US569401A - Multiple-station telephone-circuit - Google Patents

Description

(N0 Modl.) 2 Sheets-Sheet 1.

J. A. BARRETT. MULTIPLE STATION TELEPHONE CIRCUIT. No. 569,401.

Patented Oct. 13, 1896.

Fig. 2.

(No'ModeL) 2SheetSheet 2 J. A. BARRETT.

MULTIPLE STATION TELEPHONE GIRGUIT.

N 5 9.401.- Patented Oct. 13, 1896.-

. I x N W 3 [x 0; 2 g i I l l 9 M I I M J Inventor,

JOHN A. BARRETT, OF RUTLAND, VERMONT, ASSIGNOR TO THE AMERICAN BELL TELEPHONE COMPANY, OF BOSTON, MASSACHUSETTS.

MULTIPLE-STATION TELEPHONE-CIRCUIT.

SPECIFICATION forming part of Letters Patent No. 569,401, dated October 13, 1896.

I Application filed January 2'7, 1896. Serial No. 577,049- (No model.)

T at whom it may concern:

Be it known that 1, JOHN A. BARRETT, residing at Rutland, in the county of Rutland and State of Vermont, have invented cer- 5 tain Improvements in MultipleStation TelephoneCircuits, of which the following is a specification.

This invention relates to telephone-exchange circuits and apparatus, and more par- IO ticularly to circuits of that class which connect a number of subscribers stations with the central ofiice and which are known in exchanges as party lines. Its objects are as follows: to ring the call-bells of the several subscribers stations selectively; that is, to sound the call-signal from the central office at the desired substation only, the others being excluded; to set a signal indicating to the eye that the line is occupied when such is the case, and at the same time to prevent the telephones from being switched into the circuit at all substations on the line or lines concerned in a communication except the stations making or responding to the call; to provide for the operation of these selective and other signals without introducing the impedance of electromagnets into the talking-circuit, and to provide a disconnecting or clearing-out signal operative by either of the two stations which have been comm unicating with each other, also without introducing impedance into the talking-circuit.

Each multiple-station subscribers circuit is a metallic circuit, and at each station I place the usual telephones, a call-bell, the busy-line indicator and telephone connection controlling or locking device, a single electromagnet for actuating both of them, the ordinary automatic telephone-switch and a special electromagnetic switch or circuitchanging relay controlling the selective operation of the call-bells, and the collective operation of the busy-indicators and the looking devices.

When at rest, the metallic telephone-circuit is led at each substation through a circuit-breaker carried by the automatic telephone-switch and at the central station is provided with a suitable call-receiving annunciator and a generator, which may be common to a number of circuits, maintaining a normal current on the circuit. Calls, therefore, are sent inwardly from the substation to the central station by simply removing the lGCGlVlllg-tGlGIJhOHG from its supportingswitch, for while the said switch is passing from one position to the other the circuitbreaker it carries momentarily opens the circuit, whereupon the current from the central-oflice generator ceases to flow and the annunciator at the central oi'iice gives its callsignal.

The substation-telephones are in a normally open bridge between the main-line con ductors, and by the action of removing the receiving-telephone from the switch-support this bridge is closed and the telephones are brought into the metallic talking-circuit. The transmitter induction-coil primary and secondary circuits are arranged in the usual manner, a local transmitter-battery being employed whose circuit through the transmitter and primary is controlled by the automatic switch, so that it is closed when the telephones are brought into the main metallic circuit and opened again when by replacing the telephone upon its support it is withdrawn from the talking-circuit.

The call and busy signal and the telephonelock device are controlled at each substation by the special selective switch or relaybefore mentioned. In sending call-signals the relays at the several stations are adjusted each to respond to a definite strength of callingcurrent and to be irresponsive when a stronger or weaker current passes through their coils, and the calls are made selective by adjusting each of the several relays ditferently,whereby each is enabled to respond as a call-signal to its own predetermined current and to no 0 other; but the said relays are also all construoted and adjusted to respond collectively to a current of considerably greater strength than any which are employed in sending callsignals, and thereupon to set a busy-signal, 5 showing at all stations that the line is occupied in the transmission of intelligence, and to lock the automatic switch-levers at all stations except those actually engaged in such transmission.

The selective relay at each substation actuates these appliances by controlling two normally open local circuits, supplied with currentwhen closed, from a suitable battery, which conveniently may be the same as that which supplies current for the transmitter.

The first local circuit contains the electromagnetic call-bell, and the second contains an electromagnet whose armature-lever actuates the busyindicating signal and carries a belt which on the attraction of the armature moves into the path of the automatic telephone-switch lever, preventing it from moving when the telephone is taken there from.

The electronutgnetic coils of the several selective relays of a party-line metallic circuit are not included in the metallic talking-circuit, but are connected in a distinct signaling-circuit composed of the two conductors of the metallic circuit joined in parallel to constitute a single-line conductor and having a ground or independent return. The said coils are connected half in one of the two parallel line-wires and half in the other, as shown, this arrangement being symmetrical and conducing to a maintenance of an electrical balance between the said two 0011- ductors in their functions when serving as the two sides of the metallic talking-circuit. Thus while the telephone-currents and inward call-signals traverse the metallic circuit the outgoing signal-currents are trans mitted in a ground return-circuit whose line conductor is formed of the two sides of the metallic circuit bunched to form a single wire of greater size.

To prevent the diversion of the voice-currents from the metallic telephone-circuit into other port-ions of the system of main-line conductors,where their presence is undesirable, or from being in any way short-circuited between earth terminal conneetions, a choking or impedance coil is placed in circuit with each line conductor between the automatic switch connections and the earth branch at the last substation of the circuit, and two others (one for each conductor) are similarly placed at the central station.

'W hen two circuits are united at the central station to permit the exchange of conversation between any of their respective substations, a double conductor connection joins the two wires of one to those of the other through interposed condensers. A steady current of appropriate strength is thrown upon the two wires in parallel of both of the said circuits to maintain the display of the busyindieating signal, and the locked disconnection of the telephones at all disengaged substations, and a disconnecting-signal annunciator is associated with both circuits in such a way that it is made responsive to the replacement of the receiving-telephone upon the automatic switch-lever serving as its support. This disconnecting-antinnciator has l'ou r windings, and although two of them are associated with one of the united substationcircuits and the remaining two with the other, and although, as stated, the said diseormecting-signal is under the control of the tele )hone-switch at the substations olf both circuits, so as to be responsive to the replacement of the telephone at either station, none of the said windings are in the talkingcircuit, two being placed as long as the two lines are united for conversation in short circuits of the normal signal-current generator formed by electrically uniting the ends of the central-station terminal loops of the two main circuits which are severed from the substation portions of the said main circuits by the insertion of the co1niecti1ig-1')lng, and the other two being placed in the selective-relay grounded circuits of the two lines.

The plan of dividing the exciting-coils oi the selective-relay magnet at each substation into two portions and of placing one portion in each conductor of the talking-circuit, together with the above-mentioned arrangement of the disconnecting-aimunciator at the central stationpvhereby electromagnetic helices in one case are so connected with the talking-circuit that their adverse action is neutralized by the equal opposed action of others and in the other case are excluded altogether from the talking-circuit, enables me to provide a talking-circuit composed of two multiple-station lines in which the voice-cur rents circulate without material impedance from the electromagnets at intermediate stations or elsewhere. I provide also at the central station a key or switch which when operated introduces the operators telephones into a bridge between the two conductors, uniting the two circuits for conversation, which introduces a meter to indicate the strength of the current passing over the circuit for outgoing signals formed of the two conductors in parallel, and which establishes a branch connection between the generator producing the said current and a group of keys controlling the different strengths of current required to operate the selective rclays which govern the signaling and locking devices at the substations.

In the drawings accompanying this specification, Figure 1 is a view in elevation of my new selective switching-relay. Fig. is a diagram representing the appliances and their circuit connections of a substation apparatus embodying my invention, including the selective switch and the localcircuits and devices which it controls. Fig. .3 is a similar View of the disconnecting-signal and its circuits. Fig. dis a diagram of two substationcircuits which may be united at a central sta tion for reciprocal conversation, together with their normal sign aling connections, their switchboard connections, and their accessory apparatus. Fig. 2 represents the electrical arrangement of the terminal substation of a multiple station telephone-circuit l and the plug-socket connection at the central station S. The said circuit has two main- line conductors 1 and 2 extending from the central station S through any suitable number of way or intermediate stations (not shown) to the said terminal substation, where they are grounded after passing, respectively, through choking or impedance coils f and f All of the other substations have similar apparatus and connections, but the terminal one is chosen for description, since, necessarily, it alone has the terminal ground.

T is the receiving-telephone; t, the transmitter; g the transmitter in duction-coil, and g the automatic telephone-switch. The said receiver and the secondary winding of the induction-coil are in anormally open bridge or branch 3 of the metallic talking-circuit and the transmitter and primary in a local circuit 4:, including a local battery 77., all being controlled in the usual manner by the automatic switch.

S is the selective switching-relay, and I its actuating-electromagnet. The helices of the said magnet are in a grounded circuit which has for its main conductor the two lines 1 and 2, bunched in parallel to form a single conductor, over which the currents to operate such magnet are sent, and united at the last substation to a terminal ground connection r. One half, 6 of the coils of the said magnet are connected up in the conductor 1 and the other half, i in the cond uctor 2 in such manner thatthe signaling-current passing in the same direction through both conductors shall cooperate in the two coils to produce a magnetized condition of the cores.

Obviously when the telephones are in use and voice-currents are traversing the metallic circuit the said currents circulate in opposite directions in the two line conductors 1 and 2, and the coils 2' and therefore oppose to them no appreciable impedance, since such magnetism as the current in one line-wire tends to excite in the magnet-core is neutralized by an equal but opposed magnetism which the current in the other line tends to set up.

B is the call-bell; k the visual busy-signal indicator; the telephoneswitch lock or bolt, and k the actuating-electromagnet for the said indicator and bolt, the call-bell being contained in a normally open local circuit 5 of the battery h, having two points at which it may be controlled or opened and closed by the relay S while the electromagnet 7c is included in a second normally open local circuit 6 of the same battery, having one point where it may be closed or opened by the said relay.

To ad apt the automatic telephone-switch g in my system for the automatic transmission of the call and disconnecting signals to the central station, it is arranged as follows: The switch-lever carries two contact-pieces g and g and has contact-springs g 9 which bear upon the contact-surfaces of these pieces g g, the said contact-surfaces being interrupted by inlaid sections of insulating material. The contact-piece g and its spring 9 and piece g and its spring g are interposed in the line conductors 1 and 2, respectively. In both normal and alternate position of the switch the circuits through the contact-pieces and 70 their springs are complete; but as the switchhook rises from its normal position to its alternate position the circuit is momentarily interrupted, owing to the passage of the noncondncting sections under the contactsprings, so that if there be a current normally on the circuit it ceases for an instant to flow, and a signal can thus be produced on an an nunciator in the normal central-office connections. Manifestly the circuit is also momen- 8o tarily interrupted when the receiving-telephone is replaced, and I utilize this circumstance, as hereinafter detailed, to produce aclearing-out signal.

The selective circuit-controlling-switch relay of my invention may be described in a general manner as comprising an electromagnet and its armature, means for opposing the movement of the armature by progressivelyincreasing forces throughout its range of travel, whereby its travel is divided into several stages, local-circuit contacts controlled by the armature to be closed at the end of its initial stage of travel, other local-circuit contacts adapted to be opened in its subse- 5 quent travel, and still others to be closed or other mechanism to be operated in its final movement. The first and second mentioned contacts are included serially in the same circuit, which may contain any suitable re- :00 sponsive instrument, so that by means of a current of predetermined strength in the mag net the relay may be caused to close the circuit through the instrument, While with a weaker current it will remain inert, or with a [05 stronger current it will close and instantly thereafter interrupt the said circuit. The last-mentioned contacts or mechanism may control any desired device or instrument, and may be caused to close or open the electric I10 circuits or to operate the said devices in response to currents sufficient to throw the armatures to the extreme positions of their travel. The principles and preferred style of construction of this selective relay are in- 1 I 5 dicated by Fig. 1, and such a relay (differently adjusted) is located at each substation.

The selective relay S (shown in Fig. 1) comprises an electromagnet I and three pivoted levers'b Z) 11 which impinge upon one r20 another successively. Lever b carries the armature of the electromagnet. Its longer arm rests normally upon an adjustable stop b which has an insulating-tip. Levers Z) and 6 reston other stops b and b the for- 12 5 mer of which forms a conductive contact with the lever and the latter of which has an insulating-tip. Lever b has also an alternate contact I) in electrical connection with the frame carrying the stops. All the 1 0 levers are journaled in insulating-bushings b in the frame. These levers are balanced upon their pivots by counterweights c 0 0 respectively, and carry other movable weights 0" c c, by which they may be adjusted to require different forces to lift them. Lever U carries a downwardly-projecting stud c of metal, upon which lever 71 impinges when the latter is raised and through which lever Z) communicates motion to lever U Lever Z) is furnished with a similarly-disposed stud of insulating material, placed to engage with lever U In adjusting this instrument the weight should be so placed that the lever will be raised into contact with stud c by a predetermined current-say ten. millialnperes. \Veight c on lever b should then be placed to permit the lifting of the latter lever by any current in excess of ten milliamperes, while weight 0 will permit the raising of its lever only by a greatly-increased current.

The lever l) of relay S is united to one terminal of the bell B, whose other terminal is united to one pole of battery 71. The resting-contact U of lever U connects with the other pole of the same battery. llence when the lever L is raised into contact with the stud carried on lever b the local circuit 5 of the battery it containing the bell ll is closed. \Vhen the lever Z) is moved through a further stage of its travel, it lifts lever Z1 and the contact between the latter and its stop U is severed, breaking the local bell-circuit.

The busy-circuit indicator 7& and telephone connection-lock 7e" are likewise operated by the switching-relay S by means of the local circuit t of the battery It and the actuatingmagnet 7.: contained therein, and are responsive to such movements of its armature a as result in raising the third lever 1) thereof. Lever l) and its contact-stop b are the normally-separated terminals of the said local circuit, so that when the lever moves into contact with the stop the circuit 6 is closed, its magnet is excited, the armature thereof attracted, and the indicator moves to a position of display, showing that the line is oeeupied or in use at some other station. The detent or bolt 7r at the same time is moved into the path of the switch-lever g", and projecting under the end thereof prevents it from being moved to bring the telephones into circuit, and by this means all stations are prevented from heedlessly interrupting any communication which may be in progress.

When the magnet I is traversed by a current of appropriate strength, the local circuit 5 of the bell is closed and the bell is rung to give the call. \Vhen a moderately-increased current passes through the magnet-coils, the levers I) and b acting together, as described, again open the local circuit 5, so that the station-bell will not ring, and it should be stated that if the increased current be initially sent the said local circuit will open at b so promptly after it closes at c that the bell will not have time to ring. \Vith a still stronger current through the relay-coils and a correspondingly greater excitement of the magnet the lever b is moved through its final stage and lifts both of the other levers, causing the lever b" to close upon its contact-stop if, and thus to com plete circuit 6, setting the indicator and locking the telephone-switch to prevent the com nection of the telephone-bridge.

The use of the apparatus described, in a complete telephone-line equipped with several stations and terminating in a central office, may now be considered. The complete apparatus is represented. in Fig. l-. The line conductors l and 2 are shown as forming a circuit of three stations, (designated M, M, and M At each station they include the two helices of the magnet l and contact-points of the switch g". The signatbell, indicator, and telephone at the substations are not here shown, having been sufficiently described.

For permitting the selective signaling of any of the stations M, M and ill the levers l) are differently weighted, so as to respond to currents of differei'it strengths in the line conductors. Thus lever Z) at station iii may respond to ten milliamperes, the same lever at station M to twenty milliamperes, and the lever at station 31'' to thirty i'nilliamperes. The lever at each station should be so weighted that it will be lifted by a current a little in excess of that to which the correspondingleverl) will respond. All the levers Z) are so heavily weighted that they require for their movement a current considerably in excess of that required to lift the lever (1 at station M. It will be apparent that with such an adjustment of the different switching-relays a current of ten millialnperes through the conductors l and 2 jointly or in parallel will bring lever I) at station M into contact with lever U at the same station and will thus close the local circuit at that station and ring the bell ll. The selective relays at the other stations will remain inert. A current of twenty milliamperes in the line-circuit will move the lever l) at station M through the second stage of its travel, and will thus interrupt the circuit 5, including the bell, before the latter has responded; but the same current will. bring lover I) at station hl into position to close the circuit 5 at that station and ring the bell there and will not be sufficiently strong to affect the relay at station Bl. at all. In the same way a current of thirty milliamperes will cause the interruption of the bellcircuits 5 at stations M and M but will bring about the closing of the bell-circuit at station M and will thus give the call-signal at that station.

A greater cu rrent-say forty lnillia mperes will lift the entire series of levers at all stations, and thus will close the local circuits at the different substations, displaying the annuneiators and lochin g the telephone-switches at all the stations where the telephones have not alreadybeen taken from the switch-hooks. Thus any of the stations on the party line maybe signaled independently of the others, and after the sending of the signal the instruments at all stations not signaled may be making connection between two lines.

locked, so as to prevent their use, and indicators may be displayed to show the occupied condition of the line.

Line conductors 1 and 2 are led at the cen tral station S to the springs n n of the springjack N. These springs are normally in contact with other springs n 07. by which the conductors 1 and 2 are continued to the two poles of the battery or other source of current, the line-annunciator p, of any suitable type, being included in either conductor, as shown. The spring-jack N has also other switch-sprin gs a nlwhich are connected with line conductors l and 2, respectively, through small iin pedance-coils 01 72.. \Vith this springjack a plug Q is employed having two pairs g g g and g, respectively, of contact-strips entering between and registering with the two pairs 77, It' '21111Cl or n of switch-sprin gs in the spring-jack and. also a piece g, which makes contact with the two springs 71 and 12 when the plug is inserted into the spring-jack. Two plugs Q and Q of this type are employed in The two like contact-strips g of the plugs Q and Q? are united through a conductor 7 of the plug-circuit. The two other contacts (1 are likewise united through a conductor 8. These conductors 7 and 8 both include condensers, (designated as s and 3 respectively.) The contacts g and g of each plug are connected together and constitute the terminals of con ductors 9 and 10, respectively. The contact pieces q form the terminals of two conduc- I tors 11 and 12.

The operator at the switchboard has the usual telephones t and a key to for connecting the telephones with the plug-circuit. She has also a pair of switches or keys 1: and v either of which is adapted to connect the source to of signaling-current to one of the lines, a set of keys a; for varying the strength of the current from battery to, and an indicator or meter y for showing the strength of current flowing to the line.

The key a has the usual pair of switchsprings u with their anvils, which are adapted when the plunger of the key is depressed to complete the bridge 13 of the plug circuit 7 8. The same key has also other switch-sprin gs u and 19,10 and 10 The spring 10 is thrust against an anvil u when it is forced outward. Springu rests normally on the contact-anvil u from which it is separated when the plunger of the key is depressed. Springs a and 107 have normal restin g-anvils, which are connected together, and alternate anvils with which they engage when the springs are thrust apart. A clearing-out annnnciator z of the type shown in Fig. 3 is also furnished with each pair of cords. This clearing-out annunciator, as represented in Fig. 3, has a magnet c", a pivoted armature c and a light shield e hung before the armature.

A permanent polarity is imparted to the core 0 by a permanent magnet c whose poles of like sign are presented to the armature and, in cooperation with the core, serve to retain the armature normally in its vertical concealed position. For use in the plug-circuit adapted to the mode of selective signaling of the present invention this magnet has four windings, (designated in the drawings c c c and 0 Two of these windings, c and e, tend when traversed by current of appropriate direction to oppose or neutralize the permanent magnetism of the device and thus to release the armature and permit the display of its face. The other two helices, c and c act to magnetize the core in the same direction as its permanent polarity. lVhen the armature is released, it must fall away to such a distance that the attraction of the permanent magnet alone shall be insufiicient to cause its return, but that such attraction assisted by the magnetism evoked by coils c and a shall draw it back or reset it.

The conductors 9 and 10 are united after traversing the helices e and c which tend to oppose the magnetism of the permanent magnet, and thence are led through a conductor 14, including the spring U5 and its anvil n of key u, to one terminal of battery 0. The other coils, e and 6 which tend to assist the magnetism of the permanent magnet, are connected in the two conductors 11 and 12, respectively, which then extend to the switches v and c Through these switches the circuits of these two conductors are united and are thence led through a wire 15 to the springs n and n of key it. In the normal position of this key the circuit is continued through springs 10 and u to battery 10. The alternate contacts 1 and r of switches r and '0 are led by wire 16 through the normally open contacts 00 9: and 00 of the composite key at and thence, still by wire 16, to the anvil u of key a. The contact-anvils of buttons 00 00 and a are connected in multiple with conductor 16 through resistance-coils of different magnitude, so that by depressing button a certain predetermined current-for example, ten milliamperes-may be permitted to flow through the line-circuit, or by depressing button 00 or button 00 a current of twenty milliamperes or thirty milliamperes will flow to line. The meter y is included in the wire 17, whose terminals are the external contactpieces of springs to and M.

In each substation-circuit when atrest current flows continually from battery 0 through line conductors 1 and 2, circulating in opposite directions in the magnet-coils i at the different stations, and the eitect of this current flowing through the coils of annunciator 1) holds the armature (1 thereof in its quiescent position.

The entire series of operations of signaling from a substation, giving the order to the attendant at the central station, and signaling to the required station of the party line may e sea lei be described with relation to the single party line shown, since no operation of the process is different in connecting two different lines. A subscriber requiring connection between his station and another simply removes his telephone from its switch-hook. The switchhook g in rising momentarily opens each of the line conductors 1 and 2, interrupting the current through the annunciator p and thus permitting it to display its indicator. In response to this signal the operator inserts plug Q into the spring iack N. This operation effects a rear 'angement of the circuits as follows: The line conductors 1 and 2 are extended to the conductors 8 and 7, respectively, of the plug-circuit, while the springs 11. and n. are disconnected from their normal contactsprings 11 and n and from the eontinuations of line conductors 1 and 2, extending to bat tery 0. These last springs are short-circuited through contact-pieces Q3 and q of the plug, thus forming a closed circuit of low resistancc, including the annunciator p and battery 0. The increased current in this circuit effects the restoration or resetting of the annunciator p. The operator next depresses the plunger of key "it, whereby the bridge-conductor l3, includingthe telephones i, is completed and the telephones are brought into connection with the plug-circuit. The subscriber may new address the operator and state with what station connection is required. It will be observed that the line conductors 1 and 2 have at this moment a connection through the two impedance-coils n and a" and the two springs 11- and n in parallel, through the contactpiece q of the plug, and thence through wire 11, coil 6 switch 1', wire 15, spring indicator 1 spring u, and battery u" to ground. Through this circuit when the switch 1; is turned to its contact 35) a current flows which tends to increase the magnetism in the core of clearing out annnnciator .2, and which hence holds in place the indicator of that annunciator. Another circuit exists normally from battery 0 through contact u" and spring 11 wire 14, cell c, eonductor 9, thence through contact-piece q of plug Q. and spring n to battery 0, which, when it is complete, permits a current to circulate through coil e in the direction and of proper strength to neutralize this current through coil e but the latter circuit is at this n1o ment interrupted at the contact between the spring a and the point (t of the key n.

Suppose that station M has transmitted the initial call-signal, and that the station with which connection is required is M if the switch is not already in contact with point it is so placed, whereby a circuit is formed to wire 16. The button is then depressed, whereby a current of thirty milliamperes is permitted to flow to the line-circuit. This current is sufficient to lift the levers b and b at station M and M interru 1 )ting the bellcircuits at these stations and to lift the lever Z) at station M so as to close the bell-circuit at this last station. The call-signal is thus transmitted to station ill, the instruments at the other stations remaining unaffected.

hen the subscriber at the signaled station has responded and addressed the operator, the latter may turn the switch 0 to its point 3!), whereby a direct circuit will be completed from battery 1r through conductor 11 and through the line-wi res 11. and 2, permitting a sui'iiciently heavy current to flow through this circuit to raise the three levers at star tion M5 This movement of these levers closes the local circuit 6, (see Fig. 2,) dis plays the busy signal, and locks the telephone-switch at that station. Subscribers at stations M and M may then converse without interrupt-ion from the subscriber at the intermediate station. Having iinished the process of completing connection between subscribers, the operator releases the key '11, whereby the telephone is cut off from the dug-circuit and the indicator 7 is discon nected from the other apparatus, a direct circuit being completed through springs 11" and n At the same time the circuit .t'rom battery 0 through wire it and coil eis closed and the current for neutralizing the magncb ism arising from coil 6 is permitted to How. The core of the clearing-out annuneiator has then only what magnetism may be produced from the permanent magnet, which is sul'licicnt to maintain its indicator in position. 'When, after the completion of the conversation, either subscriber replaces his telephone on its switch-hook, the line conductors are again momentarily interrupted and the current through coil e of the clearing-out annunciatoris broken. The coile, which tends to demagnetize the core of the magnet, now remains alone active, and hence causes the indicator of the annunciator to fall. The signal for disconnection is thus given.

W hen the plug Q is removed from the spring-jack, the apparatus is returned to its normal position.

If desired, the operator may place the key it again in position to connect her telephone with the plug-circuit for the purpose of as suring herself that the conversation iinished. If this be done, the circuit of coil c is again interrupted while that of c is closed, and the indicator of the clearing-out annunciator is returned to its concealed position. This arrangement of the clearing-out annunciator dispenses with the necessity of having its coils in the talking-circuit, and therefore relieves the said circuit from the impedance they would introduce.

When connection is to be made between two different lines, the operator, after the re ception ol the order, will insert plug Q into the spring-jack of the required line, will. bring the switch t into contact with *u, and operate the proper button of call-key a: to transmit the desired selective signal. The

circuits thus formed are the counterparts of those described and the mode of operation does not differ. If the call-initiating line be a party line with several stations, the insertion of plug Q into the spring-jack n in answering the initial call will permit current to flow through wires 15 and conductor 11 to the line sufficient to lock the switches of all those telephones which are not in. use at the different stations and to set the indicators at the same stations.

In cases where the visible signal denoting an occupied line and the telephone-switch lock are not desired the third lever of the electromagnetic switch or relay can be dispensed with without interfering with the other features of the invention in any way whatsoever.

Having thus described my invention, I claim- 1. A multiplestation metallic telephonecircuit, and a telephone at each station in a normally open bridge or branch thereof, controlled by an automatic telephone-switch, in combination with an independent signalingcircuit havinga line conductor formed of the two wires of the said metallic circuit joined in parallel, a selective relay at each station in the said signaling-circuit; and an associated call-signal instrum ent controlled thereby, each station-relay being adjusted to actuate its call instrument on the passage through its coils of a definite and different strength of calling-current, and to maintain the irresponsiveness of the said call instrument on the passage of stronger or weaker callcurrents.

2. The combination in a telephone system, of the two wires of a telephone party line, forming in series the direct and return conductors of a metallic telephone-circuit, and in parallel the single conductor of a ground return-signaling circuit, and a telephone at each subscribers station connected or adapted for connection in the said metallic circuit, or in a normally discontinuous bridge or branch thereof, with a selective switch or relay connected in the said signaling-circuit at each substation, and independent call and busy signals, and a telephone connectionlock, associated with said relay and controlled thereby; the several station-relays being adjusted to actuate their associated call-signals selectively, with a definite strength of callingcurrent different for each, and to actuate their associated busy-signals, and telephonelocking devices collectively, when excited by an actuating-current of strength greater than that of the strongest calling-current, substantially as described.

3. A grounded signaling-circuit extending from a central station to a number of subscribers stations, having a line conductor.-

controlling devices for progressively and successivel y closing and opening the said local bell-circuit, the said relay being adjusted to close the said local circuit and operate the bell with a current of definite and predetermined strength flowing in the signaling-circuit, and to close and instantly reopen the said circuit and thereby prevent the signal from being given,on the passage of a stronger current, substantially as described.

4:. In a telephone system, the two wires of a telephone party line, forming in series the two line conductors of the metallic telephonecircuit, and in parallel, the single conductor of a ground return-signal circuit, in combination at each subscribers station with a telephone in the said metallic circuit or in a bridge or branch thereof, and an electromagnetic signal instrument in the said grounded circuit, the electromagnetic coils of the said instrument being connected half in circuit with one line conductor and half in circuit with the other, in such manner that the two said halves may cooperate magnetically in the signaling-circuit, and oppose each other magnetically in the talking-circuit, whereby a number of signaling-magnets may be connected with a telephone-circuit without introducing impedance.

5. In combination with the two wires of a multiple-station telephone-line forming severally the outgoing and return conductors of a metallic talking-circuit, and jointly when connected in parallel the single conductor of a ground return-signaling circuit; a subscribers station apparatus comprising a telephone, and an automatic lever-switch controlling the connections thereof, two local circuits containing respectively the station call-bell, and the actuating-electromagnet of a visual busy-signal and a locking device for the said telephone switch-lever; and a selective electromagnetic switch or relay in the main signaling-circuit, provided with a series of armature-actuated circuit-changing levers controlling the said local circuits, and adapted to close the local bell-circuit; to hold it open;

and to close the busy-signal and switch-loch circuit, according to the strength of current flowing in the main signaling-circuit, substantially as described.

6. In a telephone subscribers station appara-tus the combination of a relay or electromagnetic switch comprising an electromagnet connected in the main signaling-circuit, a lever attached to the armature thereof, a second lever hung in the path of the first to be actuated thereby, and carrying a front contact-stop therefor, and a third lever hung in the path of the second to be operated thereby, with two normally open local circuits, one containing the station call-bell and leading through the first and second levers, the front contact of the first, and the resting-contact of the second, and the other containing the electromagnet of a busy-signal indicator and telephone-switch lock, and leading through the third lever and. its front contact, whereby the first local circuit may be closed, or closed and imn'iediately opened, and the second 10- cal circuit closed, as the relay-armature is by different main-line currents partially or fully attracted, and moves one, two or all of the said levers; substantially as described.

7. In a telephone-station a )paratus, a selective relay comprising an electromagnet, a pivoted lever mounted on the armature thereof, another pivoted lever lying in the path of movement of the said armature-lever, and a third pivoted lever mounted in the path of the second, the third lever being adapted to be operated by the second, and the second by the first, as the arrnature-lever eomple tes successive portions of its stroke, and independent circuit-changers controlled by the said levers respectively, substantially as described.

8. The combination in a telephone signaling-circuit, of a series of selective relays or switches one at each station, each comprising an electromagnet, an armature therefor and a pivoted lex'er mounted thereon and carrying a circuit-closer, a second pivoted lever mounted in the path of the armature-lever and carrying a circuit-breaker, and a third pivoted lever mounted in the path of the sec 0nd and carrying a circuit-closer, the third lever being adapted to be actuated by the second, and that by the first, each after its actuating-lever has begun its stroke, and two local circuits for each relay, one containing a call-bell, the circuit-closer of the first lever and the circuit-breaker of the second, and the other containing the electromagnct of a busy-indicator, and telephoneloek; and the circuit of the third lever, the said relays being selectively adjusted to initially respond by moving their first lever only to a definite strength of current different for each station, and to respond collectively by moving all of their levers, to a current stronger than the strongest eallii'ig-current, substantially as described.

9. In a selective switch, the combination with an eleetrenmgnet and a lever actuated thereby, means for opposing the movement of the lever by forces increasing progressively through successive stages of travel, a pair of contact-points adapted to be closed in its first stage of movement, another pair adapted to be separated in its second stage, and a third pair adapted to be closed in its third stage, as described.

it). The combination in a selective switch, of an eleetromagnet and pivot-ed lever carrying the armature thereof, another pivoted lever lying in the path of movement of the armature-lever, and a third pivoted lever in the path of the second-mentioned lever, adjustable weights upon each of the lovers, and switclrcontaets controlled by each lever, as described.

11. In combination with a telephone-line having at its subsei ibers stations a telephoneswitch adapted when operated to interrupt the line-circuit, a disconnecting or cleaningout annunciator having an indicator and a permanently polarized electromagnet new mally retaining the indicator in its dormant or concealed position, the said indicator having two equal and opposite]y-aeting helices, one of these, that tending to reinforce the permanent magnetism being in the main signaling-circuit formed by connecting the two wires of the talking-circuit in parallel, to gether with a source of en rrent, and the other in an independent circuit together with a similar source of current, whereby the said annuneiatoris maintained inert while the telephone-circuit remains unbroken at the substation, but is responsive to the interruption thereof, as described.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses, this 2 th day of January, 18.)(3.

JOHN A. llAltlili'F.

\Vitnesses:

Tnonns D. Locinvooo, G. LAWRENCE Burrs.

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