US1040629A - Telephone system. - Google Patents

Description

E. R. UORWIN.

TELEPHONE SYSTEM.

APPLICATION FILED FEB. 3, l 1,040,529.V

D98. RBNEWED AUG. 14, i911.

Patented Oct. 8, 1912.

ulb/VENTURI WITNESSES:

UNITED STATES PATENT @It LICE ELMER R. CGRVVIN, OF CHICAGO, ILLINOIS, ASSIGNOR 'lO CORGVIN 'IVIJLEI-GNE IIAIU- .FACTURING COMPANY, or

CHICAGO, ILLINOIS, A. CORPORATION F ILLINOIS.

TELEPHONE SYSTEM.

Patented Oct. t, it) Renewed August 14, 1911. Serial No. 644,042.

To alli whom it may concern:

Be it known that I, ELMER R. ConwiN, a

vcitizen of the United States of America, re-

siding at Chicago, in Cook county, Illinois, have invented a new and useful Telephone System, of which the following is a specification, reference being had to the accompanying drawing, illustrating same.

My invention relates to telephone systems and-deals 'principally with the signaling in such systems.

The-.principal objects of my invention are to provide an improved' automatic-ringing arrangement for telephone systems; to provide improved means for operating the supervisory signals in such systems; and to provide improved means for automatically controlling the operators circuit in connection With the plug-cord connecting circuits for such systems.l

Other obects will be apparent from the following specification.

In this invention I supply a'ringing relay, an operators disconnecting relay, and a supervisory signal, all associated with a plug of the plug-cord connecting circuit, with current' from a line connect-ion extending through a third conductor of the cord, plug and-line-jaclr, for operating the said .devicesA jvvhen connection is made with the line.

Then I provide a locking` relay in the plugcord circuit and supply this relay with current' through the said line connection when the subscriber removes his receiver from the switch-hook While connection is made With the line, to cause the latter said relay to lock the ringing relay in a non-ringing position until the connecting plug is removed from the line jack. I also provide. a supervisory relay for controlling the supervisorysignal, and an impedance coil, both associated with the said plu of the plugcord circuit, through which tic subscribers line is supplied with current for talking purposes during conversation. The supervisory 'relay in addition to cont-rolling the supervisory signal also places the locking relay `in locked position -when Ithe subscriberl removes his receiver from the switch-hook While connection is made Withthe line.

V I preferably provide each of the pair of plugs in a plug-cord connecting circuit with all of the relays above mentioned, to provide automatic ringing `tor each of the plugs and to properly control the operators circuit and supervisory signals as will be herefinait-er described, but l wish it to be understood that I may do away with the ringing `relay and the locking relay associated with one of the plugs ii it is desired to ring out over only one plug of the pair.

I will now describe my invention moro in det-ail, by reference to the accompanying 4drawing which illustrates two subscribers telephone lines and the plug-cord connecting circuit theretor, the whole being adapted, and provided with apparatus, to carry out my present invention.

Attention is called to my two co-pcnding applications 'Serial No. 590,352, tiled November 2, 1910 and Serial No. (525,088, filed `May i, i911.

In the drawings thc lines A and B are each provided with a substation in which the circuit of the line closed when the receiver is removed from the switch-hook, 1n

`the usual manner, the circuit of the line` being open when the receiver the switch-hook.

The limbs 1 and Q ot' cach line extend to terminals 3 and i, respectively, ot a springjackC. VVhenaplug D or E is inserted is hung upon `into a jack C the spring contact-members 3 and 4 are disengaged from contacts 5 and `source F being grounded.

respectively. Each contact G is connected through a line lamp 7 and a common line pilot relay 8 to pole J of a comnmnsource of electricity F, the opposite pole l0 ot contact is connected to, ground.

In the plug-cord connecting circuit the talking strands 1l and l2 ot' cach plug I) and E are connected together through condensers l'i and 111-. respectively. Each plug D and E has a ringing relay l5 associated therewith to control contacts 1(3--17 and 18-19 in the respective talking strands 'll and l2, the said ccntacts being normally closed. ,ll/'hen eitherA ot thc relays l5 I5 is energized, spring n'icinbers lf3 and 18 are caused to dis-engage contacts 1T and 19, respectively, and lo engage contacts 20 and 21, respectively, contacts 20 and Q1 being connected through` conductors Q2 and 23, respectively, to a ringing generator G.

Each of the plugs I) and .E is provided with a third strand or conductor Qaadapted to furnish a ground connection through a Each spring-4 'IIL jack-spring 5 when the plug is connected.`

with a line jack, to furnish current supply e www@ pair of operators disconnect relays 25 and 26 are connected from' the respective strands v24 24' of the plugs D and E, to pole 9 `of battery-F, such connections causing these relays to beco1 ne energized when their respective plugs are connected with line jacks. The

secondary of an operators inductioncoil, an

operators receiver, and a condenser, are' bridged from talking strand 11, on one side .of condenser 13, to talking strand 12, on the other sidev of condenser 14, through normally-closed contacts `V30-31 and 32-33 of each of the relays and 26, in multiple, so that the operators set will be entirely disconnected from the talking strands 1l and 12A i of the cord circuit when both of the relays 25 and 26 are energized.

, The arrangement of the operators relays 25 and 26, and their function, are the same -as in my copending application for -Letters Patent on telephone system, Serial No. 349,374, but the means for supplying these relays with current for energizing same is new in this 1nvention.

To each strand 24 of the plugs D'and E is connected the corresponding ringing relay I 15, through a normally-closed contact 34-35 of a locking relay 36, the circuit from each ringing relay 15 extending through conductor 37, rotary intermittent circuit-closer H, ringing pilot relay 38, and conductor 39, to pole 9 of battery F. Each supervisory lamp 40 is also connected to the corresponding strand 24, through a normally-closed contact 41-42 of'a corresponding supervisory relay 43, the circuit from each lamp 40 extending through a supervisorypilot. relay 44 'to pole 9 ol' battery F.

From talking strand 11, on opposite sides of condenser 13, are connected a pair of impedance coils` 45 45 to ground. From talking strand 12, on opposite sides of condenser 14, are connected a pair of supervisory relays 43 43,' to pole 9 of battery'F. When either of the supervisory. relays 43 `43 is energized it causes-spring 42 thereof to disengage contact 41 and to engage contact 46 which leads to the'winding of the corresponding locking relay 36. When either'of the locking relays 36 36 is energized itl causes spring 35 thereof to disen age contact 34 and` to engage contact 4 spring 35 being connected to the corresponding strand 24. The operation of the system is as follows:

i When a party at substation A desires to make a call, he lifts his telephone receiver from the switch-hook in the usual manner, which closes the circuitbetween limbs 1 and i 2 of his line and therebycauses current to flow from pole9 of battery F, through line pilot relay 8, line lamp 7, contact 6 4, line in'this circuit causes line lamp 7 to light and also energizesv the line pilot relay 3 and' thereby causes same to light lthe-line piloti lamp 48 as well undci stood. The line lamp 7 now-signals the operator at the central sta? tionvfor a connection and the operator inserts one of the plugs DA or E into the' jack C of line Ato answer 'thecalL The plug contacts 11, 12 and 24V now engage -jack springs f3, 4- and 5, respectively, thereby opening jack contacts 3--5 and 4-,6, eX- tinguishing the line llamp 7, denergizingy the line pilot relay 8 and allowing its arm ture ;to release, and closing a number of circuits through battery Ill-.Which circuits will nowl lbe tgaced and explained as follows: A

First: From pole 9 of battery' F through -supervisory relay 43 on Athe connected-plugv `side lof the cord-circuit, contact 19-18,

Qstrand -12, jack-spring 4, line A, jack-spring :3, strand 11, contact 16-17, `and impedance Icoil 45 to ground. Current from battery F z flowing through lthis. circuit energizes relay 43 and thereby causes its armature to be `;attracted and to open contact 41-'42 and close contact 42-46. Contact 411-42 now f :being openl prevents the supervisory lamp 40 from displayingA ajsignal. Contact 42`-46v being closed closes a circuit from pole 9 of battery F, through locking relay 36, contact i46-42, strand-.24, and. jack-spring. 5 to ground. Current from battery F owing :through this 'latter circuit energizes relay y36. and thereby causes its armature to be attracted and open contact 34"-35'and closeA contact 35-47. Contact 34--35 now being kopen prevents ringing relay 15 from becoming energized. Contacts 35e-47 being closed closes a circuit from pole 9 of battery F, g

through relay 36, Contact 47-3 5, strand 24, and jaclespring 5 to ground. Current from battery-F -Howing through this latter circuit will keep relay 36 energized and its armature attracted, even if contact 46-42 is opened, contacts 47-35'and 46-42 being in multiple in the circuit of relay 36. Thus the armature of relay 36 is locked in attracted posit-ion uni 1l the connecting is removed from the line jack C. Second: From pol'e 9 of batteryI F,

plug

through one of the operators disconnect rey lays 25 or 26, (say 25) strand 24 of the connected plug, and jack-spring 5 to ground.v

Currentrom battery F flowing through this circuit energizes relay 25 and thereby causes vits armatures to be attracted and to open contacts 30-31 and 32w33. Although contacts 30-31 and 32-33 of relay 25.are now open, the operators telephone set is still bridged vacross the plug-cord talking circuit from talking strand 11, through contacts 30-31- and 32-33 of relay 26, to talking strand 12.

The operator now receives from the party at substation A, instruct-ions to connect his line for conversation with substation B, whereupon the operator inserts the idle connecting plug of the pair into the .line jack C otl line B. This insertion of the plug into the jack C ot' line B closes a number of circuits through battery F, which cir nits Will now be traced and explained as `follows:

First: From pole 9 ot battery F through the operators disconnect relay Q6, strand 2&1. of the calling plug, and jack-spring of line B, to groiuul. Current from battery l" flowing through this circuit enerfrizes relay 26 and thereby causes its armatures to be attract-ed and to open contacts StL-31 and 32W 33. Now the opcrators telephone set is entirely cut otl' from the talking strands 11, and 12 of the plug-cord circuit.

Second From pole 9 of battery F through conductor 39, ringing pilot relay 38, interinittent circuit-closer ll,lconductor 37, ring'- ing relay 15 associated with the calling plug, contact of locking relay 36, strand 211 of the calling plug, and Jaclespring 5 of line B, to ground. Current from battery F flowing through this circuit when the circuit closer H closes the circuit, cnergizes ringing relay 15 intermittently and thereby causes its armatures to be attracted and to open contacts 16-17 and 18-19, respectively, and close contacts 1t--20 and 15S-21, respec: tively. lVhile the ringing relay 15 is enen gized, a circuit. is closed from ringing genn crator Gr, through conductor 2Q, Contact 20--16 o't ringing relay 15 which is aesociated with the calling plug, strand 11, jackspring 3, limb 1 of line B, the ringer and condenser at substation B, limb 2 oit line B, jack-spring Llf, strand 12, contact 15S-21, and conductor 23, back to the generator ti'. Current flowing from the generator G through this circuit rings the ringer at substation B and thereby signals the party at this telephone. The ringer at substation B is rung intermittently, due to the fact that the ringing generator circuit over line B is closed intermittently by ringing relay 15 which is energized intermittently from battery F through the intermittent circuit closer H. At the time the ringing relay 15 is energized, the ringing pilot relay 3S, being in the same circuit, is also energized and the armature thereof attracted t0 light the ringing pilot lamp 49 as Well understood. It will be seen that the ringing relay 15 connects the source of ringjng,mcyihirrent` Gr direct with the cord strands and line, without causing the ringing current to traverse any coils or vother resistances or im edances at the central station which woul hinder its flow somewhat. It will also be seen that the ringing relay 15 primarily controls the application .of ringing the circuit ofthe ringing relay 15, yurbe connection 1s made with afirme,

current to the linea1f1dv that the interrupter H primarily controls and jack-spring 5 o1 line B, to ground.`

Current Yfrom battery l" llowing through this circuit light the supervisor lamp 40 which shows to the operator that the circiut ot .line l5 is open, and also cncrgizcs relay 44 which lights the supervisory pilot lamp 50 in a manner well understood.

When connection is niadc with line B, jack contacts SM5 and 1--t are opened, thereby rendering the liuc lamp 7 incapable of displaying a signal.

l'lvhen the party at substation B answers his call and li't'ts his receiver from the switclnhoolt, he closes the circuit between limbs 1 and 2 ot' his line and thereby closes a circuit from pole t) oat battery F, through supervisory relay 43 which is associated with the ailing plug, contact 19-18, strand 12, jaclcspring a, line B, jack-spring 3, strand 11, contact itl-47, and impedance coil .L5 to ground, when the circuit. of ringing relay 15 is opened at the intermittent circuit-closer lil'. Current 'troni battery F .lowing through this circuit,l includingI Strands 11 and 12 and line B, cncrgizes rclay 43 and thereby causes its armature to be attracted and to open contact fil-t2 and vclose contact l2-#113. Contact 11M-l2 being opened extinguishes lamp 10 which indicates to the operator that the party at subetation B has answered his call, and also rleenergizes relay flft and thereby causes saine to extinguish the supervisory pilot lanip 50. Contact 1%46 being closed closes a circuit l'r'oin pole 9 ot' battery F, through lockingrelay 36, contact 11G-#12, strand 24 ol the calling plug, and jack-spring 5 to ground. Current from battery l" [lowing through this circuit cnergizes relay 36 and thereby causes its armature to be attracted and to open contact 354-35 and close contact 35-111 Contact 34-35 being opened renders ringing relay 15 incapable ot further operation and thereby stops the ringing over line B. Contact 35t7 being closed closes a circuit itrorn pole 9 of battery F, through locking relay 3G, contact '417-135, strand 2li of the calling plug, and jackspring 5 to ground. Current from battery F flowing through this latter circuit. will lkeep relay 36 energized and its armature attracted, even' it' contact Lllt-112 is opened, contacts 47-35 and Litl-'12 being in multiple in the circuit of relay 36. Thus the ar mature of relay 3G is locked in attracted position until the connecting plu" associated therewith is removed from the ine jack'C. .Now the parties at substations'li and B are connected for conversatitm with each other, over limbs 1 and Q of their lines and talking strands 11 and 12 of the plug; cort l circuit.

- When the conversation is completed, the

party at substationv A hangs his receiver upon the switch-hook, which breaks the circuit of his line in a manner .well understood .and vthereby stops the ow' off'curreiit through the supervisory relay 43` which .is

associated with lineA A. This ,supervisory l relay 43 is now denergi'zed whereupon the armature thereofV releases andfijcloses; the back contact 41--42 which closes a circuit from pole 9 of battery'F, through su'joervifl sory'pilotrelay 44, the supervisey lamp v40 which is associated with line X contact 41-42, strand 24, andspring-contact 5 of the'connection terminal oiline A, to ground,

Current iiowing ,from `battery F through. .5 .this latter circuit causes -`the! supervisory vlamp 40 to light and thereby onvey to' the" operator the signal for. disconnection of line A, aii'dalso energizes` relay 44. and thereby causes sameto 'light the supervisorypilot lam 1- 50. T e paity at substation B by hanging his receiver Auponvthe switch-hook, controls ciricuits, and gives his disconnect signal tothe operator, the same as just describedA in connection with line A. Now the operator, having received. vboth disconnectl signals from substations A and B, withdraws the connecting plugs from the line terminals or jacks and thereby opens the circuits of the locking -relays- 36 36 `and the operators disconnect relays 2526, over the line connections, thus djenergizingall of the relays 36, 36, 25 and 26 and causing the armatures thereof to release. Relays 36 36 now close contacts 34-35 34-35 in the circuits of ringing ren laysY 15 15, but these relays are not Venergized' by `such contacts -being closed because the circuits of the relays 15 l5 over the linev 'connections .are now ope-n at the connecting' plugs. rlhe'withdrawal of the connecting plugs from the line terminals also opens the circuits of the supervisory lamps .4040, and

of the supervisory pilot relay 44, over the linel connections, and thereby extinguishes the supervisory lamps 40 40 and deiiergizes the relay 44 which'exting'uishes the supervisorypilot lamp 50. Now all of the circuits -and apparatus are restored to normal positionand condition preparatory` for an other cycle of operations as just described.

It will be seen that the locking relays 36 36 keep the ringing relay 15 from ringing backon the lines after the parties at the substa-A tions A and B have hung their receivers upon the switch-hooks andthe supervisory relays 43' 43. have been denergized and opened contacts`42-46v42-46 in the `irst= closed paths through the lockingrelays 36 36, While connection is still made with the lines. y

It will be vseen that I have provided a telephone exchange system including telephone lines extending from sub-stations to roaches.

:an exchange,l a cord` circpitA hailing? tiv. plugs, each of which mayfbe'usedas. altemy .swering` plug `and each .of which may be used.. as aconnecting 4plug',l an :loperatelr-a' j telephone, two, magnets, onaassociated [each plug andseachfwheli .inert,s'erving 1n-l dependently of the other tocqnnect the op# ier'ators telephone .withthe cordcircuit, 'and jmeans4 operated by each'plug Vwhen' taken- Affoi' use, for eiectin' the energization of its associate magnet, 1w ereby when both plugs .are taken for use, the4 operators telephone gis cut out of circuit .and when yonly one plug l is taken for use, he Vloperations telephone reitlnaiwis in circuit. Y

l dolnot wish to limit this invention to all ofthe particular detailsof construction, or ito theparticular types of apparatus,- herein shown, vas many modications may be made therein without departing from the scope of the appended claims.;l

What l. claim asmy invention is gthereforfa source of ringing current, a ring- .ing relay for connecting the 'source of ring- 1. A telephone'line, a, connectii'ig circuit A 4ing current with the `connecting circuit, a .second relay associated with the connectingl f ci'rcuit to be operated by current over the :line when connection is. made therewith, a

:single wound lockingl relay controllingthe circuit of the ringing relay and being under control vof the said second relay, meanswheieby the said second relay energize's locking relay with current over a line c yneet-ion when the said second relay is rated, and means whereby the said lcck-ing lrelay closes its 'own circuit when o'p'e`i""atedand thereby locks itself in operated posi-4 ;tion -until the connecting-circuit isdisconnectedI from 'the line.

los

2. 4A telephone line,`a connecting c ircuit n therefoig'a sourceV of ringing current asso- ;ciated with the connecting circuit, a ringing "relay for connecting the source ofrnging 'current'with the connecting circuit, a single wound .locking relay controlling the circuit of the ringing relay, means for energizing {the locking relay with current'over a line connection when connection is made vaith the line, lto operate the locking relay, and 'means whereby the locking 'relay closes :its

V'own circuit through a line connection, when the ringing relay with current over a line connection to operate the said relay, an intermittent circuit-closer in circuit with the ringing relay for operating the latter intermittently, a supervisory relay connected with the metallic connecting circuit to be operated by current over the metallic line a single wound locking relay controlling the circuit of the ringing relay, a supervisory signal under control of the supervisory relay, means whereby the locking relay is initially under the control of the supervisory relay, means whereby the supervisory relay when operated energizes the locking relay with current over the said third lline connection for operating the locking relay, the latter said relay being provided with means for closing its' own circuit through the said third line connection when operated whereby it locks itself in operated position luntil the connectingcircuit is disconnected from the line.

fir A plurality of telephone lines, a connecting circuit for the lines, said connecting circuit terminating in a pair of connecting plu-gs adapted to be connected with the lines, an operators telephone set normally connected with the connecting circuit, an operators disconnect relay for each connecting plug through which the operators telephone set is connected, in multiple, with the connecting circuit, and means whereby the said relays are supplied with current over respective line connections, for operating the said relays, when connection is made between the corresponding connecting plugs and the lines, whereby the operator-s telcphone set is disconnected from the connecting circuit when both or the said relays are operated,

5. A plurality of telephone lines, a connecting circuit for the lines. said connecting circuit having a metallic talking circuit extending therethrough and terminating in a pair ot' connectingplugs adapted to he connected with the lines, an operatos telephone set. normally bridged across the metallic talking circuit oit' the connecting circuit, a pair ot operatoi"s disconnect relays associated with the respective connect-ing plugs and through which the operators telephone set is bridged, `in multiple, across the metallic talking `circuit ot the connecting circuit, a third conductor in each connecting plug and a third ciintact-member' for each line cooperating with the said third conffluctors ot theconnectingplugs, the said oporators rclays being connected in circuit wit-h the respective third conductors of the connecting plugs whereby the said relays are supplied with current over the respective said thirdconductorv connections between the corresponding connecting plugs and the lines, when connection is made with the lines, for operating the said relays whereby the operators telephone set Iis entirely disconnected from bothstrands of the metallic talking circuit of the connecting circuit when both of the connecting plugs are connected with respective lines.

(i. The combination with a plurality of telephone lines and Aa connecting circuit therefor terminating in a pair of connecting plugs, of an operators telephone set asso ciated with the connecting circuit, a relay associated with cach connecting plug, and means .independent of the telephone line circuits ior energizing each relay through a line jack terminal and a line connection leading to battery, during 4the time connection is made with the line, the said relays connecting the opera-tors telephone set with the connecting circuit when at least one of them is denergimd', and disconnecting the opcrators telephone set from the connecting circuit when `both are energized. 7. A metallic telephone line, a connecting circuit for the line, a source of ringing current associated with the connecting circuit, a ringing relay associated with the connecting circuit whereby the source of ringing current is connected direct with both limbs of the metallic line when connection is made therewith, an interruptor for primarily controlling the circuit of the ringing relay when connection is made with the line, whereby the ringing relay is operated intermittently, a locking relay for controlling the circuit of the ringing relay, and means ior operating the locking relay when connection is made with the line and the latter is taken for use.

8. The combination with telephone lines, of a connecting circuit for the lines, a source ol ringing current, a ringing relay operated over a circuit including a line connection and adapted and arranged to primarily connect the source of ringing current direct with a portion 'of the connecting circuit and a line, when connection is made with a line, whereby all other apparatus is eliminated 'from the ringing circuit, a locking relay for controlling the `circuit of the ringing relay, and means for operating the locking relay when connection is made with a line and the latter is taken for use.

9. The combination with telephone lines, ot' a connecting circuit for the lines, a source of ringing current, means operated over a circuit including a line connection for automatically connecting the source oi ringing current direct with a line when connection is made therewith, whereby all other apparatus is eliminated from the ringing circuit, locking mechanism for controlling the said automatic connecting means, and means for operating said locking mechanism when the line is taken for use while Vconnection is made therewith.

10. A telephone system having metallic jlines, 1a' connecting circuit for lines, a lsource of ringing current'associated with the fconnectingcircuit, ringin lmechanism open ated over a circuitV inclu mg a'lmeconnec-` ,tion andautomatically controlling the ap plication of ringing current direct to both 'fio * made therewith, lockin ,trolling vthe said ringlng mechanism, and

imbs of ametallic line lwhen connection is mechanism for conmeans for operating said locking mechanism when the line is taken for use while connec- 'tion is `made` therewith. l

11. A telephone exchange system includ- "V ing a plurality of telephone lines, 'a connect- "515' ing circuit for' the linesterminatin in a pair of connecting plugs, anvoperator s telephone set associated with the connecting circuit, an operators relay associated with each 4connecting plug, `means independent-'of the telephone line circuits for energizing each relay through a line jack terminal and aline `connection leading to battery, during the time connection is made with the line, the

said' relays connecting the; operators telephone setwith the connecting circuit when l at least one of them is denergized, anddisconnecting circuit terminating in a pair oir' connecting plugs adapted Ato be connected with the lines, an operators telephone set l `normally connected with the connecting cir cuit, an operators disconnect relay 4for each connecting plug through;which the operators telephone set is connected in multiple, A

with the connecting circuit, means whereby the said relays are supplied with current over respective line connections, for operatf ing the said relays, when connection is made between the corresponding connecting plugs and the lines, whereby the operators telephone set is disconnected from the connect- .ing circuit when both of the said relays are o erated, a source of ringing current assoclated with the connecting circuit, ringing mechanism automatically controlling the application of ringing currentl direct to both limbs of a metallic line when connection is made therewith locking mechanism for contrdlling the said ringing mechanism, and

`made therewith.` y l 14. A telephone exchange system includi'ng telephone lines extending from sub-stanoiosa@ means 'for operating the said locking mechanism when the line is taken for use whiley connection is made therewith. r

13. A telephone system having metallic lines, a connecting .circuit for the lines, a

source of ringing current associated with made therewith, a locking relay for control-l ling the said ringing relay, and means for operating the said `'locking relay when the line is taken for use while, connection is tions to an exchange, a cord circuit having two plugs, each of which may be used as an answering plug and each of which may be` used as a connecting plug, an operators. telephone,1 two vmagnets, one associated with each plug andeach, when inert, serving 1n dependently of the other to connect thel .operators telephone with the .cord circuit,

and means operated by each ,plug when taken for use, for effecting the energization of its associate magnet, whereby when both plugs are taken for use, the operators telephone, is cutout of circuit, and when only one plug is taken for use, the operators tele;V phone remains in circuit.

' 15. A telephone exchange system-v including telephone lines extendingl from substations to an exchange, a cordycircuit having two plugs, each of ,whichmay be usedasan answering plug and each of which may be used as a connecting plug, an operators telephone, -two magnets, one associated with each plug and each, when inert, serving independently ofthe other to connect the operators telephone with the cordlcircuit, and means jointly operated vby each plug and the line jackwith which such plug is engaged,

for use, the operators telephone' is` cut out i* for effecting the energization of its assoclate 4 magnet, whereby when both plugs are takeny of circuit, and.l when only one plug is taken for use, the operators telephone remains' in circuit. i As inventor of thel foregomg l hereunto subscribe my name inthe presence of two subscribing witnesses, this 30th day of Jannary, e.A l 4.

- ELMEB R. coRWiN.'

Witnesses:

. FREDERICK R. PARKER, i

C. C. NEWBUnN.

.Genies efthis patent may te obtained for lvev cents each, by addressing the Y commissionato? Washington, il. t3.

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