US845452A

US845452A - Telephone trunking system.

Info

Publication number: US845452A
Application number: US12076802A
Authority: US
Inventors: Francis W Dunbar
Original assignee: Kellogg Switchboard and Supply Co
Current assignee: Kellogg Switchboard and Supply Co
Priority date: 1902-08-23
Filing date: 1902-08-23
Publication date: 1907-02-26
Anticipated expiration: 1924-02-26

Description

Na. 845,452. PATENTED EEB. 26,1907.

F. -W.-DUNBAR.

TELEPHONE TRUNKING SYSTEM.

APP'LIGATION FILED AUG.23. 1902.

2 SHEETS-SHBBT 1.

rm: NORRIS PETERS ca., WASHINGTON, n c.

No. 845,452.- a PATENTEDFEB. 26 1907.

' P. 'WLDU-NBAR.

TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED AUG.23, 1902.

UNITED STATES PATENT OFFICE.

FRANCIS W. DUNBAR, OF CHICAGO, ILLINOIS, ASSIGNOR T O KELLOGG SWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A

CORPORATION OF ILLINOIS.

Specification of Letters Patent.

Patented Feb. 26, 1907.

Application filed August 23, 1902. Serial No. 120,768.

T0 00 whom, it may concern:

Be it known that I, FRANCIS W. DUNBAR, a citizen of the United States of America, and a resident of Chicago, county of Cook, and State of Illinois, have invented a certain new and useful Improvement in Telephone Trunking Systems, of which the following is a specification.

My inventon relates, primarily, totelephone trunk-circuits and apparatus cooperating therewith, whereby telephone subscribers whose lines terminate at difierent central oflices or central stations may be 'connected together for conversational purposes.

In common, battery telephone systems there are two main types of circuits employed. In both types the subscribers lines are provided at the central oflice with a linesignal-controlling electromagnet and a connection to the common battery, whereby when a subscriber desires to call the central oflice he closes the limbs of the lines together at his station, preferably by taking up his receiver, thus completing the circuit of the common battery through said electromagnet to operate the same, and thereby indicate a call at the central office. The limbs of the telephone-line are also carried through the normally closed contacts of a cut.off relay at the central orlice, which relay when operated serves to open the line to the battery, and thereby render the line-signal inoperative. In one type of circuits the winding of this cutoff relay is entirely free from and unconnected with the line-circuit, while in the other type the winding of said relay is connected with the line-circuit and is adapted to be operated by current over a portion of the talking-circuit when a connection is established therewith. In the former type of lines a third wire must of necessity be carried through the switchboard and be provided with a special contact in each of the springjacks or connection-terminals of the subscribers line. In view of this arrangement the said special contacts are made use of to determine the busy or idle condition of the subscribers line. In the other type of lines the cut-off relays are connected directly with the talking-circuit and are energized over a portion of the same when a connection is established, whereby the third wire throughout the switchboard and the third contact of I the spring-jacks are dispensed with. These lines are therefore termed two-wire lines.

My present invention relates to trunk-circults and apparatus whereby lines of the two different types may be connected together in such manner that the usual and best method of operating the trunk-circuits bet-ween eX changes may be employed. The central o'l'lice at which the call for a connection originates is known in telephonic parlance as the A or outgoing oflice and the trunks so used as the outgoing trunks, while the oflice at which the connection is completed is known as the B or incoming office and the trunks as the incoming trunks.

The invention also consists of the features and arrangements hereinafter described, and particularly pointed out in the appended claims.

My invention is illustrated in the accompanying drawings, in which the same reference characters designate like p arts throughout the several view s, and in which- Figure 1 is a diagram showing a trunking system leading between two central oflxces, the subscribers lines at one ofhce being of the two-wire type, while the lines of the other office are of the type employing local ('lI'CL its for the cut-ofi' relays and testing-contar ts. F ig. 2 is a similar view showing a slight ircdification in the trunk and with sutscrilers lines at both ofhces employing local circuits for testing and for the cut-off relays. Fig. 3 is a detailed view of the difi'erential supervisory relay employed.

Referring to 1* ig. 1, L designates one of the plurality of subscribers lines terminating at the central ofiice C. This line extends in two limls 2 and 8 from the subscribers station A to the said central ofliee C, where it is fitted with suitable answering and multiple jacks or connection-terminals J J At the subscribers station the usual telephone instruments are provided and consist of a transmitter 4, a receiver 5, a ringer or callbell 6, and the condenser 7. The switchhook 8 is adapted in its normal position and when the receiver is plat ed thereon to open the circuit through the transmitter 4 and receiver 5 and to close it through the callbell 6 and condenser 7. A retardation-coil 9 is connected at the substation when the hook is raised in parallel with the receiver and condenser 7 to provide a path transparent to steady currents, but opaque to voice-currents 3 include, respectively, the armatures or 5 springs 10 and 11' of the cutoil' relay R, which is permanently legged to ground "from the sleeve-contacts j of the jacks J J. The armature or spring 10 is normally connected with ground through the conductor I) 12, while the opposite armature 11 is normally connected with conductor 13, contain.- ing the line-relay R for the line, said conductor leading to the live or ungrounded pole of the central battery B, the opposite pole of which is grounded. The line-relay R controls, through its armature, the circuit of the line-signal S. The forward contacts 14 and 15 of the cut-oil relay R are adapted to connect the jacks and the switchboardsection of the line with the external line-cir cuit when the said cut-ofl' relay is energized. This, it is to be understood, is a typical two- Wire line-circuit and is the particular kind With which I prefer to use my trunk-circuits, although I do not wish to so limit the use of the invention in all respects. At the central ofl'ice C the usual operators cord-circuit is provided, said cord-circuit having an answering-plug P and a calling-plug P, each being 0 provided with a tip-contact p and a sleevecontact 9 adapted to register with like contact-suri'aces and j in the acl s of the line when the plug is inserted therein. The tipcontaets or the plugs are connected together 5 by means of the tip-strands t and t of the cord-circuit and the interposed condenser 0, while the sleeve-contacts are likewise connected by the sleeve-strands s and s and the interposed condenser 0 A conductor 16 extends from the grounded pole of the battery B to the tip-strand t and contains the Winding of the tip supervisory relay r associated with the answering-plug P, while the live pole of the battery is connected, by means of conductor 17, with the answering sleeve-strand s and includes the winding or the sleeve supervisory relay 7". These re lays r and r" serve to control the circuit of the supervisory lamp S associated with the answering-plug P, the "former relay serving to normally close said circuit of the lamp, While the latter relay normally opens the same. The battery 13 is associated with the opposite or calling end oi the cordcircuit and is connected by conductors 18 and 19 with the tip and sleeve strands t and 8, respec tively, the former conductor including the winding 01 the supervisory relay 7", while the latter conductor includes the similar relay These relays serve, in a manner similar to the relays r and r, to control the circuit of the supervisory lamp S, associated. with the calling-plug P The relays r and r are conveniently referred to as the tip-relays, and relays r and l at their opposite terminais with the t I he line conductors 2 and eeaeee r as the sleeve-relays, since they me were neeted with and operated by euri ent [h over the coriespondii; strands ol the circuit. The tip-str: 1 i t ol the caihn testing plug l is normally open through H extra spring or movable co i i-t it) at sleeve-relay 1' but ad aptei;

to be (lflf :l the said spring and its forward (0: isn't iii when the relay is energized. 'l he be. t tact 22 of this extra spring 20 is co"; through the medium of co one side of the highv 1. inmedance relay 1-, inown as the lay, the other side ol which is groitmle i. The armatiue 01'. this relayis likewise g= oufdt, ed, and its forward context is c cried .i .ih the primary Windin oi the op tion-coil 25 by me? ol eond other end of the said primary up i nected, through the 'inei'lium ol 0 to the live pole ol the battery is", a .e tion-coil 27 being included in this The operators transmitter its i one side to conductor 26, inlez'mez primary coil and the coil 127,:i11d 1.11. the oi hz=- no side through conductor :2) to giom il. condenser c is included i the operatic-k cond user a", in a bridge bet ol the cord-circuit by mean; key and indicated dis Branch connections 31 posite sides oi the re eiver and sero: an. order-hey 7;", rec ted with circuit or wire 33, h groundedalterii ator g is adapted to l resistance-hunt), with the tip-stii 1 H the stated g to the cilia e t i'ii'm ewe e cord-circuit by means of the t spri g 7a, the SlCOYO-(K "art 01" s con? ected with batter, 26 and resistance 26 A trunk-circuit is show tween the central ollices a d (r circuit being titted at the outg multiple jacks, such as J J or number. The tr .nlec reu

t exte limbs

35 and 36 to the (e iral ollire '1" it is provided with suitable means {or the condi n. of the wanted e, m the desired subscriber, and with sig able the operator to noper'iy atte; Y neetion. The tip and sleeve co and 236 terminate at the iatrot p the wi;:-.din.gs w and w' of the 1-epeatEn; y-

which are (OT-JEZQCiGll together thmuuzi *terposed conderser e The op in 1 's w" and w of the said repeaii :l'

are ('(Ii'lllilhfifl together through the brim; B Which is common to the exrlta: e J to the incoming trunks at said excite...

sleeve strands t and s of the trunk-cord, which strands terminate in the corresponding contacts p and p of the trunk-plug P. A trunk-relay r is connected with the sleevestrand 86 of the trunk by means of conductor 37 and upon the opposite side, by conductor 3S,with the spring-contact 39 of the ditlerential supervisory relay r The normal contact 40 01' said sprlng 38 is connected by conductor 41 with the tip-conductor 35 of the trunk.

A disconnect-signal S and a ringingsignal S are provided for the incoming end of the trunk. The common conductor 42 leads to the individual branches 43 and 44, containing these limbs, which branches are again connected by a conductor 45, leading to the forward contact of a grounded spring 46 of the difl'erential relay T In one of the par llel branches the normal branch 43, containing the disconnect-lamp S and the armature of the trunk-relay 1, is located and is so arranged as to normally close the same. An additional grounded spring 47 is provided for the differential relay r and when actuated makes contact with sprin 39 of said relay and opens the circuit between the spring 39 and contact 40. The operators receiver 48 is adapted to be bridged across the trunkcord, together with the secondary of her in duction-coil 49 and a condenser c, by means oi a listening-key 7%, it being understood that these keys are only diagrammatic representations of any ordinary listening-key, the springs of which are operated by a single lever or push-button. The operators transmitter 50, which is in circuit with the primary of the induction-coil 49, may be charged from the battery B or by means of a local battery.

An order wire or circuit 33 extends from the central oilice C to the o'flice C A ringing-generator g is adapted to be connected between ground and the tip-spring 70 of the ringing-key, the sleeve-spring k thereof being grounded when operated. A resistancelamp 5] is placed in the path of the ringingcurrent. The subscribers line L ternunating at this oilice, is provided with a number of multiple jacks J J, each of which has the usual tip and sleeve contacts and j and with third contacts 7' which are adapted to be grounded when a connecting-plug is in serted in the ack. These springs 3' are connected with one side of the cut-oil relay R the opposite terminal of which is connected, by means of a conductor 52, with the live pole of the battery B Test-rings 7' are provided for the several jacks and are insulated both when the line is not in use and during a connection. These rings are connected by a conductor 53 with the forward contact of spring 54 of the cut-off relay, said spring being grounded through a suitable resistance 55. A line-signal S is provided for the line I and is connected with the live pole of the battery by conductor 52 and at its opposite terminal with the line conductor 3, which is normally open at the subscribers station. A bell 6 is provided at the latter station and is connected between the tip limb of the line and ground when the telephone is upon the hook 8, but is disconnected therefrom when the telephone is in use.

The operation is as follows: The A subscriber desiring a connection with a subscriber located at another exchange rernoves his receiver from the hook, and thereby closes a path for current between the limbs 2 and 3 of his line through the transmitter 4 and retardation-coil 9, the condenser 7 and receiver 5 being connected in parallel with the retardation-coil. The closing of this circuit permits current to flow from the battery B through conductor 18, line-relay 1x spring 11 of cut-oft relay R, limb 3 of the telephone-line, through retardation-coil 9 and transmitter 4 at the substation and thence over limb 2 back to the central oflice, and spring 10 cf ctt-ofl relay R, through conductor 12, to ground. The line-relay R is thus operated and closes the circuit of the signal-lamp S to ground from the conductor 13. The operator upon seeing the line-si nal exposed inserts the answering-plug P into the a swering-jack J of the subscribers line and connects her telephone t0 with the cord, circuit by depressing the listening-key 7c 70 to receive the order from the subscriber. The ins rtion of the plug P closes a circuit thro gh the cut-off relay R from the live pole of the battery B through condtctor 17, sleeve superi isory relay 1 sleeve strand 8, sleeve-con acts 1)" and j of the plug and jack, thence th; u h the wincin; of the cut-off relay R to ground. The operation of this relay disconnects the armatures 10 and 11 .rom the ground-wire 12 and from the battery-re d 13 and connects them 1h; ough the tor-ward contacts 14 and 15 of said armatures to the normally disconnected jacks J J. lie operation of the supervisory relay 1 over the path just traced serves to close, through its armature and tr nt contact, the circuit of the stipervisory signal S which is associated with the 1; l; g r but it is prevented from glowing by the operation of the tip supervisory relay W, a hich is connected in the conductor 16 and receives current over telephone-line and the tip-strand t of the cord-circuit and through the conductor 16 to the grounded pole of the battery B as soon as the cutotl relay R is operated. The supervisory signal S therefore remains inert while the battery B furnishes curren over the metallic telephone-line for the operation of the supervisory relays and for conversation al purposes. The opera tors transmitter 28 is receiving current at this tine from the battery B over the conductor 26, through retardation-coil 27, thence through the trans'i-nitter 28, and over conductor 29 to ground. When sound Waves strike the transinitter 28, the current flowing tl'ieiethrough is varied, which causes a variation oi the charge in the condenser c and a corresponding surge of current through the primary or her iiuluction-roil These induce voice-currents in the secondary, Which are transmitted to the line, and the operator is therefore able to converse With the calling subscriber.

Upon learning that a subscriber in the exchange 0* is desired the A operator deeresses the order-key le to connect her telephone with the order Wire or circuit 33 and repeats the number of the Wanted subscriber to the B operator, Whose head-teleplione 48 is per inanently connected with said order-n ire. The latter operator designates to the A operator the trunk to be used and proceeds to test the condition of the Wanted line vith the tip of the plug or the incoming trunk named. If the line is idle, no click ill be received, for the reason that the test-rings j of the subscribers line are insulated from ground; but if the line is'busy the test-contacts will be connected through resistance 55 to ground, and since the tip-contact of the plug is connected with the live pole of battery is a complete circuit will be established and the operator Will receive a click, owing to the variation or the charge of the condenser 0. Upon finding the line idle the plug 1* is inserted in one of the multiple jacks oi the line wanted. The A operator, having received the number of the trunk to be used, inserts the calling-plug it of her cord-circuit in the jack of the trunk at her ection. The insertion of the plug P closes a circuit from the live pole of the battery B at the A oilice through conductor 19, the sleeve supervisory relay 1' sleeve-strand s" of the cord-circiit, sleevecontacts of the plug and jack, and over the sleeve-conductor 3c of the trunk through conductor 37, the trunlorelay r, conductor 38, spring 39 of relay r and spring i? to ground. This circuit is established at the incoming end by reason of the plug P having been inserted in the jack of the line, whereby a path for current from the live pole of the battery B" is established over the the-strand oi" the trunk-cord and tip side of the subscribers line and thence tarough the grounded signaling-bell at the substation. This op- GIiLtBS the ditlerential relay r and closes its springs 46 and 47 upon their forward contacts. By means oi the current in the path over the trunk just traced the supervisory signal S i:1 the cord-circuit is operated, and thus indicate to the A operator that the called subscriber has not yet responded. l he actuation of differential relay r at he incoming end connects a ground upon the llll'll) branches but as the trunk-relay r is operated When the lamp S lights it indicates to the B operator that the called subscriber has not yet replied. 111 calling the sulzsciilzer at the station D the ringingdroy 76 76 is di pressed, which sends current over the tip side of the line and through the grounded signaling-bell. In. case of the response of the called subscriber during ringing the groiuuhd hey it in the sleeve-strand of the trunk-cord provides a ready path to earth for the lt tirn ringing-current. Upon the response oi the called shbszriher the t .vo li :nbs oi the metallic circuit are closed togc ther, and current from the battery B ilons over the metallic line,

the transmitter at the station D and at the same time closing the niagi'ujtic e lects oi' the differential relay 1", which consequently roleases its springs 46 and -l7, the Former serring to open the circuit of the l'ii'iging-lninp it", to thereby extinguish it and indicate to the B operator "hat the called subscriber has respondcd, uhile the other spring l? peril its contacts 39 and 4-0 to close together, and thus connect the trunk-relay r of the nutallic (ircuit oi the trunli, whereby current is alien id to flow over the metallic circuit oi the trunk from the battery B and since the said trunk relay is o1 low resistance it is niainteinrd tittuated during conversation and the same time permits a su'llicient lion oi current to energiiae the tip supervisory relay r in the It. (or(,lcirci.it, which serves to extinguish l io supervisory lamp S to indicate to the j operator that the called subscriber has res; on: led. The S'LllJSGIillKlS are now connechd together "for conversation. The latt'; furnishing current to the line L for tell ing purposes and for the operation ol the ('1 t-oll relay and supervisory relays. The lottery B is furnishing current for the operation ol" the trunk and supervisory relays, \i'hilo the battery B" provides the called line ith talliing-curront and serves also to operate the several relays. The ringing-lamp 3 is n vented from operating by the clecnergixalion of di'l'l erential rclaji' r, \\"l.ile the disconnrcllamp has its path opened at a second point by the trunk-relay r Upon. the to 'mination of the COHVUl'l-ltll ion the sutscrihers telephones are returned in their books, with the result in ti 1 use oi" line L that the supervisory signal S is operated, and at line L" the di'll'erential relay 1- is open ated ly reason of the path for currrnt l b ing estatlished over the tip side oi the line through the grounded signaling-tell. Thus the actuation of dill'ercntial relay opens the metallic circuit of the trunh-lino to thrrely render the tip supervisory relay in the cord-circuit inoperative, which closes the circuit of the supervisory signal S" and lights it. 'i his indicates to the A operator the hanging up of the D sul scrile "s tcle iihono. .l he cord-circuit is then disconnected from the thus furnishing current for the operation oi i trunk and the subscribers line, thus restoring all parts to normal position at the A office. The disconnection of the cord-circuit deenergizes the trunk-relay r at the incoming end, which closes the circuit of the disconnect-lamp S and causes it to indicate the fact of the disconnection at the A office. The B operator upon seeing signal S therefore takes down the connection at her office, thus restoring all parts to normal position.

Fig. 2 shows specifically the same arrangement at the incoming ofhce, the subscrib ers line L being the same and the trunk-circuit being the same, except that the trunk-relay is adapted to be connected between the tip side of the trunk-circuit and ground through the medium of the grounded spring 47 of the differential relay r instead of being connected from the sleeve side, as in the case of Fig. 1. At the A office the subscribers lines are of the type shown at L which is the same as the line L at the B office and the parts have been correspondingly designated. The cordcircuit for use at this office is of the type employing differential supervisory relays-that is, the relays are disposed with their windings in .the opposite sides of the cord-circuit. whereby when current flows over the metallic line said relays are irresponsive and the supervisory signals controlled thereby are inert but when current flows over one side of the line or a greater portion flows over one side,

so as to unbalance the magnetic effects of the two windings, the said two relays are energized and the lamps are lighted. The batteries B and B are arranged as indicated. and the windings 0 and 0 of the repeatingcoil 0 are arranged in inductive relation, while the windings 0 and 0 are likewise situated. Vi hen the subscriber A calls the central office, the line-signal S is operated by current over the metallic line. The operator inserts the plug P of the cord-circuit into the answering-jack of the line, and thereby closes the local circuit of the cut-off relay R which is energized from the battery B. This disconnects the line-signal S and connects the test-rings of the jacks to ground. The supervisory signal S remains inert on account of the current flowing over the metallic line through the substation. In order to establish connection with the trunk, the Aoperator inserts the plug P in one of the jacks thereof, and, 'as explained with reference to Fig. 1, the plug P of the line has already been inserted in the jack of the wanted line, whereby the differential relay r at the in coming end is operated. A path for current.- is therefore established over the tip side of the trunk and through the trunk-relay 1 to ground, the current in this path serving to operate the differential supervisory relay r to close the circuit of supervisory lamp S to thereby indicate that the connection has been made at the called end and that the subscriber-has not yet responded. As soon as the called sulscriter responds the metallic circuit of the trunk is completed, which permits current from the battery B in the A cord-circuit to flow over the metallic circuit of the trunk to thereby render the differential supervisory relay r inoperative. .The supervisory signal 8 is rendered inert and indicates to the A operator that the called subscriber has responded. The remainder of the operation is the same as described w ith reference to Fig. 1 and is not deemed necessary to repeat. The several parts of the apparatus have been designated by the same reference characters as in Fig. 1, so that the operation will be readily understood.

Fig. 3 shows the superposed windings of the differential relay, such as is used in both the cord-circuit and trunk of Fig. 2 and the LlllIlk of Fig. 1,' these windings being superposed for the purpose of rendering them'neutral to the. rapidly-varying voice-currents and at the same time permitting theoperation of the relay when current fiows through one winding only.

The ground connections heretofore referred tomay and in practice usually are one and the same, or they may be the common oliice-return. It is also apparent that the other poles of the batteries may be 5 grounded so far as the general operation of the system is concerned, it being only necessary to reverse the connections from those shown in the drawing. It is also apparent, so far as some features of the invention are concerned, that the lines may terminate in single cords and plugs in place of the double cords shown and described and that the trunks may terminate in jacks in place of plugs and cords.

While I have described one method of carrying out the invention, I would have it understood that the said invention is not to be so limited, as it is apparent that various changes and substitutions may be made therein and still come within its scope and principle; but

Vi hat I do claim as my invention, and desire to secure by Letters Patent, is

1. The combination with a trunk-line, of a cord-circuit to connect with its outgoing end and a called-subscribers line with which its incoming end is connect-ed, .a disconnect signal for said incoming end, means operated by current flowing over the called-subscribers line when connection is made therewith for placing said signal in condition to operate,

and further means controlled by the connection of said cord-circuit with the trunk for rendering said signal inoperative, substantially as described.

2. The combination with a trunk-line, of a cord-circuit to connect with its outgoing end and a called-subscribers line with which its 1ncom1ng end is connected, a disconnect-signal for said 1ncom1ng end, means operated by signal being placed in operative condition by current flowing over said side of the trunk circuit to ground, a relay having a winding energized when the called subscriber responds for disconnecting said ground and connecting the two sides of the trunk together to permit current to flow over b oth sides thereof, said flow of current serving to render the supervisory signal inoperative, substantially as described.

12. The combination with a telephone-line adapted to connect with a cord-circuit at its outgoing end and connected with a called telephone-line at its incoming end, of a supervisory signal associated with the cord-circuit and placed in condition to operate by cur rent flowing over one side of the talking-circuit when the cord-circuit is connected with the trunk, a trunk-relay at the inconiing end ofthe trunk connected between the said side and ground, and means to connect said trunk-relay in the nietallic circuit of the trunk when the subscriber responds, said relay being of low resistance so as to permit a sufficient flow of current in the trunk-line to render said supervisory signal inoperative, substantially as described.

13. The combination with a trunk-line adapted to connect with a calling telephoneline at its outgoing end and a called telephone-line at its incoming end, of a disconnect-signal at the incoming end of the trunk placed in condition to operate by current over a portion of the talking-circuit when connection is established with the, called line, a trunk-relay actuated by current over the trunk as long as the connection exists at its outgoing end to prevent the operation of said signal, substantially as described.

14. The combination with a trunk line adapted to connect with a calling telephoneline at its outgoing end and a called telephone-line at its incoming end, of a disconnect-signal at the incoming end of the trunk placed in condition to operate by current over a portion of the talking-circuit when connection is established with the called line, a trunk-relay actuated by current over the trunk when connection is established with the line, and means for maintaining said relay actuated during conversation, said relay serving when energized to prevent the operation of said signal, sub stantially as described.

15. The combination with a trunk-line adapted to connect with a calling telephoneline at its outgoing end and a called telephone-line at its incoming end, of a disconnect-signal for said incoming end placed in condition to operate by current flowing over a portion of the talking-circuit when the trunk is connected with the called line, and means actuated by current iiowing over one side only of the trunl-:line to prevent the actuation of said signal when the called-subscriber's telephone is not in use and the conlnection exists at the outgoing end of the trunk, sus'istantially as described.

16. The combination with a trunk-line adapted to connect with a calling telephoneline at its outgoing end and a called telephone-line at its incoming end, of a disconnect-signal for said incoming end, means operated by current flowing over a portion of the talking-circuit w hen connection is made with the called line for placing said signal in condition to operate and further means controlled by the connection at the outgoing end of the trunk for rendering said signal inoperative, said latter means being operated by current over one side of the trunk and ground, substantially as described.

17. The combination with a trunk-line adapted to connect with a calling telephoneline at its outgoing end and a called telephone-line at its incoming end, of a disconnect-signal for said incoming end placed in condition to operate by current flowing over a portion of the talking-circuit when the trunk is connected with the called line, and means to prevent the actuation of said signal during such connection and w hen the callingline is connected with the trunk, said means being actuated by current over one side only of the trunk when the calledsubscribers telephone is not in use and over the metallic trunk-line during conversation, substantially as described.

18. The combination with a trunk-line adapted to be connected with a calling telephone-line at its outgoing end and a called telephonedine at its incoming end, of a disconnect-signal for said incoming end, means orezated by current over a portion of the talking-circuit when connection is made with the called line -for placing said signal in condition to operate, and further means controlled by current sent over the trunk-circuit when the calling telephone-line is connected with the trunk for preventing the actuation of said signal, said latter means being operated over one side of the trunk and ground when the called-subscrib ers telephone is not in use and over the metallic circuit during conversation, whereby said signal can only be operated when the said connection is severed at the outgoing end, substantially as described.

19. The combination with a trunk-line adapted to connect with a calling-line at its outgoing end and a called telephone-line at its incoming end, of a disconnect-signal for said incomin end, means actuated by current flowing over a part of the talking-circuit when connection is established with the called line for controlling the circuit of said signal at one point to place it in condition to operate and further means governed by the connection of the calling-line with the trunk and operated over one side of the trunk and ground for controlling the circuit of said sig- ICC nal at another point to prevent its operation, substantially as described.

20. The combination. with a truqlscirouit adapted to connect at its outgoii-g end with. a calling telephone-lire and at its incoming end with a called telephone-line, of a disconne" signal for said incomir plated in c n 7 tion to operate by curt t tlowing over a portion of the t: liiilg- *ircuit when the trunk is connected with the called telephonedine, and a trunk-relay energized. by current .llowi g over one side oi the trunk and ground when the Cttllzf l'OiQPllOilQ-lilfi is connected *ith the OtlbQOllg ejld. of the trun and the calledsubscribers telephone is not in use, and energized during conversation by curreit over the metallic circuit, d latter relay servii'ig wh energized to re der said signal inoperative, subst. ially as described.

21. The combination. with. a trun ;-circuit adapted to connect at its outgoing end with a calling te ephojedine ai l at its incon g end with a called telephone-line, of a relay at the incoming end actuated by current over a portion. of the talkingcircuit when. connection is established with the called line, a trunk-relay actuate by currert over the trunk when. co ts at the outgoing end, ant Lal at the incomii .g end entirely controlled by said two relays to cause it to give discor t lication when. connection is severed at the outg g end and still exists at the incoming end, substantially as described.

22. The combination with a trunk-circrit extending between dillerent switcl1boardsections and adapted to connect telephonelines together for conversation, of a sir-pervisory signal associated with the oittgoing end adapted to be operated by ClUlGIlt over one side or the tallring-circr it thereol" when. connection. exists therewith and to be rendered inoperative by current over the :u etallic circuit thereof, a relay at the incon g end. of the trunk actuated when connection is establ shed with the coded line to permit the flow of current over th said one side of the outgoing end, and means for perniitti g current to flow over the said nietallic ciici it of the outgoing end when the called party responds, substantially as described.

23. The con": ination with a tru1k-ci.rcrit extending between dill'erent switchboard sections and adapted to connect telephonelines together for conversation, of a supervisory'sigiual associated. with the outgoing; end of the trunk placed ia condition to operate when a connection is established at said end by current over one side of the talkingcircnit of said outgoing end, a relay at the incoming end of the trunk controlling the circuit of the said oi tgcing end, said relay being operative when the connection is established with the called line and before the response of the called party and inoperative during conversation, substantially as (le i'ihml.

24. The combination with a t. ii li-circiit extending between. dill'ercnt :erwitclibciiiilsections and adapted to coiir tct telephonelines together for cenveitatioii, ot a FF. poivieory signal associated with the ongoing end placed. in condition to operate when a connection is established at said end, a relay at the incoming end of the trunk controlling the path for c'tirrent over the outgoing end, said relay liieing energized. when the connection is established with the called-s1; bscril iors line and deener ized when the called subscriber responds to permit in the latte; coo dition a How of current over the outgoing on d oi the trunk su'llicicut to render saiil stpci visory signal inoperative, substantially as K tscribed.

25. The cen'ibination with a tronlt-rirccit extending between dill'erent switrhboawh sections and adapted to connect telephonelines togetl'ier or conycrsation, ct tlitl')tltviscry signal associated with the outgoing end of the trunk placed in. condition to opcr ate by current {lowing over a portion oi" the talking-circuit when connection is est cl ilishod at said end, a relay at the incoming Lilt'l ot the trunk controlling the path for coxrcnr over the outgoing end, said relay being enorgized when the connection is established wit h the called line to periiit current to [low over the outgoing end of the trunk to acti'ate said supervisory signal, and ireans for tllit 'iit l'fjlb ing said relay when. the called subscriber rcspends, whereby a low-resistarce path tor current over the outgoing end ol. the trout: is completed to permit a s lliciout [low ol' current thereover to render the said H'lilifi'itlrhill' signal inoperative, substantially as (lest-til not 26. The combination with a tronlc-circi.it extending between dilleieut switcliboa'rih sections and adapted to coiuicct telephonelines together for conversation, of a supervisory signal associated. with the outgoing end, an electroinagi'ietic winding in the pat h of current over one side of the ltlllilll.,' fll'(i it oi the outgoing end oi the lil uh to place said signal in condition to operate, a second wiztl ing in the path of crjrrent over the other tl'lt of said end to render said signal inoperative when energized, an clectronagnetminding at the inco'iring end energized when the counection established with the called line and when the called-partys telephone is not in so, to complete the path tor citrreut over the said one side of the outgoing end, and a second electronia :t-winding at the incoming end to be CIlG'l lZtXl when the callczl party answers to c the completion ol' the path for current over the said iretallic cit-cit. sol;- stazitially as described.

27. The coi'nbination with a tru "v extending between dill'erent switchhoardsections and adapted to connect telephonetogether for conversation, of a supervisory lines together for conversation, of a supervisory signal associated with the outgoing end, a trunk-relay at the incoming end of the trunk actuated by current from over the outgoing end when a connection exists at said latter end, a signal at the incoming end whose actuation depends upon said relay, a second relay at the incoming end serving when energized to complete a path for current through said trunk-relay over one side of the outgoing end and when denergized to complete a path over the metallic circuit of the outgoing end, whereby a suitable actuation of the said supervisory signal is secured and at the same time the signal at the incoming end is suitably controlled by the trunk-relay, substantially as described.

28. The combination with a trunk-circuit extending between difiere'nt switchboardsections and adapted to connect telephonelines together for conversation, of a supervisory signal associated'with the outgoing signal associated with the outgoing end,- a trunk-relay at the incoming end of the trunk actuated by current from over the outgoing end when a connection exists therewith, a signal whose actuation depends upon said relay, and a second relay actuated over one side of the called telephone-line and ground when a connection is established therewith to complete a path for current through said trunk-relay over one side of the outgoing end, said second relay being deenergized when the called subscriber responds to thereby cause the completion of apath for said trunk-relay over the metallic circuit of the outgoing end, whereby a suitable actuation of the said supervisory signal is secured and at the same time the signal at the incoming end is suitably controlled b y the trunk-relay, substantially as described. 4

31. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephoneend, a trunk-relay at the incoming end of the 1 lines together for conversation, of a trunktrunk actuated by current from over the outrelay at the incoming end adapted to be acgoing end when connection exists at said lattuated by current over the trunk from the ter end, a signal at the incoming end whose actuation depends upon said relay, and a second relay at the incoming end actuated by current over a portion of the talking-circuit when'connection is established with the called line to close the circuit of said trunkrelay over one side of the said outgoing end, said relay being rendered inoperative by current over the metallic circuit when the called party responds, whereby a suitable actuation of the said supervisory signal is secured and at the same time the signal at the incoming end is suitably controlled by the trunkrelay, substantially as described.

29. The combination with a trunk-circuit extending between diflerent switchboardsections and adapted to connect telephonelines together for conversation, of a supervisory signal associated with the outgoing end, a trunk-relay at the incoming end of the trunk actuated by current from over the out going end when connection exists therewith, a signal whose actuation depends upon said relay, and a second relay at the incoming end actuated by current over the called telephone-line before the subscriber responds to complete a path for said trunk-relay over one side of the outgoing end, said second relay being deenergized when the called subscriber responds to thus close a path over the metallic circuit of the outgoing end for said trunk-relay, whereby a suitable actuation of the said supervisory signal is secured and at the same time the signal at the incoming end is suitably controlled by the trunk-relay, substantially as described.

30. The combination with a trunlvcircuit extending between diii erent switchboard-sections and adapted to connect telephone-lines outgoing end when connection exists at said end, a second relay at the incoming end of the trunk controlling the circuit of said trunkrelay and suitably actuated by current over the talking-circuit when connection exists with the called line, and a signal at the incoming end controlled solely by said two relays, substantially as described.

32. The combination with a trunk-circuit extending between different switchboard-sections and adapted to connect telephone-lines together for conversation, of a supervisory signal associated with the outgoing end, a trunk-relay at the incoming end of the trunk actuated by current from over the outgoing end when connection exists at said latter end, a signal at the incoming end whose actuation depends upon said relay, and of a differential relay at the incoming end of the trunk suitably actuated when connection exists with the called line and serving to control the circuit of the trunk-relay, whereby a suitable actuation of the said supervisory signal is secured and at the same time the signal at the incoming end is suitably controlled by the trunk-relay, substantially as described.

83. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephonelines together for conversation, of a signal at the incoming end of the trunk, a trunk-relay at the incoming end actuated by current over 34. The combination with a trunk-circuit extending ietween diflerent switchboardsections and adapted to connect telephonelines together for conversation, of a ditl'erential relay at the incoming end having a winding in each side of the tall ing-circuit and unresponsive to current in the metallic line,

and a signal at the incoming end whose actnation depends upon said relay, substantially as described.

35. The combination with a trunk-circuit extending between di'l'lerent switchboardsections and adapted to connect telephonelines together for conversation, of a supervisory signal associated with the outgoing end, a trunk-relay at the incoming end of the trunk actuated by current from over the outgoing end when connection exists at said latter end, a signal at the incoming end whose actuation depends upon said relay, and a second relay at the incoming end having ditl'erential coils, one in each side of the talking circuit, one of said coils being included in the path of current over one side of the called line and through the grounded signaling-bell branch when connection is made with the line, whereby the differential relay is actuated to close the circuit of said trunk-relay over one side of the outgoing end and when the called party responds the said (li'l'lerential relay is rendered inoperative to thereby close the circuit of said trunk-relay over the me tallic circuit of the outgoing end,whereby a suitable actuation of said supervisory signal is secured and at the same time the signal at the incoming end is suitably controlled by the trunlcrelay, substantially as described.

36. The combination with a trunk-circuit extending between di'tlerent switchboardsections and adapted to connect telephonelines together for conversation, of a disconnect-signal at the incoming end, a di'l'lerential relay having a coil in each side of the talking-circuit at the incoming end, said relay being actuated by current through one of its coils when connection has been established with the called line and the calledpartys telephone is not in use to place said signal in condition to operate and said relay being rendered inoperative by current in the metallic line when the called party answers, and a trunk-relay actuated by current sent over the outgoing end of the trunk to prevent said signal operating when connection exists at the outgoing end. substantially as described.

37. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephone lines together for conversation, of a supervisory signal associated with the outgoing end, atrunk-relay at the incoming end of the trunk actuated by current from over the outgoing end when connection exists at said latter end, a signal at the incoming end whose actuation depends upon said relay, and. a sec- I end relay at the incoming end having dill'ei ntial coils, one in each side of the talkingcircuit, one of said coils being included in the path of current over one side of the called line and through. the grounded signaling-bell branch when connection is made with the line, whereby the diil'l erential relay is actuated to close the circuit of said trunk-relay over one side of the outgoing end and when the called party responds the said dil'l'erential relay is rendered inoperative to thereby close the circuit of said trunk-relay over the int. tallic circuit of the outgoing end, said (litterential relay also controlling the circuit of the trunk-relay, whereby a suitable actuation ol the said supervisory signal is secured and at the sajne tine the signal at the incoming end is suitably controlled by the trunk-relay, substantially as described.

38. The combination with a trunl'\:ci1'cnit extending between different switchboardsections and adapted to connect telephonelines together for conversation, of a disconnect-signal at the incoming end, a dillerential relay having a coil in each side of the talking circuit at the incoming end, said relay being actuated by current through one of its coils over one side of the called telephone-line to the substation and thence through the grounded signaling-bell to place said signal in condition to operate, and said relay being rendered inoperative by current in the metallic line when the called party answers, and a trunkrelay actuated by current sent. over the outgoing end of the trunk to prevent said signal operating when. connection. exists at the outgoing end, substantially as described.

39. The combination with a trunk-circuit extending between di'llerent switchboanlsections and adapted to connecttelephonelines together for conversation, of a ringing signal for the incoming end of the trunk, a relay actuated by current over one side of the called line when connection is established therewith to place said signal in condition to operate, and means actuated by current in the metallic line when the called party answers to render said signal inoperative, substantially as described.

40. The combination with a trunk-circuit extending between different switchboard sections and adapted to connect telephonelines together for conversation, of a ringing signal for the incoming end of the trunk, a relay actuated by current over one side oi the called line and the grounded signalingbell at the substation for placing said signal in condition to operate, and means lot rendering said signal inoperative when the called party responds, substantially 28 described.

41. The combination with a trunk-line extending between different switchboanl-sections and adapted to connect telephonedines together for conversation, of a riiiiging signal ICS for the incoming end of the trunk, a relay actuated by current over a portion of the tip side of the talking-circuit and called line to place said signal in condition to operate, and means responsive to current in the metallic line when the called party responds for rendering said signal inoperative, substantially as described.

42. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephonelines together for conversation, of a ringing signal for the incoming end of the trunk, a relay actuated over a portion of the talking-circuit and called line when connection is established with the called line to place said signal in condition to operate, and means for rendering said relay inoperative when the called party responds to thereby render said signalinoperative, substantially as described.

43. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephonelines together for conversation, of a ringing signal for the incoming end of the trunk, a relay actuated over a portion of the talkingcircuit and called line when connection is es tablished with the called line to place said signal in condition to operate, and means for deenergizing said relay when the called party responds to thereby render said signal inoperative, substantially as described.

44. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephonelines together for conversation, of a ringing signal for the incoming end of the trunk, a relay actuated over a portion of the talkingcircuit and called line when connection is established with the called line to place said signal in condition to operate, and means actuated by current in the metallic line when the called party answers for rendering said relay inoperative to thereby retire said sig nal, substantially as described.

45. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephonelines together for conversation, of a ringing signal for the incoming end of the trunk, a differential relay having a coil in each side of the talking-circuit, means for closing a path through one of the coils when connection is established "with the called line to operate the same and thereby place said. signal in condition to operate, said relay being rendered inoperative by current in the metallic line when the called party responds to thereby render said signal inert, substantially as described.

46. The combination with a trunk-circuit extending between different switchboard sections and adapted to connect telephonelines together for conversation, of a ringing signal for the incoming end of the trunk, a

differential relay having a coil in each side of the talk1ng-c1rcu1t, means for closing circult through one of said coils and over one side of the called-line to ground at the substation when connection is established with the said line and the subscribers telephone is not in use, to thereby operate the same and actuate the signal, said relay being rendered inoperative by current in the metallic line when the called party answers to thereby render the said signal inert, substantially as described.

47. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephonelines together for conversation, of a trunkrelay at the incoming end of the trunk actuated by current from over the outgoing end when connection exists at the latter end, a signal at the incoming end whose actuation depends upon said relay, a second relay at the incoming end having differential coils, one coil in each side of the talking-circuit, a source of current, one of said coils being in the path of current from said source over one side of the talking-circuit when connection is made with the line, whereby the differential relay is actuated at such time, and means for including the said source of current between the said coils and in the me tallic circuit of the called line when the called subscriber responds, whereby the said relay is rendered inoperative and the substation-transmitter is charged for talking purposes, substantially as described.

48. T16 combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephonelines together for conversation, of a disconnect-signal for the incoming end of the trunk, means actuated by current over one side of a called telephone-line to place said signal in conditlon to operate, and means actuated by current over the trunk from the outgoing end when connection exists with said end to prevent said signal operating, substantially as described.

49. The combination with a trunk-circuitextending between different switchboardsections and adapted to connect telephone- 1 lines together for conversation, of a disconnect-signal for the incoming end of the trunk, means actuated by current flowing over one side of a called telephone-line to the substation and ground. to place said signal in condition to operate, and means actuated by current over the trunk from the outgoing end when connection exists at said end to prevent said signal operating, substantially as described.

50. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect telephone lines together for conversation, of a disconnect-signal for the incoming end of the trunk,

means actuated by current over one side of the called telephone-line and through the grounded bell the substation to place said signal in COllt .ition to operate, andineans actuated by current over the trunk from the outgoing end when connection exists at said end to prevent said. signal operating, substantially as do cribed.

5.1. The combination with a trunk-circuit extending between Citlerent switchboardsections and adapted to connect telephone lines together for conversation, of a disconneot-signal for the incoming end of the trunk, means actuated by current over the tip side of the called telephone-line and through the grounded bell at the substation to place said signal in condition to operate, and iineans actuated by current over the trunk from the outgoing end when connection exists at said end to prevent said signal operating, substantially as described.

52. The combination with a trunk-circuit extending between ditl'erent switchboardsections and adapted to connect telephone lines together for conversation, oi a disconnect-signal for the incoming end of the trunk, a relay actuated by current over one side of the called. telephone-line to place said. signal in condition to operate, and a second relay actuated by current over the trunk from the outgoing end when connection exists at said end to prevent said signal operating, substantially as described.

53. The combination with a trunlecircuit extending between ei'tl'erent switchboard sections and adapted to connect telephonelines together for conversation, of a (inconnect-signal lor the incoming end oi the trunk, a relay actuated by current over one side of the called telephone-line and through the grounded signaling-bell at the substation to place said signal in condition to operate, and a second relay actuated by current over the trunk from the outgoing end when connection exists at said end to prevent theoperation of said signal, substantially as described.

54. The combination with a trunk-circuit extending between ditlerent switchlmardsections and adapted to connect telephonelines together for conversation, of a disconnect-signal for the incoming end. of the trunk, a relay actuated. over a portion of the tip sice of the line to place said. signal in condition to operate, and a second relay actuated by current over the trunk 't'ron'i the outgoing end to renter said signal inoperative, sul'istantially as described.

55. The combination with a trunk-c' su t extending between diflerent switchboardsections and adapted to connect telephon lines together for conversation, of a ringing signal for the incoming end of the trunk placed in condition. to operateby current over one side of the called line to the substation means actuated. by current flowing over the nietallic circuit when the subscriljim responds for rendering said signal inoperative. substantially as described.

56. The combination with a trui'ilt-circu t extending between different switchboardsections and adapted to connect subscribers lines together for conversation, of a supe visory relay at the outgoing end actuated by current over said end and ground when connection is established at both ends of the trunk, a supervisory signal controlled by said relay, and nteans actuated upon the response of the called subscriber 'lor disconnecting said. ground. connection to render the supervisory relay and signal inoperative, sn 1 stantially as described.

57. The combination with a trunk-circuit extending between different switchboardsections and adapted to connect subscribe s lines together for conversation, of a supervisory signaling device and a source oi eurrent at the outgoing end. connected between ground and the talking-circuit, a ground connection from said end at the incoming end of the trunk during connection wit h the called line to provide a rcturnpath l'or current from said source and norms for disconnecting said ground connection when the called party answers, substantially as (lescribed.

58. The combination with a trunk-circuit adapted to connect tolephonelines togeth r for conversation, of a supervisory signal associated with. the outgoing end. of the trunk placed in condition to operate by cur-rein over the tip side only oil the trunk when connection is established at said end and wiili the called line at the other end, and. ireaiis operated when a called party responds to porn it a flow of current over both sides i the trunk to thereby render the said signal inoperative, substantially as described.

59, The combination with a trunk: ircu i' adapted to connect telephone-lines together for conversation, a supervisory signal associated with the outgoing end of the trunk, an electroiragnet-winding energized by cu rent flowing over one side of the trunk to place said signal in condition to operate when a connection is established at said end. and means operated upon. the response of the called party to pernit a flow of current over both sides of the trunk, and an electromagnetwinding in the path of said latter current and adapted to render said supervisory signal inoperative, substantially as described.

60. The co'lnbination with a trunk-circuit adapted to connect telephone-lines together for conversation, of a supervisory signal asso ciated with the outgoing end of the trunk, an electromagnetic device having two windings, one winding being disposed in the pat h of current over one side only of the trunk,

and through the grounded signaling-bell, and i and adapted when energized to operate said lOC signal, and means operated when the called party lesponds to permit a flow of current over both sides of the trunk, and a second winding of said electromagnetic device in the path of the latter current and adapted when energized to render said signal inoperative, substantially as described.

61. The combination with a trunk-circuit adapted to connect telephone-lines together for conversation, of a supervisory signaling device associated with the outgoing end of the trunk having two differential windings connected in the path for current over opposite sides of the trunk, a path for current being completed through one winding and over the tip side of the trunk only when connection has been established at both ends of the trunk, and means operated when the called party responds to permit a flow of current over both sides of the trunk, and through the other Winding of said signaling device to thereby render the signal inoperative, substantially as described.

62. The combination with a trunk-circuit adapted to connect telephone-lines together for conversation, of a trunk-circuit, asupervisory signal associated with the outgoing end of the trunk placed in condition to operate by current over the tip side of the trunk with return over a third conductor, the metallic circuit of the trunk being open to prevent a flow of current thereover, and means operated when the called party responds to disconnect said third conductor and complete the metallic circuit of the trunk to permit a flow of current thereover to render said supervisory signal inoperative, substantially as described.

63. The combination with a trunk-circuit adapted to connect telephone-lines together for conversation, of a supervisory signal associated with the outgoing end of the trunk, an electromagnet-winding connected in the path of current over the tip side of the trunk and ground, and adapted when energized to place said signal in condition to operate, the metallic circuit of the trunk being open to prevent a flow of current thereover, and means operated when the called party responds to disconnect the ground and complete the metallic circuit to permit a flow of current thereover, and a second electromagnetwinding at the outgoing end, the path of the latter current being adapted when energized to render said supervisory signal inoperative, substantially as described.

64. The combination with a trunk-circuit adapted to connect telephone-lines together for conversation, of a supervisory signaling device associated with the outgoing end of called party responds to disconnect the ground from the tip side of the trunk and to connect the two sides of the trunk together to permit a flow of current thereover through the other differential winding of said signaling device, whereby the signal is rendered inert, substantially as described.

65. The combination with a trunk-circuit adapted to connect telephone-lines together for conversation, of a supervisory signaling device associated with the outgoing end'of the trunk having difierential windings placed in the opposite sides of the talking-circuit and responsive to current over one side of the circuit, the signal being inert when current flows over both sides of the circuit, means for directing an excessive current through one winding when connection is established at the outgoing end to render the signal inoperative, and means actuated upon the response of the called subscriber for equalizing the magnetic effect of the current through said coils when the called subscriber responds whereby the signal is rendered inoperative, substantially as described.

66. The combination with a trunk-circuit adapted to connect telephone-lines together for conversation, of a relay at the incoming end actuated over a portion of the talkingcircuit when the trunk is connected with the called line, a trunk-relay at said end actuated by current over the tip side of the outgoing end of the trunk only and ground when the connection is established at the outgoing end and before the called subscriber responds, and a signal at the incoming end whose actuation depends upon said two relays, substantially as described.

67. The combination with a trunk-circuit adapted to connect telephone-lines together for conversation, of a disconnect-signal at the incoming end of the trunk, a relay at said end actuated over a portion of the talking-circuit to place said signal in condition to operate when a connection is established with the called line, and a trunk-relay actuated over the tip side only of the outgoing end of the trunk to prevent the operation of said signal, substantially as described.

Signed by me at Chicago, county of Cook, State of Illinois, this 29th day of July, 1902.

FRANCIS W. DUNBAR.

Witnesses:

ROBERT Lnwrs AMEs, G. BEDER.