Improvements in Telephone Systems and in Apparatus therefor.
Year: 1899

page_text: Date of Application, 12th June, 1899
Complete Specification Left, 12th Mar., 1900-Accepted, 12th July, 1900
PROVISIONAL SPECIFICATION.
Improvements in Telephone Systems and in Apparatus therefor.
We, ARTHUR THOMAS MILNOR THOMSON, of No. 51, Beauval Road, East Dulwich
in the County of Kent, Electrical Engineer, and PERCY WARNFORD-DAVIS, of Pomona
Buildings, Fore Street, in the Administrative County of London, Gentleman, do hereby
declare the nature of this invention to be as follows.
This invention relates to certain improvements in telephone systems and in
apparatus for automatically electrically or magnetically signalling, recording or
indicating at a distance, and is especially applicable for signalling, recording or
indicating connections required in complex telephonic intercommunication.
The invention is more especially designed with a view to simplify, facilitate,
expedite and lessen the cost of working complex telephone connections such as
required in large towns or wherever the number of subscribers or users is very large
and consequently the system as a whole very busy, but of course it is also applicable
to any lesser demands.
The main objects of the invention are:-(1) To render it unnecessary and in fact
impossible for verbal communication between subscriber and operator and vice versa,
and so provide secret communication between two subscribers to the system and to
prevent mistakes in passing connections required by the subscriber to the Exchange,
and also to save subscribers' time by not having to wait at the telephone whilst the
connection is being made. (2) To simplify, cheapen and expedite the construction
of the telephone Exchange switchboards. (3) To cheapen the cost of operating
Exchange telephone systems by reducing the number of operators required.
Before describing the new group of apparatus itself it may be well to mention here
in order to render what follows more intelligible, that part of this apparatus is located
at the Exchange and part in the subscribers' room; that the operators in this system
are not provided with telephone receivers and transmitters; and that the source of the
electric or magnetic current for automatically signalling, indicating, recording and
clearing the connections is situated either at the Exchange, or may be at the
subscriber's end.
.:
Our invention consists in a group of apparatus comprising signalling and printing'
or indicating devices and in the combination of this group of apparatus with ordinary
telephonic instruments and connections.
The instrument which forms the addition to the usual telephone outfit at the sub-
scriber's office is herein-after called the "indicator latent switch" or, briefly, the
"latent switch." This switch consists of an electro-magnet in connection with a
special switch at the Exchange, a stationary plate, carrying the various parts which
.מ

page_text: plate may be rectangular or of any other angular conformation contacts formed on
the face of flat plates or slides mounted on the face of the foundation plate in such
manner as to be slidable-thereon in a horizontal direction. In this case the said
contacts are ridges or ribs preferably produced by fluting, grooving or corrugating the
surface of the said movable plates. There are five of these contact plates mounted one
above the other, flat upon the face of the foundation plate the uppermost one repre-
senting the Exchanges and the others in succession the units, tens, hundreds and
thousands in such manner as to be capable of being slid or moved to and fro in a
horizontal direction. For effecting this movement as and when desired, a rack may
be fixed on the back of each plate and worked by a pinion mounted on a spindle which
also bears at its other end a pointer or index finger which radially traverses a dial
provided with numerals, words or characters or other information or signs desired.
The main or winding-up lever of the switch moves a contact mounted so as to be
capable of moving freely over the contact ridges on the face of the movable plates
above described. One method of mounting it is to attach it to a block having a
screw-threaded hole through it, the said block being threaded upon a screw spindle
pivoted at each end in step-bearings so as to be free to rotate but incapable of any
longitudinal motion. The screw cut on this spindle is preferably what is known as a
"helical" thread, that is; similar to an archimedean screw.
The remainder of the apparatus consists of an electro magnet and clock-work
mechanism for releasing the switch as in the former case.
This switch may be used in any position. When used vertically the nut-block on
the helical spindle bearing the contact spring or strip will be raised by a hand lever
segmental rack engaging in one of the toothed wheels of the clock-work which rotates
the spindle and so raises the said nut, whilst in its downward motion it will fall by
gravity. Should, however, it be desirable to place the instrument in any other
position, say horizontal, the movements of this nut-block, it is obvious, might be
effected by means of a spring which is either wound up or extended when the block
is moved in one direction and consequently the potential energy thereby stored in it
will constitute the force necessary to automatically impel the block in the other
direction when desired.
The action of this modification of the apparatus is as follows:-
Assume a subscriber A desires to be connected with another B: The apparatus
being all in order for starting a call, all the movable contact plates will be lying
retracted wholly behind the foundation plate, that is to say, the end edges of these
movable plates do not project in the least beyond the edge of the plate upon which
they slide. Perhaps it will be most convenient to explain now why this
so. The
edge of the foundation plate is cut "square," that is, stands vertical with the ground,
whilst the forward end edges of the sliding plates are oblique or cut off at an angle to
the horizontal so that during the forward sliding motion of the said plates their angle
or point is presented first beyond the edge of the foundation plate and these movable
plates, as will be remembered, having contacts formed by rectilineal ridges covering
one side or surface, it follows that when the point of the angle only is projecting, only
one of such ridges and consequently only one contact is presented beyond the edge of
the foundation plate and that the further the plate is projected beyond the edge the
greater the number of contact ridges exposed."
Now, to return to the description of the working. A first sets his pointers by means
of knobs, turning them to the name and numerals representing respectively B's
exchange and his number on that exchange. These actions cause the forward motion
and consequent projection more or less of the ridged contact plates, because these plates,
through the medium of a rack and pinion or other suitable mechanism, are connected
with their respective pointers.
Having thus set the number and exchange desired, he then winds up the nut-block
mounted on the helical spindle and bearing the other contact, by simply turning the
segmental rack lever from, say right to left. This rotates the helical spindle and
consequently carries up the nut-block threaded on it and on the said block coming in
contact with the top bar or bearing-block of the said spindle, which block is in

page_text: electrical connection with the line wire, a current is thereby sent along the wire to the.
local Exchange which current actuates the compound indicator to the right or left as
the case may be, which shews an operator, No. 1, whether the call is for a subscriber
on her own or some other exchange. In the former case she will simply connect the
caller's line on a local junction to the switch-board as before, this action automatically
dropping an indicator there which an operator No. 2 attends to. This operator then
puts her printer in circuit to find out the number required and when ascertained she
completes the call by connecting this number with the local junction.
Should the call be for a subscriber on another Exchange, operator No. 1 will first
put her printer in circuit to find out which Exchange is required. This action
energises the electro-magnet causing a pulsation of its armature which releases the
detent which is holding the clock-work of the calling-subscriber's switch. Immediately
the clockwork is released the nut-block bearing the contact at the end of
spring commences to fall and during its travel causes the said contact to rub over the
flutings or corrugations forming the contacts on the movable plates before described.
It can of course only rub over those which project in its path.
The first set of
contacts it meets with is that representing the various Exchanges and assuming the
Exchange required to be the fourth from the commencement it touches four contacts
and then a special contact lying across the bottom edge of this movable plate. On
this special contact being touched by the one on the nut-block as it passes down, it
causes a pulsation of the operator's printer, or indicator which thereupon prints or
indicates the name of the Exchange to which the subscriber's switch has been set.
After passing the contacts representing the Exchanges it is arrested in its descent by
means of a suitable stop device which may be a tooth formed on the edge of a plain
disc constituting part of the clockwork, which disc is so arranged as to present this
tooth at the moment when the contact-bearing nut-block has fallen about half-way
down the helical spindle; at all events below all the contacts on the sliding plate
representing the exchanges. The operator now connects the calling-subscriber with
an operator. No. 2 at the exchange printed on her tape or indicated by the movable
numbers. This second operation then likewise switches current on the calling-sub-
scriber's switch, which again releases the nut-block-contact which thereupon completes
its descent, its contact piece in its passage rubbing over all the contacts of the movable
slides representing the number desired; of course only touching such contacts as lie
in its path. This causes the pulsations of the operator's printer as before, but this
time it prints the number instead of the exchange: This operator having ascertained
the number has now only to connect A's line with that of B in the usual manner by
inserting the subscriber's plug or jack-knife in the jack or socket, and the call is
completed.
After A has set his instrument he pays no further attention till his bell rings.
Under normal conditions his bell will ring only when his line is actually connected
to B's line and if B is engaged, a signal to that effect will be given automatically to
A who will be able to repeat the call in a minute or so by merely setting his switch
lever again.
The clearing signals for disconnection are automatically given to the Exchange
or exchanges by the action of the subscribers hanging up their instruments: When
the conversation is at an end the ring-off indicator is automatically operated by the
action of banging up the receiver; the weight of the receiver being employed to
lower the armature of an electro-magnet situated in the subscriber's switch case or
other convenient place, into the field of the said magnet the said armature being held
normally beyond the field range by means of a spring. It will be understood that as
soon as this armature is within the field it is attracted on to the magnet and thus
completes a circuit which throws down the ring-off indicators or actuates the
disconnection signal as desired. All the indicators remain down until the plugs are
removed out of the jacks, and thereupon the current is cut off, releasing the armature
above mentioned which under the influence of its spring assumes its normal position
beyond the field of the magnet.
Should, however, the call be for a subscriber not on the local exchange but on some.

page_text: other distant Exchange, which fact is ascertained from the position of the compound
indicator, as above explained, operator No. at the calling-board will put her printer
in circuit to find which Exchange is required, that is to say, she will plug or switch
current on to the circuit containing the electro-magnet which governs the actions of
the calling-subscriber's switch lever, thereby liberating it and causing it to pass over
in contact with the notches on the edge of the fixed disc and so print or indicate the
name of the Exchange required on the tape in her printer, and the further procedure
to complete the call will be exactly the same as in the former case.
The above is a description of what may be called the rectangular or gravity form of
the apparatus as regards the subscriber's switch, because the back or foundation plate
bearing the contacts is of that form and the contact block runs down by gravity
traversing by its contact spring the contacts on the edge of the said disc. This.
construction may, however, be somewhat modified without exceeding the scope of the
invention, as follows:-
Instead of the rectangular foundation plate and ridges for contacts upon the faces of
slides, the said plate may be a disc perforated around with holes near its edge and
having teeth or notches surrounding its periphery the said holes and notches.
being arranged in four sets of 11, one each for units, tens, hundreds, and thousands,
and one other set, which may consist of any number, representing different
exchanges or other offices or connections; the first four sets being for setting the
number, and the odd set for the name of the exchange of the called-subscriber as
distinguished from the calling-subscriber, as will be hereafter more fully described.
Suitably pivoted so as to pass in front of these holes are levers, one for each set
of holes, each lever having a knob at its extremity on the outside and a pin
projecting on the inside.
This pin passes over and opposite the holes so that it
may be set by hand into any one of them belonging to its own set, and is
prevented by stops from passing on to any other set, so that each of these levers
has a limited range. On the outside of the case containing this mechanism are
marked the numerals 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and a mark representing zero
opposite to each of the four sets of holes, and opposite the fifth or remaining
set are marked the names or characters or signs representing same, of the various
exchanges or other special connections that may be necessary, such, for example, as
"trunk call." It will thus be understood that from the outside of the instrument
the levers can be set to any exchange, or its equivalent and also to any number on
that exchange by simply moving the levers into the right holes accordingly. It has
now to be shewn how this set information is automatically communicated to the
exchange.
As above stated there are notches on the periphery of the disc. These notches
constitute so many contacts, and in order to close the circuit with any one of the
contacts there is provided a pivoted switch arın or lever carrying a flexible contact
piece at its free end. This lever is so arranged that its spring contact piece can be
passed over in contact with the whole range of notches on the periphery of the disc,
and is therefore not confined to any particular set of notches as the levers above
referred to are confined to their respective set of holes. This switch lever then, when
passed from one end to the other of its range in one direction, simultaneously winds
up a coiled spring which is in connection with a train of wheels, which in turn is in
connection with the armature of the electro-magnet first mentioned.
There are in addition to the above mechanism five pivoted arms the free ends of
which project in the pathway of the spring contact piece carried by the switch lever;
and, finally, there is another electro-magnet which is in electrical connection with a
compound indicator at the exchange.
Now, assuming a subscriber, A, wishes to speak with another subscriber, B, at a
distance, all A has to do is to first set the Exchange lever opposite to the exchange
desired as marked on the front of the case, then move in succession the four other
levers into the holes corresponding to the right numerals composing B's number on
that exchange, and having done this he then moves the switch lever round from one
end to the other of its range which action, as before explained, winds up the clock-

page_text: work and it also automatically by contact operates, that is, sets the compound
indicator in the local exchange, which indicator automatically, according as it swings
to the right or to the left, for example, informs the attendant there whether that
exchange or some other exchange is required; this also simultaneously locks the
latent switch so that it is now under the control of the operator at the Exchange.
On receipt of this signal an attendant at the exchange-which for convenience of
description we will call No. 1 operator-switches current on A's electro-magnet
which thereupon attracts its armature which in turn liberates the train of clockwork
and the switch lever, which latter, under the influence of the spring, which it will be
remembered was wound up by the movement of this switch when setting it, starts on
its journey over the notches on the periphery of the main disc, the contact spring
on the end of the said lever touching and riding. over each of the notches in succes-
sion. Each notch or contact it touches causes a pulsation to be given to a printing
apparatus, which will be described later on, causing this printing device to record the
name of the exchange only of the called subscriber. When this switch lever has
travelled over all the notches representing exchanges it is automatically stopped
mechanically by a notch or projection on one of the train of wheels composing the
clockwork of the latent switch. Operator No. 1 can now see by the position of the
compound indicator whether the exchange required is that exchange or some other
distant exchange, although if the latter she does not know either the number or
what other exchange, and she then has to ascertain this by switching current on to
the subscriber's latent switch which thereupon is liberated and actuates her printer
or its equivalent indicator. If the call is for a subscriber on the same exchange,"
operator No. 1 has merely to connect her line on a local junction connection to the
switch-board, this action automatically dropping an indicator there. The operator
(No. 2) at the switching board then puts her printing apparatus in circuit which
again releases the subscriber's switch, that is, the latent switch lever by energising
the electro-magnet and causing a pulsation of its armature which is thereby caused
to withdraw a detent from the notch which has been holding the said lever back.
The printing machines of the operators are a modification of an ordinary recording
telegraph consisting of a revolubly mounted wheel having the desired inatter,
(numbers, words, or the like) affixed to or formed on its periphery, said wheel being
rotated step by step with the assistance of levers and a pawl-and-ratchet device so as
to bring the desired word or number under the fixed printing hammer. The
printing apparatus of No. I operator is not exactly similar to that of operator No. 2.
The apparatus of No. 1 bears the names or equivalent numerals, characters or signs
of the various exchanges or offices on its periphery whilst that of No. 2 bears the
numerals 1 to 9 and also a 0 and a dash or dot mark for a zero point, making.
11 signs in all.
These printers may be operated either direct by the energy of the pulsations of an
electro-magnetic armature or through the intervention of clockwork. However in
this description we are assuming they are operated direct by electricity by magnetic
action.
To return to the description, operator No. 1 having released the calling-subscriber's
switch, the name of the exchange desired is thereby automatically printed upon the
tape in her printer or else works numbers or signs on the principle of a revolution.
counter which simply indicate as distinguished from printing the number desired, but
as we are now describing what is done when the call is for a subscriber on the same
exchange she need not wait to see what her printer prints, or, what is better still, the
subscriber's switch can be so constructed as not to actuate the operator's printer as
the indicator has already informed her by its position that the call is on her own
exchange.
For this reason, to save time in the event of a call on the local exchange, the
subscriber's or latent switch winding-up lever will be so arranged that the subscriber
either cannot move it beyond the notches representing the numbers, or else that if
capable of moving beyond, it instantly springs back over the notches representing
exchanges without coming in contact with them and so by avoiding the printing of

page_text: the exchange desired, saving the time necessary to effect it and setting the lever
immediately in position ready to print or indicate the number only.
The operator at the switching board then puts her printer or indicator in circuit
which again releases the subscriber's switch lever, which proceeds on its journey over
the notches or contacts representing numerals making as before a pulsation of the
printing lever or its equivalent indicator for every notch, so that for example, if 4 is
the number to be printed there will be caused four beats or pulsations of the lever
which actuates the pawl producing the rotary movement of the printing disc, or
indicating discs if an indicator be used, so as to bring Figure 4 immediately beneath
the printing hammer; the current is then momentarily sent round another path by
the contact on the end of the subscriber's switch lever coming in contact with a pin
on the lever set in the hole representing the numeral 4. Immediately this contact is
made it causes a pulsation of the lever constituting the printing hammer or operating
the indicator as the case may be, which thereupon taps or presses down the tape
upon the face of the type and prints the Figure 4, or turns the indicator so as to
expose Figure 4, as required.
Means of the usual construction for automatically inking the type and advancing
the tape are provided.
It may be observed here that the subscriber by the progress of his switch lever can
conveniently and at a glance see how his call is maturing in its different stages.
Thus the subscriber's switch lever passes in succession over all notches representing
the numerals, printing or indicating at the exchange during its journey the number
of the distant connection desired. Immediately the operator (No. 2) at the switching
board knows what number is required she simply inserts the calling subscriber's plug
into the spring-jack or coupling socket bearing that number thereby completing the
call by completing the circuit on the said line. Both subscribers, the calling and
the called, are informned automatically and simultaneously of this connection by the
ringing of a bell at their instrument, these signals being brought about by the
temporary connection, made by the plug as it is being inserted in the jack, with a
spring contact within the jack, said contact being thereby temporarily connected
with the current from a magnetic generator, and on inserting the plug further in the
jack or socket the two ends of it make contact with the called-subscriber's circuit as
usual making it possible for the two subscribers to speak with one another through
their telephones in the ordinary manner.
With regard to the function of the five pivoted arms which project in the pathway
of the contact spring on the end of the subscriber's switch lever, these are moved in
one direction by all the levers when the call is being set and are replaced at their
zero positions in succession by the contact of the travelling switch lever as it meets
with first one and then another on its journey. The function of these five levers is
to raise the travelling contact spring out of contact with those teeth or notches in
each section of the disc which it should clear. Thus assuming again Figure 4 to be
the first figure of the number desired then after the switch lever has made the first
four contacts it meets with the end of one of these five levers, which presses it outwards
away from the remaining seven notches in that section, the switch lever contact
simultaneously carrying the one of the five levers along with it until the said one
comes to its zero where it is stopped by a stop, the switch lever then rides over the
end of this lever and proceeds on its journey meeting successively with all the
levers.
In the gravity form of the subscriber's latent switch, instead of the fluted contact
plates being movable so as to expose in the pathway only just the number of contacts
required to be made, by cutting the front edge of the plates to an angle as above
described, the said contact-plates may be stationary and Lave a triangular piece of
insulant movable over or across their surface so as by the movement of this piece of
insulant more or less over the contacts leaves exposed only just the number of contacts
desired.
We have said in the opening statement that it is impossible for the subscribers to
speak with the operators at the exchange. By this must not be understood that no

page_text: verbal communication of any description is possible from the subscribers to the
exchange; the operators certainly, will have no telephones because they will not
require them, but other officials may be supplied with them as usual and a subscriber
may ring up and communicate them in the usual manner, when required.
We have also said that the switch by which the operator No. 1 switches current on
and so releases the subscribers' latent switch is a special one but have not hitherto
explained its special construction; this is as follows:-
The switch consists of a plug and a jack-or-spring socket for same. The plug is of
the usual construction except that the subscriber's line is preferably connected to its
underside a short distance from the back end as distinguished from connecting it to
the said in such manner as to be when straightened out in alignment with the plug.
The object of this preferential position is to avoid the line getting damaged by the
constant pressing of a bent line against the end of the plug as is now necessary to
insert it fully into the jack.
The jack or socket may have two spring contacts at the bottom and two at the top
and the connection of these springs with the line wires and with indicators is such
that on the operator bringing the plug down to its horizontal position which would be
done when a subscriber signals a want, contact is broken with the indicators connected
with the lower spring in the jack and made with the printer or other indicators in
connection with the upper spring in the jack.
Any or all of the various mechanisms or apparatus above described may be enclosed
in casings which may be of magnetic or non-magnetic materials or a combination of
both if desired.
PHILLIPS & LEIGH,
Agents for the Applicants.
Improvements in Telephone Systems and in Apparatus therefor.
We, ARTHUR THOMAS MILNOR THOMSON, of No. 51, Beauval Road, East Dulwich
in the County of Surrey, Electrical Engineer, and PERCY WARNFORD-DAVIS, of Pomona
Buildings, Fore Street, in the Administrative County of London, Gentleman, do
hereby declare the nature of this invention and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:
This invention relates to improvements in telephone systems and in apparatus
therefor.
The invention is more especially designed with a view to simplify, facilitate,
expedite and lessen the cost of working of complex telephone connections such as are
required for an efficient service in large towns, that is to say, wherever the number of
subscribers or users is very large, and consequently the system as a whole very busy,
but of course it is applicable to any lesser demands.
The main objects of the invention are:-(1) To do away with the verbal inter-
communication between the subscribers or users and the operators at the Exchange
now necessary in order for one subscriber to be put into communication with another
or one Exchange with another, as the case may be, and thus avoid all the attendant
inconveniences, and substitute therefor what may be called a secret service because
the operators at the Exchange have no means by which to overbear the conversation
between two users. (2) To do away entirely with the present multiple switchboard
and so simplify and cheapen the outfit and expedite the operating at the Exchange
and cost of operating and maintaining the system and service.

page_text: The invention consists, then, in certain apparatus and in the grouping group or
combination of these apparatus comprising signalling, printing and indicating devices,
and in the combination of this group of apparatus with ordinary or well-known telephonic
instruments and connections to form a complete novel telephonic system.
Before describing the new group of apparatus itself it may be well to mention here
in order to render what follows the more intelligible, that part of this apparatus is
located at the subscriber's end of the line and is substituted for the present ringing-
up or signal transmitting apparatus of an ordinary telephone set, and part at the
exchange; that the operators at the exchange in this system are not provided with
telephone receivers and transmitters, and that the source of the electric or magnetic
current employed for automatically signalling, indicating, recording and clearing the
connections is situated preferably at the exchange, but as in some cases it may be
more desirable to locate it at the user's end of the line, it is to be understood that we
do not bind ourselves in this respect.
We will now proceed to describe our invention in detail, reference being had to the
accompanying drawings illustrating same, and in which :-
Figure is a rear elevation of one form of the indicator-switch, telephone apparatus,
and connections at the subscriber's or user's end of the line.
Figures 2, 3 and 4 are respectively a cross-section and side and front elevations of
the gravity latent switch, Figure 1; the cross-section being taken on the line 2-2 of
Figure 4.
Figure 5 is a plan of the printer used to print the names of exchanges, and shows
how it is connected with the special switch.
Figure 6 is an elevation of the special switch at the exchange consisting of an
oscillatory spring-jack and plug, the latter being shown inserted and in the position
for operating a call; its connections with the exchange-printer, line wires, and special
indicator, are also shown.
Figure 7 is the special oscillatory indicator which distinguishes a call on the local
exchange from one for a distant exchange, its connections with the jack at the
switching board, the special switch, the exchange-printer and the line wires.
"
Figure 8 is a section of the exchange-printer taken on the line 8-8 of Figure 5.
Figure 9 is a diagraminatic plan of the latent switch L.S the "engaged or
"busy" signal E.S., the exchange-printer E.P., the special jack-switch J.S., the
special indicator S.I., and their connections,
Figures 10 and 11 are respectively an end view and front elevation of the special
indicator S.I.
Figure 12 is a diagrammatic plan of the numerical printer N.P., clearing relays
C.R., visual signals V.S., and their connections.
Figure 13 is a front elevation of the circular form of the indicator-switch.
Figure 14 is a rear elevation of the apparatus shown in Figure 13, with the cover-
plate removed, exposing the mechanism.
Figure 15 is a detailed sectional elevation of the arms.
Figure 16 is a plan of the contact spring.
Figure 17 is a diagram of the entire system shewing the apparatus and connections
necessary for a complete call from one subscriber to another, the gravity form of latent
switch being employed, L.S., being the latent switch; E.S. the "engaged" or "busy"
signal; E.P., the exchange-printer; J.S. the special jack switch; S.I., the special
indicator; N.P., the numerical-printer; C.R., the clearing relays; V.S., the visual
signals.
Figure 18 is a back elevation of the modified form of rotary latent switch wherein
the contact plates as well as the travelling winding-up lever, are pivoted.
Figure 19 is an inverted plan view of Figure 18.
Figure 20 is a side elevation of Figure 18, looking towards the left-hand thereof.
Figure 21 is a diagram of the instrument shewn in Figures 18, 19, and 20, and its
connections and circuits as arranged for a complete call.
LATENT SWITCH (GRAVITY TYPE)
The instrument or apparatus substituted for the usual telephone call set or outſt.

page_text: at the subscriber's office or end of the line is an indicator-latent-switch and is herein-
after for brevity referred to as the latent-switch.
This switch in one modification is shewn in detail in Figures 1, 2, 3 and 4 and is
composed substantially as follows:-
On a base or foundation plate 1 is mounted in a bracket 2 an electro-magnet 3, one
terminal of which may be electrically connected on the one hand by means of the wire 3',
insulated make-and-break contact 32-33 and line wire L,.or on the other hand by.
the wire 31, insulated make-and-break contact 34-35 and line wire L² with a special
switch situated at the exchange preferably near the originating operator, that is, the
operator who first receives the call. This special switch will be described in its turn
later on, but I may here briefly remark that it is preferably of the spring-jack-and-
plug type and is shown in detail at J.S. in Figure 6, and in diagrammatic form in
combination in other figures; the line wires L1, L2 terminating at the exchange in
the plug J.P. of the said switch. The other terminal of the magnet 3 is connected
as indicated by the plate E, to earth.
Mounted also upon the base plate 1 at the back thereof, are five plates 4, 5, 6, 7
and 8 bearing a number of raised contacts indicated respectively by 41, 51, 61, 7¹ and 8¹,
in or upon their exposed or rear surface; the said contacts being advantageously
formed as ridges or ribs produced by merely fluting, grooving or corrugating the
plates, but may be produced in any other suitable way. These plates are mounted
upon the foundation plate in such manner as to be slidable thereon transversely, in
a substantially horizontal direction; the mechanism by which they are moved being
advantageously as shown, consisting of a spindle 9 rotatably mounted in the base
plate 1, a toothed pinion 10 fast on the rear end of said spindle, a rack 11 formed in
or secured fast to the front face of the movable contact plates and always in
engagement with said pinion, and a milled thumb-nut 12 screwed fast on the outer
or front end of the spindle 9, so that turning this nut in either direction causes a
corresponding sliding movement of the contact plates by reason of the pinion 10
engaging in the teeth of the rack 11, which it moves, the contact plates sliding
between the foundation plate 1 and guides 13.
The contacts on the plate 4 represent the various exchanges in the town or city'
area and also, where necessary, special services such as trunk or long distance calls,
that is, to exchanges in towns or cities outside the area of the others, Telegraph Office,
Post Office, Special Messenger Service and also certain special officials in such offices,
such as Clerk-in-Charge &c., &c. The contacts on plates 5, 6, 7 and 8 represent
respectively the thousands, hundreds, tens and units of the subscribers' numbers.
The movable plates are all in electrical connection with the metallic foundation
plate 1, wires 43 serving to emphasize this connection.
It will be observed in Figure 1, that the plates in question are cut off obliquely at
their outer ends, terminating at their upper edge in a point, whilst the edge of the
foundation plate is cut "squarely or at right-angles to the top and bottom
edges of the movable plates. The object of this is to enable the exposure beyond
the edge of the foundation plate, of a single one or any number of the contacts at
will, by simply turning the thumb-nut in the outward direction so as to advance the
contact plate to the desired extent. In order to inform the user from the outside of
the apparatus as to how much to advance the plates so as to expose the right number
of contacts to give a call correctly, disc-wheels or dials 14 having notches 15 in their
periphery, and figures, letters or other signs or combinations of figures, letters or signs
on their outer face, preferably near to the periphery, may be fixed on the spindles 9
outside in front of the foundation plate 1 between it and the thumb-nuts or knobs 12.
The said numerals or other characters or signs correspond to the number of contacts
exposed, and as these contacts, as above stated, represent the different exchanges,
special services and orders of numerals constituting the subscribers' numbers, the
user by simply turning the knobs or thumb-nuts 12 can set these dials to any exchange
and number on that exchange desired.
In the construction shewn in these drawings, the spring 16 acts in conjunction with
-the notches 15 in the periphery of the dials, each of the notches being exactly in

page_text: alignment with the numeral, character or sign on the dial, and thus serves as a gnide
or pointer by which the adjustment may be effected with facility and accuracy. The
adjustment may however be effected in several other ways and I do not therefore
confine myself to any particular device in this respect; for example, the discs 14 may
not be fast on the spindle 9, but supported around it, and the spindle may carry an
index or radial pointer which can be turned to any of the positions by the thumb-nut 12.
Or again, the dial may be fast on the spindle but entirely enclosed or covered up with
the exception of one little window in a cover plate through which one of the numerals,
characters or words may be exposed at a time.
The contact finger which works in conjunction with the contact plates 4, 5, 6, 7 and 8,
is, of course, electricallyinsulated from them and is carried by a movable earth-connected
block 17. This block is mounted upon a support in such manner as to, be capable of
moving transversely over or past all the contacts on the contact plates should all
these contacts be exposed in its path, its contact finger 30 brushing across the
contacts as it travels.
As a means of support for the block in question, we prefer to mount it upon a screw
spindle 18 having preferably a "helical" thread, the block having a correspondingly
screw-ti.readed hole through it. The block is threaded on the spindle and the latter
supported in end bearings in such manner as to be capable of being freely rotated
about its axis, but incapable of any longitudinal movement.
This spindle is rotated in one direction by hand by means of the toothed-sector
lever 25, (best seen in Figure 2) which is pivoted to the frame at 0, and engages with
a pinion 19 fast on a toothed wheel 20 which engages with teeth 18 on the spindle 18;
the movement being preferably regulated by means of a fan 28 through the
intervention of a train of wheels consisting of the pinion 29 fast on the fan spindle,
the toothed wheel 20 in engagement with a pinion 21 fast on a toothed wheel 22
which engages with a pinion 23 fast on a toothed wheel 24 which is in engagement
with the pinion 29 on the fun.
The armature 26 of the magnet 3 is pivoted at 27, and the extremity remote from
the magnet is provided with a pin 27¹ which normally, that is, when the magnet is
de-energised and therefore not holding its armature, is in engagement with or
resting against a notch or stop-tooth formed in or upon the periphery of a plain
wheel or disc 90 mounted fast on one of the spindles of the winding-up train of
wheels, preferably the one bearing the toothed wheel 20. The co-operation of this
pin and tooth or notch serves to hold the train of wheels when wound up to prevent it
running down until purposely released by a current from the exchange, as is fully
explained in turn hereafter.
R.C. is a revolution-counting device which may be combined with the latent switch
when calls are paid for by ineter. It may be of any well-known construction as far
as the actual counting mechanism is concerned but in order to adapt it to the switch,
we provide it with an external toothed wheel 76, and the block 17 with a crank pin 77,
so that should a call be "effective," the said pin just when the said block reaches
the end of its stroke will strike in the teeth of the wheel 76, and thus revolve the set
of numbered dises of the counter and so register the number of calls made and act as
a meter which will always be in sight so that the calls may be checked as made.
Instead of the contact plates being movable to expose the number of contacts
desired, these plates may be fixed and a movable insulator adapted to move over them
so as to cover up a more or less number of the contacts employed, and thus leave
exposed only as many as may be required for the call.
The main or winding-up lever serves to rotate the spindle 18 in one direction which
winds up the block 17, or causes it to ascend or move in one direction carrying with it
the contact 30 which brushes across all the contacts on the contact plates which lie
in its path at the moment.
This indicator-switch may be used in any position. When used vertically, the nut-
block 17 on the helical spindle 18 bearing the flexible contact spring or strip 30, will
be raised by the hand-lever sector-rack 25 engaging in the pinion 19 fast on the
toothed wheel 20, which rotates the helical spindle and so raises the said nut, whilst

page_text: in its downward motion it will fall by gravity. Should, however, it be desirable to
use the instrument in any other position, say horizontal, the movement of this nut-
block in the unwinding direction it is obvious might be effected by means of a spring
(or other source of power) which is either wound up or extended when the nut is
moved in the other direction by the winding-lever 25, and consequently the potential
energy thereby stored in it will constitute the latent force necessary to automatically
return the block to its initial position when released.
31 is a spring catch made to engage in a hole 32 in the back of the dial 14, bearing
the numerals or characters corresponding to the various exchanges, etc., whenever the
said hole in this dial is presented to the tooth on the end of the said spring-catch 31.
The object of this is fully described under the heading "calling and operating".
The electro-magnet 3 is normally de-energised, in fact cut out of circuit altogether
by the make-and-break contacts 3-33 and 34-35.
33 are guide arms on the block 17 which arms co-operating with the guide-bar 34
along which they travel when the said block is in motion, serve to keep the block free
from any lateral play.
The block 17 is preferably connected to earth, this connection being indicated iu
the drawings by the earth plate E¹.
The contact plates 4, 5, 6, 7 and 8 are connected with the line wire L' and the
contacts 42, 52, 62, 72 and 82 with the line wire L
In Figure 9 the connection of this switch with the printing,apparatus, jack-switch
and special indicator at the Exchange is shown.
EXCHANGE-PRINTER.
The exchange-printer, that is, the printing apparatus which prints the name or its
equivalent of the exchange or other special office desired in a call, and operated
electrically by means of the Latent Switch just above described, is shown in detail in
Figures 5 and 8, also its connections with the special jack-switch J.S., and the special.
indicator S.I., Figures 6 and 7. This printer is a modification of an ordinary printing.
or recording telegraph. It consists of an electro-magnet C.M., hereinafter referred to.
as the contact magnet, electrically connected with the line-wire I, jack-spring 52, and.
earthed at E2 through a battery, P.B., a type-wheel 35, bearing in type, letters,
figures, words or other characters or signs representing the various exchanges, and
other offices if desirable; the types being arranged around the periphery of the wheel
and the number of them corresponding with the number of contacts 4' on the exchange
contact plate 4, of the Latent Switch.
This type wheel is operated automatically by the co-operation of the magnet 3
travelling contact 30 and the contacts 4' of the Latent Switch in conjunction with
electric currents emanating preferably from the battery P.B., but not necessarily, from
the exchange; the working being effected through the medium of the armature 36,
pivoted at O', of the magnet C.M., the ratchet escape wheel 37, the pawl or detent 38,
and the double tripping lever 39, the detailed actions of which will be described later
on under "Calling and Operating." Another electro-magnet P.M., hereinafter referred
to as the printing magnet, is electrically connected with the line wire 12 and governs
an armature 40, pivoted at O2, the tripping lever 39 above mentioned,type hammer 41,
a pair of feed rollers 42, and a detent 43, which latter in conjunction with the
ratchet 45 on one of these rollers turns the roller and advances the tape for spacing
purposes by friction with its surface. A lever 46 pivoted at Os and bearing a tooth 47
adapted to be brought into and out of engagement with the teeth of the escape
ratchet 37, will be described as regards its function further on. The supply of paper-
tape may be carried as usual in the form of a roll upon a skeleton bobbin 48 mounted
in a bracket so as to be free to revolve.
This printing apparatus may be at will electrically connected with the line-wires.as
above stated through the medium of the special switch next described.
OSCILLATORY JACK-SWITCH.
This switch is a modification of the well-known iack-and-ulug tyne. The line
i
2

page_text: wires Land L2 terminate in a plug J.P., the wire I, in the metallic sleeve of the plug,
and the wire L2 in the metallic tip of the plug; the tip and sleeve being of course
electrically insulated one from the other.
This plug J.P. is a modification of the ordinary one, having its lines leading in
through a stem or arm 58 which projects out from about the centre of the underneath
side of the plug and at right angles thereto; the object being to prevent the wires
getting broken by frequent bending as they do when they are led in at the rear end of
the plug, because in the latter case pushing the plug into and pulling it out of the
jack or socket bends the wires in reverse directions, and this frequently repeated, as it
necessarily is in busy exchanges, breaks the wires necessitating their frequent renewal.
It will be noticed that with the design of plug shown in Figure 6, the wires are always
quite clear of the rear end of the plug, so that this can be thrust in the jack as usual
without fear of crushing the cord containing the wires between the hand and the rear
end of the plug: moreover the rigid stem provides a firm grip with which to pull the
plug out of the socket with greater facility.
The jack consists of the casing 59, but instead of the bush 60 of insulating material
at the entrance of the jack for the reception of the plug being stationary as usual,
it is pivoted at 0' so as to permit the plug when inserted to be tilted so that its tip
points downward, as shown in dotted lines.
Normally the plug J.P. rests in the jack in an oblique position, with its tip
pointing downwards; a spring 61 engaging in notches 62 in the oscillatory bush
being provided to hold the bush in the position in which it is put. The free end of
said spring rests normally in one or other of said notches and rides out of them when
the bush is moved, which can be done with slight force, but not by the mere weight
of the plug.
A set of spring contacts 52, 53, 54, 55, 56, 57 are fixed in an insulating block 63
secured in the rear end of the casing 59. The springs 52 and 53 are shown electrically
connected through the plug J.P. with the line wires L' and I respectively, and
through connection wires with the exchange-printer, and when the plug 49 is
inserted in the jack horizontally as shown in Figure 6, these two springs make contact,
one with the tip, and the other with the sleeve of the plug, so that the said printer
at the exchange may be thereby thrown into circuit with the subscriber's Latent
Switch when desired.
66
The springs 54 and 56 are connected through a generator or battery E.B. to earth,
indicated by the plate E. These are for the purpose of giving the "engaged" or
busy" signal to the calling-subscriber when the called-subscriber's line is already
engaged; the indicator in question consisting of either a special magnetic bell or an
electric bell 76 and electro-inagnetic device 77, such as shown in combination at E.S.
figure 9, and which is further described under "calling and operating" page 21.
Normally the plug J.P. being in the inclined position, makes contact by its tip
with the spring contact 55 and by the sleeve with the contact 57 slightly depressing
these two contact springs so that they break contact with the two springs 54 and 56.
Consequently, when the said plug is either drawn out or lowered into the horizontal
position, the two springs 55 and 57 being thereby released, spring up and make
contact with the two springs 54 and 56, as shewn in figure 6 and thus automatically
actuate the indicator E.S. when the line is engaged, as desired.
The contact springs 55 and 57 are in electrical connection with the special
indicator S.I. at the originating-board and jack S.B. at the switching board, these
connections being obvious from a glance at Figures 6 and 7 or Figure 9.
In Figure 9, the two contact springs 55 and 57 are shewn in contact with two
stud-contacts, these latter being merely substitutes for the contact springs 54 and 56
in Figure 6.
Any one or more of the contact springs shown in the jack J.S., Figure 6 may be
replaced by contact studs or other suitable form of contact.
SPECIAL INDICATOR.
The special indicator is shame in detail
14
11

page_text: tion with the Exchange printing apparatus in Figures 9 and 17. It consists of two
electro-magnets 64 and 65, the one coil 64 having one of its terminals normally in
electrical connection with the line-wire L', and the one 65 one of its terminals in
connection with the line-wire L through the medium of the plug J.P. jack S.B. and
springs 55 and 57 of the jack switch J.S., the plug normally resting in the said jack
in an oblique position so that the tip 50 of the said plug is in contact with the
spring 55 and sleeve 51 in contact with the spring 57 as shewn in dotted lines. The
other two terminals of the coils in question are connected through a battery to earth,
indicated by the plate E³. The poles of this electro-magnetic device have their inner
sides which face each other preferably finished obliquely as shown at 66, and between
these poles is hung or pivoted the armature 67 in such manner that it can oscillate
from the one side to the other. At the opposite end of this armature is a rigid cross-
bar on each extremity of which is fixed at an angle thereto a disc or plate 68, 69,
which discs advantageously differ in color or are otherwise rendered visibly
distinguishable. In front of the armature and supported centrally between the two
magnets is a window 70; the whole being so arranged, as will be seen, that attraction
of the armature to one pole or the other causes one of the discs or plates 68 or 69
on the ends of its cross-bar to appear at the window 70.
This indicator and its functions are further dealt with under the heading "calling
and operating," but it may be here briefly mentioned that it serves to indicate at a
glance to an operator at the exchange whether a call is for a subscriber on that
exchange or some other or distant one, and this is understood according to which
disc 68 or 69 is presented at the window 70, or other predetermined arrangement as the
case may be. Figure 7 shows the armature of this indicator in one of the positions
it assumes the instant a call is made by means of the Latent Switch, first above
described or a modification thereof.
THE NUMERICAL PRINTER AND ITS CIRCUITS.
The instrument or apparatus called the "numerical-printer" and shewn at N.P
Figure 12, is the device for automatically printing the subscribers' numbers. It
consists accordingly of a type-wheel 91, bearing, preferably arranged in a circle
around its periphery, the numbers 1 to 9, a 0 and a dot or dash or other sign repre-
senting zero. There are thus eleven signs in all corresponding with the eleven
contact-ridges, 5', 6', 7' and 8', on each of the plates 5, 6, 7 and 8 of the Latent
Switch shewn in Figure 1. This type-wheel is connected with a ratchet-and-pawl
mechanism, substantially similar to that described above in connection with the
exchange printer. It is also similarly connected with electro-magnetic devices and
provided with a paper-tape roll, inking and spacing devices, and may also be fitted
with means for bringing the type-wheel back to zero each time after it has printed';
this latter contrivance being to save the type-wheel having to make a complete
revolution after printing each figure of the called-subscriber's number.
V.S., V.S., are two visual or light signals operated by currents sent through relays
C.R., C.R. R3 and Rare resistances bridged across the line-wires preferably at the
points and in the manner shewn in the drawings and serve to prevent the balance of
the line being upset by the earthing at E7. These signals V.S. light up at each
operating-board simultaneously on the operator's plug being inserted in the jack L.S.B.
and they remain alight until cut out of circuit when cutting in the numerical-printer.
They are also subsequently lit by earthing the current on the lines automatically by
the weight of the receivers when placed on the switch-hooks at the end of a
conversation, and thus also serve as clearing signals to the operators.
The functioning of the above signals is also further described under "calling and
operating" further on.

page_text: venience we will call "A," wishes to speak with a subscriber "B," B's number being,
say, 4105 on the local exchange, and this exchange being indicated by the numeral 2
on the exchange-dial 4. "A " is therefore the calling-subscriber and "B" the
called-subscriber, and the call and operating thereof will be effected by the combina-
tion of apparatus herein before described; the subscriber's latent switch employed
being of the gravity type-as in Figure 1.
To start the call "A" first sets the dials of the latent switch to the exchange and
number on that exchange assigned to B. This is done by merely turning the knobs 12
in the outward direction, these actions advancing the respective contact plates till
they expose just the right number of contacts corresponding to the exchange and
number desired, and as the exchange assumed in the present call is the local one, and
the numeral 2 on the corresponding dial 14 denotes this exchange, "A" simply turns
the said dial until the spring pointer 16 drops into the notch of the said dial imme-
diately over the Figure 2 on the face of the dial, thus advancing as desired the
plate 4, through the medium of the rack-and-pinion device at the back, and exposing
two of its contacts 4' in the path of the contact brush 30 on the travelling block 17.
"A" next in like manner sets the numerical-dials 5, 6, 7 and 8 respectively to 4,
1, 0, and 5, thus setting B's number and exposing in the path of the contact brush 30,
corresponding numbers of contacts. Having done this, "A" next winds up this
switch by simply bringing round the hand lever 25 by means of its handle as far as it
will go towards the opposite side, this action through the medium of the toothed
sector on the said lever, the wheel 20, pinion 19 and teeth 18' on the spindle 18,
rotating the latter which thereupon carries up the nut-block 17 bearing the contact
brush 30. The height to which this block will be thereby raised depends always
npon whether the call is for a subscriber on the local exchange or some other
Exchange. For calls on the local Exchange it is arranged so that the block will be
arrested when it bas arrived about half-way up in order that the contact 30 shall not
actuate the exchange-printer at the exchange, on its descent or return travel because
that is of course unnecessary for a call on the local exchange, as the special
indicator (see that heading) will have in the meantime indicated it; it is only
required when B's number is on some other exchange to inform the operator at the
local Exchange what other Exchange is required.
This arresting of the contact block 17 is automatically brought about by the tooth on
the upper end of the spring catch 31 springing into the hole 32 in the exchange-
dial as soon as the said hole is presented to it, which as before explained is arranged
to take place whenever the dial is set for local exchange.
On the lower or tail end of this spring catch 31, is a projection 73 which is brought
into the path of the travelling block 17, or rather into the path of an insulated
stud 74 on the said block, when the upper end of the spring catch 31 is in engagement
with the hole 32 in the exchange-dial, by reason of the said spring turning on its
pivot 75, and thereby titling its tail end backwards.
Just after the block arrives at the point at which it is arrested as above explained,
it drops slightly and presses the contact 35 against the contact stud 3 which is in
electrical connection with the line wire L which in turn is in connection with the
special indicator S.I. (see Figure 7) at the exchange, through the plug J.P. and
springs 55 and 57 in the special jack switch J.S.
The current waiting on the line is thereby earthed but the current is only a feeble
one from the battery I.B. and not sufficient to energise the electro-magnet 3, (see
Figure 1) although this current will traverse this coil to earth, but the said current is
sufficient for actuating the special indicator S.I. at the exchange, which it does
immediately the travelling block makes the said contact. The normal position of the
armature of the indicator S.I. is central, as shewn in Figure 9.
The two line wires L1 and L2 terminate in the jack plug J.P., the one L' in the
sleeve 51 of the plug and the one L2 in the tip 50. This plug, as already explained,
normally rests in the jack switch J.S. in the inclined position as indicated in dotted
lines in Figure 6, consequently making contact, with the springs 55 and 57 which
.close the circuit in which the indicator, Figure 7, is included.

page_text: This indicator S.I. having been actuated, one of the discs (the one indicating "local
exchange") is thereby presented at the little window 70, as in Figure 7, thus
indicating the operator who first receives the call, and hereinafter referred to as the
originating-operator that the call is for a number on that exchange. The call having.
been thus announced, the operating is commenced by the originating-operator at
the calling-board pulling the plug J.P. out of the jack J.S., thereby locking
the subscriber's switch by cutting out all connection with the indicator S.I:
The contact springs 5 and 57 thereupon spring up and make contact with the two
contact springs 54 and 56 respectively which are connected through the battery
E.B. to earth, indicated by the earth plate E+. This is for the purpose of giving
the "engaged ог "busy" signal to any other calling subscriber automatically
indicating to him that the line is engaged.
"
"
"
This "busy or engaged "indicator preferably takes the form of a bell-indicator
such as shown at E.S., Figure 9, wherein it consists of an ordinary electric single-
stroke bell 76 and an electro-magnetic device 77 the armature 82 of the latter being
pivoted at 78 and bears at one end a plate 79 bearing the word "engaged or
similar information, this plate being exposed at an aperture 80 in a board 81 in front,
whenever the armature is attracted by the magnet. The bell 76 in its entirety might
obviously be dispensed with and in lieu thereof a simple gong might be mounted
within reach of the armature 82 to strike.
The plug J.P. is then inserted in a jack of a local junction connection leading
from the calling-board to the switching-board, this action putting the visual signals
V.S. in circuit and consequently lighting them. The operator there then plugs
the jack leading to the numerical-printer to ascertain the number wanted.
The numerical-printer being now in circuit, the current on the line L' emanating
from the battery N.C.B. is strong enough to energise the coil 3, Figure 1, causing it
to attract its armature and thus release the catch 27¹ at the end of the lever out of the
notch in the wheel 90 and thus releasing the winding-up mechanism. The block 17
carrying the contact 30 then commences its descent breaking the contact at 34-35 and
consequently taking the "earth" E off the line, said contact 30 brushing in succession
those contact ridges of the plates 5, 6, 7 and 8 which lie in its path and thereby giving
a corresponding number of pulsations to the armature 36' of what I will call the
contact inagnet C.M' of the printer in question, thus rotating the type wheel to
the figure to be printed, and on the contact 30 arriving in its descent at the contact
studs 5, 6, 72 and 82, it earths at E¹ the current now coming from the battery N.P.B
which causes a pulsation of the armature 40 of what I will call the printing magnet P.M¹
thereby pressing the printing hammer and paper against the type and thus producing
the imprint. This action in detail, is as follows-To the armature 36¹ is pivoted
at 83 (see Fig. 5 for the details) a bent-lever 39 and at 84 a pawl 38 so that the said
armature carries with it when attracted this bent lever, the tip of which on coming
in contact with a fixed stop 85 becomes depressed thereby throwing out its other leg
on which there is a pin 86 which latter pushes back the detent 43 off the tips of the
pawl 38 and a lever 46 having a tooth 47, thereby releasing the said pawl and lever,
both of which, being spring pressed, immediately engage in the teeth of the ratchet
escape wheel 37.
Each time the armature 36¹ drops, it causes by means of the pawl 38
a tooth-by-tooth rotation of the ratchet 37 which in turn rotates the respective type
wheel 35; these pulsations occurring for every contact on the plates 5, 6, 7 and 8
brushed by the contact spring 30, thus causing the proper type to be presented to
the type hammer and on the said contact spring arriving at each of the contact
studs 5, 6, 72, 82, a pulsation is given to the armature 40¹ of the printing magnet P.M.'.
On this armature being attracted by its magnet, the printing haminer 41 strikes the
paper against the type wheel thereby printing on the paper the number, character or
sign which is presented at that point of the type wheel immediately above the bammer
at the moment; simultaneously the detent 43, is raised and during the descent of the
armature the detent 43 again catches on the ends of the pawl 38 and toothed lever 46,
bringing the former ont of the teeth of the ratchet escape 37, and the tooth on the
lever 46 also out of engagement with the said, escape wheel, thus leaving the latter

page_text: free to be turned back to its zero or initial position under the influence of a coiled
spring 105 within the barrel of the said wheel which spring has of course been wound
up by the pawl 38, during the pulsations of the armature 36¹. When the armature
drops, it also brings down with it the detent 43', which, catching in its descent in one
of the teeth of the ratchet 45 fast on the friction roller 42, rotates this roller which,
by friction rotates the other roller 42, and advances the paper tape between them for
spacing purposes after each imprint. The number being thus ascertained and printed
for future reference, the call is completed by connecting the line assigned to this
number, by taking the plug out of the jack 49 and putting it into the called-
subscriber's jack S.B¹. The operator then depresses a key K connected in the lines
which action causes a signal(bell C.B. to ring) to be given to both subscribers, indicating
that the connection required is completed.
The above is a description of the series of events or operations which take place to
put one subscriber in connection with another on the local Exchange. We will now
proceed to describe what would take place had B's number been on some other or
distant Exchange.
"A" would set his dials as before except that the Exchange dial would of course. be
set to an Exchange other than the local, and thus the spring catch 31 would uot this
time be able to drop into the hole 32 in the said dial and consequently would not tilt
its tail end into the path of the block 17 and obstruct its upward passage as before, so
that when the switch is wound up by the toothed sector lever 25, the block 17 will be
thereby carried right to the top and press the spring 32, against the contact stud 3³
thereby earthing the latent current on the line L, the said current originating at the
battery I.B.; thus actuating the special indicator (Figure 7) at the Exchange, as
before. The operator at the calling-board now knowing that the call is for some distant
Exchange, must ascertain which one, so instead of pulling the subscriber's plug J.P.
out of the jack J.S. simply brings it down into the horizontal position shewn in full-
lines in Figure 6 thus cutting out of circuit the indicator S.I. and cutting in circuit
the Exchange-printer E.P. (Figures 5 and 8) which thereupon prints the name of the
Exchange wanted. The contact springs 5 and 57 being thus released, fly up and
make contact with the two other springs 54 and 56 which are connected through a
generator or battery to earth indicated by the earth plate E. This is for the purpose
of giving the "engaged" or "busy" signal as previously explained. The mechanism
and operation of the Exchange-printer are almost identical with those of the numerical-
printer so need not be here repeated; the only difference consisting in the type wheel
containing on its periphery words, numerals, characters or other signs denoting the
Exchanges, &c., instead of the numerals for the numbers as in the other printer.
Either or both of these printers may be made simpler if desired, by eliminating the
mechanism for returning the type wheel back to zero after each print.
The name of the distant Exchange being thus ascertained the originating operator
plugs A's line direct into a jack corresponding to L.S.B. leading to the switching board
of that Exchange instead of as in the former case to the switchnig board at the same
Exchange, and the call is then completed by the operator at this switching board as in
the former case.
Thus without any intercourse with the operators at the Exchange, the most com-
plex telephonic service can be supplied by means of the operations and the combination
of apparatus above described.
Most of the apparatus is of novel construction and specially adapted, one instrument
to the other as well as the whole system, to carry out the invention in the best way,
although in a fundamental form some of the instruments I am aware are not novel for
other uses than telephony.
The apparatus and the system described in this Specification have been devised with
the London system in view, so that certain modifications, which however are obvious,
must be made in some of the apparatus and also in the way they are grouped, to adapt
them to the service to be supplied. For instance, the Exchange printer herein
described is constructed to print the names or equivalents therefor of Exchanges and
other offices numbering fifty in all, but it is obvious that this number is entirely

page_text: dependent upon the number of Exchanges, &c. And where there are no junction
Exchanges, the Exchange dial and exchange contact plates can be dispensed with
entirely. As regards grouping, the combinations may be also altered to suit the
requirements and some of the instruments may be omitted entirely, for instance the
compound indicator might be dispensed with where there is only one Exchange, that
is, where there are no junction or distant Exchanges. And again, other equivalent
instruments may be substituted for those eliminated, for example instead of the sub-
scriber's latent switch being made to operate a printing device, the latter may be
eliminated and a revolution counter or a counter-indicator substituted therefor, the
said counter-indicator being operated by impulses imparted to a lever armature in
exactly the same way as the printer is worked.
The end of a conversation is made known to the operators in the Exchange by
the following means:-
92 (see Figure 1) is an electro-magnet normally de-energised but supplied when
required by a current from the Exchange, so that the clearing signal can be received
there, said current being derived from the batteries R.O., indicating "ring off,” shewn
in Figures 12 and 17. The armature 93 of this magnet is held normally out of or
beyond the magnetic field by means of the spring 94 but is automatically brought into
the field when the hand telephone set 95 is placed on the switch-hook arm, by reason
of the weight bearing down the said hook which by its central stem 96 depresses the
pivoted link 97 causing the detent 98 on the latter to catch on the tip of the armature 93
and pull it down. Immediately, the armature is in the field the spring 94 makes
contact with contact 100 which is earthed at E thereby earthing the current on the
lines, which energises the coil 92 and the armature 93 is drawn on to the magnet, in
which position it makes contact with the two contact springs 99 and 100 thereby
closing the circuit, putting an "earth" on the lines by reason of the springs 101 and 102
being in contact with the link 97 so that the clearing signal can be received in
the Exchange, the spring 101 being in connection with the wire L' and the spring 102
in connection with the line wire L. This earthing of the current on the lines
causes the lamps V.S. to light up which serves as the clearing out signal to the
operators in the Exchange.
The subscriber's latent-switch instrument may be modified in construction without
departing from the principle of the invention, one such modification being that shewn
in Figures 13, 14, 15 and 16, in which:-103 is an electro-magnet corresponding to
the one 3, and 104-93-98 an electro magnetic device corresponding to the one
denoted by the same numbers in Figure 1; both of these devices performing the
saine functions as those in that modification. Instead of the five independently
movable contact plates we have here one circular fixed one 105', and the contacts are
formed on its periphery instead of its face, 107 denoting said contacts; and instead of
the five independently movable dials there is but one large fixed one which is fixed
or formed advantageously, on the outside of the front of the containing case as shewn
in Figure 13. The travelling contact 30 is attached to the outer end of a pivoted
lever 112 which is so connected with a spring-advantageously a coiled one in a box,
similar to the nainspring of a watch-that turning the lever on its pivot in one
direction winds up the spring. Radiating from and movable about the same pivot
are ten arms extending over the contact plate to just beyond its circumference; five
of these arms 108, are used for setting the call, these five being provided each at
its free or outer end with a pointer to guide the adjustment and a knob 109 by which
to move them by hand. In order to cause these arms to remain where adjusted at
each call they are provided on their under or rear side with a pin 110 (see Figure 15)
which may be engaged in any one of a number of small holes 106 in the contact plate,
said holes being near and opposite to the sets of contacts and corresponding in num-
ber with same. The said knobs and pointers project through a circular slot in the
casing, as shewn in Figure 13.
The five other arms 113, have their outer extremities insulated and serve as carriers
to carry the travelling contact finger 30, when travelling in the unwinding or back-
ward direction, off those contacts 107 which according to the setting of the call it is

page_text: not to make contact with; this being effected by the arms 113 being moved along
until stopped by a fixed stop at their respective zero positions 110 by the contact
spring 30 catching against them when the winding up lever 112 is being moved round
to wind up the switch, and on its return the contact 30 rides on the tip of each one in
succession, thus being lifted off the contacts 107 until it (the arm 113) is stopped by
by a stop on the arms 108 when the contact spring 30 yields and passes over said
arms 113 and makes contact with all the remaining contacts of each set, which has
the effect of giving the required number of pulsations to the printer at the Exchange
as in the former case.
-
33, 33, and 34-33 are make-and-brake contacts which correspond to and perform
exactly the same functions as those similarly denoted in Figure 1, that is to say the
winding up lever 112 on coming in contact with them when wound up causes an
earthing of the latent current always on the lines, and thus the indicator S.I. to
be actuated accordingly, and then the operator at the Exchange puts one of the
printers in circuit according to the information required and thus shifts the current
from the indicator battery I.B. to the printer battery, which latter being more
powerful energises the coil 103, which thereupon attracts its armature and releases
the winding up lever 112 bearing the travelling contact 30, which travels over the
contacts 107 exposed in its path as before. The contact plate as before is con-
nected with the line L. 111 are contacts which correspond to those 42, 52, 62, 72 and 8*
in Figure 1 and are accordingly connected to line L2; the contact finger 30 is earthed
as also the electro magnet 103.
Figures 18, 19, 20, and 21 illustrate a further modification of the circular form of
latent switch, wherein the contact plates as well as the travelling arm are pivoted.
Around a circular frame 114 are fixed three segment-shaped plates 115 having on
their faces concentric ridges or contacts of such shape that moving the dials 6, 7, 8
round, turns these plates so as to expose to the moving contact any number of these
ridges to correspond with the number required in a call.
This modification has been made with a view to rendering the latent switch more
applicable to all sizes of Exchanges, that is, to meet the requirements of all services,
without departing from the main principle; and rendering the parts nearly all inter-
changeable and of a standard pattern and size, including the frame works for the
switch-boards; so that it will not be necessary to have the parts of the instrument
of different size, or instruments of different pattern for different sized systems. This
of itself would be a manifest advantage, and the similarity of the apparatus and in the
circuits would render the fitting and maintenance of systems simpler, cheaper and
better in every way.
We will describe the apparatus and working of a switch-board built for 500 sub-
scribers and this description, read in conjunction with the former description, will we
think, give all the information necessary.
It must be borne in mind that this board is for a "local" Exchange with, if
necessary, the means of working in conjunction with one or two sub-Exchanges,
trunks etc., as there are 5 ridges on the hundreds plate spare for this purpose.
I will afterwards show how this mechanism and apparatus is applied for a larger
system :-
A single-flag indicator, S.I., and a 3-point spring jack, JS', are the only apparatus
requisite on a subscriber's circuit in the Exchange. We propose that the indicators
should be fitted in a framework inclined from the face of the board at an angle more
in line of sight of the operators, as shewn in Figure 21. The spring jack is of the
ordinary pattern. We use the double-cord system as being preferable to that described
before. The cords, C, are arranged in the usual way in front of the operator, but the
shelf through which they run slopes downward from the spring-jacks, thus allowing
the operator to get nearer the work and have a longer reach and to have more
command over her work. There would usually be 50 pairs of cords fitted but this
number could be increased or decreased according to the requirements of the service.
The back plugs J.P.1 of each pair contain lamps, 121, for clearing, and the front
plug J.P. rests on a socket-contact S.C. The normal position of the socket-contact

page_text: puts the pair of cords through one of the printers, the cords being divided into sections
of, say, ten pairs to each printer. The latter are fitted just above the spring-jacks and
we propose to have one for every hundred subscribers, but this number can also be
increased or decreased according to requirements.
The latent switch is provided with a pivoted travelling arm, 116, similar to that on
the rotary pattern switch before described but bearing a spring 117 and a contact
stud, 118 the former being connected to the 1 line and the latter to earth. The
arm 116 in travelling over the ridges on the plates 115 allows the spring 117 to ride
over the ridges and on each ridge to rise and make contact with the stud and the
necessary pulsations are carried over the line to the printer. Studs 119 are fixed
after each ridge plate, bearing a contact joined to L line, and after the travelling
arm passes over the ridge, the earth stud on the arm makes contact with these studs,
which send a pulsation over the L line and so print the numbers.
The same motive-power is used as in the rotary switch before described and the
general arrangement of the instrument otherwise than the modifications described
above, is similar to that description. We have not shown these details in the drawing,
as they are the same as in the other drawings.
The subscriber, then, turns the dials 115 to the number wanted and turns the
arm 116 to wind the switch, this earthing the line as before and giving the signal S.I'.
to the operator, (through the stud 118 making contact with spring 120), who inserts
the back plug of a pair into that subscriber's jack, and the front cord being connected
to the printer N.P. through the socket contact S.C., and the number is thereby
printed. The operator then takes the front plug and inserts it in the jack of the
number printed, and presses the ringing button as before.
This completes the operation for connecting, and on receipt of the clearing signal
by the lighting of the lamp in the back plug, in front of which lamp is a transparent
number, the operator clears this and also the corresponding plug which contains a
dise in its rear end with a corresponding number to that on the lamp. It is understood,
of course, that the subscriber's apparatus for signalling to clear is the same as previously
described, and it is shewn in this Figure 21 similarly constructed and connected as in
Figure 1.
"
This disposes of the "local or smaller switchboard for five hundred subscribers
and under, and we will now explain the addition to the apparatus necessary to serve
a large system.
The subscriber's instrument is the same as above described with the addition of extra
contact plates as required.
By adding another plate 115 we have capacity for 10,000 subscribers or ten
Exchanges of 1000 subscribers. By adding a fifth plate we have ten exchanges of
10,000 subscribers. With a sixth plate the ultimate capacity of any system is
reached, as there would then be one hundred Exchanges of 10,000 subscribers each.
The originating-board is the same in all details as the above-described switch-
board, with the exception that a double-flag indicator is used in place of the single-
flag one S.I', and a 4-point jack in place of the 3-way jack J.SI, the former having an
arrangement for the two inner contact springs being put to earth through a battery,
on the insertion of the plug, so as to give the "busy" signal E.S. to another subscriber
if calling-up through the "switching" board.
Outgoing junctions to other Exchanges and to the incoming or switching-board
are fitted over the home section jacks. The visual signal lamps V.S. may be fitted
over these jacks or in the back plug of the pair as 121, as in the local board.
latter being thought preferable,
The operations therefore will be as follows:-
The
Subscriber sets his dials to distant Exchange number wanted and winds the
switch.
Indicator flag signals the want.
Operator inserts back plug (bearing lamp) in home-section jack, and number of
Exchange prints.

page_text: Operator takes front plug and inserts in disengaged junction to distant Exchange..
Signal lamp in plug lights at distant Exchange and operator there inserts plug in
printer. Number prints.
Operator takes plug out of printer and inserts in jack of number printed.
Presses ringing key which rings up both subscribers.
On completion of conversation lamps light at both Exchanges on subscribers
hanging their telephones up and operators clear the connecting cords, and lamps
go out.
The incoming or switching boards would be exactly as before explained.
It will be obvious to anyone experienced in the art, that various modifications
of apparatus and circuits could be used without departing from the spirit of this
arrangement and the one formerly described, but the above suggests itself to us as
being the simplest and most perfect.
It will be seen that with the suggested means of printing the Exchanges as
numbers instead of names, it will be possible to discard the large pattern Exchange
printers, and use all one pattern, viz., the numerical printers.
Thus this invention embraces consists of a group of apparatus for automatically
electrically signalling connections required from subscribers to the Telephone
Exchange operators and from one Exchange to another without either subscriber or
operator speaking, thus securing secrecy of messages, as telephone instruments form
no part necessarily of the operator's apparatus, and they are therefore unable to
66 tap" or tamper with the wires.
The circuits are very materially simplified, and multiple switch-boards even for
the largest Exchanges are dispensed with, thereby saving enormous expense in
construction and maintenance, and doing away with numberless sources of faults
and wrong connections.
With this system it would be possible to carry on the operating with from 20%
to 50% of the staff required by the systems now in usc.
It is considered to be an improvement on the purely automatic systems as it is
available for the largest as well as the smallest Exchanges or groups, whereas the
automatic systerns will only work satisfactorily up to a limited number and the
mechanism is necessarily too elaborate and costly.
In the case of multiple switch-boards the cost per subscriber's line increases as an
Exchange grows, but with this system the cost per line would always remain the same
and the prime cost per line would be very much less.
The novelty of the invention consists in part, of the general arrangement or
combination of the parts which in different forms have been used for other purposes
but not for telephony, and also some of the parts are novel, such for instance as the
apparatus or latent switch at the subscriber's end whereby the dials can be set to the
number required and the switch is worked preferably by currents from the Exchange,
when the operator is ready to operate the call. We however desire it to be understood
that we do not claim a latent switch in its broadest sense, as we are aware of the
Prior Patents of Mills No. 3,789 of 1885 and of Herzog No. 3,813 of 1885.
Having now particularly described and ascertained the nature of our said invention
and in what manner the same is to be performed, we declare that what we
claim is
11. A cemi automatic latent signalling switch for actuating and-eqntrolling-a
distant indicator-or-signal, consisting of a frame-in-electrical--connection-with-one
terminal of the circuit movable contact plates;--a--contact-piece,-en--the--frame, an
externally-serew-threaded-spindle-rotatably--mounted in, but insulated--from;--the
frame; means for rotating the spindle-in-one--direction, a-travelling-nut--block
mounted--on--said spindle,-and-a-contact-carried-by-the-nut-block-in-electrical
connection-with-the-other-terminal of the-circuit, and adapted to brush-the-contacts
en-the-plates-and-frame; substantially as described-und óhown.
M

page_text: 2. The combination-with-an-electric-circuit-and--a--distant--indicator--or--signal
included-in-the-circuit, of the semi-automatic latent-signalling-switch-for-netuating
and controlling the said indicator or- signal,--consisting of a-frame -in--electrical
Ponnection-with-ono-terminal of the circuit, movable-contact-platos,-a-contact--piece
en--the-frame,--an-externally-serow-thread--spindle rotatably mounted--in, but
insulated-from-said--frame--means-for-rotating--the-spindle-in-one--direction,--
travelling nut-block-mounted-on-the-spindle-and-a-contact carried by the nut--block
in-electrical connection-with-the-other-terminal-of-the circuit,-and-adapted-to--brush
the contacts-on-the-plates-and-frame,-substantially as described-and-shown.
3. The combination-with-the-electric circuit--and--a- distant--indicator-or--signal
included-in-the-cirenit, and the semi automatic-latent signalling switch for actuating
and-controlling-the said indicator-or-signal, consisting-of-a-frame--in--electrical
connection-with-one-terminal-of-eirenit,-morable-contact-plates;-contact--on--frame,
serew spindle-rotatably mounted-in-the--frame, travelling-contact-block-on said
spindle-in-electrical-connection with other terminal-of-said--circuit,--of--8--revolution
counter-actuated-by-a-projection-on the said travelling contact-block--engaging--ou
its-downward travel-in-the-driving-wheel-of-the-counter;-substantially-as--described
and-shown.
4. The combination with an electric-circuit, a-distant-indicator or signal included
in-the-circuit,-and-the-semi-automatic latent signalling-switch-consisting of-a-frame
in-electrical-connection-with-one-terminal-of the-circuit,-contact-on-the-frame, screw
threaded-spindle-rotatably-mounted-in, but insulated--from--the--frame--means--for
rotating the spindle,--travelling nut-block,--contact on-said-block-in-electrical
connection-with-other-terminal of-the-circnit-and-adapted-to--brush-the--contact--on
the-frame, of-an-electro-magnetic printing device, a-simple-switch-for--cutting--said
printer-in-circuit-and-mean--for--actuating--said--printer-from--the--semi-automatic
Intent-switch, consisting of the adjustable-contact-plate,--an--electro-magnet,--the
Armature-of-which-is-adapted-to-release the travelling contact-which--then-falls by
gravity-its-contact brushing-the-contacts-on-the-adjustable--plate-thereby--causing
the-pulsations-of-the-printer,-substantially-as-described-and-shown,
5. In-apparatus for use in connection with telephonic--intercommunication,--the
combination-with-an-electric-circuit,-of-the-latent--switch--the--special--compound
indicator, the special jack--switch, the line-wires, the Exchange printer-having
mechanism arranged and adapted to return the type wheel-to-nere-or initial-position
after-ench-print, and means for actuating, locking,-and-releasing-the--latent--switch,
substantially-as-described-and-set-forth
6:—In-apparatas for use in connection-with--telophonie--intercommuniention, the
combination-with--an-electric--circuit, of the latent--switch, the--special--compound
indicator, the-special jack-switch, the-lines-wires, the Exchange printer, and moans
for-nctuating, locking and releasing-the-latent-switch, substantially as described and
set-ferth.
In-apparatus-for use-in--connection with--telephonic intercommunication, the
combination--with-an-electric-circuit, of the latent switch,-the--compound indicator,
the-jack-switch-the-line-wires. a-step-by-step-indicating-pointer;--and--means--for
actuating locking-and-releasing the latent switch, substantially as described--and
set-forth.
S. In-apparatus-for-use-in-connection--with--telephonic--intercommunication-the
combination-with-an electric-circuit of the latent--switch, the--compound- indicator,
the jack-switch, the line-wires, the Exchange-printer, having mechanism-adapted-to
return-the-type-wheel to initial position-after each print,-and-means-for-actuating,
locking-and-releasing the latont switch, of-the--numerical-printer, and--oscillatory
jack-switch, adapted-to-cut-said-printer in--and--out-of-circuit--with-the-compound
indicator,-and-visual-signals, all-constructed,-combined, and operated, substantially
us-described and-set-forth.
0. The combination with--apparatus--constituting-a-complete-semi-automatic
system-compriping-in-combination with-electric-circuits, telephone-transmitter--und
receiver, indicator bell "ongagod" or "busy"-the-means-for-bringing-the armature

page_text: of the clearing electro-magnet-into-the-magnetic-field-automatically by the weight-of
the-transmittor--and-the-receiver--when--on-the--switch-hook-the-latent-switch, the
automatic-revolution-counter,the-line-wires,the-oscillatory-jack-switch-and-plug, the
compound--indicator-the-exchange printer, the-visual-signal-devices-the-numerical
printer-and-intermediate-jack-switch-for-connecting-it-with-the-line,
cembined-and-operating-substantially-as-described and set forth.
all-constructed,
10. In-a-latent switch for use in-connection with signalling telephonic--connec-
tions-desired, the-combination with-the-exchange-dial-and-travelling-contact-block;
of a hole-and-spring-pressed catch-adapted-to--engage--in-maid--hole--when--same--is
presented to-it,-n-projection-on-the--tail--ond-of-said-catch--adapted-to--project--in
the path-of-the-travelling-contact-block-automatically-on-the--dial being--set--to--#
predetermined-point, substantially-ns-described.
1. In-apparatus-for use-in-connection-with-telephonic-intercommunication,-the
combination with the latent-switch-of the device-for-registering the-number-of--calls
consisting of the travelling contact-block,-a-projecting-pin-on-the--travelling-contact
black and-a-revolution-counting--device--actuated-by--the--said--projecting---pin;
substantially-as-described-and-set forth.
--electrie
12. An electrical indienting-device consisting of-the-combination-with-an-e
creuit-of-two separate-electric-magnets, poles of the magnets turned inwards towards
each-other-an-armature rotatably-pivoted between the poles-in-such manner-as--to
swing--towards--the--pole--which--is--energised--at the moment--and--dises--at---the
extremities-of-the--opposite-end of said--armature coloured-or-otherwise--rendered
distinct substantially as described and set forth.
13. The combination with-a-jack-plug-boaring-the-ends-of-the-two line-wires, ot
the-compound-spring-jack-consisting of six--contucts, two-for--electrical--connection
with-a-printer-or-recorder-two-others-for--electrical--connection-with--an-indicator
und two-intermediate-ones-for-connection-with-nn-electro-magnetie-signalling-device;
substantially-as-described.
44. The apparatus-whereby-a-signal-is-transmitted-t
1-ton-distance-by-the--weight
of the telephone-hand-set-when-placed-on-the-switch--hook,--consisting of--the-com-
bination-with-the-stem-of-the-switch-hook; of electro-magnet-the-armature--of-same
pivoted--normally out-of-the-magnetic--field,----piroted-lover-earrying-n--detent
adapted-to-engage-when--lowered-on-the-tip of the-free-end-of-the-said armature-end
bring it into the magnetic-field; two-contacts-constituting terminals-of-the--electric
circuit in-which is-included-an-electrical-signalling-device, substantially as described
and-set-forth:
10. The--means-by--which-any--"earthing" of the line-wires-constituting--an
electric-circuit-is-antomatically-indicated, consisting--of--the--combination--with--the
line-wires-of-the-special-compound-indicator-the-line-wires connected-to--two--of--the
terminals thereof-und-the-other-two-connected through a battery-or-other-source--of
electric energy to-earth, substantially-as-described.
16. In-an-electric-or--magnetic--printing-apparatus comprising--a--type-wheel;
means for-rotating same step by step, means for--inking--the-type, a magnetic--or
electro-magnetic-device-for-actuating-the-armature-through a ratchet-and-pawl-for
rotating-the-type-wheel and-a-magnetie-or-electro-magnetic-device-for-actuating the
printing hammer, the-combination therewith-of-a-spring located in-the-type-wheel
and tending always-to-hold-the-wheel-at-zero, the bent- lever pivoted--on-the
rotation--arm,--the--double-detent--pivoted-on--the-printing-armature--adapted-to
engage-with-the-actuating pawl and-a-pivoted toothed-lover-and-bring them-out-of
engagement-with-the-ratchet-to-free-the-type-wheel, substantially as described.
17 The combination with-an-apparatus,-for-use--in-connection--with telephonic
intercommunication-and-an-electric circuit, of the circular--type--of--semi-automatic
latent-switch, consisting of a fixed-plate-having-contacts arranged-in-groups-around
its-periphery-radial-levers-adapted-to-be-set-to-any point of its-circumference, train
of-elockwork-and-radial-hand-fever-for-winding up the switch-contact on said hand
lever-adapted-to-brush-in-its-passage all the contacts-exposed-in-its path and electro-

page_text: magnetic-device-for-releasing said-train-of-wheels-when-desired, substantially-as-and
for-the-purpose-described-and-set-forth,
13. The modification-of-the-rotary-type of latent switch, consisting--in--the
movable-contact-plates-being-pivoted so as to be capable of movement--in-a--eircular
path, and for-the-purpose-described.
1. 10. The semi-automatic system of telephonic exchange, substantially as
magnetic-device-for-releasing said-train-of-wheels-when-desired, substantially-as-and
for-the-purpose-described-and-set-for th
18. The modification-of-the-rotary-type of Intent switch, consisting--in--the
movable-contact-plates-being-pivoted so as to be capable of movement--in-a-circular
path, and for-the-purpose-described.
1. 10 The semi-automatic system of telephonic exchange, substantially as
described and set forth.
2: The apparatus or latent switch at the subscriber's end substantially as
described and illustrated.