IMPROVEMENTS IN TELEGRAPHIC AND TELEPHONIC APPARATUS
Year: 1883

page_text: LETTERS PATENT to Daniel Sinclair and John Lorimer Corbett, both of
Glasgow in the County of Lanark for an Invention of "IMPROVEMENTS IN
TELEGRAPHIC AND TELEPHONIC APPARATUS"
PROVISIONAL SPECIFICATION left by the said Daniel Sinclair and John
Lorimer Corbett at the Office of the Commissioners of Patents on the
31st December 1883.
DANIEL SINCLAIR, and JOHN LORIMER CORBETT, both of Glasgow, in the
county of Lanark, "IMPROVEMENTS IN TELEGRAPHIC AND TELEPHONIC APPARATUS,”
This Invention is a development of the improvements in telegraphic and
telephonic apparatus described in the Specification of Letters Patent granted to
Daniel Sinclair and dated 7th July 1883 N° 3380.
The objects of the present Invention are (1) to improve the construction and
simplify the arrangement of the apparatus for enabling branch exchanges to be
worked automatically as described in the Specification referred to; and (2) to
enable a number of subscribers in a district to be connected to a central exchange
by a single trunk wire, through which any subscriber may call or be called by the
central office, and be placed in communication with any other subscriber on the
telegraphic or telephonic system without passing through a branch exchange.
These objects we attain by fitting, in the one case, in the branch exchange, and
in the other case in each subscribers office, an instrument in its general features
resembling that described in the aforementioned Specification as provided for each
branch exchange (but of improved construction), and making suitable electrical
connections as hereinafter described.
This improved instrument consists of a box or casing in which are fitted two
electro-magnets arranged to act on separate ratchets secured one on a central
vertical spindle, and the other on a hollow spindle insulated from the former, as in
the arrangement described in the Specification already referred to, but with only.
one pointer or finder which is fixed to the central spindle by preference, and is
arranged to act on a contact making or circuit closing device fitted on each of a
Paine d

page_text: series of indicators which are ranged radially round the spindles.
In one
modification, a single wire connects the improved instrument to the central
exchange and serves to convey the currents which actuate the electro-magnet
acting through the ratchet on the pointer or finder spindle, as well as the impulses
from the telephonic or telegraphic transmitting instrument; and the other electro
magnet, acting on the ratchet of the hollow spindle, is actuated by a current from
a local battery when a subscriber rings and causes the indicator drop connected
with his wire to fall and close a battery circuit. The hollow spindle carries a
horizontal disc or plate formed with a number of inclined or wedge like pieces
arranged in a circle like the teeth of a crown wheel, and in number equal to the
number of subscribers connected to the instrument; and immediately over this
disc is an insulated disc having notches cut round its periphery at points above
the spaces between the wedges or teeth on the disc below. The uncut portions of
the upper disc are covered with vulcanite or other insulating material, or the disc
may be formed of a non-conducting material. On to this notched disc a horizontal
arm extending inwards from each indicator drop projects, and rests on the uncut
portion of the periphery or hangs over the notches according to the position of the
disc which is turned with the hollow spindle at each action of the electro magnet to
an extent that the notches and uncut portions are alternately brought under the
indicator arms, this motion being obtained by having twice as many teeth on the
actuating ratchet as there are indicators on the instrument.
The subscribers' wires are led to the indicators in the branch exchange instrument
(a separate indicator being provided for each subscriber) and each wire is electrically
connected to a light spring which is carried by the indicator drop, and which in its
normal position (before the subscriber rings) is resting at its outer end in electrical
contact with the terminal of the indicator coil, the other terminal of the coil being
connected to earth. When the subscriber rings, the indicator drop falls, but only
to a very limited extent, as the horizontal projecting arm on that indicator drop
falls through one of the notches in the upper disc and drops on to the lower disc,
while a second arm or a knob on the lower end of the indicator drop presses
a spring to make contact and close the circuit through the local battery which is
connected by a loop to the spring and a button under each indicator. The closing
of the battery circuit in this way causes a current to be sent through the electro-
magnet which is connected to it, and the ratchet wheel on the hollow spindle
is turned to the extent of one tooth, the crown wheel and ratchet disc being
thereby turned to the extent of half a tooth, so that while the indicator arm of the
subscriber who has rung is in contact with the lower disc and now rests on one
of the wedges or crown teeth, the indicator arms connected to the remaining
subscribers' wires rest on the insulated uncut pieces of the upper disc. On the
edge of the crown toothed disc or on the hollow spindle, bears a spring which is
electrically connected to the trunk wire leading from the instrument to the central
exchange, so that the subscriber who has rung is in electrical connection with the
central exchange through his wire to the indicator drop, thence through the drop
arm resting on the crown toothed disc and thence through the contact spring and
the trunk line.
The dropping of the indicator also lifts off the light spring to which the
subscriber's wire is connected, out of contact with the terminal of the indicator
coil, and as there is no longer a connection to earth in the branch exchange the
current is conducted to the trunk wire to the central exchange. Any other
subscriber calling up the exchange at the same time will be unable to cause his
indicator drop to fall, owing to the horizontal arm on it resting on the insulated
disc, and he may continue ringing and thus know that another subscriber is
engaged with the central exchange.
The current transmitted by the wire of the subscriber who is in communication
with the central exchange may be made to bring down an indicator drop in the
exchange in the usual way, and may at the same time cut off the connection to
earth there. The operator in the central exchange seeing the indicator drop fall

page_text: places the receiving telephone to his ear and speaking to the transmitting
instrument asks what the subscriber wants. If the subscriber wishes to be
placed in communication with a subscriber directly connected to the central
exchange, the operator makes the connection through the usual switch board; but
if the calling subscriber should wish to communicate with another subscriber
on the same branch exchange or on a similar branch exchange, the operator sends
a number of powerful currents by means of a step-by-step sending instrument or
commutator direct to the electro magnet which is connected to the ratchet of the
central spindle of the branch exchange instrument, or sends a number of weaker
currents through a relay to this electro magnet, and by means of the ratchet and
pawl actuated by the electro magnet, brings round the pointer or finder on the
central spindle until it is opposite the indicator of the subscriber wanted.
For example, if number 10 on the branch exchange be wanted the operator
sends twenty currents which bring the pointer round step-by-step from zero to
number 10, there being two ratchet teeth for each indicator. The pointer or finder
is formed with a bent or inclined edge or flange at or near its end which comes in
contact with the end of the spring on the indicator drop which in the normal
position makes contact and closes the circuit through the subscriber's indicator coil
to earth. The pointer when brought over this spring depresses the inner end and
raises its outer end out of contact with the terminal of the coil thereby cutting off
the subscriber from earth, and at the same time comes into contact with a spring
electrically connected to the trunk wire thereby placing the subscriber wanted
in communication with the central exchange, and the operator rings up the
subscriber. As both subscribers are now in electrical connection with the central
exchange through the same wire, it follows that they are in direct communication
and can now speak to each other, the trunk wire only serving as a convenient
medium through which the exchange operator can tap the subscribers wires, and
know when the conversation is ended, or if the operator replaces the indicator drop of
the branch exchange the trunk wire serves as a connection to earth, and enables
the subscribers to ring off and again cause the indicator drop at the central exchange
to fall. The operator then sends as many currents as may be required to bring round
the pointer or finder to zero, being guided by a dial on his sending instrument
having a number of divisions corresponding to the subscribers indicators. At the
zero point (of the branch exchange instrument) which is in one of the divisions of
the circle and takes the place of one of the subscriber's indicators, there is a fixed
terminal of a wire connected to one pole of the battery, and a spring electrically
connected to the other pole of the battery, the electro magnet of the hollow spindle
ratchet being in circuit, and this spring is pressed into contact with the fixed
terminal by the end of the pointer, whereby the circuit is closed and a current is
sent through the electro magnet, and the hollow spindle is turned to the extent of
one tooth of the ratchet, thus bringing the notched disc round to a position in
which the arms of the indicators are no longer resting on the insulated pieces, but
are over the notches and are each free to fall whenever the corresponding subscriber
rings. The arm which fell when the last subscriber rang, is also raised up by the
turning of the discs, the tooth on which it rests being inclined and projecting
upwards, so that by the movement of the disc it is raised and the indicator drop
engages with the hooked end of the indicator armature.
Instead of employing a single trunk wire, two wires may be used to connect the
branch exchange instrument to the central exchange, the one wire serving to
transmit the intermittent currents to the electro magnet operating the central
spindle with the pointer, and the other wire being used to make the connection
between subscribers.
In applying the Invention, in districts where there is no branch exchange, to
connect a number of subscribers to the central exchange by a single trunk wire,
an instrument similar to that described as placed at the branch exchange, but of a
smaller size, and provided only with a single indicator, is fitted in each subscribers
office in convenient proximity to the telephone or telegraph instrument. The

page_text: telephone line wire is connected to the indicator drop as before described, and the
spring bearing on the crown disc or hollow spindle is connected by a branch line
to the trunk wire.
The ringing up of the central exchange is effected from the subscribers telephone
through the indicator of the instrument and through the contact made with the
crown toothed disc, the action of turning the disc to the extent of a tooth of the
ratchet being effected as before described; and when one subscriber is in
communication with the exchange no other subscriber on the trunk wire can call
the exchange unless that subscriber has been put in communication with the first
subscriber by the exchange operator, because when the first subscriber rings the
discs of all the instruments move simultaneously and cut off all the other
subscribers from the exchange. Otherwise a double trunk wire may be employed.
In either case a considerable saving may be effected in the mileage of wire used
when there are a number of subscribers in the same district.
The arrangements described as applied to work a branch telephone exchange
automatically, and as applied to connect a number of telephone subscribers on a
single trunk wire without passing through a branch exchange, are equally
applicable, when telegraphic sending and receiving instruments are used; and the
arrangement last described is particularly applicable in connecting a number of
telegraph offices in villages or small towns which do not have special wire
from a larger town in the neighbourhood, as the messages sent from one office to
another cannot be read by the operators at any other than the transmitting and
receiving offices and at the central office.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Daniel Sinclair and John Lorimer Corbett in the Patent Office on
the 27th June 1884.
DANIEL SINCLAIR and JOHN LORIMER CORBETT, both of Glasgow, in the
county of Lanark. "IMPROVEMENTS IN TELEGRAPHIC AND TELEPHONIC APPARATUS,"
Our said Invention is a development of the improvements in telegraphic and
telephonic apparatus described in the Specification of Letters Patent granted to
Daniel Sinclair, and dated 7th July 1883, N° 3380.
The objects of the present Invention are (1) to improve the construction and
simplify the arrangement of the apparatus for enabling branch exchanges to be
worked automatically as described in the Specification referred to; (2) to enable a
number of subscribers in a district to be connected to a central exchange by a
single trunk wire (with or without a return wire) through which any subscriber
may call or be called by the central office, and be placed in communication with
any other subscriber on the telegraphic or telephonic system without passing
through a branch exchange.
These objects we attain by fitting in the one case in the branch exchange, and
in the other case in each subscriber's office, an instrument in its general features
resembling that described in the aforementioned Specification as provided for each
branch exchange (but of improved construction) and making suitable electrical
connections as hereinafter described.
This improved instrument, which is illustrated in the vertical section and plan
in Figures 1 and 2 of the accompanying drawings, consists of a box or casing A in
which are fitted two electro-magnets B, C, arranged to act on separate ratchets D, E,
secured to one D on a central vertical spindle d, and the other E on a hollow
spindle e insulated from the former as in the arrangement described in the
Specification already referred to, but with only one pointer or finder F which is
fixed to the central spindle d by preference, and is arranged to act on a contact
making or circuit closing device, fitted on each of a series of indicators G which
are ranged radially round the spindles d, e. In this modification, a single wire W
connects the improved instrument to the central exchange, and serves to convey
the currents which actuate the electro magnet B acting through the ratchet D on
the pointer or finder spindle d as well as the impulses from the telephonic or
telegraphic transmitting instrument; and the other electro-magnet C acting on the
ratchet E of the hollow spindle e is actuated by a current from a local battery X
when a subscriber rings and causes the indicator drop G¹ connected with his wire
to fall and by making contact with a spring g¹ to close the local battery circuit.
The hollow spindle e carries a horizontal disc or plate H formed with a number of
inclined or wedge like pieces h arranged in a circle like the teeth of a crown wheel,
and in number equal to the number of subscribers connected to the instrument; and
immediately over this disc is an insulated disc H having notches h¹ cut round its
periphery at points above the spaces between the wedges or teeth h on the disc H
below. The uncut portions of the upper disc H are covered with vulcanite or
other insulating material or the disc may be formed of nonconducting material.
On to this notched disc, a horizontal arm G2 extending inwards from each indicator
drop G projects and rests on the uncut portion of the periphery or hangs over the
notches h¹ according to the position of the disc H which is turned with the hollow
spindle e at each action of the electro magnet C to an extent that the notches '
and the uncut portions are alternately brought under the indicator arms, this
motion being obtained by having twice as many teeth on the actuating ratchet E
as there are indicators on the instrument. The subscribers wires w are led to the
indicators in the branch exchange instrument (a separate indicator G being provided
for each subscriber) and each wire wis electrically connected by a wire w to a light

page_text: spring which is carried by the indicator drop G¹, and which in its normal position
(before the subscriber rings) is resting at its outer end in electrical contact with the
terminal t of the indicator coil, the other terminal of the coil being connected to
earth by a common earth wire W₁. When the subscriber rings, the indicator
drop G falls, but only to a very limited extent, as the horizontal projecting
arm G2 on that indicator drop falls through one of the notches in the upper
disc Hand drops on to the lower disc H while it also, or a second arm or a knob
on the lower end of the indicator drop, presses the spring g₁ to make contact and
close the circuit through the local battery which is connected by a loop wire x to
the spring g' and a button under each indicator. The closing of the battery
circuit in this way causes a current to be sent through the electro magnet C which
is connected to it, and the ratchet wheel E on the hollow spindle e, is turned to
the extent of one tooth, the crown wheel H and ratchet disc H¹ being thereby
turned to the extent of half a tooth, so that while the indicator arm G² of the
subscriber who has rung is in contact with the lower disc H and now rests on one
of the wedges or crown teeth h, the indicator arms connected to the remaining
subscribers wires rest on the insulated uncut pieces of the upper disc H¹. On the
edge of the crown toothed disc H or on the hollow spindle e bears a spring I which
is electrically connected to the trunk wire W leading from the instrument to the
central exchange, so that the subscriber who has rung is in electrical connection
with the central exchange through his wire w to the indicator drop G¹, thence
through the drop arm G² resting on the crown toothed disc H and thence through
the contact spring I and the trunk line W. The dropping of the indicator also
lifts off the light spring i to which the subscribers wire wis connected, out of
contact with the terminal t of the indicator coil, and as there is no longer a
connection to earth in the branch exchange the current is conducted by the trunk
wire W to the central exchange. Any other subscriber calling up the exchange
at the same time will be unable to cause his indicator drop G to fall, owing to the
horizontal arm G on it resting on the insulated disc H' and he may continue
ringing, and thus know that another subscriber is engaged with the central
exchange.
The current transmitted by the wire of the subscriber who is in communication
with the central exchange may be made to bring down an indicator drop in the
exchange in the usual way, and may be at the same time cut off the connection to
earth there.
The operator in the central exchange seeing the indicator drop fall places the
receiving telephone to his ear and speaking to the transmitting instrument asks
what the subscriber wants. If the subscriber wishes to be placed in communication
with a subscriber directly connected to the central exchange, the operator makes
the connection through the usual switch board, but if the calling subscriber should
wish to communicate with another subscriber on the sanie branch exchange, or on
a similar branch exchange, the operator sends a number of powerful currents by
means of a step-by-step sending instrument or communicator direct to the electro
maguet B which is connected to the ratchet D of the central spindle d of the
branch exchange instrument, or sends a number of weaker currents through a
relay to this electro magnet, and by means of the ratchet D and pawl D¹ actuated
by the electro magnet B brings round the pointer or finder F on the central
spindle d until it is opposite the indicator G of the subscriber wanted.
example, if number 10 on the branch exchange be wanted the operator sends
twenty currents which bring the pointer round step-by-step from
number 10, there being two ratchet teeth on the ratchet D for each indicator,
as indicated in figure 3 which shows the ratchet and pawl detached. The pointer
or finder F is formed with a bent or inclined edge or flange at or near its end
which comes in contact with the end of the spring i on the indicator drop, which
in the normal position makes contact and closes the circuit through the subscriber's
indicator coil to earth. The pointer when brought over this spring i depresses the
inner end and raises its outer end out of contact with the terminal t of the coil,
For
zero to

page_text: thereby cutting off the subscriber from earth, and at the same time brings the
spring i into contact with the spring which is electrically connected to the trunk
wire W, thereby placing the subscriber wanted in communication with the central
exchange, and the operator rings up the subscriber. As both subscribers are now
in electrical connection with the exchange through the same wire, it follows that
they are in direct communication and can now speak to each other, the trunk wire
only serving as a convenient medium through which the exchange operator can
tap the subscribers wires, and know when the conversation is ended; or if the
operator replaces the indicator drop of the branch exchange the trunk wire serves
as a connection to earth, and enables the subscriber to ring off and again cause
the indicator drop at the central exchange to fall. The operator then sends as
many currents as may be required to bring round the pointer or finder F to zero,
being guided by a dial on his sending instrument having a number of divisions
corresponding to the subscribers indicators. At the zero point (of the branch
exchange instrument) which is in one of the divisions of the circle and takes the
place of one of the subscriber's indicators, there is a fixed terminal T of a wire
connected to one pole of the battery and a spring S, electrically connected to the
other pole of the battery, the electro-magnet C of the hollow spindle ratchet E
being in circuit, and this spring S is pressed into contact with the fixed terminal T
by the end of the pointer F whereby the circuit is closed and a current is sent
through the electro magnet C, and the hollow spindle e is turned to the extent of
one tooth of the ratchet E thus bringing the notched disc H¹ round to a position
in which the arms of the indicators are no longer resting on the insulated pieces,
but are over the notches h¹ and are each free to fall whenever the corresponding
subscriber rings. The arm G2 which fell when the last subscriber rang,
also
raised up by the turning of the disc H, the tooth h on which it rests being inclined
and projecting upwards, so that by the movement of the disc the arm
raised and the indicator drop G₁ engages with the hooked end of the indicator
armature g².
is
Instead of employing a single trunk wire, two wires may be used to connect the
branch exchange instrument to the central exchange, the one wire serving to transmit
the intermittent currents to the electro magnet operating the central spindle with
the pointer, and the other wire being used to make the connection between
subscribers. In lieu of employing the electro magnets and ratchet devices to
actuate the spindles carrying the crown tooth disc H and the finder F, such spindles
may be actuated by clockwork on the closing of a local battery circuit in a manner
similar to that described in the Specification filed with our application for patent
N° 8541 dated 3rd June 1884.
In applying the Invention in districts where there is no branch exchange to
connect a number of subscribers to the central exchange by a single trunk wire,
an instrument similar to that described as placed at the branch exchange, but of a
smaller size, and provided only with a single indicator, is fitted in each subscriber's
office in convenient proximity to the telephone or telegraph instrument. The
telephone line wire is connected to the indicator drop as before described and the
spring bearing on the crown disc or hollow spindle is connected by a branch line to
the trunk wire.
The ringing up of the central exchange is effected from the subscribers telephone
through the indicator of the instrument and through the contact made with the
crown toothed disc, the action of turning the disc to the extent of a tooth of the
ratchet being effected as before described, and when one subscriber is in communi-
cation with the exchange no other subscriber on the trunk wire can call the
exchange unless that subscriber has been put in communication with the first
subscriber by the exchange operator, because when the first subscriber rings the
discs of all the instruments move simultaneously and cut off all the other
subscribers from the exchange. Otherwise a double trunk wire may be employed.
In either case a considerable saving may be effected in the mileage of wire used
when there are a number of subscribers in the same district.

page_text: The arrangement described as applied to work a branch telephone exchange
automatically, and as applied to connect a number of telephone subscribers on a
single trunk wire without passing through a branch exchange, are equally applicable
when telegraphic sending and receiving instruments are used; and the arrangement
last described is particularly applicable in connecting a number of telegraph offices
in villages or small towns which do not have a special wire from a larger town in
the neighbourhood, as the messages sent from one office to another cannot be read
by the operators at any other than the transmitting and receiving offices and at
the central office.
Having thus particularly described the nature of our said Invention, and in what
manner the same is to be performed, we declare that what we claim is,-
First. The arrangement or combination of parts forming the improved branch
exchange instrument herein described and illustrated.
Second. In a branch exchange instrument the construction and arrangement
of the discs H, H', actuated automatically as described and for the purpose
set forth.
Third. The arrangement of springs and devices connected with the subscribers
indicators of a branch exchange instrument, substantially as described and
illustrated.
Fourth. The arrangement of a series of single branch exchange instruments of
the kind described on a single wire connecting a number of telephone subscribers
in a district to a central exchange, or connecting a number of telegraph stations
with a central station, the arrangement being such that when one subscriber or
station is placed in communication with the central exchange or station the
remaining subscribers or stations are cut off from such communication, substantially
as herein described.
In witness whereof we the said Daniel Sinclair and John Lorimer Corbett have
hereunto set our hands and seals this Twenty-sixth day of June, in the year of our
Lord, One thousand eight hundred and eighty four.
Witness
WALLACE FAIRWEATHER C.E.
Fell. Inst. Patent Agents
96 Buchanan Street
Glasgow.
D SINCLAIR
(L.S.)
JOHN, L, CORBETT (L.S.)