Lines, Circuits and Apparatus for Telephonic Intercommunication.
Year: 1899

page_text: France),
Date of Application (in United Kingdom), 28th Mar., 1899
Complete Specification Left, 28th Dec., 1893-Accepted, 17th Mar.,
PROVISIONAL SPECIFICATION.
1900
Lines, Circuits and Apparatus for Telephonic Intercommunication.
We, G. ABOILARD ET CIE, of 46, Avenue de Breteuil, Paris, Electrical Engineers, do
hereby declare the nature of this invention to be as follows:-
Figure 1 shows junction lines connecting two central telephone exchanges.
The auxiliary junction lines between central telephone exchanges are used to
connect subscribers lines on one exchange with the required lines on another
exchange. A separate group of junction lines being used for communication in the
reverse direction.
The end of the junction line at the calling end is called outgoing, and the operator
whose duty it is to establish connection between the calling line and the junction line
is called the outgoing operator, or operator A.
The other end of the junction line used to connect with the called subscriber, is
known as the incoming line. The operator who attends to the connection with the
called subscriber is called the incoming operator, or operator B.
The duties of operator A consist in answering the signal of the calling line, and
connecting it with a junction line, also in instructing the corresponding operator B
to connect this junction line with the called subscriber. Operator A controls the
connection, and does not disconnect until the conversation is finished.
The duties of operator B consist in testing the called line, telling operator A
which junction line is to be used, connecting this line with the called subscriber,
ringing the latter, and disconnecting when the clearing signal is received, the latter
being controlled both by operator A, and the called subscriber.
Figure 1 shows a system of junction wire in which the outgoing ends have
switchboards A provided with indicators for automatic signalling or with ordinary
indicators.
Generally in telephone exchange systems which include both lines worked by
current from a magneto, and lines worked by automatic signalling it is better to
make use of automatic clearing signals as these are more certain.
The application of this principle can be completed by the additional safeguard that
the clearing signal to operator B shall be controlled, on the one hand, by the called
subscriber, and on the other hand, by operator A.
Further, operator B can be given a warning signal, the object of which is to
prevent her using the same junction line the incoming end of which is free but the
outgoing end of which is occupied or connected with a called subscriber.
In Figure 1 two lines are shown connected to switchboards in the separate exchanges,
a junction line connecting the two switchboards and the proposed arrangement for
connecting the junction line with the subscribers connected to the switchboards.
The exchange at A is supposed to have lines connected, the indicators of which are

page_text: actuated by a magneto, or battery current placed at the subscribers office. The
exchange at B is supposed to be connected to lines in which the calling signal is given
automatical y and which work on the common battery system. The installation at C
consists of a transmitter d, a receiver d¹, a bell ², a generator d³, switchbook d+,
which connects either the bell and generator or the instrument with the line wires 1
and 2. The line wires 1 and 2, are connected to the jacks e on the switchboard at A.
The outgoing contacts of the break jack e being connected to the terminals of the
indicator f.
The switchboard at A is provided with pairs of plugs of the usual kind g and g²
which are connected together through the circuits 3 and 4, including a clearing out
drop g, the listening key g³, which is used to connect the operators instrument h
with the plug circuits. The installation at C¹³, consists of a transmitter d, a
receiver d', a bell d, a switchhook d, and a condenser d³.
The hell d of the installation at C¹ is always a shunt across the line circuit in series
with the condenser d³, the object of the latter being to prevent continuous
currents from going through the bell coils.
The wires 5,6 of the line connect the installation at C with the jacks e of the
exchange at B, and then to the normal contacts of the cut-out relay f³, the springs of
which are connected to the poles of the calling battery . In the conductor 6 is
inserted a relay which is used to actuate tue secondary calling signal ƒ which is
associated with the jack e.
The electro-magnet of the cut-out relay f is inserted in the conductor 7, which
connects the bushes e of the jacks e to earth.
The junction line 8-9 terminates at the A exchange in a jack k, provided with
contacts me and me, which at the insertion of the plug bring about the connection
between the cironits 3 and 4, and the wires 8 and 9 of the junction wire.
At the exchange B, the line 8-9 terminates in the plug kl, which can be inserted
in the jack e of the lines belonging to the B exchange.
The jeton line 8-9 is not continuously metallic, between the extreme outgoing
and incoming point.
At A exchange the coils of the translator are placed in circuit with 8-9.
The first portion of the local line permanently connects the outgoing jack with coil ²
of the translator l.
The second portion of the local line is connected to coils and 13 of the same
translator.
Normally the two coils 2 and 3 are on open circuit, by reason of the contacts
of the relay m being broken, the moveable contacts ne¹ and m³ of which are connected
to earth.
The electro-magnet of the relay m forins part of a local circuit 10 containing a
battery, the circuit being closed by the auxiliary contacts m* and m³ of the outgoing
jack k.
The second portion of the circuit 8-9 is thus normally open and is closed with an
earth connection, when a plug is inserted in jack by means of the closing of the
contacts of and m³ and the contacts of the relay m.
At the incoming exchange B is placed in the same manner, a translator
interrupts the metallic continuity of the junction line 8-9.
1, which
The second portion of the line connects the coils 2 and 3 of the translator at the
outgoing end to the closed coil a³ of the translator at the incoming end.
The coils n2 and 3 of this translator are connected to the third circuit of the
junction line 8-9, and the inner ends to a battery o, one of the poles of which is
connected to earth.
The battery is thus placed in series with the third metal portion of the
circuit 8-9, which terminates at the incoming plug . Between the translator n
and the plug the junction wire is provided with a key p, the purpose
of which is to control the connection of the tip of the plug with the
operator's receiver q, to allow the latter to test the line required. At the same time
the key p controls the connection between the ringing generator and the plug k¹.

page_text: The action of the key p is partly manual, and partly automatic. The key p includes
two springs and 2, having respectively normal contacts and pt and acting
contacts and p. The key p includes in addition, an auxiliary spring p, having an
outer contact 8, which is made at the same time as the contacts p and . The
springs of this key p can be disconnected from the normal contacts, and placed in
their working position by a wedge po, which is attached to a special movable plunger,
the return of which to its normal position is controlled by an electro-magnet p10, which
attracts the armature pll acting as stop to the movable portion of the key.
The spring is connected to the tip of the plug ¹, its normal contact p³ is
connected to the coil 2 of the translator n. The spring p is connected to the
collars of the plug k¹, its normal contact p is connected to the coil n³ of the
translator n.
.
The acting contact p of the spring p² is connected by the conductor 11 and the
relay po to the free pole of the earthed generator r. The contacts p' and p³ form
part of a local circuit which will be described later.
When the button of the key is depressed, the double wedge p is forced between the
two springs and p². The arinature 2 retains the wedge in this position as long as
the relay pic is inert. As soon as the relay p10 is excited, the armature p is
attructed, and releases the double wedge which returns to its normal position on
account of the pressure of the springs and p³.
The springs p and in this case again rest on their normal contacts p³ and p^.
In the conductor 9 between the battery o and the plug k¹ is inserted the relay u to
operate a controlling signal. The relay u is excited by the current of the battery o
which operates the transmitter of the called subscriber. Each junction wire is pro-
vided with a relay the arms of which v¹ and v² have respectively normal contacts and
outer contacts v³ and vª.
The conductor 12 connects the arm v¹ with the contact p of the key p. The
conductor 13 connects to the operator's receiver 9, and ends at the normal contact
of the same arm v², the acting contact of which is put directly to earth by the
conductor 14. The other contacts of the relay form part of a local circuit.
The relay to is inserted in the conductor 15, which connects the centre of the coil n'
of the translator n with the free pole of the earthed battery x. The battery x
can in practice be the same as the battery v. This relay w controls the clearing
signal for operator B.
The armnature of the relay w controls a group of local circuits. The object of these
local circuits is as follows:-
has been
1. When the plug is inserted in a jack e, and as soon as the key
depressed, the lampy remains alight as long as the relay is not excited, that is to say,
until the called subscriber takes his receiver off the hook.
2. To place the same signal y under the control of the relay w when the plug k¹´is
taken out of the jack e, in order that the signal'y may act as a warning sigual,
controlled by operator A.
The lanp yand the coil of the relay vare placed in series in the conductor 16, which
connects the free pole of the earthed battery x to the body a² of the plug kl.
The contacts of the relay u control the shunt 17, which includes a resistance coil.
A point in the shunt 17 between the relay u, and this resistance coil is con-
nected by the conductor 18 to the arm of the relay o via the contacts of the
relay w.
The normal contact of the arm v² represents the end of the conductor 19 which is
put to earth through the resistance coil 2.
The acting contact of the same arm ³ represents the end of the conductor 20
which leads to the spring p' of the key p, the outer contact of which p³ is connected
by the conductor to the free pole of the battery 2.
It follows that the connections are such that the relay v provides in the one case
for the earthed battery x, a path independent of the plug k¹, but controlled by the
relay . which keeps the lamp y alight as long as the relay w is excited, that is to
way, as long as the plug g³ remains in the outgoing jack k.
:

page_text: On the contrary as long as the plug k¹ is in the jacke the relay v provides, together
with this plug k³, another path for the earthed battery z, this circuit making the
lampy dependent on a shunt, the continuity of which depends on the sane relay w,
the action of which is in this case reverse.l, that is to say, to light the lamp y when
the relay w is not excited.
The relay u and the key p together with the relay 10 control the lamp y during the
time the plug k¹ is in the jack e.
Supposing that the subscriber C calls the central exchange by means of his
generator, which operates his calling signal f. The operator A immediately inserts
the answering plug g in the jack e corresponding to this calling signal, and at the
same time connects her instrument h to the circuit 3-4 of the selected cord, and
thus ascertains that the subscriber C asks for the subscriber C¹ connected to another
exchange B.
Operator A by means of a call key connects her instrument with a call wire
permanently connected with operator B's instrument and gives the latter instructions
to connect subscriber C with subscriber C¹.
Operator B sees that junction line 8-9 is free and advises operator A that this
line 8-9 is to be used for the connection. Operator A immediately inserts the plug gl
in the outgoing jack k, corresponding with the indicated line 8-9. Ou her side,
operator B with the tips of her plug k¹ touches the bush e¹ of the jack e corresponding
with the line asked for.
If the line C asked for is engaged the free pole of the test battery is connected
with the bushes et, and gives the well known click in operator B's receiver q.
As soon as the tips of the plug touches the bush el, the current from the testing
battery can flow to earth through the contacts p³, p³ of key p, the conductor 12, the
contacts v¹,, the conductor 13, the receiver 7, and finally the earth of operator B's
receiver, who hears the click showing that the line asked for is engaged.
On the contrary, if the line asked for is free, no current can pass through this test
circuit, consequently no sound is heard in the receiver 7, and the operator concludes
that she can insert the plug in the jack e with subscriber C¹.
The preceding movements of the operators A and B put the apparatus and
circuits in the proper position for connecting telephonically the two subscriber's
instruments C, C¹.
As we have already seen this telephonic circuit is not complete as a continuou
metallic circuit as it is interrupted at the exchange A by the translator 1, and at
the exchange B by the translator n, although these sane translators provide
continuity by induction, that is to say, continuity of circuit for telephonic currents
between the two subscriber's instruments C and C¹.
At the exchange B, when the plug ¹ is inserted into the jack e, the junction
wire 8-9 is cut by the ringing key p, the acting contacts of which are made in order
to connect the ringing generator with the line of the subscriber wanted C¹.
To describe this in detail the current from the generator passes through the
conductor 11, the electro-magnet po, the closed contacts ps p², a portion of the
conductor 9, up to the jack e, the wire 6, the bell of the subscribers instrument C¹,
the return wire 5 up to the jack e, a portion of the conductor 8, as far as the closed
contacts pl p³, the conductor 12, the conductor 14 and to earth, passing through the
closed contacts v1 of the relay v, which is excited by the current from the battery 2,
the circuit being through the conductor 16, the bush e¹ of the jack e, the conductor 7,
and earth through the electro-magnet fl of the cut-out relay, the normal contacts
of which are thus opened in such a way as to disconnect the line 5-6 from the
relay and earth.
As has just been shown directly the operator B inserts the plug k¹ into the jack e,
the generator r rings the bell of the wanted subscriber C¹.
Tuis ringing current flows through the relay 10. When the relay v is excited at
the moment that the plug k¹ is inserted into the jack e, it closes the contact v¹ vo,
which puts earth and the conductor 14 into contact with the conductor 12, at the
same time. this conductor 12 is disconnected from the conductor 13 which includes

page_text: operator B's receiver q, so that this operator is free to immediately deal with other
co:nmunications.
The normal circuit. of the battery is through the conductors 16 and 17, and
through the lamp y, but at this moment the lampy is shunted by the conductor 21,
the contacts p p the conductor 20 the contacts 5 v2 and the conductor 18 through
the contacts of the relay in.
This shunt is thus controlled by the relay w the excitation of which depends on
the introduction of the plug g¹ into the outgoing jack k, nt the exchange A.
From what has preceded it is seen that when the bell of the subscriber's instru-
ment C¹ is actuated by the generator r the lamp y not lit, but it is under the control
of operator A by means of the relay w. If for any reason whatever, for example on
account of the called subscriber not replying, operator A severs the connection with
the junction wire by taking the plug g¹ out of the jack k, she breaks at the same
time the local circuit of the relay in, and consequently stops the flow of current from
the battery through the relay which becomes inert anil breaks the shunt of the
lamp y which lights, that is to say gives the clearing signal to operator B, who takes
the plug, out of the jack e of the line C¹ asked for.
Under ordinary circumstances the called subscriber replies to the call and by taking
his receiver off the hook makes an alteration in the circuit of his instrument in such
a manner as to cause a very considerable increase in the calling current from the
generator r, with the result that the electro-magnet 10 of the key p is excited and
attracts its ar nature p¹¹ and this releases the plunger of the key p. The acting
contacts p5 and 6, connected to the pole of the generator r thus no longer touch the
springs pl p, which resume their sition against the normal contacts p³ p², and
thus establish the continuity of the junction line 8-9.
The circuit is then in the required condition to ensure the transmission of tele-
phonic currents between the subscriber's instruments C and C¹.
and
This
The return of the key p to its normal position also breaks the contact p p",
this breaks the shunt 21, 20, 18 of the lump y, controlled by the relay w.
shunt is replaced by another shunt 17, controlled by the relay u, which at this
particular time excited by the current from the battery o in the circuit of the called
sub-criber C. All the apparatus are at this time in the proper position to ensure
conversation. Nevertheless there is no necessity for either of the operators A or B to
be looking after this connection until the clearing signal shows that their attention is
required.
The subscriber C gives the clearing signal by hanging up his receiver and
operating his generator d³, which actuates the clearing signal y² at exchange A.
At the subscriber's instrument C¹ to give the clearing signal, it is only necessary
to replace the receiver on the hook; this breaks the battery circuit o through the
relay u, the armature of which resumes its normal position, breaking the shunt 17
of the lamp y, the lighting of which gives the clearing signal to operator B.
As previously mentioned, it is in practice more advantageous to break communica-
tion in reply to the automatic clearing signal y at exchange B. As soon as operator B
sees the lamp y light while the plug is in the jack e she immediately takes this
plug out of the jack e, and replaces it in its proper position near the lamp y.
Taking out the plug stops the flow of current through the relay v, which resumes
its normal position breaking the circuit 18-20 at the contact at the same time
putting the conductor 18 to earth by means of the normal contact 4, and the con-
ductor 19. As a result, a new path is provided for the battery to light the lamp y
through the conductors 16, 18, 19 and earth. This new local circuit is controlled by
the relay w independently of all other apparatus.
This new function of the relay w is the reverse of its previous work, indeed in this
new circuit the lamp y remains alight as long as the relay w is excited, that is to
say, as long as the plug g' is in the jack kat exchange A. It will be seen then that
if at exchange B the lamp y remains alight after the connection is severed, it is
because this same connection has not been cleared at exchange A. The signal y
serves during the interval as a warning signal, the aim of which is to prevent

page_text: operator B from selecting this junction line for a new connection as long as the
plug has not been taken out of the jack kat exchange A.
The lamp y acts thus as a calling, or clearing, signal under the control of operator A
when the called subscriber is being rung; the same lamp y also acts as a controlling,
or clearing, signal under the control of the called subscribed after he has replied to
the call, and finally, after the connection has been cleared at exchange B the same
lamp y acts as a warning signal to prevent the junction wire being used again as long
as it is not free at exchange A.
It will have been seen from the description of the system that the working of
the junction wire at exchange B is independent of the type of the switchboard
at A.
It is only necessary that the exchange A should be provided with apparatus which
will ensure the working of the relay wat the exchange B as has been described and
this should be brought into play by connecting or clearing the junction wire at its
outgoing end A.
Figure 2 shows a junction line system arranged so that the clearing signal for the
incoming operator B shall be actuated when the called subscriber replaces his receiver
on the hook, although this incoming operator B should not disconnect until after
receiving the signal to do so given by the warning signal controlled by the outgoing
operator A. Nevertheless in case operator B has disconnected before the signal has
been given by operator A it is necessary that the warning signal should remain
operative as long as the outgoing end of the junction wire is not free at
exchange A.
In Figure 2 the subscriber's instruments G and G each include a transmitter a, a
receiver a¹, a bell a³, a condenser a³, a switchbook at, working in the ordinary
manner.
Line: 1-2 connect these instruments to the jacks b, of the switchboards A, B,
where apparatus of well known types, such as cut off relays e, calling relays c,
auxiliary calling signals f, and the calling battery & put to earth, is placed.
The outgoing exchange A is connected to the incoming exchange B, by the junction
line 10-11.
The exchange A is provided with pairs of ordinary plugs ii, connected by the
conductors 5-6 the metallic continuity of which is broken by the usual translator k,
between the inner ends of which is placed the common battery.
Only apparatus at the exchanges A B which is indispensible to the understanding
of the mechanism of the system has been shown. It is understood that in practice
other apparatus such as ringing keys, controlling signals etc., can be attached.
The conductor 6 connecting the collars of the plugs i and of , includes a
controlling relay m, placed between the plug i, and the translator k. This relay m
governs, in the ordinary way, the controlling signal m¹. The jack q represents
the outgoing end of the junction line 10-11, the incoming end of which line is
represented by the plug 7. The arrangement of the junction line 10-11 is very
similar to that of the conductors connecting the pairs of plugs with the
exchange A.
At the exchange B the translator is inserted in the line 10-11.
"
The condenser is placed between the inner ends of the pair of coils at
the translator connected to the middle side of the loop 10-11 coming from the
exchange A. The second metallic side of the junction line is represented by the
conductors 13-14 which connect the plug q¹ to the second pair of coils at
the translator 7, the inner ends of these cils being connected to the cominon
battery, one pole of which corresponding with the conductor 13 is earthed. The
controlling relay t is inserted in the conductor 14, and is used to control the shunt 16
of the signal which is associated with the plug q¹.
The plug q can be connected with the ringing current by means of the ringing
key u.
To the body of the plug q¹ is attached the conductor 15 coming from the free
pole of the battery v, by way of the lamp or signal t¹ and the coil of the relay w.

page_text: A second signal is also associated with the plug 7'. This signal acts as a
warning signal to prevent operator B from clearing the connection before it has been
disconnected at exchange A.
This signal is controlled by the two relays w and y. The relay y is inserted in a
branch to earth from the conductor 11 coming from the exchange A.
When the relay w is excited it closes its two pairs of contacts w w³ and in² 20%.
When the relay y is excited it closes its three contacts y¹ y² y³. The normal
position of the spring y is between the armature y, and the outer contact y³.
The conductor 17 connects the free pole of the battery to the one side of the
lampa, through a resistance coil. The other side of the lamp is connected to two
conductors 18-19 going respectively to the contact w³ and the spring y¹.
The urinatures w₁ and y² are connected to earth.
A point of the conductor 17 between the lamp and the resistance coil, is connected
by the conductor 20 to the spring w³, the contact of which w' is connected by the
conductor 21 to the contact y³ of the relay y.
It follows that the excitation of one of the two relays wor y, creates a path to
earth for the battery v, through the conductor 17, the lamp, and one of the two
conductors 18 and 19.
If the two relays wand y are excited simultaneously the lamp is shunted by the
conductors 20-21, which prevents in this case the lamp from lighting.
Operator A's instrument should be connected with that of operator B z¹, by means
of a call wire 22, the key in which is placed near operator A.
Supposing that the subscriber G on the exchange A asks for subscriber G¹ on
exchange B.
Operator A who receives this call transmits it to operator B by means of call
wire 22.
corre-
Operator B selects a junction line from among those that are free and designates
this to operator A, who immediately inserts in the jack the calling plug
sponding to the answering plug already inserted in the jack 6 of the calling
subscriber G.
At the same time as she designates the junction wire the operator B takes the
plug 7, and after the usual test inserts this plug q' in the jack b of the called
subscriber G¹
The insertion of the plug q' in the jack b of the called subscriber closes the local
circuit 15-4 of the battery which thus actuates the cut off relay e, disconnecting
the line 1-2 from the battery d and from the relay c.
The circuit through the subscriber's instrument G¹, from the battery a in the
exchange B, is open as long as the subscriber's receiver is on the hook, consequently
the relay t is inert, and allows the lamp t¹ to remain lighted by the current Howing
along the conductors 15-4. This current also excites the relay w, the contacts of
which w w and uw are closed. At the same time the relay y is also excited
inasmuch as the plug i at the exchange A is in the jack q. of the line 10-11,
consequently the battery bas its circuit closed by the conductor 6-11 and by the
relay to earth. It follows that the contacts y1 y2 y3 of the relay y are closed at the
same time as the contacts of the relay w.
.
Closing the contacts to w³ has the effect of creating a closed circuit for the battery
through the lamp x, passing through the conductors 17-18 to earth. The closed
contact yy also puts the conductor 19 to earth, but at the same time the closing of
the contacts 2 w' and y² y³ completes the shunt 20-21 of the lamp x, which is thus
not lighted as long as the two relays w and y are excited simultaneously.
It has been shown that the lamp is alight as long as the receiver of the subcribers
instrument G¹ is not taken off the hook and at the same time the lamp a remains
unlighted.
As soon as subscriber G¹ replies to the call the lamps m' at the exchange A,
and at the exchange B remain unlighted as long as the conversation
lasts.
-
When the conversation is finished, putting the receiver on the hook at the

page_text: snbscriber's instrument G lights the limp m¹ at the exchange A, and putting
the receiver on the hook at the subscriber's instrument G' lights the lamp t¹ at the
exchange B.
The two operators, A and B, are thus advised when their respective subscribers
replace their receivers on the hook, and the connection can be cleare.i. As in practice
it is recognised that the clearing signal given by the calling subscriber is more
certain than that given by the called subscriber, it follows that as soon as operator A
receives the clearing signal by the lighting of the lamp m³, she immediately takes out
the plugs from the jacks 6 and 7.
Taking out the plug from the jack q breaks the circnit of the battery through
the relay y which becomes inert and breaks the shunt 20-21 of the lamp x, which
can then be traversed by the current from the battery v and through the
conductor 17-18, the contacts w w³ to earth. The lamp x immediately lights, this
gives operator B the signal to disconnect as the two lamps and t¹ burn simul-
taneously, provided that subscriber G¹ has also replaced his receiver on the hook.
Operator B, then takes out the plug q¹ from the jack b, which breaks the
circuit 15-4, extinguishing the lamp t¹ and rendering the relay w inert.
The return of the relay w to its normal position breaks the circuit 17-18 and this
extinguishes the lamp x.
It follows that all the signals become inert after plugs ¹ q¹ are replaced in their
normal position.
The lamp can serve as a warning signal advising the operator B that the outgoing
end of the junction wire-10-11 is not free.
This is useful in case operator B is satisfied to take the lighting of the lamp tas a
clearing signal, or still more so in case she severs the connection with the called
subscriber through a mistake. In this case the lighting of the lamp & indicates to
the operator B that the outgoing end of the line is not free.
The advantage of the signal a as a warning signal is also very great when the
exchange A is fitted with ordinary indicators operated by generators or by batteries
fitted at the subscribers instrument.
The latter subscribers very often neglect to give the clearing signal as this signal
requires an additional operation. It is seen that in this case the clearing signal given
automatically by the lamp t' at the exchange B, is regarded at the latter exchange as
a clearing signal, the lamp being looked on as a warning signal.
Figure 3 represents two subscribers' instruments A and A' at the central
exchanges A and B.
The outgoing exchange A is connected with the incoming exchange B by junction
line 10-11.
The subscriber a to call the central exchange A has only to take his telephone off
the book, for immediately the calling signal d¹ will be given by the well known
operation of the calling battery f, and the relay d.
In reply to this call operator A inserts the plug h in the jack b of the calling
subscriber and at the same time by means of the listening key h³ she connects ber
instrument c with the circuit 4-5 of the plugs h h¹, in such a way as to receive, for
example, the order to connect the subscriber a with the subscriber a¹ belonging to
the exchange B.
The operator A inserting the plug h in the jack b of the calling subscriber A closes
the local circuit 6-3 of the battery h10, this excites the cut-off relay e, and
disconnects the line 1-2 from the battery fand from earth.
At the same time the circuit of the battery is closed by the line 1-2 and the
subscribers' instrument A in such a way as to excite the relay h* which can thus close
the shunt 8 of the controlling signal 48 which then remains inert.
The operator A transmits the order of the subscriber A to the operator B, using
for this purpose the call wire 19.
Operator B seeing that the junction wire 10-11 is free, indicates this immediately
to operator A, who at once inserts the plug h' in the outgoing jack j of this junction
line 10 11

page_text: The insertion of the plug h¹ in the jack j, closes the local circuit 7-12 of the
battery 0, this lights the lamp h as the battery h³ has not yet its circuit closed by
the conductor ō and the conductor 11 of the junction line, consequently the shunt 9
of the lamp ho remains open.
While the outgoing operator A is thus making the connection required to connect
the subscriber a to the exchange B, operator B on her part tests the required line
tonching the tip of the plug & against the bush 6' of the jack b.
If the subscriber al is engaged a battery 10 or a battery is connected to the
hushes of the jacks b of this line. It follows that a current will pass in this case by
the tip of the plug, the closed contact pl p³ of the relay p. the conductor, 13, the
receiver to the earth of the instrument of operator B, who then hears the character.
istic click indicating that the line is engaged.
If the called subscriber is free no current passes through the receiver which
remains silent and operator B therefore concludes that she may insert the plug in
the jack b of the called subscriber a, afterwards depressing her ringing key t in
such a way as to connect the called subscriber's instrument a¹ with the ringing
generator.
The insertion of the plug in the jack b closes the circuit 14-3 of the battery r
which can then light the lamp and excite the relay p, the moveable levers of
which pl p², are attracted against their respective contacts pp, so that the cou-
ductor 10 of the junction wire is connected to the tip of the plug and consequently
to the wire 1 of subscriber al's line.
The excitation of the relay p breaks the contact pl p³ so that the receiver i is dis-
connected from the tip of the plug k, at the same time the closed contact p² p³ com-
pletes a local circuit 15 containing the lamp m.
It will have been seen that in the circuit 14-3 the battery r lights the lamp as
long as the relay n remains inert, that is to say, as long as the called subscriber has
not replied to the call,
On the other hand the insertion of the plug in the jack j at the exchange A,
closes, for the earthed battery r at the exchange B, a circuit through the conductor 18,
the coil o³ of the relay o, the conductor 10 of the junction wire, the tip of the plug h¹
and the conductor 4 to the earth of the battery h³.
As a result the relay o is excited and closes the contacts of o³ so as to complete the
shunt 17 of the lamp m which remains unlighted in spite of the passage of the current
of the battery in the circuit 19, p², p³, 15 and earth comprising the lamp m and its
shunt 17.
When the subscriber a¹ takes his receiver off the hook the battery h³ at the
exchange A has its circuit closed through the subscriber's instrument a¹ through the
conductor 5, including the relay h', the conductor of the junction line 11 containing
the relay n, the wire of line 2, the subscribers instrument a¹, the wire of line 1, the
conductor of junction line 10 the conductor 4 and earth at h³.
The two relays h and n are thus excited respectively at exchange A and at
exchange B. The excitation of the relay h' closes the shunt 9 of the lamp h which
is extinguished thus showing operator A that the subscriber a¹ has answered..
The excitation of the relay closes the shunt 16 of the lamp which is extin-
guished and thus shows operator B that the subscriber a¹ has answered.
.
The shunt 16 includes the coil n of the relay n which is excited as long as the
plug remains in the jack b irrespective of the condition of the subscriber's instru̟-
ment a' or the junction wire 10-11. The sole purpose of the lamp is thus to show
the operator B if the subscriber replies to the call in order if necessary to ring again
or whether to clear the connection if the subscriber does not eventually reply.
Supposing that the subscriber a' replies to the call, taking his receiver off the
hook.
In this case the two instruments a and a¹ are in telephonic cominunication.
The two lamps 8 and 9 at the exchange A are unlighted indicating to operator A
that the two subscribers a and a' have their receivers off the hooks.
The two lamps and m at the exchange B are unlighted, indicating to operator B

page_text: by the lamp that the receiver of the called subscriber a¹ is off the hook, and by the
lamp m that at the exchange A the plug is in the jack j of the junction
wire 10-11.
Putting the receiver on the hook at one of the two subscribers instruments a or a¹
only lights one of the lamps * and h at the exchange A. As soon as both the
lamps and are lighted operator A concludes that conversation is finished and
takes the two plugs and h¹ out of the jacks 6 and j.
Taking the plug h¹ out of the jack breaks the circuit 18-10-4 of the battery "
at the exchange B where the relay o becomes inert breaking the shuut 17 of the
lamp m.
The lamp m thus becomes lighted by the current from the battery r, passing
through the conductor 19, the closed contacts p² and the conductor 15 to earth.
The lighting of the lamp m indicates to operator B that the connection has been
cleared, she at once takes the plug out of the jack b, rendering relays n and p inert
and placing all apparatus in normal position.
-
The detailed descriptions of Figures 1-2-3 enable the mechanism of Figures 1-
1 and 1-1° to be easily understood. They are based on the same principles and for
practical working are associated with all the apparatus necessary to the proper working
of the intercommunication.
Thus Figure 1 represents a junction line 1-2 the outgoing end of which, or
jack a, is situated in the outgoing exchange A and the incoming end, or plug b, is
situated in the incoming exchange B.
The exchange A is supposed to be on the system well known as a relay board with
common battery, and it is considered sufficient to represent this exchange A by the
essential apparatus at one pair of plugs c and c¹ associated with the controlling
signals d and d¹.
The operator A's instrument e can transmit by the call wire 3-4 orders to operator B's
instrument f.
Operator A can also by this circuit 3-4 attract the attention of operator B by
dropping the indicator g, the shutter of which controls the auxiliary signal g¹ which
can be common to a group of indicators g.
The junction line 1-2 is provided at the exchange B with the translator h, because
the distance between the two exchanges A and B is supposed to be very great. The
battery h¹ of 24 volts. in the translator thus serves to supply the called subscriber's
instrument, and to excite the relay h² as long as the called subscriber's receiver is off
the hook. The armature of the relay h² governs the controlling signal d¹ at the
exchange A, in such a manner that the signal d' at the exchange A shews in the ordi-
nary way when the called subscriber replies and finishes his conversation.
At the exchange B the relay i is excited by the battery when the circuit 5-6-1
is closed to earth, i.e. when the plug c is in the jack a at the exchange A. In the
same way relay j is excited by the battery h¹ when the circuit through the con-
ductor 5 and the body of the plug 6 is closed to earth, i.c. when the plug 6 is in the
jack of the called subscriber.
The relay controls the shunt 16-17-7-8 of the lamp k as long as the relay i
is excited t.e. while the communication lasts; consequently the lamp k only lights
after the breaking of the shunt 16-17-7-8 caused by the clearing of the connection
at exchange A. It follows that the lamp k gives operator B the clearing signal as
soon as the plug e' is taken out of the jack a at the exchange A.
On the other hand when the relay ; is inert ie. when the plug b is in its normal
position, the relay i controls the circuit of the battery passing through the
conductor 5, the lamp k and the conductors 8-7-9 to earth.
This circuit is only closed when the relay i is excited, i.e. when the plug c¹ is in
the jack a
It will be seen that in this case the lamp k acts as a warning signal.
The relay j controls the continuity of the test circuit through the tip of the plug b,
the conductor 1, the acting contact of the key l, the conductor 10, the normal contact
of the relay j, the conductor 11-4, the receiver of the instrument f, the secondary

page_text: circuit of the induction coil m the conductor 3, the retardation coil n and the
conductor 12 to earth.
This circuit is cut as soon as the relay j is excited i.c. as soon as the plug 6 is
inserted in the jack of the called subscriber.
When the relay is excited and at the same time the relay is inert, the calling
generator o is connected with the called subscribers line through the conductor 13,
the interrupter o¹, the conductor 14, the coil of the relay 11, the acting contact of
relay j, the conductor 10, the acting contact of the key l, the conductor 1, the
tip of the plug b, the called subscriber's line, returning through the conductor 2, the
acting contact of the ringing key l, and the conductor 15 to earth.
This circuit is automatically cut as soon as the relay A is excited, i.e. as soon as
the called sub-criber takes his telephone off the hook.
The key p allows the operator B to electrically restore the shutter of the indicator g
by closing the circuit of the battery h¹ through the conductors 5-16-18 the acting
contacts of the key p, the conductor 19, the 50 ohm. coil of the indicator g, and the
conductor 20 to earth.
As soon as the called subscriber takes his receiver off the hook the relay lis
excited, allowing the key to automatically resume its normal position in
such a way
It is thus
to re-establish the continuity of line 1-2.
28
seen that the mechanism of Figure 1ª proceeds on the principles laid down in
Figures 1, 2, 3.
Figure 1 differs only from Figure 1 by leaving out the translator at the
exchange B, on the supposition that the junction line 1-2 is short enough to allow
the called subscriber's instrument to be supplied with current from the central battery
at the exchange A.
In Figure 1b letters and figures of reference have been given exactly the same as
those on Figure 1 in order to shew the similarity of working of the two systems.
The arrangement shewn on Figure 1° can be used when the outgoing exchange A
is on a system worked by magneto and the incoming exchange B on the relay and
common battery system. The exchange B is not provided with a translator because
it is supposed that the junction line is short enough to allow the translator to be
installed at the outgoing exchange A. The inside ends of the second pair of 150 ohm.
coils of the translator h at the exchange A are connected to the acting contacts of the
relay which is excited as long as the plug c is in the outgoing jack a,
consequently the battery ³ of about 24 volts, at the exchange A can supply the
called subscriber's instrument on exchange B with current as long as the plug c¹ is
in the jack a.
In Figure 1e letters and figures of reference have been given exactly the same as
those on Figures 1 and 1, in order to shew the similarity of working of the systems.
Figure 1 applies to the same case as Figure 1° but it is supposed that the
distance between the 2 exchanges A and B are sufficiently great to render it
advisable to employ a translator at the outgoing exchange B. In Figure 1ª exactly
similar figures and letters have been given as in 1, 1, and 1°, in order to show the
similarity in the working of these systems which are in accordance with the principle
shown in the diagrammatic figures 1, 2 and 3.
Figure 4 represents a junction line 3-4 where the incoming end B is provided
with a system of apparatus which performs automatically the following operations.
1. The incoming operators instrument is disconnected from the line after the
plug has been inserted in the jack.
2. The ringing current is connected with the called subscribers, line when the
plug is inserted in the jack.
3. The ringing current is disconnected directly the subscriber replies.
4. The controlling signal remains inoperative during the time the subscriber is
being rung but it is put again under the control of the called subscriber as soon as
the latter replies to the call thus enabling it to be used as a clearing signal for
operator B.
In Figure 4 the special application of this apparatus for a junction line is shown

page_text: but it is obvious that the same principles are applicable to all kinds of lines and to
cord circuits for making connections on any kind of switchboard.
In order to make the working of the system more easily understood, let us suppose
that the outgoing operator A transmits, by means of the call wire 5, an order to
operator B to connect the auxiliary junction line 3-4 with the line 1-2 of a wanted
subscriber connected with exchange B.
The first thing operator B has to do is to raise the plug g and test the jack 6 of
the subscriber wanted by touching the tip of this plug against the bush 68 of the
jack. If the line 1-2 is engaged the bush is at the potential of the testing
battery, and in this case each time the tip of the plug touches the bush 3 a current
passes through the tip of the plug, the conductor 7, the normal contacts of the
relay, the conductor 8, the normal contacts m² m² of the relay m¹, the conductor 10,
and operator B's receiver p to earth which gives the characteristic click, showing that
the line is engaged. If the line is free operator B does not receive any click. It
may be pointed out that.during this test the conductors 7 and 8 are disconnected
from the conductor 4 of the junction wire, and consequently whatever may be the
electric condition of this line, no disturbance can be caused by it in the receiver p
at the time that operator B makes the test.
If operator B ascertains that the line wanted is free, she inserts the plug g in the
jack 6 putting the conductors 6 and 7 respectively in contact with the wires of the
line 2 and 1, at the same time closing the circuit 11-14-15 of the battery o,
the current from which actuates the cut off relay c in such a way as to disconnect
the line 1-2 from the relay d and from the earthed buttery e.
"
In the same circuit the current from the battery excites the relay / which then
attracts the two springs and, against the contacts and I, which are connected
to the two sides of the generator n, which is thus connected to the called subscriber's
instrument, through the conductors 6-2-1-7-9, and rings his bell a².
The excitation of the relay breaks the contact 1 of the spring thus disconnecting
the conductor 7 from the conductor 8, i.. operator B's instrument is disconnected
from the plug g during the automatic calling of the line wanted. As soon as the
called subscriber takes his receiver off the hook, i.e. switches his line on to his
transmitter and receiver, the ringing current froin the generator n becomes strong
enough to excite the relay the armature of which is attracted closing the circuit
16-17, containing the coil m³ of the relay m¹. In this circuit 16-17 the battery o
excites the relay the springs of which m² and are attracted respectively against
their contacts m³ and m² altering the circuits as follows:
The conductor 11 is disconnected from the battery o and consequently the relay l
becomes inert and permits its springs 12 and 13 to return to their normal position
against the contacts and respectively, so that the conductor 3 of the junction line
is extended by the conductor 6 up to the collar of the plug g.
In the same manner the closing of the contact m² m³, reconnects the conductor 4
of the junction line to the conductor 8 which is itself connected again to the
conductor 7 by the closed contact 13 1º, so that the conductor 4 is extended up to the
tip of the plug 9.
The conductor 10 is disconnected from the conductor 8 so that the receiver p is
disconnected entirely from the circuit of the junction line which connects exchange A
to the subscriber wanted.
A local circuit m³, m7, 12, 13, 14, 15, is formed for the battery o, the current
flowing through the coil me of the relay m³, and the lamp which is controlled by
the shunt 17-16 the continuity of which depends on the relay k.
This local circuit 12-13-14-15 is independent of the relay k, consequently the
current which passes through the coil maintains the excitation of the relay m' as
long as the plug g remains in the jack b.
To sum up, it is seen that after having tested the line wanted, the insertion of the
plug in the jack disconnects the receiver from the junction line, and connects the
source of ringing current to the subscribers line wanted; the reply of the wanted
subscriber disconnects the source of ringing current from the junction line, and
extends the conductors of this line up to the instrument of the wanted subscriber,

page_text: in such a way as to complete the telephonic connection of the calling subscriber with
the wanted subscriber.
The controlling signal remains inoperative while the subscriber wanted is being
rung, but this subscriber after having taken his receiver off the hook controls this
signal which can thus act as a clearing signal for the incoming operator.
If it is wished that the incoming operator B shall not disconnect until after receiving
the clearing signal from the outgoing exchange A a clearing signal controlled by the
operator A can be added to the apparatus shewn in Figure 4, without in any way
modifying the principles of the system shewn in Figure 4.
Excellent results are obtained with a voltage of 20 volts. for the battery o 50 ohms.
resistance in the coil m° and 13 ohms. resistance in the coil m³ of the relay m¹,
100 ohms. resistance in the coil of the relay 1, 85 ohms. resistance in the coil of the
cut off relay c and by putting in a 10 volt. lamp k¹.
Figure 5 shows another application of the principles laid down in the description
of Figure 4.
Figures 6 to 8 show constructional details of the automatic apparatus employed in
Figure 5, where it is used to carry out automatically the following operations :-
1st. After the insertion of the plug in the jack to disconnect the incoming operator's
receiver, and, at the same time, to connect the wanted subscriber's line with the
calling generator circuit.
2nd. After the reply of the wanted subscriber, to disconnect the source of ringing
current, to establish the telephonic continuity of the junction circuit between the
calling subscriber and the called subscriber, and in addition to put the controlling
signal in a position to give the clearing signal.
Figure 5 represents a junction line 1-2 used for connecting the outgoing
exchange A with the incoming exchange B, where the junction line terminates in a
plug g, with which is associated the controlling signal j, governed by the relay i and
the automatic apparatus which includes the two relays and the mechanism of
which will be explained in detail.
The subscriber's instrument E fitted with ordinary apparatus is connected by the
line 3-4 to the usual apparatus in the central exchange B.
Figure 6 shews an elevation of the automatic apparatus k l.
Figure 7 is a plan of the same apparatus.
Figure 8 is an elevation of the opposite side to that of Figure 6.
The axes of the cores of the two electro-magnets k and are placed in the same
straight line (see Figures 6-7-8).
The pole pieces ¹², and, of each electro-magnet are bent inwards, the
pieces and are joined and firmly attached to one another.
Each electro-magnet is provided with an armature placed between the body of the
coil and the inner ends of the pole pieces. Thus the armature ³ of the relay k is
fixed to the pole piece by means of a fine metal spring such as a very flexible
iron spring having a thickness of about 8 of a millimetre.
The free end of the armature ks is so placed in relation to the inner side of the
bent end of the pole piece k² that if the electro-magnet is excited it attracts the free
end of the armature which tends to adhere to the inner side of the bent end of the
pole piece k² in order to complete the magnetic circuit of the coil.
In the same manner the armature of the relay is fixed by one of its ends to the
pole piece the other end being placed in such relation to the inner side of the bent
end of the pole piece that it is attracted by 12 when the electro-magnet / is excite.l.
. The pole piece carries 4 spring; m m³, and n n' firm'y secured between b'ocks of
an insulating material fixed to the pole piece these springs are parallel to the axis
of the electro magnet.
Normally the free ends of the springs n and n¹ rest against insulating studs n² n³
which project from the other side of the pole piece 12.
The spring m normally rests against the insulating stud m² which projects from
the outer side of the pole piece while the spring m³ normally rests against the
metallic contact m³ which is fixed to the pole piece but insulated from it.

page_text: The spring a carries a metallic contact n arranged to touch the corresponding
contact on the spring m when the spring n is raised by the armature l³.
Underneath this contact n the armature carries a stud of insulated material [
for the purpose of raising the spring n against the spring m when the armature (³ is
attracted by the pole piece 1².
At the same distance near the insulating stud the armature carries another
metallic stud placed exactly under the spring n¹. The metallic stud 1 is for the
purpose of raising the spring n² against the insulating stud me of the spring m¹ when
the armature is attracted by the pole piece in such a way as to raise at the same
time the spring m² which is thus taken off its normal contact m³.
The pole piece of the relay k carries in the same way two springs o and o'
insulated from it. The free ends of these springs o and o' normally rest below the free
ends of the springs m and m¹ in such a way as to make contact with the latter
springs and to raise them off their normal contacts when the armature ³ is attracted
by the pole piece k².
Normally these springs o and o³, rest respectively against the insulating studs o
and os fixed on the outer side of the bent end of the pole piece k².
Normally the springs and n¹ rest against the insulating studs n² and n³
respectively, while the springs m and m³ rest against the insulating stud m² and the
metallic contact m³ respectively. In the same way, springs o and of rest on the
insulating studs o² and o* respectively, and further these springs o and o¹ are insulated
from the springs m and m².
When the armature is attracted by the pole piece these springs o and o¹ raise
the springs m and m³ which are thus separated from their normal contacts m² and m³.
If afterwards the armature 13 becomes also attracted by the pole piece the
insulating stud raises the spring off the insulating stud n at the same time the
contact of this spring n is forced against the spring in such a way as to raise
this spring m and to disconnect it from the free end of the spring o with which it
was in contact as the relay k is supposed to be excited.
On the other hand, the metallic stud 6 of the armature also raises the spring n¹
and forces it against the insulating stud n of the spring m¹. The latter spring m¹
is thus raised off the spring o' with which it was in contact.
The automatic apparatus k-l can be placed in any position in the central exchange,
(see Figure 5). The conductor 9 connects the spring m³ to the conductor 1; the
conductor 2 of the junction line is broken, the portion of the conductor 2 coming from
the exchange A is connected with the spring n the other portion of the conductor 2
coming from the contact g² of the plug g, and from the relay i is connected to the
spring m. The spring o' is connected to earth. The spring o is connected to a metallic
brush constantly in contact with the revolving commutator p, which is composed of two
segments one of which p¹ extends over a quarter of the periphery and the other of
which p² extends over nearly the whole of the remaining three quarters of the
periphery of the commutator p.
The segment represents the free pole of the earthed generator p³ (an alternating
ringing current) the other segment p² represents the free pole of an earthed battery r
the electro-motive force of which should he nearly equal to that of the battery h.
The commutator p should be arranged in such a way as to make a complete
revolution in 12 seconds so that the generator p³ and the battery rare alternatively
placed in contact with the spring o, the duration of these contacts during a complete
revolution of p being respectively 3 second for p³ and 9 secours for r.
Operator B is provided with the usual receiver q by means of which she can
receive through conductor 10, orders from operator A and test in the ordinary
manner the jacks of the lines wanted.
The earthed receiver g is connected by the conductor 11 to the metallic stud m³.
The body y³ of the plug g is connected to a series of conductors coming from the
free pole of the earthed battery r. These conductors are factors in the working of
the cut-off relay f, the controlling signal j and the automatic ringing apparatus kl.
One side of the relay lc is connected by the conductor 12 to the free pole of the

page_text: battery r, in the same way one side of the relay is also connected by the conductor 13
with the free pole of r.
The other side of k is connected to the conductor 14 which includes the signal j,
being afterwards connected to the conductor 15 coming from the body g³ of the plug.
The other side of is connected by the conductor 16 to the armature i¹ of the
relay, and by the conductor 17 to the armature of the relay l, and consequently to
the metallic contact of this armature 1.
The contact n¹ is connected by the conductor 18 to the conductor 14 coming from
the other side of the relay k.
The contact stud 12 of the relay i is connected by the conductor 19 to the con-
ductor 15 coming from g³.
The battery can have an electro-motive force of 10 volts., the relay fa resistance
of 20 ohms., the lamp j be adapted for 4 volts. and 2 amperes the relay k 30 ohms.
and the relay 16 ohms.
In order to better understand the mechanism of the system of the automatic
apparatus kl let us suppose that a subscriber at the outgoing exchange A asks to be
connected to a subscriber E at the incoming exchange B. Operator A transmits this
order to operator B by the call wire 10.
The junction line 1-2 to be used is designated by one of the two operators A
or B, following the methods already described.
Operator B takes up the plug g corresponding to the selected junction line 1-2
and applies the tip g₁ of this plug to the bush of the jack 61 corresponding to the
subscribers line wanted.
In this manner she connects by the conductor 1-9-11 her receiver 9 to the bush
thus tested as the spring m¹ normally rests on its metallic contact m³.
If the line asked for is already engaged a battery is connected to the bushes of
the jacks of this line so that the current of this battery will flow to earth through
the receiver q causing a click to be heard each time that operator B touches the
tip gl of the plug against the bush of the jack tested.
If the line tested is free the receiver 9 remains silent, and the operator at
once inserts the plug y in the jack 61 putting g³ in contact with the bush of
jack and completing the local circuit of the battery r the current from which
passes through the conductors 12-14-15 and 7 including the relay the
lamp j and the cut-off relay f.
This current is not sufficient to light the lamp j, but it is sufficient to excite the
relays k and f
The excitation of the cut-off relay disconnects the line 3-4 from earth and from
the battery c.
The excitation of the relay 4 raises the springs o and o³ and puts them in contact
with the springs m and m³ respectively in such a way as to break the contact m² m³,
that is to say, to disconnect the receiver 7 from the plug 9 and at the same time
to connect the circuit 1-2 of this plug with the ringing current.
To describe this in detail the conductor 1 is put to earth by the spring o' and the
conductor 2 is connected with the revolving commutator p through the contact m. o.
The rotation of the commutator p, connects alternately the free poles of r and of p³
to the conductor 2, consequently during the passage of the current from the
generator på the bell a² of the subscriber E rings.
As the condenser a³ and the bell a² enormously reduce the strength of the current
in this ringing circuit, it follows that the relay i is not excited either by the
generator or by the battery r.
As soon as the receiver of the called subscriber E is taken off the hook the
line 3-4 is switched at this instrument through a much lower resistance increasing
the strength of the current froin either p³ or by r sufficiently to excite the relay i
which thus attracts its armature against the contact stud i³.
Two ends are served by sending the current from the battery over the line
between the intervals of ringing. The first is that the cutting out of circuit of the
automatic apparatus kl and the completion of the junction line circuit shall take

page_text: place immediately after the receiver of the called subscriber is taken off the hook
whatever may be the position of the rotary commutator p. The second is that the
excitation of the relay i shall depend on the continuous current rather than on an
alternating one such as that of the ringing generator.
The attraction of the armature against its contact closes a local circuit
through the conductor 13-16-19, including the relay , which is thus excited
putting the spring n in contact with the spring at the same time separating the
springs me and m³ from the springs o and o¹ and closing contact is n¹.
The conductor 2 is thus completed and extended up to the contact g² of the plug.
The ringing current is broken and the commutator p is disconnected from
the junction circuit.
The local circuits are modified as follows:-
A circuit is formed by the conductors 13-16-17 and 18 including the relay and
placed in shunt with the relay k. But, as this circuit is independent of the
contacts and it follows that the relay 7 is no longer placed under the control of
the relay i, that is to say, the relay will remain excited as long as the circuit 12-
13-16-17-18-14-15-7 exists, that is to say, as long as the plug g remains in
the jack b¹.
The resistance of the circuit is thus sufficiently diminished, by the relay & being
placed in shunt with the relay k for the current to light the lamp j.
It will he noticed that the lamp
is placed under the control of the relay & which
closes or opens the shant 19-16 of this lamp.
It will have been seen that while the subscriber wanted is being called the lampj
remains unlighted, on account of the high resistance of the circuit consequently
operator B cannot receive a false signal.
After the reply of the called subscriber and the breaking of the calling circuit the
controlling signal i becomes effective and passes under the control of the relay i,
the working of which depends as usual on the position of the receiver of the subscriber
wanted.
When the conversation is finished, the receiver at the instruments E is replaced
on the hook, the relay i is no longer excited by the battery h, and the shunt 19-16
of the lamp is broken, consequently this lamp lights, and can thus give the
clearing signal to operator B who clears the connection taking the plug 9 out of
the jack b¹.
Taking the plug out of the jack deprives the relays and k of current from the
battery, consequently the automatic apparatus k l resumes its normal position.
Figure 9 shows the junction line 1-2 used to connect an outgoing exchange A,
whether of the magneto type or common battery to an incoming exchange B of the
common battery and relay type.
The incoming exchange B is provided with two visual signals j and k. The
signal is controlled by the outgoing exchange A and serves as a clearing signal for
the incoming operator B. Further at the coinmencement of communication the
signal k allows operator B to see whether the junction line is free and whether
operator A has not mistaken the junction line, that is to say, if she has properly
inserted her calling plug c¹ in the outgoing jack A of the junction line 1-2 which
has been indicated to her.
The other visual signal j serves as a controlling signal for the incoming operator B,
and indicates to her the exact moment when the called subscriber takes his telephone
off the hook to answer the call.
From the time when the called subscriber answers his call, the controlling signal ; is
extinguished and remains so during the communication, so that from this time the
control of the junction line passes from the incoming exchange B to the outgoing
exchange A, which remains the sole judge as to the time to clear the connection.
The outgoing exchange A is represented in Figure 9 by the pair of plugs c c¹ by
the operator's instrument e and by the jack a which represents the outgoing end of
the junction line 1-2. The incoming exchange B is represented by all the apparatus
indispensible for the working of the junction line 1—2.

page_text: At the incoming exchange the junction line is provided with a translator h and a
common source of current h¹ used for supplying current to the called subscriber's
instrument.
The incoming end of the line 1-2 is represented by the plug b.
Between the translator and the plug b is placed operator B's instrument ƒ, the
listening key and the ringing keys l¹ and 12.
The working of the relays i, 2 and 3 and the visual signals j and k will be
explained later.
In order to better understand the mechanism of Figure 9, the successive movements
of operators A and B to put a subscriber at the exchange A in communication with a
subscriber B will now be shown.
Operator A having received an order from the calling subscriber transmits it
immediately to operator B, by depressing her call key e¹ which puts her instrument e
across the call wire permanently connected with operator B's instrument f.
Operator B then receives the number of the subscriber wanted whose line she tests
in the ordinary manner and indicates to operator A the junction line selected to
establish the communication asked for.
To test the line wanted operator B chooses a free plug band raises it from its
socket thus closing the local circuit 5, 6, 7 of the battery through the lamp k.
If the lamp lights, operator B concludes that the junction line is free. In practice
for the lamp k to remain unlighted it is necessary that its shunt 8-9 shall be closed,
that is to say that the relay i shall be excited which can only be if at the exchange A
a plug c is in the outgoing jack a, corresponding to the plug & chosen by the
operator B.
Supposing that the outgoing jack a is free the relay i remains inert and the lamp k
lights as soon as operator B raises the plug 6 to test the line wanted, applying the
tip of the plug b to the bush of the jack b¹ of the line wanted at the same time
depressing her listening key l.
If the line wanted is engaged the bush of jack b¹ is at the same potential as the
battery of the exchange B, while the point of the plug which is connected to
the conductor 1 finds earth at the battery h¹.
The key being depressed that is to say, on its outer contacts bridges the
instrument f, and the condenser n across the line 1-2.
The plate of the condenser n connected to the receiver f is thus to earth.
"
The
It follows that if the tip of the plug b touches the bush of an engaged jack b¹
the condenser is immediately charged and discharges when the contact ceases.
charging and discharging currents from the condenser n traverse the receiver f and
produce the usual click indicating that the line wanted is engaged.
On the contrary, if the line wanted is free the bush of the jack b¹ is to earth and no
charging or discharging currents from the condenser n traverse the receiver f which
remains silent.
Taking the latter case the operator B inserts the plug 6 in the jack b¹, at the
same time informing operator A the number of the junction line 1-2 corresponding
to this plug b.
The lamp k remains alight up to the moment when operator A inserts the calling
plug c¹ into the outgoing jack a, which has been designated.
Operator B is thus informed whether her instructions have been understood.
If the lampk remains alight it is necessary to repeat the instructions to operator A,
and rectify the mistake made by that operator.
•
Supposing that the operator A inserts the plug c in the outgoing jack a, this
actuates the relay i at the exchange B; the circuit of the battery i is closed by the
conductor 10, the relay i, the conductor 1, the tips of the plug c¹ and the earth of the
battery cat the exchange A.
The armature of the relay i is attracted and the shunt 8-9 is closed, extinguishing
the lamp k.
As soon as the operator B inserts the plug 6 in the jack wanted 6¹ it closes the
local circuit of the battery 12 through the conductors 11-12, and the bush of the

page_text: jack to earth. This local circuit contains the lanp j, which lights and remains
alight as long as the shunt 13-14 is not closed, that is to say, as long as the relay j
remains inert. But, as will be seen later the relay j remains inert as long as the
relay his not excited by the current from the battery h² through the called
subscriber's instrument.
Immediately after having inserted the plug
a ringing current to the called subscriber by
keys 11 or 12.
in the jack 1, the operator B sends
means of one of the usual ringing
The relay he remains inert as long as the called subscriber does not take his
receiver off the hook, but the armature of the relay h² controls the circuit of the
battery c² at the exchange A, through the controlling relay c³, the collar of the
plug c, the conductors 2-15 the contact stud of the relay h³, the conductor 16,
the coil of the relay j and the conductor 17 to earth.
This circuit is closed as soon as the relay h² is excited, that is to say, as soon as the
called subscriber answers.
It follows that the extinguishing of the lamp j, by the closing of the shunt 13-14
informs the operator B that the called subscriber has replied.
Further, as the closing of the shunt 13-14 is made through the coil 3 of the
relay j¹ this latter relay will remain from this time permanently excited as long as
plug bremains in the jack b'.
The first effect of the called subscriber replying in to extinguish the controlling
lump, and at the same time to keep this lamp junlighted during the remainder of
conversation in order to relieve the operator B from the need of controlling the
junction line from the time when the called subscriber has replied to the call.
The second effect of the called subscriber's reply is to simultaneously actuate the
relay at the exchange A that is to say to close the shunt of the lamp d' which is
extinguished thereby advising operator A that the called subscriber has answered.
It is seen that the two operators A and B are simultaneously and independently
of each other informed of the precise moment when the called subscriber replies.
The advantage of these two independent controlling signals is to enable
operator B to at once judge whether it is necessary to ring the subscriber again and
in case of no reply operator A can give the clearing signal by taking the plug c¹ out
of the jack a.
Let us suppose that the called subscriber takes his receiver off the hook and thus
extinguishes the two controlling signals j and d¹..
From this moment the control of the communication passes entirely to the
Exchange A, which remains the sole judge of the time to clear the connection. To
do this operator A takes the plug c out of the jack a, breaking the circuit of the
battery through the relay i. "The shunt 8-9 is thus broken, consequently the
lamp is lighted by the current from the battery through the circuit 5, 6, 7, to
earth, thus giving the clearing signal to operator B, who has only to take the plug />
out of the jack and replace this plug 6 in its socket ', in order to break the contact
of the socket ¹, that is to say, to break the circuit 5, 6, 7, of the lamp / which is
immediately extinguished.
After the clearing of the connection at the outgoing exchange A, and at the
incoming exchange B, all the apparatus of the junction line 1-2 revert to their
normal state, and thus render this junction line 1-2 free to establish a fresh
connection between a subscriber on the exchange A, and one on the exchange B.
Figure 10 shows how a junction line for connection between different switch
boards situated in the same building can be arranged. Suppose for example, that it
is desired to connect a trunk section A with a subscribers section B.
Operator A inserts a plug in the individual jack of the trunk line which calls,
afterwards she inserts the second plug of the same pair in the jack of the junction line
whose plug or incoming end is at the section where the line asked for is accessible.
At the same time operator A gives the order to operator B to complete the com-
munication by connecting the incoming end of the junction line with the line of the
subscriber wanted.

page_text: The control of the communication is entirely reserved to operator A, who clears
the connection as soon as the controlling signals show that the conversation is
finished.
The clearing of the connection at A gives automatically the clearing signal at B,
where the operator clears the connection leaving the junction line free for a fresh
connection.
The subscriber's instrument a is fitted in the usual way for a common battery
system, it is connected by the line 1-2 to the switchboard B, where the line 1-2
is fitted with the usual apparatus, such as the jack c, the calling relay d, associated
with the calling signal and the calling battery l
The trunk station a¹ may be of the magneto type, it is connected by the line 3-4
to the trunk switchboard A, where it is fitted with the jack fand calling signal y of
the trunk section.
The switchboards A and B are connected by the junction line 5-6, where the
outgoing end is fitted with the jack i, placed on the switchboard A, and where the
incoming end terminates in the plug ¹ placed on the switchboard B.
Operator A has ordinary pairs of plugs and cords to establish communication
between the trunk line 3-4 and the junction line 5-6.
The bush of the jacki is connected with body
1.wisted up with the conductors 5 and 6.
of the plug by the conductor 9,
The bush of the jack c is connected to earth through a resistance m. On the
switchboard A the body of the plug on the trunk section is connected by
the conductor 11 to the pole of the battery n.
The conductor 11 includes the lamp o and the supplementary battery p, of the
same polarity as the battery n. The shunt 13 of the lamp o is controlled by the
relay q, associated with the cord circuits k, h¹.
The shunt 13 includes a low resistance r. The body of the plug is connected to
the free pole of the battery n by the conductor 12, including the lamp o¹, associated
with the plug i¹ of the switchboard.
The resistance m is calculated in relation to the lamps o and o' and the battery »
so that neither of the two lamps shall be lighted when the circuit is closed
through the two lamps simultaneously (without of course taking into account the
battery p).
It follows that clearing the connection at A allows the full current from the
battery n to pass through the lamp o' which lights immediately in front of operator B,
indicating to her that the connection can be cleared.
In the same manner in the closed circuit 11-9-10 the battery p has an electro-
motive force sufficient to light the lamp o but the presence of the lamp o in the
circuit is sufficient to keep the lamp o from being lighted by the current of the
battery n.
The resistance is such that the lamp o is extinguished when the shunt 13 is
closed by the excitation of the relay q, the working of which relay depends on the
instrument of the wanted subscriber A, when the transformer 8 is in circuit, that is
to say, when the key w is in normal position as indicated in the diagram.
When the position of the key w is reversed the junction circuit becomes metallic,
the translator & being cut out of the circuit 16-17. In this case the contact w¹ w
of the key w puts the coil 2 to earth, so that the relay q is constantly excited closing
the shunt 13 and so extinguishing the lamp o.
P
Good results are obtained from a battery n of 20 volts. with a battery 1 of 4 volts.,
with lamps o and o¹ of 4 volts. and 2 amperes, with resistance m of 40 ohms. and a
resistance of 20 ohms.
"
Supposing that the instrument a¹ of the exchange A calls for instrument a on
exchange B.
The putting into action of the generator 6* of the instrument a¹ causes the shutter
of the indicator g on the trunk section A to fall, when the operator immediately
inserts the answering plug k in the jack f, afterwards depressing her listening key v
to connect her instrument to the circuit 14-16, 15-17, in order to be ready to

page_text: receive the order for the trunk instrument al asking to the connected to the sub-
scriber's instrument . Operator A transmits this order to operator B by means of
the call wire, and at the same time operator A inserts the plug k¹ in the jack i of a
junction line 5-6 ending in a plug placed within reach of operator B, to whom she
indicates at the same time the number of the junction line she has chosen.
Operator B takes the plug which has been indicated to her by operator A, and
tests with this plug i¹ the jack c of the instrument a asked for. If the line wanted
is free operator B inserts the plug in the jack e, completing the circuit of the
battery t, in the translators of the plug circuit kk' of the switchboard A.
The effect of the insertion of the plug in the jack c is to close the circuit of
the battery by the conductor 16-17 the conductors 5-6, the line 1-2 and the
instrument called a.
At the same time this closes the circuit of the batteries and p by the conductors
12-11-9-10 and earth.
As has been said before the electrical conditions of this circuit are such that the
battery n cannot light the lamp o' at the exchange B while the battery p can light
the lamp o on the switchboard A as long as the shunt 13 is not closed. But the
closing of the shunt 13 depends on the relay which is traversed by the current of
the battery in the circuit which includes the instrument & of the subscriber
wanted.
It follows that as long as the receiver at a is on the hook the relay q remains inert
and consequently the lamp o remains alight.
Further, the fact of the lighting of the lamp o proves to operator A that the plug i¹
has been inserted in the jack c on the switch board B, that is to say, that operator B
bas executed the order correctly.
Operator A can send a ringing current to wanted subscriber's instrument « by
depressing her ringing key w.
The reply of the called subscriber a is indicated to operator A by the extinction of
-the controlling lamp o as the fact of this reply excites the relay g by the passage of
the current from the battery & the circuit of which is closed through the called
subscriber's instrument a. If the instrument at a is of the magneto type or if the
resistance of the circuit connecting the instruments and a¹ becomes very great, or
if the circuit is subject to interruptions rendering conversation difficult, it is better
to cut off the local earth of the exchange A and to connect the instruments a a¹ by a
metallic circuit, reversing the key w, that is to say, disconnecting the translator s
from the circuit 16-17. In this case operator A controls the connection by means of
her listening key r, as the lamp o is rendered inoperative by the excitation of the
relay traversed by the current from the battery t, the circuit of which is closed
through the relay 9 and the closed contact w¹, w² to earth.
Usually the key w is in such a position as to bring the translators into use. In
this case as soon as the conversation is finished and the subscriber a has hung up his
receiver the lamp o lights, giving the clearing signal to operator A who takes the
plugs and out of the jacks fand i. The fact of taking the plug h out of the
jack i breaks the circuit 11-9 which allows the lamp o¹ on the switchboard B to light
as this lamp o¹ now receives the full current from the battery n through the cor-
ductors 12-10 to earth.
The lighting of the lamp o is considered by the operator B as a clearing signal
and she immediately takes out the plug ¹ from the jack e which puts all apparatus
in the normal condition.
The attached figures have all been drawn up to show this system of intercom-
munication which is sufficient for all practical requirements. In these figures the
source of common electrical energy is represented by batteries of accumulators.
It is well known that common electrical energy can be furnished from a dynamo
arranged to produce no noise on the line, further, in order to obtain more security a
battery of accumulators can be placed across the poles of the dynamo, so that this
battery may be charged by the dynamo, and so contribute in concert with the

page_text: dynamo current for such a system. If the dynamo should fail or stop, the battery
will continue to furnish the necessary current for the working of the system.
In principle the dynamo is only used to charge the battery, while this supplies the
current for the busiest hours of the day, as the battery alone is left in circuit to
supply the current during the less busy hours, for example, during the night.
To prevent the dynamo from producing noise on the line we recommend the two
following methods.
The first method consists in inserting retardation coils having a high impedance, but a
low ohmic resistance, between the conductors of the line and the poles of the dynamo.
The second method consists in driving the dynamo at a very high speed and
further by subdividing the commutator into a number of segments, calculated so
that the number of pulsations of the commutator shall exceed six to eight thousand.
a second, for at this rate the noise on the line becomes inaudible.
Dated this 16th day of March 1899.
G. ABOILARD ET CIE.
COMPLETE SPECIFICATION.
Lines, Circuits and Apparatus for Telephonic Intercommunication.
We, G. ABOILARD ET CIE, of 46, Avenue de Breteuil, Paris, Electrical Engineers, do
hereby declare the nature of this invention and in what manner the same is to be.
perforined to be particularly described and ascertained in and by the following:
statement:-
The drawings herein referred to are those left with the Provisional Specification.
Figure 1 shows junction lines connecting two central telephone exchanges.
The auxiliary junction lines between central telephone exchanges are used to
connect subscribers lines on one exchange with the required lines on another
exchange. A separate group of junction lines being used for communication in the
reverse direction.
The end of the junction line at the calling end is called outgoing, and the operator
whose duty it is to establish connection between the calling line and the junction line.
is called the outgoing operator, or operator A.
The other end of the junction line used to connect with the called subscriber, is
known as the incoming line. The operator who attends to the connection with the
culled subscriber is called the incoming operator, or operator B.
The duties of operator A consist in answering the signal of the calling line, and,
connecting it with a junction line, also in instructing the corresponding operator B
to connect this junction line with the called subscriber. Operator A controls the
connection, and does not disconnect until the conversation is finished.
The duties of operator B consist in testing the called line, telling operator A
which junction line is to be used, connecting this line with the called subscriber,
ringing the latter, and disconnecting when the clearing signal is received, the latter
being controlled both by operator A, and the called subscriber.
Figure 1 shows a system of junction wire in which the outgoing ends have switch-
boards A provided with indicators for automatic signalling or with ordinary indicators..
Generally in telephone exchange systems which include, both lines worked by
current from a magneto, and lines worked by automatic signalling it is better to
make use of automatic clearing signals as these are more certain.
The application of this principle can be completed by the additional safeguard that.
the clearing sigual to operator B shall be controlled, on the one hand, by the called
subscriber, and on the other hand, by operator A.
Further, operator B can be given a warning signal, the object of which is to
prevent her using a junction line the incoming end of which is free but the
outgoing end of which is occupied or connected with a calling subscriber.
In Figure 1 two lines are shown connected to switchboards in the separate exchanges,
a junction line connecting the two switchboards and the proposed arrangement for
connecting the junction line with the subscribers connected to the switchboards.
The exhange at A is supposed to have lines connected, the indicators of which are

page_text: actuated by a magneto, or battery current placed at the subscribers office. The
exchange at B is supposed to be connected to lines in which the calling signal is given
automatically and which work on the common battery system. The installation at C
consists of a transmitter d, a receiver d³, a bell d², a generator d³, switchhook d*,
which connects either the bell and generator or the instrument with the line wires 1
and 2. The line wires 1 and 2, are connected to the jacks e on the switchboard at A.
The outgoing contacts of the break jack e being connected to the terminals of the
indicator f.
The switchboard at A is provided with pairs of plugs of the usual kind g and g¹
which are connected together through the circuits 3 and 4, including a clearing out 1
trop g², the listening key g³, which is used to connect the operators instrument h
with the plug circuits.
The installation at C³, consists of a transmitter d, a receiver d', a bell ď³, a
switchhook d*, and a condenser d³.
The bell d² of the installation at C¹ is always a shunt across the line circuit in series 1
with the condenser d³, the object of the latter being to prevent continuous
currents from going through the bell coils.
The wires 5, 6 of the line connect the installation at C with the jacks e of the
exchange at B, and then to the normal contacts of the cut-out relay f¹, the springs of
which are connected to the poles of the calling battery . In the conductor 6 is
inserted a relay f which is used to actuate the secondary calling signal f which is
associated with the jack e.
The electro-magnet of the cut-out relay is inserted in the conductor 7, which
connects the bushes e¹ of the jacks e to earth.
The junction line 8-9 terminates at the A exchange in a jack k, (provided with!
contacts m* and m³), which at the insertion of the plug bring about the connection
between the circuits 3 and 4, and the wires 8 and 9 of the junction wire.
At the exchange B, the line 8-9 terminates in the plug k², which can be inserted
in the jack e of the lines belonging to the B exchange.
The junction line 8-9 is not continuously metallic, between the extreme outgoing
and incoming points.
At A exchange the coils of the translator are placed in circuit with 8—9.
The first portion of the local line permanently connects the outgoing jack with coil
of the translator l.
The second portion of the local line is connected to coils and of the same
translator.
Normally the two coils and are on open circuit, by reason of the contacts
of the relay in being broken, the moveable contacts m³ and m² of which are connected
to earth.
The electro-magnet of the relay m forins part of a local circuit 10 containing a
battery, the circuit being closed by the auxiliary contacts m* and m³ of the outgoing
jack k.
The second portion of the circuit 8-9 is thus normally open and is closed with an
earth connection, when a plug is inserted in jack k by means of the closing of the
contacts of m² m² and the contacts of the relay m.
At the incoming exchange B is placed in the saine manner, a translator 12, which
interrupts the metallic continuity of the junction line 8-9.
The second portion of the line connects the coils 2 and 3 of the translator at the
outgoing end to the closed coil n' of the translator at the incoming end.
The coils n and n³ of this translator are connected to the third circuit of the
junction line 8-9, and the inner ends to a battery o, one of the poles of which is
connected to earth.
The battery o is thus placed in series with the third metal portion of the
circuit 8-9, which terminates at the incoming plug k¹. Between the translator n
and the plug the junction wire is provided with a key p, the purpose
of which is to control the connection of the tip of the plug ¹ with the
operator's receiver to allow the latter to test the line required. At the same time
the key p controls the connection between the ringing generator and the plug k³.

page_text: The action of the key p is partly manual, and partly automatic. The key p includes
two springs pl and p², having respectively normal contacts p³ and pt and acting
contacts p and pe. The key p includes in addition, an auxiliary spring p², having an
outer contact p³, which is made at the same time as the contacts p and p. The
springs of this key p can be disconnected from the normal contacts, and placed in
their working position by a wedge pº, which is attached to a special moveable plunger,
the return of which to its normal position is controlled by an electro-magnet pio, which
attracts the armature p11 acting as stop to the moveable portion of the key.
The spring pl is connected to the tips of the plug k¹, its normal contact p³ is
connected to the coil 2 of the translator n. The spring p is connected to the
collar s¹ of the plug k¹, its normal contact p is connected to the coil n of the
translator n.
The acting contact p" of the spring p² is connected by the conductor 11 and the
relay po to the free pole of the earthed generator r. The contacts 27 and p³ form
part of a local circuit which will be described later.
When the button of the key is depressed, the double wedge p is forced between the
two springs pl and p². The armature p₁ retains the wedge in this position as long as
the relay pic is inert. As soon as the relay po is excited, the armature p₁ is
attracted and releases the double wedge which returns to its normal position on
account of the pressure of the springs p¹ and p².
The springs p and p' in this case again rest on their normal contacts p³ and p².
In the conductor 9 between the battery o and the plug ¹ is inserted the relay u to
operate a controlling signal. The relay u is excited by the current of the battery o
which operates the transmitter of the called subscriber. Each junction wire is pro-
vided with a relay the arms of which v¹ and v² have respectively normal contacts and
outer contacts v³ and vº.
The conductor 12 connects the arm vl with the contact p of the key p. The
conductor 13 connects to the operator's receiver 9, and ends at the normal contact
of the same arm v¹, the acting contact of which is put directly to earth by the
conductor 14. The other contacts of the relay v form part of a local circuit.
The relay to is inserted in the conductor 15, which connects the centre of the coil n¹
of the translator n with the free pole of the earthed battery x. The battery x
can in practice be the same as the battery o. This relay w controls the clearing
signal for operator B.
The armature of the relay w controls a group of local circuits. The object of these
local circuits is as follows:-—
1. When the plug ¹ is inserted in a jack e, and as soon as the key p has been
depressed, the lamp y remains alight as long as the relay " is not excited, that is to say,
until the called subscriber takes his receiver off the hook.
2. To place the same signal y under the control of the relay w when the plug ¹ is
taken out of the jack e, in order that the signal y may act as a warning signal,
controlled by operator A.
The lamp y and the coil of the relay v are placed in series in the conductor 16 which
connects the free pole of the earthed battery to the body s² of the plug k¹.
The contacts of the relay u control the shunt 17, which includes a resistance coil.
A point in the shunt 17 between the relay u, and this resistance coil, is con-
nected by the conductor 18 to the arm 2 of the relay via the contacts of the
relay w.
The normal contact of the arm v² represents the end of the conductor 19 which is
put to earth through the resistance coil z.
The acting contact 5 of the same arm v² represents the end of the conductor 20
which leads to the spring p³ of the key p the outer contact of which p³ is connected
by the conductor ¹ to the free pole of the battery x.
It follows that the connections are such that the relay v provides in the one case
for the earthed battery a, a path independent of the plug 4, but controlled by the
relay w, which keeps the lamp y alight as long as the relay as is excited, that is to
say, as long as the plug g¹ remains in the outgoing jack k,

page_text: On the contrary as long as the plug is in the jacke the relay v provides, together
with this plug, another path for the earthed battery x, this circuit making the
lamp y dependent on a shunt, the continuity of which depends on the same relay w,
the action of which is in this case reversed, that is to say, to light the lamp y when
the relay w is not excited.
The relay u and the key p together with the relay to control the lamp y during the
time the plug is in the jack e.
Supposing that the subscriber C calls the central exchange by means of his
generator ds, which operates his calling signal f. The operator A immediately inserts
the answering plug g in the jack e corresponding to this calling signal, and at the
same time connects her instrument to the circuit 3-4 of the selected cord, and
thus ascertains that the subscriber C asks for the subscriber C¹ connected to another
exchange B.
Operator A by means of a call key connects her instrument with a call wire
permanently connected with operator B's instrument and gives the latter instructions
to connect subscriber C with subscriber C¹.
Operator B sees that junction line 8-9 is free and advises operator A that this
line 8-9 is to be used for the connection. Operator A immediately inserts the plug g¹
in the outgoing jack k, corresponding with the indicated line 8-9. On her side,
operator B with the tips of her plug k¹ touches the bush e² of the jack e corresponding
with the line asked for.
If the line asked for is engaged the free pole of the test battery is connected
with the bushes e¹, and gives the well known click in operator B's receiver q.
As soon as the tips of the plug touches the bush e, the current from the testing
battery can flow to earth through the contacts p¹, p of key p, the conductor 12, the
contacts r,, the conductor 13, the receiver 7, and finally the earth of operator B's
receiver, who hears the click showing that the line asked for is engaged.
On the contrary, if the line asked for is free, no current can pass through this test
circuit, consequently no sound is heard in the receiver 7, and the operator concludes
that she can insert the plug in the jack e with subscriber C¹.
The preceding moveinents of the operators A and B put the apparatus and
circuits in the proper position for connecting telephonically the two subscriber's
instruments C 01.
As we have already seen this telephonic circuit is not complete as a continuous
metallic circuit as it is interrupted at the exchange A by the translator 1, and at
the exchange B by the translator n, although these same translators provide
continuity by induction, that is to say, continuity of circuit for telephonic currents
between the two subscriber's instruments C and C¹
At the exchange B, when the plug is inserted into the jack e, the junction
wire 8-9 is cut by the ringing key p, the acting contacts of which are made in order
to connect the ringing generator with the line of the subscriber wanted C¹.
To describe this in detail the current from the generator passes through the
conductor 11, the electro magnet po, the closed contacts p p², a portion of the
conductor 9, up to the jack c, the wire 6, the bell of the subscribers instrument C³,
the return wire 5 up to the jack e, a portion of the conductor 8, as far as the closed
contacts p p³, the conductor 12, the conductor 14 and to earth, passing through the
closed contacts of the relay v, which is excited by the current from the battery x,
the circuit being through the conductor 16, the bush e¹ of the jack e, the conductor 7,
and earth through the electro magnet f¹ of the cut out relay, the normal contacts
of which are thus opened in such a way as to disconnect the line 5-6 from the
relay and earth.
As has just been shown directly the operator B inserts the plug into the jack e,
the generator rings the bell of the wanted subscriber C¹.
This ringing current flows through the relay 10. When the relay v is excited at
the moment that the plug is inserted into the jack e, it closes the contact v1 ",
which puts earth and the conductor 14 into contact with the conductor 12, at the
same time this conductor 12 is disconnected from the conductor 13 which includes

page_text: operator B's receiver q, so that this operator is free to immediately deal with other
communications.
The normal circuit of the battery is through the conductors 16 and 17, and
through the lamp y, but at this moment the lamp y is shunted by the conductor 21,
the contacts pps the conductor 20 the contacts v³ v² and the conductor 18 through
the contacts of the relay w.
This shunt is thus controlled by the relay w the excitation of which depends on
the introduction of the plug g¹ into the outgoing jack k, at the exchange A.
From what has preceded it is seen that when the bell of the subscriber's instru-
ment C¹ is actuated by the generator the lampy is not lit, but it is under the control
of operator A by means of the relay w. If for any reason whatever, for example on
account of the called subscriber not replying, operator A severs the connection with
the junction wire by taking the plug g¹ out of the jack, she breaks at the same
time the local circuit of the relay m, and consequently stops the flow of current from
the battery through the relay to which becomes inert and breaks the shunt of the
lampy which lights, that is to say, gives the clearing signal to operator B, who takes
the plug, out of the jack e of the line C¹ asked for.
Under ordinary circumstances the called subscriber replies to the call and by taking
his receiver off the hook makes an alteration in the circuit of his instrument in such
a manner as to cause a very considerable increase in the calling current froin the
generator 7, with the result that the electro-inagnet 2,10 of the key p is excited and
attracts its armature 2 and this releases the plunger of the key p. The acting
contacts p and 6 connected to the pole of the generator r thus no longer touch the
springs pl p², which resume their position against the normal contacts på p¹, and
thus establish the continuity of the junction line 8-9.
The circuit is then in the required condition to ensure the transmission of tele-
phonic currents between the subscriber's instraments C and C¹.
This
The return of the key p to its normal position also breaks the contact p7 p, and
this breaks the shunt 21, 20, 18 of the lamp y, controlled by the relay w.
shunt is replaced by another shunt 17, controlled by the relay u, which at this
particular time is excited by the current from the battery o in the circuit of the called
subscriber C¹. All the apparatus are at this time in the proper position to ensure
conversation. Nevertheless there is no necessity for either of the operators A or.B to
be looking after this connection until the clearing signal shows that their attention is
required.
The subscriber C gives the clearing signal by hanging up his receiver and
operating his generator d³, which actuates the clearing signal 2 at exchange A.
At the subscriber's instrument C' to give the clearing signal, it is only necessary
to replace the receiver on the hook; this breaks the battery circuit o through the
relay u, the armature of which resumes its normal position, breaking the shunt 17
of the lampy, the lighting of which gives the clearing signal to operator B.
As previously mentioned, it is in practice more advantageous to break communica-
tion in reply to the automatic clearing signal y at exchange B. As soon as operator B
sees the lamp y light while the plug is in the jack e she immediately takes this
plug k¹ out of the jack e, and replaces it in its proper position near the lamp y.
Taking out the plug k stops the flow of current through the relay v, which resumes
its normal position breaking the circuit 18-20 at the contact at the same time
putting the conductor 18 to earth by means of the normal contact v³, and the con-
ductor 19. As a result, a new path is provided for the battery to light the lamp
through the conductors 16, 18, 19 and earth. This new local circuit is controlled by
the relay w independently of all other apparatus.
This new function of the relay w is the reverse of its previous work, indeed in this
new circuit the lamp y remains alight as long as the relay w is excited, that is to
say, as long as the plug g' is in the jack kat exchange A. It will be seen then that
if at exchange B the lampy remains alight after the connection is severed, it is
because this same connection has not been cleared at exchange A. The signal y
serves during the interval as a warning signal, the aim of which is to prevent

page_text: operator B from selecting this junction line for a new connection as long as the
plug g' has not been taken out of the jack kat exchange A.
The lamp y acts thus as a calling, or clearing, signal under the control of operator A
when the called subscriber is being rung; the same lamp y also acts as a controlling,
or clearing, signal under the control of the called subscriber after he has replied to
the call, and finally, after the connection has been cleared at exchange B the same
lampy acts as a warning signal to prevent the junction wire being used again as long
as it is not free at exchange A.
It will have been seen from the description of the system that the working of
the junction wire at exchange B is independent of the type of the switchboard
at A.
It is only necessary that the exchange A should be provided with apparatus which
will ensure the working of the relay wat the exchange B as has been described and
this should be brought into play by connecting or clearing the junction wire at its
outgoing end A.
Figure 2 shows a junction line system arranged so that the clearing signal for the
incoming operator B shall be actuated when the called subscriber replaces his receiver
on the book, although this incoming operator B should not disconnect until after
receiving the signal to do so given by the warning signal controlled by the outgoing
operator A. Nevertheless in case operator B has disconnected before the signal has
been given by operator. A it is necessary that the warning signal should remain
operative as long as the outgoing end of the junction wire is not free at
exchange A.
In Figure 2 the subscriber's instruments G and G' each include a transmitter n, a
receiver a, a bell a², a condenser ³, a switchhook at, working in the ordinary
manner.
Lines 1-2 connect these instruments to the jacks b, of the switchboards A, B,
where apparatus of well known types, such as cut off relays e, calling relays c,
auxiliary calling signals f, and the calling battery & put to earth, is placed.
The outgoing exchange A is connected to the incoming exchange B, by the junction
line 10-11.
The exchange A is provided with pairs of ordinary plugs ii, connected by the
conductors 5-6 and the usual translator coils, between the inner ends of which is
placed the common battery.
Only apparatus at the exchanges A B which is indispensible to the understanding
of the mechanism of the system has been shown. It is understood that in practice
other apparatus such as ringing keys, controlling signals etc., can be attached.
The conductor 6 connecting the collars of the plugs i and of ¹, includes a
controlling relay m, placed between the plug i, and the translator k. This relay m
governs, in the ordinary way, the controlling signal m¹. The jack 9 represents
The outgoing end of the junction line 10-11, the incoming end of which line is
represented by the plug q¹. The arrangement of the junction line 10-11 is very
similar to that of the conductors connecting the pairs of plugs with the
exchange A.
At the exchange B the translator is inserted in the line 10-11.
T
The condenser 1 is placed between the inner ends of the pair of coils at
the translator connected to the middle side of the loop 10-11 coming from the
exchange A. The second metallic side of the junction line is represented by the
conductors 13-14 which connect the plug q¹ to the second pair of coils at
the translator ", the inner ends of these coils being connected to the common
battery, one pole of which corresponding with the conductor 13 is earthed. The
controlling relay t is inserted in the conductor 14, and is used to control the shunt 16
of the signal t¹ which is associated with the plug 2¹
The plug q¹ can be connected with the ringing current by means of the ringing
key u.
To the body of the plug q' is attached the conductor 15 coming from the free
pole of the battery v, by way of the lamp or signal t¹ and the coil of the relay w,

page_text: A second signal x is also associated with the plug q¹. This signal a acts as a
warning signal to prevent operator B from clearing the connection before it has been
disconnected at exchange A.
This signal is controlled by the two relays w and y. The relay y is inserted in a
branch to earth from the conductor 11 coming from the exchange A.
When the relay w is excited it closes its-two pairs of contacts w w³ and w² w¹.
When the relay y is excited it closes its three contacts y¹ y y³. The normal
position of the spring y₁ is between the armature y², and the outer contact y³.
The conductor 17 connects the free pole of the battery to the one side of the
lamp z, through a resistance coil. The other side of the lamp is connected to two
conductors 18-19 going respectively to the contact 203 and the spring y¹.
The armatures w¹ and y² are connected to earth.
A point of the conductor 17 between the lamp and the resistance coil, is connected
by the conductor 20 to the spring w³, the contact of which w* is connected by the
conductor 21 to the contact y³ of the relay y.
It follows that the excitation of one of the two relays w or y, creates a path to
earth for the battery v, through the conductor 17, the lamp x, and one of the two
conductors 18 and 19.
If the two relays wand y are excited simultaneously the lamp is shunted by the
conductors 20-21, which prevents in this case the lamp from lighting.
Operator A's instrument should be connected with that of operator, B z¹, by means
of a call wire 22, the key in which is placed near operator A.
Supposing that the subscriber G on the exchange A asks for subscriber G'on
exchange B.
Operator A who receives this call transmits it to operator B by means of call
wire 22.
corre-
Operator B selects a junction line from among those that are free and designates
this to operator A, who immediately inserts in the jack 7 the calling plug
sponding to the answering plug i already inserted in the jack of the calling
subscriber G.
At the same time as she designates the junction wire the operator B takes the
plug 7, and after the usual test inserts this plug 7' in the jack 6 of the called
subscriber G¹.
The insertion of the plug q' in the jack b of the called subscriber closes the local
circuit 15-4 of the battery which thus actuates the cut off relay e, disconnecting
the line 1-2 from the battery d and from the relay c.
The circuit through the subscriber's instrument G¹, from the battery s in the
exchange B, is open as long as the subscriber's receiver is on the hook, consequently
the relay t is inert, and allows the lamp t¹ to remain lighted by the current flowing
along the conductors 15-4. This current also excites the relay w, the contacts of
which wand are closed. At the same time the relay y is also excited
inasmuch as the plug i at the exchange A is in the jack of the line 10-11,
consequently the battery has its circuit closed by the conductor 6-11 and by the
relay to earth. It follows that the contacts y¹ y² y³ of the relay y are closed at the
same time as the contacts of the relay w.
Closing the contacts w¹ w³ has the effect of creating a closed circuit for the battery v
through the lamp a, passing through the conductors 17-18 to earth. The closed
contact y¹ y² also puts the conductor 19 to earth, but at the same time the closing of
the contacts ww and y³ ³ completes the shunt 20-21 of the lamp x, which is thus
not lighted as long as the two relays w and y are excited simultaneously.
It has been shown that the lamp is alight as long as the receiver of the subcribers
instrument G¹ is not taken off the hook and at the same time the lamp & remains
unlighted.
As soon as subscriber G¹ replies to the call the lamps m¹ at the exchange A,
x and t¹ at the exchange B remain unlighted as long as the conversation
lasts.
When the conversation is finished, putting the receiver on the hook at the

page_text: subscriber's instrument G lights the lamp m² at the exchange A, and putting
the receiver on the hook at the subscriber's instrument G¹ lights the lamp t¹ at the
exchange B.
The two operators, A and B, are thus advised when their respective subscribers
replace their receivers on the hook, and the connection can be cleared. As in practice
it is recognised that the clearing signal given by the calling subscriber is more
certain than that given by the called subscriber, it follows that as soon as operator A
receives the clearing signal by the lighting of the lamp m³, she immediately takes out
the plugs from the jacks b and q.
Taking out the plug i from the jack q breaks the circuit of the battery / through
the relay y which becomes inert and breaks the shunt 20-21 of the lamp a, which
can then be traversed by the current from the battery v and through the
conductor 17-18, the contacts w¹w to earth. The lamp immediately lights, this
gives operator B the signal to disconnect as the two lamps x and t¹ burn simul-
taneously, provided that subscriber G' has also replaced his receiver on the hook.
Operator B then takes out the plug q¹ from the jack b, which breaks the
circuit 15-4, extinguishing the lamp and rendering the relay w inert.
The return of the relay to to its normal position breaks the circuit 17-18 and this
extinguishes the lamp x.
It follows that all the signals become inert after plugs i q¹ are replaced in their
normal position.
The lamp can serve as a warning signal advising the operator B that the outgoing
end of the junction wire 10-11 is not free.
This is useful in case operator B is satisfied to take the lighting of the lamp t¹ as a
clearing signal, or still more so in case she severs the connection with the called
subscriber through a mistake. In this case the lighting of the lamp & indicates to
the operator B that the outgoing end of the line is not free.
The advantage of the signal as a warning signal is also very great when the
exchange A is fitted with ordinary indicators operated by generators or by batteries
fitted at the subscribers instrument.
The latter subscribers very often neglect to give the clearing signal as this signal
requires an additional operation. It is seen that in this case the clearing signal given
automatically by the lamp t¹ at the exchange B, is regarded at the latter exchange as
a clearing signal, the lamp being looked on as a warning signal.
Figure 3 represents two subscribers' instruments a and a at the central
exchanges A and B.
The outgoing exchange A is connected with the incoming exchange B by junction
line 10-11.
The subscriber to call the central exchange A has only to take his telephone off
the hook, for immediately the calling signal d will be given by the well known
operation of the calling battery f, and the relay d.
In reply to this call operator A inserts the plug h in the jack b of the calling
subscriber and at the same time by means of the listening key ³ she connects her
instrument c with the circuit 4-5 of the plugs h h¹, in such a way as to receive, for
example, the order to connect the subscriber a with the subscriber a¹ belonging to
the exchange B.
The operator A inserting the plug h in the jack b of the calling subscriber A closes
the local circuit 6-3 of the battery h10, this excites the cut-off relay e, and
disconnects the line 1-2 from the battery f and from earth.
At the same time the circuit of the battery h³ is closed by the line 1-2 and the
subscribers' instrument A in such a way as to excite the relay he which can thus close
the shunt 8 of the controlling signals which then remains inert.
The operator A transmits the order of the subscriber A to the operator. B, using
for this purpose the call wire 19.
Operator B seeing that the junction wire 10-11 is free, indicates this immediately
to operator A, who at once inserts the plug in the outgoing jack j of this junction
line 10-11.

page_text: The insertion of the plug h¹ in the jack j, closes the local circuit 7-12 of the
battery ho, this lights the lamp h as the battery he has not yet its circuit closed by
the conductor 5 and the conductor 11 of the junction line, consequently the shunt 9
of the lamp he remains open.
While the outgoing operator A is thus making the connection required to connect
the subscriber a to the exchange B, operator B on her part tests the required line
touching the tip kl of the plug against the bush b¹ of the jack b.
If the subscriber a¹ is engaged a battery 10 or a battery r is connected to the
bushes of the jacks b of this line. It follows that a current will pass in this case by
the tip of the plug, the closed contact p¹ p³ of the relay p, the conductor 13, the
receiver i to the earth of the instrument of operator B, who then hears the character-
istic click indicating that the line is engaged.
If the called subscriber is free no current passes through the receiver which
remains silent and operator B therefore concludes that she may insert the plug k in
the jack 6 of the called subscriber a¹, afterwards depressing her ringing key in
such a way as to connect the called subscriber's instrument at with the ringing
generator.
The insertion of the plug in the jack b closes the circuit 14-3 of the battery r
which can then light the lamp and excite the relay 'p, the moveable levers of
which pl p, are attracted against their respective contacts p p³, so that the con-
ductor 10 of the junction wire is connected to the tip of the plug and consequently
to the wire 1 of subscriber a¹'s line.
The excitation of the relay p breaks the contact p³ p³ so that the receiver i is dis-
connected from the tip of the plug k, at the same time the closed contact p³ p³ com-
pletes a local circuit 15 containing the lamp m.
It will have been seen that in the circuit 14-3 the battery r lights the lamp las
long as the relay n remains inert, that is to say, as long as the called subscriber has
not replied to the call.
On the other hand the insertion of the plug 4¹ in the jack j at the exchange A,
closes, for the earthed battery at the exchange B, a circuit through the conductor 18,
the coil o³ of the relay o, the conductor 10 of the junction wire, the tip of the plug hi
and the conductor 4 to the earth of the battery h³.
As a result the relay o is excited and closes the contacts o¹ o³ so as to complete the
shunt 17 of the lamp m which remains unlighted in spite of the passage of the current
of the battery in the circuit 19, p³, p³, 15 and earth comprising the lamp m and its
shunt 17.
When the subscriber a¹ takes his receiver off the hook the battery h³ at the
exchange A has its circuit closed through the subscriber's instrument a¹ through the
conductor 5, including the relay 7, the conductor of the junction line 11 containing
the relay n, the wire of line 2, the subscribers instrument a¹, the wire of line 1, the
conductor of junction line 10 the conductor 4 and earth at h³.
The two relays h and n are thus excited respectively at exchange A and at
exchange B. The excitation of the relay h' closes the shunt 9 of the lamp he which
is extinguished thus showing operator A that the subscriber a¹ has answered.
The excitation of the relay closes the shunt 16 of the lamp which is extin-
guished and thus shows operator B that the subscriber a¹ has answered.
The shunt 16 includes the coil n of the relay n which is excited as long as the
plug k remains in the jack b irrespective of the condition of the subscriber's instru-
ment a¹ or the junction wire 10-11. The sole purpose of the lamp is thus to show
the operator B if the subscriber replies to the call in order if necessary to ring again
or whether to clear the connection if the subscriber does not eventually reply.
Supposing that the subscriber a¹ replies to the call, taking his receiver off the
hook.
In this case the two instruments a and a¹ are in telephonic communication.
The two lamps he and hº at the exchange A are unlighted indicating to operator A
that the two subscribers a and a¹ have their receivers off the hooks.
The two lamps land m at the exchange B are unlighted, indicating to operator B

page_text: by the lamp that the receiver of the called subscriber a¹ is off the hook, and by the
lamp m that at the exchange A the plug is in the jack j of the junction
wire 10-11.
Putting the receiver on the hook at one of the two subscribers instruments « or a¹
only lights one of the lamps 1 and 2 at the exchange A. As soon as both the
lamps and are lighted operator A concludes that conversation is finished and
takes the two plugs and h¹ out of the jacks b and j.
Taking the plug h¹ out of the jack j breaks the circuit 18-10-4 of the battery r
at the exchange where the relay o becomes inert breaking the shuut 17 of the
lamp m.
The lamp m thus becomes lighted by the current from the battery, passing
through the conductor 19, the closed contacts and the conductor 15 to earth.
The lighting of the lamp m indicates to operator B that the connection has been
cleared, she at once takes the plug k out of the jack b, rendering relays n and P inert
and placing all apparatus in normal position.
The detailed descriptions of Figures 1, 2, 3 enable the mechanism of Figures 1-
1b and 1-1 to be easily understood. They are based on the saine principles and for
practical working are associated with all the apparatus necessary to the proper working
of the intercommunication.
Thus Figure 1 represents a junction line 1-2, the outgoing end of which, or
jack a, is situated in the outgoing exchange A and the incoming end, or plug b, is
situated in the incoming exchange B.
The exchange A is supposed to be on the system well known as a relay board with
common battery, and it is considered sufficient to represent this exchange A by the
essential apparatus at one pair of plugs c and c associated with the controlling
signals d and d¹.
The operator A's instrument e can transmit by the call wire 3--4 orders to operator B's
instrument f.
Operator A can also by this circuit 3-4 attract the attention of operator B by
dropping the indicator g, the shutter of which controls the auxiliary signal g¹ which
can be common to a group of indicators g.
The junction line 1-2 is provided at the exchange B with the translator h, because
the distance between the two exchanges A and B is supposed to be very great. The
battery of 24 volts. in the translator h thus serves to supply the called subscriber's
instruinent, and to excite the relay as long as the called subscriber's receiver is off
the hook. The armature of the relay governs the controlling signal d' at the
exchange A, in such a manner that the signal d' at the exchange A shews in the ordi-
nary way when the called subscriber replies and finishes his conversation.
At the exchange B the relay i is excited by the battery when the circuit 5-6-1
is closed to earth, i.e. when the plug c² is in the jack at the exchange A. In the
same way relay j is excited by the battery h¹ when the circuit through the con-
ductor 5 and the body of the plug bis closed to earth, i.e. when the plug 6 is in the
jack of the called subscriber.
The relay controls the shunt 16-17-7-8 of the lamp / as long as the relay ;
is excited i.e. while the communication lasts; consequently the lamp k only lights
after the breaking of the shunt 16-17-7-8 caused by the clearing of the connection
at exchange A. It follows that the lamp k gives operator B the clearing signal as
soon as the plug c¹ is taken out of the jack a at the exchange A.
On the other hand when the relay j is inert i.e. when the plug b is in its normal
position, the relay i controls the circuit of the battery passing through the
conductor 5, the lamp k and the conductors 8-7-9 to earth.
This circuit is only closed when the relay i is excited, i.e. when the plug c¹ is in
the jack .
It will be seen that in this case the lamp k acts as a warning signal.
The relay controls the continuity of the test circuit through the tip of the plug b,
the conductor 1, the acting contact of the key l, the conductor 10, the normal contact
of the relay j, the conductor 11-4, the receiver of the instrument f, the secondary

page_text: circuit of the induction coil m, the conductor 3, the retardation coil n, and the
conductor 12 to earth.
This circuit is cut as soon as the relay j is excited, i.e. as soon as the plug 6 is
inserted in the jack of the called subscriber.
When the relay j is excited and at the same time the relay is inert, the calling
generator o is connected with the called subscribers line through the conductor 13,
the interrupter o¹, the conductor 14, the coil of the relay 11, the acting contact of
relay, the conductor 10, the acting contact of the key l, the conductor 1, the
tip of the plug b, the called subscriber's line, returning through the conductor 2, the
acting contact of the ringing key l, and the conductor 15 to earth.
This circuit is automatically cut as soon as the relay l¹ is excited, i.e. as soɔn as
the called subscriber takes his telephone off the hook.
The key p allows the operator B to electrically restore the shutter of the indicator g
by closing the circuit of the battery h¹ through the conductors 5-16-18 the acting
contacts of the key p, the conductor 19, the 50 ohm. coil of the indicator g, and the
conductor 20 to earth.
As soon as the called subscriber takes his receiver off the hook the relay l¹ is
excited, allowing the key to automatically resume its normal position in
such a way
It is thus
as to re-establish the continuity of line 1-2.
seen that the mechanism of Figure 1ª proceeds on the principles laid down in
Figures 1, 2, 3.
Figure 1b differs only fro:n Figure 1 by leaving out the translator at the
exchange B, on the supposition that the junction line 1-2 is short enough to allow
the called subscriber's instrument to be supplied with current from the central battery
at the exchange A.
.
In Figure 1 letters and figures of reference have been given exactly the same as
those on Figure 1 in order to shew the similarity of working of the two systems..
The arrangement shewn on Figure 1 can be used when the outgoing exchange A
is ou a system worked by inagneto and the incoming exchange B on the relay and
common battery system. The exchange B is not provided with a translator because
it is supposed that the junction line is short enough to allow the translator to be
installed at the outgoing exchange A. The inside ends of the second pair of 150 ohm.
coils of the translator h at the exchange A are connected to the acting contacts of the
relay which is excited as long as the plug c is in the outgoing jack ay
consequently the battery h³ of about 24 volts., at the exchange A can supply the
called subscriber's instrument on exchange B with current as long as the plug c¹ is
in the jack a.
In Figure 1 letters and figures of reference have been given exactly the same as
those on Figures 1 and 1', in order to shew the similarity of working of the systems.
Figure 1 applies to the same case as Figure 1 but it is supposed that the
distance between the 2 exchanges A and B are sufficiently great to render it
advisable to employ a translator at the outgoing exchange B. In Figure 1ª exactly
similar figures and letters have been given as in 1, 1b, and 1°, in order to show the
similarity in the working of these systems which are in accordance with the principle
shown in the diagrammatic figures 1, 2 and 3.
Figure 4 represents a junction line 3-4 where the incoming end B is provided
with a system of apparatus which performs automatically the following operations.
1. The incoming operators instrument is disconnected from the line after the
plug has been inserted in the jack.
2. The ringing current is connected with the called subscriber's line when the
plug is inserted in the jack.
3. The ringing current is disconnected directly the subscriber replies.
4. The controlling signal remains inoperative during the time the subscriber is
being rung but it is put again under the control of the called subscriber as soon as
the latter replies to the call thus enabling it to be used as a clearing signal for
operator B.
In Figure 4 the special application of this apparatus for a junction line is shown

page_text: but it is obvious that the same principles are applicable to all kinds of lines and to
cord circuits for making connections on any kind of switchboard.
In order to make the working of the system more easily understood, let us suppose
that the outgoing operator A transmits, by means of the call wire 5, an order to
operator B to connect the auxiliary junction line 3-1 with the line 1-2 of a wanted
subscriber connected with exchange B.
The first thing operator B has to do is to raise the plug g and test the jack b of
the subscriber wanted by touching the tip of this plug against the bush of the
jack. If the line 1-2 is engaged the bush 43 is at the potential of the testing
battery, and in this case each time the tip of the plug touches the bush a current
passes through the tip of the plug, the conductor 7, the normal contacts 13 of the
relay, the conductor 8, the normal contacts m² m² of the relay m², the conductor 10,
and operator B's receiver p to earth which gives the characteristic click, showing that
the line engaged. If the line is free operator B does not receive any click. It
may be pointed out that during this test the conductors 7 and 8 are disconnected
from the conductor 4 of the junction wire, and consequently whatever may be the
electric condition of this line, no disturbance can be caused by it in the receiver
at the time that operator B makes the test.
If operator B ascertains that the line wanted is free, she inserts the plug g in the
jack 6 putting the conductors 6 and 7 respectively in contact with the wires of the
line 2 and 1, at the same time closing the circuit 11-14-15 of the battery v,
the current from which actuates the cut off relay in such a way as to disconnect
the line 1-2 from the relay / and from the earthed battery e.
In the same circuit the current from the battery o excites the relay / which then
attracts the two springs and, against the contacts and I, which are connected
to the two sides of the generator n, which is thus connected to the called subscriber's
instrument, through the conductors 6-2-1-7-9 and rings his bell a³.
The excitation of the relay breaks the contact of the spring 1 thus disconnecting
the conductor 7 from the conductor 8, i.e. operator B's instrument is disconnected
from the plug g during the automatic calling of the line wanted. As soon as the
called subscriber takes his receiver off the hook, i.e. switches his line on to his
transmitter and receiver, the ringing current from the generator n becomes strong
enough to excite the relay k the armature of which is attracted closing the circuit
16-17, containing the coil me of the relay m¹. In this circuit 16-17 the battery
excites the relay m¹ the springs of which m² and m³ are attracted respectively against
their contacts m³ and m² altering the circuits as follows :-
The conductor 11 is disconnected from the battery o and consequently the relay
becomes inert and permits its springs 12 and 18 to return to their normal position
against the contacts and 16 respectively so that the conductor 3 of the junction line
is extended by the conductor 6 up to the collar of the plug g.
In the same manner the closing of the contact m² m³, reconnects the conductor 4
of the junction line to the conductor 8 which is itself connected again to the
conductor 7 by the closed contact 13 10, so that the conductor 4 is extended up to the
tip of the plug g.
The conductor 10 is disconnected from the conductor 8 so that the receiver p is
disconnected entirely from the circuit of the junction line which connects exchange A
to the subscriber wanted.
A local circuit m³, m7, 12, 13, 14, 15, is formed for the battery o, the current
flowing through the coil m³ of the relay m¹, and the lamp k¹ which is controlled by
the shunt 17-16 the continuity of which depends on the relay k.
This local circuit 12-13-14-15 is independent of the relay k, consequently the
current which passes through the coil m³ maintains the excitation of the relay m³ as
long as the plug g remains in the jack b.
To sum up, it is seen that after having tested the line wanted, the insertion of the
plug in the jack disconnects the receiver from the junction line, and connects the
source of ringing current to the subscribers line wanted, the reply of the wanted
subscriber disconnects the source of ringing current from the junction line, and
extends the conductors of this line up to the instrument of the wanted subscriber,

page_text: in such a way as to complete the telephonic connection of the calling subscriber with
the wanted subscriber.
Cilig
The controlling signal remains inoperative while the subscriber wanted is b this
rung, but this subscriber after having taken his receiver off the hook controls
signal which can thus act as a clearing signal for the incoming operator.
If it is wished that the incoming operator B shall not disconnect until after receiving
the clearing signal from the outgoing exchange A a clearing signal controlled by the
operator A can be added to the apparatus shown in Figure 4, without in any way
modifying the principles of the system shown in Figure 4.
Excellent results are obtained with a voltage of 20 volts. for the battery o 50 ohms.
resistance in the coil m' and 13 ohms. resistance in the coil m³ of the relay m²,
100 ohms. resistance in the coil of the relay L, 85 ohms. resistance in the coil of the
cut off relay c and by putting in a 10 volt. lamp k¹.
Figure 5 shows another application of the principles laid down in the description
of Figure 4.
Figures 6 to 8 show constructional details of the automatic apparatus employed in
Figure 5, where it is used to carry out automatically the following operations :-
1st. After the insertion of the plug in the jack to disconnect the incoming operator's
receiver, and, at the same time, to connect the wanted subscriber's line with the
calling generator circuit.
2nd. After the reply of the wanted subscriber, to disconnect the source of ringing
current, to establish the telephonic continuity of the junction circuit between the
calling subscriber and the called subscriber, and in addition to put the controlling
signal in a position to give the clearing signal.
Figure 5 represents a junction line 1-2 used for connecting the outgoing
exchange A with the incoming exchange B, where the junction line terminates in a
plug g, with which is associated the controlling signal. j, governed by the relay i and
the automatic apparatus which includes the two relays and k the mechanism of
which will be explained in detail.
The subscriber's instrument E fitted with ordinary apparatus is connected by the
line 3-4 to the usual apparatus in the central exchange B.
Figure 6 shows an elevation of the automatic apparatus k l.
Figure 7 is a plan of the same apparatus.
Figure 8 is an elevation of the opposite side to that of Figure 6.
The axes of the cores of the two electro-magnets k and I are placed in the same
straight line (see Figures 6-7-8).
The pole pieces ¹², and 11 12, of each electro-magnet are bent inwards, the
pieces and 12 are joined and firmly attached to one another.
Each electro magnet is provided with an armature placed between the body of the
coil and the inner ends of the pole pieces. Thus the armature of the relay k is
fixed to the pole piece k by means of a fine metal spring such as a very flexible
iron spring having a thickness of about 1 of a millimetre.
The free end of the armature is so placed in relation to the inner side of the
bent end of the pole piece ² that if the electro-magnet is excited it attracts the free
end of the armature which tends to adhere to the inner side of the bent end of the
pole piece k² in order to complete the magnetic circuit of the coil.
In the same manner the armature 18 of the relay is fixed by one of its ends to the
pole piece the other end being placed in such relation to the inner side of the bent
end of the pole piece that it is attracted by 12 when the electro magnet / is excited.
The pole piece carries 4 springs m m³ and n n¹ firmly secured between blocks of
an insulating material fixed to the pole piece ¹ these springs are parallel to the axis
of the electro magnet.
Normally the free ends of the springs » and n¹ rest against insulating studs n² n³
which project from the other side of the pole piece l.
The spring m normally rests against the insulating stud m² which projects from
the outer side of the pole piece 2 while the spring m¹ normally rests against the
metallic contact m³ which is fixed to the pole piece but insulated from it.

page_text: The spring a carries a metallic contact n arranged to touch the corresponding
contact on the spring m when the spring n is raised by the arinature 13.
Underneath this contact n the armature carries a stud of insulated material
for the purpose of raising the spring n against the spring m when the arinature (³ is
attracted by the pole piece l².
At the same distance near the insulating stud the armature carries another
metallic stud 1 placed exactly under the spring n¹. The metallic stud is for the
purpose of raising the spring n¹ against the insulating stud m' of the spring m¹ when
the armature 13 is attracted by the pole piece in such a way as to raise at the same
time the spring m¹ which is thus taken off its normal contact m³.
The pole piece k¹ of the relay k carries in the same way two springs o and o'
insulated from it. The free ends of these springs o and o' normally rest below the free
ends of the springs m and m³ in such a way as to make contact with the latter
springs and to raise thein off their normal contacts when the armature ³ is attracted
by the pole piece k².
Normally these springs o and o¹, rest respectively against the insulating studs o³
and fixed on the outer side of the bent end of the pole piece k².
Normally the springs and n¹ rest against the insulating studs n² and n³
respectively, while the springs m and m² rest against the insulating stud m² and the
metallic contact m³ respectively. In the same way springs o and o¹ rest on the
insulating studs o² and of respectively, and further these springs o and o³ are insulated
from the springs m and m³.
When the armature is attracted by the pole piece these springs o and o¹ raise
the springs m and m² which are thus separated from their normal contacts m² and m³.
If afterwards the armature 13 becomes also attracted by the pole piece the
insulating stud 1 raises the spring off the insulating stud n at the same time the
contact of this spring n is forced against the spring in such a way as to raise
this spring m and to disconnect it from the free end of the spring with which it
was in contact as the relay k is supposed to be excited.
72
On the other hand, the metallic stud 16 of the armature also raises the spring n¹
and forces it against the insulating stud n* of the spring m. The latter spring m¹
is thus raised off the spring o' with which it was in contact.
The automatic apparatus k-l can be placed in any position in the central exchange,
(see Figure 5). The conductor 9 connects the spring m² to the conductor 1; the
conductor 2 of the junction line is broken, the portion of the conductor 2 coming from
the exchange A is connected with the spring n the other portion of the conductor 2
coming from the contact g² of the plug g, and from the relay i is connected to the
spring m. The spring of is connected to earth. The spring o is connected to a metallic
brush constantly in contact with the revolving commutator p, which is composed of two
segments one of which p¹ extends over a quarter of the periphery and the other of
which p² extends over nearly the whole of the remaining three quarters of the
periphery of the commutator p.
The segment pl represents the free pole of the earthed generator p³ (an alternating
ringing current) the other segment p² represents the free pole of an earthed battery r
the electro-motive force of which should he nearly equal to that of the battery h.
The commutator p should be arranged in such a way as to make a complete
revolution in 12 seconds so that the generator ps and the battery rare alternatively
placed in contact with the spring o, the duration of these contacts during a complete
revolution of p being respectively 3 seconds for p³ and 9 seconds for r.
Operator B is provided with the usual receiver q by means of which she can
receive through conductor 10, orders from operator A and test in the ordinary
manner the jacks of the lines wanted.
g
The earthed receiver q is connected by the conductor 11 to the metallic stud m³.
The body g of the plug g is connected to a series of conductors coming from the
free pole of the earthed battery r. These conductors are factors in the working of
the cut-off relay f, the controlling signal ; and the automatic ringing apparatus kl.
One side of the relay k is connected by the conductor 12 to the free pole of the

page_text: battery r, in the same way one side of the relay is also connected by the conductor 13
with the free pole of r.
The other side of k is connected to the conductor 14 which includes the signal j,
being afterwards connected to the conductor 15 coming from the body g³ of the plug.
The other side of is connected by the conductor 16 to the armature i¹ of the
relay i, and by the conductor 17 to the armature 13 of the relay l, and consequently to
the metallic contact of this armature P³.
The contact n¹ is connected by the conductor 18 to the conductor 14 coming from
the other side of the relay k.
The contact stud 12 of the relay i is connected by the conductor 19 to the con-
ductor 15 coming from g³.
The battery can have an electro-motive force of 10 volts., the relay f a resistance
of 20 ohms., the lampj be adapted for 4 volts. and 2 amperes the relay k 30 ohms.
and the relay 6 ohms.
In order to better understand the mechanism of the system of the automatic
apparatus k let us suppose that a subscriber at the outgoing exchange A asks to be
connected to a subscriber E at the incoming exchange B. Operator A transmits this
order to operator B by the call wire 10.
The junction line 1-2 to be used is designated by one of the two operators A
or B, following the methods already described.
Operator B takes up the plug g corresponding to the selected junction line 1-2
and applies the tip g₁ of this plug to the bush of the jack 61 corresponding to the
subscribers line wanted.
In this manner she connects by the conductor 1-9-11 her receiver q to the bush
thus tested as the spring m³ normally rests on its metallic contact m³.
If the line asked for is already engaged a battery is connected to the bushes of
the jacks of this line so that the current of this battery will flow to earth through
the receiver g causing a click to be heard each time that operator B touches the
tip g of the plug against the bush of the jack tested.
If the line tested is free the receiver 7 remains silent, and the operator at
once inserts the plug g in the jack b¹ putting g³ in contact with the bush of
jack and completing the local circuit of the battery the current from which
passes through the conductors 12-14-15 and 7 including the relay k the
lamp j and the cut off relay f.
This current is not sufficient to light the lamp; but it is sufficient to excite the
relays k and f
The excitation of the cut-off relay f disconnects the line 3-4 from earth and from
the battery c.
The excitation of the relay k raises the springs and o¹ and puts them in contact.
with the springs m and m¹ respectively in such a way as to break the contact m¹ m³,
that is to say, to disconnect the receiver g from the plug g and at the same time
to connect the circuit 1-2 of this plug with the ringing current.
To describe this in detail the conductor 1 is put to earth by the spring o¹ and the
conductor 2 is connected with the revolving commutator p through the contact m, o.
The rotation of the commutator p, connects alternately the free poles of r and of p³
to the conductor 2, consequently during the passage of the current from the
generator p³ the bell a² of the subscriber E rings.
As the condenser a³ and the bell a² enormously reduce the strength of the current
in this ringing circuit, it follows that the relay i is not excited either by the
generator p³ or by the battery r.
As soon as the receiver of the called subscriber E is taken off the hook the
line 3-4 is switched at this instrument through a much lower resistance increasing
the strength of the current from either p³ or by r sufficiently to excite the relay i
which thus attracts its armature against the contact stud 12.
Two ends are served by sending the current from the battery r over the line
between the intervals of ringing. The first is that the cutting out of circuit of the
automatic apparatus k land the completion of the junction line circuit shall take

page_text: place immediately after the receiver of the called subscriber is taken off the hook
whatever may be the position of the rotary commutator p. The second is that the
excitation of the relay i shall depend on the continuous current rather than on an
alternating one such as that of the ringing generator.
The attraction of the armature against its contact closes a local circuit
through the conductor 13-16-19, including the relay l, which is thus excited
putting the spring n in contact with the spring m at the same time separating the
springs m and m¹ from the springs o and o¹ and closing contact i³ n¹.
The conductor 2 is thus completed and extended up to the contact 92 of the plug.
The ringing current is broken and the commutator p is disconnected from
the junction circuit.
The local circuits are modified as follows:―
A circuit is formed by the conductors 13-16-17 and 18 including the relay / and
placed in shunt with the relay h. But, as this circuit is independent of the
contacts and 12 it follows that the relay 7 is no longer placed under the control of
the relay i, that is to say, the relay will remain excited as long as the circuit 12-
13-16-17-18-14-15-7 exists, that is to say, as long as the plug g remains in
the jack b¹.
The resistance of the circuit is thus sufficiently diminished, by the relay / being
placed in shunt with the relay k for the current to light the lamp j.
It will be noticed that the lamp jis placed under the control of the relay ȧ which
closes or opens the shunt 19-16 of this lamp.
It will have been seen that while the subscriber wanted is being called the lamp j
remains unlighted, on account of the high resistance of the circuit consequently
operator B cannot receive a false signal.
After the reply of the called subscriber and the breaking of the calling circuit the
controlling signal j becomes effective and passes under the control of the relay i,
the working of which depends as usual on the position of the receiver of the subscriber
wanted.
When the conversation is finished, the receiver at the instruments E is replaced
on the hook, the relay i is no longer excited by the battery h, and the shunt 19-16
of the lamp j is broken, consequently this lamp lights, and can thus give the
clearing signal to operator B who clears the connection taking the plug 9 out of
the jack b¹.
Taking the plug out of the jack deprives the relays and / of current from the
battery, consequently the automatic apparatus k / resumes its normal position.
Figure 9 shows the junction line 1-2 used to connect an outgoing exchange A,
whether of the magneto type or common battery to an incoming exchange B of the
common battery and relay type.
The incoming exchange B is provided with two visual signals j and k. The
signal k is controlled by the outgoing exchange A and serves as a clearing signal for
the incoming operator B. Further at the commencement of communication the
signal allows operator B to see whether the junction line is free and whether
operator A has not mistaken the junction line, that is to say, if she has properly
inserted her calling plug c¹ in the outgoing jack A of the junction line 1-2 which
has been indicated to her.
The other visual signal j serves as a controlling signal for the incoming operator B,
and indicates to her the exact moment when the called subscriber takes his telephone
off the hook to answer the call.
From the time when the called subscriber answers his call, the controlling signal is
extinguished and remains so during the communication, so that from this time the
control of the junction line passes from the incoming exchange B to the outgoing
exchange A, which remains the sole judge as to the time to clear the connection.
The outgoing exchange A is represented in Figure 9 by the pair of plugs c c by
the operator's instrument e and by the jack a which represents the outgoing end of
the junction line 1-2. The incoming exchange B is represented by all the apparatus
indispensible for the working of the junction line 1-2.

page_text: At the incoming exchange the junction line is provided with a translator h and a
common source of current h¹ used for supplying current to the called subscriber's
instrument.
The incoming end of the line 1-2 is represented by the plug b.
Between the trauslator h and the plug b is placed operator B's instrument f, the
listening key and the ringing keys and P.
The working of the relays i, 2 and j and the visual signals j and k will be
explained later.
In order to better understand the mechanism of Figure 9, the successive movements
of operators A and B to put a subscriber at the exchange A in communication with a
subscriber B will now be shown.
Operator A having received an order from the calling subscriber transmits it
immediately to operator B, by depressing her call key e¹ which puts her instrument e
across the call wire permanently connected with operator B's instrument f.
Operator B then receives the number of the subscriber wanted whose line she tests
in the ordinary manner and indicates to operator A the junction line selected to
establish the communication asked for.
k
To test the line wanted operator B chooses a free plug and raises it from its
socket thus closing the local circuit 5, 6, 7 of the battery through the lamp k.
If the lamp & lights, operator B concludes that the junction line is free. In practice
for the lamp k to remain unlighted it is necessary that its shunt 8-9 shall be closed,
that is to say, that the relay i shall be excited which can only be if at the exchange A
a plug c is in the outgoing jack a, corresponding to the plug 6 chosen by the
operator B.
Supposing that the outgoing jack a is free the relay i remains inert and the lamp /
lights as soon as operator B raises the plug 6 to test the line wanted, applying the
tip of the plug b to the bush of the jack 61 of the line wanted at the same time
depressing her listening key l.
If the line wanted is engaged the bush of jack 61 is at the same potential as the
battery of the exchange B, while the point of the plug which is connected to
the conductor 1 finds earth at the battery h¹.
The key being depressed that is to say, on its outer contacts bridges the
instrument f, and the condenser across the line 1-2.
The plate of the condenser n connected to the receiver f is thus to earth.
It follows that if the tip of the plug b touches the bush of an engaged jack 6¹
The
the condenser n is immediately charged and discharges when the contact ceases.
charging and discharging currents from the condenser n traverse the receiver f and
produce the usual click indicating that the line wanted is engaged.
On the contrary, if the line wanted is free the bush of the jack 6¹ is to earth and no
charging or discharging currents from the condenser traverse the receiver f which
reinains silent.
Taking the latter case the operator B inserts the plug 6 in the jack b¹, at the
same time informing operator A the number of the junction line 1-2 corresponding
to this plug b.
The lamp k remains alight up to the moment when operator A inserts the calling
piug c¹ into the outgoing jack a, which has been designated.
Operator B is thus informed whether her instructions have been understood.
If the lamp k remains alight it is necessary to repeat the instructions to operator A,
and rectify the mistake made by that operator.
Supposing that the operator A inserts the plug c in the outgoing jack a, this
actuates the relay i at the exchange B; the circuit of the battery i is closed by the
conductor 10, the relay i, the conductor 1, the tips of the plug c¹ and the earth of the
battery c² at the exchange A.
The armature of the relay i is attracted and the shunt 8-9 is closed, extinguishing
the lamp k.
As soon as the operator B inserts the plug 6 in the jack wanted 6' it closes the
local circuit of the battery 1 through the conductors 11-12, and the bush of the

page_text: jack to earth. This local circuit contains the lamp j, which lights and remains
alight as long as the shunt 13-14 is not closed, that is to say, as long as the relay j
remains inert. But, as will be seen later the relay j remains inert as long as the
relay h² is not excited by the current from the battery h¹ through the called
subscriber's instrument.
Immediately after having inserted the plug 6 in the jack 1, the operator B sends
a ringing current to the called subscriber by means of one of the usual ringing
keys or 1².
•
The relay h² remains inert as long as the called subscriber does not take his
receiver off the hook, but the armature of the relay h² controls the circuit of the
hattery cat the exchange A, through the controlling relay, the collar of the
plug c¹, the conductors 2-15 the contact stud of the relay h³, the conductor 16,
the coil je of the relay j and the conductor 17 to earth.
This circuit is closed as soon as the relay h² is excited, that is to say, as soon as the
called subscriber answers.
It follows that the extinguishing of the lamp j, by the closing of the shunt 13-14
informs the operator B that the called subscriber has replied.
Further, as the closing of the shunt 13-14 is made through the coil is of the
relay j this latter relay will remain from this time permanently excited as long as
plug b remains in the jack b'.
The first effect of the called subscriber replying is to extinguish the controlling
lamp j, and at the same time to keep this lamp j unlighted during the remainder of
conversation in order to relieve the operator B from the need of controlling the
junction line from the time when the called subscriber has replied to the call.
The second effect of the called subscriber's reply is to simultaneously actuate the
relay cat the exchange A that is to say to close the shunt of the lamp d¹ which is
extinguished thereby advising operator A that the called subscriber has answered.
It is seen that the two operators A and B are simultaneously and independently
of each other informed of the precise moment when the called subscriber replies.
The advantage of these two independent controlling signals is to enable
operator B to at once judge whether it is necessary to ring the subscriber again and
in case of no reply operator A can give the clearing signal by taking the plug c¹ out
of the jack a.
Let us suppose that the called subscriber takes his receiver off the hook and thus
extinguishes the two controlling signals j and d¹.
From this moment the control of the communication passes entirely to the
exchange A, which remains the sole judge of the time to clear the connection. To
do this operator A takes the plug c¹ out of the jack a, breaking the circuit of the
battery through the relay i. The shunt 8-9 is thus broken, consequently the
lamp k is lighted by the current from the battery through the circuit 5, 6, 7, to
earth, thus giving the clearing signal to operator B, who has only to take the plug
out of the jack b¹ and replace this plug b in its socket k¹, in order to break the contact
of the socket ', that is to say, to break the circuit 5, 6, 7, of the lamp k which is
immediately extinguished.
After the clearing of the connection at the outgoing exchange A, and at the
incoming exchange B, all the apparatus of the junction line 1-2 revert to their
normal state, and thus render this junction line 1-2 free to establish a fresh
connection between a subscriber on the exchange A, and one on the exchange B.
Figure 10 shows how a junction line for connection between different switch
boards situated in the same building can be arranged. Suppose for example, that it
is desired to connect a trunk section A with a subscriber's section B.
Operator A inserts a plug in the individual jack of the trunk line which calls,
afterwards she inserts the second plug of the same pair in the jack of the junction line
whose plug or incoming end is at the section where the line asked for is accessible.
At the same time operator A gives the order to operator B to complete the com-
munication by connecting the incoming end of the junction line with the line of the
subscriber wanted.

page_text: The control of the communication is entirely reserved to operator A, who clears
the connection as soon as the controlling signals show that the conversation is
finished.
The clearing of the connection at A gives automatically the clearing signal at B,
where the operator clears the connection leaving the junction line free for a fresh
connection.
The subscriber's instrument a is fitted in the usual way for a common battery
system, it is connected by the line 1-2 to the switchboard B where the line 1-2
is fitted with the usual apparatus, such as the jack c, the calling relay d associated
with the calling signal and the calling battery l.
The trunk station a' may be of the magneto type, it is connected by the line 3-4
to the trunk switchboard A where it is fitted with the jack f and calling signal g of
the trunk section.
The switchboards A and B are connected by the junction line 5-6, where the.
outgoing end is fitted with the jack i, placed on the switch board A, and where the
incoming end terminates in the plug ¹ placed on the switchboard B.
Operator A has ordinary pairs of plugs and cords k¹ to establish communication
between the trunk line 3-4 and the junction line 5-6.
The bush of the jack i is connected with body
twisted up with the conductors 5 and 6.
of the plug i¹ by the conductor 9,
The bush of the jack c is connected to earth through a resistance m. On the
switchboard A the body 18 of the plug k¹ un the trunk section is connected by
the conductor 11 to the pole of the battery n.
The conductor 11 includes the lamp o and the supplementary battery p, of the
same polarity as the battery n. The shunt 13 of the lamp o is controlled by the
relay q, associated with the cord circuits k, k¹.
The shunt 13 includes a low resistance r.
The body of the plug is connected to
the free pole of the battery n by the conductor 12, including the lamp o¹, associated
with the plug of the switchboard.
The resistance m is calculated in relation to the lamps o and o¹ and the battery "
so that neither of the two lamps shall be lighted when the circuit is closed
through the two lamps simultaneously (without of course taking into account the
battery p).
It follows that clearing the connection at A allows the full current from the
battery n to pass through the lamp o' which lights immediately in front of operator B,
indicating to her that the connection can be cleared.
In the same manner in the closed circuit 11-9-10 the battery p has an electro-
motive force sufficient to light the lamp o but the presence of the lamp o in the
circuit is sufficient to keep the lamp of from being lighted by the current of the
battery n.
The resistance is such that the lamp o is extinguished when the shunt 13 is
closed by the excitation of the relay q, the working of which relay depends on the
instrument of the wanted subscriber A, when the transformer 8 is in circuit, that is
to say, when the key w is in normal position as indicated in the diagram.
When the position of the key w is reversed the junction circuit becomes metallic,
the translator & being cut out of the circuit 16-17. In this case the contact w¹ w²
of the key w puts the coil & to earth, so that the relay q is constantly excited closing
the shunt 13 and so extinguishing the lamp o.
Good results are obtained from a battery n of 20 volts. with a battery p of 4 volts.,
with lamps o and o¹ of 4 volts. and 2 amperes, with resistance m of 40 ohms. and a
resistance of 20 ohms.
Supposing that the instrument a¹ of the exchange A calls for instrument a on
exchange B.
The putting into action of the generator 6' of the instrument a¹ causes the shutter
of the indicator g on the trunk section A to fall, when the operator immediately
inserts the answering plug k in the jack f, afterwards depressing her listening key v
to connect her instrument to the circuit 14-16, 15-17, in order to be ready to

page_text: receive the order for the trunk instrument a¹ asking to the connected to the sub-
scriber's instrument a. Operator A transmits this order to operator B by means of
the call wire, and at the same time operator A inserts the plug k¹ in the jack i of a
junction line 5-6 ending in a plug placed within reach of operator B, to whom she
indicates at the same time the number of the junction line she has chosen.
Operator B takes the plug which has been indicated to her by operator A, and
tests with this plug i¹ the jack c of the instrument a asked for. If the line wanted
is free operator B inserts the plug in the jack e, completing the circuit of the
battery t, in the translators of the plug circuit kk¹ of the switchboard A.
The effect of the insertion of the plug in the jack c is to close the circuit of 1
the battery by the conductor 16-17 the conductors 5-6, the line 1-2 and the
instrument called a.
At the same time this closes the circuit of the batteries n and p by the conductors
12-11-9-10 and earth.
As has been said before the electrical conditions of this circuit are such that the
battery n cannot light the lamp o¹ at the exchange B while the battery p can light
the lamp o on the switchboard A as long as the shunt 13 is not closed. But the
closing of the shunt 13 depends on the relay g which is traversed by the current of
the battery in the circuit which includes the instrument a of the subscriber
wanted.
It follows that as long as the receiver at a is on the hook the relay q remains inert
and consequently the lamp o remains alight.
Further, the fact of the lighting of the lamp o proves to operator A that the plug i
has been inserted in the jack c on the switch board B, that is to say, that operator B
has executed the order correctly.
Operator A can send a ringing current to wanted subscriber's instrument a by
depressing her ringing key w.
The reply of the called subscriber a is indicated to operator A by the extinction of
the controlling lamp o as the fact of this reply excites the relay 9 by the passage of
the current from the battery t the circuit of which is closed through the called
subscriber's instrument a. If the instrument at a is of the magneto type or if the
resistance of the circuit connecting the instruments a and a¹ becomes very great, or
if the circuit is subject to interruptions rendering conversation difficult, it is better
to cut off the local earth of the exchange A and to connect the instruments a a¹ by a
metallic circuit, reversing the key w, that is to say, disconnecting the translator &
from the circuit 16-17. In this case operator A controls the connection by means of
her listening key v, as the lamp o is rendered inoperative by the excitation of the
relay traversed by the current from the battery t, the circuit of which is closed
through the relay 9 and the closed contact w¹, 10² to earth.
9
Usually the key wo is in such a position as to bring the translators into use. In
this case as soon as the conversation is finished and the subscriber a has hung up his
receiver the lamp o lights, giving the clearing signal to operator A who takes the
plugs and k¹ out of the jacks fand i. The fact of taking the plug k out of the
jack i breaks the circuit 11-9 which allows the lamp o¹ on the switchboard B to light
as this lamp of now receives the full current from the battery n through the con-
ductors 12-10 to earth.
The lighting of the lamp o is considered by the operator B as a clearing signal
and she immediately takes out the plug from the jack e which puts all apparatus
in the normal condition.
The attached figures have all been drawn up to show this system of intercom-
munication which is sufficient for all practical requirements. In these figures the
source of common electrical energy is represented by batteries of accumulators.
It is well known that common electrical energy can be furnished from a dynamo
arranged to produce no noise on the line, further, in order to obtain more security a
battery of accumulators can be placed across the poles of the dynamo, so that this
battery may be charged by the dynamo, and so contribute in concert with the

page_text: dynamo current for such a system. If the dynamo should fail or stop, the battery
will continue to furnish the necessary current for the working of the system.
In principle the dynamo is only used to charge the battery, while this supplies the
current for the busiest hours of the day as the battery alone is left in circuit to
supply the current during the less busy hours for example, during the night.
To prevent the dynamo from producing noise on the line we recommend the two
following methods.
The first method consists in inserting retardation coils having a high impedance,
but a low ohmic resistance, between the conductors of the line and the poles of the
dynamo.
The second method consists in driving the dynamo at a very high speed and
further by subdividing the commutator into a number of segments, calculated so
that the number of pulsations of the commutator shall exceed six to eight thousand
a second, for at this rate the noise on the line becomes inaudible.
•
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:-
1. The arrangement of signalling mechanism for junction lines in such manner
that a visual signal at the incoming end of a junction line acts as a calling or clearing
signal under control of the operator at the outgoing end whilst a calling current is
being sent to the called subscriber the same visual signal also serving as a controlling
or clearing signal for the called subscriber and also as a warning signal to prevent the
junction line from being reused until it has been set free at the outgoing end sub-
stantially as herein before described.
2. The use of visual controlling and disconnecting signals placed at the incoming
exchanges of the junction lines, these signals being brought into action by a current
furnished by the outgoing exchange and controlled by the called subscribers instru-
ment belonging to the incoming exchange.
3. The installation of the source of electric energy at the incoming point of the
junction line, the controlling signal of the outgoing exchange of the junction line
being controlled by a relay itself controlled by the called instrument belonging to the
incoming exchange.
4. A supervisory signal situated in one exchange controlled by a relay which is
controlled by a subscriber belonging to another exchange.
5. The mechanism as described for applying the source of ringing current com-
bined with the automatic arrangement for cutting off such ringing current.
6. The automatic breaking of the testing circuit at the incoming point of the
junction line substantially as described.
7. The use of an electro magnet for passing a ringing current to the line and which
likewise breaks the circuit of the operators instrument at the moment of and by
establishing communication with the line.
8. The breaking of the ringing current by means of a controlling relay.
9. The employment of both continuous current and ringing current to facilitate
the working of the relay controlling the application of the ringing current to the
line.
10. The employment of supervisory signals at the outgoing and incoming ends of
the junction wire, the signals in each case being controlled by relays which are them-
selves controlled by the called subscriber.
11. The employment of means for rendering inert the supervisory signals directly
the called subscriber replies.
12. The employment of coils having a small ohmic resistance but high impedance
in the circuit of the generator charging the central battery while the latter is energis-
ing the lines of the system as and for the purpose described.
13. Running the generator at a high speed and subdividing the commutator in

page_text: such a way as to obtain alternations exceeding 6 or 8 thousand per second so that
they are inaudible in the telephones as described.
14. The hereinbefore arrangements of apparatus and circuits substantially as
described.
L: BOL
n