IMPROVEMENTS IN TELEPHONIC AND TELEGRAPHIC APPARATUS
Year: 1884

page_text: We, CHRISTINA WATSON CORBETT, Teacher, and JOHN LORIMER CORBETT,
Watchmaker, both of 69 Union Street, Glasgow, in the County of Lanark, do
hereby declare the nature of our said Invention for "IMPROVEMENTS IN TELEPHONIC
AND TELEGRAPHIC APPARATUS;" to be as follows:-
The main object of our Invention is to provide improved apparatus in connection
with branch exchanges of telephonic systems, whereby an operator at the central
exchange may place in communication with each other any two subscribers
connected to the same branch exchange, or a subscriber on the branch with a
subscriber on any other portion of the system. The improved apparatus is also
applicable in connection with telegraph lines for enabling the operator at a central
office to select out of a series of district stations connected to the same wire, the
station to which he wishes to transmit a message; and to place any two stations
in direct communication with each other while cutting out the remaining stations.
At each branch exchange of the telephonic system is placed an instrument or
apparatus consisting of a series of electro-magnetic indicators similar to those
employed in telephonic exchanges to indicate that a subscriber has called, but
without the usual "drop" or "annunciator," one indicator being provided for each
subscriber on the exchange, and the whole being located radially round a rotating
drum or disc operated intermittently by clockwork mechanism, which is brought
into action by means of an electro-magnet and an escapement device. This electro-
magnet is energised by a local battery at the branch exchange, on the closing of
the battery circuit through the electro-magnet. The circuit is normally open, but
is closed by an electro-magnet or relay brought into action by a current-sending
device at the central exchange. For each make-and-break or current transmitted
from the central exchange, a corresponding make-and-break, or closing and opening
of the battery circuit at the branch and an action of the electro-magnet and
escapement take place, whereby the drum or disc operated by the clock-work is
advanced one step or division of its rotation. The number of steps or divisions is
greater by two than the number of subscriber's indicators, to make provision for a
zero point at which all the indicators are connected to earth and a step at which
the subscribers are all cut off from earth. When the instrument is at zero, any
one of the subscribers on the branch exchange may ring up the central exchange,
and cut out the other subscribers, the action being as follows:-The current
Doll

page_text: transmitted by the subscriber causes a vibratory motion of the armature of his
indicator at the branch exchange, whereby a spring or other contact-making device
fitted on the inner end of such armature is brought into contact with the terminal
of a local battery wire, and closes the circuit through that battery and the electro-
magnet of the indicator which is in the same circuit. The electro-magnet is
thereby energised and attracts the armature. A spring arm fitted over the
armature but insulated from it, and in the subscribers circuit, is by the action of the
armature raised from an earth connection at its inner end, and by being depressed
at its outer end is brought into electrical connection with a terminal of the trunk
wire leading to the central exchange, so that the subscriber in ringing up the
branch calls the central exchange.
The same action of the indicator armature presses together and makes contact
between two springs or terminals to close the circuit through the other local
battery which actuates the electro-magnet and escapement of the clock-work, and
the drum or disc is advanced one step beyond the zero point. By this movement
the current through the clock-work and operating electro-magnet, which can only
be closed by the subscriber when at the zero point is now broken. This motion of
the drum or disc on its axis is also accompanied by a rising movement effected by
pins or cam surfaces between it and a stationary disc below, and the drum or disc
in rising lifts the spring arm on the top of each indicator out of contact with the
earth connection without raising them to such an extent as to place the opposite
end of each spring arm in connection with the terminals of the trunk line, and all
the subscribers excepting the one who first calls the exchange are cut off from
earth and cannot ring. The first subscriber having called, the central exchange,
asks the operator to connect him with the subscriber with whom he wishes to
communicate. If that subscriber is connected direct to the central exchange, the
usual switch board arrangement is employed to connect the subscribers, but if the
subscriber wanted, is on the same or on a similar branch exchange, the central
exchange operator transmits as many currents to the relay or electro-magnet
acting on the escapement and clockwork mechanism at the branch exchange as will
advance the druin or disc until a projection on it comes into contact with the spring
arm over the indicator of the subscriber wanted. For example, if the subscriber
wanted is No 4 on the branch exchange, the operator sends four currents, which
bring the projection on the drum or disc from the step in advance of zero until it
is under the spring arm on the indicator of N° 4, and presses the opposite end of
that arm into contact with the terminal of the trunk wire. The first subscriber
and the one wanted by him are then both connected to the trunk line and are
therefore in direct communication with each other. When the conversation ceases,
either subscriber may call the central exchange operator who will disconnect the
subscribers by transmitting as many currents to the relay or magnet of the
clockwork as will send round the drum or disc to the zero position where it again
falls and allows all the subscribers indicator arms to connect to earth. Just before
reaching the zero point, the projection on the drum or disc iu its movement
presses together and makes contact between two springs or terminals of the local
battery connected to the indicator magnets, and thereby short circuits the electro-
magnet of the indicator of the subscriber who first called. This electro-magnet
thereupon ceases to attract its armature, and the armature being freed allows tho
spring arm over it to make contact with the earth connection.
Dated this Second day of October 1884.
W. R. M. THOMSON & Co.,
Agents for the Applicants.
5

page_text: We CHRISTINA WATSON CORBETT Teacher and JoHN LORIMER CORBETT Watch-
maker both of 69 Union Street Glasgow in the County of Lanark do hereby
declare the nature of our Invention for "IMPROVEMENTS IN TELEPHONIC AND
TELEGRAPHIC APPARATUS " and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement:-
The main object of our invention is to provide improved apparatus in connection
with branch exchanges of telephonic systems whereby an operator at the central
exchange may place in communication with each other any two subscribers
connected to the same branch exchange or a subscriber on the branch with a
subscriber on any other portion of the system. The improved apparatus is also
applicable in connection with telegraph lines for enabling the operator at a central
office to select out of a series of district stations connected to the same wire tho
station to which he wishes to transmit a message and to place any two stations in
direct communication with each other while cutting out the remaining stations.
In carrying out our invention we place at each branch exchange of the telephonic
system an instrument or apparatus as illustrated in elevation and plan in figures 1
and 2 of the accompanying drawings and which consists of a series of electro
magnetic indicators A similar to those employed in telephonic exchanges to indicate
that a subscriber has called but without the usual "drop" or "annunciator" one
indicator being provided for each subscriber on the exchange and the whole being
located radially round a rotating drum or disc B operated intermittently by
clock work mechanism C which is brought into action by means of an electro
magnet D and an escapement device E. This electro-magnet D is energised by a
local battery F at the branch exchange on the closing of the battery circuit through
the electro magnet D. The circuit is normally open but is closed by an electro
magnet or relay G which is brought into action by a current sending device at tho
central exchange and whose armature G acts upon springs in the circuit and
brings them into contact. For each make and break or current transmitted from
the central exchange a corresponding depression of the armature G and make and
break or closing and opening of the battery circuit by the springs g at the branch
and an action of the electro magnet D and escapement E take place whereby the
drum or disc B operated by the clock work C is released and advanced one step or
division of its rotation. The number of steps or divisions is greater by two
than the number of subscribers indicators A to make provision for a zero point O
at which all the indicators are connected to earth and a step O' at which the
subscribers are all cut off from earth. When the instrument is at zero, any one of
the subscribers on the branch exchange may ring up the central exchange and cut
out the other subscribers the action being as follows:-The current transmitted by
the subscriber causes a vibratory motion of the armature a of his indicator A at
the branch exchange whereby a spring or other contact making device / fitted on
the inner end of such arinature is bought into contact with the terminal H of a
second local battery wire L and closes the circuit through that battery and the

page_text: electro magnet of the indicator A which is in the same circuit. The electro
magnet A is thereby energised and attracts the armature a. One of the subscriber's
indicators or electro magnets A is shown to a larger scale in elevation and plan in
figures 3 and 4. A spring arm a fitted over the armature but insulated from it
and in the subscribers circuit is by the action of the armature raised from an earth
connection between the pin i and torminal I at its inner and and by being
depressed at its outer end is brought into electrical connection with a terminal J
(which may be formed by a cup of mercury) of the trunk wire T leading to the
central exchange so that the subscriber in ringing up the branch calls the central
exchange.
The same action of the indicator armature a by means of the arm a² and pin k
presses together and makes contact between two springs or terminals K K to close
the circuit through the first local battery F which actuates the electro-magnet D
and escapement E of the clock work C, and the drum or disc B is advanced to O¹
or one step beyond the zero point. By this movement the current through the
clock work C and operating electro magnet 1 which can only be closed by the
subscriber when at the zero point is now broken. The motion of the drum or
disc B on its axis at this point is also accompanied by a rising movement effected
by pins or cam surfaces 6' between it and a stationary disc B below and the drum
or disc B in rising lifts the spring arın a¹ on the top of each indicator out of
contact with the terminal I forming the earth connection, without raising them to
such an extent as to place the opposite end of each spring arm in connection with
the terminals J of the trunk line and all the subscribers excepting the one who
first calls the exchange are cut off from earth and cannot ring. The first subscriber
having called the central exchange asks the operator to connect him with the
subscriber with whom he wishes to communicate. If that subscriber is connected
direct to the central exchange the usual switch board arrangement is employed to
connect the subscribers, but if the subscriber wanted is on the same or on a similar
branch exchange the central exchange operator transmits as many currents to the
relay or electro magnet G (which closes the local battery circuit of the electro
magnet D acting on the escapment and clock work mechanism at the branch
exchange) as will advance the drum or disc B until a projection b on it comes into
contact with the spring arm a¹ over the indicator of the subscriber wanted. For
example if the subscriber wanted is No 4 on the branch exchange the operator
sends four currents which bring the projection b on the drum or disc B from the
step O' in advance of zero until it is under the spring arm a¹ on the indicator of
No 4 and presses the opposite end of that arm into contact with the terminal J of
the trunk wire T. The first subscriber and the one wanted by him are then both
connected to the trunk line and are therefore in direct cominunication with each
other. When the conversation ceases either subscriber may call the central
exchange operator who will disconnect the subscribers by transmitting as many
currents to the relay G and magnet D of the clockwork as will send round the
drum or disc to the zero position at O where it again falls and allows all the
subscribers indicator arms to connect to the earth terminal I. Just before reaching
the zero point the projection on the drum or disc or a corresponding projection m
on a wheel on the lower end of the disc spindle in its movement raises a spring M
and breaks the local battery circuit L or it may press together and make contact
between two springs or terminals of the local battery L connected to the indicator
magnets and thereby short-circuit the electro magnet of the indicator A of the
subscriber who first called. This electro magnet thereupon ceases to attract its
armature a and the armature being freed allows the pin i on the spring arm a¹
over it to make contact with the earth connection I.
The entering trunk wire from the central exchange is connected direct to the
relay G but a resistance may be interposed in the return wire of the circuit in
order that the exchange operator in transmitting currents may operate the relay
without acting on the subscribers indicators.

page_text: Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is
1st The arrangement or combination of parts forming the improved telephonic or
telegraphic branch exchange instrument herein described and illustrated.
2. In a telephonic exchange instrument the arrangement in combination with a
series of subscribers indicators of the drum or disc B operated by clockwork or
other devices and provided with means for cutting off the subscribers connection
to earth and of connecting the subscribers individually to the central exchange
substantially as described and illustrated.
3. The arrangement in a telephone or telegraph exchange instrument of an electro
magnet or subscriber's indicator (A) provided with means for closing a battery
circuit through the electro magnet coils and thereby automatically connecting the
subscriber to the central exchange when the subscriber calls the branch, substantially
as described and illustrated.