Improvements in Telephony and Apparatus therefor.
Year: 1891

page_text: Date of Application, 6th Aug., 1891
Complete Specification Left. 5th May. 1892-Accepted, 11th June, 1892
PROVISIONAL SPECIFICATION.
Improvements in Telephony and Apparatus therefor.
I, MILO GIFFORD KELLOGG, of 135 47th Street, Chicago, Illinois, United
States of America, Electrical Engineer, do hereby declare the nature of this
invention to be as follows:-
My invention relates to metallic circuit telephone exchange systems and
especially to multiple switch board systems. It relates especially to clearing out
signal receiving apparatus for such systems and to calling apparatus which may
be operated in connection with said clearing out signal receiving apparatus.
Heretofore various systems have been employed for receiving clearing out signals
when two subscribers' lines are connected into a metallic circuit. Among them have
been the system of leaving the line annunciators of both lines in bridge or cross
connection to the circuit; the system of leaving the two line annunciators out of
circuit and switching at will a special clearing out annunciator into a bridge or
cross connection to the circuit and leaving it thus connected; the system of
leaving the line annunciators of both lines out of the circuit and including a
special clearing out annunciator in the direct or main circuit and the system of
leaving the annunciators of one of the lines (preferably the one on which the
calling for the connection originated) in a bridge or cross connection to the
circuit, the annunciator of the other line being in the mean time out of circuit
with the line.
In the system which forms a part of my present invention I provide at the switch
board (or at each board when the multiple system is employed) pairs of double or
loop switch plugs, each plug being adapted to be placed in each line switch at its
board. The two contact pieces of each plug are connected to the two contact
pieces of the mate to the plug, respectively, by means of two flexible switch cord
conducting circuits and a clearing out annunciator is permanently connected or
bridged across between the two conducting circuits of each pair of plugs. The
switch contacts and circuit connections of the lines are arranged in any usual
way such that when the two plugs of a pair of plugs are placed in the switches of
two lines the lines are connected together in a complete metallic circuit and neither
of the line annunciators is in the circuit nor in a bridge connection. It is
evident that when with the apparatus described above two lines are connected
together into a metallic circuit for conversation the special clearing out
annunciator of the pair of plugs used must permanently, or so long as the lines
are thus connected bridge or cross connect their circuit.
Among the advantages of this system are that it requires fewer switch contacts
and connections than other systems, thus reducing the liability to disarrangement
cf apparatus and poor contacts to operate through.
In connection with the system of clearing out annunciators described above I
provide for each pair of plugs a switch and connections by which the operator to
whom the plugs are assigned may at will connect her telephone into another bridge
or cross connection to the two flexible conductors in order that she may receive
calls by placing either plug into any line switch or may bridge or cross connect
with her telephone the circuit of two lines connected together through the plugs.
For the best operation of the system I prefer that the clearing out annunciators
should be of comparatively high resistance and be such as to offer considerable
retardation to the passage of telephone currents.
In connection with the system of clearing out annunciators heretofore described
and in other telephone exchange systems in which a special clearing out
annunciator bridges or cross
connects the circuit of two lines left connected

page_text: together in metallic circuit for conversation I provide calling apparatus and con-
nections such that the calling current from an operator's calling generator to any
subscriber's station passes from the office ground through the two sides or branches
of the subscriber's metallic circuit line in parallel or derived circuit and thence to
a normal ground connection at the subscriber's station and that the clearing out
annunciator shall bridge or cross connect the two sides of the parallel or derived
circuit and that the resistances of the corresponding parts of the parallel circuit
shall be approximately the same. With such a construction and arrangement of
apparatus when a calling current is sent over a circuit which is bridged by a
clearing out annunciator, the annunciator will not be operated by the current.
This system of calling is of especial use where the clearing out annunciator
permanently bridges the circuits between two plugs used, as the operator can at
all cases send a signal to the subscriber wanted without operating the clearing out
annunciator. It is also of use where two metallic circuit lines of two exchange
offices are connected together by means of a metallic trunk wire and a clearing
out annunciator in each office is left to bridge the circuit as the operator in one
office can send a calling current to the subscribers stations without operating the
clearing out annunciator in the other office.
In connection with the calling system heretofore described I provide switch
connections at each subscriber's station by which his line is grounded through his
signal receiving bell while his telephone is on its switch and the ground connec-
tion is automatically removed by the act of removing the telephone from the
switch for use. By this means when the calling subscriber's telephone is off its
switch his bell will not be rung by any signal current connected with the circuit,
but if after making his request for any connection he replaces his telephone on its
switch his bell will be rung by such a current.
As a modification of the system of calling heretofore described I also provide
two calling keys for each pair of plugs, one connected on each side of the
annunciator which permanently bridges the conducting circuits of the plugs with
contacts and connections by which the annunciator is disconnected from a plug
when a key is depressed or operated and the calling generator is made to bridge
across to the two conductors connected to the plug. By this means an operator
may always send a calling current to a line without operating one of her clearing
out annunciators.
Dated this 27th day of July 1891.
MILO GIFFORD KELLOGG.
COMPLETE SPECIFICATION.
Improvements in Telephony and Apparatus therefor.
1, 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:-
My invention relates to metallic circuit telephone exchange systems and
especially to multiple switch board systems. It relates especially to clearing out
signal receiving apparatus for such systems and to calling apparatus which may be
operated in connection with said clearing out signal receiving apparatus.
Heretofore various systems have been employed for receiving clearing out
signals when two subscribers' lines are connected into a metallic circuit. Among
them have been the system of leaving the line annunciators of both lines in bridge
or cross connection to the circuit; the system of leaving the two line annunciators
out of circuit and switching at will a special clearing out annunciator into a bridge
'or cross connection to the circuit and leaving it thus connected; the system of
leaving the line annunciators of both lines out of the circuit. and including a special
clearing out annunciator in the direct or main circuit and the system of leaving

page_text: the annunciators of one of the lines (preferably the one on which the calling
for the connection originated) in a bridge or cross connection to the circuit,
the annunciator of the other line being in the mean time out of circuit with
the line.
In the system which forms a part of my present invention I provide at the switch
board (or at each board when the multiple system is employed) pairs of double or
loop switch plugs, each plug being adapted to be placed in each line switch at its
board. The two contact pieces of each plug are connected to the two contact
pieces of the mate to the plug, respectively, by means of two flexible switch cord
conducting circuits and a clearing out annunciator is permanently connected or
bridged across between the two conducting circuits of each pair of plugs. The
switch contacts and circuit connections of the lines are arranged in any usual way
such that when the two plugs of a pair of plugs are placed in the switches of two
lines the lines are connected together in a complete metallic circuit and neither of
the line annunciators is in the circuit nor in a bridge connection. It is evident
that when with the apparatus described above two lines are connected together into
a metallic circuit for conversation the special clearing out annunciator of the pair
of plugs used must permanently, or so long as the lines are thus connected bridge
or cross connect their circuit.
Among the advantages of this system are that it requires fewer switch contacts
and connections than other systems, thus reducing the liability to disarrangement
of apparatus and poor contacts to operate through.
In connection with the system of clearing out annunciators described above I
provide for each pair of plugs a switch and connections by which the operator to
whom the plugs are assigned may at will connect her telephone into another bridge
or cross connection to the two flexible conductors in order that she may receive
calls by placing either plug into any line switch or may bridge or cross connect
with her telephone the circuit of two lines connected together through the plugs.
For the best operation of the system I prefer that the clearing out annunciator
should be of comparatively high resistance and be such as to offer considerable
retardation to the passage of telephone currents.
In connection with the system of clearing out annunciators heretofore described
and in other telephone exchange systems in which a special clearing out annunciator
bridges or cross connects the circuit of two lines left connected together in metallic
circuit for conversation I provide calling apparatus and connections such that the
calling current from an operator's calling generator to any subscriber's station
passes from the office ground through the two sides or branches of the subscriber's
metallic circuit line in parallel or derived circuit and thence to a normal ground
connection at the subscriber's station and that the clearing out annunciator shall
bridge or cross connect the two sides of the parallel or derived circuit and that the
resistances of the corresponding parts of the parallel circuit shall be approximately
With such a construction and arrangement of apparatus when a calling
current is sent over a circuit which is bridged by a clearing out annunciator, the
annunciator will not be operated by the current. This system of calling is of especial
use where the clearing out annunciator permanently bridges the circuits between
two plugs used, as the operator can at all cases send a signal to the subscriber
wanted without operating the clearing out annunciator. It is also of use where
two metallic circuit lines of two exchange offices are connected together by means
of a metallic trunk wire and a clearing out annunciator in each office is left to
bridge the circuit as the operator in one office can send a calling current to the
subscribers stations without operating the clearing out annunciator in the other
the same.
office.
In connection with the calling system heretofore described I provide switch con-
nections at each subscriber's station by which his line is grounded through his
signal receiving bell while his telephone is on its switch and the ground connection
is automatically removed by the act of removing the telephone from the switch for
use. By this means when the calling subscriber's telephone is off its switch his

page_text: bell will not be rung by any signal current connected with the circuit, but if after
making his request for any connection he replaces his telephone on its switch his
bell will be rung by such a current.
As a modification of the system of calling heretofore described I also provide
two calling keys for each pair of plugs, one connected on each side of the
annunciator which permanently bridges the conducting circuits of the plugs with
contacts and connections by which the annunciator is disconnected from a plug
when a key is depressed or operated and the calling generator is made to bridge
across to the two conductors connected to the plug. By this means an operator
may always send a calling current to a line without operating one of her clearing
out annunciators.
In the accompanying drawings illustrating my invention:
Figure 1 shews a central office multiple switch board system for metallic circuit
lines with the main line switch board apparatus and connections.
Figure 2 is a front view of a section of one of the boards shown in sectional
view in Figure 1.
Figure 3 is a diagram showing an operator's cord or connecting apparatus which
may be used at any switch board.
Figure 4 is a diagram showing the apparatus which may be used at any
subscriber's station.
Figure 5 is a diagram showing a modification of the operator's cord or connecting
apparatus applicable to certain features of my invention.
In Figure 1, A A are sectional views of sections of two switch boards to which
the same lines connect. Each board has a spring jack or similar switch for each
line of the exchange. Each switch has a hole adapted to receive any of the loop
switch plugs (shown in Figure 3 and marked D D). It has also a pair of
contacts normally in contact, marked g, h, and a third contact piece marked,
insulated from the rest except by the circuit connections. When a plug is
inserted into a switch hole it separates the two normally closed contacts
switch and its two contact pieces form connection with the two contacts g and j of
the switch.
w, w, are line annunciators, one for each line of the exchange.
of the
The connection of each metallic circuit line to its switches and annunciators is
substantially as shewn and as follows: one side or branch of the line passes
normally successively through the switch contacts g, h, of its switches on the
various boards of the exchange, passing in each case to contact piece g first. From
the last contact of the switches a circuit connection passes through the annunciator
of the line and thence through the test battery B₁, common to all the lines, to the
ground. The other side or branch of the line is connected to the contacts jj of
the switches of the line.
In the operator's cord or connecting apparatus shewn in Figure 3, D D are a
pair of loop switch plugs, each adapted to be placed in any switch hole at its board
and when so placed to separate the two contacts yh of the switch; while the two
contacts of the plug form connection with the two contacts g and j of the switch,
respectively.
The two contact pieces of one of the switch plugs are connected with the two
contact pieces of its mate, respectively, by two flexible switch conductors.
v is a clearing out annunciator for the pair of plugs placed in a bridge or cross
connecting circuit to the two flexible switch conductors. This bridge circuit is
permanent or solid and unbroken by switch contacts.
Y is a looping-in switch for the pair of plugs. This looping-in switch has two
levers connected to the two flexible switch conductors, respectively. It has also
three pairs of contact bolts, with which, respectively, the switch levers may at the
will of the operator be placed in contact.
t is the operator's telephone, the two sides of which are connected to the two
bolts respectively, of a pair of the contact bolts of the switch Y. The circuit
connection which connects the two spools of the telephone is grounded.

page_text: ཨ་ns སྦTI
the two contact bolts of another pair of the switch bolts.
Other Stue to
The third pair of contact bolts of the switch Y are not connected with any
apparatus and on them the switch levers normally rest and also rest when two
subscribers lines are left connected together for conversation by means of the
switch plugs.
Each operator has as many pairs of switch plugs as she may need in order to
properly answer the calls and make the connections required of her. For each pair
of plugs there is a clearing out annunciatore and a looping-in switch Y. Each
operator has a telephone and one calling generator will answer for the exchange.
The parts are suitably arranged and mounted for the work of the operator.
In the subscriber's station apparatus, shewn in Figure 4, 1 is the telephone
switch, 2 the subscriber's telephone, 3 the calling generator and 4 the subscriber's
signal receiving bell.
The switch 1, is the ordinary gravity switch operated by the weight of the
telephone when placed upon it.
2 is the ordinary hand magneto receiving telephone. It may be supplemented by
a transmitting telephone as required.
The calling generator 3, has the usual automatic device by which its armature
is shunted or short circuited from the circuit while the generator is not being
operated.
The signal receiving bell is such as will respond to currents passing through it
which are sent from the operator's calling generator.
The circuits of the subscriber's station apparatus are as shown but may be varied
therefrom and produce substantially the same results. When the telephone is on
its switch it is shunted or short circuited from the line circuit and when it is
removed from the switch the shunt or short circuit is opened. The armature of the
calling generator is as heretofore stated shunted or short circuited, except when the
generator is operated. The signal receiving bell is in a ground connection of
the line which is closed while the telephone is on the switch and opened when the
telephone is removed from the switch.
The subscriber's station apparatus should be so connected into the line circuit
that the calling generator is between the ground connection through the signal
receiving bell and the normal ground connection at the central office through the
line annunciator.
There are as many switch boards in the central office as may be required for the
size of the exchange. The line annunciators are distributed among the various
boards so that each operator will have substantially the same number of calls to
attend to.
The operation of the system is as follows: When a subscriber wishes to make a
call he operates his calling generator and his line annunciator will be operated to
indicate a call. The operator, ou observing the call, places one of her switch
plugs D in the switch of the line and moves the looping-in switch Y of the pair of
plugs so that the telephone bridges or cross connects their two flexible switch
conductors. By this operation the line is disconnected from its ground connection
through its annunciator and the test battery B₁ and the operator's telephone is on
closed metallic circuit with the line. The subscriber has in the mean time taken
his telephone from its switch and now converses with the operator and tells what
line he wants.
When the operator and subscriber are thus conversing, the clearing out
annunciator of the pair of plugs is in parallel or derived circuit with the operator's
telephone. The annunciator is however of such construction as to offer considerable
resistance or retardation to telephone currents and will therefore not materially
reduce the telephone currents through the telephones.
When the operator finds out what line is wanted she tests the line, as will here-
after be indicated, to find out whether it is already switched or in use. If she
finds that it is not in use she places the other plug of the pair of plugs in its line

page_text: Switch, the two lines are thus connected together in a closed metallic circuit for
conversation and the second line is also disconnected from the ground connection
through its annunciator and the test battery B. The closed metallic circuit is
bridged or cross connected by the clearing out annunciator and also by the
telephone of the operator.
The operator then moves the switch Y of the pair of plugs so that its levers are
in contact with the bolts which are connected to the calling generator B. A calling
current will thereby pass through the signal receiving bell of the subscriber wanted
and ring the bell. The circuit through which the calling current passes is from the
ground through the calling generator to both sides or branches of the line in derived
or parallel circuit and thence to ground at the subscriber's station through his
signal bell. The resistance of the two sides or branches of the parallel circuit
should be practically the same and practically the same amount of current will
therefore pass through both. The clearing out annunciatore will not be operated
on sending the signal because the resistances of the various parts of the circuit are
such that practically no current will then pass through it.
If the subscriber with whom the call originated had replaced his telephone on its
switch, calling current would pass through his signal bell also and ring it.
The operator, after sending the calling current to line, places the switch Y so
that neither the telephone nor the generator is connected to the line. The two
lines are then connected in a closed metallic circuit for conversation and this circuit
is bridged or cross connected by the clearing out annunciator v only.
The operator can at any time connect her telephone in another bridge or cross
connection to the closed circuit of the lines and determine by listening whether the
subscribers are through conversation.
When they are through conversation either may operate his calling generator
and send a current through his metallic circuit line, which will pass through the
clearing out annunciator which bridges or connects the two sides of the circuit
and operate the annunciator. The operator will then remove the plugs from the
line switches and the two lines are again in their normal condition.
The arrangement of calling herein described, whereby the clearing out annun-
ciator which bridges or cross connects a complete metallic circuit between two
subscribers is not operated, or caused to indicate, when the operator sends a signal
to line, is of especial use where connections are made through two or more central
offices, each of which has a clearing out annunciator which bridges the circuit.
Otherwise the operator at another central office than that where the call is being
made might have a clearing out annunciator indicate a call and not know whether
it is occasioned by another operator calling or by a subscriber sending a clearing
out signal.
Various modifications of the system of exchange operation are possible which
would still embody my invention; for example the two sides of each metallic circuit
line may be normally on closed circuit to each other at the central office and the
line annunciator switched from the circuit by the opening of a pair of switch contacts
when a plug is placed into one of its switches for connection with another line; or
the line annunciators may remain in circuit with their various lines when the lines
are switched, and when two lines are then connected together into a closed metallic
circuit for conversation the circuit will be bridged or cross connected by the two
line annunciators, as well as by the clearing out annunciator of the pair of plugs
used in making the connection. In such an arrangement the line annunciators also
should be of such a construction as to offer considerable resistance and retardation
to telephone currents. With such an organization it is possible for a subscriber to
operate his line annunciator in sending in a call and to operate the clearing out
annunciator and not operate his line annunciator, in sending a clearing out signal,
by special arrangements of apparatus and circuits known in the art.
In the modification of the operators cord or connecting apparatus shown in
Figure 5, the clearing out annunciator v bridges or cross connects the two flexible
conductors connecting the pair of plugs. By means of the switch Y the operator's

page_text: t
telephone may, at the will of the operator, be placed in another bridge or cross
connecting circuit to said conductors. By means of the two keys kk the operator
may disconnect the two contacts of either plug from the other plug and from the
clearing out annunciator and connect its two contacts to the two sides respectively
of the calling generator B. With this arrangement of apparatus the subscriber's
signal receiving bell will be normally in the direct metallic circuit of his line and
not in the normal ground connection of the line. This modification embodies
the clearing out feature of my invention but not the signalling feature of it.
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, two metallic circuit lines and switching or
connecting devices at the central office for connecting them together in metallic
circuit for conversation, in combination with a special clearing out annunciator at
the central office in a bridge or cross-connecting circuit to said metallic circuit, an
operator's telephone and switching devices by which the operator may at will
establish through said telephone a second bridge or cross connecting circuit to
said metallic circuit.
2. In a telephone exchange system, metallic circuit lines, a switch board at the
central office and a switch on said board for each of said lines, each switch having
two contact pieces to which the two sides or branches of its line are respectively
connected, in combination with a pair of loop switch plugs, each plug adapted to
be placed into each of said switches and when placed into a switch its two contact
pieces forming connection with the two contact pieces of the switch, the two contact
pieces of one plug being connected to the two contact pieces of the other plug,
respectively by two flexible switch conductors and a clearing out annunciator in a
permanent or solid bridge or cross connection between said conductors.
3. In a telephone exchange system, two metallic circuit lines and a loop switching
or connecting device at the central office temporarily connecting them together into
a metallic circuit for conversation, in combination with a clearing out annunciator
special to said loop switching or connecting device in a permanent or solid bridge
or cross connection between the two loop conductors of said device.
4. In a telephone exchange systemi, two metallic circuit lines and a loop
switching or connecting device at the central office temporarily connecting them
together into a metallic circuit for conversation, in combination with a clearing out
annunciator special to said loop switching or connecting device in a permanent or
solid bridge or cross connection between the two loop conductors of said device, an
operator's telephone and switching apparatus whereby at the will of the operator
said telephone is connected in another bridge or cross connection to said loop
conductors.
5. In a telephone exchange system, two metallic circuit lines and a loop
switching or connecting device at the central office temporarily connecting them
together into a inetallic circuit for conversation, a clearing out annunciator special
to said loop switching or connecting device, an operator's telephone and switching
apparatus whereby the operator may at will leave said metallic circuit bridged by
two connections containing the annunciator and telephone respectively or by one
circuit containing the annunciator.
6. In a telephone system, two metallic circuit lines normally on closed circuit at
their subscriber's stations and temporarily connected together in metallic circuit for
conversation, in combination with a calling generator or battery at the central
office grounded on one side, and temporarily connected on its other side for calling
to the two sides or branches of said metallic circuit, a normal ground connection
for each line at its subscriber's station and a signal bell in each of such ground
connections.
7. In a telephone exchange system, two metallic circuit lines normally on closed
circuit at their subscriber's stations and temporarily connected together in metallic

page_text: circuit for conversation, in combination with a clearing out annunciator at the
central office in a bridge or cross connection to said metallic circuit.
8. In a telephone exchange system, two metallic circuit lines normally on closed
circuit at their subscriber's stations and temporarily connected together at the
central office, a ground connection for each line at its subscriber's station normally
closed by the telephone but opened on the taking of the telephone from the switch,
and a signal receiving bell at each subscriber's station in the ground connection of
his line, in combination with an annunciator at the central office in a bridge or
cross connection between the two sides or branches of the metallic circuit, and a
calling generator or battery at the central office grounded on one side and tem-
porarily connected for calling to the two sides or branches of said metallic circuit,
the resistance of the two parallel circuits or conductors from said bridge to the
ground connection at each subscribers station being normally substantially equal;
whereby the signal receiving bell at either subscriber's station is rung by the calling
current when his telephone is on its switch but the annunciator in the bridge
connection is not operated by said current.
Dated this 5th day of Nov 1800
CARPMAEL & Co.,
Agents for the Applicant.