US1672971A - Automatic telephone system - Google Patents

Description

J nie 12. 1928. 1,672,971

' B. D. VVI LLIS AUTOMATIC TELEPHQNE SYSTEM iW Barnard DHIZZIE June 12, 1928. 1,672,971

B. D. WILLIS AUTOMATI C TELEPHONE SYSTEM Original Filed March 10. 1922 3 fh t -sh t 2 June 12, 1928.

B. D. WILLIS AUTOMATIC, TELEPHONE SYSTEM 3 Sheets-Sheet 3 Orizinal Filed M rch 10. 1922 Patented June 12, 1928.

sin s 1,672,911 PATENT oFi ifc ri.

:en'nimni) n. wens; on e m RARK, ILLINOIS ASSIGNOR, B'Y vmsm: .assrenrinnrs,

TOAUTOMATIC ELECTRIC me; or CHICAGO; ILLINOISQA' CORPORATION or DELA- WARE.

AUTOMATIC TELEPiEroNE .sY-srniir.

.2. u :1 ,I.'.; J 1. l L; 21 .2 2.1.1 LEI" Application filed March 10, 1922, Serial No. 542,673. Renewed August 3, 1927.

The present. inventionrelates general to niulti-office telephone systems comprising both manual and automatic .offic'esi. but is concerned more I particularly with the. inter; connecting. trunks. in such a systeiri that carry traffic fronia. manual. to an automatic otficej and the principal. feature relates to h Pre Q ael fi ee w mpale? which are likely to. occur my en "an operator plugs into a jaClL ljltl1. Wl11Ch there connected a trunk leading to an automatic switch- '1 1 :tir .1 1 'f Other objectswhicl have to dowiththe carrying out of the general scheme will be pointed out and explained. fully hereinafter. Referring now to the drawings compr sing 2,, ldz3if h a laid. ou i- -p a i h the corresponding lines at the end thereof in alignment, they represent by means of the usual circuit diagrams a sufiicient amount of apparatus for a co'mplete connection' from a calling substation A inaymanual office to 1; called substation .Atjn afprivate branch exchangev ,which private I branch exqhange is associated with automatic office. The apparatus shown in Fig. 1', together with the manual equipment in Fig. 2comprising the operators trunk circuit Q, is assumed to be located inthe manual'oflice; the. remaining equipment shown inrFig. 2 in the automatic attire: and the equipment in Fig. 3 in the private branch exchange.

The eq uipn ent shpwn in. Fig. 1 comprisin}: the substation .A and. associatedequin ment. and the operators cord vcircuit Dis manual equipment of a, well known type. However. the calling end ot the} cord c-iricuit O is slightly modified as will be pointed out tully hereina-fter t The operators trunk circuit QC, Fig.v 2, is 'n ovided for the pu'rpose of permitting a B operator to set up, an automatic connection after she hasbeen signalled and the numbenhas been repeated to her by the A operator. c l 3 The automaticselectors Eand E,.Fig.- 2, which aredenoted by the dotted, rectangles lwarino: those. reference characters. are assumed to ,be ctthefwell known vertical and retarir tvpe having theifrba'nk contacts arranged, inkhorizontal rows orl:leve ls.,, The circuits of these switches are wellltnown and consequently do not need; to be shown...

The connector H is mechanically identical with eitherofth'e selectors E and Most ottliefcirc iits of this connector, however, have bee n omitted, only the line, release, and back bridge relays being shown. The line switch G is provided to take care of. calls. incoming fromlthe branch exchange over the trunk comprising conductors 52 agate, This line switchis of the well known rotary type of which the wipers have no normalposition and move inatorward direction only. The circuit 'sfof" this switch are rtu shown and willbe describedhe'reiriafter. a. m H H Automatioswitclies similar tQthe-Seliectors E andE'. the connectorali and. the line switch. C referred to above, are shown and described in .Aut or natic Telephonytwhich is a, book; ritten by Smith. an c mpbens book ljublishcdi McGraw-Hill Book Company. NewYork N Y. T ope er tr i k i a i is provided with the line: lamp L and associated equipment for receiving incoming calls and is. provided with, the calling vice key K? which is. used. to zconnect wup the common calling device S when an outgoing; call is being made. The operations otthe various circuitsdnvolved Will be explained in detail hereinafter. a

Thecperatorscord circuitO is a manual cord circuit of the. well known double plug type... The circuits of thisc rd circuit are shown. complete and will be described fully hereinafter v i The substationA' is an ordinary manual substation and identical. with the substation ,AtFlg. .1

. flhe ap paratu I having-been described in general, will. now be described in connection with a detailed description of. itsoperation. For this nurposeit willbeassumed that the fillbwlllllflfttsubstation Fig. 1,.in the manualnoflice desires to converse with the subscriber .at substationAf, Fig.3, in the private branch. exchange, which private branch exchange is a branch; of the automatic office. llvhenthc receiver is removed atsubs'tation A, a -.c1reu1t ns closed over line conductors l1 and -12ior line relay 14 which,

upon energizing, closes a circuit for the line,

lamn lt I The-operator, upon noting the lighted conditionot the, lamp L. inserts the answering plug; of an idle cord circuit, the plug P of the cord circuit 0 for example, into the jack J, whereupon cut off relay 13 energizes in series with supervisory lamp L, thereby clearing the calling line, whereupon the lamp L becomes extinguished. Supervisory it time.

The operator now throws her key K, which is a combined listening and ringing key, into listening position, thereby connecting up the conductors from her head set with the right hand strands of the cord circuit. After obtaining the desired number from the calling subscriber by conversing with him in the usual manner, the operator inserts the plug P into the jack J, after having ascertained that the associated trunk is idle by touching the tip of her cord with the sleeve of the jack. When the tip of the plug P comes into engagement with the tip spring of the jack J, the following circuit is closed: from ground by way of the tip of the plug P, corresponding contact of the jack J, conductor 25, relay 28 at the B operators position, Fig. 2, armature 39 and its resting contact, and resistance 36 to bat-- tery. Relay 28, upon energizing, removes the short circuit from around sleeve relay 29 at armature 35, whereupon sleeve relay 29 energizes in series with resistance 34 and inseries with relay 17 of the cord circuit 0. Relay 17 in the cord circuit 0, upon energizing, does a circuit for the supervisory lamp L and relay 29 in the trunk circuit 0, upon energizing, opens atarmature 38 another point in the shunt which was around it, prior to the energization of relay 28, at the same time closing a circuit for the signal lamp L by way of armature 41 andits resting contact, whereupon the lamp L becomes lighted. As a further result of the energization of relay 29, it disconnects relay 28 from battery at armature 39 and connects itby way of armature 42 and its resting contact and the condenser shown to the right hand winding of the tone machine TM. When this occurs relay 28 deenergizes and the A operator, who still has her listening key tl'llOWlL llEEllS the tone produced by the tone machine TM. As a still further result of the energization of sleeve relay 29, it closes at armature 40 a bridge across the conductors of the trunk extending to the selector E in the distant automatic ofiice as follows: from the lower conductor of the trunk extending to the selector E, by way of the normally closed contacts controlled by spring 48 of the key K, armature 40 and its working contact, polarized relay 31, and the normally closedcontacts controlled by spring 4-7 of the key K to the upper conductor of the trunk extending to the selector E. In response to the closing of this bridge the line and releace relays (not shown; of the selector E energize, thereby preparing the switch for operation in the usual manner. Polarized relay. 31 energizes but in a direction opposite to that in which it must energize to operate spring 43.

Before going. further with the operation, a few points in connection with the arrangement to prevent preliminary impulses will be considered. As pointed out in the preceding paragraph, a bridge is closed across the conductors of the trunk extending to the selector E in the automatic exchange at armature 40 of sleeve relay 29 upon the energization of that relay. This relay, as explained, is energized over the sleeve conductor of the 'ack J and, since there is a battery potential upon the ring contact of the plug P as well as upon the sleeve contact thereof, the said sleeve relay 20 might beenergized and deenergized, thereby delivering a preliminary impulse tothe selector E, as the plug is being inserted into the jack if it were not for the fact that the said sleeve relay 29 is normally short circuited, as shown. Obviously, however sleeve relay 29, being normally short circuited, does not energize until the tip contact of the plug comes into engagement with the tip contact of the jack at which time the sleeve contact of the plug will have firmly engaged the sleeve contact of the jack.

To continue with the operation, the B operator, upon observing the lighted condition of the lamp L, operates her key K which is a combined listeningand calling device key, thereby connecting up her head set in the mannershown so as to enable her to converse with the A operator. As a further result of the key K being operated, it closes at its upper pair of contacts a circuit for relay 30, Relay 30, upon energizing, opens the circuit of the signal lamp L at armature 11, whereupon the said lamp becomes extinguished, and at the said armature 11 and its working contact closes a locking circuit for itself which circuit includes armature 38 and its working contact. As a further result of the energization of relay 30, it disconnects the tone lead of the tone machine TM from the trunk, thereby apprisingthe A operator immediately of the fact that the B operator has responded. As a still further result of the key K being operated it closes at its lower pair of contacts a circuit for relay which circuit includes the resting contact of armature 37 and said armature. Relay 33, upon energizing, closes a locking circuit for itself at armature 46 independent of the key K, and at armature 45 places impedance 32 in bridge of the conductors 25 and 27. When this occurs supervisory relay 16 of the cord circuit 0, upon energizing, places a shunt around the -1narginally adjusted relay "17, whereupon the said relay deenergizes,thereby extinguishinglthesupervisory lamp L which gives the*A" operatoranswering supervision. Asa further result of the liey K being thrownpit places'the calling device S andthe release pushbutton-Rin bridge of the conductors o'fthe trunk extending to the selector E, at the same tinie removthereby placing'the line relayot' the selector E underthe control ofthe calling device S.

The A operator, upon noting the discontinuance of the toneywhieh tone is-discon- 1 nected when the key K" is thrown, as describedfrepeats the desired number to'the B operator, and, uponbeing confirmed by the Boperator that thelatter hasheard the number correctly she restores her listeningkey K to normal. lt will be noted that the calling snbscriber is able tohear the Aj'operator repeat thenumber to the B operator and consequently it the A operator has not heard the nui'nber correctly or if' for any reason she doesnotgive the correct number to l the 9B operator; he may make'the"desiredcorrection.

The B operator, after having been inforiiied of the desired nui'nber, manipulates thecallnrg'devfceS 1n accordance with the various digits thereof; thereby operating the selectorsE and E and the connector H with the'i esult that thewipers ofthelat ter are broughtinto engagement with an'idle trunk leading to the 'desired branclrexchange,

which trunk it willflbe assumed is the trunk shownin the drawings andconiprising conductors 52 and '52-). It will hefiioted that if the fB operator 'inakesa' iiiis talt'e while dialling the'ni'in'iber she may release the partly established connection by operating the release push button R and then proceed to dial the number over again. The"Bopei-ator restores the key K" to norinalafter shehas finished dialling the number." i

When the private wiper of the connector H comes into engagement with thetest contact of the trunk'eXtending'to the private branch exchange, a circuit is closed over private normal conductor 54 for switchingrelay 56 andsteppinginagnet57 oftheline switch C in series Stepping inagnet57 does not energize over this circuit/on account of the high resistance of switching relay 56 and the latter, upon energizing?disconnects i'ts arniat-ures from their resting contacts, thereby clearing the'c'alledtruhkof itsbattery and ground connections, but owing toa' mechanical interlocking devicetnot shown) be tween the arinat-ure of this relay and the arinatureofliiie relay 55,; the said switching relay 56 is not able to operate ftilly and conseqeently, since its ai inatures do not come into engageiiieht with their working contacts, the switch wipers are not connected up.

coining lighted atthis tiiiie.

In the connector H, the switching relay thereof, upon energizing, connects up the line 'wipersfto the ring out off relay (not shown); \whereuponringing current is projectedflout over the trunk to the private branch erchange; @Thi sringing currentuis repeated through the repeating coil in the truiikci'rcuit- T and operates relay 166 through theirnediuni of its bridged winding. Relay 66, uponfenergizing, closes alockingcircuit for itself in multiple with theline a inp L at armature 72, whereupon the said line lamp L 'beconies lighted. As further 1 result of the energization of relay 66;it prepares a circuit for sleeve relay .67 at armature 73. i

The branch exchangeoperatorfuponnoting the lighted condition of the line lar'npL, inserts the plugof an idle cord circuihthe plug 1 ofthe cordcircuitOfor example, into the jack J thereby completing acircuit for sleeve relay 67 in serieswithsupervisory la np L. Sleeve relay 67, uponenergizing, closesa locking circuit for itself qlndependentof relay 66 andopensthe locking circuit of relay (36 and the circuit ofline'lamp [F at armature 71, whereupon the said relay 66 de energizesand thewline' lamp 'L becomes er;- tingu sl'ied. As a turtherresult of the energization of relay 67 1tTd1SCO11I1ECtS the left hand winding ot ring up rela 66 from in ii bridge ofthe tip and ring con uctorsxolthe jack J atarniature'r't), and adarniaturebi) brid es the polarized relay 65 around the con enser associated with the left hand Winding of the repeating coil. WVhen this occurs, the ring cut off relay ofthe connector H (not shown) energizes, 5 thereby connect- In the connector H back bridge rel-a1? 66, up onehergizing over thecalled trun ,re-

verses the incon'iing trunk conductors as regards their connection with the windings of line relay'50. When this occurs, polarized relay3l inthe B operators trunkcircuit O" energizes in the opposite direction, thereby bringing spring-4t3 into engagement with its working contact. Spring 43; upon coniingihto engagement with its'working contact, bridges relay 28across the conductors "25 and by way ott-he working contact of 'arrnature39 and'said'arrnature Relay 28,

upon energizing, opensthe circuit ofrelay 33 at armature 37. Relay 33, upon deenergizing, opens a further point In its circuit at armature 46, and at armature 45 removes lay 31.

The calling subscriber may now converse with the branch exchange operator and the operator, upon learning with which line he desires to be connected, inserts the calling plug P into the jack J of the desired line,

'where'upon supervisory lamp L becomes lighted in series with the cut off relay associated with the said jack J and the said cut off relay. upon energizing, clears the called line of its battery and ground connections.

The operator now signals the called subscriber by throwing her key K to ringing position momentarily, and when the called subscriber responds by removing his receiver supervisory relay 76, upon energizing, places a shunt around supervisory lamp L whereupon the said lamp becomes extinguished, thereby giving the operator answcring supervision. The calling and called subscribers may now converse with each other in the usual manner, the talking circuits being outlined by the heavy conductors, and when the conversation is completed the two subscribers replace their receivers.

When the receiver is replaced at substation A, the circuit of supervisory relay 76 is opened and the said relay, upon deenergizing, removes the shunt from around the supervisory lamp L, whereupon the said lamp becomes lighted.

\Vhen the receiveris replaced at the calling substation A, the circuit of supervisory relay 15 is opened and the said relay, upon deenergizing, removes the shunt from around supervisory lamp L, whereupon the said lamp becomes lighted.

The branch exchange operatornow has a disconnect signal from the called subscriber and the A? operator in the manual oflice has received a disconnect signal from the calling subscriber. Assuming that the branch exchange operator pulls down the connection first, back bridge relay 66 of the connector H is deenergized, its circuit being opened in a manner to be explained fully hereinafter, and reverses the incoming trunk conductors back to normal. When this occurs, the polarized supervisory relay 31. in the B operators trunkcircuit O is energized in the opposite direction, thereby permitting spring 43 to move out of engagement with its working contact. thereby removing relay 28 from in bridge of the trunk conductors 25 and 27. When this occurs, supervisory relay 16 in the cordcircuit 0, upon deenergizing, removes the shunt from around relay 17 whereupon the said relay energizes, thereby closin a circuit for the supervisory lamp L en the said lamp L becomes lighted the operator pulls down the connection. In the present case, however, since the A operator in the manual otfice is handling the call and since-the disconnect signal which she receives comes'from the calling subscriber, it is reasonable to assume that she will pull down the connection before the branch exchange operator takes down her cord.

lVith the assumption as noted above, the supervisory lam L of the cord circuit 0 becomes extinguished and the cut off relay 13 deenergizes when the plug P is removed from the jack'J, and when the plug P is removed from the jack J, the circuit of sleeve relay 29 and relay 28 in the B operators trunk circuit 0 is opened, whereupon the relays 28 and 29 deenergize. Relay 29, upon deenergizing, opens the bridge across the conductors of the trunk extending to the automatic switches, whereupon polarized relay 31 deenergizes and the automatic switches are released in the usual manner.

In response to the release of the connector H, the circuit of switching relay 56 of the line switch C is opened and the said relay, upon deenergizing, connects, up line relay to the trunk conductors 52 and 53. lVhen this occurs, line relay 55 energizes over the bridge across the trunk conductors in the private branch exchange, whereupon the line switch C operates in the usual manner toselect an idle trunk. This, however, is merely an incidental operation at this time. In the private branch exchange, polarized relay is energized in the opposite direction upon the connecting up of the line relay of the line switch C in place of the back bridge relay 66 of the connector H, owing to the conductors 52 and 53 being reversed at the banks of the said connector H. When this occurs, spring 68, upon moving out of engagement with its associated contact, opens the circuit of supervisory relay 75 in the cord circuit 0 and the said relay, upon deenergizing, removes the shunt from around supervisory lamp L, whereupon the said lamp becomes lighted.

The private branch exchange operator upon noting the lighted condition of the lamps L and L. pulls down the connection. When the plug is removed from the jack J super-- visory lamp L becomes extinguished and the cut off relay associated with the said jack J deenergizes. When the plug is removed from the jack J supervisory lamp L becomes extinguished and sleeve relay 67 deenergizes, thereby removing polarized relay 65 from in shunt of the condenser associated with the left hand windings of the repeating coil. When this occurs, the trunk which has been seized by the line switch C, Fig. 2, is freed in the usual manner. The entire,

outlined by the heavy conductors, and when the conversation is completed they both replace their receivers. When the receiver is replaced at substation A the supervisory lamp L becomes lighted in the usual manner.

When the receiver is replaced at the called substation in the automatic oflice, the back bridge relay of the connector in use deenergizes, thereby reversing the current flow in the established connection back to normal, whereupon the polarized relay in the trunk circuit T, opens the bridge across the tip and rin conductors of the jack J 2 at spring 68. W en this occurs, supervisory relay 76 in the cord circuit 0 deenergizes, and the lamp L becomes lighted.

The operator, upon notin the lighted condition of the lamps L an L pulls down i the connection. When the plug Pis removed from the jack J supervisory lam L becomes extinguished and the cut 0 relay of the said jack deenergizes. When the plug P is removed from the jack J supervisory lamp L becomes extinguished and sleeve relay 67, upon deenergizing, opens the bridge across the trunk conductors 52 and 53, whereupon the automatic switches are restored to normal in the usual manner.

The entire connection is now released and the apparatus used therein is restored to normal.

The various features of the invention, having been described and ascertained, will now be pointed out in the appended claims.

What is claimed is:

1. In a telephone system, a trunk termlnating at one end at an operators posltion and at the other end in an automatic switch, a spring jack associated with said trunk at said operators position, said spring jack having a pair of line conductors and a test conductor, a lug havin conductors connected therewith ada ted to connect with said conductors of sai jack when said plug is inserted into said jack, a first relay bridged across said line conductors, a second relay, normally inoperative, connected with said test conductor, circuit connections for operating said first relay over said line conductors in series when said plu is inserted into said jack, means contraled by said first relay for rendering said second relay operative, and means controlled by said second relay for closing a control circuit for said automatic switch over said trunk.

2. In a telephone system, an A o rators position, a B operators position, means whereby an operator at said A position can extend a connection to said B osition, means including automatic switch- 1ng mechanism whereby an operator at said B position can extend the connection on toward a called subscriber, means responsive to the connection being extended to said B 3. In a telephones stem, two manual switchboards, a trunk ine connecting said switchboards, a signal at the second switchboard, a si nalling machine, means for operating said signal and for connecting said machine to the trunk line when the same is taken for use by an operator at the first switchboard, the said machine bein effective to transmit an audible signal to t e calling 0 erator, a listening key at said second switc board, and means responsive to the actuation of said key for disconnectin said machine from the trunk line to noti the calling operator that the other operator is listening.

4. In a telephone system, a trunk line extending from a jack to an automatic switch, a relay for closing a bridge across said trunk line to operate said switch, a plug adapted to be inserted in said jack, a circuit for said relay including the sleeve of said plug, a second relay for closing said circuit, and a circuit for said second relay including the tip of said plug.

5. In a telephone system, a trunk line extending from a jack to an automatic switch, a relay for closing a bridge across said trunk line to operate said switch, a plug adapted to be inserted 'in said jack, a circuit for said relay including the sleeve of said plug, a second relay for closing said circuit, a cord circuit terminatin in said plug, and a circuit for said secon rela including the tip and ring strands of sai cord circuit in series. r

6. In a telephone system, a manual exchange and an automatic exchange, a dialling operators position at the manual exchange, atrunk line comin from the subscribers switchboard in t e manual exchange and extending through the dialling position to an automatic switch in the automatic exchange, means whereby a manual exchange operator can signal the dialling operator when an automatic exchange connection is wanted, a supervisory signal controlled over the two side! of'said trunk line in series by the response of the dialling operator to notify the manual exchange operator thereof, means whereb the dialling operator can control said switch and other switches to complete the desired connection, and means whereby the dialling operator can disconnect herself from the trunk line before the called subscriber answers without affecting said supervisory signal.

7. In a telephone system, a trunk line comprising two inductively connected sections. operators equipment at the junction of said essen sections, a relayenergized responsive ,to

the answering of a call over' the first section of said trunk'line bytheop'eratjor, alocking circuit for saidrelay, contacts on said're'lay tor closing a bridge across the first 'section,

means controlled by the operator l'orcoun pleting the connection over the second section, a relay controlled by the'response of the'called party for closing a second'bridge across the first section, a relay in said second bridge, an'd contacts on said last mentioned relay for opening said locking en-'- cuit. 1

8 In a telephone system, manual switchboards, atr'unk line connectingsai'd switchboards, a signal at one of said switchboards, means for operating said signal, a' relay for connecting said signal operating means to'the trunk line when the same is taken for use by an operator at one oi's'aid SWltClb boards, a listening key atanother of said switchboards, and means responsive to the actuation of said key for disconnecting said signal operating means from the trunk line to notify the calling operator that the other operator is listening.

9. In a telephone system, a trunk line connecting two exchange-s, a relay having one terminal connected to one conductor of said trunk line and the other terminal connected to battery, means for establishing a circuit for said relay including only one talking conductor of said trunk line and ground return when a call is being extended over said trunk, means for establishing a metallic circuit for said relay including both conductors of said trunk line, call and supervisory signals, means for controlling said relay over one of its circuits to control said call signal, and means for controlling said relay over the other of its circuits to control said supervisory signal.

10. In a telephone system, a two way trunk circuit terminating at one end in a jack and at the other end in a set of bank contacts, an automatic switch for extending a calling line by way of said contacts to said trunk circuit to extend a call there over in one direction, said switch including means for applying ringing current to said trunk circuit, a plug ending cord circuit for exten-ding a calling line to said trunk circuit by way of said jack to extend a call over said trunk circuit in the other direction, said cord circuit including means for supplying talking battery, and a relay normally bridged across said trunk circuit, said relay energized by said ringing current responsive to the extension of a calling line in said one direction and energized by said talking battery responsive to the extension of a calling line in said other direction.

11. In a telephone system, a two way trunk circuit terminating in a jack and bank contacts, automatic switches for connecting a calling line by way of said contacts to said trunk circuit at one end, aplugendingcord circuit tor connecting a calling line to said trunk circuit by way ot' said at]; at theother end, a relay normallybridged abross said trunk circuit and energized responsive "to the connection of a calling line to said trunk "switchboards, a trunk line including a sleeve conductor connecting said switchboards, a call lamp at the second switchboard,arelay at the second switchboard connected to the sleeve conductor of said trunk Ilneand normally shunted, a cord circuitat the first switchboard for extending a connection to said trunk line, and means responsive to the extensionoi said conncction tor removing said shunt and allowing 'said relay to ener gize to light said lamp.

13. In a. manual to automatic trunk circuit, a source of signalling current, a relay energized responsive to the seizure of the trunk at the manual end for connecting said source to the trunk, a dialling key, and a second relay energized responsive to the actuation of said key for disconnecting said source from the trunk.

14. In a manual to automatic trunk circuit, a source of signalling current, a relay energized responsive to the seizure of the trunk at the manual end, for connecting said source to the trunk, a dialling key, a second relay energized responsive to the actuation of said key for disconnecting said source from the trunk, and a locking circuit for said second relay controlled by said first relay.

15. A manual to automatic trunk extending from a jack to an automatic switch, a relay energized over the sleeve of said jack, a call signal operated over a circuit controlled by said relay, a dialling key inserted in said trunk, a second relay energized responsive to the actuation of said dialling ke' and contacts on said second relay for su stituting the said second relay for the said signal in the circuit controlled by the first relay whereby the signal is deactuated and the second relay is looked under control of the first relay.

16. A manual to automatic trunk extending from a jack to an automatic switch, condensers in series with the talking conductors of the trunk between the jack and the automatic switch, means responsive to the establishment of a connection to the trunk by way of the jack for establishing a direct current bridge across the ends of the talking conductors terminating in the automatic switch, an operators headset and dialling equipment, a combined listening and dialling key, for splitting the talking conductors at a point between the condenser and the automatic switch, means controlled by said key for connecting the dialling equipment across the end of the trunk terminating in the automatic switch to operate the switch and for connecting the operators headset across the other end of the trunk, and means controlled by the key for establishing a direct current bridge across the end of the trunk terminating in the plug.

17. A manual to automatic trunk extending from a jack to an automatic switch, condensers in series with the talking conductors of the trunk between the jack and the automatic switch, means responsive to the establishment of a connection to the trunk by way of the jack for establishing a direct current bridge across the ends of the talking conductors terminating in the automatic switch, an operators headset and dialling equipment, a combined listening and dialling key, for splitting the talking conductors at a point between the condenser and the automatic switch, means controlled by said key for connecting the dialling equipment across the end of the trunk terminating in the automatic switch to operate the switch and for connecting the operators headset across the other end of the trunk, means controlled by the key for establishing a direct current bridge across the end of the trunk terminating in the plug, means effective upon the actuation of the key and establishment of the last named bridge for maintain- .ing saidlast named bridge upon the restoration of the key, and means effective upon the answering of the call set up over the automatic switch for opening said last mentioned bridge.

In witness whereof, I hereunto subscribe my name this first day of March, A. 1)., 1922.

BERNARD D. YVILLIS.

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