US825626A - Combined telephone-exchange and alarm system. - Google Patents

Description

No. 825,626. PATENTED JULY 10, 1906. H. G. WEBSTER.

OOMBINEDTELEPHONE EXCHANGE AND ALARM SYSTEM.

APPLICATION FILED 00T.10, 1904.

2 SHEETS-SHEET l No. 825,626. PATENTED JULY 10, 1906.

v H. G. WEBSTER. COMBINED TELEPHONE EXCHANGE AND ALARM SYSTEM.

APPLICATION FILED 0G'1.10,1904.

2 SHEETS-SHEET 2-.

3 Plwl l m l UNITED sTATEs PATENT. oEETcE.

HARRY G. WEBSTER. OF CHICAGO. ILLINOIS, ASSIHNOR TO MILO (i. KELLOGG, OF CHICAGO, ILLINOIS.

COMBINED TELEPHONE-EXCHANGE AND ALARM SYSTEM.

Application filed October 1 If) (all whmiz/ it may ((HIJIRIIL.

Be it known that I, HARRY G. WEns'r R, a cit zen of the United States, and aresident of Chicago, county of Cook, and State of Illinois, have'invented certain new and useful Improvements in a Combined lelephone Exchange and Alarm System, of which the following is a full, clear, concise, and exact description, reference being bad to the accompanying drawings,-forming' part of this specification.

My inW-ntion relates'to systei-ns in which l line-circuits extending from subscribers statrons to a tele'phone-exchange and adapted tor interconnection thereat are utilized for the transmission of special, fire, burglar, and

other alarm signals in addition to their ordinary telephonic use.

The object of my invention is to provide 1 an improvement upon a system proposed heretofore in which the line-circuit is at all times available tor the transmission ot an alarm signal and in which the alarm-sending and alarm-receiving apparatus does not cause any interference with telephonic signaling or conversation except upon the sending of an alarm signal, when the telephonic requirements may be disregarded. In such a system it is desirable that any accidental derangement of either limb of the telephones line be automatically indicated .at the alarmrecciving station, and it is also of advantage to maintain the alarm service by means of one limb only of the telephone-line in case the othr r limb be accidentally broken. desirable that the electrostatic balance of the line be preserved without the use of artilicial resistance and that the alarm mechanism be of simple and reliable character.

The improvement of my present invention consists in novel mrans for meeting these requirements, and it is in this respect a species under the gci'ieric invention set forth in the above application.

Other advantages of my improved system will be apparent to Lh..so skilled in the. art from the following description.

In accordance with my invention l associate with the telephone-line a grounded source of current and an electromagnet having two opposing windings of equal energizing capacity, one winding being in circuit with each line-limb, respectively. The circuit of these windings is normally closed through a It is also Specification of Letters Patent.

:atentea July 10, 1906.

0,1904. Serial No. 227,876.

l l l j l l device in a local circuit.

high resistance or impedance in bridge of the two limbs, having a ground connection at a point intermediate of the two limbs. and the inductance of the path from either line-limb to ground through this bridge connection is substantially the same. As long as the linelimbs remain intact the How of current through one winding of the magnet will be somewhat greater than that through the other, and the magnet will therefore be energized to a limited extent. In case the telephone is in use the flow of current through the two windings will be increased, but their relative energizing effect will still remain unequal, and in cascthat line-limb connected with the active or live side of the battery be connected directly to ground a relatively strong current will llow through one winding only. energizing the magnet to its greatest extent. Alarm-scnding mechanism is provided of the nature of the. ordinary makeand-break" wheel of the district telegraph box or of other construction, so arranged as to make and break a circuit of the line-limbs or the'earth connection m a predetermined manner, and thus intermittently decnergize the 'electromagnet, which by its armature and contacts controls an alarm-indicating In a preferred form when energized to its greatest extent the electromagnct controls associated mechanism adapted to cause the display of a special signal to indicate the accidental grounding of the circuit. Also in its preferred form my invention contemplates a line-circuit in which the source of current is grounded at its center point and in which the bridged impedance, while having substantially the same inductance between its grounded center and each line-limb, is of greater ohmic resistance in one side than in the other, thus providing a structure in which the alarm-signal may be. transmitted over one limb only of the line in case the opposite limb should become accidcntally broken. The two windings of the elcctromagnct may be superimposed or may be twin windings or may be located upon opposito ends of the magnet-core, in which case they would bc provided with non-inductive shunts or other well-known means for preventing their interference with the rapidlyalternating telephonic currents. The organization illustrated also comprises means by which any electromagnet, with its associatedlocal circuit apparatus, may be brought into association with any line of the telephone system in a systematic and workmanlike manner and without disturbing the perma-' nent wiring.

The .invention will be further illustrated and described in the accompanying drawings,

in whichce'ssory apparatus, the

Figure l'is a diagram illustrating two subscribers lines extending in a metallic circuit from the substations to a central-battery telephone-exchange switchboard of the two- Wire type, with the connecting cord and acsystem being organized and equipped in accordance with the referred forms of my invention. Fig. 2 illustrates a modification of the connections of the brid ed impedance and the make-amt break mec ianism. Figs. 3 and '4 illustrate, myinvention in its simpler form, in which the central battery is not grounded at its center and in which the resistance of the blidged impedance is the same for each side of the circuit in a switchboard system of the threewire type. Fig. 5 illustrates well known cord connecting apparatus for association with the line-circuit of Figs. 3 and 4. Fig. 6 indicates means for associating the special ele'ctroina-gnet with any telephone-line of the system without disturbing the permanent exchange-wiring. l

Like characters reler to like parts in the several drawings. v

Referringto Fig. l, the subscribers stations A and Bare provided with the usual apparatus, adapted, preferably, for use with a central source of current-supply and comprising a receiver 1* and transmitter t in a circuit which normally stands open at the hookswitch It, the bell I) and condenser 11 being in permanent bridge of the line. \Vhilc l have thus illustrated one particular l'o'rm of substation arrangement, it will be apparent to those skilled in the. art that numerous other arrangements may be equally well employed in my invention, and 1 therefore do not wish to be limited to the particular one shown. The limbs l and 2 of the line extend to the central oliice and are there connected, limb 1 through armaturct} and contact 9 of the cutoff relay 3 and the winding of relay 4 to the negativeside ol thebattery (3, and limb 2 throu 'harmature 7 and contact 8 of the cutoff re ay, and resistance 1.1 to the positive side of the same battery. \Vhile .i have here shown the connection of resistance 1 I, it will be understood from the following description that this resistance is only used in such lines .as have alarm equipments, the other lines directly connected from contact 8 to The subscrlber in calling raises his receiver and com being -pletes the low-resistance circuit, including his transmitter and hook-switch contact, to actue 6 5 ate the relay 4, lighting his line-lamp Upon 18 of the cord-circuit. plied to the insertion of an answering-plug i. the operation of relay 3 breaks the normal connection' of the line-limbs through relay i and resistance 11 to the battery C, thus extinguish-- ing the line-lamp andconnects them to the spring-jacks 10 and thence to strands 1.6 and Current is now supthe line A from battery Q through relays 12 and 14, which control the circuit ol the supervisory lamp 20, the lamp remaining dark as long as current flows throughr'elay 12. The operator tests, plugs -in, and, ri'ngs a wanted subscriber in the usual way with calling-plug O and r1ngmg-key g g, While ringing. the relay 3 is energized by current front battery E and. generator G, and after the ringing-key is released relay 15 of the cordcircuit and relay 3 of line B areenergized by current from battery D. The relay 15 when thus actuated cuts off the test-relay 2'2. and completes the circuit of strand supervisory lamp 21. When the called sub- 'scriber answers, current is furnished his instrument through relays 15 and 13, and the energization of relay 13 opens the. circuit of lamp 21, causing its eii acement as long as the. subscribers hook-switch; contact remains closed. The subscribers are now able to converse over cord-strands 1G 17 and i8 19, which include the condensers dd of cord circuit. The hanging up otboth receivers deprives the relays 12 and 13 of current, thus allowing them to complete the circuits of lamps 20 and 21, which being illuminated constitute the disci)nnect-signal. re ulartelephonic operation of-thc'system h v V aml is not interfered with by the presence o the alarm apparatus associated with any of the lines. Those lines which are to be utilizcdtor alarm service are provided with a magnet F, having two energizing-wmdmgs (one for each limb of theline, respectively) ol equal energizing capacity and connected diffcrentially or in such a manner that the energizing eiiect of the telephonic currents will-be opposed in the two windings. These windings, as will be understood cy those skilled in the art, may be twin or parallel windings or may be superimposed or concentric windings and will in either-*asc present no objectionable impedance to the telephonic currents. This magnet, as will be hereinafter explained, controls mechanismlor causing an alarm or other signal at. the alarm-receiving station. At the alarm-sending station or This is the 17 through its'contacts and also completes the circuit ot IIO other convenient point an impedance l is provided in bridge. of the two-line. limbs, having its center point connected ,to earth, as indicated, and this bridged connection also includes the nonrimluctive resistance. 4;. It is to be understood that in the organization of this figure this bridged impedance is to be arranged in any suitable. manner bywhich the inductance. from either limb to'ground -break wheel n.

shall be substantially equal, while the ohmic resistance between either limb and ground is to be subst-antiallydill'ercm. I and resistance i are therefore only conventional illustrations of such an arrangement,

and I do not limit myself to any specificstructure for this-bridge. Alarm-sending apparatus M is provided at a point intermediate of the impetlancebridge and the magnet F, which may be of the character of the wellknown district messenger-box or similar apparatus, arranged to be released manually or gether with the thermostatic or other circuit v breaking devices (indicated atf.) In case an alarm is to be given the opening of this circuit, as indicated'at f, in connection with line B causes the deenergization of magnet 25, allowing the arm 26 to be retracted by its associated spring, disengaging stop 24 and allowing the revolution of the make-and- As this wheel rev'olves' the pro'ections upon its periphery will cause limhs 1 and? to be interrupted at contacts 27 in accordance with a predetermined code, as will be well understood by those skilled in the art. This portion of the structure is shown in its normal position at line A, while at line B it is shown in operation. The batteries C or I) being grounded at'their central point, the operation of the system is as follows: Under the normal condition ol disuse of the telephone apparatus the circuit of battery C is closed through the line-limbs and the bridged impedance indicated at I, and were this impedanceduidge of equal ohmic resistance in its two halves the current in limbs 1 and 2 would be substantially equal and the magnet F would be unenergized. It is to be understood in this connection that the resistance 1 1 is substantially the same as that of relay at and that the ohmic resistance of the two line,- limbs themselves is substantially equal. Upon the insertion of a plug, the linebeing then supplied with current through relays 12 14 or relays 13 15, which are of equal resistance in either case, the conditions would be I the same, and they would not be altered by the completion of the circuit through the subscribers instrument either belore or after the insertion of a plug. Inasmuch, however,

that half of the impedancedn'idge associated with limb 2 includesadditional resistance,'as indicated at i, the current in this limb of the line will be of lesser vaiue than that in limb 1, and the magnet F will there- 'lhe impet'lance to the preponderance of currentin limb 1. t This. limited cncrgization, as I have shown, will be n'iaintained either before or after the insertion of a connecting-ping and re ardless of whether the substatitm-telephone is or is not in use. Being thus energized, the magnet in the structure indicated completes, by its armature 31, a circuitot battery 30, which includes the movable contact-piece 32, normally held against.- stop'33 by spring 35 and the magnet 28 of the alarm-indicating device. H. While this indicating device is aconventional illustration of the ordinary telegraphic register, it is to be understood that other alarm-indicating devices may be used which are adapted to respond to the control of magnet F. In case an alarm-signal is to be given the actuation of the make-and-break mechanism interrupts the circuit of the line-limbs in the predetermined characteristic manner, depriving the relay F of all current at each interruption, which consequently opens and closes the local circuit in the manner rer uired to give the alarrrnsignal. 'lhis operated condition is that indicatedin' the drawing of line B. The bridged impedance I being of relatively high resistance, it is to be noted that in ed such direct earth connection will cause a material increase in current-flow in the corresponding line-limb. This increased current will consequently energize the ma net I attract its armature, and complete a circuit which may be traced from battery 30, through armature 3.1, contactqiiece 32, contact-34, and lamp 29, causing the illuminat-ion of the lamp, which constitutes a groundsignal. The circuit of magnet 28 being still maintained at contact-piece 3'3 and armature 31, no alarm indication is given at this time. .As will be well unt'lerstoml the tension ol' contact-piece 32 may be adjusted by means of spring 35 or in any other well-known way, and likewise the lamp 2!) may be replaced by various other signaling devices known to the art. It will also be observed that should limb l or 2 ol the line become m'cidentally broken at any point current will still continue to llow over the line-limb remaining intact, energizing the relay i and causing its proper actuation to indicate either an alarmsignal or a groumbsignal at the proper time. During the process of calling a st'ibscriber the relay 1* is energized by current from battery E and generator (1, a sullicient portion being i diverted to ground through the impedance ll to cause a preponderating ell'ect. in the windl ing associated with limb 1. Pig. 2 indicates a modification ol'the circuit-brealting and substation arrangement of Fig. l, the make-altd-break device being indicat-ed diagrammatically at M: ln this modi- "lication the impedance I may in itsell'orex 65 fore be'energized to an extent proportionate i ternally be provided with additional resistcase either limb becomes accidentallyground-- to a greater extent, causing it to still turther sistance between limb 2 lirnbs instead of being carried through th cont-acts of the illttliO-alndbftuli device are COntiLnous, and the make-and break device is included in the ground branch, as indicated by contact-brush 36,1estingupon the uninsu lated portion of wheel 37, whi ch is cormected to ground. As in the case of Fig. l the normal current-flow will be greater through limb tionot this ground branch the current in both cut-oll rel:i-y4l,\\'l1i(-'ii is included in a strictlV '44 40, through th 1 than through limb 2. When, however, the alarni-sending-apparata1s is released, as indicated by the revolution oi wheel 37, the ground branch from the i mpedance-bridge is broken as each insulatedsegn'ient ol' the wheel 37 passes under. brush 36. At each interruplinelimbs becomes substantially the same, and the magnet F is consequently dcincrgized, thus causing the operation of. the alarm indicating device in the manner previously described. The modification of Fig. 2 dill'ers, therefore, from the structure of Fig. l in that the magnet F is actuated through the removal of the prep'onderating current in one of its windings rather than through the subtraction of current from both windings.

In Figs. 3, 4, and 5 are indicated modifications ofmy invention ascmbodicd in a well. known telephonc-cxchaage system of What is known as the three-wire type. This system dill'ers lrom that oi the previous drawings in that the cut-oil relay associate! with one I), limb of the tallcirig-circuit. is replaced by a local circuit having separate spring-jack terminals 40 and corresponding plug-terminals 44. In its telephonic operation the subscriber calls in the usual manner by removing his receiver from its hooleswitch, thus completing a circuit of battery (l, through linerelay the contacts of the cnt-oll relay il, tl'ie'limi-limbs and the substation instrument, thus energizing relay 4 and lighting the telephone-line lamp 5. When the operator inserts a plug, the circuit from the cut-oll' relay is completed from the battery t, through resistance 48, lamp 2t), plug and jack contacts 0 winding of relay 41 to the return side of the battery, thus energizing the relay and under normal conditions causing the lamp 20 to light. Through the insertion of a plug the current of battery C is now turnished to the line through the Windings7 l and 72 of" repeating-coil J, cord-strands 16 and 18,

and plug-contacts 42 and 43, which engage corresponding contact-pieces of t jacks 3t), and the subscriber being at his telephone the relay 45, which is included in strand 18, is energizet and by its contact completes a cir cuit it. shunt of lamp 20, which includes the resistance 47, and causes the extinguislnnent ol the lamp. The operator listens, tests, and

giog in completes a similar circuit 'for the mlbscriber who to be called, which includes the windings 723 and 74- ol' therepeating-coil. The.subscribers circuits are thus inductively united for conversation by means of the re- 75 pending-coil rather than by condensers, as in Either subscriber can his superyisory h1s l1()0l-S\V1Cll,

at their positive terminalsand that the imthe relay 45 8o it is to be noted pedanc-e l is indicated as having substantially c the same resistance between each line-limb and ground. Also that the make-and-brea'k device indicated at M is only adapted to open the circuit ,ol line-limb 1, the opposite limb being permanently continuous Referring" to Fig. 3, it will be seen that during the dis use ot' the telephone relay F, which has its windings arrange-d similarly to the relay F of F ig. l, is energized by current from battery (7 through relay 4,1imb 1, device M, and impedance l to ground, and that during the use of the telephone, while a circuit of decreased resistance is completed through both relaywindings the energization of relay F still depends upon'the preponderanceof current.

through the circuit of lnnb 1, which includes the ground at I. is Upon the insertion of the. *onn'ccting-plug, current now being furnished to the line through the substantially equal windings of the repeating-coil J, the conditions of current-[low through relay F remain the same, it being understood that the relays -15 or 46 may be made of sufliciently low resistance toproduce no objectionable unbalancing ell'ect in the circuit. It will also be seen that when calling a subscriber the relay F will be energized by current from the genorator G [lowing to' ground at impedance I. it under any of the conditions stated the alarm-sending mechanism (indicated atM) be actuated, the consequent opening ot'liinb 1 through the passage of the insulated segments of wheel 37 under contact-piece 36 will cause the actuation otrelay F, thus controlling the circuit of battery 30 to cause an alarm indication.

The modification of Fig. '4 that of Fig. 3 only in that the windings of the relay F corresponding to relay F, are arranged upon opposite ends of-the magnetdifiers from g sake of .simplicit core rather than being parallel or concentric wound, as indicated in Fig. 3. The windings of relay F 2 are arranged to present no obj ectionable impedance to the telephonic currents either by the non-inductive shunts (indicated at 38) or in any other well known' these arrangements have been omitted from the drawings of the three-wire system for the only. -As.will be understood fromthis escription by those skilled in theart, the entirealarm-service arrangeme it of Fig. bodied in the 3, 4, and 5. 3

Fig. '6 indicates means by which any'line of a'tele hone-exchange system may be provided 1 may be equally well emthree-wire system of Figs.

aratus with any particular line trolled a the flexihl connection is made by the two pairs of jumpers, as indicated at 53' 54 and 55 56. In case it were desired to shift the magnet and its associated mechanism to some other line it would only be necessaryjto disconnect these removable jum ers-from terminals 49 and. 50 and transfertli ratus is to be shifted, removing its jumpers 51 and 52,.as previously described. It willthus be understood by. those skilled in the art that this arran ement provides means whereby any set of erm-receiving mechanism may be interchangeably connected with any telephone-line circuit of the system in a neat and workmanlike manner and without disturbing any of the permanent wiring. To recapitulate, my invention contemplates a structure in; which means may be provided for any line of a telephone-exchangesystem whereby a continuous current ismaintained in the line of unequal value in the two-line limbs. ciated with the line whereby this current not indicate an arrangebecome accidentallyv h the special-alarm apparatus. The two limbs ofthe lineenter the exchange, ter- I e jumper-wires are removed and em to the correspond ing-terminals of the line to which the appa-- Alarm-sending mechanism is assomay be interrupted or intermittently made .of -equal value in both limbs in a predtere mined manner. Alarm-receiving mechanism is associated with the line which will re spond to such interruptions or changes in value of this normal current ina. manner to give an alarm-signal, and this alarm-receiving mechanism may be arranged to give a ound-signal in response to an increased ow of current over one-line limb through its direct connection to earth.

While several batteriesC, D, and E are shown in the-drawings, it will be understood thatthese may be one and the same battery, and also that the various grounds indicated wire connected with the grounded terminal of the central battery.

-It willalso be understood that in the structures of the various drawings the brid ed resistance or impedance I is sufiiciently'high to revent a normal current-flow which wou dinterfere with the telephonic operation of the line-relay 4. or the supervisory relays in the cord-circuits.

It will also be evident to those skilled in the art that man modifications of this system may be made without de arting from th'e'spirit of my invention, and Ftherefore do not-wish to be limited to the tures shown and described; but

I claim 1. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, means for normally maintaining acurrent in the circuit of unequal value for. the two limbs and means for interrrupting said current'in a predeten mined manner and signal-controlling mech: anism responsive to such interruptions. I

2. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, means for normally maintaining a current in the circuit of unequal value for the two limbs and alarmsendmg mechanism for interrupting said current in a predetermined manner and alarmreceiving mechanism responsive to such interruptions. v

3. In av telephonaexchange system, the

precise struca substation toj the -exchange, means for normally maintaining 'a current 111 the circuit of for changing the normal current to one of equal value for the, two line-limbs and signalcontrolling mechanism responsive to such change in'value;

4. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, means for normally maintaining a current in the circuit of unequal value for the two limbs and alarmsending mechanism for changing the normal 1 current to one of-equal value for the two lineare or may be replaced by a common return unequal value for thetwo" limbs and means combination '0f a*linecircuit extending from limbs and alarm-receiving mechanism re- 6. a telephone-exchange system, "the I combination of a .line circuit extending from a substation to the exchange, means for normally maintaining a. current in the circuit of unequal value for the two limbs and alarm-- sending mechanism for intermittently changing the normal current to one of equal value for the two limbs and alarm-receiving mech- 3 an intermediate point by a third conductor, an electromagnet associated with the line 'adapted to be normally energized by a preanism responsive to such changes in value.

7. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange','a source-of'current for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an electromagnet associated with the line adapted to be normally energized by a pre-' ponderance of current in one line-limb, means for interruptingthe circuit of said source in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

8. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from ponderance of current in one line-limb, means for, interrupting the circuit of the line-limbs in apredetermined manner and mechanism controlledby the electromagnet-for causing an alarm indication.

9. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of cur rent for the line, a resistance in bridge of the line connected to said source of current-from an intermediate point by a third conductor,

an electromagnet associated with the line adapted to be normally energized by a preponderance ofcurrent in one line-limb, means for interrupting the circuit of said third conductorin a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

10. In atelcphone-exchange system, the

' combination of a line-circuit extending from a substation to the.exchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from an-intermediate point by a third conductor,

an electromagnet associated with the line adapted to be'normally energized by a p1.e-'

onderanceof current in one line-limb, means for interrupting the circuit of said resistance and third conductor in a predetermined manner-and mechanism controlled the electromagnet for causing an alarm indication.

11.. In a telephone-exchange system, the

- combination of a'line-circuit extending from asubstation to the exchange, a-source of current for the line, a resistance inbridge of the line connected to said source of current from an intermediate point by a. third conductor,

an electromagnet' associated with-the line adapted to be normally energized by current in one line-limb only, means for interrupting the circuit of said source: in a predetermine manner and mechanism controlled by the electromagnet for causing an alarm indica-j tion.

12. Ina telephone-exchange system, the

. combination o'f'a line-circuit extending from a substation to the exchange, a source of current for the line,,a; resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an electromagnet associated with the line adapted to be normally energized by current in one line-limb only, means for interrupting the circuit of the line-limbs in a predetermined manner and mechanism controlled b the electromagnet for causing an alarmindi-fl cation.

13. In a telephone-exchange system, the combination of a line-circuit extending from.

a substation to the exchange, a source of current for the line, a resistance inbridge of the line connected to said source ofcurrent from an intermediate point bya third conductor, an electromagnet associated with the line adapted to be normally energized by current in one line-limb only, means for interrupting the circuit of said third conductor in a pretrolled b the electromagnet for causing an alarm in ica'tion.

14. In a telephone-exchangesystem, the combination of aline-circuit' extending from determined manner and mechanismf con-.

a substation to the exchange, a source of current for the line, a resistance in bridge of theline-connected to said source of current from an intermediate point by a third conductor, an .electromagnet associated with the line adapted to be normally energized by currentin one line-limb only, means for interrupting the circuit of said resistance and third conductor in a predetermined manner and mechanism controlled by the electromagnet 'for causing 2 n alarm indication.

15. In a telephone-exchange system, the

combination of a line-circuit extendingfrom a substation to tlieexchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor,

an electromagnet associated with the line normally energized by current in the circuit of said third conductor, means for interrupting the c rcuit of said source in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

16. in a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a resistance in bridge'of the line connected to said source of current from an intermediate point by a third conductor, an electromagnet associated with the line normally energized by current in the circuit of said third conductor, means for interrupting the circuit of the line limbs in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

17. in a telcplrune-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of cur rent [or the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an clcctromagnet associated with the line normally energized by current in the circuit of said third conductor, means for interrupting the circuit of said third conductor in a 1n'cdcterminial manner and l110-7ll3I1lSHl con trolled by the clcctromagnet for causing an alarm indication.

is. in a tclephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a resistance in bridge of the line conncc ted to said source of current from an intermediate point by a third conductor, an elcctromagnct associated with the line normally energized by current in the circuit of said third conductor, means for interrupting the circuit of said resistance and third o nductor in a predetermined manner and mechanism controlled by the elcctronmgnet for causing an alarm indication.

in. In a telephonecxchangc system, the combination at a line-circuit extending from a' substation to the exchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an electronntgnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said source ina predetel-mined man; ner and mechanism controlled by the electromagnet for causing an alarm indication.

20. In a telepllone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line. a resistance in bridge of the hnc connected to said source of current from an intermediate point by a third conductor,

an electromagnet associated with the line.

[normally energized to a limited extent by current in the circuit of said resistance and I third comluctor, means tor interrupting the circuit of said source in a prcdctermined manner and mechanism controlled by the limited energization ol the electromagnct for causing I an alarm indication. I 21. In a telcphonc-exchange system, the combination of a line-circuit extending'l'roni a substation to the exchange, a source of cmi rent for the line, a resistance in bridge of the line connected to said source olcurrent from I an intermediate point by a third conductor,- Ian electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said source in a predetermined manner and mechanism controlled by the limited energization of the elcctronmgnet for causing an alarm indication and controlled by the i greater energization ol' the elcctromagnet tor causing a separate indication. 22. In a telephonc-exchangc system, the combination ola line-circuit extending from a substation to the exchange, a source of current for the line, a resistance in bridge of the line connected to said source ol current from I an intermediate point by a third conductor, an electromagnet associated with the line normally energized to a limited extent by current in the circuit ol' said resistance and third conductor, means to! interrupting the circuit of the line-limbs in a prcdctcrmined manner and mechanism controlled by the electromagnet for causing an alarm indication.

23. in a tclc drone-exchange system, the combination ol a line-circuit extending from a substation to the exchange, a source of current for the line, a rcsistancc in bridge of the line connected to said soul'cc of current from an intermediate point by a third conductor, an electromagnct associated with the line normally energized to a limited extent current in the circuit ol said ltSiStzlIlC'l-F and third conductor, means for interrupting the circuit of the lino-limbs in a predctermincd mannerand mechanism controlled by the limilcd cncrgization ol' the elcctronmgnet for causing an alarm indication.

24. ln a telcplmnc-cxchangc system, the combination of a line-circuit extending from I a substation to the exchange, a source of cur rent tor the line, a resistance in bridge of the line connected to said sourcc'ot current from an intermediate point by a third conductor, an clectromagnct associated with the line i normally cncrgizcd to a limited extent by ,1 current in the circuit of said resistance and l third conductor, means for interrupting the circuit ol' the line-limbs in a prmletcrmined l i manner and nn-chanism controlled by the lmnlcd cnergizal' ion of thc electroniagnct for causing an alarm indication and controlled IlO 1o normally energized by the greater energization of the electromagnet for causing a separate indication.-

25. In a telephone-e. change system, the combination of a hne-c'rcuit extending from a substation to the excl: nige, a source of cur rent for the line, a resistz, nee in bridge of theline connected to said SOLL'CG of current trom 5 the electromagnet for causing an alarm indi cation.

26. In a tole honeexchange system, the

combination ot' a line-circuit extending from a substation to the exchange, a source of cur- 2o rent (or the line, a resistance in bridge of the line connected to said source et' current l r'om an intermediate point by a third an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit ol said third conductor in a predetermined manner and mechanism controlled by the hunted energization of the electromagnet 3o tor causing an alarm imlication.

27.,ln a telephone-exchange system, the combination ol' :1 line-circuit extending from a substation to the exchange, a source of current l'or the-line, a resistance in bridge of the line connected to said source ol current t'rom an intermediatepoint by a-third conductor. an electroniagnet associated \\']l h the hue normally energized to a limited extent b cur.

rent in the clrc-uit of said resistance and third 0 conductor, means l'or interrupting thecircziit of said third conductor in a predetermined manner and mechanism contmllcd by the limited energizatioirol the electronnlgnet l'or causing an alarm indication and ctmtrolled by the greater energization of the electromagnet for causing a separate indication.

28. In a telephone-exchange system, the combination of. a .linoec'irmiit extending l'rom a substation to'tho exchange, a source ol current tor the line, a resistance in bridge of the line connected to said source of current trom an intermediate point by a third conductor, an elect rom agnet associated with the line normallyenergized to a limited extent by current in the circuit of said resistance and third comtuctor, means [or interrupting the circuit. oi said resistanmand third conductor in a predetermined manner, and mechanism con trolled by the eloctromagnet tor causing an alarm indication.

29. In a tolephone-exchango system, the combination ol'a line-circuit extending from a substation tothe exchange, a source of current for the line, a resistance in bridge of the conductor.

a substation to the exchange, a

"line connected to said source of current from an intermediate point by a third conductor, an electromagnet associated with the line normally energized to a limited'extent by current in the circuit of said resistance and tim d conductor, means for interrupting the circuit of said resistance and third conductor in a predetermined manner and mechanism con-v trolled by the limited energization of the electromagnet for causing an tion.

30. In a telephone exchange system, the combination of a line-circuit extending from source of ourbridge of the alarm indicarent for the line, a resistance in line connected to said source of current from.

an intermediate point by a third conductor, an electromagnet associated with the line normally energized to a rent in the circuit of said resistance and third conductor, means tor interrupting the circuit of said resistance and third conductor in a predett mined manner and mechanism con trolled by the limited energization of the electromagnet tor ca-nsing'a'n alarm indication and cortrolled by the greater energization at the eh ctromagnet for causing a separate indication 31. In av telephone-exchange system, the combinatien ot a line-circuit extending from a substation to the exchange, a source of current tor the line, a resistance in bridge of the line connect ed to said source of current from an intermediate point by a third conductor, an electr omagnet associated with the line normally energized to a limited extent by current in the circuit ot' said resistance and third conductor and adapted to be energized to a greater extent through the. direct connection ot a line-limb through saidthird conductor, means l'or interrupting the circuit of said sonrce'in a predetermined manner and mechanism c:.ntrolled by the electroinagnot for causing an alarm indication.

32. In a tele hone-exchange system, the combination of a lhie-circuit extending from asubstation to the exchange, a source of current tor the line, a resistance in bridge of the line connected to said source of current from 'an intermediate point by a third conductor,

an electromagnet associated with the line normally energized to a. limited extent bycurrent in the circuit ol' said resistance and third condtuitor and adapted to be energized to a greater extent through the direct connection ol a line-limb through said third conductor, vmeans tor interrupting the circuit of said source. in a predetermined manner and mech- 'anism controlled by the limited energization of the. elect-romagnet for causing an alarm imlication. i 1 7 3 3. In a telephoneexchange system, the combination of a line-circuit extending from a substation to the exchange, a source of ourlimited extent by cur- I IIO senses A rent for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized a greater extent through the direct connection of a line-lint. through said third conductor, means for interrupting the circuit of said source in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication and controlled by the greater energization )f the elec tromagnet for causing a separate indication.

In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct con nection of a linedimb through said third con ductor, means for interrupting the circuit of the line-limbs in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm imlication.

In a telcphone-cxchangc system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an clectroniagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor, means for interrupting the circuit of the line-limbs in a prcdeterminml manner and mechanism controlled by the limited energization of the clectromagnet for causing an alarm indication.

36. ln a telc1drone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third coiuluctor, an clcctromagnct associated with the linenorinally energized to a limited extent by curr nt in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor, means for interrupting the circuit of the linelimbs in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication and controlled by the greater energization of the electromagnet for causing a separate indication.

37. In atelephone-exchangi-i system, the

combination of a line-circuit extending from a substation to the exchange, a source-of cur rent for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an electromagnet associated With' the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct con nection of a line-lilnb through said third conductor, means for interrupting the circuit of said third conductor in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

38. In a telephone-exchange system, the combination of a line-circuit extending from substation to the exchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an electromagnet associated with the line normally energized to a limited extent by cur rent in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third. conductor, means for interrupting the circuit of said third conductor in a pred-etiu'm-ined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication.

39. In a tclephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from, an intermediate point by a third conductor, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conducto means for interrupting the circuit of aid third coni'luctor in a predetcrminei'l manner and mechanism controlled by the limited energization ol' the elcctronmgnet for causing an alarm indication and controlled by the greater cncrgization of the ciectromagnet for causing a separate indication.

40. in a telephone-cxchange system, the

combination of a line-circuit extending from a substation to the exchange, a source of cur rent for the line, resistance in bridge of the line connected to said source oi current from an intermediate pointby a third conductor, an electromagnet associated with the line rent in the c rcuit of said resistance normally energized to alimit ed extent bycurand third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor, means for interrupting sistance and third conductor in a predetermined manner and mechanism controlled by the elcctroniagnet for causing an alarm indication.

41. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source ot cur rent for the line, a resistance in bridge of the line connected to said source of current from an intermediate po nt by an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct-connection of a line-limb through said third conductor, means for interrupting the circuit of said resistance and third conductor in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication.

42. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a resistance in bridge of the line connected to said source of current from an intermediate point by a third conductor, an electromagnet, associated with the line normallyenergized current in the circuit of said resistance and third conductorand adapted to be energized to a greater extent through the direct connection of a linclimb through said third conductor, means for interrupting the circuit of said resistance and third conductor in a pre determined manner and mechanism controlled by the limited energiza-tion oi the electromagnet for causing an alarm indica tion and controlled by the greater cnergization of the electromagnet f or causing a. separate indication.

43. In a telephone-exchange system, the combination "of a lincscircuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each line limb of substantially unequal value, an electromagnct associated with tho line adapted to be normally energized by a. preponderance of current in one lino-limb, means for interrupting the circuit of said source in a predetermined manner and mechanism controlled by the olectromagnet for causing an alarm indication.

44, In a telephone-exchange system, the combination of a line-circuit extending from the circuit of said reto a limited extent by controlled by the electromagnet a substation to the exchange, a source of cur rent for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value, an electromagnet associated with the line adapted to be normally energized by a preponderance of current in one line-limb, means for interrupting the circuit of the line-limbs in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

45. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current {or the line, a third conductor connecting the l-ine-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value, an electromagnet associated with the line adapted to be normally energized by a preponderance of current in one line-limb, means for interrupting the circuit of said third conductor in a predetermined manner and mechanism for causing an alarm indication. I

46. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of cure rent for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially une ual value, an electromagnet associated wit 1 the line adapted to be normally energized by a preponderance of current in one line-limb, means for inter rupting the circuit of said resistance and third conr'luctor in a predetermined manner and mechanism controlled by the electro' magnet for causing an alarm indication.

47 In a telcphone-exchange system, the combination of. a line-circuit extending a substation to the. exchange, a source of current I or the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for ear-,h'line limb of substantially unequal value, an electromagnet associated with the line adapted to be normally energized by current in one line-limb only, means forinterrupting the circuit oi said source in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

48. In a telephono-exchange system, the combination of a line-circuit extending IIOHL a-substation to the exchange, a source of current for the line, atliird conductor connectr ing the line-limbs to said source of current said connection being exterior to the ex change and including resistance for each linefrom lillll: ol suhsianliall unequal value, an elertroinagnet asst-elated with the line adapted to he normally energized by current in one line-limb on y, means lor interrupting the circuit ol the line-limbs in a predetermined I -liinb only, means l' r interrupting the nit ol Ilnrrl wilder-tor in a predeler- All}: an alarm inditelrnhonewxchange system, the iol' n l ii(,'-('li'('llll extending l'roin n t [be "luin e, a source ol cur in; line. a third rouducior connectline-lin'ibs to said s ur e i current d rerun-(lion liming exterior to the exchange and including resistanre l t)lt%t1(lllltit :l' subsiantially unequal Value, an elect associated with tlie'l'ine adapted to normally energized by current in one line-inn?) only, ineans ior interrupting the circuit or said resistance and third conductor in, av nri-tleteriniin-il manner and inechanisni rrolled by the electron: :net for causing I iitmliolr telephiinn-exchange system, the ion el' a lizn circuit aiding lroni ubstaiion to the X(lt;ll1flti, 1 source of 'ur the line. a third coinluctor connecti: limbs in said s u e olcurrent [on or-in; lf-litniit to the we iif-EP and including l'thlh lllllli' l'or each lineol substantially unequal r: lue, an elecnet associa ed \i'i h the line ni'irnniily I Iced by rnrrenii in the circuit ol said conductor moans lor interrupting the circuit oi said source in a predetermined manner and mechanism controlled by l lie UlQClJOIIltlgllC for causing an alarm indie Lion.

said rot exterior to exchangeandniclud 'r-z "anrel' rer linelimb of subslinliallr nu tnmiag netassocial energized by ear. 1l-i1 (l t'UlltlLlCiUi'. 1

value, an elec- Err-e norna manner and nieclianisin controlled by the electroinagiiel for causing an alarm indica- Lion.

53 in a telephone- ,xeha-nge system, the combination ol :1 line-circuit extending from a sulist a Lion t0 the exchange, a source of can rent for the line, a third conductor connect ine; tlie line-lin1bs to said source of current s'aideonneciion being exterior to the exhange and including resistance for each linellilll) ol substantiall unequal value, an electroniag'net. associated with the line normally energized b current in the circuit of sa d third t'ondut'lor, means lor interrupting. the circuit of said third conductor in a predetermined marine and n'ieclianisin controlled by the ii-lectronnignet for causing an alarm-ind i'nlion.

in a teie; hone-exi'zhange system, the combination iii a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductm connecting the line-limos to said source of current said connection being exterior to the exoiangi and including resistance for each linelini'n oi snbsiant iallji' unequal value, an eleclroinagnet associated nit/h the line norn'ielly energ 'd by current in the circuit of said third CUDLliHlOI', means for interrupting the circuit oi said res' mun-e and third conductor in a predeterinined manner and mechanism controlled by the eleciroinagnet. for causing change and including; resistance l'or each line linib oi substantially unequal value, an elect roinannet associated with the line normally energized to a limited extent by current in the circuit oi said resistance and third condue-tor, means for interrupting the circuit of said source in a predetermined manner and mechanism controlled by the electroinngnet for causing an alarm indication.

Fill in a telephon exchange system, the combination oi" a line ircuit extending from a substation to l llt excl ingc, a source of current for llu line, a third conductor connecting the line-liinbs to said source of current said connection being exterior to the ex c :a rqe and including resistance for each lineliinb ol suhstanlir ll unequal Value, an electroinagnet associaie l with the line normally f energized lo a hunted extent ny current in iireuit of said rsmistcnce and third cerduclor, means for interrupting the circuit said source in a predetermined manner and mechanism controlled by the limited ener giza-fion oi :ue clutiomagnet for causing an ale .n indication.

,--- i M1,, it r H," w 4- ()1. in .i bu Lonnie-exchange system, che

ITO

, rent for the line, a third conductor connectcombination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimh ot substantially unequal value, an electromagnet associated With the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means i or interrupting the circuit of said source in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication and controlled by the greater energization of the electromagnet for causing a separate indication.

58. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value, tromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of the line-limbs in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

59. In a telephoneexchange system, the combination of a line-circuit extending from a substation to the exchange, a source of curing t'he linedimbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value, an electromagnet associated with the line normally energized to a limited extent by, current in the circuit. of said resistance and third conductor, means for interrupting the circuit of the line-limbs in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication.

60. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of the line-limbs in a predetermined manner and mechanism controlled by the limited energization of the electroma net for causing an alarm indication and controlled by the an elec-.

greater energization of the electromagnet for causing a separate indication.

61. In a telephone-exchange system,'the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to .said source of current said connection being exterior to the exchange and including resistance for each line limb of substantially unequal value, an elec tromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said third conductor in a predetermined manner and mechanism controlled by the electromagnet forfcausing an alarm indication.

62. Ina telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, athird conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value, an electromagnet associated with the line normally en'ergized to a limited extent by current in the circuit of said'resistance and third conductor, means for interrupting the circuit of said third conductor in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication;

63; In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of cur rent for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value,-an electrom agnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting thecircuit of said third conductor in a predetermined manner and'mechanism controlled by the limited energization of the electromagnet for causing an alarm indication and controlled by the greater energization of the electromagnet for causing a separate indication. t,

64. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, the line-limbs to said. source of current said connection being exterior to the exchange and including resistance for each line-limb of substantially unequal value, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said resistance and a third conductor connecting magnet for causing an alarm indication.

65. Ina telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of cur rent for the line, athird conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each line-limb of substantially unequal value, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said resistance and third conductor in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication.

66. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current said connection being exteriorto the exchange and including resistance for each line-limb of subitantialiy unequal value, an electromagnet associated With the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said resistance and third conducto in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication and controlled by the greater energization of the electromagnet for causing a separate indication.

67. In a telephone-exchange system, the

combination of a line-circuit extending from substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each line-limb of subst-antially unequal value, an electromagnet associated with the line normally energized a limited extent by current in the circuit of said resist nce and. third conductor and adaptit x cd be energized to a greater extent through the direct connection of a line-limb through said third conducotcu, ireans for interrupting he circuit of saio source in a predetermined n anner an d mechanism control l ed by the electromagnet for causing an alarm indication.

68. In a telephone-exchange system, the combination or a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connectingthe line-limbs to said source of current saidconnection being exterior to the exchange and including resistance for each line-limb of substantially unequal 'alue, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistances-nil third conductor and adapted to be energized to a greater extent through the direct connection Oi a line-limb through said third conductor, means for interruptin' the circuit of said source in a predetermine manner and mechanism controlled by the limited energization of the electrom agnet for causing an alarm indication.

69. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connectingthe line-limbs to said source of current said connection being exterior to the exchange and including resistance for each line-limb of substantially unequal value, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor, means for interrupting the circuit of said source in a predeterminer manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication and controlled by the greater energization of the electromagnet for causing a separate indication.

70. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of cur rent for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each line-limb of substantially unequal value, an electromagnet associated with the line normally ener-- gized to a limited extent by current in the circuit of said resistance and third conduc-- said connection being exterior to the exchange and including resistance for each line- IIO limb of substantially unequal value, an electromagnct associated with the line normally energized to a limited extent by current in the circuit of said resistance and third con' ductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor,

means for interrupting the circuit of the linelimbs in a predetermined manner and mechanism controlled by the limited energization' of the electromagnet for causing an alarm indication.

72. In a telephone-exchange system, the

tromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor, means for interrupting the circuit of: the line limbs in a. predetermined manner and mechanism controlled by the limited energization of the electrom'agnet for causing an alarm indication and controlled by the greater-energization of the electroniagnet for causing a separate indication.

73. In a telephorie-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line", a third conductor connect.- ing the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value, an electromagnet associated with the line normally 3o energized to a limited extent by current 111 5o ductor and the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor, means for interrupting the circuit of said third conductor in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

74. In a telephone-excliange system, the combination of a line-circuitextending from a substation to the exchange, a source of current for the line, ing the line-limbs to said source of current said connection being exterior to the ex change and including resistance i or each line- 'limb of substantially unequal value, an electrornagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conadapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor, means for interrupting the circuit oi" said third conductor in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication.

75. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a, third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value, an elec-' a third conductor connect-v tromag'net associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor, means for interrupting the circuit of said third conductor in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication greater energization of the electromagnet for causing a separate indication.

76. In a telephone-exchange system, the combination of a line-circuit-extending from a substation to the exchange, a source of cure rent for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the ex- :hange and including resistance for eachlinelimb of substantially unequal value, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through said third conductor, means for interrupting the circuit of said resistance and third conductor in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

77. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of curr'ent'for the line, a third conductor connecting the line-limbs to said source of current said connection being exterior to the exchange and incl tin. .esistance for each line-limb of substantially unequal value, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct coimection of a linelimb through said third conductor, means for interrupting the circuit of said resistance and third conductor in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication.

78. In a telephone-exchange system, the combination of a line-circuit extending from and controlled by the a substation to the exchange, a source of cur interrupting the circuit of saidresi'stancc and an eleetroi'uaguet assi'iciated with the line third conductor in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication and controlled by vthe greater energization of the electromaguet for causing a separate indication.

79. in a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connect ing the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each line-limb of substantially unequal value but oi substantially equal impedanceto variable currents, an electromaguet associated with the line adapted to be normally energized by a preponderance of current in one line-limb, means for interrupting the circuit of said source in a predetermined m anner and mechanism controlled by the electromagnet for causing an alarm indication.

80. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each line-limb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line adapted to be normally energized by a preponderance oi current in oneline-limb, means for interrupting the circuit of the linelinibs a predetermined manner. and mechanism controlled by the electromagnet for causing an alarm indication.

81. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and inclu ding resistance for each line-limb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line adapted to be normally energized by a preponderance of current in one line-limb, means for interrupti'm the circuit of said third conductor in a prer etermined manner and mech anism controlled by the electromagnet for causing an alarm indication.

82-. In atelephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, asource of current for the line, third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each lineimb of substantially unequal value but of substantially equal impedance to variable currents,

i l l adapted to benormallx' energizml by a preponderance or current in oi u line-limb. means lor interrupting the circuit ol' said resistance and third conductor in a preiletermiued mauuer and mechanism conllolled by the elcetro magnet for causing an alarm indication.

83. In a telplmile-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source oi. current for the line, a third conductor connecting the line-limbs to said source ol urrent, said connection being exterior to the exchange and including lPSiSitlllUO for each line-limb of Substantially unequal value but of substantially equal impedance to variable currents, an electromaguet associated with the line adapted to be normally energized by current in one line-limb only, means For iuterrimtiug the circuit of said source in a )rcdeterminerl manner and mechanism controiled by the electromagnet for causing an alarm indication.

84. In a telephone-exchauge system, he combination oi a. line-circuit extending from a substation to the exchange, a source ol' current for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each line-limb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line adapted to be normally energized by current in one line-limb only, means for interrupting the circuit of the line-limbs in a predetermined manner and mechanism controlled by the electromaguet for causing an alarm iudieation.

In a telephom exchange system, the combination of a lineeclrcuit extending from a substation to the exchange, a source of cur-- rent for the line, a third conductor connect-- ing the linedimbs to said source ol' current, said connect ion being exterior to t he cxcha ngc and inclm'liug resistance for each line-limb of substantially unequal value but of substantially equal impedance to variable cur rents, an electromaguet associated with the line ad aptcd to be normally emergimid by cur-- rent in one line-limb (ally, means for interrupting the circuit of said third conductor in apredetermined iniinucr :1 ud mecluinism controlled by the elcctromagnet for causing an alarm indication.

86. In a telephondexchango system, the combinationoi' a line-circuit extending from a substation to the exchange. a source c cur rent for the line, a third conductor connecting the line-limbs to said source cl current, said connection being exterior to the exchange and including resistrmce for each line-limb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line a substation to the exchange,

. substantially equal change and including resistance for each linelimb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line normally energized by current inthe circuit of said third conductor, means for mterrupting the circuit of said source in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm ind ition.

88. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value but of impedance to variable currents, an electromagnet associated with the line normally energized by current in the circuit of said third conductor, means for interrupting the circuit of the line-limbs 'n a predetermined manner, and mechanism controlled by the electromagnet for causing an alarm indication.

89. In a telephone-exchange system, the combination of a line-circuit extending from a source oi current for the line, a third conductor connect ing the line-limbs to said source oi current, said connection being exterior to the ex change and including resistance for each linelimb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line normally energized by current in the circuit of said third conductor, means for interrupting the circuit of said third conductor in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

90. In a telephone-exchangesystem, the combination of a'linecircuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs-to said source of current, said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value but substantially equal impedance to variable currents, an electromagnet associated with the V by the electromagnet line normally energized by current in the cir-' cuit of said third conductor, means for interrupting the circuit of said resistance and third conductor in a predetermined manner and -mechanismcontrolled by the electro magnet for causing an alarm indication.

91. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of'current for the line, a third conductor connecting the line-limbs to said source of current,

said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated-With the line normally energized to a limited extent by current in the circuit of said resist ance and third conductor, means for interrupting the circuit of said source in a predetermined manner and mechanism controlled for causing an alarm indication.

, 92. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of curo rent for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value but of 5 substantially equal impedance to variable currents, an electromagnet associated with the line normally energized to a limited extent by current n the circuit of said resist ance and third conductor, means tor 1nter-- 10o rupting the circuit of said source in a prede- .termined manner and mechanism controlled substantially equal impedance to variable currents, an electromagnet associated with the line normally energized to a limited ex- 11 5 tent by current in the circuit of said resistance and thirdconductor, means for interrupting the circuit of said source in a predetermined manner and mechanism controlled by the limited energization of the electro- I2o magnet for causing an alarm indication and controlled by the greater energization of the electromagnetfor causing a separate indication.

94. In a telephone-exchange system, the combinationof a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each linelimb. of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of the line-limbs in a pre determined manner and mechanism controlled by the electromagnet for causing an alarm indication.

95. In .a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of cur- 'rent for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet'associated with the line normally energized to a limited. ex-

tent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of the line-limbs in a predetermined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication.

96. In atelephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the ex change and including resistance for each linelimb of substantially unequal value-but of substantially equal impedance to variable currents, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of the line-limbs in a pre* determined manner and mechanism controlled by the limited energization of the electromagnet for causing an alarm indication and controlled by the greater'energization of the electromagnet for causing a separate indication 97. In a telephone-exchange system, the.

combination of a line-circuit extending from asubstation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance-for each linelimb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line normally energized to a limited ex tent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said third conductor in a predetermined manner and mechanism controlled by the electromagnet for causing said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line normally energized to'a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said third conductor in a predetermined manner and mechanism controlled by the limited energization of the electromagnetfor causing an alarm indica-' tionh 99. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third-conductor connecting the line-limbs to'said source of current, said connection being exterior to the ex change and including resistance for each linelimb ofsubstantially unequal value but of substantially equal impedance to variable currents, an'electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said third conductor in a predetermined mannerand mechanism controlled bythe limited energization of the tent by current in the circuit of said resistance and third conductor, means for interrupting the circuit of said resistance and third conductor in a predetermined manner and mechanism controlled by the, electromagnet for causing an alarm indication.

101. In a telephone-exchange system, the

combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value but of substantiallyequal impedance to variable currents, anelectromagnct associated with.

the line normally energized to a limited extent by current in the circuit of said resistance and third comluctor, means for inter rupting the circuit of said resistance and third conductor in a predetermined manner and mechanism controlled by the limited energization of the clectromagnet for causing an alarm indication.

102. In a tclephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value but of substantially equal impedance to variable currents, an electromagne't associated with the line normally energized 'to a limited. ex tent by current in the circuit of saidresistance and third conductor, means for interrupting the circuit of said resistance and third conductor in a predetermined manner and mechanism controlled by the limited energization ol' the electron'iagnet' for causing an alarm indication and controlled by the greater energization of the electr m1agnet for causing a separate indication.

Y 103. In a telephone-cxchangc systen' the combination ol" a line-circuit extending'from a substation to the exchange, a source of current for the line, a third conductor connectmg the line-limbs to said source of current,

said connection being exterior to the exchange and including resistance for each linelimb of substantially unequal value but of substantially equal impedance to variable currents, an clectromagnet associated with the line normally energized to a limited extent bycurrcnt inthe circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of" a line-limb through said third conductor, means for interrupting the circuit ol" said source in a predetermined manner and mechanism controlled by the electromagnet for causing an alarm indication.

104. In combination of a line-circuit extending-from a substation to the exchange, a source of current for the line, a third conductor connecting the line-limbs to said source or current, said connection being exterior to the exchange and including resistance for each linelimb ol" substantially unequal value but of.

substantially equal impedance to yariable currents, an electromagnet associated with the line normally energized to a limited extent by current in the circuit ci s-aid resistance and third conductor and adapted to be energized to a greater-extent through the dirccticonnection of a linelimb through said a telephone-exchange system, the

third conductor, means for interrupting the circuit of said source in a predetermined manner and mechanism controlled by the limited cnergization of the clcctromagnet for causing an alarm indication.

105. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for the line, a third conductor connect- -ing the line-limbs to said source of current, said connection being exterior to the ex change and including resistance for each linelimb of" substantially unequal value but of substantially equal impedance to variable currents, an electromagnet associated with the line normally energized to a limited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct connection of a line-limb through Said circuit of said. source in a predetermined manner and mechanism controlled by the by the reater energization of the electromagnet or causing a separate1nd1cat1on.'

106. In a telephone-exchange system, the

a substation to the exchange, a source of emrent for the line, a third conductor connecting the line-limbs to said source of current, said connection being exterior to the ex-.

limb of substantiallyunequal value but of substantially equal impedance to variable currents, an electroniagnet associated with the line normally energized to a limited exance and third conductor and adapted to e energized to a greater extent throughthe direct connection of a hne-lnnb through said circuit of the line-limbs in a predetermined manner and n'iechanism controlled by the electromagnet for causing an alarm indication. g

107. In a telephone-exchange system, the combination of a line-circuit extending from a substation to the exchange, a source of current for'the line, a third-conductor connectchange and including resistance for each linelimb of substantially unequal yalue but of substantially equal impedance to variable currents, an electromagnet associated with. the line normally energized to alirn'ited extent by current in the circuit of said resistance and third conductor and adapted to be energized to a greater extent through the direct cdnnection of a line-limb through said third conductor, means-for interrupting the circuit oi the line-limbs in a predetermined imanner and mechanism controlled by the third conductor, means for interrupting the limited energization of the electromagnet for causing an alarm indication and controlled,

combination of a line-circuit extending from change and including resistance for each lineq tent by current in the circuit of said resi tthird conductor, means for interrupting thev ing the line-limbs tosaid source of current, i said connection being exterior to the ex-- izo

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