US825685A - Combined telephone exchange and alarm system. - Google Patents

Description

PATBNTED JULY 10, 1906.

H. G. WEBSTER. COMBINED TELEPHONE EXCHANGE AND ALARM SYST APPLICATION FILED 0OT.17. 1904.

2 SHEETS-SHEET 1- PATENTED JULY 10, 1906.

' H. G. WEBSTER.

COMBINED TELEPHONE EXCHANGE AND ALARM SYSTEM.

- APPLICATION FILED 00111. 1904.

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HARRY G. WEBSTER, OF CHIGAGQILLINOIS, ASSIGNOR TO MILO Gr. KELLOGG, OF CHICAGO, ILLINOIS.

Specification of Letters Patent.

Fatented. July 10, 1906.

Application filed October 17,1904. Serial No. 228,756.

To all whom it may concern:

Be it known that I, HARRY G. WEBSTER, a citizen of the United States, and a resident of Chicago, county of Cook, and State of Illinois, have invented certain new and useful Improvements in a Combined Telephone EX- change and Alarm System, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to systems in which line-circuits extending from subscribers stations to a telephone-exchange and adapted for 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 an improvement upon the system illustrated and described in my application, Serial N 0. 204,978, filed April 26, 1904. In said appli cation I have illustrated an organization in which the line-circuit is at all times available for the transmission of 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 grounding of either limb of the telephone-line be automatically indicated at the alarm-receiving station, and it is preferable that this ground indication be given' by means of an indicator distinct and separate from that which indicates an alarmsignal, and it is also desirable that the accidental grounding of either line-limb shall not cause the actuation of the alarm-indicator.

The improvement of my present invention consists in improving means for securing this ground indication in such a system as I have outlined, and it is in this respect'a species under the generic invention set forth in the above application.

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

In a preferred form of my present invention I associate with that line-limb leading from the live or active side of the centraloflice-battery an electromagnet which serves when intermittently denergized to cause the actuation or display of an alarm-signal, and I associate with that line-limb leading to the return side of the central-office battery an elec tromagnet adapted to control the display of the ground-indicator. The return side of this central battery has the customary connection to ground. The circuit of these electromagnets is normally closed through the two linelimbs and a resistance or impedance in bridge of the limbs at a point beyond the alarm-sending mechanism. This alarm-sending mechanism may be of the nature of the ordinary make-and-break" apparatus of the ordinary district telegraph-box or of other construction, so arranged as to break and make a circui t of the line-limbs in a predetermined manner, and the normally closed contact or contacts of this device may be included in the circuit of the line-limbs at a point intermediate of the aforesaid electromagnets and the bridged impedance. The current which normally flows through the electromagnets and the line-limbs while of sufiicient strength to energize the electromagnets is not of sufficient strength to interfere with the proper operation of the telephone-exchange signals. l/Vhen the telephone is in use, the current which then flows through the line-limbs and the substation apparatus has a considerably higher value than the normal current; but inasmuch as the electromagnets referred to are already energized this increased current does not change the normal condition of the alarm-indicating or ground-indicating mech' anism. If under the normal condition of the line or during the use of the telephone an alarm-indicating device will still receive cur v and the magnet consequently denergized.

These electromagnets are preferably re1ay magnets controlling by means of their contacts local circuits which include the alarmindicating and ground-indicating devices. The alarm-indicating device may be in the form of an ordinary telegraphic register or other suitable mechanism adapted to re--- spond to the interruptions of the make-andbreak alarm sending mechanism. The ground-indicating device may be in the form of an'electromechanical signal or preferably may consist of a small incandescent lamp Which by its illumination indicates the pres- .ence of an accidental ground upon the circuit of the line-limbs. My invention also comprises means by which these electromagnets with their associated signal-indicating mechanism may be brought into ase sociation with any line of the telephone system in a systematic and workmanlike manner without disturbing the permanent wiring.

The invention will be further illustrated and described in the accompanying drawings, in which Figure 1 is a diagram illustrating a preferred form of my invention in which two subscribers lines are shown extending in metallic circuit from the substation to a centralb-attery telephone-exchange switchboard of the two-wire type, together with the customary connecting-cord and accessory apparatus.

Fig. 2 illustrates a modification of the localcircuit apparatus associated with the two relay-magnets. Fig. '3 illustrates my inventi on in a switchboard system of the two-wire type, the relay-magnets being in bridge of the two line-limbs rather than serially in cluded therein, as in Fig. 1. Fig. 4 indicates a well-known cord connecting apparatus adapted for association with the line-circuit of the system indicated in Fig. 3. Fig. 5 indicates means for associating the electromagnets .and their associated mechanism with any telephone-line of the system without disturbing the permanent wiring.

Like characters refer to like parts in the several drawings.

Referring to Fig. 1, the subscribers stations A and B are 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 circ-uit which normally stands open at the hookswitch'h, the bell b and condenser 0 being in permanent bridge of the line. While I have thus {illustrated one particular form of substation arrangement, it will be apparent to those skilled in the art that numerous other arrangements may be equally well employed in myinvention, and I therefore do not wish to be limited to the particular one shown.

The limbs 1 and 2 of the line extend to the central office and are there connected, limb 1 through armature 7 and contact 79 of the cut-off relay 3 and through the winding of relay 4 to the active side of the battery C and limb 2 through armature 6 and its back contact to the return side of the same battery. The subscriber in calling raises his receiver and completes the low-resistance circuit, including his transmitter and hook-switch contact, to actuate the relay 4, lighting his linelamp 5. Upon the insertion of an answeringplug P the operation ofrelay 3 breaks the normal connection of the line-limbs through relay 4 and armature 6 to the battery C, thus extinguishing the line-lamp, and connects them to the spring-jacks 8 and thence to strands 9 and 10 of the cord-circuit. Current is now supplied to the line A from battery C through relays 13 and 14, which control the circuit of the supervisory lamp 17, the lamp remaining dark as long as current flows through both relays. The operator tests, plugs in, and rings a wanted subscriber in'the usual way with calling-plug O and ringing-key g g. While ringing, the relay 3 is energized by current from battery E and generator G, and after the ringing-key is released relay 16 of the cord-circuit and relay 3 of line B are energized by current from battery D. The relay 16 when thus actuated cuts off the test-relay 19 and completes the circuit of strand 11 through its contacts and also completes the circuit of supervisory lamp 18. When the called subscriber answers, current is furnished his instrument through relays 15 and 16, and the energization of relay 15 opens the circuit of lamp 18, causing its eifacement as long as the subscribers hook-switch contact remains closed. The subscribers are now able to converse over cord-strands 9 11 and 10 12, which include the condensers cl cl. The hanging up of both receivers deprives the relays 13 and 15 of current, thus allowing them to complete the circuits of lamps 17 and 18, which being illuminated constitute the disconnect-signal. This is the regular telephonic operation of the system, as will be well understood by those skilled in the art, and is not interfered with by the presence of the alarm apparatus associated with any of the lines. Those lines which are to be utilized for alarm service are provided with magnets F and F, included in limbs 1 and 2, respectively, and in the struc ture of Fig. 1 these relays are so arranged that their windings will present no objectionable impedance to the rapidly-alternating telephonic currents, either by means of the bridged condensers 24 and 25 or in any other well-known manner. These relays, as will be hereinafter explained, control mechanism for causing alarm-signals and ground-signals to be indicated at the alarm-receiving station. Atthe alarm-sending station or other convenient point a resistance 6 is provided in bridge of the two line-limbs, this-resistance being preferably inductive resistance and so proportioned that the current-flow therethrough over the two line-limbs sh all be sufficient to energize the relays F and F", but will be insufficient to interfere with the regular operation of the relays 4, 13, or 15 of the telephoneeXchange system. Alarm-sending apparatus M is provided at apoint intermediate of the bridged resistance and the magnets F and F, which may be of the character of the well-known district messenger-box or similar apparatus adapted to be released manually or automatically, and this mechanism controls by its contacts the circuit of the two linelimbs. In the diagrammaticillustration of the drawings the make-and-break wheel n is normally prevented from revolving through the engagement of stop 22 with releasing-arm 21, the said arm being held in its position through the attraction of magnet m, which is included in the circuit of battery 20, together with the thermostatic or other circuit breaking devices, (indicated at f.) 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 m, allowing the arm 21 to be retracted by its associated spring, th'us disengaging stop 22 and allowing the revolution of the make-and-break wheel n. As this wheel revolves the projections upon 1ts periphery will cause limbs 1 and 2 to be interrupted at contacts 23 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. As has been pointed out, the magnets of the relays F and F are normally energized by the comparatively weak current which flows through resistance 71. WVhen the subscriber calls by removing his receiver, the increased current-flow which then energizes relay 4 maintains the energization of the aforesaid magnets. When the line is switched for conversation, the magnets are then energized by current flowing through relays 13 and 14 or 15 and 16, and when the ringing-key is actuated the energization of the magnets is maintained by current from battery E and generator G. The magnet of relay F when thus energized completes by its armature 26 a circuit of battery 28 through magnet 30 of the alarm-indicating device H. While this device is conventionally illustrated as an ordinary telegraphic register, it is under stood that other alarm-indicating devices may be used which are adapted to respond to the control of the relay F. A ground-indicating signal is provided and included in another circuit of battery 28, which is controlled jointly by relays F and F. This signal may be the incandescent lamp 29 (shown in'the drawings) or any other suitable signal adapted to respond to the control of its circuit through battery 28. This circuit is normally interrupted at armature 27 through the energization of relay F and is adapted to be interrupted at armature 26 in case relay F becomes deenergized. The operation of the system is as follows: When an alarm-signal is to be sent, the operation of the alarmsending mechanism at M intermittently interrupts the circuit of the line-limbs. At each interruption the relays F and F are deenergized, and relay F controls by its armature 26 the circuit of magnet 30 of the alarmindicating device II to give the required alarm indication. The armature 27 of relay F is also retracted at each interruption engaging its back contact; but as at this time armature 26 is out of engagement with its front contact the circuit of signal 29 is not completed and no ground indication is given. This condition is indicated in the drawings of the apparatus associated with line B. It has been shown that both relays F and F are energized by current flowing over the two linelimbs at all times except when an alarm-signal is to be sent. In case, however, either limb becomes accidentally grounded at a point intermediate of the two relays referred to a short circuit is formed between such point of grounding and the grounded or return side of the central battery. This short circuit while still allowing current to flow through relay F, thus maintaining its energization, will deprive relay F of substantially all current, causing its deenergization. Under this condition the retraction of its armature 27 completes the circuit of the groundsignal device, which maybe traced as follows: from battery 28 through armature 26 and its associated front contact, through armature 27 with its associated back contact, and through lamp 29 to the opposite side of the battery. This local circuit will be maintained as long as relay F is deenergized and relay F remains energized, the alarm-indicating device H being unaffected, for the reason that its circuit is maintained in its normally closed condition through the continued attraction of armature 26. It will also be seen that if the accidental ground be located upon any portion of the circuit of the line-limbs except that extending from magnet F through I limb 1 to its associated contact 23 the opera tion of the alarm-sending apparatus would still cause the alarm indication. Under such a condition the interruption of the circuit of relay F by the alarm-sending mechanism would allow the retraction of armature 26, thus opening and closing the circuit of magnet 30, causing the proper alarm indication. The retraction of armature 26 would also at each interruption open the circuit of lamp 29 through battery 28, thus giving a series of flashes which would positively indicate the condition of the circuit. While I have shown a particular local-circuit arrangement I and indicated diagrammatically certain mechanism in connection with the electro magnets of relays F and F, I do not wish to be limited to the precise circuit arrangements or signaling devices indicated. The structure is one in which the simultaneous energization of both magnets maintains the normalcondition of the indicating devices, in which the deenergization of both magnets causes an alarm indication, but not a ground indication, and in which the simultaneous energization of the magnet associated with the active side of the central battery and deenergization of the magnet associated with the grounded side of the battery causes the ground indication without altering the normal condition of the alarm-indicatin device.- While I have shown the magnets as t erelaymagnets F and F, it is obvious that these might be electromagnets acting jointly to control the display of suitable signals mechanically rather than by means of a local circuit and battery. Other arrangements of the ground-indicating device and alarm-indicating device responsive to the control as determined by the circuit conditions which I have outlined might be made without departing from the spirit of my invention, and I therefore do not wish to be limited to any particular arran ement controlled by the electromagnets, (1ndicated at F and F Fig. 2 indicates an alternative arrangement for the local circuits of the ground-indicator and alarm-indicator, the alarm-indicator in this case being in a normally open circuit rather than in a normally closed circuit, as shown in Fig. 1. It will be seen that under normal conditions both relays being energized the circuit of battery 28 through magnet 30 stands normally 0 en at the back contact of armature 26, whi e the circuit of lamp 29 stands normally open at the back contact of armature 27. During the sending of an alarm-signal, both relays being simultaneously deenergized, the retraction of both armatures completes the circuit of magnet 30, as will readily be seen, causing the required alarm indication. If the circuit of the line-limbs becomes accidentally grounded, as has been previously described, the consequent retraction of armature 27 will complete the circuit of lamp 29, causing its illumination to indicate such ground; but if relay F be at the same time dee'nergized, as through the sending of an alarm-signal, the retraction of its armature 26 opens the circuit of lamp 29, Cpreventing its illumination.

In Figs. 3 an 4 are indicated modifications of my invention as embodied in the wellknown telephone-exchange system of what is known as the three-wire type. This system differs from that of the previous drawings with respect to the telephone-exchange apparatus in that the cut-off relay 3, assofor the cut-off relay is completed from the battery 0 through resistance 45, lamp 17, plug and jack contacts 41 38, through the windingof relay 34 to the return side of the battery, thus energizing the relay 34 and under normal conditions causing the lamp 17 to be illuminated. Through the insertion of the plug current from battery 0 is now furnished to the line through the windings 46 and 47 of repeating-coil R, cord- strands 9 and 10, and the corresponding plug and jack contacts, and the subscriber being at his telephone the relay 42, which is included in strand 10, is energized and by its contact completes a circuit in shunt of lamp 17, which includes the resistance 44 and causes the eX- tinguishment of the lamp. The operator listens, tests, and rings in the well-known manner and by plugging in completes similar circuits for the line of the subscriber who is to be called. The subscribers circuits are thus inductively united for conversation by means of the repeating-coil rather than by the condensers, as in the system of Fig. 1. Either subscriber can cause the illumination of his supervisory lamp 17 or 18 by actuating his hook-switch, thus energizing or deenergizing the relay 42 or 43, and the illumination of both lamps constitutes the customary disconnect-signal. The manipulations of the operator and subscriber and the action of the signals governed thereby are thus seen to be the same as in the system previously illustrated. With reference to the alarm apparatus it will be noted that the relays F and F instead of being serially included in the line-limbs, as in the system of Fig. 1, are here in bridge of the two limbs and are directly connected to the central battery C. The alarm-sending mechanism is indicated in simplified form at M; but it will be understood that this mechanism is similar to that indicated or specified in connection with Fig. 1 and that whilein Fig. 3 the alarm-sending mechanism is indicated as controlling contacts in one line-limb only it will be understood that similar contacts for the other line-limb may be controlled by the same mechanism. It will be seen in this view, Fig. 3, that as long as the circuit of the line-limbs remains normal the two relays are energized by current from batteryO and that this energization is not interfered with by any of the telephonic operations of the system. If the circuit of the line-limbs is opened as through the operation of the alarm-sending mechanism, both relays are denergized, controlling the local circuit of the alarm-indicating mechanism H in the manner required to indicate an alarmsignal; also, that if the circuit of the line-limbs be--- comes grounded at a point intermediate of the two relays the consequent denergization of relay F will allow the retraction of armature 27, thus completing the circuit of battery 28 through lamp 29, causing its illumination to indicate the presence of such an accidental ground. It is to be noted that resist ance 35 of Fig. 3 and resistance 39 of Fig. 4 are not ordinarily required in the telephonic operation of the exchange system indicated. Their interposition is required in the present structure to avoid short-circuiting the relay F through a direct connection to the return side of the battery in case the resistances are omitted.

It is to be understood that my invention may be embodied in other telephone-exchange structures than those illustrated and described and that while in Fig. 1 I have shown the electromagnet-windings included serially in the line-limbs and in Fig. 3 in bridge of the line-limbs that method of asso ciation maybe employed which is best adapted to the particular exchange system under consideration.

Fig. 5 indicates means by which any line of a telephone-exchange system may be provided with the special alarm apparatus. The two limbs of the line enter the exchange and terminate in the customary manner upon the distributing-rack K at terminals and are ordinarily carried through this rack by the jumper-wires (indicated at 51 and 52) to terminals 53, and thence by permanently-connected wires to the other apparatus of the switchboard system. The energizing-windings of the magnets or relays F and F are permanently wired to terminals 59 of the same or an adjacent section of the distributing-rack and are provided with the customary protective devices, (indicated at 58.) In case it is desired to associate these magnets and their controlled mechanism with any particular line the jumper-wires referred to are removed and connection is made with the terminals 59 by the two pairs of jumpers, as indicated at 54 55 and 56 57. In case it were desired to shift the magnets and their associated mechanism to some other line it would only be necessary to disconnect these last-mentioned jumpers from terminals 50 and 53 and transfer them to the corresponding terminals of the line to which the apparatus is to be shifted, removing its jumpers 51 and 52, as previously described. It will thus be understood by those skilled in the art that this arrangement provides means whereby any set of alarm-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 wirin IVhile several batteries C, D, and E are shown in the drawings, it will be understood that these may be one and the same battery and also that the various grounds indicated are or may be replaced by a common returnwire connected with the grounded terminal of the central battery. It will also be evident to those skilled in the art that various modifications of my invention may be made without departing from its spirit, and I therefore do not wish to be limited to the precise structures shown and described; but

I claim- 1. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism having an energizing-winding in circuit with each line-limb and said source of current, means for intermittently interrupting the circuit of the line in apredetermined manner and an alarm-indicating device controlled by said mechanism adapted to respond to interruptions of current in both windings.

2. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each linelimb respectively, means for intermittently interrupting the circuit of the line in a predetermined manner and a ground-indicating device controlled by said mechanism adapted to respond to an interruption of current in one winding only.

3. In a telephone-exchange system the combination of a normally closed metallic telephone-line including asource of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each line limb respectively, means for intermittently interrupting the circuit of the line in a predetermined manner, an alarm-indicating device controlled by said mechanism adapted to respond to interruptions of current in both windings and a ground-indicating device controlled by said mechanism adapted to respond to an interruption of current in one winding only.

4. In a telephone-exchange system the combination of a normally closed metallic telephonedine including a source of current at the exchange, electromagnetic mechan ism controlled by two energizing-windings, one winding being associated with each linelimb respectively, means for intermittently interrupting the circuit of the line in a predetermined manner and means whereby the IIO interruption of current in one winding will cause a ground indication.

5. In a tele hone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each linelimb respectively, means for intermittently interrupting the circuit of the line in a predetermined manner and means whereby the interruption of current in both windings will cause an alarm indication.

6. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each line-limb respectively, means for intermittently interrupting the circuit of the line in a predetermined manner and means whereby the inter ruption of current in one Winding will cause a ground indication and the interrruption of current in both windings will cause an alarm indication.

7. In a telephoneexchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each line-limb respectively, means for intermittently interrupting the circuit of said windings in a predetermined manner anda ground-indicating device controlled by said mechanism adapted to respond to an interruption of current in one winding only.

8. In a tele hone-exchange system the combination oi .a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-vvindings, one winding being associated with each line-limb respectively, means for intermittently interrupting the circuit of said windings in a predetermined manner, an alarm-indicating de vice controlled by said mechanism adapted to respond to interruptions of current in both windings and a ground-indicating device controlled by said mechanism adapted to respond to an interruption of current in one Winding only.

9. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each liiie-limb respectively, means for intermittently interrupting the circuit of said windings in a predetermined manner and means whereby the interruption of current in one winding will cause a ground indication.

10. In a telephone-exchange system the combination of a normally closed metallic determined manner and means whereby the interruption of current in both windings will cause an alarm indication.

11. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each line-limb respectively, means for intermittently interrupting the circuit of said windings in a predetermined manner and means whereby the interruption of current in one winding will cause a ground indication and the interruption of current in both windings will cause'an alarm indication.

12. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each line-limb respectively, means for intermittently inter- 5 rupting the circuit of said source of current in a predetermined manner and a ground-indicating device controlled by said mechanism adapted to respond to an interruption of current in one winding only.

13. In a telephone exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each line-limb respectively, means for intermittently interrupting the circuit of said source of current in a predetermined manner, an alarm-indi eating device controlled by said mechanism adapted to respond to interruptions of current in both windings and a ground-indicating device controlled by said mechanism adapted to respond to an interruption'of current in one winding only.

14. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each line-limb respectively, means for intermittently interrupting the circuit of said source of current in a predetermined manner and means whereby the interruption of current in one winding will cause a ground indication.

15. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism saaess controlled by two energizing-windings, one winding being associated with each line-limb respectively, means for intermittently interrupting the circuit of said source of current in apredetermined manner and means whereby the interruption of current in both windings will cause an alarm indication.

16. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each line-limb respectively, means for intermittently interrupting the circuit of said source of current in a predetermined manner and means whereby the interruption of current in one winding will cause a ground indication and the interruption of current in both windings will cause an alarm indication.

17. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizingavindings, one winding being associated with each line-limb respectively, an alarm-sending device adapted to intermittently interrupt the circuit of the line in a predetermined manner and a ground-indicating device controlled by said mechanism adapted to respond to an interruption of current in one winding only.

18. In a telephone-exchange system the combination of a normally closed metallic telephone'line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one winding being associated with each line-limb respectively, an alarm-sending device adapted to intermittently interrupt the circuit of the line in a predetermined manner, an alarm indicating device controlled by said mechanism adapted to respond to interruptions of current in both windings and a ground-indicating device controlled by said mechanism adapted to respond to an interruption of current in one winding only.

19. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizmg-windings, one winding being associated with each line-limb respectively, an alarm-sending device adapted to intermittently interrupt the circuit of the line in a predetermined manner and means whereby the interruption of current in one winding will cause a ground indication.

20. In a telephone-exchange system the combination of a normally closed metallic telephoneline including a source of current at the exchange, electromagnetic mechanism controlled by two enel'gizingavindings, one winding being associated with each line-limb respectively, an alarm-sending device adapted to intermittently interrupt the circuit of the line in a predetermined manner and means whereby the interruption of current in both windings will cause an alarm indication.

21. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a source of current at the exchange, electromagnetic mechanism controlled by two energizing-windings, one Winding being associated with each line-limb respectively, an alarm-sending device adapted to intermittently interrupt the circuit of the line in a predetermined manner and means whereby the interruption of current in one winding will cause a ground indication and the interruption of current in both windings will cause an alarm indication.

22. In a telephone-eXchange system the combination of a normally closed metallic telephone-line including a grounded source of current at the exchange, an energizin winding associated with that line-limb lea ing from the active terminal of said source and an energizing-winding associated with that line-limb leading from the grounded terminal of said source, an alarm-sending device adaptedto intermittently interrupt the circuit of said windings in a predetermined manner, and mechanism controlled by the first-mentioned winding adapted to actuate an alarm-indicator.

23. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a grounded source of current at the exchange, an energizin winding associated with that line-limb lea ing from the active terminal of said source and an energizing-winding associated with that line-limb leading from the grounded terminal of said source, an alarm-sending device adapted to intermittently interrupt the circuit of said windings in a predetermined manner and mechanism controlled by both windings adapted to control the display of a ground-indicator.

24. In a telephone-exchan e system the combination of a normally 0 osed metallic telephone-line including a grounded source of current at the exchange, an energizingwinding associated with that line-limb leading from the active terminal of said source and an energizin -winding associated with that line-limb lea ing from the grounded terminal oi said source, an alarm-sending device adapted to intermittently interrupt the circuit of said windings in a predetermined manner, mechanism controlled by the firstmentioned winding adapted to actuate an alarm-indicator and mechanism controlled by both windin s adapted to control the display of a groun -indicator.

25. In a telephone-exchan e system the combination of a normally 0 osed metallic telephone-line including a grounded source of current at the exchange, an energizingwinding associated with that line-limb leading from the active terminal of said source and an energizing-winding associated with that line-limb leading from the grounded terminal of said source, an alarm-sending device adapted to intermittently interrupt the circuit of said windings in a predetermined manner 'andmechanism controlled by the said windings whereby the interruption of current in one winding only will cause the actuation of a ground-indicator and the interruption of current in both windings will cause the actuation ofan alarm-indicator.

26. In a telephone-exchange system the combination of a normally closed metallic telephone-line including a grounded source of current at the exchange, an energizingwinding associated with that line-limb leading from the active terminal of said source and an energizing-winding associated with that line-limb leading from the grounded terminal of said source, an alarm-sending device adapted to intermittently interrupt the circuit of said windings in a predetermined manner,- mechanism controlled by the firstmentioned winding adapted to actuate an alarm-indicator and means whereby an interruption of current in the last-mentioned windin will cause a ground indication.

27. n a telephone-exchange system the combination of a normally closed metallic telephone-line including a grounded source oi current at the exchange, an energizingwinding associated with that line-limb leading from the active terminal of said source and an energizing-winding associated with thatline-limb leading from the grounded terminal of said source, an alarm-sending device adapted to intermittently interrupt the circuit of said windings in a predetermined manner, mechanism controlled by the first-mentioned winding adapted to actuate an alarm-indicator and means associated with said windings whereby the grounding of either line-limb at a point intermediate of the two windings will cause the actuation of a ground-indicator without actuating the alarm-indicator. 4

In witness whereof I hereunto subscribe my name this 14th day of October, A. D. 1904.

HARRY G. WEBSTER. Witnesses:

L. D. KELLoee, A. H. DYSON.

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