US923035A - Telephone system. - Google Patents

Description

A'. H. DYSON. TELEPHONE SYSTEM. APPLICATION FILED JAN. 20, 1902.

Patented May 25, 1909.

THE Manus Psrsns co4, wnsumarmy, n. n:4

- l,Unrrnnfsrirrns ALFRED iinYsoN,

y rvTo all 'whomfit may cri/:wem:

fj citizen ofthe United Uiy y No. 923,035.

OF CHICAGO, ILLINOIS, ASSIGNOR TO AMERICAN ELECTRIC TELEPHONE COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION.

TELEPHONE SYSTEM.

Be itknown that I, ALFRED H. DYsoN, a

States, residing at Chicago, inthe county of Cook and State of Illinois, have invented a certain new and useful Improvement in Telephone Systems, of

which the following is a specification.

My invention relates to telephone systems I. iny general, but'more particularly to telephone l I() 7 connected by systems involving two or more exchanges trunk lines, and especially to `the"supervisory or clearing out signals by which y the operators at the different exchanges are `advisedy that'the subscribers are4 through talking. Iny telephone systems of this character it is the practice, for example,

to `connect ,two exchanges by means of a f trunk line, and to in this `way make it possible for asubscriber ofone exchange to com municatey with a subscriber of the other exchange.y The operator at the exchange receiving the call 1s ordinarily termed the originating operator,y while the operator at the other exchange isgusually known as the trunking operator.7` i Wlhen a call is sent in to the 'originating operator, the latter then 'communicates with the other exchange, stat ing the number ofthe subscriber called for. y f t' The trunking operator then insertsthe plug fcalled subscriber, and at the same time the yorigmatlng operator of the trunk cord ycircuit in the jack of the n is instructed to insert the plug ofthe cord circuit in the jack ofthe trunk line between the two exchanges. In this way' the calling subscriber is connected up with the called subscriber, and when the lattery answers the callthe two sub-stations are then in. circuit. f It is also the practice to provide the exchangeswith clearing out or sov thatthe operator at supervisory signals,

yknow when the subeach exchange may scribers have 'finished their conversation.

kkticularly relates,

yceiver byr light two f supervisoryClamps,

` Inthe system to which my invention parthe `hanging up of the rethe called subscriber operates to one at the A`switchboard of the trunking operator, and

` the other at the switchboard of the originatingv operator at the other exchange.

y In this lway both operators are advised that the called subscriber is through talking. The arrangement is also such that when the calling subscriberhangs up the receiver, a super l fvisory lamp is lightedat the switchboard of Specification of Letters Patent. n `Application filed January 20, 1902. Serial No. 90,383.

Patented May 2 5, 1909.

the originating operator, and when the latter withdraws the plug from the ack of the trunk line7 a supervisory signal, preferably a lamp, is also operated at the switchboard of the trunking operator. In this way the trunking operator simply acts on the instru@ tions of the originating operator, and makes such connections and disconnections as are operator.

While, as stated, my invention relates generally to trunking telephone systems, it relates more particularly to the clearing outV or supervisory signals for the two exchanges, and especially to the circuit arrangement whereby the originating operator advises the trunking operator that the calling subscriber is through talking and has hung up the re ceiver.

Generally stated, it is the object of my invention to provide a simple and efficient circuit arrangement vfor operating and controlling the clearing out signals of a trunk line system of the complete metallic circuit and double supervisory type.

A special object of my invention is to provide an improved trunking cord circuit, con sisting preferably of but a single plug and cord.

A further object is to provide local circuits and an improved arrangement of relays for operating the supervisory or clearing out signals at the trunking exchange.

It is also an object of my'invention to avoid the use of objectionable grounded circuits between the two exchanges'7 and to thereby render the supervisory or clearing out signals between the two exchanges more certain in their operation.

A further object of my invention is to provide an improved arrangement of relays and supervisory lamps in the single cord of a trunking cord circuit.

In addition to these, it is also an object of my invention to provide features of improvement tending to increase the general efficiency, and to render a system of this character more serviceable and reliable in its operation. Y

To the foregoing and other useful ends, `my invention consists in matters hereinafter set forth and claimed.

The accompanying drawing is a diagram `showing the usual or ordinary cord circuit called Yfor and signaled by the originatingcertain details and to serve as the calling for the originating operator, the trunling cord circuit for the trunking operator at the other exchange, the two cord circuits being shown connected bythe trunk line between the ktwo exchanges, and the apparatus at the called station, together with the substation line and terminal apparatus, being shown connectedwith the cord circuit of the trunking operator.

As thus illustrated, the arrangement involves a sub-station having a receiver 1, a receiver hook 2, a bell 3, grounded at 4, and the two contact points 5 and 6. 1t will be understood, however, that the apparatus thus located at the sub-station can be of any suitable form or character, and that only such parts or instruments are shown as is necessaryT to an understanding of the invention. The said sub-station is connected by metallic line conductors 7 and 3 with the central station or exchange. As shown in the drawing, this exchange is provided with a multiple` switchboard, and with. a suitable line or calling signal. The switchboard apparatus involves a conductor 9, forming mediu'ml of electrical connection between thel ground 10 and the contact 11, the latter being normally in contact with the contact piece 13. Contact pieces 12, 13, 14, 15, 16

and 17 are also provided, the strips or contactpieces 13, 14 and 16 being preferably movable and connected by insulation. The contact piece 16 is adapted to be engaged by the armature 18 of the relay 19, when the latter isvenergized by the insertion of the trunk cord circuit plug inthe jack of the switchboard. The coil of said relay is preferably connected by a conductor 20 with the battery 21,v thelatter being grounded at 22. From the pole of this battery a conductor 23 leads to the coil of the relay 24, and from this relay the current passes through conductor 25 to the contact piece 17, which is normally in contact with the movable contact piece 16. This relay can be arranged or line signal for the sub-station having the receiver 1. A conductor 26 connects the relay 19 with the jacks on the switchboard. The conductors 27, 28 and 30 connect certain of the said contact pieceswith the said jacks, while the conductor 29 leads from one of said contact pieces through the resistance 31 to the ground at 32. The conductors 33, 34, 35 and 36 serve as medium of electrical connection between the jacks. As illustrated, the upper jack comprises the casing or testing ring contact 37, the sleeve contact 33, and the tip contact 39. The contact piece is connected with the tip contact strip 39 by insulation- 41. The contact piece 40 is adapted to engage the contact point 42 when the plug is inserted, completing a circuit yfrom the battery 21 through the relay 19 and the ground 22 and 43. The lower jack, which is shown in use, the plug of the trunliing cord circuit being inserted, coniprises the ground 44 and contact 45, and the contact strips or springs 46, 47, 43 and 49. It will be seen that the jacks are similar in form and construction.

The plug which is inserted in the lower ack comprises the tip contact and the sleeve contact 51, connected respectively with the tip and sleeve strands 53 and 52 of the single cord with which the trunking operator is provided at the exchange. where the said jacks are located. This single cord comprises the springs 54 and 55 vof the ringing key, and the adjacent contacts 56, 57, 53 and 59, it being' observed that the said springs are normally.

in contact with contacts 56-and 53. Conductors 60 and 61 lead respectively from the contact points 57 and 56, while conductors 62 and 64 lead respectively from the contacts 59 and 58. There is also a conductor 63, a spring 65 of the ringing key, and adjacent contact points 66 and 67. The other spring 68 of the ringing key is arranged to cooperate with the contact points 69 and 70. ductor 71 connects the contact point 70 with the ringing generator 72, which is adapted to ring the bell 3 at the sub-station. The said generator is preferably grounded at 73. The conductors 74 and 75 connect the contact points 67 and 69 with the springs 76 and 77 of the listening key. This listening key can be provided with contact points 78 and 79, the latter connected by a conductor S0 and the coil S1 with the operators receiver or head telephone 82. The conductor 33 connects this receiver to the contact point 73. The springs 76 and 77 are connected by conductors 34 and 85 with 'the coils S6 and 87 of the differential relay B. preferably provided Awith a condenser S9, and a contact point.

A contact point 83, a conductor 90, and an armature 91 are associated with the said relay B. This armature is preferably normally point and is also preferably grounded at 92. The conductor 93, the repeating coil 94, the battery 95, the repeating coil 96 and the conductor 97 are connected up in series with the coils of said differential tery is preferably grounded at 93. The said repeating coils 94 and 96 serve to ind ctively connect the two parts of the single cord. In the other part of the cord circuit the said repeating coils 94 and 96-are separated by a condenser 99. A conductor 100 connects the repeating coil 96 with the conductor 126 of the trunk linel between the two exchanges, while the conductors 101, 103 and the coil of the relay 104 form a bridging connectionA across this part of the cord circuit. The conductor 102 preferably leads from the conductor 101 to an associated contact piece. This relay 104 is provided `with an armature 105, which normally bears against a Contact A conaway from the said contact 1* relay. The said bat- I The conductor 30 is 1'5" L to the battery and the other to a relay. ycontact piece '114 is preferably connected 106 can beconnectedfby a conductor 108 with ythe supervisory lainp or clearing out signal 109. A conductor 110 preferably leads from said lamp or clearing out signal to an associatedcontact piece, and this single cord for the trunking operator is also preferably kprovided with a second clearing out signal or supervisory lanip 111. yThe conductors 112 and 113 lead from this lanip 111, one leading The with the said conductor 102, while the contact piece 115 is grounded. rlhe contact piece 116 is connected with the conductor 110. K' The contact piece 117 is preferably connected to move the contact piece 115 when engaged by the armature 118 of the relay 119. This relay. is connected `in parallel with the lamp 111, the coil of the relay and the lamp being preferably of eqinl resistance. The

conductor 120 connects said relay with a battery, ywhile the conductor 121 and the resistancey 122 `forni lnediurn of electrical con- `nection between the contact piece 115 and the ground 123. Thebattery 124 is conrnected, as stated, with both the lainp 111 and the relay 119, and is preferably grounded at 125.` The cord circuit thus provided serves as thek connecting nieans by which the trunking operator is enabled. to establish communiand 130 of an ordinary jack.

"fc/ation between the sub-station and the other f exchange. 1t will be observed that this cord kcircuit consists of but a single cord-that is n to say, there is but 'one plug, the other end of die cordy circuit being connected directly to the `conductors 126 and 1.27, constituting the `complete metallic hne connection between the two exchanges. f

"At the second exchange, or at the eX- change where the call is supposed to originate, 'the said trunlr'line terminals are connected'withthe tip and sleeve contacts 129 At this second i exchange thecord circuit is illustrated as of the usual forin and character, and 1s such as is ordinarily employed in exchanges for conc .necting' up two subscribers of the saine eX- change. This cord circuit for the originating roperator is provided with a plug having tip and sleeve contacts 131 and 132, connected krespectively with the tip and sleeve straijidsf133 and 134 ofthe said cord circuit. `These strands lead preferably to the springs 135"A and 136 of the ringing key.

A conf ductor-137 and a ringing generator 138,

"grounded, at 139 and connected by a cony,ductor '140' with a contact point 141, are preferably associated with said ringing key.

;, y1t will also be observed that contact points 142 143 and 144 are provided, the latter being connected with the said conductor 137.

Thev operators listening circuit includes a coiiductor145, a kcondenser 14.6, a'contact lain point 147, a spring 148 of the listening key, and a conductor 149 connecting this spring with the contact point 142. The conductor 150 connects the other spring 151 of the listening key with the contact point 143. The listening contact 152 and the conductor 153 are connected with the receiver of the operators talking and listening set, and the condenser 146 is connected by the coil 154 and the conductor 155 with the said operators receiver 156. The ground 157, together with the conductor 158 and the arniature 159 are associated with the differential relay C. This armature is normally away from the relay, and is arranged to close a supervisory lamp circuit by engaging the contact point 160. Said relay is provided with the differentially wound coils 161 and 163, the foriner connected with the spring 151 by a conductor 162. A like conductor 164 connects the relay coil 163 with the said spring 148 of the listening key. The y supervisory lainp or clearing out signal 165 is interposed between the conductors 166 and 167, the latter being connected with the relay contact point 160. The relay coil 163 is connected with a battery by a conductor 168, while the saine battery is connected with the relay coil 161 by a conductor 169.

The repeating coils 170 and 1.71 are arranged C;

at each side of said battery. The conductor 172 and the ground 173 are connected with the said battery, which is preferably coniposed of two separate batteries 174 and 175. This cord circuit is also provided with a second supervisory signal 176, it being observed that the system throughout is of the double supervisory character. This supervisory 176 is connected by a conductor 177 with the battery 174. The said lainp is also preferably connected by a conductor 178 with the contact point 179 of the differential relay D. This relay D, it will be observed, is arranged inthe other hall' of the cord circuit, and is substantially like the relay C. The contact point 179 is arranged to coperate with the armature 180 of said relay, said arinature being preferably grounded at 181. are preferably connected with the two repeating coils by conductors 184 and 185. As with the relay C, these coils 182 and 183 are connected with the tip and sleeve contacts 186 and 187 of the other plug. This plug having the tip and sleeve contacts 186 and 187, is adapted to cooperate with the jack of the calling subscriber in establishing coni inunication between the latter and the eX- change at which the originating operator is located. This jack, and in fact, all of the switchboard apparatus at the terminal of the calling subscribers line, can be substantially identical with that shown at the terminal of the line running from the sub-station of the called subscriber. For this reason, l

'system comprises the sub-station of a called have illustrated but one sub-station, and have shown only the .switchboard apparatus for this station.

Thus it will be seen that as illustrated the Subscriber, .the switchboard apparatus at which the line lof the sub-station terminates, the single cord and cord circuits of the trunking'operator at the iirst exchange, and the cord circuit of the originating operator at the exchange Where the call is assumed to have originated. As stated, the trunking cord circuit is shown connectedwith :the originating operators cord circuit by means of the conductoi constituting what is commonly known as a Htrunk line. As shown, the calling and the called subscribers are assumed to be connected and carrying-on conversation. In such case, the relays 19 and 104 are-energized, While the differential relays B, C and D, owing to their differential Winding, allow the voice and talking currents to pass without being energized. lt is the disconnecting vapparatus and the circuit arrangement lfor the clearing out signals, to which my invention particularly relates, and assumin(T that the two subscribers are through talking, the operations are as follows: Then the called subscriber hangs up the receiver 1, a groundedline circuit is immediately comi pleted from the ground 4 through the bell 3 and the contact point 5 to the receiver hook orswitch 2, thence through the line conductor S and the relay contact piece 13 to the adjacent contact piece 12, thence through conductor 30 to the tip contact 47, from the latter through the plug tip 50 and the cord strand 53 to the key spring 55, thence through the contact 56 and the conductor 61 to the liey spring 65, through contact 67 and conductor 74 to 1ey spring 76, thence through y conductor S4 and relay coil 86 to conductor 97, through the latter and the repeating coil 96 to battery 95, and thence to ground at 9S and back to the ground connection at The completion of this circuit serves to energize relay B, and to draw the armature 91 into .contact Withthe contact point S3. The energizing ofthe differential relay B is, it will be seen, due to the fact that the returning of the receiver to the hool at the sub-station operates to open the sleeve side .of the circuit, thereby cutting out the coil S7, and in this Way permitting the coil 36, which is in the tip side of the circuit, to energize the relay The energizing of this relay operates to close the local circuit from the ground 92 through the armature 91 to the contact 83, thence through the conductor 90 to the lamp 111, through the latter and the conductor 112 to the battery 124, thence to the ground at 125and back to the ground at 92. he closing of this local circuit operates to light the said supervisory lamp 111, thereby adelV vising the trunlring operator that the called l for lsubscriber has hung up the receiver atthe subestation. ith the relay 119 arranged in parallel With the said lamp 111, it Will also be seen that a second local circuit is closed through the ground 92 and the armature 91 to the contact point 88, thence through conductors 90 and 113 to the relay 119, through the conductor 120 to the battery 124, and thence to the ground at 125 and back to the ground connection at 92. This shunting et' the current serves to energize the relay 119, which immediately draws up its armature 11.8. The said armature in moving toward the core of the relay 119 engages the lower contact spring 117, and causes both the latter and the contact spring 115 to move upward and into engagement respectively with the contacts 116 and 114. The shifting of these contact pieces operates to close a grounded trunling line circuit from the ground 123 through the resistance 122 and the conductor 121. to the contact piece 115, thence through contact 114 and conductors 162 and 101 to the conductor 100, through the latter to the conductor 126 of the trunking line, through the tip contact 129 of the jack at the originating exchange, thence through the plug tip 131 and the cord strand 133 to the lrey spring 135, through contact point 143 and conductor 150 to conductor 162, thence through the coil 161 and the dillerential relay C, through conductor 169 and the repeating coil 170 to the battery 175, thence through conductor 172 to ground at 173, and back through ground to the ground connection at 123. The circuit thus established through the ground and part of the trunlring line is energized by the battery 17 5, and as the coil 161. of the di'lierential relay C is included in this circuit, it is therefore apparent that the latter will be energized and Yill attract its armature 159. This armature when attracted engages the contact point 160, thereby completing a local circuit from the ground 157 through the conductor 15S to the armature 159, thence through Contact point 166 and conductor 167 to the supervi-L sory lamp 165, through this lamp and the conductor 166 to the battery 175, thence through conductor 172 to the ground at 173, and thence back to the ground at 157. This, it will be seen., operates to light the lamp 165, so as to advise the originating operator at the exchange of the calling subscriber that the called for subscriber is through talking and has hung up the receiver. Thus it Will be seen that the act of the called subscriber in hanging up the receiver operates to light both the lamps 1.11. and 165, and to consequently indicate to both the trunking operator and the originating operator that a disconnection may be made as soon as the callmg subscriber is through and sends in a signal to that eiect. The trunling operator, however, pays no attention to this signal, and

ydoes ynot'remove the plug of the trunking cord circuitfrom the jack until a disconnectv ing signal is received from the originating operator at the other exchange.

- yVVhenthe calling subscriber is through and i hangs kup'the receiver, -a grounded line circuit is completed through the supervisory ylamp 176, and the originating operator seeing f y this signalunderstands that the subscriber at the sub-station from whence the calling kfcame'is through and ready to be discono f 'nected The originating `operator then withl"drawstheplug of the cord circuit from the gized circuit in which the re jack having the tip and sleeve contacts 129 and 180, and this act on the part of the originating operator breaks or o )ens the eneray 104 is ini y eluded.y LThis relay -104is, itwill be observed,

n battery y1 7 5 seQuently,

j i operator withdraws the plug from the trunking line jack,

this relay 104 is deenergized, and its armature 105 is allowed to fall back Tinto contact with the contact point 106. y This operates to complete a local circuit f from the ground 107 through the armature lamp 109 and the conductor 110 to the con- 105 and the contact pointy 106 to the 'conductor 108,'thence through the supervisory V tact pointll, through the contact spring f causes thecurrent from battery i they supervisory [,117 and the contact 128 to the battery 124, thence to the ground at 125 and back to the ground connection107. 5 This, it will be seen, 124 to light lamp ,109 through a short local circuit. This lamp when lighted indil cates that the calling subscriber has signaled for a'disconnection, and thatthe originating operator has withdrawn the cord plug from line from the trunkinffcord circuit.

the trunking yline jack. The trunking operatoracting on this signalfrom the originating operator, withdraws ythe plug of the ksingle trunking cord from the jack, having the tip and sleeve contacts 47 and 48, and 1n this way disconnects the called subscribers Thus in disconnecting, the `called subscriber can signal boththe trunking operator and the originating operator atthe two exchanges, and

, the originating operatory is permitted to com- Y lamps.

pletely supervise and control the disconnecting, and to indicate to the trunking operator the time at which it is proper for the latter to make the final disconnection.

f. It will be seen thatthe cord circuit for the trunking operator, althoughconsisting of but a single cord and plug, is advantageously and desirably providedwith two supervisory One of these lamps serves as a clearing out signaller a subscriber, while the t be observed that both lamps are other lamp serves asa clearing out signal for the operator .at the other exchange. It will lighted by comparatively short local circuits. lt will also be observed that the local circuit for the lamp 109 is preferably provided with two switch points, one normally closed by the relay 104, and the other held normally open by the relay 119. While the subscribers are talking, the normally closed switch pointyis held open by the relay 104, which latter is under the control ol' the originating operator at the other exchange. It is' only when the subscriber hangs up the receiver 1 that the relay 119 is operated, so as to close the normally open switch point. lt will also be seen that this relay 119 is energized by and included in a comparatively short local circuit, and that in this way there is no necessity of providing objectionable grounded circuits between the two exchanges -for causing the operation of the lamp 109. This lamp is simply brought into operation by the breaking or opening of the trunk line circuit, so as to release the relay armature 105. The arrangement also affords opportunity for an advantageous and effective use ol a differential relay in a single cord trunk circuit. As a further advantage, the circuit arrangement enables the originating operator to know when the called subscriber answers the call. ln establishing connection between the two subscribers, the lamp 165 continues to glow or burn until the called subscriber answers the call. lt will be seen, therefore, that with the foregoing combination of relays and circuits, a complete and satisfactory supervision of the entire trunking system is afforded both operators, and that at the saine time the arrangement is simple and thoroughly eflicient. Furthermore, no objectionable grounded or other circuit connections are employed, the certainty and efliciency of the system being particularly insured by the local circuit arrangement for operating the supervisory lamps in the cord circuit of' the trunking operator. ln addition, the arrangement does not preclude the use of a complete metallic talking circuit.

That 1 claim as my invention is:

1. ln a telephone system, the combination of sub-stations, exchanges having suitable line connection with said sub-stations, a trunk line between said exchanges, an operators cord circuit at one exchange, a trunking operators cord circuit at the other exchange, a supervisory signal associated with the said cord circuit of the trunking operator, a local circuit for operating said supervisory signal, a source of current supply included in said local circuit, a relay associated with said local circuit and adapted to hold the latter open while the subscribers are talking, a source of current supply associated with said operators cord circuit, and a trunk line circuit including said relay and said source of' current supply, said trunk line circuit being broken and the said local cause the operation lamp circuit at onepoin't, a

pervisory lamp lighted ators cord circuit at cuit open when the subscribers operators cord circuit vis disconnected from.

the'trunkline, and the denergization oi said relay operating to close said local ciicuit and ol' said supervisory signal.`

2; In a ti'unking telephone system, the combination of a single cord and plug for the trunking operator, two supervisory lamps 1D" associated with said single cord, vsuitable local circuits and a source of current supply for operatingsaid supervisory lamps, and a differential relay for controlling they iiow of current through one lamp, and a plurality of re- 1` lays for contiolling the ilow of current through the Votliei lamp.

3; In a trunking telephone system, the combination of a single cord and plug for the trunking operator, a double cord for the 20. originating operator, a trunk line between the two operators, a supervisory lamp associated with the said single cord, a source ol'l current supply and a circuit for lighting said lamp, a relay and circuit for closing said relay and a source `oi current supply and a suitable ciicuit for holding said lamp circuit open-at another point while the subscribers are talking, the said lamp circuit being closed and the suwhen the said double cord for the originating operator is disconnected from the trunk line.

4. In a trunking system, the combination of two sub-stations, two exchanges, coin- 35 plete metallic line connection between each exchange and its allotted sub-station, coinplete metallic line connection between said exchanges, a trunking operators .cord circuit at one exchange, an originating operthe other exchange, a supervisory lamp associated with said trunking operators cord circuit, a local circuit including said supervisory lamp, a relay adapted to be energized and to hold said local cirare talking, a source of current supply in the oiigiiiatiiig operators cord circuit for energizing said relay,- a second supervisory lampl associated witli'said trunking operators cord circuit, a

local circuit and a source ot' current supply for lighting said second supervisory lamp,`

and a diiierential relay foi' controlling the operation of said second supervisory lamp.

5. In a trunking telephone system, a

trunkingoperators cord circuit, a supervisory lamp associated with said cord circuit, a local circuit and a source of current supply for lighting said lamp, a shunt around said lamp, Va relay located in said shunt, a second super- 6 OV visory lamp and a localcircuit for lighting the same, the local circuit of said second supervisory lamp being open at two points while the subscribers are talking, an armature and contact pieces for closing said local circuit at one point, said armature being associated with and operated by said relay, and a switch for automatically closing said local circuit at said other open point.

6. In a trunking telephone system, a trunking operators cord circuit, a local circuit iovided with two switch points, relays for c osing said switch points, a supervisory lamp and a source of current supply included in said local circuit, a trunkline connected with one of said relays, and a sub-station line and a suitable relay for controlling the operation of the other of said relays.

7. In a trunking telephone system the combination of a single cord and plug for the trunking operator, a switchboard having jacks associated with said single cord,a substation having suitable line connection with said switchboard, a trunk line permanently connected vwith said single cord, two supervisory lamps associated withsaid single cord, local circuits and suitable sources ol current supply for lighting said lamps, two relays for controlling two switch points in one of said local circuits, and a diii'erentially wound relay for controlling a switch point in another of said. local circuits.

8. In a trunking telephone system the combination of a trunking operators cord circuit, a trunk line permanently connected withsaid trunking operators cord circuit, an originating operators cord circuit, a suitable plug and jack for establishing connection between said trunk` line and said originating operators cord circuit, supervisory lamps associated with'l said originating operators coid circuit, local circuits and la suitable source of current supply for lighting said lamps, diiierentially wound relays for closing said local circuits, a switchboard associated with said trunking operators cord circuit, av

sub-station having suitable line'connection with said switchboard, a switchboard asso-A ciated withsaid originating operators cord circuit, a sub-station having suitable line connection with said last mentioned switchboard, supervisory lamps associated with said trunking operators cord circuit, a differential relay and a local circuit and a source of current supply for causing the lighting of one of said lamps in thetrunking operators cord circuit, and a pair of relays and a local' circuit, together with a suitable source of current supply for controlling the lighting of the otherof said supervisory lamps for the trunking operator.

9. In a telephone systeinthe combination of sub-stations and a central station and line connection between the same, a cord circuit located at said central station, a supervisory lamp and a suitable source of current supply associated with saidcord circuit, ashunt eX- tending Iaround said lamp, al relay in said shunt, and a signal circuit having a switch point controlled by said relay, together with a supervisory relay for controlling a norm ally f l'ellt Supply; f lay in said shunt, said relay having the same y trollingvsaid diiierential relay over "open Switchpoint in the circuit of said lamp and relay.'

10. ln a telephone system, a cord circuit, a lampsignal associated-with said cord circuit and adapted yfor indicating the condition of a line, a source of current supply, a local circuit including said lamp signal and. source of our* a shunt around said lamp, a re- Aresistance ask said lamp signal, a supervisory larnp for indicating thecondition of another line and a local circuit for operating the same, the local circuit for said supervisory lamp being yprovided with a switch point, and said relay being provided with an armature for opening and closing said switch point.

1 1, ln a telephone exchange system, the

' combination kol" a trunk line, a talking circuit including said trunk line, a differential relay in the talking circuit, the windings of said relay neutralizing each other when thus connectediny series, a suitable relayi'or conthe trunk line, suitable circuit connections controlled by said differential relay, and a third relay 'cooperating with said suitable relay to control the said diferential relay.

i k12. yln a telephone exchange system, the combination of a trunk line, a talking circuit including said trunk line, a diiiierential relay in the talking circuit, the windings of said rec lay neutralizing each other when thus connected in series, a suitable relay for controlling said diiiierential relay over the trunk line, suitable circuitxconnections controlled by said differential relay, a differentially woundelectro-magnet having its neutralizing coils bridged in series across the talking circuit, and means by which said electrol magnet cooperates with said suitable relay to control said differential relay. l 13. ln a telephone exchange system, the l combination of a trunk line, a talking circuit l including said trunk line, a differential relay l in the talking circuit, the windings of said re lay neutralizing each other when thus conl nected in series, a suitable relay for controlling said differential relay over the trunk l line, suitable circuit connections controlled by said differential relay, and a third relay cooperating with said suitable relay to control the said differential relay, and common l batteries for `feeding talking current through the differential coils to said circuit.

111. In a telephone exchange system, the combination of a trunk line, a talking circuit including said trunk line, a differential relay in the talking circuit, the windings of said relay neutralizing each other when thus connected in series, a suitable relay for controlling said di'liierential relay over the trunk l line, suitable circuit connections controlled by said diiierential relay, a differentially wound electro-magnet having its neutralizing cuit, and means by which said electro-mag net cooperates with said suitable relay to control said differential relay, and common batteries for feeding talking current through the differential coils to said circuit.

Signed by me at ,Chicago, Cook county, Illinois, this 16th day of January, 1902. i ALFRED H. DYSON.

Vitnesses:

ARTHUR F. DURAND, HARRY l. BAUMGARTNRR.

` coils bridged in series across the talking cir- 1 i l l l

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