US1191917A - Telephone trunking and supervisory system. - Google Patents

Description

w; L. CAMPBELL. TELEPHONE TRUNKING AND SUPERVISORY SYSTEM.

APPLICATION FILED FEB. 26, 11907- Iatented July 18, 1916.

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W. L. CAMPBELL. TELEPHONE TRUNKING ANDSUPERVISORY SYSTEM.

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WILSON L. SAMPBELL, OF CHICAGO, ILLINOIS. ASSlifi-NOR. BY MESNE ASSEGNMENTS, T9 FIRST TRUST AND SAVINGS BANK.

TRUSTEE. OF CHICAGO, ILLINGIS.

TELEPHQNE TRUNKING AND SUPERVKSQBY SYSTEM.

Specification of Letters Patent.

Ilatcntcd July 1916.

Application filed February 26, 19071 Serial Ho. 359,406.

To 0/5 hom it may concern Beitflmown that l. Wimox L. Cameraman oi the llnited States of America. and re. lent of Chicago. (look county. Illinois. have invented a certain new and 11S?- ful luiprm'enicnt in 'llelephone Trunking and Supervisory Systems. of which the following. a :qiecitmation. I My invention relates to telephone systems. and more especially to systems in which means are provided for enabling a calling subscriber to establish connection with the desired line, without the aid ot' operators.

Objects of my invention are to provide means for enabling any subscriber to establish connection with a special service line. such. for example. as a line leading to one or more operators positions. whereby the said calling subscriber may report trouble or receive information or obtain such other service as may be desired; to provide a special service line having provisions for en abling the first o 'ierator thereon to transfer all incoming calls to the next operator. and for enabling the second operator to transfer the calls to' the third operator-{and so on throughmit the series of operators. according to requirements: to provide an arrangement by which a calling subscriber may extend connection from his line over one. or more trunk lines to a connector, and may then cause the said onnector to establish connection with a special service line leading to one or more operators the said con nector being prefe ably what is commonly known as a rotary connectorthat is to say. a connector which will automatically rotate like a trunk selector until it finds an idle line; to provide lamp signals for attracting the attention of the operators on the special service lines. which lamp. signals can be brought into operation by the calling subscriber when he presses his ringing key said lamps being controlled by relays which are responsive to the ringing-current; to provide pilot lamps tor the different operators positions. one pilot lamp being common toall the operat .1; who occupy first position on the group of special service lines. another pilot lamp being common to all operators hooccupy second position on the group of special service lines. and so on throughout the series of positions on the said special service lines; and to provide certain details and features of improvement general eilici n and ci'nnbii'ations lending to increase the 7 c y and serviceability of a system of this particular character.

To the foregoing and other useful ends, my inven irm ms s in matters he ein disclosed and min i.

In the account. ring drawings. Figure 1 is a 'liz-i' rain sh ing a substation A (:onneeted with a central otlicc comprising a central battery li li;l\ lug. preferably. its positive terminal grounded at t. and automatic swit hes t. l and ll. in conncctioi'i with which I hare elected to explain my invention. The switch (7 is commonly known as a filstsr-lectoi; the switch D as a second selector. and the switch E as a connector. At F is represented. a lmsy-signaling machine. and at ll is shown a ringer generator.

in :1. which is a, diagram. are shown several manual circuits comprised in my invention and located at the central ollice, at which place i. J and K represent, respecti ely. a fir t. second and a last operators position. Obviously. however, other such operat rs" positions may be inserted. as. for example. between the positions J and K, substantial y as position J is placed between l and K. In connection with these m nual circuits there shown a night alarm rangement L. The keys (1. Z) and c, whereby the incoming trunk line may be extended from one operator's position to another. are shown in normal position. The arrangement of the system is such that the attendant at position I may. by operating the springs at the left of key a. extend the trunk line (shown leading from Fig. 1 to Fig. 2. and which. while key a. normal, terminates at position I) to the operator at .l where the signal will be received without signaling position I. Similarly the .optrator at J may operate the springs on the left of key 7; and in turn transfer the incoming trunk line to the next position.

Figs. l and 2 taken together show means whereby or automatic subscriber may establish conn ction with a trouble-recording or other oyu-rators board The substation A may be of any suitable type. and comprises, for example, a receiver 2. switrlrhook 3. inductionoil 4 (which coil consists of the primary winding 5 and secondary winding (3). transmitter 7, local battery 9 and the ringer 9. In addition to the above-mentioned parts an impulse Wheel .at once be recognized.

10 is provided which has the usual vertical impulse teeth 11 that are adapted to operate the vertical impulse spring 12. The impulse wheel carries the rotary impulse tooth 13 which operates the rotary impulse spring H. The switch-hook has radiating from its body a number of cam-arms 15, 16 and 17, and is pivotally secured to the keyboard (not shown) at the point 18 about which it operates when the receiver is removed. The operation is produced by a spring (not shown) for the purpose of changing certain circuit connections to be disclosed. The cam-arnr15 controls the so-called locking arm 19. After the dial is rotated the lock ing arm 19 occupies the position shown at substation A, the mechanical operations of which are well known; and at the same time the coiiperating ground springs 20 and 21 engage, thus placing the ground post 22 in contact with the substation ground G, whereby, when the subscriber releases the dial after rotating it as described, the vertical impulse teeth 11 will then cause the vertical impulse spring 12 to come into contact with the ground post 22; and immediately after, the rotary impulse tooth 13 causes the rotary impulse spring 14 to come into contact with the same ground post 22. 'hen the switch-hook is down the cam-arm 17 maintains a contact with the spring 23, thereby bridging the ringer 9 across the line. The springs 21 and 25, and 26 and 27 are then disengaged, and the primary circuit including the winding 5 in series with the transmitter 7 and local battery 8 is interrupted by the separation of the springs 26 and 27. The disengagement of the springs 24 and 25 removes the secondary winding 6 in series with the receiver 2 from across the line. The signaling device where by a subscriber may signal another after a connection has been established comprises a push-button 28 and a spring '29, which latter normally engages the contact point 30; but, when the push-button 28 is pressed the spring 29 leaves the contact point 30 and engages the contact point 31 which is connected with Means whereby the subscriber may'release the central station apparatus brought into service comprises three springs 32, 33 and 31, known as the release springs and so controlled by the cam-arln 16 that when the switch-hook descends the three release springs are brought into contact, thereby grounding both of the subscrlbefs line conductors simultaneously.

The first-selector C is of the well-known type disclosed in United States Patent No. 815,321, granted March 13, 1906, to Keith, Erickson & Erickson, and upon referring to Fig. 1 its various relays and magnets will As illustrated, 61 and 62 indicate the vertical and rotary line the substation ground G,

relays by means of which the switch is operated; 61 indicates the bridge-cut-off relay for controlling the connection between said line relays and the battery; 37 indicates the vertical magnet for raising the shaft vertically; 38 indicates the rotary magnet for rotating the shaft and shaft wipers; 3 9 indicates the private magnet by means of which the side switch is controlled; 41" indicates the release magnet for restoring the switch after operation; and 40 indicates the Mick-release relay by means of which the selector is released after the side switch passes to third position.

The second-selector D is quite similar to the first-selector C and comprises vertical and rotary line relays 35 and 36, respectively. vertical and rotary magnets 37 and 38, private magnet 39, release relay 40 and a release n'iagnet 41. Furthermore, it will be noticed that the bridge-cut-oil' relay of the second-selecti'ir does not appear, the line relays 35 and 36 being connected directly to the battery lead; also, that the line relays 35 and 36 are provided with the trunk-release springs 42 and 43 which are similar to the release spring of the connector disclosed in United States Patent, No. 815,176, granted March 13, 1906, to Keith, Erickson & Erickson.

The connector switch E, commonly known as a rotary connector, is a modification of the connector disclosed in the said connector patent. The vertical and rotary line relays H and 45, respectively, are provided with the usual connector springs. The vertical and rotary magnets 16 and 17 are'under the control of the vertical line relay 44.

.Inaddition, the rotary magnet 17 is provided with the interrupter spring 18 by means of which the said connector may be automatically rotated (like the first-selector) when the private Wiper engages grounded contact points. Hence, with this provision, whereby the connector may be auton'iatically rotated in addition to being rotated in the usual manner, the rotary element combines the rotary characteristics of the first-selector and the connector disclosed in both of said patents. A new feature of this connector is the private relay 19 which is controlled by the rotary line relay 45. The former in turn controls the private magnet 50 under certain conditions, as will be more fully explained hereinafter. The function and operation of the back-bridge relays 51 and 52 are well-known; also, the ringer relay 53 and the release magnet 54 are controlled and operated as explained in the said connector patent.

Atthe signal-receiving board the operaators set (Fig. 2) comprises a key a which is adapted to operate the group springs, as shown. The relay 55 is provided for closing a circuit through the signal lamp 56 of operators.

which indicates to the attendant that a subscribe! has seized the allotted line. The pilot relay 5? is common to a group of trunk line signal lamps, of which group lamp 556 isa member. The said relay, when energized, operates to close a circuit-through the pilot lamp 58. At (1 is shown an operator's telephone set.- At the second operators position J is shown a duplicate of the apparatus and circuits of the position I. The only difference in the last position; K is found in the key 0; for there the left-hand group of springs, whereby the trunluline is extended to the next succeeding position, is omitted.

Assuming that the automatic "subscriber A Wishes to communicate with thec'entral oflice, he may do so by calling a number that will placehim in connection. with theirotary connector E, which connector he then operates in order to establish connection with a trunk line leading to some operator or sets His ohjqect in doing so may be to report trouble, obtain intorin'ation, call for toll connection, or any other similar ob: ject. To start with, it will be assumed that the number of the line that to the operators sets, shown in Fig. 2, is 8111. The number 8111, however, may be given to a set of lines, each line terminating in a different manual set, such as the one shown in Fig.

2. Theobj'ect of such an arrangement is that if the firstdine ofgroup Silt is busy the rotary connector E will automatically otate until it finds the first idle line, in the same manner that the selector switches operate when they are selecting trunks. Obviously, such an arrangement is necessary in an exchange where a number of subscribers are liable to call very close together.

It will be obvious, furthermore, that the connector E may be provided with a number of such groups, each of which may be given a separate and distinct number, such as 8115,

8121, or any other number which is applica are to such a connector, each of: which groups may be used for an absolutely diii erent and distinct purpose. V-Zith' the arrangement shown in Fig. l the last, contact of the group to which the line leadirg. to Fig. 2 belongs is connected with the busy machine F, so that if all the lines of that. particular group are busy the caliing subscriber may, when the corniector passes onto the last set of con-- tacts, receive the busy signal.

When the subscriber at substation it starts to call the group 8111, he operates the dial for the first digit 5*, as a result grounding the vertical and rotary line conductors 59 and 60, whereby the vertical and rotary line relays 61 and 62 become energized and operate in the wellknown manner, with the result that the firstselector side switch passes to third position, and that the selector switch-shaft Wipers 63, 4 and are placed in contact with the c0nafter the relay 49 deenergiirgi tact point 72, side switchwipe lays 3-5 and 36, respectively, the secondselector D alternately energizeand' operate to extend the subscribefis linc' conductorsffiil and GO to the connector TL- b y way of the shaft wipers 66 and 67, substantially as'lthe first-selector C operated 'eiftentli tlieflirie conductors59 and (30 todth 's e j The ground impulses given; to" the line conductors 59 and 60, respectivelyffor th'ef last two digits 1 and 1 aree'fi'ectivejin pu ating the connector E. When the conductor 59 is grounded for the third digitl the vertical line relay 44 becomes energi /Jed and operates to place the springs 63 and 69 in contact, whereby an energizing circuit is completed in the well' knoav'n manner through the vertical magnet 46, with the result-that the shaft wipers'70, 71fand 72 are raised one step. When the rotary line relay 45 energizes as a result of the ground impulse to the rotary line conductor 60, the springs 73 and 69 engage and'c-lose acircuit through the private rel ay 49 extending from ground G through the springs 6 andi73, through the private relay 49 to the battery, lead 74, thence through battery 13 to ground G. The private relay, upon energizing, operates in turn ,'to disengagerthe springs 7 5 and 7 6, and tothereby' place the springs 7 7 and 78 in contact. The engage ment ofthe springs 77 and 78 ,closes an'eners gizing circuit through the;privater magnet" 50 extending from'ground G lthrough the springs 77 and 7 8, through the private rnage net 50 to the battery lead 74, thence through battery B and to ground Gr, QiThe private magnet operates to permit [theside switch wipers 79, 80, 8I'an'd 82to'pas's from to second position, whereby the. rotary'm'ag.

net 47 comes under the control of the ve ti-' cal relay 4%. The last dig'it beiui", vertical line relay 44, upon energizii I an energizing circuit through the rotary magnet 47 which operatesto'itotate thcsha'ft wipers 70, 71*and 72 onto the first c'onta of the first level. Now when thela rt-daily impulse operates the rotary linc one of two results occurs, nairfely their case-of the side switch from. second to t tion, at once, or the connectorsha. matically rotated until anidle liisjils if the private wiper 72, busy. This is bmught When the private relay 49,,ai1d 1 I urn the private magnet 50. energize and o pelifataas previously explained, the en gluing circuit through the Private magnet maintained *iid circuit extending from the grounded 4 Pr vateer-m -v found, in first line, fa lew point 83, private magnet 'spriiigf '85, through the Winding tin pri at magnet 50 to the battery lead 74, thence through battery B and to ground G. The private magnet thus remains energized and retains the side switch in second position as long as the wiper 72 engages a busy or grounded contact. Furthermore, when the private magnet thus energizes, the spring 86 is shifted out of engagement with the spring 87 and into engagement with the spring 88, whereby a new energizing circuit is completed through the rotary magnet vate magnet is broken, whereby the said' magnet deenergizes, breaks the circuit through the rotary magnet 47 and perm-its the side switch to pass to third position, extending the line conductors 59 and to the trunk conductors 90 and 91, respectively, which latter-lead to the toll-board or desk equipped with my signal-receiving apparatus, as shown in Fig. 2.

\Vhen the subscriber at substation A presses the signaling button 28 the ringer relay 53 becomes energized in the wellknown manner, and operates to bridge the ringer generator H across the trunk conductors 90 and 91, whereby a signaling current is transmitted from the springs 92 and 93 to the side switch wiper 79, contact point 94, shaft wiper 70, vertical conductor 90, through the springs 95 and 96, springs 97 and 98, winding 99 of the lamp relay 55,

through the springs 100 and 101, 103 and 102 to the rotary trunkfconductor 91, shaft wiper 71, contact point 104, side switch wiper 80, ringer relay springs 105 and 106,

thence to the generator H. The signaling current in passing through the winding 99 energizes the relay 55, which operates to close the springs 107 and 108 in contact. The engagement of the springs 107 and 108 completes an energizing circuit through the locking winding 111 of the relay 55 and also through the signal lamp 56 in series with. the pilot relay 57. The circuit through the locking winding 111 extends from ground Gr to the springs 109 and.110, springs 107 and 108. through the winding 111, conductor 112 to the night alarm switch 113, to the battery lead 74, thence through battery B and to ground G. The operator in response to the signal operates the key a in such a manner that the springs 97 and 98, 100 and 101, and 1.09 and 110.,disengage, and the springs 97 and 116, and 101 and 117 engage. The disengagement of the springs 109 and 110 breaks the energizing circuit through the lamp 56 and the locking winding 111. The engagement of the springs 97 and 116, and 101 and 117 bridges the operators telephone set d across the trunk conductors 90 and 91, thus connecting with the calling subscriber at substation A. The subscriber at substation A and the operator at I may then communicate over a circuit shown by the heavy lines. If for any reason it is desired that operator J shall take charge of all calls coming in on the trunk conductors 90 and 91, the operator at position I operates the key a, so that the springs 96 and 102 disengage the springs 95 and 103 and engage the springs 118 and 119, respectively, thereby disconnecting'the line from position -I and extending the conductors 90 and 91 to the second position J. Now when the line is seized the signal will be received atIposition J and the signal lamp 120, relay 121, pilot relay 122and pilot lamp 123 will operate, as explained in connection with position I. Fu 'thermore, the line may in turn be extende to position K by the operation of the key b,,"so that the springs 124 and 125 disengage from the springs 126 and 127 and engage the springs 128 and 129, respectively, whereby the line is disconnected from the position. J and again extended to the position K. .The signaling current now passes from the conductor 90 through the springs 96 and 118 of key a, springs 124 and 128 of key I), springs 130 and 131 of key 0, winding 132 of relay 133, springs 134 and 135, springs 129 and 125} of key 6, springs 119 and 102 of key a to the conductor 91. The relay 133, upon energizing, closes a circuit through the locking winding 136 of the relay 133, and a circuit through the pilot relay 137 in series with the signal lamp 138. The locking circuit through the winding 136 extends from ground Gr through the springs 139 and 140, springs 141 and 142, winding 136 of the relay 133, conductor 112 (assuming that the night alarm switch 113 occupies the position shown byf'dotted lines) through the night alarm relay 143 to the battery lead 74, thence through battery B and to ground G. The circuit through the lamp 138 extends from ground Gr through the springs 139 and 140, and 141 and 142, lamp 138, pilot relay 137, conductor 112, thence to the battery B through the night alarm relay, as previously traced. The pilot relay 137 operates to close the springs 144 and 145 in contact, whereby acircuit through the pilot lamp 146 is closed. The night alarm relay 143, upon energizing, closes the springs 147 and 148 into contact, and a circuit is thereby closed through the night signal bell 149.

When the key a is operated the springs 130 and 135 disengage from thesprings .131

and 134 and engage the springs 150 and 151, respectively, whereby the lamp relay 133 is removed from across the extended line and the operators set 6' is bridged instead. Furthermore, the springs 140 and 139 disengage, and the circuit through the signal lamp 138 and locking winding 136 is broken, thus permitting the lamp relay 133,'the pilot lamp relay 137 and the night alarm relay 143 to return to normal position. It will be understood, of course, that the night alarm relay 143 (which may be cut in and out of the circuit by the switch 113) may or may not be used, as desired, the object of such tors 90and 91, and if each trunk is provided with an equipment similar to the one shown in Fig. 2, then the pilot lamp 58 may be operated whenever a call comes in to any one-ofthe :operators I of the various boards. If any of the trunk lines are extended to the operator'J, the pilot lamp 1'23 may be operated when-a call comes in to any operator J ;'and if any of the lines are extended to the operator K, the pilot lamp 146 may be operated whenever a call comes in to any one of the operators of the last position.

The relays may be of any suitable resistance, butgood results have been obtained when the lamp relays55, 121 and 133 are wound to a resistance of five hundred ohms in each winding,andthe pilot lamp relays '57, 122 and 137 and the night alarm relay 143 to a resistance of'one and eight-tenths ohms each. j

From the foregoing it. will be seen that a calling. subscriber extends connection from 'his line over one or more trunk lines -to a connector which is capable'of picking out an idle special service line. On this special service line are one ormore operators positions, and each operator, except the last of course, can transfer all incoming calls to the next opera-tor, according to requirements.

' It will be understood, of course, that the said connectors can be employed on a percentage basis.that isto say, it will be understood that the connectors can be less in number 'thanthe total number of subscribers. It will also be understood that with suchan ar-' rangement the second-selectors; will in number-than the total number of subscribers, while the total number of firstselectors will be the same as the total number of subscribers, inasmuch as first-selectors are employed .as individual switches for the different subscribers. tor, as explained, is adapted to rotate like a trunk selector until it finds an idle special service line.

What I claim as my invention is 1- 1. A telephone system comprising a special service line, a plurality of operators" positions on said line, automatic means by Each connecwhich a calling subscriber extends connection to said .line, and a switch at one position for tran ferring incoming calls to another position: v

2. A telephone system comprising a special service line, automatic means by which a calling subscriber extends connection to said line, a plurality of operators positions on said line, and oneor more switching devices by which each operator, except the last, may transfer incoming calls to the next operator 3. A telephone'system comprising a spe-- cial service line, a connector adapted to make connection with said line, automatic means" for trunking a calling subscriber into connection with said connector, means by which the subscriber controls the connector to establish connection withthe special service line, a plurality of operators positions on said line, and means for transferring incoming calls from one position to another.

4. In a telephone system, the combina-' tion of a special serviceline, a plurality of operators positions on said line, means by which each'operator, except the last,"may direct the incoming calls to the next operator, an automatic connector adapted -to connect with said line, automatic means for trunking a calling subscriber into 00111160 tion with said connector, and means by which the subscriber controls the connector to complete connection with the said line.

' 5.'A telephone system comprisinga spe cial service line, a relay having two -W1Ii(1 1 ings one of which is normally bridged aci 05s the said, line a battery, a local circuit-ineluding said battery and-the, other windmg of the relay, said relay controlling said local circuit, circuit controlling .means by which the calling subscriber projects cur rent onto the line to initially energize said relay, and automatic rogressively -m0vable switching apparatus by which the calling subscriber extends connection to said line prior to the energizing of the relay.

6. A telephone system comprising a special service line, a lurality of operators telephones 'on' said ine, normally. disconnected therefrom, a lamp signal for each telephone, means by which each operatic automatically retires her allotted signal when she connects her telephone with the line, automatic means by which a calling subscriber extends connection to said line, and means by which one operator may direct the incoming calls to the next operator.

7. In a telephone system, the combination of agroup of special service lines, a plurality of operators positions on each line, automatic means for trunking a calling subscriber into connection with one of said lines,- individual signals for the operators, :1 pilot lamp common to all operators occupying first positions on said lines and a pilot lamp for each additional group of operators occupying like positions on said lines.

8. In a telephone exchange system, the combination of a line, a plurality of operators or attendants telephones on said line, a visual signal for eaclrtelephone, a calling subscribers line, automatic means for connecting the calling line with the other said line, parallel circuits for said visual signals,.relay means controlling said circuits, and means by which one operator or attendant may direct the incoming calls to the visual signal of the'next operator.

9. Ina telephone exchange system, the combination of a line, a plurality of operators or attendants telephones on said line, a call-receiving device for each telephone, a calling subscribers line, automatic means for connecting the calling line with the said other line, and means by which one operator may disconnect from the line and direct all incoming calls to the next operator.

10. In a telephone exchange system, the combination of a line, a calling subscribers line, automatic means by which the calling subscriber connects his line with the said first-mentioned line, a plurality of operators telephones on said first-mentioned line, a call-signal,,associated with each telephone, and means by which one operator may direct the incoming automatic calls to the next operator.

11. In a telephone system, a line with a plurality of operators or attendants positions -thereon, means to automatically extend connection'to said positions, the line being normally open at each position, and means for closing the line at each position and thus successively transferring calls from one operator to the next.

12. In a telephone system, a line, a plurality of call-receiving positions on saidv line, means to automatically extend connection to said positions, the line belng normally open at each position, means for eX- tending the line from one position to an other to transfer incoming calls.

13. In a telephone system, a plurality of trunk lines, a relay bridged across each trunk and individual thereto, a signal controlled by each relay, a relay common to a plurality of trunks and controlled by all of said inst-mentioned relays, a supervisory signal controlled by said last-mentioned relay, a

source of current for operating said individual relays, and a progressively movable switching device for controlling connection from said source of current for operating said relays.

14. In a telephone system, a plurality of trunk lines, a plurality of operators sets associated. with each trunk'line, a relay bridged across each trunk and individual thereto, a supervisory signal controlled by said relay, a second relay controlled by a plurality of said first-mentioned relays, a second supervisory signal controlled by said last-mentioned relay, a source 01 current for operating said bridged relays, and progressively movable automatic switching apparatus for controlling connection from said source of current for operating said relays.

15. A telephone system comprising a special service line, a connector adapted to make connection with said line, automatic means for trunking a calling subscriber into connection with said connector, circuit means by which the subscriber controls the connector to establish connection with the special service line, a lurality of operators positions on said inc, and circuit means for transferring incoming calls from one position to another.

16. Ina telephone system, the combination of a special service line, a plurality of operators positions-on said line, circuit means by which each operator, except the last, may direct the incoming calls to the next operator, an automatic connector adapted to connect with said line, automatic means for trunking a calling subscriber into connection with said connector, and circuit means by which the subscriber controls the connector to complete connection with the said line.-

17. A telephone system comprising a special service line, a plurality of operators telephones on said line, normally disconnected therefrom, a lamp signal for each telephone, circuit means by which each operator automatically retires her allotted signal when she' connects her telephone with the line, automatic means by which a calling subscriber extends connection to said line, and circuit means by which one operator may direct the incoming calls to the next operator.

18. In a telephone exchange system, the combination of a line, a plurality of operators or attendants telephones on said line, a visual signal for each telephone, a calling subscribers line, automatic means for connecting the calling line with the other said line, parallel circuits for said visual signals, relay means controlling said circuits, and

circuit means by which one operator or attendant may direct the incoming calls to the visual signal of the next operator. I 19. In a telephone exchange system, the combination of a line, a plurality of operators or attendants telephones on-said line, a call-receiving device for each telephone, a calling subscribers line, automatic means for connecting the calling line with the said other line, and circuit means by which one operator may disconnect from the line and direct all incoming calls to the next operator.

20. In a telephone exchange system, the combination of a line, a calling subscribers line, automatic means by which the calling subscriber connects his line with the said first-mentioned line, a plurality of operators telephones on said first-mentioned line, a call-signal associated with each telephone, and circuit means by which one operator may direct the incoming automatic calls to the next operator.

21. In a telephone exchange system, the combination of a line, a plurality of operators orattendants telephones on said line,

a visual signal for each telephone, a calling subscribers line, automatic means for connecting the calling line with the other said line, parallel circuits for said visual signals,

relay means controlling said circuits, and means by which one operator or attendant may direct the incoming calls to the visual signal of the next operator.

,maydisconnect from the line and direct all incoming calls to the next operator.

23. In a telephone exchange system, the combination of a line, a calling subscribers line, automatic means by which the calling subscriber connects his line with the said first mentioned line, a plurality of operators telephones on said first mentioned line, a call signal associated with each telephone, and means by which one operator may direct the incoming automatic calls to the'next operator. 1

Signed by me at Chicago, Cook county, Illinois, this 20th day of February, 1907.

' WILSON L. CAMPBELL.

.Witnesses:

J. NORBY,

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