures 1, 14, 1³, 1º, 1º, 1, and Figures 4
and 5.
Although the term " resistance bobbin " has been used throughout this specification
when referring to the interposed resistances Z1, Z2 Z3, Z, the resistances need not
be in the form of bobbins and need not be composed of wire, but may be made of
water or carbon or any other liquid or solid substance which offers sufficient
resistance to the passage of electrical currents.
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. The improvements in telephonic switching apparatus forming the complete
telephonic switching system herein described.
.
2. In a telephone exchange system, the arrangement of the subscribers' wires in
groups, with resistances interposed in each circuit or in several of the circuits of
each group, substantially as herein described with reference to Fgures 1 to 1E of
the drawings.
3. In a telephone exchange system, the improved arrangement described with
reference to Figures 2 and 3 for facilitating communication between subscribers
and the exchange.
4. In a telephone exchange system, the arrangement substantially as described
with reference to Figure 4 of a relay in connection with the earth wire and an
alarm bell actuated by the subscriber calling the exchange.
5. In a telephone exchange system, the arrangements substantially as described
with reference to Figures and 5A for short circuiting the resistance in any
individual subscribers wire.
1