Improvements in Telephony.
Year: 1890

page_text: Date of Application, 25th Mar., 1890
Complete Specification Left, 24th Dec., 1890-Accepted, 7th Feb., 1891
PROVISIONAL OF PUITIGATION
Improvements in Telephony.
I, MILO GIFFORD KELLOGG, of 135, 47th Street, Chicago, Illinois, United
States, Electrical Engineer, do hereby declare the nature of this invention to be
as follows:-
My invention relates to multiple switch board telephone exchange systems and is
adapted to the various methods of working including the single and metallic circuit
systems the single cord and the double cord switching systems, the various systems
of testing and switching and various systems of calling.
In the existing multiple switch board systems the number of switch boards at the
central office depends on the number of lines connected
the form of apparatus
upon
and upon the working capacity of the operators. Usually there is one board for
every two hundred lines. On each board is provided a switch or switching con-
nection for each line of the exchange. There is also signalling apparatus by which
each subscriber can call the central office. Also apparatus by which the operator
at any board may answer the call and connect for conversation any two lines which
have their switches or switching connection at that board.
It is evident that in the multiple switch board system as outlined above, the
number of switch boards and also the number of switches on cach board increases
with the number of lines of the exchange. For instance for an exchange of five
thousand lines there will generally be about twenty five multiple switch boards with
five thousand switches on each board and for an exchange of ten thousand lines,
about fifty boards and ten thousand switches on each board. The cost per line of
the multiple switch board system increases with the number of lines and in the large
exchanges the apparatus becomes very expensive.
The switch for each line occupies a certain space on the face of the switch board
and the size of the board which an operator can conveniently serve is limited. The
number of lines which can be operated in one exchange is therefore limited. With
the present apparatus it is found that about fifteen thousand lines is the maximum
which can be operated in one central office of an exchange system.
My invention is intended to reduce the amount of apparatus required for a given
number of lines operated in one central office, and to increase the number of lines
which can be operated in one central office.
I divide the lines of the exchange into a number of divisions and I divide the
switch boards of the exchange into the same number of divisions. Each division of
lines has its own division of boards but the lines are connected also to boards of
the other divisions as will hereafter be described. The number of divisions and
the number of boards in each division will depend on the size and activity of the
exchange. On each board of each division is a switch or switch connection for
each line of the division to which the boards belong. Each line has also a switch
or switching connection on one board in each of the other divisions. The switches
are preferably distributed so that there are approximately the same number on each
board. I provide electric calling or signalling apparatus by which each subscriber
can at will signal to the operator at one board in each division which contains a
switch or switching connection of his line. I also provide apparatus by which the
operator at any board can connect any two lines which have their switches or
switching connections at that board.
It is evident that when the lines and the boards are divided into two equal
divisions there are but little more than half as many switches or switch connections
as in a system requiring a switch on each board for each line; and that when the

page_text: lines and boards are divided into four divisions, there are but little more than one
fourth as many switches required. The cost of the switches for a given number of
lines would therefore be reduced to about one half or one quarter and the number
of lines which can be accomodated on a board of a given size can be nearly double
or quadrupled by dividing the lines and boards into two or four divisions and
connecting them substantially as described. Three or six or any other number of
divisions may be made and produce analogous results.
In the accompanying drawings designed to illustrate my invention,
Figure 1 shows a central office switch board system with connections for a
metallic circuit exchange having its lines and switch boards in four corresponding
divisions.
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 an end view of the generator armature shaft with two contact springs
bearing on diametrically opposite segments of the shaft.
Figure 6 shows a polarized annunciator which may be used at the central office.
as will hereafter be described.
Figure 7 shows a retardation coil which may be used as will hereafter be
described.
In Figure 1 four divisions of boards with two boards in cach division are
represented. Each board is shown in sectional view as a section indicated by the
line de of the switch board shown in Figure 2. The four divisions of boards are
indicated by the letters A, B, C and D respectively. The two boards of division A
are marked A' A² respectively: those of division B, B1 and B2 those of
division C, C and C and those of division D, D' and D² respectively. The two
lines shown and connected belong to divisions A and B respectively.
I prefer to designate the divisions of lines by letters or designations which shall
be similar to the designations which are given to the respective divisions of boards.
Each line is preferably indicated in the exchange catalogue or list by the letter or
designation of its division; as for instance one line may be designated 32 A.;
another 365 B, another 376 C, and a fourth 4 D.
Each line of division A has a switch or switching connection on each board of
division A and on one board of each of the other divisions; each line of division B
has a switch or switch connection on each board of division B and on one board of
each of the other divisions and cach line of each of the other divisions has a switch
on each board of its division and on one board of each of the other divisions.
Each of the switches shown in Figure 1 has a contact spring which normally
bears on
an insulated point, but is separated from the point when a switch
plug is inserted into the switch and has a third contact piece insulated from
the others. This third or insulated contact piece is so placed that a test plug can
readily be applied to it and so that one of the contact pieces of a loop switch plug
inserted into the switch will form connection with it. The switches are adapted to
receive the loop switch plugs shown in Figure 3 and when a plug is inserted into a
switch it forces the switch spring from the contact point on which it normally bears
and the two contact pieces of the plug form connection with the switch spring and
the third or insulated contact piece of the switch. gg are the contact springs of
the switches. hh the contact points on which the springs normally bear and ji are
the third or insulated contact pieces of the switches. a bare rubber strips of the
shape substantially as shown on which the metal parts of the switches are mounted
and through the front of which are the switch holes 11. These holes are rectilinear
holes adapted to receive the switch plugs and cause them to operate the switches as
described.
R is an electric rheotome or circuit breaker which may be constructed sub-

page_text: as shown or any other way so as to make and break alternately the
circuit in which it is placed.
The annunciators marked are shown in greater detail in Figure 6. They are
polarized annunciators of known construction. Other forms of annunciators may be
used which will respond or indicate to a current of only one polarity.
The retardation coils marked ww (of which there is one for each line) and shown
in greater detail in Figure 7 consist essentially of two cores of iron surrounded by
helices of fine wire and connected at their two ends by cross bars of iron. The two
helices of a coil are so connected that a current passing through the coil will
magnetize their respective cores in the same direction in the closed magnetic
circuit.
There are four polarized annunciators for each metallic circuit line. They are
located at boards of the four divisions at those boards where the line has switches
or switch connections and where the calls or connections of the line are to be
attended to. The annunciators are preferably distributed equally among the
different boards.
The lines are connected to the central office switch boards and apparatus as
follows one side or branch of a line is connected to all the contact pieces jj of the
switches of the line on the different boards. It afterwards passes successively
through two of the polarized annunciators of the line and the retardation coil of the
line to earth. The other side or branch of the line passes successively through the
several pairs of contacts g h of the switches of the line on the different boards,
passing in each case to the spring first. It then passes successively through the
circuit of the two other polarized annunciators of the line and is then connected to
earth through the rheotome R which is common to all the lines. The two
annunciators in the circuit of each side or branch of a line as above described are
so connected as to be actuated by currents of opposite polarity.
In the operator's cord apparatus shown in Figure 3 D D are a pair of loop
switch plugs adapted to be inserted into the line switches and when a plug is
inserted into a switch, it operates it as heretofore described; is the rubber insulation
of the plug and s s' are its two insulated contact pieces. The contact pieces of the
pair of plugs are connected to the other apparatus by double or loop flexible cords.
H is a switching device for a pair of plugs and cords. This switching device
has a rubber frame d which supports and insulates the various parts; ff are two
contact springs and 1, 2, 3 and 4 are contact points for the switching device, located
and insulated substantially as shown, and which form connections with springs ffƒ³
as will be described. 7 is a sliding bar which passes through frame d. It terminates
at one end in the knobe by means of which the operator may draw the bar in and
out nop is an irregularly shaped rubber piece placed at the other end of the
bar and carried by it in its reciprocating motion. Together they may be called
the commutator piece of the switch. The knob e and the piece p furnish stops
which limit the inward and outward motion of the commutator piece. When
this piece is in its inner position and are in contact with points 2 and 3
respectively.
When it is in its middle position so that the springs rest on part o, spring f is out
of contact with either 1 or 2 and spring is in contact with 4. When it is moved
to its outer position and are in contact with 1 and 3 respectively. The com-
mutator piece is placed normally or when the switching device is not in use in its
inner position described above. t is the operator's telephone. S her calling generator
or battery, S' her test battery and is a resistance coil. Each operator has one
of each of said parts. is a clearing out annunciator for the pair of cords and it
need not to be a polarized annunciator.
The connections of the operator's cord apparatus are as follows: the two contact
pieces ss of a pair of plugs are connected by two conductors of the pair of cords
and the pieces s s¹ are connected by the two other conductors. The spring of the
switching device which belongs to the pair of plugs is connected to the circuit
which connects ss, and f' is connected to the circuit which connects ss. The

page_text: operator's telephone and resistance coil are connected in a circuit which connects
points 2 and 3. The calling generator or battery is connected on one side to point 3,
on its other side to point 1. The clearing out annunciator is connected on one side
to the circuit which connects ss and on its other side to point 4. The middle part
of the telephone coil is connected to.earth through the test battery S'.
Each operator has as many pairs of switch plugs and cords, with their switching
devices and clearing out annunciators, as she may need for the work and they are
connected to her special apparatus substantially as shown and described. The cords
should be long enough so that she can reach any switch at her board and the apparatus
should be conveniently mounted for her work.
In the subscriber's station apparatus shown in Figure 4, 5 is the telephone switch,
6 is the signal receiving bell, 7 is the calling generator, 8 is the subscriber's telephone,
9, 9, 9, 9, are calling keys and 10 is a clearing out switch.
The
The calling generator is a usual construction of telephone magneto calling generator
modified as follows:-There is an insulated contact piece on the armature shaft
which is a half circle and to which one end of the armature coil is connected.
remaining parts of the circle is an insulation as shown in Figure 5. There are two
stationary insulated springs which bear on diametrically opposite parts of that part
of the shaft of which the insulated piece is a part, and which in the movement of
the armature alternately make and break connection with said insulated contact
piece. The contact springs are so placed in relation to the armature that one of
them is in contact with said insulated piece on the shaft when a current of one
polarity is generated in the coil, and the other is in contact with it when a current
of the other polarity is generated.
The calling keys 9, 9, 9, 9, are three point keys, each having one point on which
the lever normally bears and another point normally insulated from the lever
and with which it comes into contact when it is pressed or operated by the subscriber
in calling.
The clearing out switch 10 is a hand switch employed to switch an apparatus
from one circuit to another. It contains a reciprocating block carrying three
conducting plates p q and u insulated from one another. Upon plate p normally rest
a pair of springs m m, while upon plates and a normally rest pairs of springs n n
and oo respectively. The reciprocating block, with its parts is held normally
by a spring in the position shown. When the subscriber presses on the knob of the
block it moves so that m m are out of contact with plate p and are in contact with
plates 9 and u respectively and said plates 7 and u are out of contact with springs o
and are in contact with springs n n respectively.
00
The circuits of the subscriber's station apparatus are substantially as shown and
as follows: One side or branch of the line is connected through the pairs of contact
points normally in contact of two of the calling keys, passing in each case to the
lever first, and it then passes through the two pairs of contacts normally in contact
of the two other keys, passing in each case to the point first. It then connects with
the other side or branch of the line. The line is separated at a point which is in
circuit when the telephone is on its switch and the two ends are connected to the
two springs m m respectively. One of the springs which bear as heretofore described
on the armature shaft is connected to one of the springs a and the other spring n is
connected to the other side of the armature coil from that to which the msulated
contact piece on the shaft is connected. This last spring a bears on plate and the
spring o which also bears on that plate is connected with the ground."
q
The two calling keys whose connection to the line circuit was first described have
their lower contact points (those against which the levers may be pressed by the
subscriber) connected to said two contact springs respectively of the calling generator,
and the lower contact points of the two other keys are also connected to the two
springs respectively.
The telephone switch connections are such that the calling keys and clearing out
switch are not switched or shunted from the line when the apparatus is in condition
for calls to be made to the central office.

page_text: It will be seen from the drawings and the description given of the apparatus and
connections that when the subscriber presses on one of the two keys whose connection
was first described (marked A and B) and operates his calling generator, one side
or branch of the line will be disconnected from the other and have a calling current
of one polarity sent over it, and when the other key of the pair is pressed and the
generator operated, a current of the opposite polarity will go to the circuit of such
branch. The circuit is from the subscriber's ground established on pressing the key
through the armature coil to such branch of the line and through its circuit and
that of the two polarized annunciators connected in it to the office ground heretofore
described for that branch of the line. The subscriber can therefore operate, at will,
either of the two annunciators connected with said branch of the line. In like
manner he can, by operating his generator and pressing on one or the other keys
(marked C and D) operate either of the annunciators connected in circuit with the
other branch of the line. The subscriber can therefore at will cause either of his
four annunciators in the central office to indicate a call.
I prefer to mark and designate the four keys of a subscriber's station A B C
and D respectively, to correspond with the four divisions of boards at which
respectively are the annunciators which they operate.
The operation of the system is as follows: When a subscriber wishes to converse
with any other subscriber he finds out in the exchange list or otherwise the
designation or division to which the line wanted belongs. He then, by pressing on
the proper key and operating his generator, causes his annunciator which is located
at a board of the division to which the line wanted belongs to indicate a call. For
instance if the line wanted belongs to division A he would on calling press on
key A if it belongs to division B he would press on key B; if to division C on
key C, and if to division D on key D. He thereby calls an operator located at a
board where both he and the subscriber wanted has a switch or switch connection.
The operator on observing the indication places one plug of a pair of her switch
plugs in the switch of the line calling and her telephone is thereby included in a
closed circuit with the line. She then by conversation finds out what line is
wanted. The circuit is completed by the two conductors of the cord used, the
contact springs connected to them, the contact points 2 and 3 which are then
in contact with and the circuit wire, which includes the operator's telephone
and resistance coil which is connected to points 2 and 3. When the operator finds
out what line is wanted she places the contact pieces of the other plug of the pair
on the contact piece of the switch of the line wanted. If such line is not
switched at any board there is a complete test circuit established from carth
through the test battery and one portion of the telephone coil to the line wanted
and through its circuit and the pairs of contact points of its switches on the
various boards to earth through the rheotome. The operator will then hear in the
telephone the sound caused by the make and break of the rheotome if the line
tested is switched at any board, the test circuit above described is open at the pair
of contact points of the switch where the line is switched and the operator will
not distinguish the make and break of the rheotome, she will therefore know whether
or not the line is ready in use. If it is not in use she places the plug in the switch
and both lines then disconnected from their normal ground connection through the
rheotome are connected in a metallic circuit which is bridged or cross connected by
a circuit which includes the operator's telephone and resistance coil. The operator
then presses the moveable commutator piece to its inner position so that contact
springs rest on and are in contact with 1 and 3 respectively. The bridge
circuit which contains the telephone and resistance coil is thereby removed and the
metallic circuit of the two lines is bridged or cross connected by a circuit which
contains the calling generator or battery and a calling current will go in split
current over both lines and operate their signal bells. The operator then moves
the commutator piece to its central position so that the springs rest on o and both
the telephone and calling generator are disconnected from the circuit of the lines
and the circuit is bridged or cross connected by a circuit which contains the clearing

page_text: out annunciator v. This bridge circuit through the clearing out annunciator is
completed by the contact between f' and 4.
The clearing out annunciator should preferably be of high resistance and of
considerable retardation to telephone currents.
If at any time the operator desires to listen to the circuit of the two lines to
letermine whether they are through for conversation she moves the commutator
picce so that the springs ff rest on n and thereby opens the bridge connection
ihrough the clearing out annunciator and establishes a bridge connection through
the telephone and resistance coil. The resistance coil is intended to prevent an
undue amount of any telephone current which may be passing from being diverted
through the bridge circuit and be used or not according to the character of the
circuits and the resistance of the telephone and other parts.
When the subscribers are through for conversation, either one may press on his
clearing out switch and by so doing switch his generator into his closed line circuit
and on operating his generator cause the clearing out annunciator to indicate a
clearing out signal.
To clear out a connection the operator takes the plugs from the two switches and
places the commutator piece of their switching device in its normal position where
the springs f rest on points 2 and 3. The lines and the apparatus are then
ready to receive and make new calls by the same operations as heretofore
described.
It will be seen that when two lines are connected together as above described
their circuit is connected to earth at the central office through the permanent
ground connection of each line through two of its annunciators and its retardation
coil. The use of the retardation coil is to prevent or minimize any effect on the
circuit which might arise from other metallic circuits connected in like manner to
earth. The annunciators themselves offer a retardation to such an effect and the
use size and character of the special retardation coils will depend on the con-
struction and condition of the other apparatus and circuits of the exchange.
The resistance in the permanent ground connections of the lines through their
annunciators and retardation coils should be such that the clearing out current will
not pass through them to operate the annunciators.
The apparatus illustrated in the drawings is for a metallic circuit exchange in
which the lines and the switch boards are divided into four divisions and in which
the double cord system of switching is employed. My invention is applicable to
other systems of exchange and of switching and to other divisions of the boards
and lines.
When the metallic circuit lines and the boards are divided into two divisions,
the calls for each line to the two divisions of boards may be made on two annun-
ciators properly constructed and connected, when the lines and boards are divided
into three divisions three annunciators may be used located in the three divisions of
boards. When the lines and boards are divided into more than four divisions, a
special calling wire or wires may also be employed for each line in each of which
may be placed two polarized annunciators with apparatus and connections by which
the subscriber may at will operate either of them.
For ground circuit lines two polarized annunciators may be employed in the
circuit of each line; and if it is desired to have more than two divisions of boards
and lines, special calling wires may also be employed in which are placed additional
annunciators with apparatus by which the subscriber may operate at will his
annunciators located in the different divisions of boards. By this way or by other
ways the lines and boards of either a single and metallic circuit system may be
divided into any number of divisions connected as heretofore indicated and the
subscribers be provided with apparatus and connections by which they may at will
call to an operator at any of the divisions of boards and where his line has a switch
or switching connection. Special calling circuits common to several subscribers
may also be employed to transmit part or all of the calls of the exc' ange.
Batteries may also be employed in making the calls, with calling commutators or

page_text: switches by which the subscriber may at will direct currents of the proper polarity
to either calling circuit.
If a single cord system of operation were employed one switch could be employed
for each line on each board of its division and a cord and plug connection could be
used for the line on a board in each of the other divisions.
Various other systems of testing and of operation than those described and
indicated may be employed in carrying out my invention.
Dated this 25th day of March 1890.
CARPMAEL & Co.,
Avents.
COMPLETE SPECIFICATION.
Improvements in Telephony.
I, MILO GIFFORD KELLOGG, of 135, 47th Street, Chicago, Illinois, United
States, 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 multiple switch board telephone exchange systems and is
adapted to the various methods of working including the single and metallic circuit
systems the single cord and the double cord switching systems, the various systems
of testing and switching and various systems of calling.
In the existing multiple switch board systems the number of switch boards at
the central office depends on the number of lines connected, upon the form of
apparatus and upon the working capacity of the operators. Usually there is one
board for every two hundred lines. On each board is provided a switch or switching
connection for each line of the exchange. There is also signalling apparatus by
which each subscriber can call the central office. Also apparatus by which the
operator at any board may answer the call and connect for conversation any two
lines which have their switches or switching connection at that board.
It is evident that in the multiple switch board system as outlined above, the
number of switch boards and also the number of switches on each board increases
with the number of lines of the exchange. For instance for an exchange of five
thousand lines there will generally be about twenty five multiple switch boards
with five thousand switches on each board, and for an exchange of ten thousand
lines, about fifty boards and ten thousand switches on each board. The cost per
line of the multiple switch board system increases with the number of lines and in
the large exchanges the apparatus becomes very expensive.
The switch for each line occupies a certain space on the face of the switch board
and the size of the board which an operator can conveniently serve is limited. The
number of lines which can be operated in one exchange is therefore limited.
With
the present apparatus it is found that about fifteen thousand lines is the maximum
which can be operated in one central office of an exchange system.
My invention is intended to reduce the amount of apparatus required for a given
number of lines operated in one central office, and to increase the number of lines
which can be operated in one central office.
1 divide the lines of the exchange into a number of divisions and I divide the
switch boards of the exchange into the same number of divisions. Each division of
lines has its own division of boards but the lines are connected also to boards of the
other divisions as will hereafter be described. The number of divisions and the
number of boards in each division will depend on the size and activity of
the exchange.. On each board of each division is a switch or switch connection for
each line of the division to which the boards belong. Each line has also a switch
or switching connection on one board in each of the other divisions. The switches
are preferably distributed so that there are approximately the same number on each
board. I provide electric calling or signalling apparatus by which each subscriber can
at will, signal to the operator at one board in cach division which contains a switch

page_text: or switching connection of his line. I also provide apparatus by which the operator
at any board can connect any two lines which have their switches or switching
connections at that board.
It is evident that when the lines and the boards are divided into two equal
divisions there are but little more than half as many switches or switch connections
as in a system requiring a switch on each board for each line; and that when the
lines and boards are divided into four divisions there are but little more than one
fourth as many switches required. The cost of the switches for a given number
of lines would therefore be reduced to about one half or one quarter and the number
of lines which can be accomodated on a board of a given size can be nearly double
or quadrupled by dividing the lines and boards into two or four divisions and con-
necting them substantially as described. Three or six or any other number of
divisions may be made and produce analogous results.
In the drawings left with the Provisional Specification and designed to illustrate
my invention.
Figure 1 shows a central office switch board system with connections for a
metallic circuit exchange having its lines and switch boards in four corresponding
divisions.
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.
any
Figure 4 is a diagram showing the apparatus which may be used at subscriber's
station.
Figure 5 is an end view of the generator armature shaft with two contact springs
bearing on diametrically opposite segments of the shaft.
Figure 6 shows a polarized annunciator which may be used at the central office
as will hereafter be described.
Figure 7 shows a retardation coil which may be used as will hereafter be
described.
In illustrating my invention I show it applied to metallic circuit lines because
such lines are preferably in large city exchanges; the utility of the invention is not
however confined to such lines.
In Figure 1 four divisions of boards with two boards in each division are repre-
sented. Each board is shown in sectional view as a section indicated by the line de
of the switch board shown in Figure 2. The four divisions of boards are indicated
by the letters A, B, C and D respectively.
The two boards of division A. are
marked A A respectively; those of division B, 131 and B2; those of division C, C
and C2 and those of division D, D' and D2 respectively. The two lines shown
and connected belong to divisions A and B respectively.
I prefer to designate the divisions of lines by letters or designations which shall
be similar to the designations which are given to the respective divisions of boards.
Each line is preferably indicated in the exchange catalogue or list by the letter or
designation of its division; as for instance one line may be designated 32 A:
another 365 B, another 376 C, and a fourth 4 D.
Each line of division A. has a switch or switching connection on each board of
division A and on one board of each of the other divisions; each line of division B
has a switch or switch connection on each board of division B and on one board of
cach of the other divisions and each line of each of the other divisions has a switch
on each board of its division and on one board of each of the other divisions.
Each of the switches shown in Figure 1 has a contact spring which normally bears
on an insulated point, but is separated from the point when a switch plug is inserted
into the switch and has a third contact piece insulated from the others. This third
or insulated contact piece is so placed that a test plug can readily be applied to it
and so that one of the contact pieces of a loop switch plug inserted into the
switch will form connection with it. The switches are adapted to receive the loop
switch plugs shown in Figure 3 and when a plug is inserted into a switch it force

page_text: the switch spring from the contact point on which it normally bears and the two
contact pieces of the plug form connection with the switch spring and the third or
insulated contact piece of the switch. ggare the contact springs of the switches,
the contact points on which the springs normally bear and jj are the third or
insulated contact pieces of the switches. a bare rubber strips of the shape
substantially as shown on which the metal parts of the switches are mounted
and through the front of which are the switch holes 11. These holes are rectilinear
holes adapted to receive the switch plugs and cause them to operate the switches as
described.
R is an electric rheotome or circuit breaker which may be constructed substan-
tially as shown or in any other way 50 as to make and break alternately the circuit
in which it is placed.
•
The annunciators marked are shown in greater detail in Figure 6. They
are polarized annunciators of known construction. Other forms of annunciators
may be used which will respond or indicate to a current of only one polarity.
Variations of the signalling apparatus at the central office may involve variations
of the apparatus at the subscriber's station but such adaptations will be obvious to
those skilled in the art.
The retardation coils marked w (of which there is one for each line) and shown
in greater detail in Figure 7 consist essentially of two cores of iron surrounded
by helices of fine wire and connected at their two ends by cross bars of iron. The
two helices of a coil are so connected that a current passing through the coil will
magnetize their respective cores in the same direction in the closed magnetic
circuit.
There are four polarized annunciators for each metallic circuit line. They are
located at boards of the four divisions at those boards where the line has switches
or switch connections and where the calls or connections of the line are to be
attended to. The annunciators are preferably distributed equally among the
different boards.
The lines are connected to the central office switch boards and apparatus as
follows One side or branch of a line is connected to all the contact pieces of the
switches of the line on the different boards. It afterwards passes successively
through two of the polarized annunciators of the line and the retardation coil of
the line to earth. The other side or branch of the line passes successively through
the several pairs of contacts g h of the switches of the line on the different boards,
passing in each case to the spring first. It then passes successively through the
circuit of the two other polarized annunciators of the line and is then connected to
earth through the rheotome R which is common to all the lines. The two annun-
ciators in the circuit of each side or branch of a line as above described are so
connected as to be actuated by currents of opposite polarity.
In the operator's cord apparatus shown in Figure 3 D D are a pair of loop switch
plugs adapted to be inserted into the line switches and when a plug is inserted into
a switch, it operates it as already described, is the rubber insulation of the plug
and are its two insulated contact pieces. The contact pieces of the pair of
plugs are connected to the other apparatus by double or loop flexible cords.
H is a switching device for a pair of plugs and cords. This switching device
has a rubber frame d which supports and insulates the various parts; are two
contact springs and 1, 2, 3 and 4 are contact points for the switching device,
located and insulated substantially as shewn, and which form connection with
springs as will be described. 9 is a sliding bar which passes through frame d.
It terminates at one end in the knob e by means of which the operator may draw
the bar in and out; n o p is an irregularly shaped rubber piece placed at the other
end of the bar y and carried by it in its reciprocating motion. Together they may
be called the commutator piece of the switch. The knob e and the piece furnish
P
stops which limit the inward and outward motion of the commutator piece. When
this piece is in its inner position and are in contact with points 2 and 3
respectively.

page_text: When it is in its middle position so that the springs rest on part o, spring is out
of contact with either 1 or 2 and spring is in contact with 4. When it is moved
to its outer position and are in contact with 1 and 3 respectively. The com-
mutator piece is placed normally or when the switching device is not in use in its
inner position described above. t is the operator's telephone. S her calling
generator or battery, St her test battery and n is a resistance coil. Each operator
has one of each of said parts. is a clearing out annunciator for the pair of cords
and it need not to be a polarized annunciator.
The connections of the operator's cord apparatus are as follows: The two contact
pieces s of a pair of plugs are connected by two conductors of the pair of cords and
the pieces ss are connected by the two other conductors. The spring of the
switching device which belongs to the pair of plugs is connected to the circuit which
connects ss, and f¹ is connected to the circuit which connects ss. The operator's
telephone and resistance coil are connected in a circuit which connects points 2 and 3.
The calling generator or battery is connected on one side to point 3, on its other
side to point 1. The clearing out annunciator is connected on one side to the
circuit which connects ss and on its other side to point 4. The middle part of the
telephone coil is connected to earth through the test battery St.
Each operator has as many pairs of switch plugs and cords, with their switching
devices and clearing out annunciators, as she may need for the work and they are
connected to her special apparatus substantially as shewn and described. The cords
should be long enough so that she can reach any switch at her board and the
apparatus should be conveniently mounted for her work.
In the subscriber's station apparatus shown in Figure 4, 5 is the telephone switch,
6 is the signal receiving bell, 7 is the calling generator, 8 is the subscriber's
telephone, 9, 9, 9, 9, are calling keys and 10 is a clearing out switch.
The calling generator is a usual construction of telephone magneto calling
generator modified as follows:-There is an insulated contact piece on the arma-
ture shaft which is a half circle and to which one end of the armature coil
is connected. The remaining parts of the circle is an insulation as shown in
Figure 5. There are two stationary insulated springs which bear on diametrically
opposite parts of that part of the shaft of which the insulated piece is a part,
and which in the movement of the armature alternately nake and break connection
with said insulated contact piece. The contact springs are so placed in relation to
the armature that one of them is in contact with said insulated piece on the shaft
when a current of one polarity is generated in the coil, and the other is in contact
with it when a current of the other polarity is generated.
The calling keys 9, 9, 9, 9, are three point keys, each having one point on
which the lever normally bears and another point normally insulated from the
lever and with which it comes into contact when it is pressed or operated by the
subscriber in calling
The clearing out switch 10 is a hand switch employed to switch an apparatus
from one circuit to another. It contains a reciprocating block carrying three
conducting plates pq and insulated from one another. Upon plate normally
rest a pair of springs m m, while upon plates 7 and u normally rest pairs
of springs n n and o o respectively. The reciprocating block, with its parts is
held normally by a spring in the position shown. When the subscriber presses
on the knob of the block it moves so that m m are out of contact with plate p
and are in contact with plates 9 and u respectively and said plates and
are out of contact with springs o o and are in contact with springs n n respectively.
The circuits of the subscriber's station apparatus are substantially as shewn and
as follows: One side or branch of the line is connected through the pairs of
contact points normally in contact of two of the calling keys, passing in each case
to the lever first, and it then passes through the two pairs of contacts normally in
contact of the two other keys, passing in each case to the point first. It then
connects with the other side or branch of the line. The line is separated at a
int which is in circuit when the telephone is on its switch and the two ends are

page_text: connected to the two springs m m respectively. One of the springs which bear as
already described on the armature shaft is connected to one of the springs n and
the other spring a is connected to the other side of the armature coil from that to
which the insulated contact piece on the shaft is connected. This last spring n
bears on plate and the spring e which also bears on that plate is connected with
the ground.
The two calling keys whose connection to the line circuit was first described
have their lower contact points (those against which the levers may be pressed by
the subscriber) connected to said two contact springs respectively of the calling
generator, and the lower contact points of two other keys are also connected to the
two springs respectively.
The telephone switch connections are such that the calling keys and clearing out
switch are not switched or shunted from the line when the apparatus is in condition
for calls to be made to the central office.
It will be seen from the drawings and the description given of the apparatus and
connections that when the subscriber presses on one of the two keys whose
connection was first described (marked A and B) and operates his calling generator,
one side or branch of the line will be disconnected from the other and have a
calling current of one polarity sent over it, and when the other key of the pair is
pressed and the generator operated, a current of the opposite polarity will go to
the circuit of such branch. The circuit is from the subscriber's ground established
on pressing the key through the armature coil to such branch of the line and
through its circuit and that of the two polarized annunciators connected in it to the
office ground heretofore described for that branch of the line. The subscriber can
therefore operate, at will, either of the two annunciators connected with said branch
of the line. In like manner he can by operating his generator and pressing on one
or the other keys (marked C and D) operate either of the annunciators connected
in circuit with the other branch of the line. The subscriber can therefore at will
cause either of his four annunciators in the central office to indicate a call.
prefer to mark and designate the four keys of a subscriber's station A B C
and D respectively to correspond with the four divisions of boards at which
respectively are the annunciators which they operate.
;
The operation of the system is as follows: When a subscriber wishes to converse
with any other subscriber he finds out in the exchange list or otherwise the
designation or division to which the line wanted belongs. He then, by pressing on
the proper key and operating his generator, causes his annunciator which is located
at a board of the division to which the line wanted belongs to indicate a call. For
instance if the line wanted belongs to division A he would on calling press on
key A if it belongs to division B he would press on key B; if to division C on
key C, and if to division D on key D. He thereby calls an operator located at a
board where both he and the subscriber wanted has a switch or switch connection.
The operator on observing the indication places one plug of a pair of her switch
plugs in the switch of the line calling and her telephone is thereby included in a
closed circuit with the line. She then by conversation finds out what line is wanted.
The circuit is completed by the two conductors of the cord used, the contact
springs connected to them, the contact points 2 and 3 which are then in contact
with and the circuit wire, which includes the operator's telephone and resistance
coil which is connected to points 2 and 3. When the operator finds out what line
is wanted she places the contact pieces of the other plug of the pair on the contact
piece of the switch of the line wanted. If such line is not switched at any board
there is a complete test circuit established from earth through the test battery
and one portion of the telephone coil to the line wanted and through its circuit and
the pairs of contact points of its switches on the various boards to earth through
the rheotome. The operator will then hear in the telephone the sound caused
by the make and break of the rheotome; if the line tested is switched at any board,
the test circuit above described is open at the pair of contact points of the switch

page_text: where the line is switched and the operator will not distinguish the make and break
of the rheotome, she will therefore know whether or not the line is already in use.
If it is not in use she places the plug in the switch and both lines then disconnected
from their normal ground connection through the rheotome are connected in a
metallic circuit. which is bridged or cross connected by a circuit which includes the
operator's telephone and resistance coil. The operator then presses the moveable
commutator piece to its inner position so that contact springs' rest on and are
in contact with and 3 respectively. The bridge circuit which contains the
telephone and resistance coil is thereby removed and the metallic circuit of the two
lines is bridged or cross connected by a circuit which contains the calling generator
or battery and a calling current will go in split current over both lines and operate
their signal bells. The operator then moves the commutator piece to its central
position so that the springs rest on o and both the telephone and calling generator
are disconnected from the circuit of the lines and the circuit is bridged or cross
connected by a circuit which contains the clearing out annunciatore.
This bridge
circuit through the clearing out annunciator is completed by the contact
between and 4.
The clearing out annunciator should preferably be of high resistance and of
considerable retardation to telephone currents.
If at any time the operator desires to listen to the circuit of the two lines to
determine whether the conversation is finished she moves the commutator piece so
that the springs' rest on a and thereby opens the bridge connection through
the clearing out annunciator and establishes a bridge connection through the
telephone and resistance coil. The resistance coil is intended to prevent an undue
amount of any telephone current which may be passing from being diverted through
the bridge circuit and be used or not according to the character of the circuits and
the resistance of the telephone and other parts.
When the subscribers' conversation is finished, either one may press on his clearing
out switch and by so doing switch his generator into his closed line circuit and on
operating his generator cause the clearing out annunciator to indicate a clearing
out signal.
To clear out a connection the operator takes the plugs from the two switches and
places the commutator piece of their switching device in its normal position where
the springs rest on points 2 and 3. The lines and the apparatus are then ready
to receive and make new calls by the same operations as heretofore described.
It will be seen that when two lines are connected together as above described
their circuit is connected to earth at the central office through the permanent
ground connection of each line through two of its annunciators and its retardation
coil. The use of the retardation coil is to prevent or minimize any effect on the
circuit which might arise from other metallic circuits connected in like manner to
earth. The annunciators themselves offer a retardation to such an effect and the
use size and character of the special retardation coils will depend on the construction
and condition of the other apparatus and circuits of the exchange.
The resistance in the permanent ground connections of the lines through their
annunciators and retardation coils should be such that the clearing out current will
not pass through them to operate the annunciators.
The apparatus illustrated in the drawings is for a metallic circuit exchange in
which the lines and the switch boards are divided into four divisions and in which
the double cord system of switching is employed. My invention is applicable to
other systems of exchange and of switching and to other divisions of the boards
and lines.
When the metallic circuit lines and the boards are divided into two divisions, the
calls for each line to the two divisions of boards may be made on two annunciators
properly constructed and connected, when the lines and boards are divided into
three divisions three annunciators may be used located in the three divisions of
boards. When the lines and boards are divided into more than four divisions, a

page_text: special calling wire or wires may also be employed for each line in each of which
may be placed two polarized annunciators with apparatus and connections by which
the subscriber may at will operate either of them.
For ground circuit lines two polarized annunciators may be employed in the
circuit of each line and if it is desired to have more than two divisions of boards
and lines, special calling wires may also be employed in which are placed additional
annunciators with apparatus by which the subscriber may operate at will his
annunciators located in the different divisions of boards.
By this way or by
other ways the lines and boards of either a single and metallic circuit system
may be divided into any number of divisions connected as heretofore indicated and
the subscribers be provided with apparatus and connections by which they may at
will call to an operator at any of the divisions of boards and where his line has a
switch or switching connection. Special calling circuits common to several sub-
scribers may also be employed to transmit part or all of the calls of the exchange.
Batteries may also he employed in making the calls, with calling-commutators or
switches by which the subscriber may at will direct currents of the proper polarity
to either calling circuit.
If a single cords system of operation were employed one switch could be
employed for each line on each board of its division and a cord and plug connection
could be used for the line on a board in each of the other divisions.
Various other systems of testing and of operation than those described and
indicated may be employed in carrying out my invention.
I have above referred to the use of signalling apparatus or annunciators other
than the polarized annunciators which have illustrated and described. Other
ways of producing a variety of signals, or causing the actuation of a variety of
instruments or devices, by currents transmitted over a circuit are well known to
those skilled in the science of electricity. For instance, currents of different
tension may be employed to operate the annunciators; and my invention includes
all such methods by which the signalling apparatus or annunciators may be
individually operated.
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 the combination of telephone lines divided
into several divisions, multiple switch boards for said lines divided into the same
number of divisions, one division of boards for each division of lines, each line
having a switch or switch connection on each board of its division and on one board
in each of the other divisions and switch connecting apparatus whereby the
operator at any board may connect together any two lines which have their
switches or switch connections at his board substantially as set forth.
2. In a telephone exchange system, the combination of telephone lines divided
into several divisions multiple switch boards for said lines divided into the same
number of divisions, one division of boards for each division of lines cach line
having a switch or switch connection on each board of its division and on one
board of each of the other divisions, calling apparatus whereby any subscriber
may at will call to an operator at a board in each division which has a switch or
switch connection for his line and switch connecting apparatus whereby the
operator at any board may connect together any two lines which have switches
or switch connections at his board, substantially as set forth.
3. In a telephone exchange system, the combination of telephone lines divided
into several divisions, multiple switch boards for said lines, divided into the same
number of divisions, one division of boards for each division of lines, cach line
having a switch or switch connection on each board of its division and on one board
of each of the other divisions, annunciators for said lines, one annunciator for each
line in a board of each division where the line has a switch or switch connection,
electric calling apparatus whereby any subscriber may at will operate any.

page_text: annunciator which belongs to his line, and switch connecting apparatus whereby
the operator at any board may connect together any two lines which have their
switches or switch connections at his boards, substantially as set forth.
4. In a telephone exchange system the combination of telephone lines divided
into two divisions, multiple switch boards divided into two divisions, one division of
boards for cach division of lines, each line having a switch or switch connection on
cach board of its division and on one board of the other division, and electric
connecting apparatus whereby the operator at any board may connect together
any two lines which have their switches or switch connections at such board
substantially as set forth.
5. In a telephone exchange system, the combination of telephone lines divided
into two divisions, multiple switch boards divided into two divisions, one division of
boards for each division of lines, each line having a switch or switch connection on
each board, of its division and on one board of the other division, electric calling
apparatus whereby any subscriber may at will call an operator at a board of each
division where his line has a switch or switch connection and switch connecting
apparatus whereby the operator at any board may connect together any two lines
which have their switches or switch connections at his board substantially as set
forth.
6. In a telephone exchange system, the combination of telephone lines divided
into two divisions, multiple switch boards divided into two divisions, one division of
boards for each division of lines, each line having a switch or switch connection on
each board of its division and on one board of other division, two electric
annunciators for each line located at a board in each division when the line has a
switch or switch connection, electric calling apparatus whereby any subscriber may
at will operate either of his line annunciators, and connecting apparatus whereby
the operator at any board may connect together any two lines which have their
switches or switch connections at his board substantially as set forth.
7. In a telephone exchange system the combination of telephone lines divided
into two divisions, multiple switch boards divided into two divisions, one division of
boards for each division of lines, each line having a switch or switch connection on
each board of its division and on one board of the other division, two polarized
annunciators in the circuit of each line connected so as to be operated by currents
of opposite polarity, and located at boards of the two divisions where the line has a
switch or switching connection, a signalling generator at each subscriber's station
switching apparatus whereby the subscriber may at will send a current of either
polarity through his polarized annunciators and connecting apparatus whereby the
operator at any board may connect together any two lines which have their
switches or switch connections at such board substantially as set forth.
8. In a telephone exchange system, the combination of metallic circuit telephone
lines divided into two divisions, multiple switch boards divided into two divisions,
one division of boards for each division of lines, each line having a switch or
switch connection on each board of its division and on one board of the other
division, two annunciators for cach line one in each side or branch of the line,
electric calling apparatus whereby any subscriber may at will operate either of his
said line annunciators and connecting apparatus whereby the operator at any board
may connect any two lines which have their switches or switch connections at each
board, substantially as set forth.
9. In a telephonic exchange system, the combination of metallic circuit lines
divided into three divisions, multiple switch boards divided into three divisions, one
division of boards for each division of lines each line having a switch or switch
connection on each board of its division and on one board of each of the other
division, three annunciators for each line two being polarized annunciators and
connected in one branch of the line so as to be operated by currents of opposite
polarity and the other annunciator being connected in the other branch of the line,
said annunciators of a line being located at boards in the three divisions, and when
the line has a switch or switch connection calling apparatus at each subscriber's

page_text: station, whereby he may at will operate either of his line annunciators and
connecting apparatus whereby the operator at any board may connect any two
lines which have their switches or switch connections at each board substantially as
set forth.
10. In a telephone exchange system, the combination of metallic circuit lines
divided into four divisions, multiple switch boards divided into four divisions, one
division of boards for each division of lines, each line having a switch or switch
connection on each board of its division and on one board of each of the other
divisions, four polarized annunciators for each line, located at boards in each
division where the line has a switch or switch connection, two of the annunciators
being connected in one branch of the line so as to be operated by currents of
opposite polarity and the two other annunciators being connected in the other
branch of the line so as to be operated by currents of opposite polarity, a calling
generator at each subscriber's station, switching apparatus by which he may at will
send a current of either polarity over either branch of his line and connecting
apparatus whereby the operator at any board may connect any two lines which
have their switches or switch connections at such boards, substantially as set
forth.
11. In a telephone exchange system, the combination of telephone lines divided
into two divisions, multiple switch boards divided into two divisions, one division
of the board for each division of lines, each line having a switch or switch
connection on each board of its division and on one board of the other division,
two annunciators in the circuit of each line connected so as to be operated by
current transmitted over the line and located at boards of the two divisions where
the line has a switch or switch connection, a source of electrical energy from which
currents are sent over the line to operate the annunciators, apparatus whereby the
subscriber may at will cause a current to traverse the line to operate either
annunciator, and connecting apparatus whereby the operator at any board may
connect together any two lines which have their switches or switch connections at
such board.
12. In a telephone exchange system, a metallic circuit line one side or branch of
which is permanently grounded at the central office and the other side or branch of
which is connected to two or more multiple switch boards and is normally grounded
at the central oflice, in combination with switching devices at each board by which
the line may be connected in metallic circuit with another line and said second
mentioned or normal ground connection is then broken, substantially as set forth.
13. In a telephone exchange system, a metallic circuit line one side or branch of
which is permanently grounded at the central office and is connected to two or more
switch boards, and the other side or branch of which is normally grounded at the
central office and is connected to the same switch boards, in combination with
switching devices at each board by which the second or normal ground connection
may be broken and the two sides or branches of the line connected with the two
sides or branches respectively of another metallic circuit line, substantially as set
forth.
14. In a telephone exchange system, a metallic circuit line, one side or branch of
which is permanently grounded at the central office through an annunciator and the
other side or branch of which is normally grounded at the central office, in
combination with switching devices by which the second or normal ground
connection may be broken and the two sides or branches of the line connected with
the two sides or branches respectively of another metallic line but with said
annunciator not in the metallic circuit thereby established, substantially as set
forth.
15. In a telephone exchange system, a metallic circuit line, one side or branch of
which is permanently grounded at the central office through a retardation coil and
the other side or branch of which is normally grounded at the central office, in
combination with switching devices by which said second or normal ground
connection may be broken and the two sides or branches of the line connected with

page_text: the two sides or branches of another metallic circuit line but with said retardation
coil not in the metallic circuit thereby established, substantially as set forth.
16. In a telephone exchange system, two metallic circuit telephone lines, and switch
or connecting devices at the central office for connecting them together in metallic
circuit for conversation, in combination with an operator's calling generator or
battery; and switching apparatus by which the operator may connect the generator
or battery in a bridge or cross-connecting circuit between the two sides of said
combined metallic circuit.
17. 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 an annunciator at the central office
on which clearing out signals may be received, and switching apparatus by which
the operator may connect the annunciator in a circuit which bridges or cross
connects the two sides of said metallic circuit.
18. In a telephone exchange system, two metallic circuit lines, switch or con-
necting devices at the central office for connecting them together in metallic circuit
for conversation, in combination with an operator's telephone, calling generator or
battery, and a clearing out annunciator at the central office, and switching apparatus
by which the operator may connect either the telephone, the calling generator, or
annunciator in a circuit that bridges or cross-connects the two sides of the combined
metallic circuit of the two lines.
Dated this 17th day of December 1200
CARPMAEL & Co.,
Agents for the Applicant.