US1585652A - Telephone system - Google Patents

Description

May 25 1926; 1,585,652

H. D. CURRIR ET AL TELEPHONE sYs'TEM Filed April 2'7. 1921 3 Sheets-Sheet l May 25,192@ www v H. D (SUFE ETT M..

TELEPHONE SYSTEM I5 @met-Smet 2 iled April 27 1921 Mw- 25, w25 1,585,552

H. Q. CLURFER ET AL TELEPHONE SYSTEM 3 Sheets-Sheet 'S wanted number.

Patented liflay 25, i926.

narra my I-IIRAM D. CURRIER, OF CI-ICAGO, AND GEORGE R. EATON, OF OAK PARK, ILLINOIS, ASSIGNORS TO KELLOGG SWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLI- NCIS, A COR'EORATION 0F ILLNOIS.

TELEPHON E SYSTEM.

Application filed April 27, 1921. Serial No. 464,814.

l0 In the system of our invention we have abandoned the former practice which involved n. operators who'would place the1nselves in communication with a B operators head set over an order wire to transmit the An A operator at the originating ofiice would then receive the assignment of the trunk being used by the 3 operator at the distant exchange and would insert the calling plug of her cord '0 pair into the trunk thus assigned to her,

the B operator in the meantime having inserted the plug of the trunk into the jack of the called line.

In the system embodying our invention, the A operator reaches the B operator by inserting the calling plug of her cord pair into a trunk jack, which insertion starts switching mechanism that automatically extends the call to an idle operator at the distant exchange, and when this has taken place the A operator is in direct connection with the B operator. This arrangement permits us to do away with B operatorsr in the sense of operators who handle trunk connections only, and all the operators in the system put up local connections and also serve as B operators, as they also receive calls extended from distant exchanges and complete the connections required for such calls.

A feature of our invention is the provision of means'such that when a trunling call has been completed from a calling subscriber in one exchange to a line of a called subscriber in a distant exchange, the interoflice trunk is released so as to vrender it available for use immediately upon the conclusion of conversation due to the replacement of the receivers at the respective substations.

Another feature of our invention is the provision of means whereby the replacement of the receiver at the calling substation immediately operatively disconnects his line from the connected cord, and the replacement of the receiver at the called sub` station will then operate means to bring about the restoration of the switching mechanism used in extending the connection from the exchange originating the call to the distant exchange. This gives the subscriber at the calling substation instantaneous disconnect, and the replacing of the receiver at the called substation instantly disconnects the trunk from the cord at the originating exchange, thus preventing the trunk that was used from being tied up.

The above features as described, as well as others, will be more fully hereinafter described in the ensuing specification.

Referring now more in detail to our invention as illustrated in the accompanying drawings, we show A circuit diagram consisting of parts l, 2 and 3, which diagrammatically illustrate our invention.

Referring first to part l, we have illustrated a subscribers telephone substation terminating in a line circuit L and a cord circuit B suitable for interconnecting local subscribers7 lines within one exchange. The said cord circuit B may'. also be used for trunking calls to distant exchanges, and

`when its calling plug CP is inserted in a rtrunk switch jack 67 (referring now to partv 2), the automatic selecting switches C and D are set into operation to extend the call over the inter-office trunk wires a; and y, and extend it to the distant exchange E (part 8), and also directly connect the operator at the originating exchange with some operator at the distant exchange who is not busy at the time, that is, one who is not busy at the time establishing either a local or a trunk connection, for it is to be understood that at exchange E the operator will be provided with local cord circuits B in addition to a number of trunk circuits lll.

rlhe system as a whole, therefore, may consist of two exchanges B and E, at which the operators will have identical equipment, that is, a suitable number of local cord cir` cuits B, such as shown in part l, and also a suitable number of trunking cord circuits E, such as shown in part 3. Furthermore, before each operator will be suitable trunk jacks 67 connected with switchpairs, such as C ard D, so that any operator at any Cil lll

: Les

exchange can in addition to establishing local connections pass trunk calls to distant exchanges, as well as receive trunl; calls from such distant exchanges.

To describe the various instiunientalities in a general way, at A we have shown a common battery subscribers local substation connected at the exchange with a usual form of line circuit L comprising a line relay LR, a cut-oli relay CO, together with multi ple line lamps LL and jacks el. rEhe operators cord circuit B shown in part 1 coinprises an answering` plug Al3 and a calling plug Cl) connected by talking wires, which are indicated by the heavily marked lines. It is provided with answering and calling supervisory signals and the necessary relays for .controlling them, and Vwith suitable relay apparatus for providing the various features now considered necessary to a modern manually operated telephone switcliboard, such as secret service, automatic ringing, instantaneous disconnect, line lamp recall, etc.

The apparatus for transferring trunlring calls from one exchange to another includes a number of spring jacks 67 at each operators position which terminate in niultiple contacts located in nuniber et :tinde switches as C, and one of these will automatically select a jacl; 67 in which an operator has inserted a plug, such insertion serving to initiate the travel ot an idle switch C. lVhen the switch C has com pleted its operation, the switch D at the distant exchange will be set in motion, and it comprises suitable magnets, relays and oil-normal springs to eitcct the automatic selection of an idle trunk cord of the kind shown at E in part 3.

The latter has vbut a single plug 167, to which ex end the talking conductors indicated by the heavily marked lines, and suitable relay instrumentalities and circuits for testing, ringing and supervising at the exchange lil, and also for extending` the required signals back over the trunk line to the originating exchange B.

A incre complete understanding of the precise arrangement of the parts and their operation, one with the other, will he obtained 'from the following description ot operation.

le will lirst assume that a subscriber at A desires to converse with a called subscriber at F, the latters line terminating in an exchange distant 'from exchange l to which the calling subscriber belongs. rlhe removal ot' the receiver at A energizes relay LR, lighting lamps LL, which lamps are distributed at various positions in 'the switchboard. An operator seein the lanip at her position displayed, will insert the answering plug AP in a jack l of the ing line, and relay 16 instantly energizes by current through its two windings, normal Contact Il, the sleeve contacts ot the connected plug and jack and through cut-oil relay CO to ground, the latter also energizing and clearing the line 'for talking, as well as putting out the lamps LL by deenergizing the line relay LR. The relay 16 upon energization closes its contact 18 to shunt out its high resistance upper winding so that it another operator has plugged into another jack of the line oit A, such other operators relay 16 will tail to energize because ol the shunt established by the lov.' resistance winding at the lirst operators relay l6, and the second operator will no response when she asks for the number and will withdraw her plug. The operating relay 16 of the first cord by its closure ot contact 19 energizes listening relay 7 by current flowing to ground at Contact 35 of relay 34e and relay 7 upon energization closes its cont-acts 9 and 10 to connect the operators telephone set O to the calling line, and she now inquires and learns the number ot the wanted subscriber. Furthermore, by the operation ot relay 16, due to the closure ot its alternate contact 17, the supervisory relay 12 has been cut across the calling line, supplying talking current thereto, and by the opening ot its contact 141 prevents the premature display oi" supervisory signal 15, while the closure ot contact 13 actuates counter relay 53, resulting in the actuation olt magnet 551. to count a call as answered by the operator. rlhe operator at B learning hat theI line oit' the wanted subscriber erniinates at the exchange E, will now insert calling plug CP into spring jacl: 67, such spring jack being assigned tor calls to be extended to E, and she will first have actu ated lier cut-outlrey Gli to close its contacts e6 and 4-7. The insertion ot' the calling plug C? into the trunk jack 67 has established an energizing circuit for the sleeve rclay traced from battery through the winding ot relay conductors 21)() and 26?., the sleeve contacts ot connected plug Cl.j and trunk jack 67, through the winding of relay 66 to ground. A parallel circuit is also established tor relay 36 over which circuit the said relay energizes. The circuit may be traced from battery through -the winding ot relay 36, conductor 262, normal Contact 202i of relay Q04, and over conductor 201, sleeve contacts ot' the plug CP and jack 67, to ground through relay 68. As a result the relay 68 energizes and sets in travel the switch at C by closing its contact 69, which grounds starting wire SV (which extends from switch C a common wire to all relays 68 connected with spring jacks 67 adapted to be selected by the switch C). Current will now flow 'from battery through the resistance r, the winding of motor inagnet MM, normal contact 220 of olli-normal contacts ON, normal contact 83 of relay 79, conductor SW, normal contact 7 3 ot relay 72, and to ground through contact 69 0i" relay 68. The magnet MM will energize and Cle-energize over this circuit to step the switch wipers 75, 76, 77 and 78 a step from normal into engagement with the first set of contacts in search ot terminals oi" the spring jack 67, in which the plug CP has been inserted. @n the first step the oilnormal springs ON are shifted to their alternate positions and successive actuations of magnet MM are produced by its armature over a circuit through the alternate contact 220 of oft-normal contact GN, through contact 82 to ground at normal Contact 87 of relay 84. Such actuations ot magnet MM will continue, each actuation causing a step ot the wipers 75, 76, 77 and 78 until they engage multiple jacks in their banks connected to a jack 67 in which a plug CP has been placed, and which has not been already selected. As soon as this occurs the motor magnet MM will be shunted, preventing its further actuation, and this shunt may be traced 'from battery through the resistance r, the low resistance upper winding ot' relay 84, its normal contact 221, normal contact oi"l relay 79, through wiper 75, its engaged bank contact and through normal contact 74 ot' relay 72, and alternate contact 70 ot relay 68 associated with the spring jack 67, to ground. The relay 84 attracts its arma.- ture to open its normal contact 87, and to close alternate contact 87 thereby opening the circuit ot magnet MM, and the closing of alternate contact 87 elnergizes relay 7?, and the closing ot alternate contact 86 oi: relay 84 connects the high resistance/lower winding of said relay 84 in series with its upper winning and the said relay 84 locks to ground at 71, the circuit being traced from battery through resistance r, the upper winding of relay 84, its alternate contact 86., through the lower winding of" relay 84, wiper (6, through relay 72, to ground at alternate contact 71 of relay 68. The relay 72 energizes over this circuit and opens its contact 74 so that no other switch whose wiper 75 engages a multiple ot the seized contact will stop, while the opening` ot contact 73 keeps ground olt the starting wire SlV, so that when relay 79, which is new energized, closes its alternate Contact 83, the starting wire SW is extended to starting wire SW', which extends to another finder switch in the usual manner. The relay 79 having energized las above described, locks itself to ground at alternate Contact 222 of off-normal contacts ON through its alternate contact 61.

By the closure of contacts and 88 ot relay 84, the relay 94 in the distant exchange has had its windings connected across the trunk wires and y, and current Hows from closure of Contact battery through the upper winding of 94, normal contact of relay 89, over the heavily marked talking conductor via the tip contacts ot the jack 6'7 and plug CP, the alternate Contact 46 01" key CK, over the common wire to ground through the winding oi the relay 55, while another circuit is established from battery through the other winding ot relay 55, the alternate Contact 47 of key CK, through the ring contacts of the plug CP and jack 67, over the talking' conductor, and through normal Contact 98 of relay 89 and through the lower winding' of relay 94 to ground, it being remembered that at the time the operator at B inserted the calling plug CP into the jack 67, she actuated her cut-olin key CK to close contacts 46, 47 and 48. As a result the relays 94 and 55 'both energize, and itis to be understood that the relay 55 is common to all cords of a position. Vfhen the operator lirst actuated her cut-out key CK, the 48 energized the relay 57, with the result that a tone from the constantly operating interruptor mechanism 61 was transmitted via contacts 58 and 56 into the operators head telephone through the winding 66 of her induction coil, and she thus had an audible indication which vas terminated when the relay 55 was energized as just described, because the opening of contact 56 interrupted the tone circuit. By the cutting olf ot this signal she knows that thel switch C has properly performed its function and has extended the call over the wires m and r/ to the distant exchange and that the switch D is starting its travel.

rEhe starting of D is effected by the energization of relay 94, which by closing Iits alternate contact 95 energizes motor magnet MM by current from battery through the winding of magnet MM', normal contact 103 ot relay 102, normal contact 225 of otl'- normal contact-s ON to ground at alternate Contact 95 of relay 94, and said magnet by a suitable pawl and ratchet mechanism steps the wipers 104, and 106 one step from normal to engage the i'irst set of contacts leading to a trunk circuit, such as that shown at E. Upon thistirst step the contacts ON are shifted to their alternate position, and it the irst contact engaged by wiper 104 is a busy contact, it will be grounded, the manner of such grounding to be later explained. The result is that in the case of such grormded contact a circuit will be established from battery through relay 102, the alternate Contact 226 of magnet MM', Contact 97 of relay 96, Contact 91 of relay 89, through the winding of relay 101, and the wiper 104 to the `engaged busy contact and to ground. Consequently, relays 102 and 101 energize, and the latter is ot' slow release construction so that rapid interruptions ot its circuit as the switch travels are not ellective to cause its armature Contact: to restore. The opening of normal contact 103 ot relay 102 de-energizes magnet lilhl, whose retracted armature opens contact 226, which in turn cle-energizes relay 102, whereupon magnet M111 instantly is again energized by currentthrough the now closed Contact 103 of relay 102, the alternate contact 2255 olf ON, contacts 97 and 91 of relays 96 and 89, through the relay 101, through the wiper 104 and the engaged grounded contact, whereupon inagnet MM steps the wipers another step, and by the closure of its alternate Contact will again energize the relay 102 over the previously described circuit to wiper 10sL and now to ground at the next engaged oontact. if it is busy. Thus a seesaw action between relay 102 and magnet MM is produced, the slow relay 101 being in the circuit ol' whichever one o1E the other t-wo is energized, and this seesaw action will continue until the wiper 10-1 engages a contact in its bank which leads to a trunk line in the exchange E which. terminates before an operator who is not busy, that is, who is not busy establishing either trunk or local connection. when an Iidle Contact is engaged by the wiper 104tthe seesaw action terminates because the engaged Contact of such a trunk line will be characterized by a freedom from ground. lli/'hen this occurs the circuit will remain open through the slow relay 101, whose armature will retract, and the closing of its normal Contact closes an energizing circuit for the slow release relay 89 'trom battery through the winding of relay 89, normal contact 9S of relay 96, normal contact 227 ot rela-y 101, to ground through the shifted oil-normal contact 22S. Upon energization of relay 89 its contacts 90 and 93 assume their alternate position, closing` a circuit from battery thro-ugh relay o5 at B, over the lower heavily marked talking conductor to the right through wiper 106 and its engaged idle contact, through winding c oi the inductionl coil. at E, in series through the two windings of relay 107, through windingl L of the induction coil, to the left over the heavily marked talking conductor, and through the left-hand winding of relay to ground. rllhis energizes relay 107, and the closure of its alternate contact 10S energizes relay 110 from battery through relay 110 to ground at alternate Contact 106 of relay 10T, which relay 110 closes its colitact 11-1- and grounds the Contact engaged by the' wiper 10/1 or the switch B, the result being that relay S9 at D by its alternate contact 91 locks to ground via relay 101 at contact 1111-. lllhen relay 69 li operated the closure oit its contact 92 energized the relay 96.` which was immediately locked t0. ground to the olif-normal Contact 228, via

its alternate contact 99, and said relay by opening its normal Contact 9S opens the initial energizing circuit ol' relay 89, but the latters slow release construction causes it to hold its armature in operated position until the substitute circuit tor it was established, as just described. The opening ot normal contact 97 oit relay 90 has effectively prevented any reoperation ot motor magnet MM until the relay 96' cle-energized, which can only happen after the switch D restored to normal, and the contacts ON are consequently shil'ted to their original or normal position.

ileiferring now to the apparatus at E, the relay (which energized as the result ot the closure ol: contact 108) closes an energizing circuit for relay 109 from battery thi-ouch re ay 109 to ground at alternate contact or relay 110, and also closes a circuit for relay 116 from battery through relay 116, n rinal Contact 126 of relay 122 to ground at alternate Contact 11.5 of relay 110, and the closure of alternate cont-acts 111i" and 121 of relay 116 connects the operatcrs relay 158 across the talking conductors, and said relay 158 energizes by current ,i the windings oli relay at B, over which obvious 'from the preceding r1hr-.s the operatoris talking is directly connected in circuit with olf the operator at 13 through the allertz 59 and 60 of relay at ll.

i, at B now tells the operator at E the number ot the subscriber wanted, and the latter plugs into a spring jack of the wanted line, having first tested it in the usual way and 'found it idle.

1t will be observed that upon the energization ot' relay 110, the signal lamp 152 was lighted by current flowing through Said lanip 152, normal contact 136 of relay 132%, to ground at alternate contact 112 of relay 110, so that the operator at E knows which ot her trunk circuits is to be used in establishing the connection. The relay 116, in addition to cutting the operators telephone relay 158 into circuit, closes its armature contacts 118, 119, to ground, and it is to be understood that the short wires iudieated at its alternate contacts are connected to the private terminals ol all trunks belonging to the operator-s position whose head telephone is new cut into use, so that as long as the relay 116 remains energized, no otiier switch D can connect etllectively with any trunk assigned to the said operator.

Furthermore, we have illustrated at H a relay 116a which, it is to be understood. is a relay corresponding to 116 but belonging to another cord ot the saine operators position, and this in conjunction with 116 shows clearly tie exact wiring` of this part of the system, as well as an additional local cord feature which will now be briefly described.

lt has been already stated that the operator at B is provided with incoming trunks like that illustrated at E, and the operator at E not only has incoming trunks but is provided withlocal cord circuits like the one shown at ll, and it is to be understood that the wirii'ig and inter-relation of the local cord circuit and trunk cord circuits at the various operators positions in both ei;- changes are exactly alike. Now, the relay 7 shown at ll is to be understood to be the relay 7 ot a local cord circuit such as shown at B but located at E. lts switch contacts 166 are omitted for convenience in B, but

it will be understood from this diagram at,

ll that whenever the listening relay 7 oic any loc-al cord circuit is energized to cut in the operators head telephone its contact 166 is closed to ground and places ground upon a common wire. r1`his common wire has branches extending to battery through all the relays 116, 116, etc., ot the trunk circuits at this particular operators position, and the result is that when the oper-- ators telephone set is cut in on a calling line by means ot any relay 7 of any of her local cords, all the relays 116, 116, etc., of the trunk circuits oil her position will nef-- essarily be energized and will guard lthe private contacts ot her trunks at the switches l) from heilig selected so that it is quite impossible for her telephone set to be connected in on two different calls at the same time. Thus, it is made sure that a trunl: call will only land at the position o1 an operator whose telephone set is idle at the time the switch D engages the trunk.

`We lett the operator at E just having ze ceired the number ot' the called subscriber from the operator at B. 'lhe latter now restores her cut-out key CK, with the result that the windings of the calling supervisory relay CSR are substituted in the circuit with relay 107 in place of the windings ot the relay 55, and the relay 57 is cle-energized by the opening of contact L18, cutting oil the operators head telephone, and it is to be observed that when plug CP was lirst inserted in jack 67 the operation ot relay 34; cle-energized the listening relay 7, disconnecting the operators head telephone at that point, so that it is now entirely tree ot the connection. i

The relay GSR, although it now has ourrent `flowing through its windings, is not energized sulliciently to shift its contacts 32 and 33, due to the high resistance of the windings of the relay 107 at E, so that at this time the calling supervisory lamp sig-- nal 28 remains operated by current from battery through said lamp 28, normal contact 26 ot relay 22, normal contact 3 ot relay 1, contact of relay 29, contact 320i relay CSR, to ground at alternate contact of relay 34.

The operator then having found the called i line idle, inserts her plug 167 in a 'multiple jack J of the wanted line, thus closing an energizing' circuit for relay 122 in the trunk circuit and of cut-oil relay C0 ol1 the called line circuit, from battery through relay 122, sleeve contacts of the plug 167 and jack J', to ground through the winding of relay CO, and relay CO energizing clears the line. ltelay 122 upon energization opens its normal contact 126 to cle-energize relay 116, whose retracted contacts 117 and 121 disconnect the operators head telephone 168, while its other contacts 113, 119 and 120 unground the terminals of the other idle trunks at the position, rendering them selectable by switches D. The master ground Contact MG at 122 in now closed energizing the relay 133 by current from battery through the upper winding o1 relay 133, its normal contact 135, alternate contact 113 ot relay 110, to the master ground at relay 122, and the opening of contact 136 of relay 133 puts out the signa-l at 152 and closes a locking circuit for relay 133 through the lower winding from battery through its lcwer winding, alternate contact 136 to ground at alternate contact 112 ot relay 110. A. locking circuit is also closed through the upper winding of relay 133 from battery through the upper winding, its alternate contact to ground at the master ground MG or relay 122. The closure of contact 137 of relay 133 operates the countermagnet 157 through contact 139 of relay 138, to count a complete trunk call for the operator at E and relay 138 is immediately energized to ground at alternate contact 137 olf relay 133 and thereafter opens its contact 139 to prevent any possible reoperation ot the counter magnet.

Assuming that the substation F has a harn'xonic bell, the operator will now actuate one ot the ringing key buttons of the ringing key RL to close the contact 155 of the ringingkey button, and will select the one ica connected to the generator of *proper trequency, and in so doing will momentarily close the end spring contact 1511, which latter spring will energize relay 14;() by current trom battery through said relay lflO, end spring 1541, normal contact 132 oi" relay 130, to ground at MG of relay 122, and the relay 140 by the closure of its contact 142 closes a locking circuit tor itself Yfrom battery through relay lei-O, its alternate contact 142, normal contact ot relay 149, through normal contact V32 et relay 130 to ground at MG ot relay 122. The closing of contact lill oli relay lfl-.O connects the constantly rotating interruptor 159 in circuit with relay 1H, 'from battery through relay 11th-alternate Contact 141, alternate contact 111 of relay 110 to ground through the interruptor 159, and relay 11111 will be alternately enerated although the end Contact 154 restoresu as soon as the operator removes her hand 'troni the button), the Winding ot the relay 1119, alternate contact 147 ot relay 14d, tip contacts of the plug 1,07 and jack el", through condenser and call bell at the substation, back through the ring contacts ot' the jack J and plug 167 and to battery at alternate contact 1&6. Should the called subscriber at substation F reniove his receiver during a ringing interval, the slow release relay 1419 will receive enough current to actuate its armature to open its norinal contact 150, and this will -de-energise relay 140 by opening its locking circuit, and the relay 1&4 will have its connection with interrupter 159 opened at contact 141 of relay 140 and will remain cle-energized so that kringing current will no longer bev applied to the called line. is soon as normal contacts 140 and 14T ot relay lill are closed after the subscriber removes his receiver, =or it' they are closed at the tiine he does so (the contacts being in this position during a silent interval), the relay 127 is energized by current :trom battery through its low-er Winding, through winding d oft the induction coil` normal contact 146 of relay 144, through Ithe ring contacts ot the plug 167 and ack J, theclosed -sWitchhoolr contacts at F, bael: through the tip conta-cts of the plug 167 and jack el', normal contact 14:7 ot relay lst-4l, alternate contact 123 ot' relay 122, Winding Z and through .the upper winding of said relay 12'? to ground. The closure of contact 128 ot relay 127 now energizes relay 130 by current troni ground at MG^ ot' relay 122, alternate cont-act `12S ot relay 1.27 and through relay .1S-l0 to battery, and said relay 130 byY its contact 131 locks itself to said ground at MG of relay 122, and the opening oi contact 182 oit' relay 130 cuts oit all the ringing key apparatus and relays definitely from the ground hlG ot relay 122. The closure ot contact 129 ot relay 127 has short-circuited .the high re sistance upper Winding ot' the relay 107, so that the resistance in the path ot' the eurrentrllowing through the windings of relay CSR at B is very substantially reduced, and the result is that said relay CSR .new actuates its armature, and the opening of its contact puts out lainp 28 at B so that the operator in the originating exchange is thus signaled that the called subscriber at the distant exchange has answered his call.

Relay CSR upon energiaation closes its alternate contact 32 to Vestablish an energizing circuit for the relay 204, traced 'from battery through the Winding ot said relay .204, conductor 205, alternate contact 2li. ol' relay lfll, conductor 206 to ground at alternate Contact 35 ot relay 3l. 'lhe relay 204C upon energization closes a locking circuit for itselt which may be traced troni battery through the winding ot relay 20e, it alternate contact 207, conductors 20S and 20H to ,ground at alternate contact 235 oi" relay let. The relay 36, as will be remembered, was energized over a parallel circuit with relay 3% upon the insertion ot' the ca plugCP into the trunk jack 67 and said circuit ot relay 3G although in parallel with relay B-/l passed through the normal Contact ot relay 20a and was therefore initially controlled by the calling plug Gl), 'lhe relay 204 upon ene' ation opens its noi-rial contact 203, opening the initial energizi C circuit ot the relay 30, but as relay CHR is energized soon as the call ad subscriber answers, a substitute circuit is established for the said relay 30 which is traced troni battery thro-ugh the winding ot relay 25o, conductors 202 and 209, alternate contact 'lrl ot rela-y CSR, conductort4 210 and 201, to ground through relay 08 over the path previously described. The control ot .the relay `3G now under the called subscriber, for purposes as Will presently be described.

The subscribers at A and F are now in conversational circuit, 4the talking circuit being' traced from fr .to l? over the heavily marked conductors, the transn'iitter ol the substation at receiving current thro h the windings or' relay 12, while the `t' `f niitt-er at ll receives its current through the windings ot relay 12?.

llilhen the subscribers have tinished con versation, they replace their receivei and we will assumo that the subscriber at substation A. ot exchange B does so first. le consequently opens the circuit ot' his answering supervisory relay 12, and the lamp 15 is displayed by current through nornial contact 14, alternate contact 20 oit relay 10, to ground through alternate contact 35 ot relay Furthermore, the link -disconnect relay 1 is operated by current through it and traced from battery through relay 1 to ground at contact over the path just described for lainp 15, and relay 1 upon eneilgizatiou closes its alternate contacts 2 and 6, .thus opening up the talking conductors of the cord strands; and the opening Aot its alternate contact Al places the sleeve 4contact ot' the plug on open circuit, thus removing the busy test troni the multiple jacks J of the line ot A., and in so doing the cut-oil: relay CO is cle-energized tov again place the line relay LR under the control of the substation. rlhe closure of alternate contact 1l ot relay 1 maintains the relay 10 operated, however, a tute subs i,

locking circuit for said relay 16 bein'g traced through contacts 18, 4, 20 and 35 to ground.

'lhe called subscriber replacing his receiver brings about the cle-energization oi relay 127 and the relay upon restoring to normal opens its alternate Contact 129 to remove the shunt from about the upper high resistance winding ot relay 107, and this shunt removal again connects the two windings ot' relay 107 operatively in series with the relay CSR at B. Due to the high resistance of the windings ot relay 107, relay CSR now does not receive sutiicient current, and there'i'ore restores. rlhe relay CSR upon restoration opens its alternate Contact 33, which interrupts the circuit of relay 30, thus wholly disconnecting the said relay 36 'from the sleeve strand ot the cord circuit. The relay 3G upon restoration opens its alternate contacts 37 and 40, interrupting the talking conductors of the cord circuit.

Should the called subscriber at suhstation F at the distant exchange have been the iirst to replace his receiver, the operation olt the. circuit under his cont-rol would be the same just described, and the later replacing oit the receiver at the calling substation A would operate as already described.

It will be seen that as soon as the relay 36 is cut oli from the sleeve strand of the cord, the only battery connection to said cord strand is through the winding of relay 34, which relay is ot very substantial resistance, tor instance, 7000 to 7 500 ohms. Current continues tlowing through said relay and through the sleeve contacts of the plug CP and jack 67 to ground, through relay 68 at C, and this current is sutcient to maintain the relay 34 operated, but the relay 68 owing to its relatively inei'ificient construction and the adjustment of its armature, allows its armature contacts to be opened, and this results in the restoration of the switches C and D as follows: The opening of contact 71 ot relay 68 opens the locking circuit of relay 84, which delenergizes and in so doing opens the talking wires extending to wipers 77 and 78 at its Contact and 88, and by closing ot its normal contact 87 e-nergizes release magnet RM by current from battery through Riti through alternate contact S2 of relay 79, to ground at normal Contact 87, and said release magnet RM withdraws the retaining pawl of the switch and the wipers are spring-restored to normal. The opening of contact 71, of course, has cle-energized relay 72, while the restoration to Zero of the switch has placed contacts CN in their normal position, and all the mechanism at C is now at normal.

On the opening oi contacts 85 and 8S, the

relay 107 at E has its circuit opened, and consequently is cle-energized. The retraction of the armature ot relay 107 opens the circuit of relay 110 at contact 108, which deenergizes relay opening' its alternate contact 115 deenergizintg the relay 109. The opening` of contact 114 ci relay 110 removes ground from wiper 104 at E, and as the relay 109 is relatively sluggish to restore, it will keep its contact 230 open long enoulgh to insure the restoration of relay 89 at D to allow its armature to tall back, whereby its contacts 90 and 98 place the talking wipers 105 and 100 on open circuit, ing ot normal contact 92 closes an energiz ing circuit for the release magnet R34 traced from battery through said magnet, contact ci relay 90, normal contact 92 of relay 89, to ground at alternate contact 228 of ofi-normal contacts CN, and said magnet RM, upon energizing, withdraws the retaining pawl and the wipers 104, and 106 of the switch D are spring-restored to their Zero point, at which time the contacts ON are restored to normal, and the opening of Contact 22S opens the circuit of relay 96 and magnet RM', whereupon said relay 9G and magnet RM cle-energize and the apparatus of the switch is resto-red to normal.

it is thus seen that when the two subscribers have finished conversation, the replacing ot the receiver at the calling substation instantly disconnects his line from the cord circrut due to the energization of relay 1, as alreaoy described, irrespective of the wit-hdrawal of the plug AP. rlhe replacing ot the receiver at the called substation F at the distant exchange, irrespective of the replacing ot the receiver at the calling substation A caused relay CSR to deenergize, and the relay CSR in turn opens the circuit oit relay 3G, which relay upon restoration severs the cord conductors at the calling end irrespective of the withdrawal of the plug CP, thus instantly disconnecting the conductors from the trunk jack 67, which brings about the release ot the two switches C and TD, rlhis is very important inasmuch as it trees the trunk wires ce, y, which extend from one exchange to another (usually involing a very substantial investment in capital), so that the freeing et them and the rendering ot them promptly avail able 1"or another connection is an item of the great st importance in the economical operation of a telephone system.

Theeperator at B seeing the signal lamps 15 and displayed, withdraws the plugs il? and CP trom the respective jacks .l and 07, `and the withdrawal of plug' CP de-energined relay 34 and the opening of its contact de-energizes'relay 1, and the apparatus and cord circuit are at normal.

110, the latter relay 110 in while the clos- 'i' lil() The de-energization of relay 110 at E, as above described, results in the lightinget `the supervisory lamp S, from battery through the lamp S, alternate contact V125 ot relay 122, to ground at normal Contact 112 ot relay 110, and the operator at E observing the signal withdraws the plug 16'? to cle-energize relay 122 of the trunl; cord E, and the relay 122 now restoring opens its master .ground contac-v lilll, and the lapparatus of the trunk cord is placed at normal, while the withdrawal. of the plug; 167 has restored the line circuit et' called substation F by de-enero'izing eut-olf relay CO. It will be obserifed that in the preceding description of the oirieration of the cord eircuit B When used for a. trunkinl all, the signal lamp Q8 remained lighted While the called for subscriber iras being rung, the circuit of said lamp being traced through contacts' 2G, 3, 3G, to ground at relay 'illus was eiiectiye because ol the high resistance vot' the two windings ot relay i. then in circuit with the windings oi' relay CSR, such resistance beingso greatas L 4lll Y :o0 prevent the actuation of the arma-ture ot relay CSR. The cord circuit at B thus operated on the light key shellPl p 'inciple, socalled, in Which the calling' supervisory lamp is maintained lighted until the called subscriber answers. and the originating oper4 ator through said lai-np 28 has an indication ot such response.

Returningnow to the point at which the conversation Was iinished, it .the subscriber at F vas toreplace his receiver first, he would obviously` Whether the dotted circuit in E was Wired or not, by the `deeneigir/iing oi' relay 1277 cause the display of the lamp before the operator at B. Then the calling;` subscriber at A replaces his receiver this ect brings about the de-energization ol* relay 12 which de-energization would elect the energization of relay 1 and cause the display of lamp 15, and the closing` of alternate contact 3 of relay 1 will permit the continued display oli lamp 28.

Lamp 153 in the trunk circuit E is merely a guard lamp which is lighted as soon as master ground MG of relay 122 is closed. the said lamp beinglighted, indicating` to the opi-water that she has not actuated her ringing lrey lever to ring the called subscriber, As soon asshe does so, closing contact 154, the relay let-O energizes and locks, and the opening ot normal contact puts out the lamp 153.

Let it be assumed that although the called substation lbell was rungj the called subscriber did not answer the call. ln such ease the calling subscriber Will replace his receiver and denergize re lay 12 to energize relay 1. rilhe rela-y 1 upon energization brings about the lighting ot `the lamp 15 and the operator at B Cl? brings about the restoration o'l itclics C and l), as is obvious from the previous desription,

@witches C and D upon restoring, the circuit ci2 relay 107 will be opened and relay 107 will cle-energize and a." a 5 -qnence relay 110 will also de-cnergize.

liet it be assumed nonY that. a calling' sul scriber .it removes his receirer to initiate a call tor a subscriber in his orfn exchange. The operation et the line circuit and cord circuit et Figure 'l part 1,y would be the saine as that already described until aller the oil'ierator has received the uuml-ier on the called subscriber. In this case she will not actuaire the hey CK, but as usual she will test a multiple sgrin'g' l: oi' the called .subscribefs line whose line circuit and substa tion ifrould have exactly the saine arrangein t as 'hat oi the subscriber il. To raalte 1., operator touelwe die tip ot thc i u@ (ll.) to the sleere of a` jack ofthe called lire7 and il? this sleeve 'et the jacl: is busy bc cause av plug` ot another cord circuit has alinadg, liecii placed in a. multiple the jack '(nrorided always that t ie subscribers at J in elected thc autom vi" disconnect). there will be a potential ali-ove afrol-ind at 'le tested contact and an iinliulfL-e of :errentifill non* through the tip ot plug l ormai contact Ll-' el ire CK. normal contact l2 of relay lll, the closed contact F4 `i and to ground through the test l which common to an operators p sition. 'lhe relay (SQ, will close its alter-- nate Contact '(33 to close battery through the tertiary Win/ling; oi' the operati'ifs induction coilv giving -ier the cutoinarj.' busy click.

ilorcorer., the test arrangement nroi'iiles means i'or giving the operator a iierrtire tone test, it she tests a snring ja i of the line in which h l inserte-1l the ansir-serin.;y plug4 oi' cord, that is, il" the calli. i* 'bei' u its another subscriber on tern thus prmf'idinfcv for liich there are a number of subc a single line a party :ich

fe test the c the click as usual, but

'the closure or" alternate Contact (i2 will connect the rcif'ertive o thc. ogrierators head L,ing traced from the contact i252 ot rela Lll, al ernate Contact S ot relav 7, through the condenser 235 and througa the tertiary winding of the operator-s induction coil'to ground. The operator he" g the buzz will lnow i is a reverting (all, tell the culling subscriber to momentarily replace his receiver, and she will then withdraw plug Al), inserting the i g plug C?? and ring in the usual inanassuming nou' that the substation culled tor is on an idle line entirely independent ot that oil" the subscriber at A, the ojcrator receiving no click upon her test, insorts the calling plug Cl) in the tested jack, thus placing the relays 8G and 34 ot' her cord circuit in connect-ion with ground through the winding otl cut-oil" relay C@ ot the called line, and said relays 3o and 34 are both operated with results to the switching instrumentalities of the calling end ot the cord circuit, as previously described herein, and the cut-ott relay Ct) ot the called line will, of course, energize to clear the line circuit for talking and ringing, the line relay LR boing disconnected. The operator at B now actuates whichever ringing hey lever flf) will inipress current of the proper lirequency to ring the bell oi? the called substation, the Contact 49 staying in its closed position while the end springs 5l and 52 oi the ringing key are shifted to close their contacts, but only as long as tie operator holds the ringing but-ton down. By the closing ci contact 52 the relay 22 energizes over a circuit which n'iay be traced t'roin battery through relay 22, end spring contact 52, nornial contact 3 of relay l., contact 30 of relay 2f), norinal contact ot relay CSR to ground at alternate contact ot' relay 34, and relay due to the closure o'l its Contact 28, locks itsel'l to ground at contact 35, over the just described path. By the closure ot contact 5l oft the end springs, the upper winding ol the ringing' relay 4l receives current from battery through the upper winding ol' relay 4l, Contact 5l ot the end springs to ground at contact 25 of relay 22, so that the called substation is instantly rung and will continue to be rung as long as the operator lceeps the contacts 5l and 52 closed. When she releases the button, said end spring contacts 5l and 52 restore to normal, and the upper winding of relay 4l is disconnected, but the lower winding of said relay, due to the closing of alternate contact 24 of relay 22, has been connected with the constantly operating interrupter l and will be alternately energized and cle-energized, connecting and disconnecting the selected ringing generator. The flow of ringing current is to be traced from ground through the selected generator, the closed contact 49 ot the. ringing hey, lower winding of relay 29, altei-nate contact 42, of relay 4l, contact 46 ot hey il I, the tip contacts of the plug Cl? and jack of the wanted line, through the call bell at the called substation, back through the ring contacts of the plug CP and jaclr ot the called line, and to battery at alternate contact. 45 ot' relay 41. lt' the subscriber answers during a ringing interval, the re'- duced resistance at the substation caused by the ren'iov-al et his receiver will allow sutlicient current to flow through the lower winding ot relay 29 to energize it (it having previously remained inert becruse of the high resistance call bell circuit at the substation), and the said relay 29 upon energization opens its normal Contact 3() to cle-energize the relay- 22 by opening its locking circuit that extends to ground at alternate contact ot relay 34, and the said relay 22 restorii'ig does not reoperate because the Contact 52 oit the end spring is now open. tf* retracted armature contacts 23 and 27 re-establish the talking circuit at these points, and the opening of its contact 24 prevents any further operation of ringing relay 4l, which relay de-energizes, and the contacts 42 and 45 orf'relay 4l complete the talking circuit between the subscribers. The closing or" contact-s 42 and 45 also connects the two windings ot calling supervisory relay CSR to the called ior line and it energizes, since the substation receiver has been renioved. The relay CSR upon energization closes an energizing circuit for the relay 204 and the said relay in turn closes a locking circuit for itself, as previously described. rlhe relay 204 by the opening of its norinal contact 203 opens the initial energizing circuit for the relay 36, but the said relay 36 has a substitute circuit established upon the closing of alternate contact 33 ot relay CSR, thus placing the said relay CSR luider the control ot the called subscriber, for purposes as will present-ly be described.

lf the called subscriber had removed his receiver during a silent interval, the relay 4l would bein a de-energized condition and its contacts 42 and 45 would be closed and relay CSR would instantly have energized over the called-tor line, and by the opening ot its normal contact S2 the relay 22 is deenergized with results as before.

rl"he calling and called subscribe-rs are now in conversation, and when they have finished they replace their receivers. It will be assumed that the called-tor subscriber does so first. The opening of the transmitter circuit at the called substation fle-energized relay CSR and the closing ot its contact 32 will cause the lainp 28 to be lighted over a circuit from battery, through the lainp 28, norinal contact 26 of relay 22, normal contact- 3 ot relay l, normal Contact 80 of relay 29, normal contact 32 of relay CSR, to ground at alternate contact 35 et relay 34. The relay CSR upon cle-energi- /ation opens its alternate contact 33, opening Cri ,by eer-rent i through falte rra! l tacts to restore, and places the li relay .lill ot tl'ie f circ-iut as-:oc a with the called line under the contA called substation sfefitchhooli. iat-ks oi the caled` line will also i Y this tiine due to the high resistance et the relay 3ft, which reduces the potent' upon the `:aid multiple jacq so as to mal-:e the operatorie test inellicciive it' seine operator tests that line again a called li e, 'respectire ci the u'ithdrar:al of the pl (il). The callin suhcriher in replairing;` hisI recei uponiits sivithhooli opens the enero` circuit ot the relay l2 and the rcsulti cnergizaticn ot relay l2 oy the clos j its-normal contact lll, enerhi. s the relay l by current iloiving' to ground at alternate contact ot relayzl-jt, and hy the openingot" its nornial coutac Q, el and (3 all three contacts oi? plugr AP are placed on open circuit fo that the line o'f e callin@ sulif restoredl-ito its as re'nalinzf and testingipurpeses gro. i lieY .oliserved that the closing; ot alternate contact lot relay l eetahlishes a l loe.1in; circuit tor the relay iti l) I relaj.y l circuit being' tra cable through a o. c contact l 'i relay l, norinal contact 1l ot relayv l2, icl, vact Q0 and to grr und at termite contact ot relay Ell. The oi' noruial contact lill ot relay i2 cuit 'tor the supervis 'y lanip l at alternate contare o ot rel lines are non' tree. and the l 28 and i5 are hoth lirlitethiand the ,operator noting` the two lighted signals withdraws the tufo plugs, and restcrcsall appa tus ot' the cord circuit to its nornial condition.

it ywill he noted that the circuit of the calling); supervicory hung 28 extends through the hack Contact ot relay-2:2, and as the said relay is ener rized when the operator ilcprcsses her rin, ,ing butt said circuitwill he opened at hiel; contact to er ye the leinpl at this time and Will rei-nain eliaced until the callel lfgorsuhscriher replaces his receiver whereupon t-hevlainp Q8 will light, either through its original energicingcircuit., namely, via the -norlnal Contact at 25, or it the calling subscriber `has alreadyreplaced his receiver, the said lain-p will be lighted to tground 55,71

av ai. and both relay l. lille thus have what is known as the darli keyshelt method of operation.

Tillhile We have illustrated and described a particular embodiment of our invention, it is to be understood that it is ot' considerable scope, and We do not intend to be linuted to the particular devices and connections herein shown and described, but intend to include all such modifications as will suggest themselves to those skilled in the art, and to clailn the invention in its gene 1al aspects.

lVhat We claim as new and desire to secure by United States Letters Patent, is:

LA telephone system comprising telephone lines terminating in operators positions, subscribers" cord circuits and trunk circuits at each of said positions for interconnectine` said lines for conversational purposes, an operators telephone set tor each ol said positions and normally disconnected troni said cord circuits, a relay having a high and a low resistance Winding, means for connectin an operators set to a line through a cord circuit, said relay preventing" another operator troni connecting her operators set to a cord circuit when connected to said line subsequent to the connection of said i'irst cord circuit to said line, and ineans controlled vby the subscribers to operatively tree both lines from said cord circuit and said trunl; circuit -uhcn applied to the terminals it said lines` theiiireeino' ot' said lines trom the said cord circuitl being individually under the control ot each subscriber.

A telephone system comprising calling' and called telephone lines terminating;l in a plurality ot' operators positions, a subscriberis cord circuit. tor connec said lines in conversational circuit, automatic ineans inciiuliire` a relay having a high and a. lou' rcsistance Winding forpreventing more than one ope 'ator troni connecting to said calling' line at the saine time, means controlled-hy the said call ingl and called subscribers to tree said lines 't'roin said cord circuit, a pair ot relays included `in said tiret ineens and responsive to a connection ot a-cord circuitto a called line-ttor connecting said pair oi relays in parallel circuit, and a super-visent' relayv controlled by said called subscriber for placing` one oi said relays under the control oit said called subscriber for ireeinqsaid called line from theconnected' oordeircuit.

A. telephone system comprising` calling;- and vcalled subscribers inea connected for conversation by a subsc'rihers cord circuit. relay controlled ineans under the control ot each subscriber for individually freeing his line troni the connected cord circuit, includinge pair ott relays responsive to a connection of said cord circuit to a called linefor connecting said pair of relays in parallel circuit, a relay, supervisory relay, and means under thev control offthe .answering called o-risubsoriberter.energizing-saidisupervisory relay to energize said last relay for placing one of said pair of relays under the control of the'said called subscriber for freeing said called line from said connected cord circuit for disconnect purposes.

t. A telephone system con'iprising calling and called subscribers lines connected for conversation by a snbscribers cord circuit, relay controlled means under the control of the connected subscribers for individually freeing their lines from the connected cord, including a pair of relays responsive to a connection of said cord circuit to a called line for connecting said pair of relays in parallel circuit one of said relays being initially nnder the control of the. said operator, a supervisory relay electromagnetic means, means under the control of the answering called for subscriber' for energizing said supervisory relay to actuate said electromagnetic means for ren'ioving one of said pair of relays from the control of the operator and placing it under the control of the said called subsciber for freeing said called line from the said connected cord circuit while said connected cord circuit remains connected to said lines.

5. A telephone system comprising a calling subscribers line and a called subscribers line, cord circuits and trunk circuits for interconnecting said lines, means controlled by the subscribers and applied to the terminals oit said lines to operatively free both lines from said cord circuit and said trunk circuit, the freeing' of said lines from said cord and trunk circuits being individually under the control of each subscriber, auton'iatically selecting switch mechanisms for selecting said cord and trunk circuits and adapted to be connected in circuit intermediate of said cord and trunk circuit during conversation and means for releasing said switch mechanisms effective on the operative freeing of the called line.

6. A telephone system comprising calling and called telephone lines connected for conversation by a subscribers cord circuit, means controlled by the said calling` and called subscribers to free said lines from said cord circuit, a pair of relays responsive to a connection of said cord circuit to a called line for connecting said pair of relays in parallel circuit, a supervisory relay, means under the control of the answering called for subscriber for ener-- giZing said supervisory relay to place one of said relays under the control of said called subscriber for freeing said called line from the connected cord circuit, automatic selecting switch mechanism connected in circuit with said cord circuit during conversation, and means for releasing said mechanism effective on the operative free ing of the called line. V

. A telephone system comprising calling and called subscribersY lines connected for conversation by a subscribers cord circuit, relay controlled means under the control of each subscriber for individually freeing his line from the connected cord circuit, including a pair of relays responsive to a connection of said cord circuit to a called line for connecting said pair of re lays in parallel circuit, a supervisory relay, means under the control of the answering called for subscriber for energizing said supervisory relay to energize one of said relays under the control of the said called subscriber for freeingsaid called line from said connected cord circuit for disconnect purposes, automatic selecting switch mechanism connected in circuit with said cord circuit during conversation, and means for releasing said mechanism effective on the operative freeing of the called line.

8. A telephone system comprising calling and called subscribers lines connected for conversation by a subscribers cord circuit, relay controlled means under the control of the connected subscribers for individually freeing their lines from the con-` nected cord, including a pair of relays responsive to a connection of said cord cir-- cuit to a called line for connecting said pair oit' relays in parallel circuit, one of said relays being initially under the control of said operator, other means, a supervisory relay, means under the control of the answering called for subscriber for energizing said supervisory relay to actuate said other means for removing saidone of said relays from the control of the-operator and p=lacing it under the control of the said called subscriber for freeing said called line from the said connected cord circuit while said connected cord circuit remains connected to said lines, automatic selecting switch mechanism connected in circuit with said cord circuit during conversation, and means for releasing said mechanism effective on the operative freeing of the called line.

9. A telephone system including a pair of telephone lines and a central office link circuit having a pair of terminals connected one to each line, automatic selectingswitch nechanism intermediate said pair of ter` minals for controlling talking contacts in said telephone system, means controlled over each line independently of the other for placing the talking contacts of the associated terminal on open circuit (between said terminals) while they remain connected to said lines.

10. In a telephone system a calling and a called line having terminals, link circuit means including terminals connected to said first terminals interconnecting said lines for conversation, an automatic selecting switch mechanism also included in said lint,v circuit means intermediate said second terminals 'for controlling talking` contacts in said telephone system, and means independently controlled over eac-h line to operatively tree it, 'from said link circuit means and to permit restoration et said automatic switch While said link circuit terminals remain connected .to said tirs-t terminals.

1l. A telephone system `including a call ing line and a called line and link circuit means interconnectingl them including a link circuit terminal connected to a terminal ot the called line, an operators telephone set normally disconnected from said Circuit, means solely/,controlled over the called lino for operatively freeing said line from said circuit- While said terminals are connected, said means including a pair oi" single ivourul relays in energized condition betore and during; conversation, leans eilective to dccnergisc the one relay only when the called subscriber replaces his receiver. and mean-1 tor preventiup,` connection saidy operator s set to said circuit so longas said link circuit terminal is connected to the terminal ot' said called line.

12. A. telephone systemincluding a calling and a called line connected i'orconversation by link circuit terminals connecte-flL to them respectively, .automatic suitci intermediate said link circuit terminals operable for extending and closingl contacts in the talkingconductors ot said telephone system, means controlled by the calling and called subscribers to tree their lines :troni the link circuit and to permit said automatic switches to.restore While said terminals remain connected, said means including a pair of relays responsive to a connection ot said link circuit to a called line for connecting said pair of relays in parallel circuit, a third relay, and meansvunder the control ot' the .answering called for subscriber for energizing said third relay to place one of said relays under'the con trol out thel called subscriber -tor freeingsaid called line.

13. A telephone system including a calling-and a called line connected for conversation by link circuit terminarJ connected to them, apair et relays responsive to a connection oi' said link circuit to a called line, the called line, a third relay actuated on the response ot the called subscriber' to place one of said relays under control ot said subscriber, and switching means thereon controllable by said one oit said relays to operatively free said l:.lled line while the link circuit terminal remains connected to said line.

let- A telephone system, comprising telephone lincs, subscribers cord circuits for intercminecting` said subscribers lines for conversational purposes, a sleeve relay tor said cord circuit responsive to a connection et said cord circuit to a called line, a second relay energized in parallel with said sleeve relay extending through contacts oi" a third relay and initially under the control oi the operator, a supervisory relay, means under the control ot the answering` called tor subscriber tor energizing' said supervisory relay to energize said third re lay and open said initial circuit ot said seccnil relay andto close a substitute circuit for said second relay, placing it under the control olf said called subscriber and placing its substitute energizing circuit under the control ot' the called subscii'iljier.

15. A telephone system comprising; telen phone lines, subscribers cord circuits for interconnecting said subscribers lines 'for conversational purposes, a high resistant, sleeve relay responsive to a cennec said cord circuit to called lines, a second rclay, a relay initially eneroized in parallel With said sleeve relay extending through contacts of said second relay, a su iervisory relay, and means under the control ot the answering` called ior subscriber iter energizing said supervisory relay to energize said second relay for opening said initial circuit oit said third relay and ior closing a circuit for said first relay under the cor.- trol of said supervisory relay.

Signed by us at Chicago, in the county of Cook and State ot illinois, this 25 day ct April., 1921.

Images