US2131568A - Telephone system - Google Patents

Description

Sepr. 27, 1938. s. E. PETERSON TELEPHONE SYSTEM Filed March 19, 1937 BY'QW ATTORNEYS Patented Sept. 27, 1938 TELEPHONE SYSTEM 1 Seth E. Peterson, Galva, Ill.; assignor-to 'Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application March 19,

29 Claims.

The present invention relates to telephone systems and more particularly to such systems of the automatic step-by-step typehaving embodied therein apparatus automatically operable to per- 5: mit the tracingof incoming calls to any desired predeterminedsubscribers telephone.

Systems of the type mentioned conventionally comprise switch trains including step-by-step selector and connector switches for setting up and releasing connections between any pair of telephones in thev system. In suchsystems, as well as inother systems of similar character, the need fore, to provide an improved and exceedingly simple circuit arrangement, applicable to prac- Y tically any of the various modifications of the step-by-step automatic telephone system, for assisting an `attendant in tracing calls to any desired telephone embodied in the system.

More particularly, it is an object of the invention to provide an arrangement of the above character which utilizes to the fullest extent the switching equipment normally-provided for rendering ordinary telephone service.

The invention as described in detail hereinafter is illustrated as being embodied in an autostep-by-step type, wherein line, selector and connector switches, operable in the order named, are provided for establishing a connection between a rst or calling line to a second or called line. Such a connection may be regarded as comprising a talking-'loop between the two telephones, theV loop being completed when the Vcall is answered at the second or called telephone. In general, the 1 objects as set forth above are realized in` accordance with the presentinvention by providing means automatically operable as soon as the line associated with the telephone to Vbe observed is seizedby a-connector switch, and maintained operated soflong as thetalking loop is not inter- 55..rupted. atv .the called telephone, for causingthe It is an object Yof the present invention, therematic system employing a switch train of theY 1937, Serial No. '131,917 (Cl. 179-27) operation of analarm device-"provided at the central` exchange and for preventing the established'connection from being released in response to! any possible operation whichthe calling party may performat the calling telephone,` and more particular-ly in'response to the interruption of the' talking loopat the calling telephone. More specifically, this means comprises a'plurality of interrelated relays associated' With the line leading to the telephonev to be observed, which relays operate When a connection is completed'to this line to prevent-the selector switch,y preceding the operatedY connector switch, from being released when the calling party interrupts the talking loop at his telephone by hangingup his receiver. By holding'this selector switchoperated after the calling party hangs up, itis possible'for the called loartyv to informan attendant `.atthe central exchange that a call is tube-traced, whereupon this` attendant may, by observingthe condition of the aforementionedl selector switch and the line switchlwhich'has caused `the operation thereof; f determine the line on which the call was initiated. Additional means, comprising certain of the relays ofthe connector switch inV use, are provided whichareoperable in case a talking loop is not completed' at the observed telephone to cause the restoration Lof the` above-mentioned means so that the'connection may bereleasedv in the convent'ional manner when thecallingparty hangs up. As 'pointed-.outl in detail hereinafter, the aforementioned relaysare under kthe control of the answering party at the observed telephoneand function to `holda--predetermined potential, namely, ground potential, on the controlV conductor .ofthe operatedfselector vswitch after the party -at :the calling'telephone hangs up, .whereby the portionof 'the switch train preceding theoperatedfconne'ctorswitchisheld operated. TheelementsY ofthe above-mentioned means are arranged 'inan .exceptionally simple m'anner such Y thatthe control' means normally provided inthe various switchesare utilized-to thefull'est extent in vfaithfully providing-thisfform-of service. y

' The novelfeatures. believed tovlbecharacter- Y istic ofthe .invention are `set forth.v With particularity in the appended claims. The invention, bothas to its Yorganization and method of operation., together with rfurther objectsrand advantages "thereof, will best beunderstood byreferarranged in accordance with the present invention for assisting an attendant to trace calls to any desired telephone or telephones included in a system.

Referring now to the drawing, there is illustrated, for the purpose of describing the invention, an automatic telephone system of conventional form having embodied therein impulse responsive step-by-step switches for setting up and releasing connections between any pair of telephone lines. In general, the system comprises a plurality of telephones or subscribers substations, three of which are shown at A, B and C, adapted to be interconnected by means including their respective associated subscribers lines I0, II and I2 and switch trains including the aforementioned step-by-step switches. These switch trains, when established, may individually comprise the usual line switch associated with each subscribers line, a selector switch accessible to the line switch corresponding to the calling subscribers line, and a connector switch accessible to the operated selector switch and having bank contacts in which the called subscribers line terminates Thus, in the system shown, the lines l0, II and |2 terminate at line switches I3, I4 and I5, respectively, which switches have access to a group of selector switches, one of which is shown at I6. The latter switches, in turn, have Aaccess to groups of connector switches, each connector switch of each group having its bank contacts multipled to the bank contacts of the other switches in the same group and connected to serve a corresponding group of subscribers llines included in the system. Thus, the selector switch I6 has access to connector switches, one of which is shown at Il, in the bank contacts of which the subscribers line I2 terminates. It is well known that by this arrangement, any subscriber may, by proper manipulation of the impulsing device at his substation, establish a connection between his line and any other subscribers line in the system.

Each of the line switches included in the system such, for example, as the line switches I3 to I5, inclusive, may be of any desired commercial construction, although preferably is of the wellknown rotary type having three levels of bank contacts, wipers corresponding to the three levels,

a ratchet and pawl mechanism for driving the wipers, an operating magnet for actuating the ratchet and pawl mechanism, and control means whereby the operating magnet is energized when a call is initiated on the line associated'with the corresponding line switch and is de-energized when the wipers are rotated into engagement with a set of contacts corresponding to the rst idle selector switch available. Similarly, each of the selector switches included in the system may be of any desired form, although preferably is of the well-known Strowger type compris-ing bank contacts arranged in levels, each level corresponding to a particular group of connector switches, wipers for engaging the bank contacts, ratchet and pawl mechanisms for imparting translatory and rotary movements to the wipers, vertical and rotary magnetsfor driving the respective ratchet and pawl mechanisms and control means whereby, when a selector switch is iirst seized, it is automatically conditioned to be responsive to the rst digit dialed at the vcalling substation, the dialing of the first digit cause the vertical magnet to step the wipers upward opposite the level of bank contacts corresponding to the number of impulses in the digit dialed,

and the wipers are automatically rotated by the rotary magnet and associated ratchet and pawl mechanism into engagement with the set of contacts corresponding to the first idle connector in the group of connectors to which the called subscribers line extends.

The various connector switches, like the selector switches, are preferably of the Strowger type and may be identical with that illustrated at I1. In brief, the switch I'I comprises two banks of contacts arranged in levels, the individual contact sets connected to the various subscribers lines being multipled to the corresponding contact sets of other similar connector switches included in the same group. Thus, the switch I'I comprises a Contact 45 in the control contact bank which contact is connected to the control or C conductor I9 leading to the line switch I5 associated with the subscribers line I2. The corresponding line contacts 43 and 44 for the line conductors 20 and 2| of the line I2 are included in the line contact bank. The connector switch I1 also includes wipers 40, 4|, and 42 for engaging the various contact sets in the two contact banks, Vsuch for example, as the contacts 43, 44, and 45, a ratchet and pawl mechanism, not shown, for translating these wipers vertically opposite any desired contact level, a vertical magnet I 25 for actuating this ratchet and pawl mechanism, a second ratchet and pawl mechanism, not shown, for thereafter actuating the enumerated wipers into engagement with the particular contact set corresponding to the called subscribers line, a rotary magnet |26 for driving this second ratchet and pawl mechanism, a release magnet |69 for tripping the ratchet and pawl mechanisms to permit the wipers t0-42, inclusive, to return to normal, and control means comprising a plurality of interrelated relays |00, IIO, |20, |30, |40, |50, |60, and |10, their control and controlled circuits and off-normal springs |41 and |48, for controlling the operation of the vertical and rotary magnets and for performing the Various other functions normally required in this type of. switch. More specically, the last-mentioned means comprise the relays |00 and |I0, operative in the order named to condition the vertical magnet |25 for operation; the relay |20 and oft'- normal springs |41 for preventing the impulses of the third digit, dialed at the calling substation, from being transmitted to the vertical magnet |25; the line relay |00 for interrupting the circuit of the vertical magnet |25 in accordance with the impulses of the second digit; the relays ||0 and |20 for conditioning, at the end of the second digit, the rotary magnet |26 to 'Y be responsive to the impulses comprising the third digit dialed at the calling substation; the relay |00 for interrupting the circuit of the rotary magnet |26 in accordance with the impulses of the third digit; the relay |40 for partially completing the connection to the called line, for applying ringing current thereto and for applying, in case the called line is found idle, ring back-current to the incompleted talking loop extending back to the calling subscribers substation; the relay |50 for applying busy tone to this loop in case the called line is found busy and for preventing the calling line from being connected to the called line when this condition prevails; the relay |60 for completing the connection between the calling and called lines, for interrupting the application of ringing current to the called subscribers line and the application of ring back current to the calling subscribers line; and the relay |10 'for reversing battery back over the loop extending to the calling subscribers line when the called party answers.

As pointed out in detail hereinafter, the relay I0, when operated to one of its two positions,

' a connection is once established'by way of the switches I6 and |1 between two subscribers lines. This relay is also operable to the other of its two positions, to remove, atfthe contacts noted, ground potential from the same control conductor, thereby to release, under certain conditions, the selector switch -I B-when the talkingY loop is interrupted at the calling partys telephone.

Neglecting for the present the details ofthe connector switch |1 and the means associated therewith for assisting an attendant to trace calls to a predetermined subscribers telephone or telephones, the system as described above is entirely conventional in form and its operation is well understood in the art. In brief, when a subscriber such, for example, as the subscriber at the telephone A initiates a call over the line I0 to a second subscribers telephone such, for example, as the telephone C by lifting his receiver from its hook, the line switch I3 associated with the calling subscribers line operates to select an idle selector switch and to condition the same to be responsive to impulses transmitted from the impulsing device at the telephone A. As noted above, each of the selector switches has access to one or more connector switches in which the subscribers lines of the system terminate. Thus, if the selector switch I6, for example, is seized by the line switch I3, it operates in response to the dialing of the first digit at the substation A to translate its wipers vertically to a contact level corresponding to the group of connector switches at which the called line I2 terminates, following which it automatically rotates its wipers into engagement with a set of contacts corresponding to the first idle connector switch in this group such, for example, as the connector switch I1. Thereafter, and in response to the dialing of the second digit, the connectorswitch, through the operation -of its vertical magnet and the associated pawl and ratchet mechanism, translates its wipers vertically to positions opposite the respective levels of bank contacts in which the conductors I0 to 2|, inclusive, of the called subscribers line, terminate. With the switch train in this condition and when the nal or third digit is dialed, the rotary magnet of the connector switch, in cooperation with its associated ratchet and pawl mechanism, operates to drive the wipers to 42, inclusive, into engagement with the contacts 43 to 45, inclusive, corresponding to the called line I2.

The system conventionally includes means whereby ringing current and ring back tone are automatically transmitted respectively, to the substations of the called and calling parties in case the called line is idle and upon the connector wiper coming into engagement with the bank contacts at which the called subscribers line terminates. Also, in accordance with conventional practice, means are provided whereby, in the event the called line is found busy, the calling line is not connected theretor and busy tone .is transmitted .back overthe established, loop to of the called line.

In the event the calledv line is found idle and the called party answers, battery is reversed back over the: .loop whenrthe called partylifts his receiver from its hook to connect a bridge across theconductors of the called line. With the system in this condition, a `talking connection is established-betweenthe calling and called partieswhich obtains until the conversation is terminated and one of the parties hangs up.

`The arrangement is such that, when the calling `party is the rst to interrupt the talking loop by hanging up, the switch train leading to the connector switch I1 and including the selector switch I6 land the lineswitch I3 is normally released. The connector switch is, however, held in its operated position until the called party hangs vrup to remove the bridge from acrossrthe conductors .of his line.. In the event the called party is the first to interrupt the talking loop, the

entire'switch train is maintained operated until the calling party hangs up.

More particularly, the operation of the connector switch I1, in the above described sequence of operations, is initiated when the selector switch I6 seizesthis connector in response to the dialing ofthe rst digit at they calling substation by causing a bridge to be connected across the line conductors 30 and 3|, thereby to complete' a circuit for energizing -the relay |00. This circuit extends from ground at the-lowerwinding of the relay noted, through this winding, by way of the armature |14 and its associated contact |14- of the-relay |10, the conductor 29, the line conductor 3|, through the bridge across the conductors 30-5andv3|, over the conductors 30 and 28;.and through the armature |13and its associatedcontact |13- and the upper winding of the relay I 00gto battery. When energized over the above-traced circuit, thev relay |00 operates toY complete, at its armature .|0I and-associated contact.|03, a circuit'for energizing the slow-torelease hold relay I I0. The last-mentioned relay inA turn operates to connect, at its armature III,

the calling partyv to indicate the busylcondition ground tothe control or C conductor 22, to prepare, atitsarmature '||-2,- holding circuits for the relays |40.. and ISU-and to prepare, at its armature II3 and associated-contact |I4, a circuit for energizing the series connected Vertical magnet |25 and relay |20. With the.4 hold relay I|0 in itsl operatedposition, the ground applied to the control conductor 22 at the-armature II| holds the switch train including the selector switch I 0 and preceding the connector switch in its operated condition. With the control meansof the connector switch I1 in this condition, the `vertical magnet |25 is conditioned to be responsive to impulses transmitted from the impulsingdevice at the calling subscribers telephone A.v

Atthe beginning of the rst impulse of the second digit, the bridge across the line'conductors 3Q` and 3| is interrupted, therebyV to open the previouslyftraced operating circuit for the line relay |00, permitting this relay to restore and complete, at itsv armature IUI, the previously prepared circuit for energizing-the relay |20 and the vertical magnet |25 in series.V The lastmentioned circuit extends from ground at the armature |0| and its associated'contact |02, through the operated armature II3 and associatedzcontact H4,v the contacts |26 and |21 of the oit-normal springs |41', the windingof the tical magnet |25 to battery. When theslow-torelease relay |20 operates, it prepares, at its armature |2| and associated contactV |22, an obvious multiple energizing circuit for itself and the vertical magnet |25. At the beginning of the rst impulse when the line relay |00 falls back to complete the operating circuit of the vertical magnet |25, the ratchet and pawl mechanism associated with the vertical magnet causes the wipers 40, 4| and 42 to be translated one step vertically. This first step of the switch also causes the off-normal contacts |41 and |48 to be operated so that the contacts |26 and |21 are open-ed, the contacts |24 and |28 are closed and the contacts |29 and |49 are closed. Closure of the last-mentioned contacts prepares an obvious circuit for energizing the release magnet |69, and closure of the off-normal contacts |24 and |28 completes the previously prepared multiple circuit for energizing the relay |20 and the vertical magnet |25. The completion of the last-mentioned multiple circuit permits the Vertical magnet alternately to be energized and de-energized in accordance with the operation and restoration of the line relay |00 corresponding to succeeding impulses of the digit being dialed. Thus, the wipers 40 to 42, inclusive, are stepped vertically into a position opposite the level in which the called line terminates and corresponding to the impuls-es of the dialed digit.

At the end of the second digit, the circuit for energizing the line relay |00 is closed so that the previously traced circuit for the relay |20 and the vertical magnet |25 is interrupted at the armature |0|. after an interval, opening, at its armature |2| and associated contact |22, the previously mentioned multiple circuit for itself and preparing, at the same armature and its associated Contact |23, a circuit extending by way of the conductor 31, the armature |54 and the armature |45 for energizing the rotary magnet |26 and the slow-torelease relay |30 in parallel. At the beginning of the first impulse of the second digit, the line relay |00 again restores, to complete, at its armature I0 the prepared circuit for energizing the rotary magnet |26 and the relay |30. In response to such energization, the relay |30 operates to interrupt, at its armature |3| and associated contact |32, a point in the circuit for energizing the lower winding of the relay |40 and to connect at this same armature the directing or control wiper 42 to the upper terminal of the winding ofthe relay |50 over a path extending by way of the armatures |3| and |33, the armature |42 and the conductor 35. At its armature |35, the relay |30 closes a shunt around the armature |54 of the relay |50. During succeeding impulses of the second digit, the circuit for the relay |30 and the rotary magnet |26 is alternately interrupted and completed at the armature |0| of the line relay |00, in accordance with the impulses of this digit, whereby the rotary magnet causes its associated ratchet and pawl mechanism to step the wipers 40 to 42, inclusive, into engagement with the bank contacts 43 to 45, inclusive, to which the line conductors of the called line |2 are connected.

During these impulses, the relay |30, due to its slow-to-release characteristic, remains operated and, at its armature |35, maintains a shunt around the armature |54 of the relay |50 so that the circuit to the rotary magnet is not opened at the last-mentioned armature when the control wiper 42 passes over contacts corresponding to busy lines to cause energization of the relay |50.

Accordingly, the relay |20 restores In'the course of this stepping operation and each time the directing wiper 42 engages a contact corresponding to a busy line, the relay |50 operates, but without eiect at this time. At the conclusion of the series of impulses comprising the third digit, the relay |00 remains in its operated position so that the circuit for energizing the relay |30 and the rotary magnet |26 is interrupted. As a consequence, and providing the called line I2 is idle, the relay |30 falls back after an interval to again prepare, at its armature |3| and associated contact |32, a circuit for energizing the lower Winding of the relay. |40.

If the called line is idle, and when the relay |30 restores, a circuit is completed for partially energizing the relay |40, this circuit extending from battery at the cut-off relay in the line switch associated with the called line |2, over the control Conductor I9, through the contact 45, the wiper 42, the armature |3| and associated contact |32, over the conductor 38, through the lower winding of the relay |40, over the conductor 39, through the contact |52 and associated armature |5| of the relay |50, and over the release trunk or control conductor 22 to ground at the armature 'I'he relay |40 partially operates in response to such partial energization, tocomplete, at its armature |44, its previously prepared locking circuit extending by way of the conductor 25 to ground at the armature I2, thereby to cause the full operation thereof. When this occurs, the connection to the called line is partially completed at the armatures 4| and |46, direct ground is connected to the control conductor I9 at the armature |41, ground is connected to the ringing interrupter start conductor 23 at the armature |43, the circuit for energizing the relay |50 is interrupted at the armature |42, and the circuit for energizing the rotary magnet |26 is interrupted at the armature |45.

When the ringing interrupter is started, ringing current is transmitted to the bell at they called substation over a circuit extending from the ringing generator by way of the conductor 46, the

armatures |68 and |46, the wiper 40 and associated contact 43, the line conductor 2|, the bridged bell and condenser at the called partys` substation, the conductor 20, the contact 44 and associated wiper 4|, the armatures |4| and |6|, the conductor 34, and through theI lower winding of therelay |60 and battery to ground. Due to the alternating nature of this ringing current, a Voltage of the same frequency is induced in the upper winding of the relay |60. This voltage is impressed across the terminals of the receiver at the calling substation over a path which includes the conductor 66, the lower Winding of the relay |10 and the line conductor 3|. Due to the slowto-operate characteristic of the relay |60, .this relay does not operate during the ringing operation. In this manner, the called substation is signaled and the calling party is notified that the called line is idle.

When Athecalled party at the telephone C answers the call by lifting his telephone receiver from its hook, a direct current circuit is completed for energizing the lower winding of the relay |60, this circuit extending 'from ground on the conductor 46, through the armatures |68 and |46, the wiper 40, the contact 43, over the conductor 2|, through the bridge at the called substation, over the line conductor 20, through the contact 44, the wiper 4|, the two armatures |4| and |6|, and the lower winding of the relay |60 to battery. The relay |60 now operates to close 75 lil an obvious locking circuit for itself at its armature |61, to complete the talking loop between the calling and called substations at is armatures |6| and |68, to interrupt its original energizing circuit at its armature |6| and associated contact |62, to interrupt, at its armature |65 and associated contact |64, the circuit for the ringing interrupter, to interrupt at its armature |68 and the lower associated contact the previously traced ringing current circuit, thereby to discontinue the application of ringing and ring-back tones to the loops extending to the called and calling parties, respectively, and to complete, at its armature |65 and associated contact |66, a circuit for lighting the supervisory lampi No. When the locking circuit for the relay |60 is completed, a circuit is also completed for energizing the battery reversing relay |10, this circuit extending from ground at the armature ||2 by way of the conductor 25, the armature |61, the conductor 66, the lower winding of the relay |10, the armatures |68 and |46, over the line conductor 2|, through the bridge at the called substation, back over the line conductor 20, through the armatures |4| and`|6 I, over the conductor 26, and through the upper winding of the relay |10 to battery. When the relay |10 operates, it interrupts, at its armature |1|, the previously completed circuit for energizing the supervisory lamp No. l, interrupts, at its armature |16, the previously prepared circuit for the release magnet |69, prepares at this same armature a circuit for energizing the supervisory lamp No. 2 and, at its armatures |12 and |15 and their respective associated contacts |13 and |14, reverses battery back over the loop extending to the calling substation for the purpose of operating a coin collector or meter, if such service is desired. Operation of the armature |1| also co-mpletes a multiple locking circuit for the relays |40, |60 and |10, this circuit extending from ground at the armature |43 by way of the conductor 36, the armature |65, the conductor 24 and through the armature |1| to the conductor 25 where the circuit divides into three branches, one for each of the windings of the three enumerated relays.

Before describing the krelease of the connection as established in the above manner, it will be assumed that, instead of being idle, the called substation C is found busy at the time the wipers to 42, inclusive, are stepped into engagement with the contacts 43 to 45, inclusive, corresponding to the conductors of the called line. When this occurs, ground is present on the release conductor |'9 so that the wiper V42, upon engaging the contact 45, completes an obvious circuit for energizing the relay |50. This relay operates to prepare, at'its armature |51, a locking circuit for itself, which circuit is completed when the relay |30 restores after an interval, following the end of the third impulse digit. This circuit extends from ground at the armature by way of the control conductor 22, the armature 15| and associated contact |53, the contact |34 and its associated armature |33, the armature |42, the conductor 35, and through the winding of the relay to battery. In its operated position, the relay |50 opens, at its armature |54, the original circuit for energizing the relay |30 and the rotary magnet |26 and, at its armature |55, applies busy tone to the lower line conductor 3| to notify the calling subscriber A that the called line C is busy.

Continuing now with the operation of the connector switch during the release of an established connection, when the conversation is concluded and the calling party A replaces his telephone on its hook, the bridgeacross the line conductors 30 and V3| holding the line relay |00 operated, is removed. As a result, the relay |00 restores, opening, at its armature I0| and associated contact |03, the operating circuit for the relay ||0', which latter relay, after an interval, also restores. When the relay ||`0 falls back it interrupts, at its armature ||2, the original holding circuit for the relays and |40, prepares, at its armature H3 and associated contact l5, a circuit for energizing the `release magnet |69 and, at its armature I||, removes ground from the control yconductor 22. The relay |00, upon restoring and before the relay ||0 falls back, completes, at its armature |0| and associated contact 402, the previously traced circuit for energizing the relay |30. When the relay |30 operates, :it removes, at its armature |3|, the multiple ground 'from the control conductor '22, which ground extends `by way of the 'armature |41, the armature |3| and associated contact |32, the conductor 38, the lower winding of the relay |40the conductor 30, and the armature I5 By removing this multiple ground from the conductor'22, the release of the switch train preceding the connector |1`is placed under the control of the relay ||0. Thus, when the relay ||0 restores, following the operation of the slow-to-release relay |30, it, for an interval,

completely removes, at its armature ground from the conductor 22, thereby permitting the selector switch |6 and the line switch I3 to be released, in the order named, in `a manner well understood in the art.

When the relay H0 restores, shortly -after the restoration of the relay |00, it not only effects the release of the switch train preceding lthe connector |1, but interrupts, at its armature ||3, the circuit for energizing `the relay |30,1permit ting this relay to restore, which it does after an interval, thereby to return ground to the control conductor 22 Vfrom the armature |41 of the connector switch and .thus 'mark `the switch I1 as 'busy in the selector switch contact banksuntil `the connection is :cleared out at the called substathe armature |0| and its associated contact |02,

through the armature |13 and associated contact ||5, thegarmature |16, and-the supervisory lamp to battery. Although the Yoriginal locking circuit Vfor the relays |60 and V'|40 is opened, at the armature 'I |2, these relays are retained operated over the previously traced multiple locking circuit extending from ground at the armature |43. It is `to be observed lat this pointthat the connector switch |1 is still held in its operated position by virtue ofthe fact that the circuit to the release magnet |69 is held Aopen at the armature |16 of the battery reversingrelay 110.

When the party at the called V`substation C hangs up, the circuit to the relay |10 v4is interrupted by the removal of the bridge at the called substation from across the line conductors 20 and 2|, permitting this relay Ato restore and complete, at its armature |16, a circuit for the release magnet |69, this circuit extending from ground at the armature |0| by way of the armatures ||3 and |16, the closed off-normal contacts |48, and through the winding -of the magnet |69 to battery. The release magnet thereupon, in a well-known manner, -actuates its as- :Socated ratchet mechanism to permit the wipers 40 to 42, inclusive, to be restored to normal. When the wipers reach their normal-or home po'- sitions, the oi-normal Vsprings |48 and |41 are restored to normal in a well-known man-ner. Restoration of the relay |10 also causes the multiple locking circuit for the relays |40 and |60 to be opened at the armature whereby these relays are permitted to restore. Thus, the control equipment included in the connector switch is restored to normal and the switch is ready for further use.

In the event the talking loop is interrupted at the called substation C` before the calling party at the substation A hangs up, the relay |10 is the rst to fall back. This relay thereupon interrupts, at its armature the multiple locking circuit for the relays |40 and |60 and prepares, at its armature |16, a circuit for energizing the release magnet |69. Under the conditions stated, the entire switch train including the connector is held in its operated condi tion until the talking loop is interrupted at the calling substation A. When this occurs, the relay |00 restores to cause the reoperation of the relay |30 and to interrupt the circuit for the holding relay ||0. The relay |30, upon reoperating, removes multiple ground from the control conductor 22 so that, when the relay l0 restores its armature ||I, the switch train comprising the selector switch |6 and the line switch |3 is released and automatically restores to normal. The steps which follow the restoration of the relays |00 and ||0 are, from this point on, exactly the same as those described in the preceding paragraphs.

As pointed out above, occasions arise when it is extremely desirable to be able to trace calls to one or more telephones included in the system. In accordance with the present invention, means are provided, operable when a connection is once established to a called line and maintained operated so long as the established talking loop is not interrupted at the called telephone, for preventing the means comprising the relay ||0 from initiating the release of the connection in the manner described above. More specifically, this means comprises the relays and which, when operated, retain. ground potential upon the control conductor 22 independently of the relay ||0 and thereby prevent the release of the switch train comprising the line switch associated with a calling line and the selector switch seized by such a line switch. The relay |80 has its winding connected between battery and the release trunk conductor such, for example, as the conductor I9, of the subscribers line it is desired to observe. It will be understood that this conductor for each of the subscribers lines of the system is multipled to the bank contacts of the group of connector switchesat which the line terminates, so that, in the event any of these connector switches is seized on an incoming call to the line l2, the relay |80 is operated. When this relay operates, it completes, at its armature |8I, a circuit for energizing the relay |90. The last-mentioned relay has a number of armatures, one for each of the connector switches in which the conductors of the line |2 are multipled. Each of these armatures extends to the conductor corresponding to the conductor 24 of the switch Il, and their respective associated contacts are individually connected to the respective control conductors of the corresponding connector switches. Thus, the armature |9| is connected by means of a conductor 60 to the conductor 24 and thecontact associated with the armature |9| is connected over a conductor 6I to the control conductor 22. An additional armature and associated contact is embodied in the relay |90 for closing a circuit for energizing an alarm such, for example, as a bell. Such an ala-rm is schematically indicated at 62.

With the above arrangement it is to be observed that the relay ||0 when in one of its two positions, namely, its operated position, applies a predetermined potential, i. e., ground potential, to the control conductor 22 to hold the selector switch |6 and the preceding switch or switches operated. In the other of its two positions, or its restored position, this relay removes ground potential from the control conductor 22 to release the switch train. It will further be apparent that the conductors 60 and 6| comprise a normally uncompleted path for applying this same predetermined potential to the control conductor independently of the relay 0, this path extending from ground at the armature |43, by way of the conductor 36, the armature |65 and associated contact |66, the conductor 60, the armature |9l, and the conductor 6|, and being fully completed when the relay |60 operates following the completion of the talking loop between the calling and called telephones.

In the operation of the above-described arrangement and assuming that it is desired to observe incoming calls to the subscribers line l2, immediately upon the establishing of a connection to this line and when the wiper 42 engages the bank contact 45, a circuit is completed for energizing the relay |80, this circuit extending from ground at the armature |41 by way of the wiper 42, the bank contact 45, the conductor 64 and through the winding of the relay |80 to battery. The last-mentioned relay operates and, at its armature |8|, completes a circuit for energizing the relay |90, which relay, in turn, closes all of its armatures |9|,'|92, |93, |94, etc., to their respective associated contacts. The closure of the armature |95 to its associated contact initiates the operation of the alarm device 62, thereby indicating to an attendant in the eX- change wherein the connector switch is located that a call is being made to the line to be observed. If the called line is answered, the attendant may, by connecting a. telephone across the conductors 30 and 3| at the test jack 65, converse with the called party and determine whether or not the call is to be traced. It will be observed that, when the attendant plugs his telephone into the contacts of the jack 65, ground is applied to the control conductor 22 from the spring 66, so that the switch train preceding the connector switch is held operated independently of the condition of the telephones at either of the substations A or C. If the call is to be traced, the attendant may, by observing the condition of the selector switch I6 and the line switch I3, determine the line from which the cal] was initiated.

It is the function of themeans comprising the relays |80 and |90 to prevent the switch train from being released in case the calling party interrupts the talking loop immediately after its completion and before the attendant can receive instructions asrto whether or not the call should be traced. Thus, let it be assumed that the calling party hangs up shortly after the call is answered at the called substation. When this occurs, multiple ground is removed from the control conductor 22 at the armature |3| of the .trol conductor 22.

' relay` 13E),V and the. relay |.lf0 restores-,asxdescribed above. When the relay |-|0 restores, it removes .ground from the control conductorf22 at its Yarmature ill. and normally .this last operation would permit; the switch train comprising `the selector switch i5 and the line switch ISto-be released. Due to the completion Yof the previously traced path including the conductors. Bil and 6|, however,'ground is maintained on the con- Aarmature |43, until such time as the loop is interrupted Aatthe called telephone.` With the system in Vthis condition and when the loop is interrupted at the called substation by the called party replacing his receiver on its hook, the relays ill), l and Hill restore, in theordernamed.

The first-mentioned of these relays upon 4falling A back` completes, atits armature |16, the circuit for the release magnet |69 causing this magnet to operate. As a consequence the wipers 4ll-42,

;inclusive, are restored to normal andthe circuit holdingthe relay; |80 operated .is interrupted permittingthis relayto restore and open the circuit holdingxthe relay Li operated. Thereupornthe relay |99 restores to interrupt, at its armature I9! the previously traced path including the conductors @il and 6| holding ground on the control conductor 22, thereby permitting the switch train preceding the connector switchil yto be released.

It will .be evident that in an instance when the line to the telephone underV observation is seized by a connector switch, but thecall isV notv answered, the switch train should be subject to release `when the connection.isinterrupted at the telephone ofthe callingparty, .To .insurethis mode of operation there is provided means operable in case the talking loop between the calling and called. parties is not .completed for causing the release of the switch .trainutilized in setting up the connection. Thisgmeans. comprises .the

relays |00 and Htl and the release magnet |69.

Thus, when this condition'prevails, the .battery reversing relay |10 is not :operated and, consequently, whenthe relays |00 and I lil restore, in the order named, in response to the interruption of the connection at the calling telephone, the circuit for energizing the releasemagnet is coml pleted. The wipers lll-42,' inclusive, thereupon,

are restored to their respective normal positions and the .operating circuit for the relay lis opened. This relay upon "falling back in turn opensY the operating circuitv of .the relay |99. When the last-mentioned relay restores it interrupts the path including the conductors 6U and 6| for applying ground potential to the control conductor 22 independently of the contacts associated with the armature III. Hence the switch train preceding the connector switch is permitted to restore to its normal condition and the connection iscleared out.

As pointed out previously, the arrangement of .the system is such that when the linefto be obl- -served is seized by any one of the group .of lcon- ;nector switches in the bank contacts of which lthis line is multipled, groundis present on the `conductor 64 and the relays |823 v and ISS are operated. Hence, all of the armatures ISH,y |92, |93, etc., areclosed to..their respective associated The switch train preceding l'operatedso longxas said talking loop is'not inf" vcontacts:,andgthe paths for applying ground. po-

tential to theV respective control conductorsof the connectorswitches included in thegroup, independently .of their respective hold relays such, for example, as the relay lill, are prepared." 5

YSince,.however, the relays |40, land lli! do not operate when the connector` switch attempts to seize the line |2, 4the alternativeppath forap- .'plying, ground potential Lto the control-conductorv 22 :is not completed. As a result -the switchil@ '.tra'in leading to the busy line is releasable under `the control of the calling party.

From the foregoing description it will be apparent that under any conditions following the completion of atalking loopbetween a callingll substation and .the substationnnder observation,

it ispossible to trace a `call to a line Whichit said rst telephone tosaid second telephone, saidZ280 kconnection comprisinga talking loop adapted to be completed when -thecallisanswered atsaid second telephone, saidmeans normally being released When said talking loopis interrupted at said first telephone, an `alarmdevice, means rfa-3235 sponsive to the operation of said first-named means for causing theeoperation of said alarm device, and means -lresponsiveto the-completion of said talking loopfor. preventing the release of said first-named means, 4V.whereby callsV to saidfln second telephone maybe traced by an attendant.

2. Ina Vtelephone system,.a rst vtelephoneya second telephone, meansV for establishing a connectionzbetween said telephones on/a call from .said first telephoneto said second telephone, saidm` connection comprising a talking vloop adapted tobe completed when said call is answered at said second telephone, said'means normally being released when the talking loop is interrupted at said rst telephone, an alarm device, and'50 means automatically operable during the estab- "lishing of the connectionl and-maintained operatedso flcngassaidtalking. loop is not interrupted at-.saidsecond telephone for causing the operation of said alarm deviceand for preventing the" release. of .said first-named means, whereby calls to said Vsecond telephone may :be traced by an attendant.

3.y In a telephone system, arst'telephone, a

-second telephone, means Vfor establishing a con- G0 `nection between said telephoneson a call from said rst telephone to said second telephone, said connection comprising a talking loop adapt- .ed to be completed when said call is answered at said second telephone, said means normally bei ing released when said talking connection is interrupted atsaid rst telephone, an alarm device, vmeans automatically? operable during the establishing of saidconnection and `,maintained terrupted'at said second .telephone for causing the operation of said alarm fdevicevand for preventing .the -release of 'saidfrst-named means,

v` vv'vherebycalls to `said second telephoney maybe traceduby xan attendant,;:and :means operable `inzz' case said talking loop is not completed for rendering said second-named means ineffective, so that said connection may be released.

4. In a telephone system, a first telephone, a second telephone, means including a switch train for establishing a connection between said telephones on a call from said first to said second telephone, said connection comprising a talking loop adaptedto be completed when said call is answered at said second telephone, said switch train including means for initiating the release of said connection when said talking loop is interrupted at said rst telephone, an alarm device, and means operable during the establishing of said connection and maintained operated so long as said talking loop is not interrupted at said second telephone for causing the operation of said alarm device and for preventing the operation of said second-named means from releasing said connection, whereby calls to said second telehpone may be traced by an attendant.

5. In a telephone system, a irst telephone, a second telephone, means including a switch train for establishing a connection between said telephones on a call from said rst telephone to said second telephone, said connection comprising a talking loop adapted to be completed when said call is answered at said second telephone, said switch train including means for initiating the release of said connection when said talking loop is interrupted at said rst telephone, an alarm device, means operable during the establishing of said connection and maintained operated so long as said talking loop is not interrupted at said second telephone for causing the operation of said alarm device and for preventing the operation of said second-named means from releasing said connection, whereby calls to said second telephone may be traced by an attendant, and means operable in case said talking loop is not completed for rendering said thirdnamed means ineffective, so that said connection may be released.

6. In a telephone system, a rst telephone, a second telephone, means including a switch train and lines individually associated with said telephones or establishing a connection between said telephones on a call from said rst telephone to said second telephone, said connection comprising a talking loop adapted to be completed when said call is answered at said second telephone, said switch train including means for completing the connection to the line associated with said second telephone and means normally operable to initiate the release of the connection inY response to the interruption of said talking loop at said rst telephone, an alarm device, and means responsive to the operation of said secondnamed means for causing the operation of said alarm device and for preventing said third-named means from initiating the release of said connection, whereby calls to said second telephone may be traced by an attendant.

'7. In a telephone system, a first telephone, a second telephone, means including a switch train and linesindividually associated with said telephones for establishing a connection between said telephones on a call from said rst telephone to said second telephone, said connection comprising a talking loop adapted to be completed when said call is answered at said second telephone, said switch train including means for completing the connection to the line associated with said second telephone andl means normally operable to initiate the release of the connection in response to the interruption of said talking loop at said first telephone, an alarm device, and means operable in response to the operation of said second-named means and maintained operated so long as said talking loopis not interrupted at said second telephone for causing the operation of said alarm device and for preventing said third-named means from initiating the release of said connection, whereby calls to said second telephone may be traced by an attendant.

8. In a telephone system, a rst telephone, a second telephone, means including a switch train and lines individually associated with said telephones for establishing a Connection between said telephones on a call from said first telephone to said second telephone, said connection comprising a talking loop adapted to be completed when said call is answered at said second telephone, said switch train including means for completing the connection to the line associated with said second telephone and means normally operable to initiate the release of the connection in response to the interruption of said talking loop at said first telephone, an alarm device, means operable during the establishing of said connection and maintained operated so long as said talking loop is not interrupted at said second telephone for causing the operation of said alarm device and for preparing a circuit for preventing said third-named means from initiating the release of said connection, means responsive to the operation of said second-named means for completing said circuit, whereby calls to said second telephone may be traced by an attendant, and

` means operable in case the talking loop is not completed for preventing the completion' of said circuit so that said connection may be released.

9. In a telephone system, a first telephone, a

second telephone, means including a switch train and lines individually associated with said telei phones for establishing a connection between said telephones on a call from said first telephone to said second telephone, said connection comprising a talking loop adapted to be completed when said call is answered at said second telephone, said switch train including a selector switch and a connector switch for completing the connection to the line associated with said second telephone, means included in said connector switch and normally responsive to the interruption of said talking loop at said first telephone for releasing said selector switch, an alarm device, and means automatically operable during the establishing of said connection for causing the operation of said alarm device and for preventing said lastnamed means from releasing said selector switch, whereby calls to said second telephone may be traced by an attendant.

10. In a telephone system, a rst telephone, a second telephone, means including a switch train and lines individually associated with said telephones for establishing a connection between said telephones on a call from said rst telephone to said second telephone, said connection comprising a talking loop adapted to be come' pleted when said call is answered at said second telephone, said switch train including a selector switchand a connector switch for completing the connection to the line associated with said second telephone, means included in said connector switch .and normally responsive to the interruption of said talking loop at said rst telephone for releasing said connection, an alarm device, means operable during the establishing of said connection for causing the operation of said alarm device and ior preventing vsaid lastnamed means from releasing said selector switch, whereby calls to said second telephone may be traced by an attendant, and means operable in case said talmng loop is not completed for rendering said last-named means` ineffective, so that said connection may be released.

11. In a telephone system, a iirst telephone, a second telephone, a line switch associated with said rst telephone, a selector switch, a connector` switch, means including said switches, operative in the order named, for establishing a connection between said telephones on a -call from said rst telephone' to said second telephone, said connection comprising a'talking loop adapted to be completed when said call is answered at said second telephone, means included in said connector switch and normally operative to release said line switch and said selector switch when said talking loop is interrupted at said rst telephone, an alarm device, and means operated during the establishing of said connection and maintained operated so long as said talking loop is completed for causing the operation of said alarm device and for preventing the release ofV said line and selector switches, whereby calls to said secondtelephone may be traced by an attendant. 12. In a telephone System, a second telephone, lines individually associated with said telephones, means including a selector switch and a connector switch, operable in the order` named, for establishing a connection be- Y connector switch for applying a predetermined potential to said control conductor to hold saidv selector switch operated, said relay being op-l erable from one of its two positions to the other to remove said potential from said` control conductor and thereby release said selector switch when said talking loop is interrupted at said first telephone, an alarm device, and means operable during the establishing of said connection and'maintained operated so long as said talking loop is not interrupted at said second telephone for causing the operation of said alarm device and for maintaining said predetermined potential on said control conductor independently of said relay.

13. In a telephone system, a rst telephone, a second telephone, lines individually associated with said telephones, means including a selector switch and a connector switch, operable in the order named, for establishinga connection ,between said lines on a fcall from said first telephone to said second telephone, said connection comprising a talking loop adapted to be completed when the call is answered at said second telephone, said selector switch including a control conductor, a line relay in ,said connector-switch operated to one of its twoppositions in response to the seizure of said connector switch by said selector switch, a second relay operated to one of its two positions in response to the operation of said line -relay to its said one position, means responsive to the op-" eration of said second relay to its/said one pon 'sition for conditioning said connector switch to complete said connection, said second relay` including contacts, closed when said second rea rst telephone, v

lay is operated to said onerpos'itionQforapplying a predetermined potential to said control conductor thereby to hold said selector switch operated, .said second relay being operable froml its said Yone .to the other ofits two 'positions to remove said potential from said control con-y ductor and thereby'releasesaid'selector switch when said talking .loop is interrupted at saidV first telephone, an alarm device, and means operable during the'establishing of said connection and maintained operated so long as the talking loop yis notV interrupted at said second telephone for causing the operation of said' alarm device n and `for maintaining said predetermined potential on said control conductor independently of said relays.

14. In a telephone system, a iirst telephone,

a second telephone, lines individually associated ,with said telephones, means including a selectory trol conductor, a line relay in said *connectorv switch operated `to one of itsv two positions in response to the seizure of said connector switch by said selector switch, a second relay operated to one of its two positions in response'toy the operation ofvsaid line relay to its said one po. sition, means responsive to the operation of said second relay to its said one position for con-V ditioning said connector switchI to complete said connection, said second relay including'contacts, closed when said secondrelay is operated to said oneposition, for applying a predetermined potential to said control conductorthereby to hold said selector switch operated,'a normally intere rupted path for applyingV said predetermined potential to said control rconductor independeL entlyl of said contacts, an alarm device,y means operable during thel establishing of said connec-l tionf andi maintained `operated so long as said talking loop is` not interrupted at said second telephone for causing the operation` of said alarmV 1,5. In a telephone system, a connector switch including a directing wiper, means for driving said wiper and bank contacts with which saidy wiper is adapted to engage, aline including a control conductor terminating at one ofl said bank con-y tacts, a telephone on said line, a plurality of selector switches individually adapted to be oper.- ated to seize said connector switch, means com prising Vone of said selector switches.. for causing said first-named means to drive said wiper intov engagement with said one of said c.ontacts,"a relay operated to one of its twovpositions in response to the engagement of l,said wiper and said one of said contacts, means includingsaid telephone 1for switches fro-mbeing released solong as said relay is in said one of said positions.

f 16. In a telephone system, a connector switch including a directingwiper, means for-driving said wiper Vand bank contacts with which'said wiper isradapted togengage, a line including" a f control conductor terminating at` one of said bank contacts, a telephone on said line, a vplurality of selector switches individually adapted to be operated to seize said connector switch, means comprising one oi said selector switches for causing said first-named means to drive Asaid directing wiper into engagement with said one of said contacts, a relay operated to one of its two positions in response to the engagement of said wiper and said one of said contacts, means including said telephone for maintaining said relay in said one position, an alarm device operative in response to the operation of said one relay to said one position, and means comprising a portion of the control relays included in said connector switch and normally operable in establishing said connection, for preventing said one of said selector switches from being released so long as said relay is in said one of said positions.

17. In a tel-ephone system, a group of connector switches, eac-h of said switches including a directing wiper, driving means for actuating the wiper and bank contacts with which the wiper is adapted to engage, a line including a control conductor terminating at one and the corresponding contact of each of said switches, a telephone on said line, a plurality of selector switches individually adapted to be operated to seize any one of said connector switches, means comprising one of said selector switches for causing the driving means of a seized connector switch to drive its associated directing wiper into engagement with the contact at which said control conductor terminates, a relay operated to one of its two positions in response to such engagement, means including said telephone for maintaining said relay operated, an alarm device operative in response to the operation of said one relay to said one position, and means for preventing said one ofsaid selector switches from being released so long as said relay is in said one of said positions.

18. In a telephone system, a group of connectorV switches, each of said switches including a directing wiper, driving means for` actuating the wiper and bank contacts with which the wiper is adapted to engage, a line including a control conductor terminating at one andthe corresponding contact of each of said switches, a telephone on said line, a plurality of selector switches individually adapted to be operated to seize any one of said connector switches, means comprising one of said selector switches for causing the driving means of a seized connector switch to drive its associated directing wiper into engagement with the contact at which said control conductor terminates, a relay operated to one of its two positions in response to such engagement, means including said telephone for maintaining said relay operated, an alarm device operative in response to the operation of said one relay to said one position, and means comprising a portion of the control relays included in the seized connector switch and normally operable in establishing said connection, for preventing said one of said selector switches from being released so long as said relay is in said one of said positions. v

19. In a telephone system, a first telepho-ne, a second telephone, means for establishing a connection between said telephones on a call from said iirst telephone to said second telephone, said connection comprising a talking loop adapted to be completed when the call is answered at said second telephone, said means normally being released when said talking loop is interrupted at said rst telephone, an alarm device, means' automatically operable to cause the operation of said alarm device and to prevent the release of said firstnamed means, whereby calls` toy said second telephone maybe traced by an operator, and means automatically operable to prevent the operation of said last-named means from affecting the release of said first-named means when saidl'second telephone is busy at the time said call is initiated. Y

20. In a telephone system, a iirst telephone, a second telephone, means for establishing a connection between said telephones on a call from said rst to said second'telephone, said connection comprising a talking loop adapted to be completed when said call is answered at said second telephone, said means normally being released when the talking loop is interrupted at said rst telephone, an alarm device, means automatically operable during the establishing ofthe Vconnection and maintained operated so long as said talking loop is not interrupted at said second telephone for causing the operation of said alarm device and for preventing the release of said rstnamed means, whereby calls to said second telephone may be traced by an operator, and means automatically operable to prevent the operation of said last-named means from affectingthe release of said first-named means when said second tele-y phone is busy at the time said call is initiated.

21. In a telephone system, a rst telephone, a second telephone, means for establishing a connection between said telephones on a call from said iirst telephone to said second telephone, said connection comprising a talking loop adapted to be completed when the call is answered at said second telephone, said means normally being released when said talking loop is interruptedv at 'said first telephone, an alarm device, means responsive to the completion of said connection for causing the operation of said alarm device, and means responsive to the completion of said talking loop for preventing the release of said iirst-named'means by anoper-a.- tionperformed atV said first telephone, whereby calls to said second telephone may be traced by an attendant, said last-named means being inoperative in the event said second telephone is busy at the time said call is initiated.

22. In a telephone system, a rst telephon a second telephone, means for establishing a connection between said telephones on a call from said iirst telephone to said second telephone,- said connection comprising a talking loop adapted to be completed when said call is answered at said second telephone, said ymeans' normally being released when the talking loop is interruptedat said first telephone, an alarm device, means responsive to the completion of said connection for causing the operation of said alarm device, and means responsive to the completion` of said talking loop and effective soA long as said talking loop is not interrupted at said second telephone for preventing the release of said iirst'-' named means, whereby calls to said second telephone may be traced by an attendant, said lastnamed means being inoperative in the event said second telephone is busy at the .time saidcall is initiated. V 23. In a telephone system, a rst telephone, a;

second telephone, means for establishing a connection between said telephones on a call from said rst telephone to said second'telephone, said connection comprising a talking loop adaptedY to be completed when 'said call is answered at said second telephone, said means normally being released when said talking connection is in-l terrupted at said rst telephone, an alarm de vice, means responsive to the completion of said connection for causing the operation of said alarm device, means responsive to the completion of said talking loop and effective so long as said talking loop is not interrupted at said second telephone for preventing the release of4 said first-named means, whereby calls to said second telephone maybe traced by an attendant, and means for rendering said last-named means inoperative in the event said second telephone is busy at the time said call is initiate-d.

'24. In a telephone system, a rst telephone, a second telephone, means including a switch train for establishing a'connection between said telephones on a call from said rst to said second telephone, said connection comprising a talking loop adapted to be completed when said call is answered at said second telephone, said switch train including means for initiating the release of said connection when said talking loop is interrupted at said first telephone, an alarm device, means responsive to the completion of said connection for causing the operation of said alarm device, means operable when said talking loop is completed and maintained operated so long as said talking loop is not interrupted at said second telephone fer preventing the operation of said second-named means from releasing said connectiom'whereby calls to said second telephone may be traced by an attendant, and means for rendering said last-named means inoperative in the event said second telephone is busy at the time said call is initiated.

25. In a telephone system, a iirst telephone, a second telephone, means including a switch train and lines individually associated with said telephones for establishing a connection between said telephones on a call from said first telephone to said second telephone, said connectioncomprising a talking loop adapted to be completed when said call is answered at said second telephone, said switch train including means for completing the connection to the line associated with said second telephone and means normally operab-le to initiate the release of the connection in response to the interruption of said talking loop at said rst telephone, an alarm device, means responsive to the operation of said secondnamed means for causing the operation of said alarm device and for preventing said thirdnamed means from initiating the release of said connection, whereby calls to said second telephone may be traced by an attendant, and means for rendering said last-named means inoperative to aiect the release of said iirst named means in the event said second telephone is b-usy at the time said call is initiated.

26. In a telephone system, a rst telephone, a second telephone, means including a switch train and lines individually associated with said telephones for establishing a connection between said telephones on a call from said rst telephone to said second telephone, said connection comprising a talking loop adapted to be completed when said call is answered at said second telephone, said switch train including a selector switch and a connector switch for completing the connection to the line associated with said second telephone, an alarm device, means responsive to the completion of said connection for causing the operation of said alarm device, means included in said connectorswitch and normally responsive to the interruption of said talking loo-p at said i'lrst telephone for releasing said connection, means operable when said talking loop is completed for preventing' said last-named means from releasing said selector switch,iwherebyY callsto said second telephone may be traced by an attendant, and means including in said connector switch for rendering said last-named means inoperative inthe event said secondtelephone is busy at the time said call is initiated:

27. In a telephone system,'a`rst telephone,

a second telephone, lines individually.l associated with said telephones, means includinga selector switch and a co-nnector switch, operable in the order named, for establishing a connection between said lines on a call from vsaid first telephone to 'said second telephone, an alarmrdevice, means responsive to the completion of said connection for causing the operation of said alarm device, said connection -comprising a talking loop adapted to be completed when Ythe-call is answered at said second telephone, said selector switch including a control conductor, means comprising a relay in' said connector switch for applying a predetermined potential to said control conductorto hold said selector switch operated, said relay being operable from one of its two positions to the other to remove said potential from said control conductor and thereby release said selector switch when said talking loop is interrupted at said yirst telephone, a battery reversing relay in said connector switch, and means including said battery reversing relay for maintaining said predetermined potential on said control conductor independently of said rst-named relay.

28. Inan automatic telephone system, a rst telephone, a second telephone, lines. individually associated with said telephones, means including a selector switch and a connector switch, operable in the order named, for establishing a connection between said lines o-n a call from said iirst telephone to said second telephone, said connection comprising a talking loop adapted toI be completed when .the call is answered at said second telephone, said connector switch being operative to'select the line associated with said second telephone, said selector switch including a control conductor, means comprising a relay in said connector switch for applying a predetermined potential tosaid control conductor toY hold said selector switch operated, said relay being operable from one o-f its two positions to the other to .remove said potential from said control conductor and thereby release said selector switch when said talking loop is' interrupted at said rst telephone, an alarm device, a normally incomplete path for applying said potential to said control conductor to hold said selector switch operated independently of said relay, means responsive to the operation of saidr 29. In an automatic telephone system, a rst telephone, a'second telephone, lines individually associated with 4said telephones, means including a selector switch and a connector switch, operable in the order named, for establishing a connection between said lines on a call from said rst telephone to said second telephone, said connection comprising a talking loop adapted to be completed when the call is answered at said second telephone, said connector switch being operative to select the line associated with said second telephone, said selector switch including a control conductor, means comprising a relay in 5 said connector switch for applying a predeterswitch operated independently of said relay, means responsive to the oper-ation of said connector switch to select the line associated with said second telephone for causing the operation of said alarm device and for partially completing said path, means responsive to the completion of said talking loop for completing said path and for holding said path completed so long as said loop is notrinterrupted at said second telephone, and means for preventing said two last-named means from completingsaid path in the event the line associ-ated with said second telephone is busy at the time it is selected.

` SETI-I E. PETERSON.

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