Improvements in Telephony.
Year: 1890

page_text: Date of Application, 18th Apr., 1890
Complete Specification Left, 6th Jan., 1891-Accepted, 7th Mar., 1891
PROVISIONAL SPECIFICATION.
Improvements in Telephony.
I, MILO GIFFORD KELLOGG, of 135, 47th Street, Chicago, Illinois, United
States of America, Electrical Engineer, do hereby declare the nature of this inven-
tion to be as follows:-
My invention relates especially to a single cord, metallic circuit, multiple switch-
board, telephone exchange system.
In a single cord telephone exchange system each line is connected at the board
where its calls are to be answered to a flexible switch conducting cord which
terminates in a switch plug adapted to be placed for switching the line with another
line into the switch of the line to be connected to. This system requires the
insertion of but one plug into a line switch in order to make the connection between
two lines.
My invention consists first in a system and organization of apparatus, circuits
and connections for a multiple switch board, metallic circuit, single cord, telephone
exchange system whereby the operator at any board may expeditiously and with
few motions connect her telephone to a line assigned to her to answer, when a call
from the line is indicated, may test the line wanted to find whether it is already in
use, may connect the two lines together and send a calling current which will ring
the bell of the line wanted, may leave the lines connected together for conversation,
may at any time connect his telephone to their circuit to determine whether they
are through conversation, may receive on the calling annunciator of the line in
which the call originated a signal to disconnect the connection and may disconnect
the two lines and leave their apparatus in condition to receive or make new calls.
Said system and organization is I believe more simple and the operations required
are less than in other systems.
My invention consists, secondly, in a system of testing such lines by which the
lines test "busy," or in use, whether they are switched at any board or their line
annunciators indicate a call.
In the accompanying drawings illustrating my invention,
Fig. 1 is a diagram illustrating the central office apparatus, circuits and con-
nections of the system.
Figs. 2 and 3 are sectional views of a compound answering switch used for each
line at the central office.
Fig. 4 shows in detail a switch plug and
Fig. 5 a spring jack switch which may be used in the system.
Fig. 6 shows in diagram a subscriber's station apparatus to be used at each
subscriber's station.
In the central office of the exchange are as many switch boards as are found
necessary or desirable in order to properly operate the exchange. In Fig. 1 A A¹
represent sectional views of sections of two switch boards to which the same lines
connect. On each board of the exchange is a spring jack or similar switch for each
line. Each switch has a contact spring which is normally in contact with a contact
point and is separated and insulated from the point when a plug is inserted into the
switch and has a third contact piece which is normally insulated from the other
parts. This contact piece is adapted to form connection with one of the contact
pieces of a loop switch plug when the plug is inserted and to have a test plug or
contact piece applied to it for testing. The switches shown in the drawing are of a
well known construction.
For each line there is also a compound answering switch located at the board
where the plug and cord of the line are located and where its calls are to be

page_text: answered. This compound answering switch is operated on in part by the switch
plug when placed in its normal position and in part by the operator who
answers the calls of the line. The construction, operation and manipulation of
these compound answering switches will be explained in detail.
Two lines and their switches on the boards, their plugs and cords, their compound
answering switches and their annunciators are shown in Fig. 1. The answering
switch plug and cord and annunciator of one line is shown as located at one board
and that of the other line as located at the other board.
B B' represent the two compound answering switches of the lines and D D¹ their
switch plugs, to which the double, insulated flexible conducting cords are attached.
These plugs are adapted to be placed in any switch at their board and are each
adapted to be placed normally, or when not in use, in the compound answering
switch of its line, and to operate the switch as will be described. One plug is
shown in its compound answering switch and the other plug is shown out of its
switch.
In the said compound answering switches B B', a a, are sockets adapted to receive
and guide the switch plugs, and bb are pieces which support the springs and other
contacts. 1, 2, 3, 4, 5, 6, 7 and 8 are contact pieces, of which 2, 4 and 5 are springs
and the rest may be rigid points. They are insulated from each other except
through the contacts and connections substantially as shown. e is a pivoted angle
or bell crank lever piece having at one extremity the projection u and at its other
extremity the knob 'n adapted to be moved by the operator. The projection u is
adapted to engage with the irregularly. shaped piece o attached to spring 4 and to
cause the contacts to be made and broken as will be described. The parts are
made substantially as shown or of other forms and arrangements which will perform
substantially the switching operations which will be described. When the angle or
bell lever piece is in the normal position shown in Fig. 1 and the switch plug is in
its normal position in the answering switch, 1 and 2 are in contact and 3 and 4, and
5 and 6, respectively, are out of contact when then the plug is withdrawn from its
normal position, spring 2 passes from contact with 1 into contact with 8 and contacts
between 3, 4 and between 5, 6, respectively are established. When the plug is out
of its normal position and the bell crank piece is moved to its utmost limit of motion
as shown in Fig. 3 spring 5 passes into contact with point 7. When then the bell
crank piece is released by the operator, the force of the spring causes the parts to
take the position shown in Fig. 2, where springs 4 and 5 are in contact with
neither 3, 6 nor 7.
The switch plugs D D' are of a usual construction of loop switch plugs adapted
to be used with the spring jack switches. Each plug has two contact pieces
insulated from each other. one of them, s, being at the end of the plug tip, and the
other, s¹, being an insulated cylinder placed along the tip. When a plug is inserted
into a switch, the piece s presses against the spring of the switch and forces it away
from the contact point and makes connection with the spring and the other piece of
the plug (s) forms connection with the third or insulated contact piece of the
switch.
The annunciators have two contact points or pieces which are normally, or when
the annunciator does not indicate a call, in connection with each other, but which
are separated while the annunciator indicates a call. One of them, q, is indicated
as an angle piece and the other p, as a spring which is in contact with the piece q
when the annunciator drop does not indicate a call, but which is forced away from
the piece q while the drop indicates a call.
tt are operator's telephones, R. R operators calling batteries or generators, and
r. r. resistance coils. Each operator may have one of each of said parts and they are
connected to each other and to the compound answering switches substantially a
shown and as will be described. to and are calling annunciators, one for each lin
shown, R is a test battery which may be common to all the lines, G. G. are ground
connections.
The connections are substantially as follows: One side or branch of each lin

page_text: passes normally, in succession, through the pairs of contact points of the switches of
the line, passing in each case to the spring first. It then passes through the line
annunciator and the pair of contacts p q of the annunciator and is then connected to
contacts 2 and 5 of the compound answering switch of the line. This side or branch
of the line is also connected through one of the conductors of a double conductor
flexible cord to contact piece s of the switch plug of the line, the connection being
made between the switches on the one hand and the line annunciator on the other
hand. The other side or branch of the line is connected to all of said third contact
pieces of the switches of the line and, through the other conductor of the switch
cord, to contact pieces of the switch plug. It is also connected to contacts 3 and 8
of the compound answering switch of the line. One side of the operator's telephone
is connected through his resistance coil to contact 6¹ of the answering switch and
the other side of the telephone is connected to contact 4 of the answering switch.
The wire which connects the two coils of the telephone is connected to the ground.
Contact point 7 of the answering switch is connected through the operator's calling
generator or battery R to the ground. Contact point is connected through the
test battery R' to the ground. In the subscriber's station apparatus, shown in
Fig. 6, 1 is the telephone switch, is the subscriber's calling generator, 3 is his
signal receiving bell, and 4 is his telephone. The contacts and connections are
substantially as shown. When the telephone is on its switch, it is shunted or switched
from the metallic circuit. The signal receiving bell is an ordinary signal receiving
bell. It is in a circuit wire which is grounded on one side and connected to the circuit
of the line on its other side when the telephone is on its switch, but is not otherwise
thus connected to the line.
The operation of the system is as follows: When the plug of a line is in its
normal position in its compound answering switch, and the line is not switched at
any board, and its annunciator does not indicate a call, one side or branch of the
line is grounded through the test battery. When the line is in that condition and
the subscriber's telephone is on its switch and the subscriber operates his generator,
the calling annunciator of the line at the central office will be operated. When the
operator observes the call, he removes the plug from its normal position. By so
doing the connection of the line to ground is broken, by the opening of the
contacts 1, 2; and the operator's telephone is closed or bridged to the two sides or
branches of the line, by the closing of the contacts 3, 4 and 5, 6. The operator
then finds out by conversation what line is wanted. He then tests the line wanted
(as will hereafter be indicated) and if he finds the line to be "free," or not in use,
he places the switch plug in the switch of the line. By so doing the second line is
disconnected from the ground and the two lines are connected together; and their
circuit is bridged or cross connected at the central office by a circuit which contains
the operator's telephone. The operator will then move the lever e of the answering
switch of the line in which the call originated to its farthest limit of motion, as
shown in Fig. 3. The telephone is thereby disconnected from the circuit and the
calling generator or battery grounded on one side is connected on its other side,
through the connection between 5 and 7, to the circuit of the lines; and the bell of
the subscriber wanted will be rung; and the bell of the calling subscriber will also be
rung if he has replaced his telephone on its switch. The operator thereupon
releases the knob n of the compound answering switch and the angle or bell crank
piece e takes the position shown in Fig. 2, where the circuit is connected with
neither the operator's telephone nor his calling generator or battery, and the lines
are connected for conversation.
When the lines are in this condition, their circuit is bridged or cross connected
by a circuit which contains the annunciator of the calling line; and any discon-
necting signal sent by either subscriber will be indicated to the operator who made
the connection. This cross or bridge connection of the annunciator is produced by
the closing of the points 2 and 8 of the answering switch and by the arrangement
of circuits as described. The operator can at any time connect his telephone to

page_text: the circuit of the two lines, by moving the bell crank piece e to the position shown
on Fig. 1.
To disconnect two subscribers connected together for conversation, the operator
merely removes the plug from the switch and places it in its normal position in the
answering switch and places the piece e of the answering switch in its normal
position as shown in Fig. 1. The lines are then ready to receive or to make any
new calls.
The test system is as follows: When a line is not switched at any board and its
annunciator does not indicate a call, it is grounded at the central office through the
test battery B¹. When the line is in that condition and an operator, placing the
tips of the plug of another line on said third contact piece of one of its switches,
connects the line to his telephone, a complete circuit is established which contains
the telephone and the test battery; and the operator will hear a sound or click in
his telephone. Should however the line be switched at any board, either by the
use of its plug or the insertion of a plug into one of its switches, or should the
annunciator of the line indicate a call, the circuit would be open to the test battery
and the operator would hear nothing. The operator can therefore determine on
testing that either the line is switched for use or its annunciator indicates a call;
or that it is neither switched for use nor its annunciator indicates a call. In the
latter case he will be free to switch the line with another line.
By this system of testing a subscriber's line tests "busy" and is reserved to
himself as soon as he operates his generator; whereas in other systems of testing
it tests "busy" only after it is switched for use. The service of the exchange
will in this test system be more satisfactory both to the subscriber who makes the
call and to the operator who receives the call.
The operations of answering a call and making the désired connection are:
1st, to remove the switch plug; 2nd, test the line wanted (with the same plug);
3rd, place the plug in the switch of the line wanted; and 4th, move the knob of the
answering switch to its outer limit of motion.
It will be observed that, the lines being grounded at the subscriber's station
when his telephone is not switched for use, part of the current from the test battery
will go to ground them when the telephone is not switched. Enough current will,
however, pass through the operator's telephone to cause the line to test "froe
when it is not switched and its annunciator does not indicate a call. The bell
could be placed in the line circuit; and in that case it would be preferable to
have some other resistance placed in the ground connection at the subscriber's
station.
A rheotome could be used in the place of the test battery in the position above
shown for the battery and the test battery placed in any other position in the test
circuit normally established on testing.
Dated this 18th day of April 1890
CARPMAEL & Co.,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Telephony.
I, MILO GIFFORD KELLOGG, of 135, 47th Street, Chicago, Illinois, United
States of America, 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 :-
4
My invention relates especially to a single cord, metallic circuit, multiple switch- 5
board, telephone exchange system.
In a single cord telephone exchange system each line is connected at the board
where its calls are to be answered to a flexible switch conducting cord which
terminates in a switch plug adapted to be placed for switching the line with another

page_text: me to IC SWITCH OT
LO
connected to. Imis system requires the
insertion of but one plug into a line switch in order to make the connection between
two lines.
My invention consists first in a system and organization of apparatus, circuits
and connections for a multiple switch board, metallic circuit; single cord, telephone
exchange system whereby the operator at any board may expeditiously and with
few motions connect her telephone to a line assigned to her to answer, when a call
from the line is indicated, may test the line wanted to find whether it is already
in use, may connect the two lines together and send a calling current which will
ring the bell of the line wanted, may leave the lines connected together for conver-
sation, may at any time connect his telephone to their circuit to determine whether
they are through conversation, may receive on the calling annunciator of the line in
which the call originated a signal to disconnect the connection and may disconnect
the two lines and leave their apparatus in condition to receive or make new calls.
Said system and organization is I believe more simple and the operations required
are less than in other systems.
My invention consists, secondly, in a system of testing such lines by which the
lines test "busy," or in use, whether they are switched at any board or their line
annunciators indicate a call.
In
In the drawings left with the Provisional Specification illustrating my invention,
Figure 1 is a diagram illustrating the central office apparatus, circuits and con-
nections of the system, Figures 2 and 3 are sectional views of a compound answering
switch used for each line at the central office, Figure 4 shows in detail a switch
plug and Figure 5 a spring jack switch which may be used in the system. Figure 6
shows in diagram a subscriber's station apparatus to be used at each subscriber's
station. In the central office of the exchange are as many switch boards as are
found necessary or desirable in order to properly operate the exchange.
Figure 1A A' represent sectional views of sections of two switch boards to which the
same lines connect. On each board of the exchange is a spring jack or similar switch
for each line. Each switch has a contact spring which is normally in contact with
a contact point and is separated and insulated from the point when a plug is
inserted into the switch and has a third contact piece which is normally insulated
from the other parts. This contact piece is adapted to form connection with one of
the contact pieces of a loop switch plug when the plug is inserted and to have a test
plug or contact piece applied to it for testing. The switches shown in the drawing
are of a well known construction.
For each line there is also a compound answering switch located at the board
where the plug and cord of the line are located and where its calls are to be
answered. This compound answering switch is operated on in part by the switch
plug when placed in its normal position and in part by the operator who answers the
calls of the line. The construction, operation and manipulation of these compound
answering switches will be explained in detail.
Two lines and their switches on the boards, their plugs and cords, their compound
answering switches and their annunciators are shewn in Figure 1. The answering
switch plug and cord and annunciator of one line is shewn as located at one board
and that of the other line as located at the other board.
B B represent the two compound answering switches of the lines and D D'
their switch plugs, to which the double, insulated flexible conducting cords are
attached. These plugs are adapted to be placed in any switch at their board and
are each adapted to be placed normally, or when not in use, in the compound,
answering switch of its line, and to operate the switch as will be described. One
plug is shewn in its compound answering switch and the other plug is shewn out
of its switch.
In the said compound answering switches B B₁, a a are sockets adapted to receive
and guide the switch plugs, and b b are pieces which support the springs and other
contacts. 1, 2, 3, 4, 5, 6, 7 and 8 are contact pieces, of which 2, 4 and 5 are springs
and the rest may be rigid points. They are insulated from each other except

page_text: through the contacts and connections substantially as shewn. e is a pivotted angle
or bell crank lever piece having at one extremity the projection u and at its other
extremity the knob n adapted to be moved by the operator. The projection u is
adapted to engage with the irregularly shaped piece o attached to spring 4 and to
cause the contacts to be made and broken as will be described. The parts are made
substantially as shown or of other forms and arrangements which will perform
substantially the switching operations which will be described. When the angle or
bell lever piece is in the normal position shewn in Figure 1 and the switch plug is
in its normal position in the answering switch 1 and 2 are in contact and 3 and 4,
and 5 and 6, respectively, are out of contact when then the plug is withdrawn from
its normal position, spring 2 passes from contact with 1 into contact with 8 and
contacts between 3, 4 and between 5, 6, respectively are established. When the
plug is out of its normal position and the bell crank piece is moved to its utmost
limit of motion as shown in Figure 3 spring 5 passes into contact with point 7.
When then the bell crank piece is released by the operator, the force of the spring
causes the parts to take the position shewn in Figure 2, where springs 4 and 5 are
in contact with neither 3, 6 nor 7.
The switch plugs D D' are of a usual construction of loop switch plugs adapted
to be used with the spring jack switches. Each plug has two contact pieces
insulated from each other, one of them s, being at the end of the plug tip, and the
other s', being an insulated cylinder placed along the tip. When a plug is inserted
into a switch, the piece s presses against the spring of the switch and forces it away
from the contact point and makes connection with the spring and the other piece of
the plugs forms Connection with the third or insulated contact piece of the switch.
The annunciators have two contact points or pieces which are normally, or when
the annunciator does not indicate a call, in connection with each other, but which
are separated while the annunciator indicates a call. One of them q, is indicated as
an angle piece and the other p, as a spring which is in contact with the piece g,
when the annunciator drop does not indicate a call, but which is forced away from
the piece q while the drop indicates a call.
tt are operator's telephones, R R operator's calling batteries or generators, and
resistance coils. Each operator may have one of each of said parts and they are
connected to each other and to the compound answering switches substantially as
shown and as will be described. w and a are calling annunciators, one for each line
shown, R' is a test battery which may be common to all the lines, G G are ground
connections.
The connections are substantially as follows: One side or branch of each line
passes normally, in succession, through the pairs of contact points of the switches of
the line, passing in each case to the spring first. It then passes through the line
annunciator and the pair of contacts p q of the annunciator and is then connected to
contacts 2 and 5 of the compound answering switch of the line. This side or branch
of the line is also connected through one of the conductors of a double conductor
flexible cord to contact pieces of the switch plug of the line, the connection being
made between the switches on the one hand and the line annunciator on the other
hand. The other side or branch of the line is connected to all of said third contact
pieces of the switches of the line and, through the other conductor of the switch
cord, to contact piece s' of the switch plug. It is also connected to contacts 3 and 8
of the compound answering switch of the line. One side of the operator's telephone
is connected through his resistance coil to contact 6 of the answering switch and
the other side of the telephone is connected to contact 4 of the answering switch.
The wire which connects the two coils of the telephone is connected to the ground.
Contact point 7 of the answering switch is connected through the operator's calling
generator or battery R to the ground. Contact point 1 is connected through the
test battery R to the ground. In the subscriber's station apparatus, shown in
Figure 6, 1 is the telephone switch, 2 is the subscriber's calling generator, 3 is his
signal receiving bell, and 4 is his telephone. The contacts and connections are
substantially as shown. When the telephone is on its switch, it is shunted or

page_text: switched from the metallic circuit. The signal receiving bell is an ordinary signal
receiving bell.
It is in a circuit wire which is grounded on one side and connected
to the circuit of the line on its other side when the telephone is on its switch, but is
not otherwise thus connected to the line.
The operation of the system is as follows: When the plug of a line is in its normal
position in its compound answering switch, and the line is not switched at any board,
and its annunciator does not indicate a call, one side or branch of the line is grounded
through the test battery. When the line is in that condition and the subscriber's
telephone is on its switch and the subscriber operates his generator, the calling
annunciator of the line at the central office will be operated. When the operator
observes the call, he removes the plug from its normal position. By so doing the
connection of the line to ground is broken, by the opening of the contacts 1, 2 and
the operator's telephone is closed or bridged to the two sides or branches of the line,
by the closing of the contacts 3, 4 and 5, 6. The operator then finds out by con-
versation what line is wanted. He then tests the line wanted (as will hereafter be
indicated) and if he finds the line to be "free," or not in use, he places the switch
plug in the switch of the line. By so doing the second line is disconnected from
the ground and the two lines are connected together; and their circuit is bridged or
cross connected at the central office by a circuit which contains the operator's
telephone. The operator will then move the lever e of the answering switch of the
line in which the call originated to its farthest limit of motion, as shown in Figure 3.
The telephone is thereby disconnected from the circuit and the calling generator or
battery grounded on one side is connected on its other side, through the connection
between 5 and 7, to the circuit of the lines; and the bell of the subscriber wanted
will be rung; and the bell of the calling subscriber will also be rung if he has
replaced his telephone on its switch. The operator thereupon releases the knob n
of the compound answering switch and the angle or bell crank picce e takes the
position shown in Figure 2, where the circuit is connected with neither the operator's
telephone nor his calling generator or battery, and the lines are connected for
conversation.
When the lines are in this condition, their circuit is bridged or cross connected by
a circuit which contains the annunciator of the calling line; and any disconnecting
signal sent by either subscriber will be indicated to the operator who made the
connection. This cross or bridge connection of the annunciator is produced by the
closing of the points 2 and 8 of the answering switch and by the arrangement of
circuits as described. The operator can at any time connect his telephone to the
circuit of the two lines, by moving the bell crank piece e to the position shown on
Figure 1.
To disconnect two subscribers connected together for conversation, the operator
merely removes the plug from the switch and places it in its normal position in the
answering switch and places the piece e of the answering switch in its normal
position as shown in Figure 1. The lines are then ready to receive or to make any
new calls.
The test system is as follows: When a line is not switched at any board and its
annunciator does not indicate a call, it is grounded at the central office through the
test battery R. When the line is in that condition and an operator, placing the
tips of the plug of another line on said third contact piece of one of its switches,
connects the line to his telephone, a complete circuit is established which contains
the telephone and the test battery; and the operator will hear a sound or click in
his telephone. Should however the line be switched at any board, either by the
use of its plug or the insertion of a plug into one of its switches, or should the
annunciator of the line indicate a call, the circuit would be open to the test battery
and the operator would hear nothing. The operator can therefore determine on
testing that cither the line is switched for use or its annunciator indicates a call;
or that it is neither switched for use nor its annunciator indicates a call. In the
latter case he will be free to switch the line with another line.

page_text: :
By this system of testing a subscriber's line tests "busy" and is reserved to
himself as soon as he operates his generator; whereas in other systems of testing it
tests "busy" only after it is switched for use. The service of the exchange will in
this test system be more satisfactory both to the subscriber who makes the call and
to the operator who receives the call.
The operations of answering a call and making the desired connection are:
1st, to remove the switch plug; 2nd, test the line wanted (with the same
plug) 3rd, place the plug in the switch of the line wanted; and 4th, move the
knob of the answering switch to its outer limit of motion.
It will be observed that, the lines being grounded at the subscriber's station when
his telephone is not switched for use, part of the current from the test battery will
go to ground them when the telephone is not switched. Enough current will,
however, pass through the operator's telephone to cause the line to test "free"
when it is not switched and its annunciator does not indicate a call. The bell
could be placed in the line circuit; and in that case it would be preferable to have
some other resistance placed in the ground connection at the subscriber's station.
A rheotome could be used in the place of the test battery in the position above
shown for the battery and the test battery placed in any other position in the test
circuit normally established on testing.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what I
claim is :-
:-
1. In a telephone exchange system, a metallic circuit line, in combination with a
switch plug for said line, an operator's telephone, a switching device into which
said plug is normally placed and circuit connections, said switching device having
pairs of contact points normally open to each other when the plug is in its normal
position and closed to each other when the plug is withdrawn from its normal
position, thereby bridging or cross connecting the two sides or branches of the
line by a circuit connection which contains said telephone, and a commutator piece
adapted to be moved by the operator to open said pairs of contact points of the
said switching device substantially as set forth.
2. In a telephone exchange system, a metallic circuit line in combination with
a switch plug for said line, a test battery, a switching device into which said
plug is normally placed and circuit connections said switching device having a
pair of contact points closed to each other when the plug is in its normal position
and thereby grounding the line through the test battery and open to each other
when the plug is withdrawn from its normal position and thereby opening said
ground connection, substantially as set forth.
3. In a telephone exchange system, a metallic circuit line, in combination with a
switch plug for said line, a test battery, a switching device in which said plug
is normally placed, circuit connections, and a pair of contacts closed to each
other when the plug is in its normal position and thereby grounding the line
through the test battery, and open to each other when the plug is removed from
its normal position, and thereby opening said ground connections.
4. In a telephone exchange system, two metallic circuit lines temporarily
connected together for conversation, in combination with an operator's telephone,
a compound switching device with contact points and a moveable commutator
piece acting upon said points and circuit connections, whereby the operator may
at will connect his telephone in a bridge circuit to the circuit of said lines or
disconnect his telephone from their circuit, substantially as set forth.
5. In a telephone exchange system, two metallic circuit lines, temporarily
connected together for conversation, in combination with an operator's telephone
and calling battery and a compound switching device with contact points, a
"moveable commutator piece acting upon said points and circuit connections,
whereby the operator may at will connect his telephone in a bridge circuit to

page_text: the circuit of said lines or disconnect his telephone from their circuit or connect
his calling battery, grounded on one side, to the circuit of the lines, on its other
side, substantially as set forth.
6. In a telephone exchange system, two metallic circuit lines temporarily
connected together for conversation, in combination with an operator's telephone,
a resistance coil, or switching device with contact points and a moveable
commutator piece and circuit connections whereby the operator may at will
connect his telephone and resistance coil in a bridge circuit to the circuit of
said lines or disconnect them from the circuit, substantially as set forth.
7. In a telephone exchange system, a metallic circuit line, in combination with
a switch plug for said line, an operator's telephone, a compound answering switch
for the line into which the switch plug is normally placed and operated on in
part by the plug and in part by the operator and circuit connections whereby
the telephone is bridged or cross connected to the two sides or branches of the
line when the plug is withdrawn from its normal position and said bridge or
cross connection is opened by the operator on moving a commutator piece of
said switch, substantially as set forth.
8. In a telephone exchange system, a metallic circuit line, one side or branch
of which is normally grounded at the central office through a test battery, and
disconnected from said test battery when the line is switched for use and the
other side of which is normally open to the ground at the central office, in
combination with a bell at the subscriber's station through which the circuit of
the line is grounded when the subscriber's telephone is not switched for use but not
otherwise, and a test receiving instrument grounded on one side and connected on
its other side to a test plug or device adapted to be brought for testing into
connection with said open side of the line, substantially as set forth.
9. In a telephone exchange system, a metallic circuit line, one side or branch of
which is normally grounded at the central office and disconnected from the ground
while the line is switched for conversation and the other side of which is normally
open to the ground at the central office, in combination with a bell at the subscriber's
station through which the circuit of the line is grounded when the subscriber's
telephone is not switched for use but not otherwise, a test receiving instrument
grounded on one side and connected with its other side to a test plug or device
adapted to be brought for testing into connection with said open side of the line,
and a test battery in the test circuit thereby established substantially as set forth.
10. In a telephone exchange system, a metallic circuit line one side or branch of
which is normally grounded at the central office and disconnected from the ground
while the line is switched for conversation and the other side of which is normally
open to the ground at the central office, in combination with a resistance at the
subscriber's station through which the circuit of the line is grounded when the
subscriber's telephone is not switched for use but not otherwise, a test receiving
instrument grounded on one side and connected on its other side to a test plug or
device adapted to be brought for testing into connection with said normally open
side of the line and a test battery in the test circuit thereby normally established on
testing substantially as set forth.
11. In a telephone exchange system, a metallic circuit line, normally connected
with the ground at the central office, in combination with an annunciator for said
line with contact points by which the said normal connection to the ground is open
when the annunciator indicates a call, a test receiving instrument grounded on one
side and connected on its other side to a test plug adapted to be brought for testing
into connection with the line, and a battery in the test circuit thereby normally
established, substantially as set forth.
12. In a telephone exchange system, a metallic circuit line, normally connected
with the ground at the central office, in combination with annunciator and switch
contact points by which said normal connection to the ground is open when either
the line is switched for use or its annunciator indicates a call, a test receiving
nstrument grounded on one side and connected on its other side to a test plug or
R

page_text: device adapted to be brought into connection with the line, and a battery in the
test circuit thereby normally established on testing, substantially as set forth.
13. In a telephone exchange system, a subscriber's line normally connected with
the ground at the central office, in combination with an annunciator for said line
having contact points by which the normal connection of the line to the ground is
opened when the annunciator indicates a call, a test-receiving instrument grounded
on one side and connected on its other side to a test plug or device adapted to be
brought for testing, into connection with the line, and a battery in the test circuit
thereby established.
14. In a telephone exchange system, a subscriber's line, the annunciator for said
line at the central office having separable contacts through which the line circuit is
normally completed, but which are open when the annunciator indicates a call, a
test-receiving instrument, electrically connected on one side to one of said separable
contacts, and connected on its other side to a test plug or device adapted to be
brought for testing into electrical connection with the other of said separable
contacts, and a battery in the test-circuit thereby established.
Dated this 18th day of December 1890.
CARPMAEL & Co.,
Agents for the Applicant.