Central Office Apparatus and Circuits for Telephone Exchanges.
Year: 1893

page_text: being date of first Foreign Application (in 13th Oct., 1892
United States of America),
Date of Application (in United Kingdom), 13th May, 1893
Complete Specification Left, 12th Feb., 1894-Accepted, 28th Apr.,
1894
Date of Application (in United Kingdom), 13th May, 1893
Complete Specification Left, 12th Feb., 1894-Accepted, 28th Apr., 1894
PROVISIONAL SPECIFICATION.
Central Office Apparatus and Circuits for Telephone Exchanges.
I, EDWARD JULIUS HALL, of Morris in the County of Morris and State of
New Jersey, United States of America, do hereby declare the nature of this
invention to be as follows:-
This invention relates to apparatus for telephone exchange central stations by
means of which the entire work of the said central station including the receiving
sending and answering of call signals; the connection of main circuits for through
communication, the reception of disconnecting signals and the announcement of
busy lines is accomplished.
Its object is the performance of these several and other essential sub-operations,
all tending to the result of giving satisfactory telephone service with great efficiency,
with speed, and with greater economy than heretofore has been feasible.
To this end it comprises a division of the main switch board into two distinct
portions, one where calls are uniformly received and answered containing the
terminals of the lines with their spring-jacks or other circuit connections, the
annunciator drops and connecting appliances; and another on which all circuits are
represented by circuit connecting appliances such as spring jacks, and at which
connections resulting from calls received at the first portion are effected with any
desired circuit.
The first portion is preferably subdivided into operators sections to each of which
a given number of circuits may be assigned and where such circuits have their calls
answered and their connections with others initiated; for this reason it is hereinafter
referred to as a "sectional switchboard," while by reason of the special location of
its jacks and drops in the main circuits, it is also distinguished by being called the
"terminal switchboard," or "terminal, board," and it is moreover properly entitled
the "answering board" because all calls are there answered.
The second portion is not so subdivided, but it is homogeneous in construction,
and has a spring jack for all entering lines, and because it is especially arranged
to make the required connection with the second circuit, I term it the " connecting
switchboard," or the "connecting board."
Each entering substation circuit passes first to the connecting board spring
jack, and thence to a spring jack, and an annunciator at the terminal board.
The invention also comprises the combination of such a divided switchboard
with trunk conductors extending between the two parts thereof, hoth main circuits
and trunk conductors being provided with independent and double track electric
signals (preferably visual) whereby the operator at any connecting point of either
of such circuits or conductors may be promptly apprised of connections or
disconnections occurring at its complementary or corresponding connecting point,
and is therefore enabled to know whether such line or trunk is or is not already
occupied at some other point in the office.

page_text: Also the combination of the above named organizations with office instruction
circuits; with main and trunk disconnection signals; with suitable devices. whereby
both the terminal board operator, and the calling substation operator may
simultaneously be informed that a circuit called for at the connecting board is
already busy, if such be the case; and other arrangements and detailed constructions
all of which are pointed out in the Specification.
In the drawings forming a part of this Specification
Figure 1 is a diagram representing the relative arrangement of the switchboards,
with their principal circuits.
Figure 1 is a similar diagram, showing especially the arrangement of trunk
conductors.
Figure 2 is a diagram showing two main circuits complete together with an office
trunk; an instruction circuit and the full outfit of visual signals which I purpose
to employ, illustrating the mode of connecting a circuit whose call has been
received on the terminal switchboard with a second circuit at the connecting
switchboard.
Figures 3 and
are respectively side and vertical section elevations of a three
way cam key which is convenient for use in arranging the connection with
any link connection of the call generator, the operators telephone, or the
disconnecting drop.
Figure 5 shows in plan and section a compound or double circuit spring jack
adapted for use in association with the switchboard circuits and trunk conductors.
Considering first Figures 1 and 14, A is the terminal switchboard subdivided into
sections a, a³, a³, etc.; and B is the connecting switchboard. Any number of
substation lines may converge to the central station, but for perspicuity I have in
Figures 1 and 2 of the several drawings shown but two; and that number is
sufficient for explanatory purposes since no further principle of operation is involved
in the addition of others.
Land L' represent these two circuits which extend respectively from substations S
and S2; L passing the spring jack j at the connecting board, and its jack Jat
section a of the terminal board successively, and normally connecting them with its
regular call annunciator drop Z; while L in the same way passes its jacks ², J'
and reaches its call drop Z.
From each terminal section a, one or more trunk conductors as O in Figure 1
and 0, 02, 03, 04 in Figure 1A are extended to suitable points in front of and
adjacent to the connecting switchboards B, and are at both of their ends provided
(as will be hereinafter more particularly specified) with suitable connection
devices whereby at the terminal board end, they may be united with any main
circuit so as to form an extension of such main circuit to a point at the connecting
board near to the jack of the line wanted there and whereby at the said connecting
board they may form a conveniently manipulated union with such line. At each
terminal section a is also the usual number of link connectors consisting each of
flexible conductors having at each end a connecting plug adapted to be thrust into
springjacks and by these connections may be made between any two line jacks J,
if the call be for a circuit terminating on the same or the immediately adjacent
section on either side; or between any line jack J, and a trunk jack k for
connections which are to be made through the connecting board. These links c are
shown in Figures 1 and 1ª and a disconnecting drop D is shown as being included
in circuit therewith.
I place at the connecting board springjack of each main circuit a visual signal
indicator V which becomes operative whenever a plug is inserted in the terminal
board jack of such circuit, and at each of the latter jacks is a similar visual signal
indicator V responsive to the placing of a connecting plug in the corresponding
connecting board jack of the same line. The trunk conductors also are at their
terminal boards provided each with a similar indicator to denote a connection or
disconnection effected at their other end; and are likewise provided at their
terminal board ends with an annunciator drop z from which they are disconnected

page_text: when in use, but which on the withdrawal of the terminal board plug resumes its
connection so that upon it, should a main circuit not be promptly disconnected
from its trunk at the connecting board, the calls of said line may be received.
From suitable springjacks 13 at the terminal board sections order or instruction
telephone circuits 12 extend to operators telephones t³ worn or used by the
operators at the connecting board. One such circuit to each connecting board
operator will ordinarily be sufficient; and the several stem circuits 12 may have
branches 14 to the spring jacks 13 at each section, the said circuits being normally
open in each springjack until the section operators telephone circuit plug is inserted
in said jack.
The terminal and connecting boards may be in the same room, or otherwise as
preferred.
The foregoing description generally outlines the essentials of my invention and
referring to Figures 2 to 6 I will now proceed to specify its details of construction
and operation.
Two main circuits only are indicated in the diagram, as all are arranged and
worked in the same way and to delineate a greater number would simply complicate
without further elucidating the drawing.
The diagram, Figure 2, represents two main circuits L and L³ extending
respectively from telephone stations S and S to the central station where each
passes through a springjack j on the connecting board B, to
a second
springjack Jor J' on the terminal board; circuit L however terminating at
section a, and circuit L' at section a*.
The connecting and terminal switchboard portions of the apparatus are shewn as
being separated by the dotted line X X. Since metallic circuits are rapidly
coming into general use, I have shewn L' as a metallic circuit. L is an earth
completed circuit, but after reaching the terminal board, it is extended backwardly
and is grounded at g, after its extension also passes through the jack j at the
connecting board.
All of the springjacks used in this system may be made alike, although they may
be connected differently.
Any well known form of four contact spring jack may be employed and the plug
intended for use therewith must also of course have four contacts or be adapted to
control four contacts.
Figure 5 illustrates in plan and side view a form which I have found convenient
and which also is the form indicated in Figure 2.
It comprises two horizontally disposed contact springs 3 and 4 pressing normally
against resting or anvil contacts 8 and 7; and two other contact springs 5 and 6
also placed horizontally but edgewise, so that their flat surfaces oppose the edges of
the former. These have no normal contacts but so long as the jack is at rest may
form discontinuous portions of a circuit.
The several plug connectors shown P P2 and P3 may all also be of like con-
struction and have four insulated conducting surfaces mounted on a suitable
non-conducting stem i and each adapted to register and make contact with some
one of the jack springs. Thus when the plug is inserted in its jack, the
conducting surfaces 23 and 24 make contact with the main line jack springs 3 and 4
respectively, while the surfaces 25 and 26 connect with the local jack springs 5 and 6
respectively. Moreover when the plug is thrust into the jack, its action in addition
to making the said contacts is to sever the normal contact of the springs 3 and 4
with their respective anvils 8 and 7 and thus to break the normal circuit, and to
form a new circuit continuing through the said conducting surfaces 23 and 24 and
such conductors as may lead therefrom.
Tracing main circuit L we find that leaving station S, it passes by main
line L to the central station and there leads first to the connecting board B
where it connects with spring 4 of jack j. Thence by resting contact 7 and
conductor 1 to jack J at the terminal board, from spring 4 to contact 7 thereof;
thence to resting contact 8 of the second spring of said jack, by way of the call

page_text: annunciator drop Z and its connecting wires 27 and 28; and from said contact 8
to its spring 3 and by way of conductor to the second resting contact and
springs 8 and 3 of jack j at the connecting board and thence to earth at g.
The main circuit L² may in like manner be traced, the only difference being that
the return conductor instead of being grounded is extended back completely to
station S forming a metallic circuit. For distinction the two conductors thereof,
extending between the two switchboards are marked 12 and 13 respectively.
As already stated, a series of office trunk conductors extend between the
terminal board sections and different points on the connecting board. But one such
trunk is shown, that being sufficient to indicate the arrangement. H represents
the said trunk which has a terminal plug P³ at its connecting board end, and a
terminal spring jack k connecting normally by wires 37 and 38 with a drop Ź at its
terminal board end. It being assumed that all main circuits so far as they extend
through the central office apparatus are metallic, the trunk necessarily is also
formed with two conductors and ; joining the spring 3 of the jack k with the
surface 33 of the plug P³, and 1 uniting the spring 4 with the surface 34 of said
plug.
Each answering or terminal board section is provided with the usual outfit of a
number of double plug link connections Y whereby the jacks of any two circuits or
conductors may be united to constitute a continuous line of conduction. Each of
these comprises for metallic circuits two flexible main line conductors y and y' each
united at its ends to independent contact surfaces upon the terminal plugs; the
plugs P P are herein before described and in the present instance an additional
conductor wo is associated with the main line connecting link conductors for a
purpose presently to be disclosed.
The conductor y joins the contact surfaces 23 while conductor y² joins the
surfaces 24 of the two plugs P and P2 of each pair, there being shown to avoid
confusion one link connection Y only.
It will now be clear that the said plugs P P² may respectively be placed within
any two spring jacks J respectively located at the same or adjacent terminal board
sections and that when so placed, the circuits represented by such jacks will be
connected to form a compound circuit through the link connection Y.
Not only so, but it is also evident that one of the plugs P being inserted in a line
jack J and its associate in a trunk conductor jack k, the plug terminal P³ of said
trunk becomes the extended terminal of the line represented by said jack J, and
may be inserted in any connection board jack thereby establishing a through
connection between the stations S and S' of the two lines L and L2 by way of the
terminal board jack J of L, the link connection Y and the trunk conductor H.
Any of the well known keyboard systems of connecting the operators call and
telephonic apparatus may be arranged at each terminal section in connection with
the several pairs of connecting cords and lugs; I prefer however to provide for
each section a loop circuit M extending from a call generator M and transmitting
and receiving telephones t and 2 common to all of the connection links of said
section, and with a disconnecting or clearing out drop D and a three way eam
switch for each individual link connection.
The generator loop M³ extends from the generator M which may be common to
the entire switchboard to two terminal contacts 3 and 4 in each cam switch; an
electro magnetic resistance or retardation coil m, being included in each loop
conductor for a purpose to which reference will bereinafter be made.
The disconnecting drop D is provided with a conductor c having terminal
contacts and c³.
The transmitting telephone t is usually in a local battery circuit, and connects
with its main loop including the receiver t through an induction coil 1; the loop
conductors 40 and 41 being branched to terminal contacts hand in each cam
switch of a terminal switchboard section.
1
The three way cam switch E by means of which any of these appliances may be
connected with the link connection Y, and thereby with any main telephone

page_text: circuits which may be attached thereto is shown in Figures 3 and 4; since it is not
laimed as forming part of this invention it is not necessary to describe it'
specifically.
Figure 3 shows however the disconnecting drop contacts c² and c³, the generator
terminals and 4, and the main line terminals & and d' which may be placed in
contact with either of the two former alternatively.
It is not desirable at any time to introduce any of the keyboard appliances
directly into a compound talking circuit; and the switch conductors are therefore
arranged so that whenever any two lines are united by the link connection, if any
of the appliances of the operator are to be used thereon, they are connected in
bridge circuit between the two main conductors y and y².
To this end, the two principal conductors 37 and 38 of the cam switch lead from *
points e and e² on the link conductors y and y² respectively, and at the points and e
branch to two sets of contacts.
One of the pairs of branches ends in terminals n and n² which may connect with
the telephone loop; and the other ends in terminals and d² which connect
alternatively with the disconnecting drop or generator loop.
In the normal position of the cam lever which is upright the telephone and
generator loops are both open, but the disconnecting drop is in circuit between the
conductors y and y' through the contacts d c and d c³.
In the second position of the cam when depressed to one side in-which a call is
to be sent to line, the telephone and disconnecting drop loops are both open, and
the generator is connected between the conductors y and y² through the contacts d h
and h, the original contacts of d and d² with c and having been forced apart
by the descending spindle and wedge, which projects downwardly under the influence
of the cam, as shown in Figure 3.
But if the cam be turned reversely into its third position, the telephone loop
being controlled by a second spindle will be closed in bridge circuit with the main
conductors y and y² through the contacts nh n² h² without opening the circuit of
the disconnecting drop, the impedance of this being sufficient to prevent any short
circuiting of the telephone currents.
Although it is true that while the connection link Y is employed at both ends in
uniting two main circuits the telephone loop should it be connected is indeed
bridged between its two conductors, or in other words is in derived circuit with the
said two circuits, it is also true that when one of the plugs P only of such link is
in use, as in answering a call, the other plug remaining unused, the telephones
although connected in the same way are yet in direct circuit with the said plug,
the alternative route through the second plug being for the present discontinuous.
When answering calls therefore, the answering end of the connection link Y is in
fact itself the telephone loop and the answering plug, the plug terminal of
such loop.
The instruction or order circuits 12 extend between each section of the terminal
board and the several operators telephones at the connecting board. Their general'
arrangement has already been described.
This also is here shown as being a metallic circuit the two conductors thereof r
and both extending from the head telephone t³ of the connecting board to a spring
jack 13 at a section a of the terminal board.
To indicate that said order circuit passes likewise to other sections, the rudi-
mentary branches 14 are shown connecting with the conductors of circuit 12.
Being common to a plurality of sections, it is necessary that this circuit shall not
be normally closed in any of its spring jacks 13, and accordingly it will be seen
that though the jack shown has all the elements of the other jacks of the system,'
the spring contacts 3 and 4 of the main telephone circuit are the only ones which
are attached to circuit conductors; the others serving merely as plug guides
whereby it becomes possible to employ the same plug connector P in association
with this jack to give an order as will thereafter be used to connect with the trunk
jack k.
'
:

page_text: By means of these order circuits the operations at the connecting board are
readily kept under the control of the operator at the terminal board, and they are
constantly employed for the transmission of orders relating to the connection of
given trunk terminal plugs with desired lines.
There being two spring jacks for each main circuit located at two different
switchboards, it is essential that some efficient means be provided whereby it may
promptly and certainly be known at either spring jack when a connection or a
disconnection has been made at the other or in other words, whereby the engaged
or disengaged condition of a circuit at either switch board may be determined at
the other by a glance.
And though not essential, it is desirable also that means should be provided at
each connection board jack for promptly apprising the operator there, that a trunk
conductor which has been in use, and which is plugged to said jack, is now discou-
nected and that such plug therefore should now be withdrawn.
These requirements are met by the system of visual signals shown in which a
suitable visual indicator is closely associated with each connecting board spring
jack and is operated first, by placing a connecting plug in the corresponding
or complementary jack J of the same telephone circuit at the terminal board,
and second by placing the terminal plug of any trunk conductor in the connecting
board jack j.
A form of visual indicator which I have found well adapted for this purpose is
a self-restoring annunciator or if desired an ordinary incandescent lamp may be
employed, as indicated at the trunk signal of section a in Figure 1 and at section a
in Figure 14.
The former device I have illustrated in Figure 6 of this Specification and it
consists simply of a short electro magnet & which can be included in an electric
circuit and whose core has a curved tapering projection extending through a hole
in the shutter armature x. When current is passed through the coil, the shutter
is drawn up, and when the current ceases, it is permitted to fall; in the first case
.announcing a connection and in the latter a disconnection.
Such an indicator V placed beside its jack at the connecting board has one of
its coil terminals connected with the earth or with a return conductor, and the
other attached to a conductor f forming part of a normally open signalling circuit
which extends to the terminal section and there is united to the contact spring 5 of
the corresponding line jack J, which spring forms normally the open end of the
-circuit and also a circuit closer.
The plugs P of the several plug and cord connectors at each terminal section,
-each carry, as previously explained, a conducting surface 25 arranged to register
and connect with the circuit closing spring of the jack J, and the said surface is in
constant connection through conductor with one pole of a source or generator of
electricity F, such as a battery, the other pole of which connects with the return
terminal of the indicator V of the connecting board jack through the said return
conductor with which that terminal connects.
Thus when the plug P is thrust into the jack J to answer a call, the circuit
closer of the signal circuit becomes operative, and the indicator V is actuated.
announcing at the connecting board that such a plug insertion has been made, and
that the connecting board jack is blocked until the reverse operation of said
indicator which occurring on the withdrawal of said plug and the consequent
opening of the said circuit, indicates that the main circuit is once more at
liberty.
The same connecting board indicator V subserves the second purpose also. It
exhibits its block signal whenever the plug terminal of a trunk conductor is
inserted in its associated jack provided that a connection is made at the terminal
board with the jack of said trunk; consequently should a plug be found in a jack
at said connecting board the block signal having disappeared, it is at once known
that the terminal board end of said trunk has been disconnected, and that the plug
end thereof should also be withdrawn.

page_text: . It will be seen that each visual indicator V at the connecting board in addition-
to its connections which have already been described has also a branch connection to
spring contact 5 of its own jack; or . This spring has no further connection until.
a trunk plug is placed in the jack; but the contact surface 35 of such plug is united
through a conductor u associated with the trunk conductor throughout its length to
the normally unconnected contact spring 5 of the trunk jack k.
The plug P2 of each connection link Y is during a connection inserted in the-
jack k, and its contact surface 25 registers and makes contact with the said spring 5
thereof. The said contact surface 25 as well as the opposite one 26 is electrically
united to a local circuit conductor W which may mechanically be arranged in the
same flexible cord as includes the main link conductors y and y³, and which branches.
from the battery conductor 2 at the point W. The whole then may be regarded:
as a local atitomatic signal circuit open at two points, namely at the connecting
board jack, and at the trunk board jack, so that the block signal is established in
the indicator V when both circuit closers are operated, and disappears when the
plug is withdrawn from the trunk jack, thus indicating that the trunk plug should
also be withdrawn from the line jack.
In like manner each terminal board spring jack J has its protecting signal V
to indicate the use or disuse of its line at the connecting board by a trunk
plug.
The indicator V2 has one of its terminals connected by the wire m³ with a
suitable return conductor shown as the earth; and its remaining terminal is united
directly by a conductor with the spring contact 6 of the jack j of its own main.
circuit at the connecting board.
Here the signal circuit is normally open and the said spring 6 serves as the circuit
closer operated by the insertion of the trunk plug P³.
The contact surface 36 of said plug is united by a second associate conductor q of
the trunk conductors to a trunk conductor visual indicator V of the same class as
the others, and through that by conductor q² with the battery F and by conductor q³:
to the return or earth. The act of introducing the trunk plug P³ into a jack j
closes this signal circuit and causes the indicators V2 and both to set at their
block position, showing at the jack J that its circuit is in use at the connecting
board, and showing at trunk jack k that the order given over the order circuit to.
connect a given trunk plug to a given circuit has been complied with; while upon
the withdrawal of said plug, one section of the terminal switchboard receives the
signal "Clear line" and the other receives the signal "Clear trunk."
But should the connecting board end of the trunk fail to be promptly disconnected
after the withdrawal of the plug P' from the jack k, the trunk annunciator drop z
becomes temporarily the call receiving drop of the line connected at said connecting
board so that the service of such line is not neglected. A complete double track
system of automatic busy signals is thus provided. One electrical generator alone,
such as a secondary battery is, if desired, sufficient for all the visual signals, there
being no special reason for two, save that of facility of delineation.
The trunk signal v also has a subsidiary function as will presently appear. At
the connecting board B is arranged an apparatus whereby should a called for line be
found to be already occupied, the fact may readily and promptly be made known to
the connecting board operator who transferred the call; and, if desired, also to the
sub-station at which such call originated; and in practice it would be preferable to
have several such appliances.
K is an auxiliary jack made like the others and having electrical conductors
attached to but three of its spring contacts, riz.: 3, 4 and 6. Contact 6 is adapted
to register and connect with conducting surface 36 of plug P³ and thereby to be
brought into circuit with battery F. It is united to the return conductor of said
battery by the wire 50 through a revolving or vibratory circuit breaker R which
may be kept in motion by suitable mechanism (not shown) or which in a manner
well understood may be organized to start its motion as soon as current passes.
through it.

page_text: .
.
.
-
To indicate the busy condition of the line wanted the plug P2 is inserted in the
jackk and its battery conductor including the indicator V at the other end, is thus
brought into circuit with the intermittent circuit breaker R; the current is
intermitted through the said indicator which is thereby caused to flutter in response
to the action of said circuit breaker, and the terminal board operator is thus
visually informed that the line wanted is occupied.
It is sometimes desirable that the calling sub-station should also receive a similar
automatic notification, and I accomplish this by uniting the main spring contacts 3
and 4 of the jack k which register with the main circuit conducting surfaces 33
and 34 of the plug, to a loop circuit extending through conductors 52 and 53 in
which is included any convenient form of battery signal transmitter, and a
battery F. This signal may be of the same class as the circuit breaker R, or it
may be an ordinary buzzer; in an organization which has been constructed, I have
however employed in this loop, a telephone transmitter 4, and have mounted the
same in close juxta position to a phonograph p, which may be in constant
operation, and arranged to repeat continuously into such transmitter the word
busy, busy."
66
Any such signal is however transmitted over the several circuit conductors, from
the trunk plug to the sub-station and is received in the telephone or upon the bell
there, and the signal, being heard therein, automatically notifies the attendant that
the line of the station called for is engaged with another connection.
These devices however considered by themselves constitute the subject matter of
another application for Letters Patent filed of even date herewith by myself,
conjointly with Frank A. Pickernell for an Improvement in Busy Signals for
Telephone Circuits and except as elements of a combination are therefore not
claimed herein.
The operation may generally be described as follows:-Station S. signals the
central station in the usual manner. Its circuit L as already stated is through a
spring jack located on the connecting board, extending thence to the corre
sponding or complementary spring jack J at the terminal board A, section a, and
then to the terminal drop Z. The operator at the terminal board inserts the
answering plug P of any connector e into the jack J and receives the call. This
plug is for the present the terminal of the telephone loop, the three way cam being
properly turned and the instructions of the sub-station are therefore properly
received and answered. But the insertion of the plug in the jack J is an occupation
of the circuit and to forestall an interruption, by an attempt to connect with the
said circuit at its connecting board jack while such occupation continues the
operators at the said connecting board are to be informed that the circuit of
station Sis busy and the spring jack therefore blocked. This is done by providing
that the insertion of the plug at J shall close a local circuit in which is located the
signal receiver V located in close proximity to the jack j. The setting of this
signal operates to prevent the connection of circuit L at the jack j of connecting
board B with the circuit of any other customer calling for station S, which
connection otherwise might take place and interfere with the service.
A similar electric visual indicator V2 protecting the spring jack J at the terminal
board A is not required to become operative as the presence of the plug in the
jack there shows at once the line to be busy; and it does not become operative
because no plug has been placed in spring jack j to close its circuit.
The operator at the terminal section a having received the call from station S
finds that a connection with some other station, say S³ is desired. If the circuits of
station S and S² should happen to be represented on the same or adjacent terminal
boards, they may be at once connected directly with a regular link connection or
pair of switchboard cords Y in the ordinary way and in that case the circuit being
connected through the connecting board to the terminal board, in the same manner
as is circuit L, the insertion of the plug in its terminal board jack would operate
the visual signal V at its connecting board jack and would protect the connection
from interference there, also in the same manner as in the case of circuit L.

page_text: But the circuit L² of station S2 as indicated in the drawing is terminated at a
remote terminal section a' and must be reached through the connecting board.
The operator therefore inserts the second plug P2 of the pair in the spring
ack of the ordering or instruction circuit 2, extending from said spring jack by
branch and main to the head telephone of a switching operator stationed at
some point 6 at the connecting board near to the line wanted.
Over this, the said connectiug board operator is instructed to connect line L³ of
station S with the office trunk conductor O, extending between the terminal board
section a to the point b at the connecting board.
The second plug of the link connection Y would now be inserted in the jack k
of the specified trunk as shown and at the connecting board the plug terminal of
said trunk would be inserted in the jack of line L of station S
This last plug connection automatically operates the visual indicator at the
terminal board end of the office trunk, and also severs the end of line L' which
extends to the terminal board at and actuates the visual indicator V2 of said line
associated with its terminal board jack thereby indicating to the operators at that
and adjacent sections a³ and as that the line of station S' is busy.
It also in cooperation with the connection at the spring jack end of the trunk
sets the visual signal at the connecting board jack to serve as a trunk
disconnection signal.
If line L should on the reception of the order for its connection be found at the
connecting board to be already busy, the operator there would automatically signal
the fact to the answering operator and also to the calling station by inserting the
trunk plug P in the busy spring jack k thereby connecting the main line L and the
trunk signal circuits to automatic devices sending preconcerted busy signals by
means of the hereinbefore described apparatus connected with said busy jack.
Further than the loop connection of the call generator M with the three way
cam switch, I have not shewn any special call key device for signalling sub-
station Sover its line L³, but any of the ordinary and well known call key devices
may readily be subjoined to or substituted for said cam switch and loop in à
manner well understood.
In connection with the cam E, I show that the generator loop includes two
graduating electromagnetic resistances, and in practice I have found it feasible to
so arrange such resistance and retardation coils, that a regular alternating current
generator adapted to efficiently ring the ordinary polarized telephone bell will
not produce any material sound in a telephone included in the same circuit ;
the alternating currents being so graduated, and their crests so rounded, that they
do not act upon the telephone while continuing to efficiently operate bells.
. I call a generator so arranged a graduated generator and as the same is described
in a separate application for Letters Patent filed by myself and Frank A.
Pickernell as joint inventors, contemporaneously herewith, and entitled
Improvement in Signalling. Apparatus and Circuits no claim is made herein for
the same.
an
In the use of this apparatus after the order has been given to the connecting
board operator to connect a given trunk with the line wanted, the cam E is turned
to the generator side and so left, while other calls are being answered on other
cord connections.
As soon therefore as the connection is made at the connecting board, the bell at
the desired station being connected with the generator will ring continuously until
the attendant there takes down his telephone and begins to talk. But when that
is done, though the generator connection continues, the two persons talking at the
two connected stations are not disturbed thereby, because their telephones do
not respond to the graduated call currents.
The ringing however does not long continue for the operator after having attended
to other calls returns to this connection and finding the signal v set, knows that the
connection has properly been completed and reverses the cam lever so as to
disconnect the generator and bridge the disconnecting drop across the circuit. By
B

page_text: this automatic ring feature much time is saved, as the operator is enabled to attend
to other work while it is going on.
. On the conclusion of the communication either or both stations may ring off as
usual, and the disconnecting drop D is operated. The operator withdraws the
plugs P and P2 from the jacks J and k. The withdrawal of P opens the local
circuit of signal V of line L and removing said signal liberates the jack; and
restores the normal circuit of L.
The withdrawal of P* opens the local circuit of signal V of L2 and removing the
said signal notifies the connecting board operator that the trunk plug P³ should be
withdrawn from jack j³.
Until that plug is removed and circuit L³ thereby set at liberty the signal V at
the trunk jack k and V* at the terminal board jack of said circuit L² remain set, but
the station Scan still signal the central station through the trunk drop z.
And finally, the trunk plug Ps having been withdrawn from the connecting board
jack the local signal circuit of V is opened restoring that signal to its normal
state, and declaring the. trunk conductor to be at liberty; the signal V' at the
terminal board end of circuit L* being in the same local circuit is also restored
indicating the liberty of said main circuit L, and the normal state of said main
circuit is resumed.
Dated this 13th day of May 1893.
CARPMAEL & Co.,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Central Office Apparatus and Circuits for Telephone Exchanges.
I, EDWARD JULIUS HALL, of Morris, in the County of Morris and State of
New Jersey, United States of America, do hereby declare the nature of this
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-—
This invention relates to apparatus for telephone exchange central stations by
means of which the entire work of the said central station including the receiving
sending and answering of call signals; the connection of main circuits for through
communication; the reception of disconnecting signals and the announcement of
busy lines is accomplished.
Its object is the performance of these several and other essential sub-operations,
all tending to the result of giving satisfactory telephone service with great
efficiency, with speed, and with greater economy than heretofore has been feasible.
To this end it comprises a division of the main switch board into two distinct
portions, one where calls are uniformly received and answered containing the
terminals of the lines with their spring-jacks or other circuit connections, the
annunciator drops and connecting appliances; and another on which all circuits are
represented by circuit connecting appliances such as spring-jacks, and at which
connections resulting from calls received at the first portion are effected with any
desired circuit.
The first portion is preferably subdivided into operators sections to each of
which a given number of circuits may be assigned and where such circuits have
their calls answered and their connections with others initiated; for this reason it
is hereinafter referred to as a "sectional switchboard," while by reason of the
-special location of its jacks and drops in the main circuits, it is also distinguished
by being called the "terminal switchboard," or "terminal board," and it is
moreover properly entitled the "answering board" because all calls are there
answered.
The second portion is not so subdivided, but it is homogeneous in construction,
and has a spring-jack for all entering lines, and because it is especially arranged to.

page_text: make the required connection with the second circuit, I term it the “connecting
switchboard," or the "connecting board."
Each entering substation circuit passes first to the connecting board springjack,
and thence to a springjack, and an annunciator at the terminal board.
The invention also comprises the combination of such a divided switchboard with
trunk conductors extending between the two parts thereof, both main circuits and
trunk conductors being provided with independent and double track electric
signals (preferably visual) whereby the operator at any connecting point of either
of such circuits or conductors may be promptly apprised of connections or dis-
connections occurring at its complementary or corresponding connecting point, and
is therefore enabled to know whether such line or trunk is or is not already
occupied at some other point in the office.
Also the combination of the above named organizations with office instruction
circuits; with main and trunk disconnection signals; with suitable devices whereby
both the terminal board operator, and the calling substation operator may simul-
taneously be informed that a circuit called for at the connecting board is already
busy, if such be the case; and other arrangements and detailed constructions all
of which are specifically pointed out in the claims appended to this Specification.
In the drawings (left with the Provisional Specification) forming a part of
this Specification,
Figure 1 is a diagram representing the relative arrangement of the switchboards,
with their principal circuits.
Figure 1 is a similar diagram, showing especially the arrangement of trunk
conductors.
Figure 2 is a diagram showing two main circuits complete together with an.
office trunk; an instruction circuit and the full outfit of visual signals which I
purpose to employ, illustrating the mode of connecting a circuit whose call has
been received on the terminal switchboard with a second circuit at the connecting
switchboard.
Figures 3 and 4 are respectively side and vertical section elevations of a three
way cam key which is convenient for use in arranging the connection with any
link connection of the call generator, the operators telephone, or the disconnecting
drop.
Figure 5 shows in plan and section a compound or double circuit springjack
adapted for use in association with the switchboard circuits and trunk conductors.
Considering first Figures 1 and 1A, A is the terminal switchboard subdivided
into sections a, a², a³, etc.; and B is the connecting switchboard. Any number of
substation lines may converge to the central station, but for perspicuity I have in
Figures 1 and 2 of the several drawings shown but two; and that number is
sufficient for explanatory purposes since no further principle of operation is
involved in the addition of others.
L and L represent these two circuits which extend respectively from sub-
stations S and S³; L passing the spring jack; at the connecting board, and its
jack J at section a of the terminal board successively, and normally connecting
them with its regular call annunciator drop Z; while L' in the same way passes
its jacks, J, and reaches its call drop Z³.
From each terminal section a, one or more trunk conductors as O in Figure 1
and 0, 0, 0, 0, in Figure 14, are extended to suitable points in front of and
adjacent to the connecting switchboards B, an are at both of their ends provided
(as will be hereinafter more particularly specified) with suitable connection devices
whereby at the terminal board end, they may be united with any main circuit so as
to form an extension of such main circuit to a point at the connecting board near
to the jack of the line wanted there and whereby at the said connecting board they
At each terminal
may form a conveniently manipulated union with such line.
section a is also the usual number of link connectors consisting each of flexible
conductors having at each end a connecting plug adapted to be thrust into spring
jacks and by these connections may be made between any two line jacks J, if the

page_text: call be for a circuit terminating on the same or the immediately adjacent section
on either side; or between any line jack J, and a trunk jack k for connections
which are to be made through the connecting board. These links c are shown in
Figures 1 and 14 and a disconnecting drop D is shown as being included in circuit
therewith.
I place at the connecting board spring-jack of each main circuit a visual signal
indicator which becomes operative whenever a plug is inserted in the terminal
board jack of such circuit, and at each of the latter jacks is a similar visual signal
indicator V responsive to the placing of a connecting plug in the corresponding
connecting board jack of the same line. The trunk conductors also are at their
terminal boards provided each with a similar indicator v to denote a connection
or disconnection effected at their other end; and are likewise provided at their
terminal board ends with an annunciator drop z from which they are disconnected
when in use, but which on the withdrawal of the terminal board plug resumes its
connection so that upon it, should a main circuit not be promptly disconnected
from its trunk at the connecting board, the calls of said line may be received.
From suitable spring jacks 13 at the terminal board sections order or instruction
telephone circuits 12 extend to operators telephones t³ worn or used by the
operators at the connecting board. One such circuit to each connecting board
operator will ordinarily be sufficient, and the several stem circuits 12 may have
branches 14 to the spring jacks 13 at each section, the said circuits being normally
open in each springjack until the section operators telephone circuit plug is inserted
in said jack.
The terminal and connecting boards may be in the same room, or otherwise, as
preferred.
The foregoing description generally outlines the essentials of my invention and
referring to Figures 2 to 6 I will now proceed to specify its details of construction
and operation.
Two main circuits only are indicated in the diagram, as all are arranged and
worked in the same way and to delineate a greater number would simply complicate
without further elucidating the drawing.
The diagram, Figure 2, represents two main circuits L and L' extending
respectively from telephone stations S and S2 to the central station where each
passes through a springjack on the connecting board B, to a second spring-
jack J or J2 on the terminal board; circuit L however terminating at section a,
and circuit L² at section a*.
The connecting and terminal switchboard portions of the apparatus are shown
as being separated by the dotted line X X. Since metallic circuits are rapidly
coming into general use, I have shown L' as a metallic circuit. L is an earth
completed circuit, but after reaching the terminal board, it is extended backwardly
and is grounded at g, after its extension also passes through the jack ; at the
connecting board.
All of the springjacks used in this system may be made alike, although they may
be connected differently.
Any well known form of four contact springjack may be employed and the plug
intended for use therewith must also of course have four contacts or be adapted
to control four contacts.
Figure 5 illustrates in plan and side view a form which I have found convenient
and which also is the forni indicated in Figure 2.
It comprises two horizontally disposed contact springs 3 and 4 pressing normally
against resting or anvil contacts 8 and 7; and two other contact springs 5 and 6
also placed horizontally but edgewise, so that their flat surfaces oppose the edges
of the former. These have no normal contacts but so long as the jack is at rest
may form discontinuous portions of a circuit.
The several plug connectors shown P P2 and Ps may all also be of like
construction and have four insulated conducting surfaces mounted on a suitable
non-conducting stem i and each adapted to register and make contact with some

page_text: one of the jack springs. Thus when the plug is inserted in its jack, the conducting
surfaces 23 and 24 make contact with the main line jacksprings 3 and 4 respectively,
while the surfaces 25 and 26 connect with the local jacksprings 5 and 6 respectively.
Moreover when the plug is thrust into the jack, its action in addition to making
the said contacts is to sever the normal contact of the springs 3 and 4 with their
respective anvils 8 and 7 and thus to break the normal circuit, and to form a new
circuit continuing through the said connecting surfaces 23 and 24 and such
conductors as may lead therefrom.
Tracing main circuit L we find that leaving station S, it passes by main line L
to the central station and there leads first to the connecting board B where it
connects with spring 4 of jack j. Thence by resting contact 7 and conductor / to
jack J at the terminal board, from spring 4 to contact 7 thereof; thence to resting
contact 8 of the second spring of said jack, by way of the call annunciator drop Z
and its connecting wires 27 and 28; and from said contact 8 to its spring 3 and by
way of conductor to the second resting contact and springs 8 and 3 of jack j at
the connecting board and thence to earth at 9.
The main circuit L' may in like manner be traced, the only difference being that
the return conductor instead of being grounded is extended back completely to
station S forming a metallic circuit. For distinction the two conductors thereof,
extending between the two switchboards are marked 12 and 13 respectively.
As already stated, a series of office trunk conductors extend between the terminal
board sections and different points on the connecting board. But one such trunk
is shown, that being sufficient to indicate the arrangement. H represents the said
trunk which has a terminal plug P3 at its connecting board end, and a terminal
springjack k connecting normally by wires 37 and 38 with a drop Ź at its terminal
board end. It being assumed that all main circuits so far as they extend through
the central office apparatus are metallic, the trunk necessarily is also formed with
two conductors 14 and 1; 14 joining the spring 3 of the jack k with the surface 33
of the plug P3, and uniting the spring 4 with the surface 34 of said plug.
Each answering or terminal board section is provided with the usual outfit of a
number of double plug link connections Y whereby the jacks of any two circuits or
conductors may be united to constitute a continuous line of conduction. Each of
these comprises for metallic circuits two flexible main line conductors y and y³
each united at its ends to independent contact surfaces upon the terminal plugs;
the plugs P P are hereinbefore described and in the present instance an additional
conductor w is associated with the main line connecting link conductors for a purpose
presently to be disclosed.
The conductor y joins the contact surfaces 23 while conductor y joins the
surfaces 24 of the two plugs P and P2 of each pair, there being shown to avoid
confusion one link connection Y only.
It will now be clear that the said plugs P P may respectively be placed within
any two springjacks J respectively located at the same or adjacent terminal board
sections and that when so placed, the circuits represented by such jacks will be
connected to form a compound circuit through the link connection Y.
Not only so, but it is also evident that one of the plugs P being inserted in a
line jack J and its associate in a trunk conductor jack k, the plug terminal P³ of
said trunk becomes the extended terminal of the line represented by said jack J,
and may he inserted in any connection board jack thereby establishing a through
connection between the stations S and S' of the two lines L and L' by way of the
terminal board jack J of L, the link connection Y, and the trunk conductor H.
Any of the well known keyboard systems of connecting the operators call and
telephonic apparatus may be arranged at each terminal section in connection with
the several pairs of connecting cords and plugs; I prefer however to provide for
each section a loop circuit M extending from a call generator M and transmitting
and receiving telephones and t common to all of the connection links of said
section; and with a disconnecting or clearing out drop D and a three way cam
switch for each individual link connection.

page_text: The generator leop M' extends from the generator M which may be common to
the entire switchboard to two terminal contacts 3 and 4 in each cam switch; an
electro magnetic resistance or retardation coil m, being included in each loop
conductor for a purpose to which reference will hereinafter be made.
The disconnecting drop D is provided with a conductor c having terminal
contacts c² and c³.
The transmitting telephone t is usually in a local battery circuit, and connects
with its main loop including the receiver t through an induction coil I; the loop
conductors 40 and 41 being branched to terminal contacts and /* in each cam
switch of a terminal switch-board section.
The three way cam switch E by means of which any of these appliances may be
connected with the link connection Y, and thereby with any main telephone
circuits which may be attached thereto is shown in Figures 3 and 4; since it is not
claimed as forming part of this invention it is not necessary to describe it
specifically.
Figure 3 shows however the disconnecting drop contacts c² and c³, the generator
terminals h³ and h, and the main line terminals d and d which may be placed in
contact with either of the two former alternatively.
It is not desirable at any time to introduce any of the key board appliances
directly into a compound talking circuit; and the switch conductors are therefore
arranged so that whenever any two lines are united by the link connection, if any
of the appliances of the operator are to be used thereon, they are connected
in bridge circuit between the two main conductors y and y.
To this end, the two principal conductors 37 and 38 of the cam switch lead from
points e and e' on the link conductors y and y³ respectively, and at the points e³ and e*
branch to two sets of contacts.
One of the pairs of branches ends in terminals n and n² which may connect with
the telephone loop; and the other ends in terminals d and d which connect
.alternatively with the disconnecting drop or generator loop.
In the normal position of the cam lever which is upright the telephone and
generator loops are both open, but the disconnecting drop is in circuit between the
-conductors y and y through the contacts & c³ and d² c³.
In the second position of the cam when depressed to one side in which a call is
to be sent to line, the telephone and disconnecting drop loops are both open, and
the generator is connected between the conductors y and y² through the
contacts d h and a³ ³, the original contacts of d and d with c² and having been
forced apart by the descending spindle and wedge, which projects downwardly
under the influence of the cam, as shown in Figure 3.
But if the cam be turned reversely into its third position, the telephone loop
being controlled by a second spindle will be closed in bridge circuit with the main
-conductors y and y through the contacts nh nh³ without opening the circuit of
the disconnecting drop, the impedance of this being sufficient to prevent any short
-circuiting of the telephone currents.
Although it is true that while the connection link Y is employed at both ends in
uniting two main circuits the telephone loop should it be connected is indeed
bridged between its two conductors, or in other words is in derived circuit with the
two said circuits, it is also true that when one of the plugs P only of such link is in
use, as in answering a call, the other plug remaining unused, the telephones although
connected in the same way are yet in direct circuit with the said plug, the
alternative route through the second plug being for the present discontinuous.
When answering calls therefore, the answering end of the connection link Y is in
fact itself the telephone loop and the answering plug, the plug terminal of such
loop.
The instruction or order circuits 12 exterd between each section of the terminal
board and the several operators telephones at the connecting board. Their general
arrangement has already been described.
This also is here shown as being a metallic circuit the two conductors thereof r

page_text: and both extending from the head telephone t³ of the connecting board to a
spring jack 13 at a section a of the terminal board.
To indicate that said order circuit passes likewise to other sections, the
rudimentary branches 14 are shown connecting with the conductors of circuit 12..
Being common to a plurality of sections, it is necessary that this circuit shall not
be normally closed in any of its spring jacks 13, and accordingly it will be seen.
that though the jack shown has all the elements of the other jacks of the system,
the spring contacts 3 and 4 of the main telephone circuit are the only ones which
are attached to circuit conductors; the others serving merely as plug guides
whereby it becomes possible to employ the same plug connector P in association.
with this jack to give an order as will thereafter be used to connect with the trunk
jack k.
By means of these order circuits the operations at the connecting board are
readily kept under the control of the operator at the terminal board, and they are
constantly employed for the transmission of orders relating to the connection of
given trunk terminal plugs with desired lines.
There. being two spring jacks for each main circuit located at two different
switchboards, it is essential that some efficient means be provided whereby it may
promptly and certainly be known at either spring jack when a connection or a
disconnection has been made at the other or in other words, whereby the engaged
or disengaged condition of a circuit at either switch-board may be determined at
the other by a glance.
And though not essential, it is desirable also that means should be provided at
each connection board jack for promptly apprising the operator there, that a trunk
conductor which has been in use, and which is plugged to said jack, is now discon-
nected, and that such plug therefore should now be withdrawn.
These requirements are met by the system of visual signals shown in which a
suitable visual indicator is closely associated with each connecting board spring
jack and is operated first, by placing a connecting plug in the corresponding or
complementary jack J of the same telephone circuit at the terminal board, and
second by placing the terminal plug of any trunk conductor in the connecting board
jack j.
A form of visual indicator which I have found well adapted for this purpose is a
self-restoring annunciator or if desired an ordinary incandescent lamp may be
employed, as indicated at the trunk signal of section a in Figure 1 and at section a³
in Figure 1A.
The former device I have illustrated in Figure 6 of this Specification and it
consists simply of a short electro magneta which can be included in an electric
circuit and whose core has a curved tapering projection a extending through a
hole in the shutter armature ³. When current is passed through the coil, the
shutter is drawn up, and when the current ceases, it is permitted to fall; in the
first case announcing a connection and in the latter a disconnection.
Such an indicator V placed beside its jack at the connecting board has one of its
coil terminals connected with the earth' or with a return conductor, and the other.
attached to a conductor f forming part of a normally open signalling circuit which
extends to the terminal section and there is united to the contact spring 5 of the
corresponding line jack J, which spring forms normally the open end of the circuit
and also a circuit closer.
The plugs P of the several plug and cord connectors at each terminal section,
each carry, as previously explained, a conducting surface 25 arranged to register
and connect with the circuit closing spring of the jack J, and the said surface is in
constant connection through conductor with one pole of a source or generator of
electricity F, such as a battery, the other pole of which connects with the return
terminal of the indicator V of the connecting board jack through the said return
conductor with which that terminal connects.
Thus when the plug P is thrust into the jack J to answer a call, the circuit
closer of the signal circuit becomes operative, and the indicator V is actuated...

page_text: announcing at the connecting board that such a plug insertion has been made, and
that the connecting board jack is blocked until the reverse operation of said
indicator which occurring on the withdrawal of said plug and the consequent
opening of the said circuit, indicates that the main circuit is once more at
liberty.
The same connecting board indicator V subserves the second purpose also. It
exhibits its block signal whenever the plug terminal of a trunk conductor is
inserted in its associated jack provided that a connection is made at the terminal
board with the jack of said trunk; consequently should a plug be found in a jack
at said connecting board the block signal having disappeared, it is at once known
that the terminal board end of said trunk has been disconnected, and that the plug
end thereof should also be withdrawn.
It will be seen that each visual indicator V at the connecting board in addition
to its connections which have already been described has also a branch connection
to spring contact 5 of its own jack jor. This spring has no further connection
until a trunk plug is placed in the jack; but the contact surface 35 of such plug is
united through a conductor u associated with the trunk conductor throughout its
length to the normally unconnected contact spring 5 of the trunk jack k.
The plug P of each connection link Y is during a connection inserted in the
jack k, and its contact surface 25 registers and makes contact with the said spring 5
thereof. The said contact surface 25 as well as the opposite one 26 is electrically
united to a local circuit conductor w which may mechanically be arranged in the
same flexible cord as includes the main link conductors y and y, and which branches
from the battery conductor at the point to. The whole then may be regarded
as a local automatic signal circuit open at two points, namely at the connecting
board jack, and at the trunk board jack, so that the block signal is established in
the indicator V when both circuit closers are operated, and disappears when the
plug is withdrawn from the trunk jack, thus indicating that the trunk plug should
also be withdrawn from the line jack.
In like manner each terminal board spring jack J has its protecting signal V³
to indicate the use or disuse of its line at the connecting board by a trunk
plug.
The indicator V2 has one of its terminals connected by the wire m² with a
suitable return conductor shown as the earth; and its remaining terminal is united
directly by a conductor with the spring contact 6 of the jack j of its own main
circuit at the connecting board.
Here the signal circuit is normally open and the said spring 6 serves as the circuit
closer operated by the insertion of the trunk plug P³.
The contact surface 36 of said plug is united by a second associate conductor q
of the trunk conductors to a trunk conductor visual indicator V of the same class
as the others, and through that by conductor 92 with the battery F and by
conductor to the return or earth. The act of introducing the trunk plug Pa
into a jack closes this signal circuit and causes the indicators V and v both to set
at their block position, showing at the jack J that its circuit is in use at the con-
necting board, and showing at trunk jack k that the order given over the order
circuit to connect a given trunk plug to a given circuit has been complied with;
while upon the withdrawal of said plug, one section of the terminal switchboard
receives the signal "Clear line" and the other receives the signal" Clear trunk."
But should the connecting board end of the trunk fail to be promptly discon-
nected after the withdrawal of the plug P2 from the jack k, the trunk annunciator
drop z becomes temporarily the call receiving drop of the line connected at said
connecting board so that the service of such line is not neglected. A complete
double track system of automatic busy signals is thus provided. One electrical
generator alone, such as a secondary battery is, if desired, sufficient for all the
visual signals, there being no special reason for two, savo that of facility of
delineation.
The trunk signal v also has a subsidiary function as will presently appear. At

page_text: the connecting board B is arranged an apparatus whereby should a called for line
be found to be already occupied, the fact may readily and promptly be made known
to the connecting board operator who transferred the call; and, if desired, also to
the sub-station at which such call originated; and in practice it would be preferable
to have several such appliances.
K is an auxiliary jack made like the others and having electrical conductors
attached to but three of its spring contacts, viz. : 3, 4 and 6. Contact 6 is adapted
to register and connect with conducting surface 36 of plug Ps and thereby to be
brought into circuit with battery F. It is united to the return conductor of said
battery by the wire 50 through a revolving or vibratory circuit breaker R which
may be kept in motion by suitable mechanism (not shown) or which in a manner
well understood may be organized to start its motion as soon as current passes
through it.
To indicate the busy condition of the line wanted the plug P2 is inserted in
the jack k and its battery conductor including the indicator v at the other end, is
thus brought into circuit with the intermittent circuit breaker R; the current is
intermitted through the said indicator which is thereby caused to flutter in response
to the action of said circuit breaker, and the terminal board operator is thus
visually informed that the line wanted is occupied.
It is sometimes desirable that the calling sub-station should also receive a similar
automatic notification, and I accomplish this by uniting the main spring. contacts 3
and 4 of the jack k which register with the main circuit conducting surfaces 33
and 34 of the plug, to a loop circuit extending through conductors 52 and 53 in
which is included any convenient form of battery signal transmitter, and a
battery F 3. This signal may be of the same class as the circuit breaker R, or it
may be an ordinary buzzer; in an organization which has been constructed, I have
however employed in this loop, a telephone transmitter 4, and have mounted the
same in close juxtaposition to a phonograph p, which may be in constant operation,
and arranged to repeat continuously into such transmitter the word " 'busy,'
busy.'
66
"
Any such signal is however transmitted over the several circuit conductors, from
the trunk plug to the substation and is received in the telephone or upon the bell
there, and the signal being heard, therein, automatically notifies the attendant that
the line of the station called for is engaged with another connection.
These devices however considered by themselves constitute the subject matter of
another application for Letters Patent filed of even date herewith by myself,
conjointly with Frank A. Pickernell for an Improvement in Busy Signals for
Telephone Circuits and, except as elements of a combination are therefore not
claimed herein.
The operation may generally be described as follows:-Station S. signals the
central station in the usual manner. Its circuit Las already stated is through a
spring jack j located on the connecting board, extending thence to the corresponding
or complementary spring jack J at the terminal board A, section a and then to
the terminal drop Z. The operator at the terminal board inserts the answering
plug P of any connector c into the jack J and receives the call. This plug is for
the present the terminal of the telephone loop, the three way cam being properly
turned and the instructions of the substation are therefore properly received and
answered. But the insertion of the plug in the jack J is an occupation of the
circuit and to forestall an interruption, by an attempt to connect with the said
circuit at its connecting board jack while such occupation continues the operators
at the said connecting board are to be informed that the circuit of station S is busy
and the spring jack; therefore blocked. This is done by providing that the
insertion of the plug at J shall close a local circuit in which is located the signal
receiver V located in close proximity to the jack j. The setting of this signal
operates to prevent the connection of circuit L at the jack j of connecting board B
with the circuit of any other customer calling for station S, which connection
otherwise might take place and interfere with the service.

page_text: A similar electric visual indicator V 2 protecting the spring jack J at the
terminal board A. is not required to become operative as the presence of the
plug in the jack there shows at once the line to be busy; and it does not
become operative because no plug has been placed in spring jack j to close its
circuit.
The operator at the terminal section a having received the call from station S
finds that a connection with some other station, say S2, is desired. If the circuits
of station S and S2 should happen to be represented on the same or adjacent
terminal boards, they may be at once connected directly with a regular link
connection or pair of switch-board cords Y in the ordinary way and in that case
the circuit being connected through the connecting board to the terminal board, in
the same manner as is circuit L, the insertion of the plug in its terminal board
jack would operate the visual signal V at its connecting board jack and would
protect the connection from interference there, also in the same manuer as in the
case of circuit L.
But the circuit L2 of station S2 as indicated in the drawing is terminated
at a remote terminal section a 4 and must be reached through the connecting
board.
The operator therefore inserts the second plug P 2 of the pair in the spring
jack 13 of the ordering or instruction circuit 12, extending from said spring jack
by branch 14 and main 12 to the head telephone of a switching operator stationed
at some point b at the connecting board near to the line wanted.
Over this, the said connecting board operator is instructed to connect line L2 of
station S2 with the office trunk conductor O, extending between the terminal board
section a to the point b at the connecting board.
The second plug of the link connection Y would now be inserted in the jack
of the specified trunk as shown and at the connecting board the plug terminal of
said trunk would be inserted in the jack j2 of line L2 of station S 2.
This last plug connection automatically operates the visual indicator v at the
terminal board end of the office trunk, and also severs the end of line L2 which
extends to the terminal board a 4 and actuates the visual indicator V 2 of said line
associated with its terminal board jack thereby indicating to the operators at that
and adjacent sections a 3 and a 5 that the line of station S2 is busy.
It also in co-operation with the connection at the spring jack end of the trunk
sets the visual signal at the connecting board jack j2 to serve as a trunk
disconnection signal.
If line L2 should on the reception of the order for its connection be found
at the connecting board to be already busy, the operator there would automatically
signal the fact to the answering operator and also to the calling station by inserting
the trunk plug P in the busy spring jack K thereby connecting the main line L
and the trunk signal circuits to automatic devices sending preconcerted busy
signals by means of the herein before described apparatus connected with said
busy jack.
Further than the loop connection of the call generator M with the three way
cam switch, I have not shown any special call key device for signalling sub-
station S2 over its line L2, but any of the ordinary and well known call key
devices may readily be subjoined to or substituted for said cam switch and loop in
a manner well understood.
In connection with the cam E, I show that the generator loop includes two
graduating electro magnetic resistances, and in practice I have found it feasible to
so arrange such resistance and retardation coils, that a regular alternating current
generator adapted to efficiently ring the ordinary polarized telephone bell will not
produce any material sound in a telephone included in the same circuit; the
alternating currents being so graduated, and their crests so rounded, that they do
not act upon the telephone while continuing to efficiently operate bells.
1 call a generator so arranged a graduated generator and as the same is
described in a separate application for Letters Patent filed by myself and Frank

page_text: A. Pickernell as joint inventors, contemporaneously herewith, and entitled an
Improvement in Signalling Apparatus and Circuits no claim is made herein for
the same.
}
In the use of this apparatus after the order has been given to the connecting
board operator to connect a given trunk with the line wanted, the cam E is turned
to the generator-side and so left, while other calls are being answered on other cord
connections.
As soon therefore as the connection is made at the connecting board, the bell at
the desired station being connected with the generator will ring continuously until
the attendant there takes down his telephone and begins to talk. But when that is
done, though the generator connection continues, the two persons talking at the
two connected stations are not disturbed thereby, because their telephones do not
respond to the graduated call currents.
The ringing however does not long continue for the operator after having
attended to other calls returns to this connection and finding the signal v set,
knows that the connection has properly been completed and reverses the cam lever
so as to disconnect the generator and bridge the disconnecting drop across the
circuit. By this automatic ringing feature much time is saved, as the operator is
enabled to attend to other work while it is going on.
On the conclusion of the communication either or both stations may ring off as
usual, and the disconnecting drop D is operated. The operator withdraws the
plugs P and P 2 from the jacks J and k. The withdrawal of P opens the
local circuit of signal V of line L and removing said signal liberates the jack j and
restores the normal circuit of L.
The withdrawal of P 2 opens the local circuit of sigual V of L2 and removing
the said signal notifies the connecting board operator that the trunk plug P 3 should
be withdrawn from jack j 2.
Until that plug is removed and circuit L 2 thereby set at liberty the signal v at
the trunk jack k and V 2 at the terminal board jack of said circuit L2 remain
set, but the station S 2 can still signal the central station through the trunk
drop z.
And finally, the trunk plug P 3 having been withdrawn from the connecting
board jack 2 the local signal circuit of vis opened restoring that signal to its
normal state, and declaring the trunk conductor to be at liberty; the signal V 2 at
the terminal board end of circuit L 2 being in the same local circuit is also restored
indicating the liberty of said main circuit L 2, and the normal state of said main
circuit is resumed.
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 system the combination of circuits converging from
sub-stations to a central station, terminal switchboards and a connecting switch-
board at this latter station, some circuits going to one terminal board only and
others only to other boards and each circuit from a substation being led through a
spring jack at the connecting switchboard to a spring jack and call receiving device
at one of the terminal switchboards.
2. In a telephone exchange system the combination of circuits converging to a
central station, terminal switchboards and a connecting switchboard at this station,
some circuits going to one terminal board only and others only to other boards,
each circuit being led through a spring jack at the connecting switchboard to a
spring jack and call receiving device at one of the terminal switchboards, a series
of office trunk conductors extending from each terminal switchboard to the con-
necting switchboard, a spring jack at the terminal switchboard end of each of the
office trunk conductors-a series of flexible conductors at each terminal switch-
board with a plug at each end for uniting any of the terminal switchboard jacks
with the spring jack at the end of any of the office trunk conductors and a flexible

page_text: conductor at the connecting board end of each office trunk conductor with a plug.at
its end which can be inserted into the jack at the connecting board of other of the
circuits which converge to the station.
3. The combination substantially as herein before described, of an outer or con-
necting switchboard fitted with spring jack connections one for each line; an inner
or terminal switchboard formed in sections and fitted also with spring jack con-
nections for each line, on some one section substation circuits passing through the
connecting board and terminal board spring jacks successively; a plug connector
forming the terminal of an operators telephone circuit located at the terminal board
and adapted to fit in the spring jacks thereof for the purpose of answering calls; a
visual signal associated with each spring jack on the connecting board to indicate
whether the circuit of such jack is busy; and a circuit changer associated with the
corresponding spring jack on the terminal board controlling the said visual signal,
the said circuit changer being arranged to be operated by the act of making a
connection or disconnection by inserting the said plug connector into the said
corresponding spring jack for the purposes specified.
4. The combination in a telephone central station apparatus of an inner or
terminal switchboard divided into operators sections containing a given number of
spring jacks or plug sockets, each section being provided with independent
operating and supervising apparatus; an outer or connecting switchboard con-
taining spring jack connections; telephone substation circuits entering the central
station each passing through a single connecting board jack to a jack on that one of
the terminal boards at which is located its call annunciator, a series of office
trunk conductors extended from each terminal board to the connecting board, the
terminal board end of each being provided with a spring jack, and the connecting
board end with a flexible conductor and plug; whereby the said trunks are
adapted to serve as extensions through which a calling circuit at its terminal board
may connect at the connection board with called circuits terminating at other
sections; a series of double plug and cord connectors at each terminal section
for uniting the main circuit jacks to the office trunk jacks and an order or
instruction circuit extended from the several terminal board sections to an
operators telephone at the connecting switchboard substantially as and for the
purposes specified.
5. In a telephone exchange the combination substantially as hereinbefore
described of a connecting switchboard; a sectional terminal switchboard, and a
number of incoming substation lines each connecting with a spring jack at the
terminal switchboard after passing through a similar spring jack.or plug-receiving
connection on the connecting switchboard, with a series of plug and cord connectors
containing double main circuit conductors at each terminal switchboard section for
the
purpose of connecting any two circuits together through their respective jack
connections, three independent appliance circuit loops at each terminal board section,
including respectively the operators telephones the call sending generator, and the
disconnecting signal device, and a three way cam switch for each of the said plug
and cord connectors, in a bridge circuit between the said two main conductors
thereof, controlling the connection therewith of the said appliance loops, for the
purposes specified.
6. In a telephone central office system a divided switch-apparatus comprising a
terminal switchboard formed in sections, at which calls are answered and trans-
mitted, and connections initiated, each section being provided with spring jacks and
annunciators for a given number of main circuits and a switchboard at which con-
nections are made with circuits called for, the said switch board being fitted with
spring jacks only, one for each entering main circuit, each located on its circuit at
a point outside of the terminal board jack of the same circuit, in combination with
a series of office trunk conductors extending from spring jacks at each terminal
section to flexible conductors and plugs located at one or more points of the said
switchboard a series of double plug and flexible cord link connectors at each
terminal section for making connections between the main circuit and office trunk

page_text: jacks, telephones and call receiving and sending appliances adapted by suitable
switches (one for each cord) to be connected in derived circuit with the said link
connectors, and instruction or order circuits extending between a spring jack at
each answering or terminal section to which the operator may plug in and connect
his telephones, to an operators telephone at the connecting switchboard substantially
as described.
7. The combination in a telephone central office system with a divided switching
apparatus comprising a terminal switchboard formed in sections at which calls are
answered and transmitted, each section being provided with answering jacks and
annunciators for a given number of main circuits, a connecting switchboard having
a spring jack for each main circuit at which connections with called lines are
completed, a series of substation or main circuits each connected with one jack on
each board, a series of office trunk conductors extending hetween the several
terminal board sections and the connecting board, and adapted to connect the jacks
of one to those of the other, and detachable link connectors at the terminal sections
for uniting the main circuit jacks to the office trunks of an automatic visual electric
signal associated with each spring jack of each circuit and means for automatically
operating the indicator at either jack of said circuit by making a connection or
disconnection at the other.
8. The combination with a trunk conductor extending between two switchboards,
of an automatic visual electric signal consisting of an electric indicator located at
one or both termini thereof, controlled each through a circuit closer at the other
terminal which circuit closer is adapted to be actuated by the act of making a
connection or disconnection with such terminal, substantially as described herein.
9. The combination with a trunk conductor extending between two switchboards,
of an automatic visual system of electric signals to indicate at either end the
engaged or disengaged condition of the said conductor at the other the said
system comprising an electric indicator associated with each terminal of said con-
ductor, a circuit controller therefor at the other terminal of said conductor, a
normally open local circuit including a suitable generator extending between the
said indicator and controller, and means for automatically actuating such controller
and thereby operating said indicator by the act of making a connection or
disconnection with the trunk conductor terminal substantially as specified.
10. In a telephone central station apparatus a series of substation main circuits,
each passing successively through two spring jacks or like connection devices
located on different switchboards, and a series of office trunk conductors extending.
from one of the said switchboards where each said trunk has a spring jack
terminal, to the other where each has a plug terminal, combined with a visual
signal indicator located at each spring jack of the said main circuits and trunk
conductors each adapted to respond to connections or disconnections made at the
other jack of such main circuits, and at the plug end of such trunk conductors
respectively by means of circuit closing contacts electrically connecting with
said indicators and operated by the act of making such connections and
disconnections.
11. In a telephone central office system, a divided switching apparatus comprising
a terminal or answering switchboard formed in sections to which a determinate
number of substation circuits are assigned, a connecting switchboard on which all
substation main circuits are represented by a plug socket or jack, a series of such
main circuits connected serially with the connecting board and with some one section
of the terminal board, office trunk conductors extending from the sections of
terminal board, to different points at the connecting board and having at one end a
spring jack connection and at the other a plug connector, and means as indicated at
each terminal section for electrically connecting any main circuit jack with any
trunk conductor jack, combined with a system of visual signals to indicate at each
switchboard the use or disuse of a given circuit at the other board, the said signals
consisting of an electrical indicator associated with each spring jack of all main
circuits and means for automatically operating the same at either jack of any circuit

page_text: by inserting a plug in or withdrawing it from the remaining jack of such circuit,
and an auxiliary system of visual signals associated with each office trunk conductor
and comprising an electric indicator located at the end or ends thereof, and a
circuit controller therefor at the opposite end thereof arranged to be actuated by
any electric connection or disconnection made at such opposite end, whereby such
use or disuse of either end may be indicated at the other, all substantially as
.hereinbefore described.
12. In a telephone central office switching apparatus, the combination with a
series of main circuits, and a series of trunk conductors, each of both series being
furnished with a pair of connection devices whereby it may be connected with others,
of a series of normally open signal circuits extending each between the two members
of a pair of the said connection devices, a visual signal indicator in such circuits
located at each connection device of each pair, and a circuit closer for each such
-circuit and indicator located and associated with the remaining connection device of
the said pair and adapted to be actuated by each connection or disconnection made
therewith, whereby such connections or disconnections of main circuits made by
either member of a pair of connection devices are enabled simultaneously to make
or break its associated signal circuit, and to automatically announce themselves
at the other member of said pair.
13. In a telephone central station switching apparatus, the combination with two
switchboards one serving as an answering or terminal board, and being formed into
-a number of operators sections, and the other serving as a connecting board at which
the connection of the desired circuit is made, an answering telephone loop
terminating in a suitable plug connector located at each section of the said
-answering board, and office trunk conductors extending between the said two switch-
boards whereby a calling line answered at any section of the terminal board may be
temporarily extended to any desired part of the connection board; of a series of
order or instruction circuits each extending from an operator's telephone at the
-connecting switchboard to the terminal switchboard, where it divides into normally
discontinuous branches terminating at the several operators terminal sections in
.sockets adapted to receive the plug of said telephone loop substantially as described.
14. The combination of a main telephone substation circuit, a spring jack or plug
socket therefor, having main and local circuit contacts included therein, and located
.at a terminal switchboard at which calls are received and transmitted, a second
spring jack included in said circuit at a point between the first mentioned spring
jack and the substation, and located at a connecting or intermediate switch-board, a
visual signal such as a glow lamp or self restoring annunciator associated with the
latter at the said connecting board, a local circuit conductor extending from the
said signal to the local contacts of the terminal board spring jack where its circuit
is normally open, a plug connector adapted to be inserted in said spring-jack and
provided with main and local contact pieces adapted to register and connect with
those of said jack; and an electrical generator having one pole connected with the
local contact piece of said plug and the other connecting with a return conductor of
the said visual signal and adapted upon the insertion of said plug to close its own
-circuit through said visual signal, whereby the insertion of a plug at any spring-jack
at the terminal switch board is indicated at the connecting board jack of the same
line.
15. In combination with an office trunk-conductor extending between an answering
-or.terminal switchboard and a connection completing switch-board, a system of visual
signals comprising a normally open signal circuit, a source of electricity therefor,
two alternative circuit closers therefor at the connecting board, one completing the
circuit directly and thereby producing therein a steady current, and the other
completing the said circuit through a vibrator or current varying device, and
thereby producing a varying current therein, and a visual indicator such as an
incandescent lamp, or a self restoring annunciator included in the said signal circuit
at the answering board, and adapted to give distinctive signals in response to the
said circuit closers respectively, substantially as described.

page_text: 16. In combination with a telephone substation circuit, a switchboard with which.
such circuit is connected, and where its calls may be answered an independent
switchboard at which other substation circuits are represented by suitable con--
nection devices, and an office trunk conductor extending between the said
switchboards and adapted to interconnect the circuit at the first switchboard with
any desired circuit at the independent switch-board of a telephone apparatus at
the substation of the said first circuit, a visual indicator at the first switch-board
terminal of the said office trunk, and a compound busy signal transmitter located
at the independent switch-board terminal of said trunk, organised to transmit
busy signals adapted to manifest themselves audibly in said sub-station apparatus
and visually in said indicator at the said trunk terminal, whereby the busy
condition of a desired circuit may be indicated simultaneously at the calling
sub-station and at the switchboard connected therewith.
17. In a system of central telephone station apparatus, the combination with a
number of sub-stations on main circuits, an answering switchboard having a spring
jack for each circuit, a second or connecting switchboard also having a spring-jack
for each circuit, and office trunk conductors extending between the said two
switchboards of an office signalling circuit and an electrical generator therefor
associated with each trunk provided at the connecting board terminal thereof with
an absolute circuit closer operated by connecting the said terminal with a desired
line, and a current varying circuit closer operated by connecting the said terminal
with a special spring-jack, whereby steady or vibratory currents are alternatively
caused to circulate in the said signalling circuit and at the answering board
terminal thereof with a visual indicator adapted to respond with a distinctive
signal to either current, and to indicate alternatively thereby at the answering
board that connection is made with the circuit wanted or that said circuit is busy.
18. In combination with an office trunk conductor extending between an
answering or terminal switchboard and a connecting completing switch-hoard.
comprising a series of suitable spring-jacks, one for each main circuit, and a busy
signal spring-jack located at such connecting switch-board, a system of visual
signals for indicating at the said answering board the progress of a connection at
the connecting board, said system consisting of a signal circuit extending in
association with the said trunk between said switchboards, and being normally
open at the connection board, a source of electricity therefor two alternative circuit
closers therefor at the connecting board one located upon each main circuit spring--
jack adapted to complete the signal circuit directly and to establish a steady
current therein, when the trunk conductor is connected with said main circuit jack,
and the other located upon the busy signal jack, and adapted to complete the said
signalling circuit through a vibrator, a buzzer or a current varying device, and
thus to produce a varying current therein when the said trunk conductor is
connected with said busy signal jack, and a visual signal indicator included in the
said signal circuit, at the answering board and adapted to give distinctive signals
in response to and corresponding with the said circuit closers respectively, sub-.
stantially as described.
19. In combination with a main telephone circuit extending from an out-station
through an answering switchboard to an independent switchboard, at which are
located the connection devices of other main circuits, with which said circuit may
be connected for three through communications, and an audible signal receiving
instrument, such as a telephone included therein at such out-station, a local
signalling circuit extending in association with said main circuit from the said
answering switch-board to the said independent switch-board, a visual indicator
included therein at said answering switchboard and a compound busy signal trans-
mitter at said independent switchboard, provided with individual transmitting
devices for the said main and local circuits respectively and adapted to be
connected with said circuits and thereby to simultaneously operate said audible and
visual signal receivers each over its own circuit substantially as and for the
purposes specified.

page_text: 20. Telephone central office systems arranged substantially as hereinbefore
described and illustrated in the drawings annexed.
Dated this 7th day of February 1894.
CARPMAEL & Co.,
Agents for the Applicant.