Year: 1887

page_text: I, SYDNEY PITT, of Sutton, in the County of Surrey, Gentleman, (a communication
to me from abroad by Charles Ezra Scribner, of the City of Chicago in the County
of Cook, and State of Illinois, United States of America;) do hereby declare the
nature of this invention to be as follows:-
My invention relates to multiple switchboard apparatus of a telephone exchange,
and its object is to facilitate making the connections and disconnections between the
various subscriber's telephone lines of the exchange.
My invention relates more especially to that system of telephone exchange in which
the different lines terminate each in a different flexible cord, each cord being provided
with a terminal plug.
In multiple switchboard systems, as is well known to those skilled in the art, the
lines are provided each with a different switch or terminal on each of the multiple
switchboards, so that each line is connected with several switches, the different switches
of each line being distributed upon different boards. The boards are preferably placed
end to end, so as to form a continuous line of switchboards. When the boards are so
placed, each of the different boards is usually termed a section of the multiple switch-
board. I shall, however, in my description, speak of the different sections as different
boards. The object of providing several switchboards, each with a terminal for each
of the lines, is to provide room for the switchmen, or operators, to work.
In the circuit of each telephone line at the Central Office is included an individual
annunciator. These individual annunciators are distributed upon the different boards
so that the calls of a certain group of lines will be indicated upon one board and the
calls of another group of lines upon another board, and the operators at the different
boards will answer the calls of their respective groups. But, an operator having
answered the call of any particular line, is enabled to make the connection between
this calling line and the line of the subscriber called for, upon his own board, whether
the line asked for be one of said operator's particular group or any other line of the
exchange, since the operator has upon her board a terminal or switch of each of the
telephone lines.

page_text: Where the lines terminate each in a different flexible cord and plug, all connections
are made by inserting the terminal plug of one line into the switch of another line.
This system of making the connections is popularly spoken of as the " single cord
system," as distinguished from systems in which a pair of cords and plugs are used
to make the connection between two lines. In combined single cord systems with
multiple switchboard systems, the cords and plugs are distributed upon the different
boards the same as the annunciators, that is to say, the cords and plugs of each group
will be placed upon the same board with the individual annunciators of the same
group.
The number of switchboards required will depend upon the number of lines in
the exchange, the frequency of the calls and the ability of the operators to make
the connections. The importance, therefore, of reducing the motions required of the
operator in receiving an order for a connection, testing the line called for to see
whether or not it is in use, making the connection, disconnecting the operator's
telephone and signalling the subscriber called, is obvious.. It is also important to
provide facilities whereby one operator, who is not very busy, may assist an operator
of an adjoining board who happens to be receiving calls faster than she can answer
them.
Speaking more particularly, therefore, the object of my invention is to provide
apparatus whereby the operator's work may be made with the smallest possible
number of motions or steps, while, at the same time, the operators may assist one
another.
My invention consists:
First. In a device which I term a grounding switch, operated by the terminal plug
of the line, in which the grounding switch is placed.
Second. In a combined listening and ringing key for disconnecting the operator's
telephone and sending current to a line of a subscriber that has been asked for.
Third. In a special connecting cord and plug, branched from the operator's
telephone circuit and a special ringing key connected, therewith, to enable one
operator to assist another.
Fourth. In the circuits used in connection with the apparatus above mentioned.
My invention will be readily understood by reference to the accompanying
drawings, in which
Figure 1, Sheet 1, is a perspective view illustrative of one switchboard of a multiple
switchboard system of a telephone exchange.
Figures 2, 3, 4 and 5 are detailed views illustrative of the grounding switch.
Figures 6 and 7 are detailed views of the combined listening and ringing key.
Figure 8 is a detailed sectional view of one of the regular spring-jack switches
used upon the switchboards.
Figure 9 is a diagram showing two telephone lines connected with spring-jack
switches on different switchboards and the circuits and connections with an operator's
outfit at the central office.
I have indicated upon the switchboard, illustrated in Figure 1, spring-jack switches
or terminals for 105 lines, and have indicated the terminal plugs and cords of 15 lines,
together with their corresponding keys and annunciators.
I will consider that there are in one exchange 7 boards in all, duplicates each of
the board illustrated in Figure 1, these boards being preferably placed end to end.
Each of these boards would be provided with the plugs, cords, keys and annunciators
for 15 different lines in the manner illustrated in Figure 1.
It will be understood that a multiple switchboard system would not be required
for an exchange having only 105 subscribers, the multiple system being especially
designed for large exchanges where more than one board is required to give room
for the operators to work to advantage. Usually multiple systems are not used in
exchanges having less than 500 subscribers. I have illustrated the smaller number
of line terminals in order that the drawings may be readily understood, this number
being sufficient to illustrate my system.
In Figure 1 I have shown the terminal plug of line 3 inserted in the spring-jack

page_text: of No. 21 and the plug of line No. 12 inserted in the spring-jack of No. 49. The
terminal plug of line 3 being inserted in the spring-jack of another line, the key a
of said line will be pushed in so as to disconnect the telephone from circuit. In like
manner key a¹ of line 12 is shown pushed in; that is to say, in position to disconnect
the telephone from the united circuit of lines 12 and 49. The shutters of the
annunciators a² and a³ of the lines have been restored so that the annunciators may
serve as clearing-out signals. I have shown the plug b, contact plate b¹ and push
key 2 near each end of the board. The plugs and keys b, 63, and their connections
are a portion of the apparatus by means of which one operator may assist an operator
at an adjoining board. The grounding switches are placed under the shelf which
supports the plugs thereof, and do not appear in Figure 1.
I will describe the grounding switch as illustrated in Figures 2, 3, 4 and 5.
Figure 2 is a view from below of 4 grounding switches.
Figure 3 is a plan view thereof.
Figure 4 is a sectional view on line a, a, of Figure 3.
Figure 5 is a similar sectional view showing the heel of the plug inserted so as to
form a connection between the spring c and the socket c¹.
When the heel of the plug is thus inserted, said spring c is connected with the
metallic heel, and, at the same time, wedged away from contact with spring c², the
rubber stud upon spring c coming against said spring e, said spring c² is, at the same
time, lifted from its normal contact c³. When the plug is lifted from its socket,
the spring closes upon connection 2, while said connection is closed upon
connection . The object of making and breaking these connections will be explained
in connection with Figure 9.
I will now describe the disconnecting and calling key as illustrated in Figures 6
and 7, in which Figure 6 is a sectional view of one of the keys on line y y of Figure 7,
and Figure 7 a plan view showing two keys in different positions, and portions of two
other keys, all upon the same strip.
In
When the wedge of insulating material d is inserted under spring d', said spring d¹
is lifted from its connection with spring d. It is sometimes necessary to separate
contact d³ from contact d* and close contact d³ at the same time upon contact d³.
order to do this, it is only necessary to press down upon the knob a of the key, and
this may be done without reference to the position of wedge d. As will be explained
in connection with Figure 9, the separation of spring d from contact d² disconnects
the operator's telephone from circuit, and the closing of connection d³ with contact d³
serves to send current to line and call the subscriber with whom connection has been
made.
The spring-jack illustrated in Figure 8 is of well-known construction, the tip or
frame e being insulated from the line spring el, and the back contact ². A plug
inserted in the tube lifts the spring e' from its back contact e², while, at the same time,
connection is made between the tube and the spring through the medium of
the plug.
Referring now to Figure 9, line 1 is shewn connected through a series of spring-jack
switches, each switch being on a different board, to an annunciator f, and from said
annunciator to connection of its listening and ringing key; and from thence the
circuit may be traced to spring c of the grounding switch, thence through the heel of
the plug
inserted in its socket, and through said heel to the socket c', which is
permanently connected with ground.
The circuit of line 2 may be traced in like manner, through a different spring-jack
on each of the boards, and thence through its annunciator h, and thence to spring d' of its
listening and ringing key, and thence to spring c of the grounding spring-jack, and
thence through the heel of the plug i inserted therein, to the socket c, which is
permanently connected with ground.
It will be observed that line 1 is provided with a test wire 1 and line 2 with a cest
wire 2ª, the test wires being connected to contacts c² of the grounding spring-jacks,
respectively, of their lines.
It will be observed that the terminal plugs y and i are upon the same switchboard.

page_text: The telephone is connected with springs d¹ of the different listening-in keys.
When the wedge d of a listening-in key is out, as shown in Figure 9, spring d¹ rests
upon contact d². The spring d of each listening-in key being connected with
contact of the grounding spring-jack of its line, the circuit of telephone k will be
open at said spring e³ as long as the heel of the plug remains inserted in the socket.
On removing any plug from its socket, the spring c of the grounding spring-jack,
whose plug has thus been lifted, will be disconnected from its normal ground, and
coming against spring c², will carry said spring into contact with contact point c³,
as shown more clearly in Figure 4.
I will now describe the manner of making the connection and disconnection between
two telephone lines at the central office.
I will suppose that the operator at the central office sees the shutter / fall. She
will immediately lift plug i, the lifting of said plug i bringing her telephone k into the
circuit of line 2. This circuit may be traced from the ground through the test
battery 1, telephone k, spring d¹ of the listening-in key of the line, thence to the back
contact d² of said listening-in key, thence to spring of the grounding spring-jack
and thence to line spring c, the circuit between springs and being completed
through the medium of spring e². The telephone k is thus connected into the circuit
of line 2 by simply lifting plug i.
The operator listening at telephone k receives the order which is given, and then
immediately with the tip of plug i touches test piece m of the spring-jack of the line
called for.
I will suppose that the line called for is line 1. If line 1 is in use or connected
with any other of the boards, this test wire 1 will be closed with line 1 in the usual
manner by the insertion of the plug in the spring-jack of the line at the board where
the connection is made. If, however, line 1 is not in use, test wire 1" will be open.
The operator, therefore, listening at telephone as she touches the tip of the plug i to
test piece m, will know whether or not the line is in use, since, if the line is in use,
her test battery will be closed through telephone k, and she will hear the usual click.
If, however, the line is not in use, the circuit of battery will not be completed when
the tip of plug is touched to test piece m, and she will therefore hear no click in her
telephone, and will therefore know that the line is free.
Having ascertained that the line is free, the operator will insert plug i into the
spring-jack upon her board of the line called for, thus completing the connection. In
order to signal the subscriber thus called for, she has only to press down upon knob a
of her listening-in key so as to close connection d³ to connection d with which the
generator n is connected.
The two subscribers being thus connected together, the operator, by simply pressing
against the knob, forces wedge d under spring d', thus disconnecting her telephone
from the circuit of the two connected lines. The shutter of annunciator h is then.
restored so that the annunciator h may serve as a clearing-out signal.
The steps of the operator in receiving a call and making a connection are thus
briefly as follows, viz.:
1st. Lifting the plug.
:
2nd. Listening at the telephone to get the order.
3rd. Touching the tip of the plug to the test piece of the line wanted, and, at the
same time, listening at the telephone.
4th. Inserting the plug in the spring-jack of the line wanted.
5th. Pressing down on the knob of the listening-in key to throw current to the line
wanted.
6th. Disconnecting the telephone, and
7th. Restoring the shutter of the annunciator of the calling subscriber.
The apparatus is so arranged that these steps are performed in the quickest and
most convenient manner.
When the subscribers are through talking, one or the other sends current to the line,
throwing down the shutter of the annunciator h. The operator thereupon withdraws
wedged from under spring d, so as to listen in, and then disconnects the line,

page_text: restoring plug i to its normal position in the socket of its grounding spring-jack. The
shutter is again restored so as to be ready to respond to the next signal. The plug b
and cord connected therewith are connected with a key in the operator's telephone
circuit. By depressing key, the plug 6 and its cord are disconnected from the
telephone. The lever of the key b may serve as the metallic plate b¹ which is
shown in Figure 1.
I will suppose now that the operator who uses telephone k, observes that an operator
at an adjoining board is receiving more calls than she has time to answer. The
operator at telephone seeing the shutter of a line on an adjoining board fall, picks
up the plug of said line, and touching it to plate or connection 61, is in connection with
the subscriber who has sent in the call. She may thus receive the order of the
subscriber whose plug she has thus taken up, and proceed to make the necessary test.
This test is made upon her own board in the usual manner by simply touching the tip
of plug to the test piece of the spring-jack upon her board of the line called for.
Finding that the line called for is free, she at once inserts the plug which she has
picked up from an adjoining board, in the spring-jack of the line called for. She
then touches the tip of plug 6 to the heel of the plug thus inserted, at the same time
pressing down upon key 2. Current is thus sent from the generator to signal the
subscriber with whom connection has been made. The plug 6 and key 62 may be
conveniently used for testing out the lines when, for any reason, such tests may be
desired.
Dated this 29th day of December 1887.

page_text: COMPLETE SPECIFICATION.
Improvements in Apparatus for Telephone Exchanges.
I, SYDNEY PITT of Sutton in the County of Surrey, Gentleman, (a communication
to me from abroad by Charles Ezra Scribner of the City of Chicago in the County of
Cook and State of Illinois United States of America) 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 multiple switch-board apparatus of a telephone exchange
and its effect is to facilitate making the connections and disconnections between the
various subscribers telephone lines of the exchange.
.
My invention relates more especially to that system of telephone exchange in which
the different lines terminate cach in a different flexible cord, each cord being provided
with a terminal plug.
In multiple switchboard systems, as is well known to those skilled in the art, the
lines are provided each with a different switch or terminal on each of the multiple
switchboards, so that each line is connected with several switches, the different switches
of each line being distributed upon different boards. The boards are preferably placed
end to end, so as to form a continuous line of switch-boards. When the boards are so
placed, each of the different boards is usually termed a section of the multiple switch-
board. I shall however, in my description, speak of the different sections as different
boards. The object of providing several switchboards, each with a terminal for each
of the lines, is to provide room for the switchmen, or operators, to work.
In the circuit of each telephone line at the Central Office is included an individual
annunciator. These individual annunciators are distributed upon the different boards
so that the calls of a certain group of lines will be indicated upon one board and the
calls of another group of lines upon another board, and the operators at the different
boards will answer the calls of their respective groups. But, an operator having
answered the call of any particular line, is enabled to make the connection between
this calling line and the line of the subscriber called for, upon his own board, whether
the line asked for be one of said operator's particular group or any other line of
the exchange, since the operator has upon her board a terminal or switch of each
of the telephone lines.
«
Where the lines terminate each in a different flexible cord and plug, all connections
are made by inserting the terminal plug of one line into the switch of another line.
This system of making the connections is popularly spoken of as the single cord
system," as distinguished from systems in which a pair of cords and plugs are used
to make the connection between two lines. In combined single cord systems with
multiple switchboard systems, the cords and plugs are distributed upon the different
boards the same as the annunciators, that is to say, the cords and plugs of each
group will be placed upon the same board with the individual annunciators of the
same group.
The number of switchboards required will depend upon the number of lines in the

page_text: exchange, the frequency of the calls and the ability of the operators to make the
connections. The importance, therefore, of reducing the motions required of the
operator in receiving an order for a connection, testing the line called for to see
whether or not it is in use, making the connection, disconnecting the operator's
telephone and signalling the subscriber called, is obvious. It is also important to
provide facilities whereby one operator, who is not very busy, may assist an operator
of an adjoining board who happens to be receiving calls faster than she can
answer them.
Speaking more particularly, therefore, the object of my invention is to provide
apparatus whereby the operators work may be made with the smallest possible number
of motions or steps, while, at the same time, the operators may assist one another.
My invention consists:
First. In a device which I term a grounding switch, operated by the terminal plug
of the line, in which the grounding switch is placed.
Second. In a combined listening and ringing key for disconnecting the operator's
telephone and sending current to a line of a subscriber that has been asked for.
Third. In a special connecting cord and plug, branched from the operator's telephone
circuit and a special ringing key connected therewith, to enable one operator to assist
another.
Fourth. In the circuits used in connection with the apparatus above mentioned.
My invention will be readily understood by referenee to the drawings left with the
provisional specification, in which
Figure 1, Sheet 1, is a perspective view illustrative of one switchboard of a multiple
switchboard system of a telephone exchange.
Figures 2, 3, 4 and 5 are detailed views illustrative of the grounding switch.
Figure 6 and 7 are detailed views of the combined listening and ringing key.
Figure 8 is a detailed sectional view of one of the regular spring-jack switches
used upon the switchboards.
Figure 9 is a diagram shewing two telephone lines connected with spring-jack
switches on different switchboards and the circuits and connections with an operator's
outfit at the central office.
I have indicated upon the switchboard, illustrated in Figure 1, spring-jack switches
or terminals for 105 lines, and have indicated the terminal plugs and cords of 15 lines,
together with their corresponding keys and annunciators.
I will consider that there are in one exchange 7 boards in all, duplicates each of the
board illustrated in Figure 1, these boards being preferably placed end to end. Each
of these boards would be provided with the plugs, cords, keys and annunciators for 15
different lines in the manner illustrated in Figure 1.
It will be understood that a multiple switchboard system would not be required for
an exchange having only 105 subscribers, the multiple system being especially designed
for larger exchanges where more than one board is required to give room for the
operators to work to advantage. Usually multiple systems are not used in exchanges
having less than 500 subscribers. I have illustrated the smaller number of line
terminals in order that the drawings may be readily understood, this number being
sufficient to illustrate my system.
In Figure 1 I have shown the terminal plug of line
inserted in the spring-jack
of No. 21 and the plug of line No. 12 inserted in the spring-jack of No. 49. The
terminal plug of line 3 being inserted in the spring-jack of another line, the key a of
said line will be pushed in so as to disconnect the telephone from circuit. In like
manner key a¹ of line 12 is shown pushed in; that is to say, in position to disconnect
the telephone from the united circuit of lines 12 and 49. The shutters of the
annunciators a² and a³ of the lines have been restored so that the annunciators may
serve as clearing-out signals. I have shownthe plug b, contact plate and push key
near each end of the board. The plugs and keys bb and their connections are a
portion of the apparatus by means of which one operator may assist an operator at an
adjoining board. The grounding switches are placed under the shelf which supports
the plugs thereof, and do not appear in Figure 1.

page_text: I will describe the grounding switch as illustrated in Figures 2, 3, 4 and 5.
Figure 2 is a view from below of 4 grounding switches.
Figure 3 is a plan view thereof.
Figure 4 is a sectional view on line a, a, of Figure 3.
Figure 5 is a similar sectional view shewing the heel of the plug inserted so as to
form a connection between the spring c and the socket c¹.
When the heel of the plug is thus inserted, said spring c is connected with the
metallic heel, and, at the same time, wedged away from contact with spring c³, the rubber
stud upon spring e coming against said spring e, said spring c² is, at the same time, lifted
from its normal contact c³. When the plug is lifted from its socket, the spring c closes
upon connection c³, while said connection c² is closed upon connection c³. The object
of making and breaking these connections will be explained in connection with
Figure 9.
I will now describe the disconnecting and calling key as illustrated in Figures 6 and 7,
in which Figure 6 is a sectional view of one of the keys on line y y of Figure 7; and
Figure 7 a plan view showing two keys in different positions, and portions of two
other keys, all upon the same strip.
When the wedge of insulating material d is inserted under spring d', said spring d
is lifted from its connection with spring d. It is sometimes necessary to separate
contact d³ from contact d* and close contact d³ at the same time upon contact d³. In
order to do this, it is only necessary to press down upon the knob a of the key, and
this may be done without reference to the position of wedge d. As will be explained
in connection with Figure 9, the separation of-spring d¹ from contact d² disconnects
the operator's telephone from circuit, and the closing of connection d³ with contact d'
serves to send current to line, and call the subscriber with whom connection has
been made.
The spring-jack illustrated in Figure 8. is of well-known construction, the tip or
frame e being insulated from the line spring e¹, and the back contact e². A plug
inserted in the tube lifts the spring e from its back contact e³, while, at the same
time, connection is made between the tube and the spring through the medium of
the plug.
Referring now to Figure 9, line 1 is shown connected through a series of spring-
jack switches, each switch being on a different board, to an annunciator f, and from
said annunciator to connection of its listening and ringing key; and from thence
the circuit may be traced to spring e of the grounding switch, thence through the heel
of the plugg inserted in its socket, and through said heel to the socket c', which is
permanently connected with ground.
The circuit of line 2 may be traced, in like manner, through a different spring-jack
on each of the boards, and thence through its annunciator h, and thence to spring d
of its listening and ringing key, and thence to spring of the grounding spring-jack,
and thence through the heel of the plug i inserted therein, to the socket c', which is
permanently connected with ground.
It will be observed that line 1 is provided with a test wire 1ª, and line 2 with a test
wire 2ª, the test wires being connected to contacts c² of the grounding spring-jacks,
respectively, of their lines.
It will be observed that the terminal plugs g and i are upon the same switchboard.
The telephone & is connected with springs d' of the different listening-in keys.
When the wedge d of a listening-in key is out, as shown in Figure 9, spring d' rests
upon contact d². The spring of each listening-in key being connected with
contact c³ of the grounding spring-jack of its line, the circuit of telephone k will be
open at said spring 3 as long as the heel of the plug remains inserted in the socket.
On removing any plug from its socket, the spring c of the grounding spring-jack,
whose plug has thus been lifted, will be disconnected from its normal ground, and
coming against spring e², will carry said spring c³ into contact with contact point c³, as
shown more clearly in Figure 4.
I will now describe the manner of making the connection and disconnection between
two telephone lines at the central office.

page_text: will suppose that the operator at the central office sees the shutter / fall. One will
immediately lift plug i, the lifting of said. plug bringing her telephone & into the
circuit of line 2. This circuit may be traced from the ground through the test battery 1.
telephone k, spring d¹ of the listening-in key of the line, thence to the back contact d
of said listening-in key, thence to spring of the grounding spring-jack and thence
to line spring c, the circuit between springs and c being completed through the
medium of spring c². The telephone is thus connected into the circuit of line 2 by
simply lifting plug i.
The operator listening at telephone & receives the order which is given, and then
immediately with the tip of plug i touches test piece m of the spring-jack of the line
called for.
I will suppose that the line called for is line 1. If line 1 is in use or connected with
any other of the boards, this test wire 1" will be closed with line 1 in the usual manner
by the insertion of the plug in the spring-jack of the line at the board where the con-
nection is made. If, however, line 1 is not in use, test wire 1" will be open. The
operator, therefore, listening at telephone & as she touches the tip of the plug i to test
picce m, will know whether or not the line is in use, since, if the line is in use, her
testing battery will be closed through telephone k, and she will hear the usual click.
If, however, the line is not in use, the circuit of battery i will not be completed when
the tip of plug i is touched to test piece m, and she will therefore hear no click in her
telephone, and will therefore know that the line is free.
Having ascertained that the line is free, the operator will insert plug i into the
spring-jack upon her board of the line called for, thus completing the connection. In
order to signal the subscriber thus called for, she has only to press down upon knob a
of her listening-in key so as to close connection d³ to connection d with which the
generator n is connected.
The two subscribers being thus connected together, the operator, by simply pressing
against the knob, forces wedge d under spring d', thus disconnecting her telephone
from the circuit of the two connected lines. The shutter of annunciator is then
restored so that the annunciator h may serve as a clearing out signal.
The steps of the operator in receiving a call and making a connection are thus
briefly as follows, viz.
1st. Lifting the plug.
2nd. Listening at the telephone to get the order.
3rd. Touching the tip of the plug to the test piece of the line wanted, and, at the
same time, listening at the telephone.
4th. Inserting the plug in the spring-jack of the line wanted.
5th. Pressing down on the knob of the listening-in key to throw current to the
line wanted.
6th. Disconnecting the telephone, and
7th. Restoring the shutter of the annunciator of the calling subscriber.
The apparatus is so arranged that these steps are performed in the quickest and
most convenient manner.
When the subscribers are through talking, one or the other sends current to the line
throwing down the shutter of the annunciator h. The operator thereupon withdraws
wedge d from under spring d³, so as to listen in, and then disconnects the line,
restoring plug i to its normal position in the socket of its grounding spring-jack. The
shutter is again restored so as to be ready to respond to the next signal. The plug b
and cord connected therewith are connected with a key b' in the operator's telephone
circuit. By depressing key 63, the plug and its cord are disconnected from the
telephone k. The lever 6 of the key 62 may serve as the metallic plate 6¹ which is
shown in Figure 1.
k
I will suppose now that the operator who uses telephone k, observes that an operator
at an adjoining board is receiving more calls than she has time to answer. The
operator at telephone & seeing the shutter of a line on an adjoining board fall, picks
up the plug of said line, and touching it to plate or connection 61, is in connection
with the subscriber who has sent in the call. She may thus receive the order of the
B

page_text: subscriber whose plug she has thus taken up, and proceed to make the necessary test.
This test is made upon her own board in the usual manner, by simply touching the
tip of plug to the test piece of the spring-jack upon her board of the line called for.
Finding that the line called for is free, she at once inserts the plug which she has
picked up from an adjoining board, in the spring-jack of the line called for. She
then touches the tip of plug 6 to the heel of the plug thus inserted, at the same
time pressing down upon the key 62. Current is thus sent from the generator to
signal the subscriber with whom connection has been made. The plug band key b²
may be conveniently used for testing out the lines when, for any reason, such tests
may be desired.
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 grounding switch when operated by the plug, substantially as described.
2. The listening and ringing key adapted to connect and disconnect a telephone
from circuit or make connection with a generator, or other source of electricity.
3. The connecting cord and plug branched from the operators telephone circuit,
and the special ringing key connected therewith to enable one operator to assist
another.
4. The circuits used in connection with the apparatus above mentioned.