An Improved Automatic Telephonic Exchange System.
Year: 1896

page_text: PROVISIONAL SPECIFICATION.
An Improved Automatic Telephonic Exchange System.
I, SALOMON BERDITSCHEWSKY-APOSTOLOFF of 23, Leadenhall Street in the City of
London, Engineer, do hereby declare the nature of this invention to be as
follows:-
My Invention relates to an improved automatic telephonic-exchange system having
for object to combine with the system of grouping described in the Specification of
my previous Patent dated the 19th day of June 1895 No. 11951 and also in another
Application for Letters Patent dated July 4th 1896 No. 14872 the provision for each
subscriber of an exclusively private metallic circuit (that is to say a circuit in which
neither earth nor a common return is used) the grouping system being available only
for manipulating and calling whilst the exclusive metallic circuits are available for
telephonic conversation, the power of establishing telephonic connection of any
other subscriber with the private metallic circuit of the subscriber called, being vested
solely in the latter so that such connection being established between any two
subscribers, absolute secrecy is ensured, it being impossible for any other subscriber
to establish connection with the same private circuit.
It has been found that owing to the great sensitiveness of telephonic instruments
the partial connection of different circuits as in grouping and common return
arrangements are productive of cross talk and other inconveniences, which it is the
object of this invention to avoid by the provision for each subscriber of a private
metallic circuit for conversation purposes, having no connection with either member
of any other circuit, the establishment of connection between any subscriber and
the private circuit of any other subscriber being only possible by the action of
the subscriber to whom that particular circuit appertains after the latter subscriber
has been "called " or "rung up."
For the purposes of my Invention each of the two members of each subscriber's
line is capable of being connected through the intervention of an electromagnetically
operated commutator at the central station appropriated to that subscriber with one or
other of two electro-magnetically propelled switches appropriated, the one to
"calling" and the other to "conversation" purposes, connection being made with
one pair of switches only at a time. The two "calling" switches of each
subscriber's line are caused the one by positive, and the other by negative current.
impulses sent from that subscriber's transmitter to travel across series of contact
strips accessible in common to the switches of all the apparatus at the central
station, the number of such contact strips in either series being equal only to the
square root of the total number of subscribers in connection with the exchange, the
contact strips of both series and the contacts on which the switches normally rest
when in their initial positions being connected in groups according to the system of
grouping described in my said former Patent so that any subscriber calling may
place the calling switches of his apparatus in connection with the contact strips
corresponding by their combination to any other subscriber and so effect connection
with the apparatus of that subscriber provided his calling switches are in their
normal positions. To each séries of such calling contacts there corresponds a series

page_text: of conversation strips which like the former are commensurate in extent with the
number of apparatus at the central station, each series of conversation strips
comprising as many separate conductors as there are subscribers in connection with
the exchange and these conductors being subdivided into as many sub series of
independent conductors as there are calling contacts, each such sub series
corresponding to a "calling" contact and containing as many independent
conductors as there are calling contacts so that for communication with each subscriber
there are provided two conductors one in each series forming together an exclusive
metallic circuit having no connection whatever other than with the normal conversation
contacts of that subscriber's apparatus at the central station and which connection is
in correspondence with the connection of the normal calling contacts and strips.
These conversation switches are transported along with the calling switches in their
motion from one calling contact to another so that when the calling switches of the
subscriber calling have been placed upon the combination of contacts corresponding
to the subscriber called, the conversation switches of the subscriber calling will be in
position with regard to the corresponding sub-series of conversation conductors to
admit of those switches being placed upon the particular conversation strips of those
sub-series which appertain to the subscriber called. This independent movement of
the conversation switches is effected, by electro-magnetic propelment mechanisms
energized by current impulses transmitted by the subscriber called, impulses of
opposite sign being sent in predetermined numbers mechanically regulated for each
subscriber.
Suitable provision is made by the commutators whereby the several electro-magnetic
apparatus which have performed their functions are cut out of action, and whereby the
calling subscriber after manipulating his calling switches as above described is enabled
to ring up the subscriber called without disturbing the other apparatus, and whereby
the calling switches are cut out of circuit before the conversation switches are moved
or brought into circuit. Provision is also made whereby after the termination of the
conversation, a certain number of impulses of a given direction sent by either
subscriber causes the return of all parts of the mechanisms of both subscribers to
their initial positions.
Dated this 9th day of October 1906
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.
COMPLETE DI ECIFICATION
An Improved Automatic Telephonic Exchange System.
I SALOMON BERDITSCHEWSKY-APOSTOLOFF, of 23 Leadenhall Street, in the City of
London, Engineer do hereby declare the nature of this invention and in what
inanner the same is to be performed, to be particularly described and ascertained in
and by the following statement :-
My Invention relates to an improved automatic telephonic exchange system having
for object to provide for each subscriber an exclusive metallic telephonic conversation
circuit (in which neither earth nor a common return wire is used) in combination
with the system of grouping described in a previous Patent dated the 19th day of
June 1895, No. 11951.
But the system of grouped circuits therein described is now employed only for
the purpose of effecting at the central station the electro-mechanical operations
incidental to the establishment of telephonic connection between any two subscribers,
whilst the exclusive metallic circuits are reserved solely for telephonic conversation.
The one set of circuits is quite independent of the other, and the power of establishing

page_text: telephonic connection with the exclusive metallic circuit of a subscriber "called" is
vested solely in that subscriber; so that when such telephonic connection has been
established between two subscribers it is impossible for any other subscriber to establish
any connection whatever with either of them, or to disturb their connection in any
way, or to overhear their conversation, so that absolute secrecy of the conversation is
ensured.
It has been found that owing to the extremely great sensitiveness of telephonio
instruments, any partial connection of different circuits (as in grouped circuits and
common return arrangements) might enable a conversation between two subscribers
to be overheard by other subscribers and is in any case productive. of "cross talk" and
humming or buzzing noises known (in French) as "la cuite," and this it is the special
object of the present invention to avoid. This is accomplished by the provision at
the exchange of metallic telephonic circuits, each 'exclusively appertaining to an
individual subscriber for conversation purposes only, such circuits having no connection
with each other or with either member of any other circuit whatever; it being only
possible for the subscriber "called" to establish telephonic connection between his
exclusive telephonie circuit and the telephone of a subscriber "calling." By this
means all the advantages of the system of grouping above referred to are retained and
yet absolute privacy of conversation is ensured.
The means by which this result is accomplished will be described with reference to
the accompanying drawings forming part of this specification. Before proceeding to
describe these in detail I will give a general description of the Invention with reference
to Figure 1 which is a diagram showing in perspective and in an elementary manner
an installation at the central station of sixteen metallic circuits and of as many
apparatus appropriated to different subscribers as is necessary to explain how, whilst
retaining the use of grouped circuits for electro-mechanical purposes, telephonic
connection by exclusive metallic circuits may be established between any two of the
sixteen subscribers. The several apparatus at the central station appropriated to the
respective subscribers are numbered I to XVI. All these apparatus are alike in
construction and operation and each is in connection with a particular subscriber's
telephone so that the description of one applies to all.
Let it be supposed that it is desired to establish telephonic connection between the
apparatus No. I and No. XV to which the telephones of the subscribers X and Z are
connected. The two wires L, L, connecting the subscriber's telephone with his
corresponding apparatus in the central station, are connected with the terminals of
a polarized relay R by means of which currents sent from the transmitter, cause the
various electro-magnetic mechanisms hereafter described to be successively operated
by the central station battery B. One of these mechanisms is a commutator S by
means of which the two wires L, L, of the subscriber's line may be put in connection
either with one or other of two pairs of electro-mechanically propelled switches, A, A*,
or C, C, appropriated the one pair A, A, to "calling" and the other pair C, C,
exclusively to "conversation" purposes, the connection of the line L, L, being only
possible with one pair of switches at a time.
The calling" switches A, A, are respectively adapted to make contact with a
series of insulating grouping conductors the two series being referred to collectively
by the letters a, a, and distinguished individually by numerals as la to 4a and
la to 4a. Those of each series are spaced at equal distances apart in the same
vertical plane and they extend horizontally any required distance in order that the
series a may be accessible in common to the switches A and the series a accessible in
common to the switches A of all the apparatus at the central station.
The number of conductors in the two series are factors whose product equals the
number of subscribers to be served, and the number being usually the same in each
of the two series is therefore equal to the square root of the number of subscribers.
Thus in the present example there are four conductors in each series a and a*.
When the switches A, A, are in their initial positions they rest normally on
contacts na, na, respectively; and these normal contacts na and na* are connected
with the conductors of the corresponding-series a, or a°, according to the system of

page_text: grouping described in the previous Patent; that is to say in the present example the
grouping of the contacts na is as follows: the contacts.na of apparatus Nos. I to
IV are connected by wires with the first conductor la; those of apparatus Nos. V to
VIII are connected with the second conductor 2a; those of apparatus Nos. IX
to XII are connected with the third conductor 3a and those of apparatus Nos. XIII,
to XVI are connected with the fourth conductor 4a.
The normal contacts na* are differently grouped as follows The contacts na of
apparatus Nos. I, Y, IX, and XIII are connected to the first conductor la; those
of apparatus Nos. II, VI, X, and XIV are connected to the second conductor 24;
those of apparatus Nos. III,, VII, XI, and XV, are connected to the third.
conductor 3a; and those of apparatus Nos, IV, VIII, XII and XVI are connected
to the fourth conductor 4a*.
The effect of this different grouping of the two series of contacts na and na*
is that, each of the sixteen possible combinations of a conductor of series a with a
conductor of series a corresponds to a different subscriber; so that any subscriber
desiring to call another subscriber need only cause the switches A, A, of his own
apparatus to be placed on the combination of conductors corresponding to the
norinal contacts na, na, of the subscriber to be "called" whereupon the latter
may be "called" provided that his switches A, A, are then situated on their normal
contacts na, na,
The means by which the switches A, A*, of the subscriber calling are placed on
the required combination of conductors will be described hereafter; for the present
it is sufficient to assume that the subscribers "calling" and "called" are respectively
represented by the telephones at X and Z, and by the apparatus Nos. I and XV at
the central station.
It will be seen by the diagram, Figure 1 that the switches A, A", of apparatus
No. I are placed in connection with the combination of conductors 4a, 3a, to which
alone the normal contacts na, na, of apparatus No. XV correspond and it will also
be seen that the switches A, A, of apparatus No. XV are on their normal con-
tacts na, na, and that when the positions of the commutators S of the two apparatus
were such that the lines of the subscribers X and Z were still in connection with the
switches A, A, of the corresponding apparatus Nos. I and XV then a bell in
telephone. Z might have been rung by currents sent from telephone X. So far,
although different in general arrangement, the principle and operation are similar
to what has been described in my former Patent, but of which it has been necessary
to repeat the description, in order that the novel part which I will now describe may
be understood.
To each series of conductors a, a, there corresponds a series of conservation
conductors, the two series being collectively referred to by the letters c, c*,
respectively, and distinguished individually as 1c to 16c, and 1c, to 16c. As they
are alike in all respects it will be sufficient to describe one series. The series cof
conversation conductors. are wires carried by insulating supports and are totally
independent and unconnected, there being as many such conductors in the series as
there are subscribers to be served... They are commensurate in length with the
number of apparatus at the central station so as to be accessible in cominon to the
conversation switches C, of all of said apparatus as hereafter described.
The series c, is divided into, as many sub-series or tiers as there are grouping
conductors in series a, and each tier comprises as many conversation conductors c, as
there are grouping conductors in the series a. These sub-series of conversation
conductors c, are in planes normal to the direction of motion of switches A; thus
this direction being vertical the planes of the sub-series of conductors c, would be
horizontal or vice-versu. Each conductor of series c, is connected by a wire with a
conversation contact.Cl situated below the series of conductors c, and accessible only
to the conversation switch C, of the apparatus to which that particular conductor
corresponds. The series c, is similar, so that for each subscriber to be served there
are provided two conductors one in series c, and one, in series c*; forming together
an exclusive metallic conversation circuit.

page_text: The conversation switches C, C*, of each subscriber's apparatus participate in the
rising movement of the switches A, A, of the same apparatus and the relation
between the conductors forming the exclusive conversation circuit of any one subscriber
and the combination of grouping conductors a, a, corresponding to that subscriber
is such that when the calling switches A, A*, of a subscriber "calling" are placed on
the combination of conductors a, a, corresponding to the subscriber "called," the
conversation switches C, C, of the subscriber "calling" will be at the proper height
to be placed on the conductors forming the exclusive metallic circuit of the
subscriber "called." Thus, in the example, the combination of grouping conductors
which corresponds to No. XV is 4a, and 3a, and the conversation circuit of No. XV.
is formed by the conductors 15c,. and 15c", which are situated at the height
corresponding to the conductors 4a, and 3a. Moreover the conductor 15c, is the
third conductor (counting from front to back) on the fourth tier whilst the
conductor 15c", is the fourth conductor on the third tier.
If then subscriber X has moved his calling switches A, A, to the position shewn
in Figure 1,he can call subscriber Z, and subscriber Z can then place X's-switches C, C*,
upon Z's conversation conductors 15c, 15c at the same time placing his own
conversation switches C, C, upon their conversation contacts C1, C1*. Consequently
the subscribers X and Z are in telephonic communication by an exclusive metallic
circuit, the connection of each subscriber's line with his calling switches being cut
off and connection being established with his conversation switches, through the agency
of the commutator S of his apparatus, this same commutator also producing other
effects as hereafter explained.
The independent movements of the calling switches A, A*, of the subscriber X and
of his commutator S are produced by electro-magnetic propel ment mechanisms
energized by current impulses from the central-station battery B under the control of
the polarized relay R of X's apparatus when that relay is influenced by current
impulses of one or other direction sent from X's transmitter; whilst the movements
of X's conversation switches C, C*, and of Z's conversation switches C, C, are produced
by their respective electro-magnetic propelment mechanisms being energized by
current impulses from the central-station battery B under the control of the relays RŘ
of both X's and Z's apparatus, when those relays are influenced by currents of the
one or other direction sent from Z's transmitter.
I will now proceed to describe the current distribution in the central station
apparatus of the "calling" and "called" subscribers with reference to the diagrains
Figures 2 and 3 which shew the apparatus of the subscribers X and Z respectively in
position for conversation. The initial positions from which they have both been
inoved may be readily imagined from the description.
The mechanisms of the two switches A, A*, being alike it will be sufficient to
describe one of them, it being premised that in order to represent diagrammatically
the positions and movements of parts which are really situated, or moved, in planes
other than the plane of the diagram, the positions of those parts relatively to the
other parts, is distorted so as to render it possible to represent them in the plane of
the diagram.
The switch A is mounted on a carriage D working as a nut propelled by a vertical
screw F capable of receiving step-by-step rotation by a ratchet and pawl propelment f
worked by electro-magnet E when energized by the current from battery B. By this
movement the switch A may be caused to make contact successively with the grouping
conductors 1a, 2a, 3a, 4a, and it is shown in Figure 2 as having been placed in
contact with conductor 4a, in which position it is retained by detent mechanism
which will be hereafter described.
The switch A is carried by a spring insulated from the carriage D. upon which are
also mounted a number of insulated springs carrying sliding contacts which work over
stationary contact strips all of which will be referred to in describing the working of
the apparatus.
The carriage D forms the guide for a rack rod G capable of being moved horizontally
by a worm Gactuated by bevel gearing g, g 1, actuated by shaft H parallel with screw F,

page_text: the bevel wheel y having a sliding connection with said shaft H. Loose upon the
screw F and shaft H are equal wheels f1,h1; geared together, the wheel f1 being in
one with wheel f. Driving connection is established between screw F and wheel f
or between shaft H and wheel h 1, by means of clutches f 2, h2, one or other of which
is thrown into engagement by the rocking motion of a T-shaped lever I, produced by
the influence of one or other of two electro-magnets E 1, E 2, as the case may be, so
that either the screw For the shaft H may be driven by the ratchet propelment f
nctuated by the electro-magnet E (when energized by currents from battery B) the
position of the lever I and consequently the operation of the serew For of the shaft H
being determined according to the positions of the commutator S, whilst the extent to
which each is operated is dependent on the number of times that E is energized for
the one and for the other respectively.
The rack rod G carries the switch C and by its longitudinal motion derived from
the rotation of shaft H the switch C is moved over the row of conductors of the
series c, to which it has been raised by the carriage D and screw F. The switch C
is represented in Diagram 2 as placed on the third conversation conductor 15c, of the
fourth tier corresponding to the fourth grouping conductor 4a.
The carriage D of switch A also carries other insulated spring contacts working
over contact strips and it is worked by screw F* and carries rack G worked by
shaft Hand carrying switch C, the actuating mechanism heing similar to that
above described and being represented by similar letters with the addition of an
asterisk, this mechanism deriving its motion from the electro-magnet E. The
alternative operation of the screw F and shaft. He is determined by the position
of the lever I which depends on the position of the commutator S which controls
the electro-magnets E 1 and E 2, in the saine way as for the screw F and shaft H,
the only difference being that whereas the electro-magnet E is energized by battery B,
only when the relay R is influenced by positive impulses, the electro-magnet E is
energized by battery B only when the relay R is influenced by negative impulses
from the transmitter.
The switch A is shewn in Figure 2 as having been placed on the third grouping
conductor 3a, and the switch C upon the fourth conversation conductor 15c of the
third tier corresponding to the third grouping conductor 3a.
There is however this difference as regards the distances through which the
switches A and A must necessarily be moved namely that whereas the switch A
need only move one step from its initial position in order to make contact with the
first grouping conductor la, the switch A must move two steps from its initial
position in order to make contact with the first grouping conductor la
The switches A A* are differently connected with the subscriber's line LL. The
switch A is only connected with the line through the normal contact nl, when the
switch is in its normal position. In this position the switch A rests upon a double
normal contact composed of two insulated contacts nl and na; nl being a line
contact connected directly to the line wire L and na being a calling contact
connected to the particular grouping conductor of the series a to which the
apparatus under consideration corresponds, according to the system of grouping
above explained. Thus in X's apparatus na is connected to lu, and in Z's apparatus
na is connected to 4a. Therefore when switch A is in its initial position it connects
na with nl and so puts the line L in connection with the corresponding grouping
conductor of series a.
The switch A is connected with the line L through the commutator S and other
connections hereafter described and this connection is maintained throughout the
motion of switch A except when the commutator S is in its fourth position.
When switch A is in its initial position it rests upon a single normal calling
contact na which is connected to the particular grouping conductor of series a to
which the apparatus under consideration corresponds, according to the system of
grouping; thus in X's apparatus na is connected to 1a and in Z's apparatus na* is
connected to 3a*.
Therefore when switch A has moved from its initial position it is cut off entirely

page_text: from the line, whereas the switch A remains in connection with the line until it
is cut off therefrom by the movement of the cominutator S which connects the
conversation switch C with the line as hereafter described.
In Figure 3, which is a diagram of Z's apparatus in position for conversation, the
same parts are similarly lettered and the only difference in position is, that whilst
switch A has not been moved from its initial position the switch C has been moved
on to the conversation contact C 1, which corresponds in height to the initial or zero
position of switch A; whereas the switch A* has been moved from its initial position
to the extent of one step and the switch C has been moved onto its conversation
contact C1, which corresponds in height to the first step from the initial or zero
position of switch A.
I will now explain in detail the various electrical connections and mechanisms by
which the switches of the two subscribers X and Z are brought to the positions.
ehewn in Figures 2 and 3 respectively.
All the apparatus at the central station being in their initial positions the
"calling "subscriber X begins by sending a certain number of positive impulses from
his transmitter battery through the line L, L, to the relay R of his apparatus at the
central station, the number of impulses so sent depending on the number of steps
which must be made by the switch A in order to reach the grouping conductor of
series a which enters into the grouping combination corresponding to subscriber Z.
In the present example the grouping conductor required to be reached is No. 4.
The succession of positive impulses, from X's transmitter causes the tongue » of
the relay R to bear so many times against the terminal 1 and thus close the circuit
of the battery B so many times through the electro-magneta E and E'. The circuits
thus closed, commence at line b + connected to the positive terminal of battery B, and
comprise line 1, tongue r, contact 1, line 2, contact strip 3, contact 4 carried by
switch A and connected to contact 5 which (when switch A is in its initial
position) bears upon two insulated contacts 6, 7. Here the circuit divides one portion
going by line 8 and line 19 to electro-magnet E, returning by lines 20, 21, 22, to the
line 6-connected to the negative terminal of the battery B. The other portion of
the circuit goes from contact 7 by line 23 to the electro-magnet E' returning, by
lines 21, 22 and b-to the negative terminal of battery B. Thus the magnet E1
has caused clutch to be put into gear each time the magnet E has been energized
and so has enabled magnet E (in moving the ratchet propelment so many teeth) to
raise switch A to the grouping conductor 4 a. A part of the current from line 19
goes through line 25 to electro-imagnet E 3 returning by lines 26 and 22 to line b-
connected to the negative terminal of the battery B.
The function of electro-magnet E 3 is to place the lever I in such position that
both clutches f2 and h 2 are out of engagement.
The screw having thus been operated so as to mise the switch A to the grouping
conductor 4a the switch is there retained by a ratchet J and pawl j.
The subscriber X now sends a certain number of negative impulses from his
transmitter battery to his relay R, the number of impulses so sent depending on the
number of steps which must be made by the switch A in order to reach the grouping
conductor of series a which enters into the grouping combination corresponding to
subscriber Z. In the present example the conductor required to be reached
is No. 3 a.
The succession of negative impulses from X's transmitter causes the tongue of
the relay R to bear so many times against the contact, and thus to close the circuit
of battery B so many times through the electro-magneta E and E 1.
thus closed commence at line b + connected to the positive terminal of the battery B,
and comprise line 1, relay tongue r, contact r, lines 27 and 28, to contact 29 of
commutator S. Thence by springs (the commutator being then in its initial
position) to two contacts 30, 31, where the circuits divide.
Froin 30 one circuit passes through lines 32 and 33 to electro-magnet E returning
by lines 34, 26, and 22 to line &- connected to the negative terminal of buttery B.
From line 32 the circuit is divided and passes by lines 35 and 36 to electro-magnet E

page_text: returning by lines 21, 22, and b-to the negative terminal of battery B. From
contact 31 the other circuit passes by line 37 to electro-magnet E 1 returning by
lines 26, 22 and 6-to the negative terminal of battery B.
Thus the magnet E 1 hns caused clutch to be put into gear each time the
magnet has been energized and so has enabled magnet E* (in moving the ratchet
propelment so many teeth) to mise switch A to the grouping conductor 3 at
same time that magnet E 3 has caused lever I to be returned to its initial position
so that both clutches and h2 are out of engagement.
The screw F having thus been operated so as to raise the switch A to the
grouping conductor 3a* the switch A is there retained by the ratchet J* and
pawl. The switch A having been moved from its initial position the circuits of
electro-magnets E, E and E 3* are broken at contacts 6 and 7 by the contact 5
having quitted those contacts.
The subscriber X now sends from his transmitter to his relay R a succession of
three current impulses, the first being positive, the second negative, and the third
positive in direction.
The first of these current impulses causes the tongue r of relay R to close the
circuit of battery B through the contract r1, and as the circuit of the electro-
imagnet E is broken.at 6 by the fact that contact 5 has quitted it, the circuit of
battery B will now be closed through the electro-magnet E S by line b + line 1,
tongue r, contact 1 line 2, contact strip 3, movable contacts 4, 5, contact strip 38,
line 39, spring contacts 40, 41, lines 42, 43, to electro-magnet E S, returning by
lines 44, 21, and 22 to line b-connected to the negative terminal of battery B. The
electro-magnet. E S being energized once, turns the bridge commutator S the distance
of one step from its initial to its second position. This bridge commutator comprises
the spring bridge contact a before mentioned and also a pair of parallel spring
contacts T and U insulated from each other and which move together over segmental
contacts tt 1 and u u 1.
The effect of this first movement of the commutator S is to break the connection
between contacts 29, 30, and 31 and consequently to break the circnit of the
magnet E and on the commutator reaching its second position the spring bridge U
connects segmental contact u with segmental contact ul.
The effect of this connection is to restore the connection of wire L of the
subscriber X's line with switch A which was broken when the switch A left the
normal contact nl. The connection of L with A is then through lines 45, 46, segment
contact w, spring bridge U, segment contact ul, line 47, contact strip 48, and sliding
contact 49 carried by the switch A and in electrical connection therewith. The
connection of L with switch A is through line 60, segment contact 4, spring
bridge T, segment contact 1, line 51, line 2, contact strip 3, and sliding contact 4,
carried by and connected with switch A*.
The next current impulse from X's transmitter passing through the relay R, being
negative, will throw the tongue r against the contact r 2 without however thereby
closing the circuit of battery B through electro-magnet E because the circuit of this
magnet was broken when the spring bridge contact a moved from its original position
and consequently X's apparatus will not now be actuated when negative currents enter
the relay. The connection of switch A with the line having been restored by the
movement of the commutator S as above mentioned, this second current impulse sent
from X's transmitter, will pass also through switch A, grouping conductor 4a, to the
normal contact na of Z's apparatus (Figure 3).
Assuming that Z's switches are in their initial positions the current passes through
switch A, relay R, switch A, and normal contact na of Z's apparatus, returning
through grouping. conductor 3a to switch A of X's apparatus. The effect of the
negative current passing through the relay R of Z's apparatus is therefore to cause
the tongue of Z's relay to bear against contact and to close the circuit of the
battery B through the electro-magnets E E 1 and E 3 of Z's apparatus, since the
commutator S of that apparatus is in its initial position. The electro-magnet E⚫ of
Z's apparatus thus being energized will actuate the propelment at same time that

page_text: the electro-magnet E 1 will throw clutch /2° into gear whereby the switch carrier D)*
will be advanced the distance of one step, thus breaking the circuit of electro-magnet E
of Z's apparatus at contacts 5, 6, this being the position shewn in the Diagram 3.
The result of this movement of Z's switch A is therefore that whilst the switch A
remains in electrical connection with its normal contact na all positive currents now
entering Z's relay will cause the battery B to energize the electro-magnet ES. The
energizing of magnet E as above mentioned produces no effect in Z's apparatus
because lever I was already in its initial position.
The third current impulse sent from X's transmitter through the relay R of
X's apparatus being positive in direction will throw the tongue against contact 1
thereby closing the circuit of the battery B through the electro-magnet ES, which
being energized causes the commutator S to be moved a second step. In this the
third position of the commutator the spring bridge contact a connects the contact 52
with contact 54 thus restoring the circuit of electro-magnet E so as to enable it to be
energized by the battery B the next time that the relay R is influenced by positive
currents. The bridge 8 at same time connects contact 52 with contact 53 thus
completing the circuit of the electro-tnagnet E 2 in order that it shall be energized
simultaneously with maguet E. The same movement of the commutator S also
breaks the circuit of the electro-magnet ES by an insulating piece 56 coming
opposite two springs 40 and 41 so that electro-magnet E S will not be energized
when positive currents influence the relay R.
The same third positive current also passes through X's switch A and grouping
conductor 3a to the normal contact na and switch A of Z's apparatus, through
Z's relay R returning by switch A, normal contact na, grouping conductor 4a, to
X's switch A. Z's relay being influenced by this positive current throws tongue
against and as the switch carrier D of Z's apparatus is not in its initial position
the circuit of battery B is closed through electro-magnet E S which being energized
moves the conmutator S of Z's apparatus one step from its initial position thus
removings from contacts 29,30,31,and breaking the circuits of electro-magnets E,E1*,
and E3 of Z's apparatus. Consequently negative currents entering the relay R
in Z's apparatus will not cause any of the electro-magnets to be energized.
The subscriber X is now in position to "ring-up"Z, which he does by sending
only negative currents from his transmitter, which currents passing from X's to
Z's apparatus as above described (without producing any effect in either apparatus)
pass on through Z's line to Z's transmitter and there energize the bell-sounding
mechanism.
The subscriber Z now sends from his transmitter a succession of three current
impulses which are respectively positive, negative, and positive in direction.
The first positive impulse influences the relay R of Z's apparatus, throws tongue-
against contact 1, and closes the circuit of battery B through electro-magnet E S
which being energized moves the commutator S of Z's apparatus a second step. In
this the third position of Z's commutator S the same effect is produced in Z's
apparatus as was fully described in respect of the same position of the commutator-S
of X's apparatus, that is to say the electro-magnets E and E2 of Z's apparatus will
thenceforth be energized when the relay R is influenced by positive impulses; and
the circuit of electro-magnet ES is cut. The same positive current also passes
through Z's switch A, normal contact n a°, grouping conductor 3a, to switch A
of X's apparatus, thence by sliding contact 4, contact strip 3, lines 2, 51, to segment
contact 1, bridge T, segment contact t, line 50, to X's relay R, returning by
lines 45, 46, segment contact u, bridge U, segment contact u 1, line 47, contact
strip 48, sliding contact 49, connected to switch A, thence by grouping conductor 4a,
to normal contact na, and so to switch A of Z's apparatus.
The relay R of X's apparatus being influenced by this positive impulse, its
tongue r is thrown against contact 1 with the result that the circuit of battery B
is closed through the electro-magnets E and E 2 which are energized so as to
cause the propelment f to be actuated and the clutch h² to be thrown into gear. so
as.to cause the shaft H to be rotated and the rack .G to be propelled forward th
B
e

page_text: distance of one step from its initial position without producing any other effect, at
the same time that the electro-magnet E 3* is energized to cause the lever I to be
Feturned to its normal position. In this position of the commutator the electro-
magnet E is in a new circuit formed by line b+, line 1, tongue r, contact r 1, line 2,
line 70, contact 52, bridge contact 8, contact 54, line and contact strip 71, sliding
contact 9, line 11, contacts 12, 13 which, (the rack G being then in its initial
position) are then joined by spring 14, line 15, sliding contact 17, contact strip 16,
Îine 18, line 19, to electro-magnet E, returning by lines 20, 21, 22, to b-. The
circuit of the electro-magnet E 2 is the same up to contact 53, thence by line 72, to
electro-magnet E 2, the return being by 21, 22, 6-.
The second impulse which is negative, produces no effect in either apparatus.
The third impulse which is positive causes the electro-magnets E, E 2 of
7's apparatus to be energized and the rack G to be advanced one step, at the same time
that electro-magnet E 3* is energized to cause lever I in Z's apparatus to be
returned to its normal position. This same current also passes to X's apparatus
and in the manner already described causes the rack G to be moved forward a second
step, the effect of which is to cause contacts 50, 57, and 58 to be connected together
by the sliding contact 59. This closure has for effect to restore the circuit of electro-
magnets E and E 2° of X's apparatus so that when the relay R of that apparatus
is influenced by negative currents, those electro-magnets will be energized
simultaneously.
The positions of the switches C of the two apparatus are now as follows:-In
X's apparatus the switch C has been moved forward two steps so that at the next step
forward it will enter upon the row of conversation conductors c opposite to which it
is then situated. The switch C of Z's apparatus has been moved one step forward
into contact with the conversation contact C1 on which it will continue to slide
forward at subsequent steps.
The subscriber Z now sends from his transmitter to the relay R of his apparatus
a succession of positive impulses followed by a succession of negative impulses
followed by a single positive impulse. The numbers of impulses of positive and
negative direction so sent in succession are determined mechanically in Z's trans-
mitter and are invariable for that particular subscriber. They are dependent on that
subscriber's grouping combination of grouping conductors a, a, so that if that
subscriber's grouping combination is expressed by the fraction formed by the
distinguishing numbers of the grouping conductors 4a, 3a, the number of impulses
of positive and negative direction may be represented respectively by the numerator
and denominator of the reciprocal with the addition in the case of the denominator
of two additional negative impulses which additional number of impulses is constant
for every subscriber. As the grouping combination differs for each subscriber
therefore the numbers of these impulses will also differ for each subscriber's transmitter.
The last single positive impulse is constant for all subscribers.
The positive impulses thus sent in succession by Z pass through his relay and also
through the switches A A of his apparatus through the normal contacts na, na,
through the grouping conductors 4d, and 3a and the switches A A of X's apparatus
to the relay R of this apparatus. The number of impulses so sent is sufficient to
cause X's conversation switch C to be advanced until it rests upon Z's conversation
conductor 15c. The effect of these impulses is to influence simultaneously the
relays R of both X's and Z's apparatus, thus closing the circuit of battery B so many
times through the electro-magnets E E 2, and E3 of both those apparatus.
In Z's apparatus the effect produced by the energizing of the electro-
magnets E, E 2, and E 3* is to cause the rack G to be advanced so that the
switch C moves along in electrical connection with the conversation contact C1.
When the rack G thus made its second step the contact 59 carried by the said rack
was caused to unite the contacts 56, 57, 58. and so restore the circuit of the
electro-magnet E, E 2 and E 3 so that these electro-magnets will be energized the
next time that the relay R of Z's apparatus is influenced by negative currents. In
X's apparatus the effect produced by the successive closures of the circuit of battery B

page_text: through the magnets E, E2, E3 is to cause the rack G to be advanced until the
switch C is placed on the conversation conductor 15c, with which it remains in
electrical connection, this conversation conductor 15e being permanently in electrical
connection with the conversation contact C1 of Z's apparatus.
The negative impulses now sent by subscriber 2 in succession pass through
the relays of both X's and Z's apparatus in the same way as described for the
succession of positive impulses. The number of negative impulses so sent in
succession is sufficient to cause X's conversation switch C to be advanced until
it rests upon Z's conversation conductor 15c*. The effect of this succession of
negative impulses is to influence simultaneously the relays R of both X's and
Z's apparatus thus closing the circuit of battery B so many times through the electro-
magnets E, E2 and E3 of both these apparatus. The circuits thus closed
through E and E 2* will be new circuits. These circuits will be formed by bt,
line 1, tongue r, contact r 2, line 27, line 73, contact strip 74, sliding contact 75,
line 76, contacts 56, 57, 58, connected by contact 59, carried by rack G. Here
the circuits divide. From contact 58 one goes by line 77, sliding contact 78,
contact strip 79, lines 80, 35 and 33 to the electro-magnet E, the return being
by lines 34, 26, 22, to b-. From contact 57 the other circuit goes by line 81,
sliding contact 82, contact strip 83, line 84, to electro-magnet E 2*, returning
by lines 26, 22, to b-.
The effect produced by the energizing of the electro-magnets E, E 2, so
many times is the same in both apparatus, of which the switches C are caused
to be advanced by their propelment mechanisms until the switch C of
X's apparatus is placed upon Z's conversation conductor 15c* whilst the switch C
of Z's apparatus slides upon Z's conversation contact C1 which is in pericanent
electrical connection with conductor 15c. The switches C in advancing the
first of these steps from their initial positions cause the contacts 14 carried by
the rack G to quit the contacts 12 and 13 and so break the circuit of the
electro-magnets E, E 2, and E3 of both apparatus so that when the succeeding
positive impulse influences the relays of those apparatus those electro-magnets
will no longer be energized. At the same time the contacts 85 also carried by
the racks Gunite the contacts 86 and 87 and so restore the circuits of the
electro-magnets E 8 of both apparatus so that the single positive impulse which
now follows the successions of positive and negative impulses will influence the
relays of those apparatus so as to cause the electro-magnets E S to be energized,
these electro-magnets being then in new circuits each formed by b+, line 1,
tongue r, contnet 1, line 2, contact strip 3, sliding contacts 4, 5, contact
strip 38, lines 39, 88 contact strip 89, sliding contact 90, line 91, contacts 86, 87,
united by contact 85, line 92, sliding contact 93, contact strip 94, lines 95, 43, electrc-
maguet E S, the return being by lines 44, 21, 22, to b-. The effect of the electro-
magnets E S being thus energized is to move the commutators S of both apparatus a
third step.
In each apparatus the effect of the commutator S being placed in the fourth
position is that the bridge contact & quits contacts 52, 53, 54, and the insulating
piece 55, quits the springs 40, 41, which are then put in electrical connection through
a metallic arc on the commutator. At the same time the bridge spring contacts T
and U having quitted contacts t1 and 1 put contacta t, u in connection with
contacts t 2 and u 2 respectively. This has for result to cut off the connection of
the subscriber's line with the switches A A* and to put each subscriber's line
in connection with the conversation switches C C of his apparatus.
The telephones of X and Z being now in connection by the exclusive metallic
circuit appertaining to Z, from the telephone of X the circuit passes by line 1, to
lines 45, 46, segment contact u, bridge U, contact u 2, line 60, contact strip 61,
sliding contact 62, line 63, spring 64, a contact strip (carried by but insulated from
rack G and connected with switch C) with which spring 64 makes contaut, switch C,
conversation conductor 15c to Z's apparatus where it enters by the conversation
contact C 1, switch C, the contact strip of rack G, spring 64, wire 63, sliding contact 62,

page_text: contact strip 61, line 60, contact 1 2, bridge U, segment contact w, line 46, line 45,
thence through line L to Z's telephone, returning thence by line L to Z's apparatus
at the central station, thence through line 50, segment contact t, bridge T, contact (2,
line 65, contact strip 66, sliding contact 67, line 68, spring 69, its contact strip on
the rack. G*, switch C*, conversation contact C1*, conversation conductor 15c* to
X's conversation switch C* thence by contact strip on rack G* of X's apparatus to
spring 69, wire 68, sliding contact 67, contact strip 66, line 65, contact t 2, bridge T,
segment contact 4, line 50, and through line L to X's telephone.
It will be easy to see that the purely telephonic metallic circuit thus constituted
is cut off from all connection with the grouping system, or any other connection, and
therefore during the conversation of X and Z any current sent by another subscriber
can reach neither their central station apparatus nor their telephones.
In order that the subscribers shall perform at their transmitters the operations
necessary for the transmission of the currents required for working the electro-
magnetic apparatus as before described, and in order that they may know when
telephonic communication is established, the transmitters are provided with indicators
electro-magnetically operated through the medium of the commutators S and which
automatically exhibit the necessary service indications as described in the previous
Patent referred to.
When the conversation is terminated, one single impulse, positive in direction, is
sent automatically from the telephone of the subscriber "calling," by the act of
this subscriber replacing his receiver on the hook. This positive impulse passes
through X's relay and through his switches C C and the telephonic circuit to the
switches C C of Z's apparatus and thence to Z's relay. The effect produced by the
relays being influenced by this positive impulse is the same in both apparatus namely
the circuit of battery B will be closed through the electro-magnet ES of each
apparatus whereby the commutator S will be moved to its fifth position, the result
being that the bridge 8 will connect contacts 96 and 97 thereby closing the circuit
of the battery B through the electro-magnets E4 and E 4. The circuit of electro-
magnet E4 is formed by b+, lines, 98, 99, 100, contact 97, bridges, contact. 96,
lines 101, 102, electro-magnet E4, returning by lines 103, 20, 21, 22, to b-. The
circuit of electro-magnet E 4* is b+, lines 98, 99, 100, contact 97, bridge s, contact 96,
lines 101, 104, electro-inagnet E 4, returning by lines 105, 26, 22, to b-.
The energizing of electro-magnets E4 and E4 has for effect to cause detents
and to be released from ratchet wheels K, K (by which the racks G, G, carrying
the switches C, C, were retained in the positions to which they had been moved as
above described) in order that the racks G G may be mechanically returned to their
initial positions by the means hereafter described.
Just before reaching their initial positions the racks G, G, will respectively close
the circuits of the electro-magnets E5 and E 5. The circuit of battery B will
thus be momentarily closed through the electro-magnet E 5 through lines 6+, 98, 109,
electro-magnet E 5, returning by line 110, contact strip 111, sliding contact 112,
line 113, contacts 108, 107, united momentarily by contact 106, carried by the
rack G, line 114, sliding contact 115, contact strip 116, lines 118, 22, to b-. The
circuit of battery B will also be momentarily closed through the circuit b+,
lines 98, 99, 119, electro-magnet E 5, returning by line 120, contact strip 121,
sliding contact 122, line 123, contacts 124, 125, united by contact 126, carried by the
rack G, line 127, sliding contact 128, contact strip 129, lines 130, 22, to b-.
The energizing of these two electro-magnets E 5, E6, will have for effect to
disengage the respective detents i, j, from the ratchet wheels J, J, thus allowing
the switch carriers D D to be mechanically returned to their initial positions. On
reaching their initial positions and whilst the bridge U (the commutator being in its
fifth position) unites the two contacts 136, and. 137, the circuit of the battery B will
be closed through the electro-magnet E6 which being energized will disengage the
detent gear by which the commutator is retained in the position to which it has been
moved, thus allowing the commutator to be mechanically returned to its initial
position. The circuit of electro-magnet E6 will be through b+, lines 98, 99, 119,

page_text: contacts 132, 133, united by sliding contact 134 (when D is in its initial position)
line 135, contact 136, bridge U (when the commutator is in the fifth position)
contact 137, line 138, electro-magnet E 6, returning by line 139, contacts 140, 141,
united by sliding contact 142 (when D is in its initial position) lines 143, 118, 22,
to b-.
The commutator S just before reaching its initial position sends a current from
battery B through the subscriber's line L L to his transmitter whereby all the
mechanisms of the transmitter are returned to their initial positions, these effects
being produced both in X's and in Z's apparatus and transmitters, so that both
are in readiness to establish connection with, or to be called by, any other subscriber.
I will now describe the constructional details of the mechanism with reference to
Figures 4 to 21 of the drawings, the same letters and numbers referring to the same
parts as in the diagrams already described so that a brief description will suffice
except in the case of those parts of which the construction needs explanation.
Figure 4 is a front elevation of the switch carriage D. Figure 5 is a side elevation of
the same switch carriage shewing also the supporting frame of the conversation
conductors. Figure 6 is a part sectional plan of the same showing the rack G.
Figure 7 is a side elevation of the framework carrying the electrical contacts with.
which the contacts on the carriage make electrical connection. Figure 8 is a
horizontal section of the same. Figures 9, 10, and 11 are detail views of the switch C.
Figure 12 is a front elevation and Figure 13 a side elevation of the switch carriage D*
and the propelling mechanisms of the screw and shaft H. Figure 14 is a plan of
the carringe D. Figure 15 is a side elevation of a portion of the contact strip
carrier. Figure 16 is a plan of the detent mechanism for retaining the carriage and
mck after being moved from their initial position. Figure 17 is a detail of Figure 16.
Figure 18 is a horizontal section of the bracket carrying the propelling mechanism.
Figures 19 and 20 are details of part of Figure 12. Figure 21 is a plan of the
magnets E 1, E 2.
Referring to Figures 4 to 11 D is the carriage of switch A fitted to slide upon a
vertical dovetail guide v bolted to the front of a framed standard V having bearer
bars 150 extending from front to back for supporting the rows of conversation
conductors c (part of one row of which only is shewn there being supposed to be 100
superposed rows, each having 100 conductors for the service of 10,000 subscribers)
formed by wires insulated from the bearers by being supported in notched strips 15ĺ
of insulating material.
The switch A carried by the carriage D moves over the contact-studs a corre-
sponding to the rows of conversation conductors c the contact-studs & appertaining
to different subscriber's apparatus being grouped together by grouping conductors as
before explained with reference to the diagrams.
The switch A moves up and down in front of a pilaster 152 of insulating material
in the face of which are embedded the contact-studs a and likewise the various
contact-strips with which the sliding spring contacts carried by the carriage D make
contact. The connections of these spring contacts and the strips on which they slide
having been already described with reference to the diagram, it is unnecessary to
refer to them more fully.
The propelment screw F which revolves in a nut 153 on the carriage D is supported.
by ball bearings in a bracket 154 at top and in a bottom bracket 163 similar to that
shewn in Figures 12, 13, 16 and 18. The shaft H is mounted in the same brackets
and the shaft F and screw H are each provided at the upper end with a barrel 155
(as shown in Figure 5 in respect of shalt H) upon which is wound a cord 156 passing
over guide pulleys to the back of the standard frame and to which is attached a
counterweight (which is raised by the winding of the cord on the barrel of the screw F
during the rising-motion of the carriage and on the barrel of the shaft H during the
forward motion of the rack) for the purpose of revolving the shaft and screw in the
reverse direction in order to return the rack and carriage to their initial positions at
the proper times.
The propelment mechanism for screw F and shaft H is not shown in these figures

page_text: but will be exactly similar to that shown in Figures 12-13, 16, 17, 18, 19, 20, in
respect of the screw F and shaft H*.
The shaft H has a groove and sliding key connection with the mitre wheel g
in gear with wheel g₁ adjustably fixed to the worm G¹ mounted to run upon a
stud supported by a bracket on carriage D and gearing with the teeth of the
rack G. This rack works in guides on the earringe D and carries the switch C
(Figures 6, 9, 10, 11,) which when the rack is advanced across a row of conversation
wires e makes contact with those wires where they bridge over a longitudinal
groove 158 in the notched strip 151 in which the wires c are supported as above
mentioned, the switch C being in electrical connection with a wire 159 (Figure 6)
lying in a groove in a longitudinal strip 160 of insulating material embedded in the
upper side of the rack, the strip 160 and wire 159 extending along the rack so that
the wire shall always be in contact with an insulated spring finger 64 carried by the
carriage D and in electrical connection with contact 62 which slides on contact 61
as before explained in reference to the diagram. In two other grooves in the
insulated strip 160 lie two insulated wires 59, 59, upon which respectively bear
insulated contact springs 57, 58, mounted on the carriage D and connected
respectively to sliding contacts 82 and 78. Behind these springs is arranged another
insulated contact spring 56 of bifurcated form which makes contact with both of the
wires 59, 59, and is connected to sliding contact 75, the wires 59, 59, stopping at
such a point that contact with springs 56, 57, 58, is not made until the rack G
has been advanced two steps from its initial position as before explained, these spring
contacts 56, 57, 58, being the equivalent of the contact strips 56, 57, 58, shewn in the.
diagrams whilst the contact strips 59 are the equivalent of the moving contact 59 in
the diagram.
As the springs 57, 58, are side by side only one of them is visible in Figure 5,
whilst in Figure 4 the forked spring 56 is obscured by springs 57, 58, while in
Figure 5 the fork 56 obscures the spring 64.
The head of the rack G which carries the switch C also carries a spring
contact 106 which just before the rack returns to its initial position passes between
a spring contact 107 and a contact 108 (see Figure 6) respectively connected to.
sliding contacts 115 and 112. On the forward movement of the rack the contact 106
does not pass between 107 and 108 but is deflected by and slides against
the inclined rear side of 107 which is faced with insulating material.
In order that each subscriber's apparatus, may be readily removable for testing
purposes, without disturbing the grouping connections of the other apparatus, the
pilaster 152 is removable from the framing V along with the guide and the switch
propelling mechanism, and the contact studs a are embedded in the pilaster 152 and
inake electrical connection with the corresponding grouping wires by spring clips
such as shewn at 161 the two lowermost of the grouping wires being shewn at 1a, 2a,
in Figures 7 and 8, and a few of the uppermost of the grouping wires being shown
in Figure 5 numbered from 92a to 100a. The terminals of the various vertical
contact strips 61, 74, 83, 79, embedded in the face of the pilaster 152 respectively
make contact with suitable springs such as 162 attached to terminals on the main
frame V so that by merely fixing the pilaster in position against the fixed framework
all the electrical connections between the parts carried by the pilaster and the fixed
framework are established at once.
Referring now to Figures 12 to 21 the carriage D of switch A is worked by
screw F and guided by similar means to those described for carriage D and the
switch moves over contact studs a corresponding to the respective rows of conversation
conductors c which are not shown in these figures, but are wires carried by notched
and grooved insulating strips supported by bearer bars as described for the series c
and shown in Figure 5. The grouping conductors la, 2a, 3a, &c. of studs a are
not shown but the studs are connected to them in the same way as studs a in
Figure 7. The contact strips 38, 3, 66, 71, 16, 89, 94, 120, 121, are embedded in an
insulating pilaster 152° and the corresponding contacts on the carriage slide upon
them as already explained with reference to carriage D and to the diagrams.

page_text: The screw F and shaft H* revolve in the bottom bracket 163 and in a top bracket
similar to that shown at 154 (Figure 5) and each is provided with a barrel and cord
for a counterweight as described in reference to F and H, Figure 5.
The screw F works through a nut adjustably fixed in the carriage and the
gearing of shaft H with rack G is precisely similar to that described in reference
to Figure 4.
The magnet. E works the ratchet wheel by compressing a spring 169 which
reacts on a lever / 3° and pawl f 4°. The operation of the wheels f1, h 1, clutches/2
and h 2* and lever I has already been described with reference to the diagram,
Figure 2. It only remains to describe the mode in which the lever I is operated
which differs slightly from that described in reference to the dingram. Instead of
the lever I being returned to its normal position by the direct force of the magnet E 3*
it is so returned by the reaction of one or other of two springs on the guide
rods, 164, 165, of the armatures of magnets E 1°, E 2, which spring was compressed
by the previous operation of the corresponding magnet. The springs are limited in
their action so that neither acts when the lever I is in its norinal position. When
the lever I is oscillated to either extreme position it is there retained by
projections 166 on a crosshead attached to the armature of magnet E 3* being caused
by a spring 168 to rise and engage at one or other side of corresponding projections 167
on the tail of lever I so that the function of magnet E 3* is not to return lever I* to
normal position but to release it, and permit of its return by one or other of the
springs 164, 165, whichever for the time being may be under compression.
The retaining ratchet wheel J (Figure 16) of screw F is engaged by pawl * to
maintain the carriage D at the height to which it is raised, and the ratchet K is
similarly engaged by ratchet & to retain the rack G, at the position to which itis.
moved across the row of conductors c*. The return motion is permitted at proper
times by the magnet E 4 disengaging pawl k which is held out of engagement by
a bell-cranked trigger lever 170, pivotted at 171, which is caused by a spring to
engage by its notched end with the end of pawl until the carriage D has descended.
Similarly pawl is disengaged from wheel J by magnet E 5 and is held out of
engagement until the descent of the carriage by another trigger lever 172 pivotted
at 173 and actuated by a spring. Just before the carriage reaches its lowest position
two bevelled strikers j 1 and k 1* strike the tail ends of the trigger levers 170
and 172 and disengage them from pawls j and k which then engage with their
respective ratchet wheels.
The sliding contacts of the rack G carrying switch C will be readily understood
without specific description the springs 86, 87, which are connected to the
contacts 90, 93, of the carriage D replacing the contact strips 86, 87, of the
diagram whilst the contact strip 85 on which they slide takes the place of
the movable contact 85 of the diagram.
The contact spring 69 connected to contact 67 of the carriage D bears upon a
contact strip 174 embedded (like the contact strip 85) in a groove in an insulating
strip carried by the rack G, this contact strip terminating in the switch spring
contact C. The rack head also carries the contact 126 which on the return of the
rack passes between spring 124 and stud 125 thus momentarily closing the circuit of
the electro-magnet E5 at the proper time for the purpose above mentioned. On the
forward motion of the rack, contact 126 produces no effect as described in respect
of 106.
The rotating commutator S is represented in face view in Figure 22 and in section
in Figure 23. In its essential features it is similar to that described in the previous
It is composed of a body portion 175 of insulating material mounted to
revolve upon a central axis 176 mounted on a base plate 177 of insulating material.
Each time the electro-magnet ES is energized the commutator receives a step by
step motion through a pawl 178 attached to the magnet armature 179 and caused
by a spring 180 to engage a series of ratchet teeth 181. The rotation of the
commutator winds up a spring 182 coiled about the axis, and the commutator is

page_text: retained after being moved each step by a detent 183 pressed by a spring 184 into
engagement with the same teeth 181.
The simultaneous disengagement of the pawl 178 and detent 183 to permit of the
commutator being returned to its initial position by spring 182 is effected by the
action of electro-magnet E 6 which being energized at the proper moment attracts
its armature 185 to which is connected a link 186 terminating in a head 187 shown
by the sectioned outline which takes under the pawl 178 and has a pin 188 in
engagement with a slot 189 in the detent 183 permitting the detent to slip over the
teeth 181 during the forward motion of the commutator. The head 187 of the
link 186 also slides against an abutment 190 so that by the pull of the magnet E6
it is caused to lift both pawl 178 and detent 183 out of engagement with teeth 181.
The different circles of contacts previously described. (in reference to the diagram
Figure 2) as being connected in a certain order by the bridge spring contacta a TU
are arranged on different levels on the insulating base plate 177 of the commutator
as shown whilst the bridge spring contacts & TU are mounted on the rotating body
portion 175 and as the whole of these parts are lettered and numbered to correspond
to the diagram they need no further description. The springs 40, 41, bear against
a metallic segment 191 by which they are put in electrical connection except when
the insulating piece 55 comes opposite to them.
The contrivance (represented diagraminatically in Figures 2 and 3) by which at
each step forward made by the commutator the circuit of the battery B is closed
through the electro-magnet that operates the service indicator in the transmitter,
consists of a contact 192 pressed by a spring against a series of segments 193
separated by intervening segments of insulating material but in one with a metallic
segment 194 against which bears another spring contact 195 these contacts 192
and 195 being connected the latter by lines 196, 99, 98, with line b+ and the former
by line 197 with line 45 and line L; line L being connected by line 198 with the
line b± connected to the middle of the battery B.
In order that a single impulse only shall be sent on the return motion of the
commutator for the purpose of returning the indicator in the transmitter to its
initial position the commutator is provided with a spring-deflector 200 past which the
contact 192 slips on the forward motion and against which it rides on the return
motion of the commutator so as to be brought into contact with a single contact 201
immediately before the commutator completes its return movement this contact 201
being in connection with the metallic segment 194.
To enable the whole commutator to be readily dismounted for testing &c. the
base 177 fits in a recess on the supporting frame and for each wire leading from it a
spring contact is provided such as shown at 202 and 203 in Figure 23 so that all the
permanent connections will be joined up by the mere net of fixing the commutator
in position.
Figure 24 is a diagrainmatic face view of the transmitter the front of the casing
being removed.
Wis the mechanism for sending and recording the succession of positive impulses
and W is the mechanism for sending and recording the succession of negative
impulses first sent 'from the transmitter when the subscriber is calling.
Y and Y are the respective mechanisms for sending the succession first of positive
impulses and then of negative impulses followed by a single positive impulse when
the subscriber has been called. The other mechanisms will be explained in the course
of the description.
Assuming that the transmitter appertains to a subscriber desiring to call another
subscriber the caller turns the handle w of the numerator W. This numerator is a
metallic numbered tape w 1 bearing numbers in succession from 000 to 100 kept
wound on a barrel w 2 by a spring barrel w 3 and from which it is drawn and wound
on to another barrel w 4, turned by the numerator handle w so that the figures on
the tape are exhibited in succession. The handle w also acts as a circuit breaker for
which purpose it carries a spring contact w5 which normally rests on two
contacts w6, w 7 so that the circuit of the dial-operating electro-magnet E 7 is only

page_text: closed when handle w is in its normal position. The barrel w 4 carries one or more
contacts w8 which as the barrel w4 is revolved make contact with two spring
contact pieces w9, w 10, for the purpose of sending positive impulses through the
subscriber's line.
The number of impulses so sent for each number exhibited by the numerator
depends upon the number of impulses necessary to raise the carriage D at the
central station from one grouping conductor to the next.
In the diagram Figure 24 it is supposed that one impulse is sufficient but the
mechanism previously described is calculated upon the supposition that several
impulses per step (say eight) would be required to be sent by the transmitter. It is
only essential that none of the impulses so sent should be sent at the moment when
the circuit breaker w5 is in its normal or closed position. The impulses having been
so sent barrel w 4 is retained by a pawl and ratchet w 11.
The mechanism W* for sending negative currents is so far identical and therefore
need not be described as the parts are similarly lettered with the addition of an
asterisk, the only difference being that the numerator tape w 1 is numbered
from 00 to 99.
The number of positive and negative impulses so sent depends upon the grouping
combination of the subscriber to be "called" as before explained.
With the mechanism W there is combined a circuit closing device formed by a
leading screw w 12 on the spindle of barrel w 2 on which screw travels a nut carrying
a contact w 13 which as soon as the screw turns makes contact with and connects
contact strips w 14, w 15, and maintains this connection until the numerator tape
begins to be wound up again as hereafter described.
To permit the use of a screw of slow pitch and ensure immediate action on closing
and breaking contact the nut would be permitted to partake slightly in the rotary
motion of the screw before travelling along it in either direction. The purpose of
this circuit closer will be explained hereafter.
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The mechanism by which three impulses, ++ in direction are sent in succession
whether the subscriber is "calling" or is "called" consists of a double armed spring
contact 204 one arm of which normally connects a pair of contacts 205 and the other
arın of which is caused to make passing contact with and so to unite the two members
of each of two pairs of contacts 206, 207, by pressing inwards a spring button 209
acting on the spring contact 204 through lovers 210.
The three currents ++ in direction are sent, the first two on the forward
motion of 204 caused by pressing in the button 209 and the last one by the return
motion produced by the return of button 209 by its spring.
The arm of contact 204 which normally connects the contacts 205 also makes
passing contact with and unites the numbers of a pair of contacts 208 situated
intermediately of the pairs of contacts 206, 207, the contacts 208 being so connected
as to form a continuation of 205; 205 or 208 being always joined by 204, when
connection at 206, 207, is broken, the purpose of 205, 208 being to permit the
reception of currents, by the electro-magnet E 7 at proper times for the operation of
the indicator dial as above mentioned.
The button 209 normally forms a stop for a lug. 211 on the shaft 212 of the
mechanism by which the subscriber when called sends to the central station
successions of positive and negative impulses followed by a single positive impulse.
This mechanism consists of a rotating contact Y which normally unites a pair of
contacts y and which at each revolution breaks the connection at y and unites a pair
of contacts y 1, there heing any required number of contacts Y according to the
number of impulses per revolution necessary for the work to be performed it being
only necessary that connection should be broken at y when connection is made
with y 1. The impulses so sent by Y are positive in direction.
The contact Y is carried by a spindle which is rotated by a spring barrel (not
shewn) which spring barrel is wound up by turning shaft 212 by means of handle 213.
The turning of the shaft 212 is permitted by a notch 214 (on the stem of
button 2C9) being brought opposite to lug 211 when button 209 is pushed in,
°

page_text: and one turn of the handle 213 is sufficient to wind up the spring barrel and to
cause it to come into action. The winding up of the spring barrel is effected through
a wheel 215 geared with a pinion 216 on the spring barrel axis and the release of
the spring barrel to allow it to perform its functions is effected by the handle 213
acting (just before it completes a single revolution) on the bevelled end of the spring
button 217 coupled to a detent lever 218. The spring and the mechanism which
controls its action is supposed to be contained within the casing 219 and the
controlling mechanism is so constructed (on the principle of the hour-and-minute
repeating mechanism of a watch) as to cause contact Y to be thrown out of action
after making the connection at y 1, the requisite number of times, and another
similar contact Y to be brought into action. This revolving contact although
apparently carried on the same axis as Y is quite independent. "Normally it unites
a pair of contacts y and when revolved it unites the pair of contacts y 1 the
requisite number of times, there being any required number of contacts Y
according to the number of impulses to be sent per revolution, it being only necessary
that connection should be broken at y* when connection is made at y 1. The
impulses so sent are negative in direction and the respective numbers of positive
and negative impulses eo sent by Y and Y will be constant for each particular
transmitter and will depend as before explained on the grouping combination of the
central station apparatus to which the transmitter corresponds.
After Yhas been so actuated the mechanism causes it to be thrown out of action
and to be again actuated to the extent necessary for sending a single positive
impulse.
The electro-magnet E7 actuates the indicator dial (which bears the necessary
service inscriptions) through the medium of a lever 220 connected to its armature and
a reciprocating pawl rod 221 engaging studs 222 on the back of the dial.
To the driving pawl rod 221 is coupled, by links and a swing lever 223 pivotted on
the axis of the dial, a retaining pawl lever 224 engaging by a lug with the same teeth
and being connected through a rod 225 with an arm 226 on the shaft 227 common to
the two pawls w 11 and w 11.
The dial is provided with a lug 228 which when the dial is caused to commence its
fourth step, strikes the return end of retaining pawl lever 224, thereby simultaneously
disengaging retaining lever 224 and driving pawl rod 221 from the teeth 222, and by
the same movement rocking shaft 227 so as to disengage pawls w 11 and w 11* from
their ratchet wheels. The driving pawl rod 221 is retained out of engagement with
the pins 222 by its ends becoming engaged with a spring latch 229 whereby also the
retaining pawl lever 224 and pawls w 11 and w 11 are held out of engagement long
enough to permit all the mechanisms to return to their initial positions. This return
to initial position is effected by the spring barrels w2 and to 2 rewinding the
numerator tapes w 1 and w 1 until these each again exhibit zero, at the same time
tliat the indicator dial is revolved backwards by a spring coiled about its axis (which
spring was wound up by the forward rotation of the dial) until a bevelled lug 230 by
striking a pin 231 on the latch 229 sets free the driving pawl lever 221 and allows all
the pawls to become re-engaged with their respective wheels, the return movement
of the dial being limited by a stop 232.
The receiver hook 233 carries a switch contact 234 which when the receiver is on
the hook unites a pair of contacts 235. When the receiver is removed from the
hook the latter on rising is caused to carry the contact 234 clear of another pair of
contacts 236 without uniting them. When the receiver is replaced on the hook 233,
the latter on descending carries the switch contact 234 against the contacts 236
thereby uniting them whilst the switch hook is moving downwards.
The means by which contact is made only during motion in one direction may be
similar to that described in reference to contact 192 and deflector 200 of the
commutator shown in Figure 22.
The effect of uniting contacts 236 is to send from that subscriber's transmitter
battery to the relays of both apparatas at the central station, the current which'
causes the commutators S of both apparatus to be moved to their fifth position as

page_text: above described. This current is only sent from the transmitter of the "calling
subscriber, since in that transmitter only has the contact w 13 united the contact
strips w 14, w 15.
By following the circuits from line L to L it will be seen that the circuit breaking
contacts 235, 205, y, y*, w 6* w 7*, w6 w7 are all on the circuit of the electro-
magnet E 7 which can therefore only be energized from the central station battery
when the circuit is completed at all these points by the corresponding contacts being
in their normal positions except that when the circuit is broken at 205, it is remade
at 208 in the intervals between the sending of the series of ++ currents. The
magnet E 7 is never energized from the transmitter battery as its circuit is always
broken as above explained when any other part of the transmitter mechanism is in
operation.
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The receiver hook lever is provided with the usual switches (not shown) by which
the transinitter microphone and battery and the receiver are connected with the line
at the proper time.
It is to be understood that the invention is in no way limited to the particular
construction of the mechanisms described either at the central station or in the
transmitters as these may be varied indefinitely the invention residing broadly in the
combined systems of circuits described and in the method of changing the line
connections from the one system to the other at the proper times.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that
what I claim is :-
The herein described automatic telephone exchange comprising a system of circuits
grouped as described for electro mechanical purposes and a system of exclusive
metallic circuits each appropriated to a different subscriber for conversation purposes,
the two systems of circuits being independent but correlated as described; and the
combination therewith of electro-magnetically-operated or controlled apparatus
appropriated to the respective subscribers each such apparatus comprising pairs of
switches respectively adapted to be brought electro mechanically into contact with
conductors of the respective systems to which they appertain, mechanism controlling
the operation of the switch operating mechanism and determining the line connections
of the switches; and of mechanisms in the transmitters whereby the connection of
the conversation switches of the calling subscriber with the called subscriber's
conversation circuit is automatically controlled by the "called" subscriber's
transmitter all substantially as specified.
Dated this 9th den of In 1907
A. M. & WM. CLARK,
53 Chancery Lane, London, Chartered Patent Agents.