IMPROVEMENTS IN AND RELATING TO TELEPHONE CENTRAL OFFICE SYSTEMS AND IN APPARATUS EMPLOYED THEREIN
Year: 1882

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, for an Invention of "IMPROVEMENTS
IN AND RELATING TO TELEPHONE CENTRAL OFFICE SYSTEMS AND IN
APPARATUS EMPLOYED THEREIN." A communication from abroad by George
Milton Hopkins, of Brooklyn, in the County of Kings and State of New York,
United States of America.
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark
at the Office of the Commissioners of Patents on the 11th February 1882.
ALEXANDER MELVILLE CLARK of 53 Chancery Lane in the County of
Middlesex, Patent Agent. "IMPROVEMENTS IN AND RELATING TO TELEPHONE
CENTRAL OFFICE SYSTEMS AND IN APPARATUS EMPLOYED THEREIN." [A commu-
nication from abroad by George Milton Hopkins, of Brooklyn, in the County of
Kings and State of New York, United States of America.]
These improvements relate to switch boards for connecting two or more line
wires at a central telephonic office and for signalling subscribers or users, and for
ascertaining their wishes through the central office telephone.
The Invention consists in movable spring switch bars combined with movable
transverse rods having cam levers for establishing a connection between two or
more of the switch bars, and at the same time removing the switch bars from the
ground connection. It also consists in a system of central office combined polarised
annunciators and relays for operating local circuits so as to move the transversc
bars carrying cam levers to disengage the cam levers and place the switch board in
its normal condition. It also consists in an arrangement of subscribers switch and
circuit whereby the subscriber may send either a positive or negative current over
the line and through the polarised annunciator and relay so as to call the attendant
at the central office, or operate the local circuit of the central office so as to return
the switch board to its normal condition.
The object of the Invention is to relieve the attendant at the central office switch
board from the necessity of replacing or removing any of the parts of the switch

page_text: board or connections after having connected the lines of two subscribers, and to
ensure the return of the switch board to its normal condition after the subscribers
have done using their lines.
All of the parts of the central office switch board are by preference secured to a
single board supported in a vertical position. Any desired number of vertical
brass spring switch bars are secured by their upper ends to a nonconducting strip
fixed to the board. The bars extend downward and their lower ends are covered
by a metal plate which is connected with the ground. Behind the lower ends of
the spring switch bars, there is a block of nonconducting material to limit the
rearward movement of the bars. One or more horizontal rock shafts extend across
the face of the switch bars a short distance from them and are journalled in posts
projecting from the board. Each shaft carries two studs which support a rod
parallel with the shaft and in about the same plane. Upon this rod are pivoted as
many cam levers as there are vertical spring switch bars on the switch board.
Theso cam levers have each a flat face which enables it to maintain a horizontal
position when the flat face is brought into contact with the switch bar, and the
handle of the lever is sufficiently heavy to disengage the lever and bring it into a
vertical position whenever its flat face is removed from the switch bar by the
means presently to be described. An arm projecting from the rock shaft carries
the armature of an electro magnet, the arm being pressed outward by an anta-
gonistic spring and the motion of the rock shaft is limited by a stop. One
terminal of the electro magnet is connected with the ground wire, and the other
terminal with the nearest post in which the rock shaft is mounted. The post at
the opposite end of each rock shaft is connected with the secondary wire of
the attendants' transmitting and receiving instrument, the latter consisting of the
transmitter, local battery, and primary wire of an induction coil in the primary
circuit and the secondary wire of the induction coil and receiving telephone in the
secondary circuit, the receiving telephone being also connected to the ground.
Between the posts and the secondary wire of the induction coil, there is a resistance
coil which prevents the local battery current from passing from one rock shaft to
another.
Upon the upper part of the board, there are as many polarised annunciators as
thero are switch bars in the series, one annunciator being connected electrically
with each switch bar. Above the polarised annunciators there is a series of
double contact signalling keys, one key for each annunciator and switch bar.
Each annunciator magnet is connected electrically with the top contact of one of
the signalling keys. The normal position of the spring of the key is in contact
with the top contact. The springs of the keys are connected respectively with
line wires which extend to the subscribers instruments, each of which is provided
with a double switch. This switch consists of two arms movable on pivots, the
pivot of the one being connected with the corresponding line wire, and the pivot
of the other being connected with the ground. There are four points of contact
on the switch which are connected with a local battery so that the two extreme
points communicate with one pole while the two intermediate points are connected
with the opposite pole. The two switch arms are connected together by a bar of
insulating material so that they may both be moved together. The lower contact
of each signalling key is connected with one pole of the main battery the other
pole of which is to earth, so that the subscribers bell may be rung at any time by
depressing the key corresponding with his line.
The main battery is connected with the pivot of the armature of each annunciator.
The polarised annunciators used in this connection are of the well known type in
which the magnetised bar carries an indicator card and is pivoted above the middle
of the space between the two poles of the annunciator electro magnet so that it
may be attracted by one pole and repelled by the other, its movement depending
upon the direction of the current. Below each magnetised bar and in a central
position relatively to the annunciator magnet, there is a small cup containing a
drop of mercury whose convex surface may be touched by the end of the said bar

page_text: in its excursions from one pole of the electro magnet to the other. The mercury
cups are connected electrically with the spring switch bars.
The operation of the device is as follows:-The subscriber moves the arms of his
switch so that a positive current is sent through the one arm of the switch over
the line to the corresponding key at the central office, thence through the
annunciator magnet spring switch bar and ground plate to the ground. The
current returns to the subscribers battery through the ground and the other arm of
the switch. The magnetised bar of the annunciator is thereby tipped which
attracts the attention of the attendant at the central office who immediately raises
the cam lever opposite the corresponding spring switch bar, thereby bringing the
bar into electrical connection with the attendants' receiving telephone through the
post of the rock shaft, resistance coil, and secondary wire of the induction coil, the
operation of raising the cam lever depressing the spring switch bar so that it breaks
contact with the ground plate. The subscribers line is then grounded through the
ground of the attendants telephone. The subscriber A. having requested to be put in
communication with subscriber B, the attendant then depresses the key corresponding
to the line wire of B, breaking connection with the annunciator and switch board
and making connection with the lower contact of the key sending a current from
the main battery through B's line and ringing the bell of subscriber B who answers
by moving his switch so as to send a current through the corresponding
annunciator. The attendant then raises the lever making contact with the spring
switch bar corresponding to B's line. The lines of A and B are now connected and
conversation may proceed between them, and when done, either of the subscribers
moves his switch-bringing the switch arms so as to send a negative current over
the line which returns the annunciator bar connected with that line to its normal
position. The bar in touching the mercury in the cup-completes a local circuit,
the effect of which is to excite the electro magnet whereby the rock shaft of the
switch board is rocked so as to withdraw the cam lovers from the spring switch
bars whereupon the latter regain their contact with the ground plate and the cam
levers swing into a vertical position.
The several parts of the switch board so far as its relation to the line upon which
the current has been reversed is concerned, are in their normal condition, but upon
the other line the magnetised annunciator bar remains unmoved until the subscriber
connected with it reverses the current on his line, when the remaining annunciator
will be readjusted and the whole will be in condition for another signal.
It is obvious that some of the forms of polarised telegraphic relay may be
substituted for the annunciators therefor. I do not limit or confine myself to the
use of the particular annunciator herein described.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Alexander Melville Clark in the Great Seal Patent Office on
the 9th August 1882.
A com-
ALEXANDER MELVILLE CLARK of 53 Chancery Lane in the County of
Middlesex Patent Agent. IMPROVEMENTS IN AND RELATING TO TELEPHONE
CENTRAL OFFICE SYSTEMS, AND IN APPARATUS EMPLOYED THEREIN.
munication from abroad by George Milton Hopkins, of Brooklyn in the County
of Kings and State of New York, United States of America.
This Invention relates to switch boards for connecting two or more line wires at
a central telephonic office, and for signalling subscribers or users, and for ascertaining
their wishes through the central office telephone. The Invention consists in
movable spring switch bars combined with movable transverse rods having cam
levers for establishing a connection between two or more of the switch bars and at
the same time removing the switch bars from the ground connection. It also
consists in a system of central office combined polarised annunciators and relays for
operating local circuits so as to move the transverse bars carrying cam levers to
disengage the cam levers and place the switch board in its normal condition. It
also consists in an arrangement of subscribers switch and circuit, whereby the
subscriber may send either a positive or negative current over the line and through
the polarised annunciator and relay so as to call the attendant at the central office
or operate the local-circuit of the central offico so as to return the switch board to
its normal condition.
The object of the Invention is to relieve the attendant at the central office switch
board from the necessity of replacing or removing any of the parts of the switch
board or connections after having connected the lines of two subscribers and to
ensure the return of the switch board to its normal condition after the subscribers
have done using their lines.
In the drawings, Figure 1 is a front elevation of a central office switch board
and a subscribers switch and battery forming a part of this improved central office
system. Figure 2 is a vertical section taken on line - in Figure 1. Similar
letters of reference indicate corresponding parts in both the figures.
All of the parts of the central office switch board are by preferenco secured to a
single board or back piece A. which is supported securely in a vertical position. Across
the board near the middle, there is a strip B of nonconducting material, to which
are secured the vertical brass spring bars a a, any desired number of which may be
used. These bars a extend downward and their lower ends are covered by a metal
plate C which is connected with the ground D by wires bb¹. Between the plate C
and board A, and behind the lower ends of the bars a, there is a block c of non-
conducting material to limit the rearward movement of the bars a. One or more
horizontal rock shafts E extend across the face of the bars & a short distance from
them, and are journalled in posts c¹³ projecting from the board A. Each shaft E
carries two studs d which support a rod e parallel with the shaft E and in about
the same plane. The rod e supports as many cam levers f as there are vertical
bars a in the switch board. The cam levers f have a flat face f¹ which enables
them to maintain a horizontal position when the flat face is brought into contact
with the bar a, and the handle of the lever is sufficiently heavy to disengage the
lever fand bring it into a vertical position whenever its flat faco is removed from
the bar a by the means presently to be described. To an arm g projecting from
the rock shaft E is attached an arinature E which is within the influence of the
electro magnet & secured to the base picce A. The arm g is pressed outward in

page_text: opposition to the attractive force of the magnet G by a spring h and the motion of
the rock shaft is limited by the stop i projecting from the post c². One terminal
of the magnet G is connected by a wire k with the ground wire b', the other
terminal of the magnet G is connected with the post c². The posts c' on the
opposite ends of the shafts E are all connected with the secondary wire of the
attendants transmitting and receiving instrument, the latter consisting of the
transmitter H, battery I, and primary wire of the induction coil J in the primary
circuit and the secondary wire of the induction coil J and receiving telephone K
in the secondary circuit. The receiving telephone is grounded through the wire 7.
Between each post c¹ and the secondary wire of the induction coil J there is a
resistance coil m which prevents the local battery current from passing from one
shaft E to another.
Upon the upper part of the board A there are as many polarised annunciators L
as there are bars a in the series, one annunciator being connected electrically with
each bar a. Above the polarised annunciators there is a series of double contact
signalling keys 1. 2. 3. 4 one key for each annunciator and bar. Each annunciator
magnet is connected electrically with the top contact n of one of the signalling keys
1. 2, etc. The normal position of the spring of the key is in contact with the top
contact 12. The springs 1. 2. 3. 4 are connected respectively with the line wires
1. 2. 3. 4 which extend to the subscribers instruments, each of which is provided
with a double switch N like that connected with the wire 2. This switch
consists of two arms op movable on the pivots o¹ p', the pivot o¹ being
connected with the line wire 2, and the pivot p' being connected with the
ground wire q. There are four points of contact r s t u on the switch which are
connected with the battery vso that the points ru communicate electrically with
one pole of the battery while the points st are connected with the opposite pole of
the battery. The two switch arms are connected together by a bar W of insulating
material so that they may both be moved together. The lower contact a¹ of each
signalling key is connected with a wire a leading to the main battery O grounded
through the wire b¹ so that the subscribers bell may be rung at any time by
depressing the key corresponding with his line. In order to trace each line and
its connections I have placed on the lines the signalling keys, the annunciators,
and the spring switch bars, the numbers 1. 2. 3 and 4 in addition to the letters of
reference. The same numbers belong to the same line in the various parts of the
switch boards. The battery O is connected with the pivot of the armature of
each annunciator L by a wire b². The polarised annunciators used in this connection
are of the well known type in which the magnetised bar & carries an indicator
card e and is pivoted above the middle of the space between the two poles of the
annunciator magnet so that it may be attracted by one pole and repelled by the
other, its movement depending upon the direction of the current. Below each
bar d and in a central position relative to the annunciator magnet, there is a
small cup containing a drop of mercury whose convex surface may be touched
by the end of the bar in its excursions from one pole of the electro magnet to
the other. The mercury cups are connected electrically with the spring switch
The normal position of the annunciators is shown by the two lower ones
in the drawing.
bars a
The operation of the device is as follows:-The subscriber at the switch N
moves the switch arms so that the arm o touches the point r, and the arm p touches
the point t, sending a positive current over the line 2 to the key 2 at the central
office, thence through the annunciator magnet 2 switch bar a, 2, ground plate C to
the ground D. The current returns to the subscribers battery through the ground,
ground wire switch arm, and point t and wire connecting the latter with the
battery. This results in tipping the bar d of the annunciator 2 which attracts the
attention of the attendant at the central office who immediately raises the cam
lever fopposite the spring switch bar a. 2. bringing the bar into electrical connection
with the attendants receiving telephono K through the post c¹, resistance coil m
and secondary wire of the induction coil J. The operation of raising the cam lever-f

page_text: depresses the spring switch bar a so that it breaks contact with the ground plate C.
The subscribers' line 2 is then grounded through the ground of the attendants
telephone K and ground wire l. Subscriber 2 then makes known his want, which
for example may be to communicate with subscriber 4. The attendant then
depresses key 4, breaking connection with the annunicator and switch board and
making connection with the lower contact a³ of the key, sending a current from
the battery through the line 4, ringing the bell of subscriber 4 who answers by
moving his switch so as to send a current through the annunciator 4, tipping its
magnetised bar d' as shown in the drawing. The attendant then raises the lever f
making contact with the spring switch bar a 4. The lines 2 and 4 are now con-
nected and conversation may proceed between subscribers 2 and 4, and when done
either of the subscribers moves his switch bringing the switch arms op into
contact with the points s u, thus sending a negative current over the line which
returns the annunciator bar connected with that line to its normal position. The
bar in touching the mercury in the cup completes a local circuit through the
wires b, bar d², mercury cup ƒ³, switch bar a. 2, cam lever f, bar e, stud d, shaft E,
post c², magnet G, and wires and b¹. The effect is to draw the armature F
towards the magnet G, turning the shaft E, withdrawing the cam levers f from
the spring switch bars a when the latter regain their contact with the ground
plate C and the cam levers swing into a vertical position. The several parts of the
switch board, so far as its relation to the line upon which the current has been
reversed is concerned, are in their normal condition, but upon the other line the
annunciator bar d remains unmoved until the subscriber connected with it
reverses the current on his line, when the remaining annunciator will be readjusted
and the whole will be in condition for another signal.
It is obvious that some of the forms of polarised telegraphic relay may be
substituted for the annunciators, therefore I do not limit or confine myself to the
use of the particular annunciator herein described.
Having described the nature of the said Invention for "Improvements in and
relating to telephone central office systems, and in apparatus employed therein,"
and the manner of performing the same, I declare that what I claim as the Invention
to be protected by the hereinbefore in part recited Letters Patent is.
1st. In a telephonic central office switch board, a series of spring bars, a series
of weighted cam levers on a support movable by an electro magnet, and a corre-
sponding series of relays for controlling a local circuit for operating the said electro
magnet constructed and combined substantially as herein specified.
2nd In a telephonic central office system the combination of the bars a, cam
levers frock shaft E, and magnet G, as herein specified
3rd The combination in a central office system of two or more spring bars a, two
or more weighted cam levers f, the rock shaft E, carrying the rod e, the magnet G,
and the annunciator L, adapted to control a local circuit, substantially as herein
specified.
4th In a telephonic central office system, the combination with the subscribers
lines, of current reversing switches and polarized annunciators whereby the sub-
scribers' can call attention at the central office, and return the annunciator to its
normal position, as herein specified.
5th In a telephonic central office switch-board the polarized annunciators L and
mercury cups f³, in combination with a local circuit, including the battery O,
magnet G, spring switch bars a and cam levers f, as herein specified.
6th In a telephonic central office switch-board, the combination of the double
contact keys, 1, 2, etc. annunciators L, bars a, and cam levers f, substantially as
specified.
7th In a telephonic central office switch-board, a series of spring bars a, a series
of cam levers f, and the ground connecting plate C, in combination with a series of
subscribers lines whereby one subscriber's line may be disconnected from the
central office ground, and connected with another subscriber's line substantially as
specified

page_text: Sth The combination of the receiving instrument K, and transmitting
instrument H with the rock shaft E, bars a, lines 1, 2, etc. and intermediate devices
substantially as herein specified.
In witness whereof I the said Alexander Melville Clark have hereunto set
my hand and seal this first day of August A D 1882
A M CLARK 17.01