IMPROVEMents in TelepHONE EXCHANGE SYSTEMS AND APPARATUS PART OF WHICH IMPROVEMENTS IS ALSO APPLICABLE TO OTHER SIMILAR PURPOSES
Year: 1882

page_text: LETTERS PATENT to Horace Hamline Eldred, of Queen Victoria Street, in the
City of London, for an Invention of "IMPROVEMents in TelepHONE EXCHANGE
SYSTEMS AND APPARATUS PART OF WHICH IMPROVEMENTS IS ALSO APPLICABLE
TO OTHER SIMILAR PURPOSES." Partly a communication from abroad by
Thomas B. Doolittle, of Bridgeport, in the County of Fairfield and State of
Connecticut, United States of America.
"
PROVISIONAL SPECIFICATION left by the said Horace Hamline Eldred
at the Office of the Commissioners of Patents on the 11th February 1882.
_HORACE HAMLIN ELDRED of Queen Victoria Street in the City of London.
"IMPROVEMENTS IN TELEPHONE EXCHANGE SYSTEMS AND APPARATUS PART OF.
WHICH IMPROVEMENTS IS ALSO APPLICABLE TO OTHER SIMILAR PURPOSES."
Partly a communication from abroad by Thomas B. Doolittle of Bridgeport in the
County of Fairfield and State of Connecticut United States of America.
This Invention relates to that system of Telephonic intercommunication for
privato and business purposes which consists of a number of Telephonic lines
assembled together and so organized that each Individual line establishes a direct
means of communication between one or more subscribers and a central or con-
necting Office. By means of such an organization each subscriber or other
authorized person provided with a telephone or other equivalent instrument may
at any time through the intervention of the Central Office with which he is
immediately connected be placed in direct communication with any other subscriber
who is connected in like manner with such central Office which is technically termed
an exchange office.
In the application of such a system to large Towns and Cities there must
necessarily be great numbers of individual subscribers provided with telephonic
Instruments. The place where these subscribers are situated will hereinafter be
designated as sub-stations each of which must be capable of being placed in direct
communication with any other at short notice whenever required. Under these
conditions however experience has shewn that the assembling together of so many
independent lines at one place and the greater frequency of calls for connection
between different subscribers which increase in much greater proportion than the
increase in the number of subscribers of sub stations gives rise to serious difficulties
and delays in performing the service of making the connections and thus greatly.
diminishes the economy efficiency and general utility of the system.

page_text: The object of this Invention is to diminish the herein before mentioned incon-
veniences by distributing the lines converging to a central station into different
groups cach group containing such a number of lines as experience shows inay be
conveniently attended by a single operator so that each such group of lines
constitutes in effect an independent central station being provided with its own
special switch-board and apparatus for transmitting and receiving signals and
making connections. The different switch boards belonging to different groups
of wires are connected together by direct wires which are technically termed
trunk wires Secondary or auxilliary central stations or exchanges inay in like
manner be located at different points within the geographical District embraced in
the operations of the general system and these should by preference be situated in
the neighbourhood of those centres of different branches of business which are
usually found in all large commercial cities. Each of these auxilliary central
stations will serve a group of subscribers located in that particular Geographical
sub-district whose private or individual lines will terminate therein. These
auxilliary exchanges are each provided with a switch board and are connected
with each other and with the principal Central Station by trunk lines arranged
upon the same principle as hereinbefore described.
The Invention comprises certain improvements in the construction of switch-
boards switches and apparatus for establishing the connection between different
lines so that the same may be effected with the utmost convenience and celerity.
The switch board at the central station consists preferably of an upright case the
upper portion of which is divided into boxes or compartments arranged in rows
the upper one being reserved especially for trunk and connecting lines. Each one
of these compartments is appropriated to a particular line either a sub station line
or a trunk line as the case may be and it contains all the special apparatus
pertaining to that particular line. The-operators-table-may be attached to the
case containing the switch board and project horizontally in front of it or it may
if desired consist of a detached table. Upon this table are mounted the connecting
devices for establishing communication between one line and another and also the
general apparatus for speaking and signalling which is designed for the use of
the operator or attendant in conversing with the subscribers and in making
connections.
one.
The special apparatus belonging to each individual line consists of a visual
signal or annunciator for receiving signals a key for transmitting signals and a
spring jack or device whereby the connections with other lines are formed. I will
now describe theso special devices in detail it being understood that the apparatus
in each compartment of the switch board is precisely similar to that in every other
The several parts of the apparatus are attached to a metallic frame which for
the sake of economy and convenience I prefer to form of a single casting consisting
of a vertical face plate having horizontal rearward extensions from the latter of
which extends vertically an angular bracket. An Electro-magnet is mounted upon
the upper rearward extension of the frame and has an armature pivoted at a
suitable point and provided with a Counterbalance of a weight just sufficient to
overbalance the armature and raise the same from the poles of the Electro magnet
when no electric current is traversing the latter. An annunciator drop or visual
signal is also provided which I prefer to construct in the following manner it being
pivoted by its lower edge at a point which is in the rear of its centro of gravity so
as to give the drop a tendency to fall forward through an angle of about 45 degrees
until stopped by the coming in contact of its bevelled lower edge with the face of
a plate. The drop is normally held in this position of unstable equilibrium by
means of a detent which is affixed thereto and projects rearwardly through a slot
in the face plate so as to take hold of the edge of the slot of the armature.
Thus it will be understood that when an electric current traverses the Electro
Magnet the armature is attracted and being drawn down towards the poles of the
Electro Magnet is disengaged from the detent which action permits the drop to fall
forward as bereinbefore explained. A key for transinitting signals is provided

page_text: which is pivotted to the metallic frame and is normally held by the pressure of an
insulated spiral spring against an insulated contact point which is termed its
resting contact. When the key is depressed its contact with the point is broken
and a new one formed with another insulated contact point beneath it which is
termed the working contact I employ a peculiar form of circuit changer called a
spring-jack which consists of a metallic bar pivoted to an insulated support while
its free end rests in a seat formed of insulating material. A contact spring is
attached to the under surface of the bar and this normally rests against a similar
contact spring attached to and in electrical connection with the frame. At the
rear of the metallic frame is attached a plate of insulating material upon which
are mounted four binding screws hereinafter termed Nos. 1, 2, 3 and 4. The
connecting wires from these binding screws are run as follows:-No. 1 is connected
by a wire with the spring jack No. 2 by another wire with the working contact
No. 3 by a third wire with the resting contact point passing through the coils of
the Electro Magnet No. 4 by a fourth wire with an insulated spring which when
required is employed to establish a connection with an audible signal or electric
bell common to all the lines which may be mounted upon the case containing the
switch or may be placed in any other convenient locality. This bell or alarm is
not in all cases an essential portion of the apparatus as the sound caused by the
falling of the Annunciator drop will usually be sufficient to notify the operator or
attendant that a signal has been transmitted from one of the substations. Ench
line entering the central station is attached to the binding screw No. 1 in its
appropriate compartment. The binding screw No. 2 of each compartiment is united
to a wire leading to one pole of a battery common to all the lines the other pole of
which is to earth. Binding screw No. 3 of each compartment is attached to a wire
leading directly to the earth while to binding screw No. 4 is connected a local
battery or branch of the main battery for operating the special audible signal
herein before referred to.
The normal circuit of each main line may be traced through its corresponding
annunciator compartment in the switch board as follows:-Entering at the binding
screw 1 it passes to the spring-jack and thence through contacts to the frame
thence through the key to the resting contact point through the coils of the Electro
Magnet to binding screw No. 3 and thence to the earth.
I will now proceed to describe the device for establishing communication at the
switch between two independent sub station lines. The operator's table is provided
with a number of switch cords or connectors. Each connector is made up of two
lengths of flexible conducting cord united by intervening stationary conductors.
Two metallic thimbles are provided which are inserted in suitable apertures passing
through the top of the table with their upper edges projecting a little above its
surface. The cords each consist of a flexible metallic conductor which is provided
with a nonconducting covering braided or woven upon it One end of the Cord is
attached by means of a screw to the switch pin which is a wedge of metal preferably
provided with an insulating handle whereby it may be conveniently manipulated.
The switch pin normally rests upon the metallic thimble and the conducting cord
connected therewith passes down through an opening within the thimble its opposite
end being attached beneath the table to one of the arms of a double circuit changer.
The flexible Conductor is made long enough to hang in a loop and a weight is hung
upon the bight of the Conductor thus tending to keep the switch pin in firma contact
with the metallic thimble. The other flexible Conductor in like manner passes
through the other thimble and is attached in precisely the same manner to the
other switch pin by means of a screw. This Conductor also carries a weight and
is attached at its opposite extremity to the other arm of the Circuit changer. The
two arms of the Circuit changer are linked together by an insulating connecting
bar which may be provided with a pin or handle for convenience of manipulation.
When this Circuit changer is in its normal position its respective arms rest upon
two metallic studs which are united beneath the table by a conducting wire. When
in this position-a continuous electrical connection exists between the two switch

page_text: pins by means of the Cords and the circuit changer. When the circuit changer is
shifted to the right its arms are removed from the studs before referred to and
placed upon similar studs. The last named studs are connected by wires with the
terminals of a Telephone which may be used either for transmitting a receiving
oral communications or a separate transmitter and receiving Telephone may be
employed if preferred. The thimbles are connected with each other and with the
earth by means of wires.
As herein before stated there are a number of independent connecting Conductors
upon cach Operators table each one of them being arranged in the manner just
described. The Telephone is however common to all the Conductors. Its respective
terminal wires are united with the corresponding studs throughout the series of
circuit changers so that when any one of them is turned to the right the Telephone
will be switched into the particular connecting circuit to which that circuit changer
appertains.
The several thimbles hereinbefore referred to are all likewise in electrical
connection with each other and with the earth.
The different switch boards in the same Office or in different Offices are connected
with each other by the trunk lines. I prefer to reserve the upper row of compart-
ments in each switch board for the trunk and connecting lines the remaining two
rows being devoted to individual subscribers lines.
The four binding screws in each compartment of each switch board are arranged
in the manner herein before described. The several line wires entering the station
are each connected to the binding screw No. 1 of their respective compartments.
The trunk or connecting lines are in like manner so arranged as to unite the
binding screw No. 1 in the proper compartment of one switch board with the
binding screw No. 1 of a corresponding compartment of the other switch board.
The number of trunk or connecting lines between different switch boards will of
course be determined by the extent of inter communication which is found to be
required between subscribers connected with different boards. The trunk lines
connecting different central offices are arranged upon the same general plan as
those connecting different switch-boards in the same office with the exception that
in large exchanges it will be more convenient to devote one or more entire switch-
boards to the trunk line connections and place that in charge of a special operator.
In small exchanges a part of one of the ordinary switch-boards will be sufficient
to accomodate all the trunk line connections required.
In order to illustrate the practical operation of the improved system I will first
describe the process of establishing communication between two sub stations
connected with the same switch board and afterwards between two sub stations
connected with different switch boards. For example if one sub station wishes to
communicate with another sub station the first transmits a call signal by means of
his battery, magneto generator or other equivalent device which signal passes
through the corresponding compartment and releases the drop of the Annunciator
allowing it to fall forward. The operator at the table inserts one of the switch
pins into the spring-jack of the said compartment and then moves the corresponding
circuit changer to the right which brings the telephone into the circuit. The 4
Circuit of the corresponding line now passes from the line wire to the spring-jack
thence through the connecting cord to the Telephone and from the Telephone
through the other portion of the connecting Cord to the other switch pin which
rests upon one of the metallic thimbles and is therefore in connection with the
earth. The operator or attendant by making use of the Telephone ascertains that 5
the sub station in question wishes to communicate with a certain sub station he
accordingly removes the second switch pin of the pair from the thimble on which
it rests thus breaking connection with the earth and inserts it in the corresponding
spring-jack still keeping his Telephone in the connecting circuit until he learns
that the Correspondents are in communication with each other. He then turns 5
bis circuit changer to the left thus removing the central Office telephone from the

page_text: circuit and leaving the two lines in direct connection with each other through the
circuit changer and flexible conductors.
If the connection is to be made between two sub stations which are connected
with different Switch boards the operation is the same as that last described up to
the point of inserting the second switch pin before doing which the operator at one
switch board first presses the key in that compartment of his switch which
communicates through one of the connecting wires with the other switch board.
This completes a circuit from the signalling battery or Generator through the
binding screw 2 and the key thence through the frame and spring-jack to the
binding screw 1 from whence it traverses a wire to the Annunciator No. 1 of
board No. 2. The signalling current operates this Annunciator and passes to the
ground in precisely the saine manner as a signal received from an individual
Subscriber. After signalling the operator of the second switch board in this
manner the operator of the first switch board places the second switch pin in the
spring-jack of the Compartment through which he signalled the second operator
and the latter then completes the connection with the required sub-station precisely
as in the first instance. The operation is similar when the subscriber desired is
connected with a different central Office. In this case connection is mado with the
trunk line switch board or compartiment and through this to the required Central
office and at that Office with the required subscriber.
After completing a connection through his own switch board each operator
restores the Annunciator drop to its normal position and leaves the charge of the
united Circuit in the hands of the Operator making the last connection. This
Operator upon learning that the correspondence has terminated transmits a call
signal by depressing the proper signal key which traverses the connecting or trunk
line to the first switch board This action releases all the Annunciator drops of the
compartments through which the connection has been made thus notifying the
several operators to restore all the connections to their normal position.
When for any reason the constant attention of an operator is not required at the
switch board a single battery or other electric generator may be connected with
the binding screws No 4 of each compartment which may be made to sound an
Electric Alarm bell whenever any one of the Annunciator drops falls forward and
closes the circuit through its contact point and spring in the manner hereinbefore
explained.
In order to provide a less complicated arrangement of switching devices at the
central station I employ apparatus which is partly automatic in its action.
For this purpose I combine with a series of independent telephone or telegraphic
lines extending from a central exchange station to a corresponding number of
sub stations a series of Electro Magnets at the Central exchange Station one of
which is included in the circuit of each of the said lines and which is alapted to
release an Annunciator drop and to simultaneously actuate a switch which latter is
so arranged as to disconnect its corresponding electro Magnet from the line and to
simultaneously form a new connection between the latter and a single normally
open earth circuit at the central exchange station containing a receiving instrument
whereby the transmission of a signal automatically switches the receiving instrument
into connection with the particular line from which the signal procee Is.
The arrangement of the apparatus in connection with each of the lines is similar
and it will suffice to described that attached to one of them.
An electro magnet is mounted upon a suitable bracket or other support which is
preferably attached to the back of an upright wooden frame or base board.
Opposite the electro magnet on the front of the board is an Annunciator drop or
other analogous signal which may consist of a plate surrounding a panel within or
upon which panel the designating number of the line may be placed. The shield
shutter or drop is hinged at its lower edge and when in its normal position stands
upright in a position of unstable equilibrium in front of the panel concealing it
from view. The drop is retained in this position by a detent on the end of a lever
to the opposite extremity of which is attached the armature of an electro magnet

page_text: The armature is ordinarily drawn away from the Electro Magnet by a spring
which at the same time acts to keep the detent engaged with the upper edge of the
drop.
When an Electric Current or pulsation is sent through the Electro Magnet the
latter attracts its armature lifts the detent and releases the drop which falls forward
and downward thus exposing the designating number or character upon the panel
behind it. Those parts of the apparatus are all well known and in themselves form
no part of this Invention.
Each of the drops is provided with a switch which is automatically operated by
the fall of the drop itself. This switch may consist of a flat spring secured at one
end by a screw. The free end of this spring normally rests against a finger
projecting from the lower edge of the drop and by its elasticity presses against the
latter sufficiently to form an Electric contact. When the drop is tilted and falls
down against a stop the finger is withdrawn and the spring is permitted to touch
a contact point.
The peculiar arrangement of Electric Circuits which forms the principal feature
of this part of the Invention will be best understood by tracing the connections of
one of the lines. This line is continuous with a wire which leads to a binding
screw in metallic connection with the spring consequently the circuit traverses the
spring drop and a wire to Electro Magnet and then by another wire to the ground
or earth wire. When the drop falls the connections are changed so that the circuit
passes from spring to a contact point and thence to a normally open earth wire in
which is placed a telephone. It is desirable to have a Magneto Electric or other
signal transmitting device and an Electro Magnet signal bell arranged in branch
circuits so that they may be thrown into or out of the normally open earth circuit
at pleasure by means of a switch.
All the normal line circuits after traversing the Electro Magnets terminate in a
common earth wire and all the line circuits by the fall of their respective drops are
disconnected therefrom and connected to the normally open earth Circuit containing
the instruments the transmitting device being common to all the branch circuits
which have been switched off by the fall of their respective drops.
The operation of the apparatus is as follows:-
An Attendant is stationed in the Central Office in the vicinity of the signal bell
transmitter and Telephone the switch being turned to suitably connect the wire.
If now a signal is received over any one of the lines the corresponding drop falls
exhibiting the designating number of the line from which the signal has come and
simultaneously connecting that line with the opon earth circuit and similarly with
any number of the lines so that if a signal is given on Bell it may be answered by
the attendant by means of the Generator after which conversation can be carried
on by switching the Telephone into circuit. When the number of lines is very
large an attendant may be stationed with his ear constantly at the Telephone so
that a person at a sub station of any line would only need to transmit his signal
and then immediately speak through the Telephone to the attendant without waiting
for his signal to be answered and thus inuch time would be saved.
The Telephonic lines are carried overhead in elevated boxes or conduits supported
by pillars any required number of which latter may be utilized as test boxes for
the wires and as branch Conduits for the conveyance of the wires into houses. The
boxes or conduits are so constructed that the wires are maintained separate or
insulated from each other either by laying each wire in a separate groove or cavity
in the box or otherwise At Street crossings the boxes or conduits are by preference
made of an arched form so as to obtain an improved asthetic effect and these arches
may be surmounted by Electric lamps the wires for which as also the Telegraph
wires may be likewise carried in the said elevated boxes or conduits or in lieu of
the wires being carried across streets above ground they may be conducted down
the pillars and across the street underground and then up the pillars at the opposite
side to the box or conduit.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Horace Hamline Eldred in the Great Seal Patent Office on the
10th August 1882.
HORACE HAMLINE ELDRED, of Queen Victoria Strect in the City of London
"IMPROVEMENTS IN TELEPHONE EXCHANGE SYSTEMS AND APPARATUS PART of
WHICH IMPROVEMENTS IS ALSO APPLICABLE TO OTHER SIMILAR PURPOSES."
Partly a communication from abroad by Thomas B. Doolittle of Bridgeport, in the
County of Fairfield, and State of Connecticut United States of America.
The said Invention relates to that system of telephonic intercommunication for
private and business purposes, which consists of a number of telephonic lines
assembled together and so organised that each individual line establishes a direct
means of communication between one or more subscribers and a central or
connecting office. By means of such an organization each subscriber or other
authorized person provided with a telephone or other equivalent instrument may
at any time, through the intervention of the central office with which he is
immediately connected, be placed in direct communication with any other subscriber
who is connected in like manner with such central office which is technically
termed an exchange office.
In the application of such a system to large towns and cities there must
necessarily be great numbers of individual subscribers provided with telephonic
instruments. The place where these subscribers are situated will hereinafter be
designated as sub-stations each of which must be capable of being placed in direct
communication with any other at short notice whenever required. Under these
conditions, however, experience has shown that the assembling together of so many
independent lines at one place, and the greater frequency of calls for connection
between different subscribers, which increase in much greater proportion than the
increase in the number of subscribers of sub stations, gives rise to serious
difficulties and delays in performing the service of making the connections and
thus greatly diminishes the economy efficiency and general utility of the system.
The object of this Invention is to diminish tho bereinbefore inentioned incon-
veniences, by distributing the lines converging to a central station into different
groups, each group containing such a number of lines as experience shows may be
conveniently attended by a single operator; so that each such group of lines
constitutes in effect an independent central station being provided with its own
special switch board and apparatus for transmitting and receiving signals and
making connections. The different switch boards belonging to different groups of
wires are connected together by direct wires which are technically termed trunk
wires. Secondary or auxilliary central stations or exchanges may in like manner
be located at different points within the geographical district embraced in the
operations of the general system and these should by preference be situated in the
neighbourhood of those centres of different branches of business which are usually
found in all large commercial cities. Each of these auxilliary central stations will
serve a group of subscribers located in that particular geographical sub-district
whose private or individual lines will terminate therein. These auxilliary
exchanges are each provided with a switch board and are connected with each
other and with the principal central station by trunk lines arranged upon the same
principle as hereinbefore described.
The invention comprises certain improvements in the construction of switch
boards switches and apparatus for establishing the connection between different
lines so that the same may be effected with the utmost convenience and celerity. -

page_text: In the accompanying drawings, Figure 1, is a perspective view of a switch
board and operator's table embodying the improvements. Figure 2, is a side
elevation partly in section of the signalling and connecting apparatus of one of
the compartments of the switch board. Figure 2 A, is a detached view of a
portion of the same. Figure 3. is a front, and Figuro 4 is a rear elevation of the
same. Figure 5 is a diagram illustrating the arrangement of the electrical
connections in the switch boards, and Figure 6. is a diagram illustrating tho
.connections between different switch boards in the same and in different offices.
The switch board represented in Figure 1. is designed to be located at a central
station and to accomodate a maximum number of fifty subscribers or sub station
lines, which is usually found to be as great a number as can be conveniently
attended by a single operator. The switch board consists preferably of an upright
case A. the upper portion of which is divided into boxes or compartments B, B.
In the drawing I have shown seventy five of these compartiments, arranged in
threo rows of Twenty five each, one above the other, the upper one being reserved
especially for trunk and connecting lines. Each compartment may conveniently
be about three and a half inches in height, and one inch in breadth, and about
four inches in depth from front to rear. Each one of these compartments is
appropriated to a particular line, either a sub-station line, or a trunk line, as the
case may be and it contains all the special apparatus pertaining to that particular
line. C. is the operator's table, which may be attached to the case A, and project
horizontally in front of it as represented in Figure 1, which is the arrangement I
prefer, or it may if desired consist of a detached table. Upon this table are
mounted the connecting devices for establishing communication between one line
and another, and also the general apparatus for speaking and signalling which is
designed for the use of the Operator or attendant in conversing with the subscribers
and in making connections.
one.
The special apparatus belonging to cach individual line consists of a visual signal-
or annunciator for receiving signals, a key for transmitting signals and a spring-
jack, or device whereby the connections with other lines are formed. I will now
describe these special devices in detail it being understood that the apparatus in
cach compartment of the switch board is precisely similar to that in every other
The several parts of the apparatus are attached to a metallic frame, which
for the sake of economy and convenience, I prefer to form of a single casting con-
sisting of a vertical face plate a (see Figures 2, 3, and 4) having horizontal rearward
extensions a, a, from the latter of which extends vertically an angular bracket az,
D is an Electro-Magnet, which is mounted upon the upper rearward extension
of the frame a,, and which has an armature d, pivoted at d₁, and provided with a
counterbalance d, of a weight just sufficient to overbalance the armature d. and
raise the same from the poles of the electro-magnet D, when no electric current is
traversing the latter. E, is an annunciator drop or visual signal, which I prefer to
construct in the manner illustrated in Figures 2, and 3, it being pivoted by its
lower edge at the point e, which point being in the rear of its centre of gravity
gives the drop a tendency to fall forward through an angle of about forty five
degrees, until stopped by the coming in contact of its bevelled lower edge c, with
the face of the plate a. The drop E. is normally held in this position of unstable
equilibrium by means of a detent c. which is affixed thereto and projects rearwardly
through a slot in the face plate so as to take hold of the edge of the slot dy in the
armature.
Thus it will be understood that when an electric current traverses the electro-
magnet D. the armature d. is attracted and being drawn down towards the poles of
the electro magnet is disengaged from the detent e, which action permits the
drop E to fall forward as herein before explained. In Figure 1 four drops aro
shown tilted forward in this position. F, is a key for transmitting signals, which
is pivoted at f, to the metallic frame a and is normally held by the pressure of an
insulated spiral spring f, against an insulated contact point g, which is termed its
resting contact. When the key is depressed its contact with the point g, is broken

page_text: and a new one formed with another insulated contact point h, beneath it,
which is termed the working contact. J, is a peculiar form of circuit changer, called
a spring-jack which consists of a metallic barj, pivoted at j, to an insulated support
while its free end rests in a seat j₁, formed of insulating material. A contact-
spring j, is attached to the under surface of the bar j, and this normally rests
against a similar contact spring j₁, attached to and in electrical connection with the
frame at a. At the rear of the metallic frame is attached a plate of insulating
material G, upon which are mounted four binding screws. In Figures 4 and 5
these are respectively numbered 1, 2, 3, and 4. The connecting wires from these
binding screws are run as follows: (See Figures 2 and 5) No 1 is connected by wire
w, with the spring jack J: No 2 by the wire w, with the working contact h;
No 3, by the wire w, with the resting contact point g, passing through the coils of
the electro magnet D: No. 4 by the wire 2, with an insulated spring H which
when required is employed to establish a connection with an audible signal or
electric bell I, common to all the lines which may be mounted upon the case of the
switch board as shown in Figure 1, or may be placed in any other convenient
locality. This bell or alarm is not in all cases an essential portion of the apparatus,
as the sound caused by the falling of the annunciator drop will usually be sufficient
to notify the operator or attendant that a signal has been transmitted from one of
the substations. Each line entering the central station is attached to the binding
screw No 1. in its appropriate compartment. The binding screw No. 2, of eacli
compartment is united to a wire leading to one pole of a battery common to all the
lines, the other pole of which is to earth. Binding screw No. 3 of each compart-
ment is attached to a wire leading directly to the earth, while to binding screw
No 4, is connected a local battery or branch of the main battery for operating the
special audible signal hereinbefore referred to.
The normal circuit of cach main line may be traced through its corresponding
annunciator compartment in the switch board as follows:-Entering at the binding
screw 1, it passes to the spring-jack J, and thence through the contacts j, and j₁, to
the frame a, a, a, thence through the key F, to the contact point g. through the
coils of the cloctro magnet D to binding screw 3. and thence to earth.
I will now proceed to describe the device for establishing communication at the
switch between two independent sub-station lines. The operator's tablo C, seen in
Figure 1, is provided with a number of switch cords or connectors. Each connector
is made up of two lengths of flexible conducting cord united by intervening
stationary conductors as seen at L, and L₁, in Figures 1 and 7. The arrangement
will be best understood by reference to Figure 7 which exhibits a section of a
portion of the operator's table together with a theoretical diagram of the electrical
connections. S, and S₁, are two metallic thimbles which are inserted in suitable
apertures passing through the top of the table C, with their upper edges
projecting a little above its surface. The cords L and L, each consist of a flexiblo
metallic conductor which is provided with a non-conducting covering braided or
woven upon it. One end of the cord L is attached by means of a screw p, to the
switch pin P which is a wedge of metal of the form shown in Figure 2 A which
is preferably provided with an insulating handle whereby it may be conveniently
manipulated. The switch-pin P normally rests upon the metallic thimble S, and
the conducting cord L connected therewith passes down through an opening
within the thimble its opposite end being attached beneath the table at 7, to one
of the arms of the double circuit changer N. The flexible conductor L is made
long enough to hang in a loop and a weight M, is hung upon the bight of the
conductor as shown in Figures 1, and 7, thus tending to keep the switch pin P' in
firm contact with the metallic thimble S. The other flexible conductor L₁, in like
manner passes through the thimble S, and is attached in precisely the same
manner to the other switch pin P. by means of a screw P₁ This conductor also
carries a weight M, and is attached at its opposite extremity to the other arm of
the circuit changer N. The two arms of the circuit changer N are linked together
by an insulating connecting bar n, which may be provided with a pin or handle

page_text: for convenience of manipulation.
When the circuit changer is in its normal
position its respective arms rest upon two metallic studs o, o, which are united
beneath the table by a conducting wire w,, as indicated by the dotted line in
Figure 7. When in this position a continuous electrical connection exists between
the two switch pins P, and P₁, by means of the cords L and L, and the circuit
changer N. When the circuit changer N is shifted to the right its arms are
removed from o, o, and placed upon similar studs t, t. The last named studs are
connected by wires w, w, with the terminals of a telephone T, which may be
used either for transmitting or receiving oral communications or a separate
transmitter, and receiving telephone may be employed if preferred. The thimbles S,
and S₁, are connected with each other and with the earth at X by means of wires
As hereinbefore stated there are a number of independent connecting conductors
upon each operator's table each one of them being arranged in the manner just
described. In Figure 1, I have shown six of these conductors each provided with
its own circuit changer N, switch pins P, and P₁, cords L and L, and weights M
and M. The telephone T is however cominon to all the Conductors. Its respective
terminal wires w, and w, are united with the corresponding studs throughout the
series of six circuit changers N, N, so that when any one of them is turned to tho
right the telephone will be switched into the particular connecting circuit to which
that circuit changer appertains.
The several thimbles S. S. S₁. S₁. hereinbefore referred to are all likewise in
electrical connection with each other, and with the earth as shown in Figure 7.
The diagram Figure 6 illustrates the manner in which different switch boards
in the same office or in different offices are connected with each other by the trunk
lines. I prefer to reserve the upper row of compartments in each switch board for
the trunk and connerting lines the remaining two rows being devoted_to_
individual subscribers lines. In Figure 6. I have shown two central stations each
having two switch boards and one central station with a single switch board. The
four binding screws in each compartment of each switch board are arranged in the
manner hereinbefore described. The several line wires entering the station are
each connected to the binding screw No. 1, of their respective compartments. The
trunk or connecting lines are in like manner so arranged as to unite the binding
screw No. 1, in the proper compartment of one switch board with the binding
screw No. 1, of a corresponding compartment of the other switch board as will be
clearly understood by reference to Figure 6. The number of trunk or connecting
lines between different switch boards will of course be determined by the extent
of intercommunication which is found to be required between subscribers connected
with different boards. The trunk lines connecting different central offices are
arranged upon the same general plan as those connecting different switch boards 4
in the same office with the exception that in large exchanges it will be more
convenient to devote one or more entire switch boards to the trunk-line con-
nections and place that in charge of a special operator. In small exchanges a
part of one of the ordinary switch boards as illustrated in Figure 1, will be
sufficient to accommodate all the trunk line connections required.
In order to illustrate the practical operation of the improved system, I will first
describe the process of establishing communication between two sub stations
connected with the same switch board and afterwards between two sub-stations
connected with different switch boards. For example if sub station No. 15 wishes
to communicate with sub-station No. 40 he first transmits a call signal by means 5
of his battery, magneto-generator or other equivalent device which signal passes
through compartment No. 15 and releases the drop of the annunciator allowing it
to fall forward as shown in Figure 1. The operator at the table C, inserts one of
the switch pins into the spring jack of compartment No. 15 as shown and then
moves the corresponding circuit changer N to the right which brings the telephone T, 5
into the circuit. The circuit of line No. 15. now passes from the line wire to the
spring jack thence through the conuecting cord to the telephone and from the

page_text: telephone through the other portion of the connecting cord to the other switch pin
which rests upon one of the metallic thimbles and is therefore in connection with
the earth. The operator or attendant by making use of the telephone T ascertains
that number 15 wishes to communicate with number 49, he accordingly removes
the second switch pin of the pair from the thimble on which it rests, thus breaking
connection with the earth and inserts it in spring jack No. 49 still keeping his
telephone in the connecting circuit until he learns that the correspondents are in
communication with each other. He then turns his circuit changer N to the left,
thus removing the central office telephone from the circuit and leaving the two
lines in direct connection with each other through the circuit changer N and
flexible conductors L, and L, as shown in Figure 1.
If the connection is to be made between two sub-stations which are connected
with different switch boards for example between No. 31 and a substation on
switch board No. 2, the operation is the same as that last described up to the point
of inserting the second switch pin before doing which the operator at switch
board No. 1 first presses the key in that compartment of his switch board which
communicates through one of the connecting wires with switch board No. 2. This
completes a circuit from the signalling battery or generator R. (see Figure 5)
through the binding screw 2, and the key F, thence through the frame and spring-
jack J, to the binding screw 1 from whence it traverses wire w, to the annunciator
No. 1 of board No. 2. The signalling current operates this annunciator and
passes to the ground in precisely the saine manner as a signal received from an
individual subscriber. After signalling the operator of the second switch board in
this manner, the operator of the first switch board places the second switch pin in
the spring jack of the compartment through which he signalled the second operator,
and the latter then completes the connection with the required sub-station precisely
as in the first instance. The operation is similar when the subscriber desired is
connected with a different central office. In this case connection is made with the
trunk line switch board or compartment, and through this to the required central
office, and at that office with the required subscriber.
After completing a connection through his own switch board each operator
restores the annunciator drop to its normal position and leaves the charge of tho
united circuit in the hands of the operator making the last connection. This
operator upon learning that the correspondence has terminated, transmits a call
signal by depressing the proper signal key which traverses the connecting or
trunk line to the first switch board. This action releases all the annunciator drops
of the compartiments through which the connection has been made, thus notifying
the several operators to restore all the connections to their normal position.
When for any reason the constant attention of an operator is not required at tho
switch board a single battery or other electric generator may be connected with
the binding screws No. 4 of each compartiment which may be made to sound an
electric alarm bell whenever any one of the annunciator drops falls forward and
closes the circuit through its contact point and spring in the manner hereinbefore
explained.
In order to provide a less complicated arrangement of switching devices at the
central station, I employ apparatus which is partly automatic in its action.
For this purpose I combine with a series of independent telephone or telegraphic
lines extending from a central exchange station to a corresponding number of
sub-stations, a series of electro-magnets at the central exchange station one of
which is included in the circuit of each of the said lines, and which is adapted to
release an annunciator drop and to simultaneouscly actuate a switch which latter
is so arranged as to disconnect its corresponding electro-magnet from the line and
to simultaneously form a new connection between the latter and a single normally
open earth circuit at the central exchange station containing a receiving instrument
whereby the transmission of a signal automatically switches the receiving instru-
ment into connection with the particular line from which the signal proceeds.
Figure 8 is a front view of a portion of the apparatus of a central exchange

page_text: station embodying this part of the invention, and Figure 9, is a side view of the
same, showing one of the annunciator drops in section with the mechanism whereby
the same is operated and also illustrating in diagram, the arrangement of the circuits.
Referring to Figure 9, I, II and III are three independent lines entering the
central station which extend to a corresponding number of sub-stations. An
indefinite number of these lines may converge to one central station, but the
arrangement in such a case does not differ from that shown in the Figure and
need not be particularly described. The arrangement of the apparatus in con-
nection with each of the lines shown is similar, and it will suffice to describe that
attached to the line designated as I.
A is an electro-magnet mounted upon a suitable bracket or other support which
is preferably attached to the back of an upright wooden frame or base board J.
Opposite the electro magnet A. on the front of the board is an annunciator drop or
other analagous signal which may consist of a plate b, surrounding a panel within
or upon which panel the designating number of the line may be placed. The
shield, shutter, or drop B is hinged at its lower edge as shown at b', and when in
its normal position, stands upright in a position of unstable equilibrium in front of
the panel concealing it from view. The drop B is retained in this position by a
detent c, on the end of the lever C, to the opposite extremity of which is attached
the armature a, of the electro magnet A. The armature is ordinarily drawn away
from the electro-magnet by a spring D. which at the same time acts to keep the
detent c, engaged with the upper edge of the drop B.
When an electro current or pulsation is sent through the electro magnet A. the
latter attracts its armature, lifts the detent and releases the drop. which falls
forward and downward into the position shown in the sectional view of the
apparatus in Figure 9. thus exposing the designating number or character upon the
panel behind it. Those parts of the apparatus are-all-well-known, and-in-them-
selves form no part of this Invention.
Each of the drops B, B is provided with a switch which is automatically
operated by the fall of the drop itself. This switch may consist of a flat spring S.
st cured at one end by a screw &. The free end of this spring normally rests against
a finger f, projecting from the lower edge of the drop B. and by its elasticity
presses against the latter sufficiently to form an electric contact. When the drop
is tilted and falls down against the stop K, the finger f, is withdrawn and the
spring S is permitted to touch the contact point l.
The peculiar arrangement of electric circuits which forms the principal feature
of this part of the Invention will be best understood by tracing the connections
of a single line, for example the line I in Figure 9. This line is continuous with
the wire 1, which leads to the screw 2, and the latter is in metallic connection
with the spring S, consequently the circuit traverses the spring S. drop B and
wire 3 to electro magnet A, and then by wire 4, to the ground or earth wire 5.
When the drop B falls the connections are changed, so that the circuit passes from
spring S. to contact point 7, and thence by wire 6 to a wire 7. as illustrated by the
apparatus in connection with line II. Wires 6, 7, 8, 9 and 10 form a norinally
open earthwire in which is placed a telephone F, and it is desirable to have a 4
magneto electric, or other signal transmitting device H and an electro magnet
signal bell G, arranged in branch circuits 11, 12 so that they may be thrown
into or out of the normally open earth circuit at pleasure by means of a switch E.
All the normal line circuits 6, 6, 6 after traversing the electro magnets A, A, A,
terminate in a common earth wire 5, and all the line circuits by the fall of their
respective drops are disconnected therefrom and connected to the normally open
earth circuit containing the instruments F. G. or H which is common to all
the branch circuits which have been switched off by the fall of their respective
drops.
The operation of the apparatus is as follows:-
An attendant is_stationed in the central office in the vicinity of the signal
hell-C
E

page_text: wire 11. It now a signal is received over any one of the lines 1, 11, 111, the
corresponding drop falls exhibiting the designating number of the line from which.
the signal has come, and simultaneously connecting that line with the open earth
circuit and similarly with any number of the lines so that if a signal is given
on bell G, it may be answered by the attendant by means of the generator H,
after which conversation can be carried on by switching the telephone F. into
circuit. When the number of lines is very large an attendant may be stationed
with his ear constantly at the telephone F, so that a person at a substation of any
line would only need to transmit his signal and then immediately speak through
the telephone to the attendant without waiting for his signal to be answered, and
thus much time would be saved.
The telephonic lines are carried over head in elevated boxes or conduits
supported by pillars, any required number of which latter may be utilized as test
boxes for the wires and as branch conduits for the conveyance of the wires into
houses. The boxes or conduits are so constructed that the wires are maintained
separate or insulated from each other, either by laying each wire in a separate
groove or cavity in the box or otherwise. At street crossings the boxes or conduits
are by preference made of an arched form so as to obtain an improved esthetic
effect, and these arches may be surmounted by Electric lamps, the wires from which
as also the telegraph wires may be likewise carried in the said elevated boxes or
conduits or in lieu of the wires being carried across streets above ground they may
be conducted down the pillars and across the street under ground, and then up the
pillars at the opposite side to the box or conduit.
The parts of the said Invention which are my own Invention are those herein
before described with reference to Figures 8 and 9 of the accompanying drawings,
the reminder has been coinmunicated to me.
Having now described and particularly ascertained the nature of the said
Invention and the manner in which the same is or may be used or carried into
effect I would observe in conclusion that what I consider to be novel and original
and therefore claim as the Invention secured to me by the herein before in part
recited Letters Patent is,
1 The combination substantially as herein before set forth with reference to
Figures 1, to 7 of the drawings, of a series of main lines, a series of independent
conductors for establishing direct connection between the terminals of any two of
the said main lines, a telephone and a series of circuit changers one for each
connecting conductor for placing the said telephone in the circuit of any one of
the said connecting conductors.
2 The combination substantially as hereinbefore set forth with reference to
Figures 1 to 7. of the drawings of a visual signal, an electro-magnet, for causing
the same to be actuated or exhibited, a key provided with a resting and a working
contact, a spring-jack having one of its terminals connected directly to a line wire
and its other terminal to the lever of the said key, a connection from the resting
contact of the said key to the earth which includes the said electro magnet and a
connection from the working contact of the said key to one pole of an electric
generator whose remaining pole is connected to the earth.
3 The improved spring-jack constructed substantially as bereinbefore set forth
consisting of a yielding metallic bar which normally rests in a non conducting seat,
a contact point which forms an electrical connection with the said bar while it
rests in the said seat, and a tapering metallic switch pin which when inserted
between the yielding bar and a non conducting seat forms an electrical connection
with the said bar and at the same time lifts it from the contact point.
4. The combination substantially as herein before set forth with reference to
Figures 1 to 7 of the drawings, of a non conducting base a metallic thimble
inserted in the said base and electrically connected with the earth a flexible
conductor provided with a non conducting envelope passing through the said
thimble, a metallic switch pin, attached to and forming the terminal of the said
flexible conductor and a weight acting upon the said flexible conductor tending to

page_text: keep its terminal or metallic pin normally in electrical contact with the said
thimble.
5. The combination substantially as herein before set forth with reference to
Figures 1 to 7 of the drawings of a non conducting base, two metallic thimbles
inserted in the said base, and each electrically connected with the earth, two
flexible conductors provided with non conducting envelopes and passing through
the said thimbles respectively, which conductors terminate in switch pins, a
telephone and a circuit changer for connecting the terminals of the said Hexible
conductors together either directly or through the telephone.
6. A series of independent telephone or telegraph lines extending from a central
exchange station to a corresponding number of substations, in combination with a
series of electro magnets at the central exchange, one in each circuit each of which
acts to release an annunciator drop and thereby to actuate a switch, the said switch
being so arranged as to disconnect its actuating electro-magnet from the line and
to form a new connection between the latter and a receiving instrument which is
included in a single normally open earth circuit substantially as set forth.
7. A normally open earth circuit containing a signalling instrument and a
telephone in combination with a series of independent circuits, a series of switches
one for each circuit and a series of electro magnets one for each circuit whereby
either or any number or all of the said independent circuits when traversed by a
signalling current or currents is or are automatically connected with the said earth-
circuit, substantially as specified.
8 An indicating annunciator drop and an electro-magnet and its armature for
actuating the same in combination with a switch automatically operated by the
movement of such drop which acts to divert the circuit extending from the
signalling station from the said electro magnet to a normally open earth circuit
-containing-a-receiving-instrument-substantially-as-heroin before-set-forth..
9 The employment of elevated boxes or conduits for containing tolephonic or
other electric wires, the said boxes or conduits being supported on pillars capable
of serving as test boxes and for the conveyance of the wires into houses all
substantially as hereinbefore described.
In witness whereof I the said Horace Hamline Eldred have hereunto set my
hand and seal this fifteenth day of June in the year of our Lord 'one
thousand eight hundred and eighty two.
-
HORACE HAMLINE ELDRED. (L.&.)