An Improved System of Telephonic Exchange Signalling.
Year: 1891

page_text: Date of Application, 3rd July, 1891
Complete Specification Left, 4th Apr.. 1892-Accepted, 7th May, 1892
PROVISIONAL SPECIFICATION.
An Improved System of Telephonic Exchange Signalling.
I, ALFRED ROSLING BENNETT, of 22, St. Albans Road, Harlesden, London,
N.W., Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
My invention has reference to means of communicating between the offices of the
subscribers to a telephonic exchange and the operators at the exchange in order
that the subscribers' requirements may be made known with certainty and celerity
to the operators.
In the two peculiar systems of telephonic signalling known as the "Law" and
the "Mann" each subscriber's instrument can be placed at will in connection with
a special wire reserved entirely for communications with the operators which special
wire extends from the subscriber's instrument to that of the operator in unbroken
metallic continuity.
By my invention it is unnecessary to lead such a special wire into the
subscribers' offices as the device hereinafter described enables such service com-
munications to be made on the wire or wires that are necessarily taken into the
subscribers' offices for the purpose of enabling them to communicate through the
exchange with other subscribers.
My invention is specially suited for use in connection with the telephonic
switching apparatus described in my Specifications No. 2748 of 1889, No. 3813 of
1889 and No. 19486 of 1890, but it may be adapted to others.
By my invention every cable, bundle or group of wires proceeding from the
exchange to the subscribers' offices, whether placed underground or suspended in
the air, contains one or more insulated wires, hereinafter termed service wires, in its
midst or close and parallel to it, which service wires need not be continued as far as
the subscribers' offices. These service wires are by preference not connected to
earth in any way at their distant extremities nor at any other points except at the
exchange, but are terminated abruptly in the manner best calculated to preserve
them in a well insulated condition. But they will nevertheless fulfil the required*
functions although less perfectly if connected to earth at their extremities and other
points through conducting paths possessing appreciable resistance or self-induction.
or both. When the subscribers' wires are laid in cables or bundles the service
wire or wires may with advantage be bound up with the others.
In
My invention is specially intended and adapted for use with exchange systems in
which the subscribers' lines are laid on the double-wire or metallic circuit plan, but
it is not impossible to employ it when the subscribers' lines are single wires.
that case the single wires are best connected to earth at the subscribers' offices only"
and not at the exchange although such an earth connection is permissible at the
exchange also providing the conducting path to earth possesses an appreciable
amount of resistance or self-induction or both.
At the exchange the service wire or wires are preferably connected to earth
through a set of telephonic instruments at which an operator is constantly listening,
but at night or when not busy the telephonic instruments may be replaced by
apparatus capable of giving an audible or visible signal in response to voltaic or
magneto currents from the subscribers' offices.
From this description it will be understood that subscribers' lines run close and
parallel to the service wires but are separated from them by an insulating medium
or dielectric which, in the case of suspended open wires, is the air and in the case of
cables or covered wires, india-rubber, paraffin, silk, or other suitable insulator.

page_text: Each cable, bundle or group of subscribers" lines practically forms with its service
wires a condenser having as many plates as there are lines or wires.
At each subscriber's office is provided a lever which when depressed actuates
apparatus by means of which the subscriber's telephone is placed intermediate
between his line and the earth even although his line is a double wireuor metallic
circuit such as is not ordinarily connected to the earth at all. When the subscriber
has depressed his lever he is able at once to speak to the operator who is listening
on the service wire or wires at the exchange because his line then forms practically
one plate of a condenser from which speech is transferred by electro-static induction
to the service wire or wires which form. another plate and thence, through the
exchange apparatus to earth. When the operator speaks the sequence of transfer
is reversed and the subscriber hears.. On releasing his, lever the subscriber's
telephone is cut off from the earth and placed in connection with his metallic circuit
in. which position he can speak with, other subscribers but not with the operator.
When insulated wires are used for the subscribers' lines the service wire or wires
may be dispensed with by enclosing each individual subscriber's wire,, or pair of
wires, or cable or bundle, of wires, wholly or partially in a metallic or conducting
sheath or wrapping which should be insulated from the earth except at the
exchange in the same way as has been described as necessary for the service wire
or wires which it replaces. At the exchange such conducting sheath or wrapping
is.connected.by means of a wire through the necessary apparatus to earth. It then
forms the operator's plate of the condenser. Owing to the large surface such a
sheath or wrapping possesses in comparison, with one or more service wires, simply
laid amongst the others it need be provided for comparatively only a short distance
from the exchange, the subscribers" lines for the remainder of the distance being
without sheathing. or wrapping and unaccompanied by parallel service wires. By
constructing a cable, coil or bundle of conductors specially designed to fulfil the
functions of a condenser the operator's plate may be entirely restricted, to, the
precincts of the exchange building. The same object may be attained. by leading
the subscribers" lines at the exchange through one circuit of an induction coil or
connecting them to one plate of an ordinary condenser; or to one coil of a phonopore.
In these cases the operator's apparatus would be connected on the; one side to, earth
and on the other side to the second circuit of the induction coil, the second plate of
the ordinary condenser or to the second coil of the phonopore.
Dated this Second day of July 1801
A. R., BENNETT.
COMPLETE SPECIFICATION..
An Improved System of Telephonic Exchange Signalling.
1, ALFRED ROSLING BENNETT, of 22, St. Albans Road, Harlesden, London,
N.W., 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 has reference to means of communicating between the offices of the
subscribers to a telephonic exchange and the operators at the exchange in, order
that the subscribers' requirements may be made known with certainty and celerity
to the operators.
In the two peculiar systems of telephonic signalling known as, the "Law"and
the "Mann" each subscriber's instrument can be placed at will in connection with
a special wire reserved entirely for communications with the operators which special
wire extends from the.subscriber's instrument to that of the operator.in. unbroken
metallic continuity.
By my invention it, is unnecessary to lead such a special wire into the
subscribers' offices as the devices, hereinafter described enables, such service com-
munications to be made on the wire or wires that are necessarily taken into the

page_text: subscribers' offices for the purpose of enabling them to communicate through the
exchange with other subscribers. My invention is specially suited for use in
connection with the switching apparatus described in my Specifications No. 2748 of
1889, No. 3813 of 1889 and No. 19186 of 1890 but it may be adapted to others.
By my invention every cable, bundle or group of wires proceeding from the
exchange to the subscribers offices, whether placed underground or suspended in
the air, contains one or more insulated wires in its midst or close or parallel to it,
hereinafter termed service wires, which service wires need not be continued as far
as the subscribers offices. These service wires are by preference not connected to
earth in any way at their distant extremities nor at any other point except at the
exchange, but are terminated abruptly in the manner best calculated to preserve
them in a well-insulated condition. But they will nevertheless fulfil the required
functions if connected to earth at their extremities and other points through.con-
ducting paths possessing resistance or self-induction. When the subscribers wires
are laid in cables or bundles the service wire or wires may with advantage be bound
up with the others.
My invention is specially intended and adapted for use with exchange systems
in which the subscribers' lines are laid on the double-wire or metallic circuit plan,
but it is not impossible to employ it when the subscribers' lines are single wires.
In that case the single wires are best connected to earth at the subscribers' offices
only and not at the exchange although such an earth connection is permissible at
the exchange provided the conducting path to earth possesses an appreciable
amount of resistance or self induction or both.
At the exchange the service wire or wires are preferably connected to earth
through a set of telephonic instruments at which an operator constantly listening,
but at night or when not busy the speaking instruments may be replaced by
apparatus capable of giving an audible or visible signal in response to voltaic or
magneto currents from subscribers' offices. Such an apparatus is the so-called
telephonic relay in which the vibration of the diaphragm of a telephonic receiver is
made to set a light arm or hammer in motion thereby making or breaking a voltaic
circuit in which is inserted a bell or other suitable device.
From the foregoing description it will be understood that subscribers' lines run
close and parallel to the service wires but are separated from them by an insulating
medium or dielectric which in the case of suspended open wires is the air and in
the case of cables or covered wires, india-rubber, paraffin, paper, silk or other
suitable insulator. Each cable, bundle or group of subscribers' lines practically
forms with its service wires a condenser having as many plates as there are lines or
wires.
At each subscriber's office is provided a lever which when depressed actuates
apparatus by means of which the subscriber's instrument is placed intermediate
between his line and the earth even although his line is a double-wire or metallic
circuit such as is not ordinarily connected to the earth at all. Such a lever and
apparatus is shown at L in Figure 1 of the accompanying drawings, but the details
may be varied considerably. When the subscriber has depressed his lever he is
able at once to speak to the operator who is listening on the service wire or wires
at the exchange, because his line then forms practically one plate of a condenser
from which speech is transferred by induction to the service wire or wires which
form another plate and thence through the exchange apparatus to earth. When
the operator speaks the sequence of transfer is reversed and the subscriber hears.
On releasing his lever the subscriber's telephone is cut off from the earth and
placed in connection with his metallic circuit in which position he can speak with
other subscribers but not with the operator.
When insulated wires are used for the subscribers' lines the service wire or wires
may be dispensed with by enclosing each individual subscriber's wire, or pair of
wires, or cable or bundle of wires, wholly or partially, in a-metallic or conducting
sheath or wrapping which should be insulated from the earth except at the
exchange in the same way as has been described as necessary for the service wire

page_text: or wires which it replaces. At the exchange such conducting sheath or wrapping
is connected by means of a wire through the necessary apparatus to carth. It then
forms the operator's plate of the condenser. Owing to the large surface such a
sheath or wrapping possesses in comparison with one or more service wires simply
laid amongst the others it need be provided for comparatively only a short distance
from the exchange the subscribers' lines for the remainder of the distance being
without such sheathing or wrapping and unaccompanied by parallel service wires.
By constructing a cable, coil or bundle of conductors specially designed to fulfil the
functions of a condenser the operator's plate may be entirely restricted to the
precincts of the exchange building. The same object may be attained by leading
the subscriber's lines through one circuit of an induction coil or connecting them to
one plate of an ordinary condenser or to one coil of a phonopore. In these cases
the operator's apparatus would be connected on the one side to earth and on the
other side to the second circuit of the induction coil, the second plate of the
ordinary condenser or to the second coil of the phonopore.
Instead of using the earth as a return between the subscribers' and operator's
instruments return metallic conductors may in every case be employed.
An effective arrangement of my invention is shown in Figure 1 of the accom-
panying drawings, in which M is the metallic circuit connecting a subscriber to the
exchange; S, S the sockets, spring-jacks or other connecting devices at the
exchange; T the subscriber's instrument; L the subscriber's lever for placing
the instrument intermediate between the inetallic circuit M and earth when it is
required to communicate with the operator; W the service wire running for a
distance parallel to or in the midst of the metallic circuit or circuits; and O the
operator's telephone. In practice both M and W may be constructed of uncovered
iron, copper, bronze or other suitable wire supported on insulators, or both M
and W may be insulated wires laid, bound or twisted closely together. When the
wires M are insulated W need not be a wire at all but a sheathing of tin or lead
foil or of metal tube insulated from the earth and enclosing the wires M. The
length of W depends on its proximity to M and to the extent of surface it exposes.
Consequently W may advantageously be a wire of large gauge and it is an object
in constructing the system to place it as close to the wires M as practicable. When
both M and W are uncovered conductors supported on insulators twelve inches
apart W should run parallel to M for not less than 880 yards. When M consists
of insulated wires and W of an insulated wire bound or twisted up with M or of a
metallic tube or sheath enclosing M, the length of W need not exceed 440 yards.
When it is desired to restrict the service wire W to the precincts of the exchange
buildings it may be coiled with a sufficient length of M on a drum, the arrangements
being otherwise unaltered, or M may be coiled on, or-within, a metallic tube, drum
or casing insulated from the carth and connected to the operator's telephone O,
which metallic tube, drum or casing performs the functions of W. This form of
my invention is shown in Figures 2 and 2 of the accompanying drawings, the
metallic circuit M being coiled, in the first case, on a metallic tube, drum or rod, W,
and, in the second case, within a metallic tube or drun. In both cases the length
of M may be 880) yards.
In Figures 3 and 34 is shown another modification of my invention in which the
functions of the service wire, W, are performed by condensers, the capacity of
which may be half a microfarad. In the first case, the wires of the metallic
circuit Mare attached respectively to the plates and of a three-plate
condenser, the middle plate of which, C, is connected to the operator's instru-
ment O. In the second case, the wires of M are severally attached to one plate of
the ordinary two-plate condensers C1 and C2, the operator's instrument, O, being
connected to the remaining plates as shown. The working of the operator's
instrument, O, will be improved by looping resistance coils in the two wires of the
metallic circuit, M, between the condensers and the sockets S, S¹.. Such resistance
coils may be of 50 Ohms resistance and upwards and those used with the same
metallic circuit should be equal in resistance.

page_text: Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what 1
claim is
1. Substantially in the manner set forth the system of intercommunication
between the subscribers and operators in a telephonic exchange system by means of
induction between a special wire, sheath, coil, plate or equivalent device, to which
the operator's instrument is connected, and the conductor or conductors of the line
itself when suitably connected to the subscriber's instrument.
2. Substantially as described and in part shown in the accompanying drawings
the various specific modes of giving effect to the said invention.
Dated this Second day of April 1892.
A. R. BENNETT.