Telephone Exchange.
Year: 1896

page_text: Date of Application, 18th Dec., 1896-Accepted, 13th Mar., 1897
CODE DUIE SIECIFICATION.
Telephone Exchange.
I, MYRON FRANCIS HILL, of 1015 Filbert Street in the City and County of
Philadelphia and State of Pennsylvania, of the United States of America, Inventor,
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:-
Reference is made to the accompanying drawings in which the same letters refer to
like parts in the different views.
My invention has for its object to reduce the great expense of manually operated
switchboard exchanges, to reduce the complication of them, and to increase the speed
of connections and disconnections in order to enable a smaller number of operators to
take care of the work of a larger number of subscribers.
The first
In accomplishing this result my invention permits a division of labor in accordance
with the well known tendencies in factories by which one set of operators answers a
calling subscriber and another set of operators calls the called subscriber.
set of operators I designate as "answering operators," and the other set as
"distributing operators."
The answering operators are distributed among answering boards forming one
division of boards and the distributing operators are placed at different sections on
the distributing board. Thus there are two divisions of boards,-an answering
division and a distributing division. Each division of boards is divided up into
sections, each section for one or two operators.
Between each section on the answering division and each section on the distributing
division run trunk lines terminating in jacks at each end.
The line circuits are not connected to jacks at any board. They terminate in two
plugs, connected in multiple, one plug at each division of boards. The plugs of the
various lines are distributed among the sections on each division. For example,
section 1 on the answering division contains the plugs of lines 1 to 200. Section 2
of the answering division contains plugs of lines 201 to 400. And so on. This
partition of lines at the answering division by numbers is not necessary.
In like manner the first section on the distributing division contains plugs of
lines.1 to 300, and section 2 contains plugs of lines 301 to 600, and so on. In this
way the lines have plugs at both divisions of boards, each line having one plug at
each division.
Some partition of subscribers' lines in groups at the distributing division is
necessary and the trunk lines at the answering sections are labelled so that the
answering operator knows what group of subscribers' lines are accessible over them.
Trunk lines running to section 1 on the distributing division, for example, may all be
labelled 1-3, since they reach to lines 1-300. Some trunk lines labelled 1-3 are
at each answering section, so any line at any answering section may be connected to
lines 1-300.
Section 2 of the distributing division has trunk lines 3-6 from each section, so
labelled at all sections.
Any character or combination of characters may be used to designate trunk.
lines as long as the operators can tell what sub-station lines are accessible through
them.
Thus it appears that each answering section has trunk lines to each distributing
section labelled to indicate where they run.
On the answering section where a line has a plug, the line is also provided with a

page_text: calling device, such as an annunciator. These annunciators are placed beyond the
reach of the operators if desired. These annunciators act as both calling and clearing
out indicators.
Each trunk line has an indicator at the distributing division, at the section to
which it runs.
When a subscriber calls, the answering operator takes up the plug of his line at
ber board and inserts it into the trunk line running to that section of the distributing
division where the called subscriber's plug is located. The operator at that
distributing section places the plug of the called subscriber in the trunk line jack at
her board.
In the drawings,
Figure 1 is a diagram view of the organization of switch-boards, lines and
trunks.
Figure 2 is a diagram view showing more in detail the circuit for conversation
between two subscribers.
Figure 3 is a skeleton diagram of the system.
In Figure 1, A, B, C, and D are subscribers' stations. Subscriber's station A is
connected to the central office by means of line wires a and a-1. These line wires
are connected in multiple to terminal plugs A-1 and A-2.
Referring to Figure 2, for these connections more in detail, it will be seen how the
subscribers' lines are connected to the plug contact. Upon the plug A-1 are
mounted on either side two contacts, the two contacts on one side of the plug being
connected in multiple to one of the line conductors. For example, the line conductor a
is connected in multiple to plug contacts a-2 and a-4. Line conductor a-1 is
connected in multiple to plug contacts a-3 and a-5. The same is true of the
contacts on plug A-2.
The connection between the plug contacts and the line conductors is shown in
connection with plug A-2. The contacts a-5 and a-3 are connected to a flexible
conductor a-7 which is connected in turn to a long flexible spring a-9 within the
tube a-11. Likewise contacts a-2 and a-4 are connected to a flexible
conductor a-6 and conducting spring a-8 in the tube a-10. These tubes may be
of insulating material or they may be metallic and insulated from each other. The
cords, springs and tubes should be so proportioned and related that the spring
never leaves the tube. All the plugs are connected to line circuits in the same
manner.
The plugs rest normally in socket bases a-12. The line conductor a-1 is
connected to a back contact a-13 normally in contact with a spring a-14, which is
connected with the calling annunciator a-15. The other side of this calling
annunciator is connected by wire a-16 to the generator G-1 which is a dynamo
whose current is toned down by impedences and condensers in the manner .well
known to telephone engineers. The annunciator a-15 is provided with a flap a-17
adapted when the coil is energized to be attracted so as to display its number, and to
close a circuit with the contact a-18. The contact a--18 is connected by wire a-19
through the pair of contacts normally closed a-20, to the ground at G. The
contacts a-20 are opened by the bend a-21 which is operated by the ridge a-22
on the plug A-2, whenever the plug is withdrawn from its base a-12 or replaced
upon its base a-12. The pairs of contacts a-13 and a-14 are at the distributing
division of boards only, and situated in the plug seats at said division. The pairs of
contacts a-20 are at the answering division of boards only.
The purpose of this organization is now evident. The subscriber A closes key
contact a 23 thereby closing the following circuit :-Ground at G, key
contacts a 23, line wire a-1, back contact a-13, spring contact a-14, annuncia-
tor a-15, battery wire a-16, battery G-1, and ground at G. This circuit operates
annunciator a-15, attracting its flap, and closing the circuit through the
contact a 18. When the subscriber opens the key contacts a-28, the annunciator
circuit is still complete through the contact a-18, wire a-19, contacts a-20, and
ground at G. When the operator at the answering division of boards lifts the plug A-2,

page_text: the contacts a-20 are momentarily opened and the flap a-17 of the annunciator
leaves the contact a-18 and is restored to its normal condition without any manual
work on the part of the operator.
After the subscriber has closed the contacts a-23, he removes his telephone from
its hook and informs the operator at the central station with what subscriber he
wishes to talk. The operator at the central station is provided with a telephone set 0,
terminating in contacts and o, adapted to make connection with the plug
contacts a 2 and a-3 so that as these contacts are preferably on the tips of her
fingers, the act of taking up the plug connects her telephone set to the calling
subscriber.
After finding out the desired subscriber the operator places the plug A-2 into a
jack J, belonging to a trunk line T, running to that section of the distributing board
where the called subscriber has a plug.
In Figure 2, the called subscriber is represented by the lino B. This line bas
plugs B-1 and B-2. The plug B-1 is at the distributing division where the
trunk line calls are distributed among the called subscribers, and the plug B-2 is
located at the answering division where the calling subscriber's wants are attended to.
In Figure 1 is shown the normal condition of the trunk lines. Trunk line T, for
example, comprises trunk wire and -1, terminating in jack J and J'. At jack J
at the answering division the wire -1 terminates in the insulated contact spring 1-2.
The trunk wire t terminates in contact spring t-3 which is normally connected to a
stud t-4, electrically connected to the switch board S. The switch board is grounded
at G as shown. At the jack J at the distributing division the trunk wires t and -1
terminate in insulated contact springs t-7 and t-5. To each trunk line wire t is
connected at the distributing division an indicator t-6, the other side of which is
connected to the battery wire a-16.
The trunk line indicators are normally on closed circuit as follows:-From ground
at G, generator G₁ battery wire a-16, indicator t-6, trunk conductor t, contact
spring -3, contact stud -4 normally connected thereto, and ground at G.
For convenience in Fig. 1, I have omitted to show the indicator magnet
in series with magnet t as this circuit is more fully shown in Fig. 2.
When a plug is inserted into a jack J the contact spring t-3 is lifted from
the contact stud -4, thereby opening the circuit of the indicator -6 and releasing
its flap. This displays a signal to the operator at the distributing board informing
her that her attention is desired at the trunk line terminating in jack J. The
operator at this board is provided with an operator's telephone set O', connected to a
plug P. The plug P is constructed in the same manner as the plugs A, A, B1, B2,
except that the contacts a-2, a-3, 6-2, 6-3 are omitted. The contacts of the
plug P and the contacts a-1, a-5, b, b5 are all so sunken below the plane
of the surface of the plugs as not to come into contact with the metal of the switch
board when inserted into a jack. The contacts p on the plug P may however not be
so sunken. The details of construction of the plugs and jacks are well known to
those experienced in the art except the sunken contacts.
The operator upon seeing this signal displayed by the indicator -6 inserts her
plug P into the jack J', thereby connecting the plug contacts p to the jack contact
springs -7 and t-5 respectively. The operator at the answering board still
maintains the contact between her thimbles o and o¹, and the plug contacts a-2
and a-3, and is thereby connected to the trunk line with her telephone set. She
then informs the operator at the distributing board, or permits the calling subscriber
to inform the operator at the distributing board what fine is desired. The operator
at the distributing board then withdraws her plug P and inserts it into the jack of
another calling trunk line, and at the same time with her thimble contacts o-2
and 3, connected to a calling generator G-2, lifts the plug B from its
base a-12, and inserts it into the jack J. The act of taking hold of the plug B'
connects the thimble contacts o-2 and 0-3 to the plug contacts b-2 and 6-3, so
that the mere act of lifting the plug from its resting place to the jack of the trunk
line sends out a calling current to the called subscriber. It is thus seen that the

page_text: amount of work which can be done by an operator at the distributing board depends
upon the rapidity with which she can remove her plug P from one trunk line jack to
another. Referring to the details of the indicator -6, it will be seen that the
indicator is provided with a flap i, resting on the normal position shown in broken
lines . The flap is pivoted at -2 and by means of a connecting rod i-3, is
operated by an armature -4. When the armature is attracted the flap is in a
vertical position. When the armature is released the flap assumes an oblique position.
The oblique position indicates to the operator that her attention is desired. Upon
the armature -4 is a catch i-5 adapted to catch hold of the end of the plug
inserted into the jack so as to retain it against the force of an ejecting spring i-6.
The plug is provided with a slot i-7, in which the catch i-5 rests. When the
indicator t-6 is again energized, the armature -4 is attracted, the catch -
leaves the slot i-7, and the spring -6 ejects the plug from the jack. This
indicator - is energized when the circuit is again grounded for clearing out.
In the same circuit is placed an additional plug retaining magnet i-8 at the
answering division, normally attracting armature i-9, but when a plug is inserted
into the jack J, releasing the armature so that its catch i-10 will retain the plug in
the jack against the force of the ejecting spring i-11. When the circuit is
energized upon clearing out, the plug is released and under the influence of the
spring 11 it is thrown out of the jack. When the plugs at the two ends of
the trunk line are thus released, they fall back to their bases a-12 without the
assistance of the operator. This may be accomplished by weights and pulleys or
by the springs a-8 and a-9 as shown, although the operator's supervision is
sometimes necessary to their proper behaviour.
When a subscriber has been called, as for example subscriber B in Figure 2, his
calling annunciator is cut off by the opening of contacts a-13 and a-14 so that he
is unable to call central, or so that when he clears out, his annunciator will not
indicate a call. These contacts are opened automatically by the withdrawal of the
plug from its base.
In like manner if subscriber A had been called, and his plug A-1 had been
switched for use, the contacts a-13 and a-14 would have been opened and his
annunciator would have been cut off from the line..
The gonerator G-2 is preferably of the direct type, and has in its circuit a tertiary
coil of an induction coil. The induction coil belongs to the distributing operator's
telephone set O' and the tertiary coil o--4 is for the purpose of detecting a variation
in the direct current from G-2. There is preferably a separate generator G-2 for
each distributing board operator though with suitably arranged resistances and
condensers this is not a necessity.
The bells at the subscribers' stations which I use with this direct current generator
are a magnet coil, with a normally open short circuit around the coil closed by the
passage of the current through the coil. In this way, there is no break in the circuit,
and the operation of the bell creates a variation in the resistance of the circuit which
is audible in the telephone set O' at the central. office of the calling operator. Upon
hearing this buzz the distributing operator knows that the subscriber is free and
connects his line to the trunk. If the called subscriber is busy, the call bells are
withdrawn from the circuit at the subscriber's station and the resistance of the circuit
is not rapidly varied; hence. the operator at central bears no buzz and knows that the
line is busy. She then informs the subscriber who is connected to the trunk line at
the answering board.
In the telephone outfit at the subscriber's station the wire a leads to the receiver 1,
secondary coil 2, and contact point 8 adapted to make connection with the contact
plate 7 on the hook 6 when the receiver. is removed from the hook. The plate 7 is
connected by the wire 22 to the line conductor a'. When the telephone receiver is
on its hook the circuit is open at contacts 7 and 8. At this time the circuit
is normally closed from wire a through wire 21, contact plate 9, contact point 10,
bells 11, and thence to line wire a'.. This circuit is opened when the telephone is
removed from its hook.

page_text: The line conductors are insulated from the hook lever. The lever is in a local
battery circuit with the battery 4, transmitter 5, primary coil 3, and contact 33, closed
when the receiver is removed for conversation. When the lever is lifted up
automatically by the spring when the receiver is removed, an insulated projection 15.
strikes a conducting lever 16 pivoted at 17, and held in its place by a tail-piece 18,
and tension spring 19 grounded through the wire 20 at G. When the receiver is
restored to its hook, the contact plate 14 connected to the line wire a strikes this
grounded lever 16 and grounds the line circuit for restoring purposes. It is obvious,
however, that the contacts a-23 may be closed manually by the subscriber in
clearing out if desired. I prefer, however, the automatic clearing-out signal.
When a subscriber hangs up his telephone receiver, the momentary grounding of
the line through the lever 16 operates the calling annunciator at central at the
answering hoard which thereupon attracts its flap indicating that a disconnection is
desired. This operation of the flap adds another ground to the line through the
contact a-18, and the pair of contacts a-20 while passing back to the
base a-12.
The first grounding of the line by the subscriber may be enough to operate
this ojector, and if so the seconding grounding of the line through the contact a-18
is superfluous.
The indicator-6 has also meanwhile released its plug, but if there has been a hitch
here, the grounding of the contact spring t-3 through the stud t-4 (see Fig. 1)
will be sure to operate this coil to release the plug. If the plug still sticks to the jack,
the indicator has, by its action on the flap i, informed the distributing operator that a
disconnection is desired. Thus safe-guard upon safe-guard are added to the operation
of this system.
The great reduction in the amount of work on the part of the operators at the two
divisions of boards enables one operator to do the work of a large number of subscribers,
perhaps even 250. In fact this is a conservative estimate.
In operation this system is quick. A subscriber closes the contacts a-23, and
takes his telephone off from its book. The indicator at central indicates the call. The
answering operator where the indicator is placed lifts the plug of the calling subscriber,
and this act cuts in her telephone set and at the same time restores the calling
annunciator. Upon finding the number of the desired subscriber she inserts the plug
already lifted into a jack of the trunk line to that part or section of the distributing
board where the called subscriber's plug is located. The act of connecting to the
trunk line automatically causes the trunk line signal at the distributing board to
answer the want. The distributing operator inserts her telephone set plug P, and.
upon finding out the line wanted from either the operator or the subscriber, (the latter,
saves time) lifts the plug of the called subscriber and if she hears the buzz of the
called subscriber's call bell in her telephone, she inserts the plug into the jack of
the trunk line, simultaneously inserting the plug P into another calling trunk line.
To make a connection it requires but one motion on the part of the answering operator
and two moves on the part of the connecting or distributing operator. A total of
three moves is required to make a connection, rendering a connection easier with this
divided switch board than with the usual multiple switch board. When the subscribers
are through with their conversation, they hang up their telephones, and this act causes
the plugs to be automatically ejected from the trunk line jacks and restored to their
bases. This disconnection is taken away from the operator, and after once establishing
a connection she needs to pay no more attention to it.
The number of jacks on a switchboard in an exchange of 10,000 subscribers is.
greatly reduced. Instead of 10,000 jacks as in the usual multiple board, there are
from 15 to 45 on each answering section, and about 50 on a distributing section.
This is on the ratio of about 15 connections for every 100 subscribers.
This enormous saving in jacks is. a big factor in the cost of putting in telephone
exchanges. Exchanges can be indefinitely extended after being planned for a certain
number. That is, a switch board built for a 1,000 may be extended to do the work
of 10,000 by mere additions.

page_text: There are, numerous alterations and substitutions that may be made without
departing from the spirit of my invention.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
1. In a telephone exchange, the combination of an answering division, a distributing
division, and line circuits each connected to two plugs, one plug at each division.
2. In a telephone exchange, the combination of an answering division, a distributing
division, and fine circuits each connected to two plugs, one plug at each division, and
circuit connecting apparatus between said divisions.
3. In a telephone exchange, the combination of an answering division, a distributing
division, line circuits, each connected to two plugs, one plug at each division, circuit
connecting apparatus between said divisions, and call receiving devices at said
answering division for said line circuits.
4. In a telephone exchange, the combination of an answering division, a distributing
division, line circuits each connected to two plugs, one plug at each division, and call
generators or devices at said distributing division adapted to signal over said line
circuits.
5. In a telephone exchange, the combination of an answering division, a distributing
division, line circuits, each connected to two plugs, one plug at each division, circuit
connecting apparatus between said divisions, and an operator's telephone at said
answering division adapted to be connected to said line circuits.
6. In a telephone exchange, in combination two divisions of boards, an answering
division, and a distributing division, line circuits each connected in multiple to a plug
at one division and another switching device at the other division, and circuit
connecting apparatus between said divisions.
7. In a telephone exchange, the combination of an answering, division, a distributing
division, line circuits each connected to a plug at the answering division and to another
switching device at the distributing division, and circuit connecting apparatus between
said divisions for interconnecting said line circuits.
8. In a telephone exchange, the combination of an answering division, a distributing
division, line circuits each connected to a plug at the distributing division and to
another switching device at the answering division, and circuit connecting apparatus
between said divisions.
9. In a telephone exchange, the combination of an answering division, a distributing
division, line circuits each connected to two plugs, one at each division, interconnecting
or trunk line circuits between said divisions for interconnecting said line circuits,
and annunciators for said line circuits at said answering division.
10. In a telephone exchange, the combination of an answering division, a distributing
division, line circuits each connected to a plug at the distributing division, and to
another switching device at the answering division, call receiving. devices at the
answering division for said line circuits, and interconnecting circuits or trunks
between said divisions, terminating at each division in spring jacks or plug sockets,
and á signalling device for each trunk at the distributing division.
11. In a telephone exchange, the combination of an answering division, a distributing.
division, line circuits each connected to a switching device at each division,
interconnecting trunk circuits between said divisions, and automatic disconnecting
apparatus for disconnecting any connected line circuits operated independently of any
operator at said divisions.
12. In a telephone exchange, the combination of an answering division, a distributing
division, line circuits each connected to switching devices at each division,
interconnecting trunk circuits, and automatic disconnecting apparatus for said trunks
to open a connection between said trunks and said line circuits.
13. In a telephone exchange, the combination of an answering division, a distributing
division, line circuits each connected to a plug at each division, trunk line circuits

page_text: between said divisions for interconnecting said line circuits, and automatic disconnectors
at each division to disconnect trunk terminals and line plugs at the will of a subscriber.
14. In a telephone exchange, the combination of an answering division, a distributing
division, line circuits each connected to a plug at one division and to a switching
device at the other division, trunk lines between said divisions, each terminating in a
spring jack at that division where said line circuits have plugs, and in other switching
devices at the other division, and automatic disconnectors for disconnecting said plugs
from said jacks at the will of the subscriber.
15. In a telophone exchange, the combination of an answering division, a distributing
division, line circuits each connected to a plug at each division, trunk lines between
said divisions for interconnecting said plugs terminating at each division in spring
jacks or plug sockets, and automatic ejectors at each jack for ejecting said plugs
therefrom at the will of a subscriber.
.
16. In a telephone exchange, in combination, an answering division, a distributing
division, line circuits each connected to a switching device at each division, inter-
connecting circuits between said divisions, call receiving devices for said line circuits
at said answering division, and an automatic restoring device for each call device
operated by the act of switching the line circuit for use.
17. In a telephone exchange, in combination, an answering division, a distributing'
division, line circuits each connected to a switching device at each division, inter-
connecting circuits between said divisions, call receiving devices at said answering
division one for each line circuit, automatic call restoring devices one for each call
device operated automatically by the act of switching the line circuit for use.
18. In a telephone exchange, in combination, an answering division, a distributing
division, line circuits each connected to a plug at said answering division and to
another switching device at the other division, a call receiving device for each line
circuit at said answering division, and an automatic restoring device for said call
device operated by the act of taking up the line plug for use.
19. In a telephone exchange, in combination, an answering division, a distributing
division, line circuits each connected to a plug at the distributing division, and to
another switching device at said answering division, call receiving devices, one for each
line circuit at the answering division, and switching devices at said distributing
division for rendering said call receiving devices inoperative while the line circuits are
in use at the distributing division.
20. In a telephone exchange, in combination, an answering division, a distributing
division, line circuits each connected to a plug at said distributing division, and to
another switching device at said answering division, interconnecting circuits between
said divisions, call receiving devices at said answering division for said line circuits,
circuit changing apparatus at said distributing division operated automatically by the
act of taking up a plug for switching purposes to render said call apparatus
irresponsive to a subscriber's call.
21. In a telephone exchange, in combination, an answering division, a distributing
division, line circuits each connected to a switching device at each division, trunk
circuits between said divisions, call annunciators at said answering division for said
line circuits at said answering division, a sub-station telephone and call set in each of
said line circuits, each set including a switch lever in a local circuit insulated from the
main line circuit, a transmitter and battery in said local circuit, and call and telephone
apparatus in main line branches connected to insulated contacts on said lever, said
circuits being opened and closed by the switching movements of said lever, and call
sending apparatus at the distributing division for operating said call apparatus at the
sub-station set.
22. In a telephone exchange, an answering division of boards divided into sections,
a distributing division of boards also divided into sections, a different group of
sub-station lines connected to terminals at each distributing section, the sub-station
lines at said distributing division being also connected to terminals, one for each line,
at said answering division, connecting circuits between each section of one division

page_text: and each section of the other division, calling apparatus at said distributing division
of boards for signalling to sub-stations, operators' telephone sets at each section of
each division adapted to be interconnected for orders, and plug and cord connecting
apparatus for connecting said sub-station lines with said connecting circuits.
23. In a telephone exchange, an answering division of boards divided into sections,
a distributing division of boards also divided into sections, a different group of
sub-station lines connected to terminals at each distributing section, the sub-station
lines at said distributing division being also connected to terminals one for each line,
at said answering division, connecting circuits between each section of one division
and each section of the other division, and automatic disconnecting and restoring
apparatus for said terminals, operating from sub-stations.
24. In a telephone exchange, masses of cords having plug terminals and having
spring retractors, said cords and springs occupying vertical positions beneath the
switch board.
25.. In a telephone exchange, a substation including transmitter, receiver, and bells,
and switch for the transfer of circuits from telephone to signalling apparatus, a line
circuit, a switch device at central for switching said line for use, a call annunciator at
central for said line circuit in circuit with an operating device at said substation, a
retaining circuit closed by the operation of said annunciator while indicating a call,
and a circuit breaker in said retaining circuit under the control of an operator for
opening said retaining circuit for the purpose of restoring said indicator.
26. In a telephone exchange, a substation including transmitter, receiver, and bells,
and a switch for the transfer of circuits from telephone to signalling apparatus, a line
circuit having a switching device at central, a call indicator at central for said
line circuit in circuit with an operating device at said substation, a retaining circuit
for said call indicator closed automatically by the operation of said indicator, and a
circuit breaker in said retaining circuit for opening said retaining circuit by the act of
switching said line circuit for use at central."
27. In a metallic circuit telephone exchange, an answering division divided into
answering sections, a distributing division divided into distributing sections, metallic
line circuits each provided with two switching terminals, one terminal at each division,
the terminals at the answering division distributed among the answering sections, and
the terminals at the distributing division distributed among the distributing sections,
local connecting circuits or trunk lines extending from each answering section to all
the distributing sections, whereby the number of sections in each division may be
indefinitely increased.
28. The combination in a divisional exchange, line circuits having terminal devices
at each division, a trunk conductor extending between two divisions, a signal located
at one terminal of said trunk conductor, a circuit including said signal and an electric
generator normally closed at the other terminal of the trunk conductor, and a circuit
breaker at the latter terminal operated automatically by the act of making connection
thereat, so that said circuit is opened and remains open as long as said trunk is
connected to.
29. In combination, a divisional exchange, line circuits having terminal switching
devices at each division, a trunk conductor extending between two divisions, a signal
located at one terminal of said trunk conductor, a circuit including said signal and a
source of electric current normally closed at the other terminal of the trunk conductor,
and a circuit breaker at the latter terminal operated automatically by the act of
making connection thereat, so that said circuit is opened when said connection
is made.
30. In combination, a divisional switchboard, a distributing division, an answering
division, operators' sections on each division, groups of metallic circuits, one group
connected to switching terminals on each section of the distributing division, the two
limbs of each metallic circuit connected to two metallic switching contacts respectively.
at its section on the distributing division, switching terminals for said metallic
circuits at said answering division, said terminals being partitioned among said
answering sections, each terminal comprising two metallic contacts connected to the

page_text: two limbs of its metallic circuit respectively, and trunk lines between each answering
section and each distributing section, whereby any line calling at an answering
section may by means of the proper trunk line secure connection to the desired
subscriber at some one section on the distributing division.
31. In a divisional exchange, a distributing division, an answering division, line
circuits connected to switching devices at both divisions, trunk circuits extending
between said divisions, and a combined busy test and subscriber's call at said.
distributing board.
32. In a divisional exchange, a distribating division, an answering division, line
circuits, each connected to a switching device at each division, trunk conductors
extending between said divisions for connecting a circuit at one division with a circuit
at the other division, a common source of current at central, call receiving devices,
one for each line circuit at the answering division, said call receiving devices adapted
to be operated by said source of current at the will of a subscriber.
Dated this 27th day of November 1896.
MYRON FRANCIS HILL.