US1574836A - Telephone-exchange system - Google Patents

Description

March 2 1926.

1'. G. MARTIN TELEPHONE EXCHANGE SYSTEM 1906 Y 8 Sheets-Sheet 1 Original Filed Oct. 20

A iozvze zwf March 2 1926.

T. G. MARTIN TELEPHONE EXCHANGE SYSTEM Original Filed Oct. 20-

March 2 1926. 1,574,836

T. G. MARTIN TELEPHONE EXCHANGE SYSTEM Original Filed Oct. 20, 1906 8 Sheets-Sheet 5 iii f0 March 2 1926.

T. G. MARTIN TELEPHONE EXCHANGE SYSTEM 1906 8 Sheets-Sheet 4 Original Filed Oct. 20

March 2,1926. v 1,574,836

T. G. MARTIN TELEPHONE EXCHANGE SYSTEM Original Filei 20, 1906 8 Sheets-Sheet 5 1 52 I v a 0 arfig EW w M. v A??? z fleys.

March 2 1926.

T. G. MARTIN TELEPHONE EXCHANGE SYSTEM Original Filed Oct. 0, 1906 8 Sheets-Sheet 6 M W R March 2 1926.

T. G. MARTIN TELEPHONE EXCHANGE SYSTEM 8 Shets-Sheet v Original Filed Oct. 20

. v RAW mm J m vw EQW 93 @Jmw Patented Mar. 2, lflZi'il.

' UhllTE.

PATNT OFFICE.

TALBOT G. MARTIN, OF CHICAGG, ILLINOIS, ASSIG'I'TOR, BY MESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC, INC, A. (36R)?OEM-LTION' 6F DELAWARE.

anrnrnonnnxcnsnen SYSTEM.

Application filed (Jctober 20, 1906, Serial No. 339,833. Renewed August 28, 1916. Serial No. 117,067.

To all whom it may concern:

Be it known that I, TALBOT G. liiim'rin, a citizen of the United States of An'ierica, and re nut of Chicago, Cool; County, Elli? nois, have ii'ivented acertain new and useful Improvement in Tolephone-Exchange Systems, of which the following is a specification.

My invention relates to automatic or semiautomatic telephone exchange systems in general, but more particularly to automatic or semi-automatic exchanges in which the automatic trunking and connecting is accomplished by switches operated on the step-by-step principle, and especially to telephone systems in which provision is made for giving service between automatic and manual subscribers,

Generally stated the object of my invention is, therefore, the provision of an improved and highly efficient telephone exchange system.

Special objects of my invention are the pro vision of improved means for givin 'service between automatic and manual subscribers; the provision of improved means whereby an automatic subscriber may be called by either an automatic or a manual subscriber, and whereby a manual subscriber may be called by either anautom'atic or a manual subscriber, a calling automatic subscriber always obtaining the connection automatically, and a. calling manual subscriber always obtaining the connection manually; the provision of improved means whereby called lines, whether RUiZOH'ifl-tlOOl manual, are made busy and protected against seizure by either automatic or manual subscribers, and whereby calling lines are also made busy, whether automatic or manual, and protected against seizure by either automatic or manual subscribers; the provision of lll'lPlOVCCl means for trunking between main or central exchange stations. or between main and sub-central stations, according to the growth and size of the system; and the provision of certain details and features of improvement and novel circuits and con'ibinations tending to increase the "general eiiiciency and serviceability of a telephone exchange system of this particular character, as well as systems in general.

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

The selectors and connectors employed in the system are of the general type disclosed in United States Letters Patent Nos. 815,321 and 815,176 both issued March 18, 1906, to Keith, Erickson & Erickson.

In the accompanying drawings, Figure 1 is a diagrammatic perspective View of the improved first-selector A as used in my system, having its line relays normally connected with the main exchange battery.

F 2 is a similar view of an improved connector C used when one automatic subscriber calls another automatic subscriber.'

'Fig. 8 is a similar view of another im proved connector B used by an automatic subscriber for establishing connection with manual subscribers.

Fig. i is a similar view of an improved selector E, usually known as the secondbulQClLOI.

Figs. 5 and 6 taken together illustrate diagran'imatically the main exchange ofiice in the system, the automatic sub cribers and switching apparatus being shown in Fig. 5, and the manualsubscribers and switching apparatus being shown in Fig. 6. TA clear idea will be had of the connection if Figs;

5 and 6 are. arranged horizontally, the former. tothe left of the latter.

Fig. 7 shows still further apparatus of the central ofiice automatic equipment. A clear understanding will be had of the arrangement if, after Figs. 5 and/6 are arranged as described, Fig. 7 is then placed beneath Fig. 5, so that the trunk conductors leading downwardly from the banks of the selector A (Fig. 5) are made to meetthe conductors leading upwardly from the selector. E (Fig. 7).

Figs. and 6 show an automatic subscriber calling a manual subscriber, and Figs. 5 and 7 indicate the automatic subscriber calling another automatic subscriber, all of the said manual and automaticsubscribers being connected with the main central exchange. V i Fig. 8 illustrates diagrammatically a manual sub-central exchange the subscribers of which may be reached by the automatic subscribers or the manual subscribers of the main exchange by way of a trunking operator whose cord circuit is shown at D. It will be understood, of course, that the subscribers of the said sub-central (Fig. 8) may also communicate with each other through their line operators by the use of any suitable cord circuit D. As a means whereby the automatic subscribers may call the subscribers at the sub-central, shown in Fig. 8, the repeater F atthe main exchange is provided.

Fig. 9 is a diagrammatic view showing a special form of cross-multipling between automatic switch contacts and manual jacks.

It will be noticed that the circuits are so arranged that the manual operator of Fig. 6 may use the same trunk line to thecord circuit D (Fig. 8) to which the repeater F (Fig. 5) is connected; but the circuits are so arranged that if an automatic subscriber seizes the trunk through the repeater F, or if the manual operator seizes the trunk, that particular trunk will be made busy to the exclusion of all operators or subscribers-that is, if the manual operator in Fig. 6 seizes the trunk line a guarding potential will be established through the medium of the repeater F to prevent any of the automatic subscribers from using the said repeater F until the manual operator surrenders the use of the trunk; the reverse being the case if an automatic subscriber seizes the repeater F. In the following, Figs. 5 and 7 will be referred to as the automatic department of the main exchange, Fig. 6 as the manual department of said exchange, and Fig. 8 as the subcentral oiiice. It will be understood that the selectors A (Fig. 5) and A (Fig.7) are identical, and that in the following it will be sufficient to describe the selector A. The second-selectors E of Figs. 5 and 7 are, of course, the same. It will also beu-nderstood that the cord circuit G is of a usual and wellknown type of line operators cord circuit, and that the operators cord circuit D. may be of any known or approved type. F urthermore, the automatic substations H and I are in turn of any suitable .or. approved type. :The same is true of the manual substations J, K, L. and M. In the system various batteries are shown. .In connection with the automatic department batter B furnishes current for operating the automatic switches, which battery has its posi-' tive terminal preferably grounded at G. In the manual department the batteries B and b are provided, with their positive terminals preferably grounded at G At the sub-central the battery B is shown having its positive terminal grounded at G Battery B, it is found, gives good results with a potential of from fifty to fifty-four volts; batteries B and b of twenty-four volts each; and battery B also of twentyfour volts.

The automatic substations, like the substation H, may be of any desired or approved type, and'as shown comprises a receiver 2 and switch-hook 3, which latter has radiating from its body a number of cam arms 4:, 5 and 6, said book being pivotally secured to the keyboard frame (not shown) by a screw 7 about which it swings when thereceiver is removed. The swinging hook is for the purpose of changing certain circuit connections to be disclosed. Furthermore, said substation has a transmitter 8, a ringer 9, an induction-coil 10 with a primary winding 11 and a secondary winding 12, a condenser 13, impulse-wheel 14 which has the usual vertical impulse teeth 15 that are adapted to operate the vertical impulse spring 16. In addition, the impulse wheel carries a rotary impulse tooth 17 which operates the. rotary impulse spring 18. The cam arm l controls the so-called locking arm 19 in such a manner that when the switchhook rises, and before the dial is rotated, the insulating tip 20 upon the end of the locking cam arm 19 that normally rests in the position shown at substation l is driven to the inner edge of the angled section of the ground spring 21, whereby when the dial is rotated by the calling subscriber the pin 22 upon the end of the locking dog 23 is able to pass beneath the locking cam to raise the said cam a trifle, causing the said insulating tip 20 to fall'behind the said angled section of the ground spring 21, permitting the said spring, therefore, to make contact with a cooperating ground spring 2%. The engagement of the ground springs 21 and 24L places the ground post 25 in connection with the substation ground G, whereby when the subscriber releases the dial after rotating it, as described, the vertical impulse teeth 15 will cause the vertical impulse spring 16 to come in contact with the ground post 25; and immediately following, the rotary impulse tooth 17 causes the rotary impulse spring 18 to come in contact with the same ground post 25.. When the switch-hook is down the cam a m 6 maintains the switch springs 26 and 27 in contact, thereby bridging the ringer 9 in series with the condenser 13 across the line. The springs 28 and 29 are then disengaged, and the primary winding 11, in series with the transmitter 8, is removed from across the line; Even after the switch-hook is raised, since the finger 30 of the cam dog 23 controls the engagement of the said springs 28 and 29, and since the said cam dog rotates in unison with the dial, if the dial is rotated the springs 28 and 29 and, therefore, the subscribers line conductors are kept separated during said rotation. The signaling device whereby a subscriber may signal another after a-connection has been established comprises a push-button 31 and spring 32, which latter normally engages the contact point 33; but when the push button 31'is pressed the spring 32 leaves the contact point 33 and engages the contact point 34 which is connected to the substation lit) 1,574.,sse

ground G The means whereby the subscriber mayv release the central station appalatus brought into service comprises three springs'35, 36 and 37 commonly known as release springs and so controlled by the cam arm 5 that when the switch-hook descends the released springs are brought into contact, thereby simultaneously grounding both sides of the subscribers lines. The said cam arm 5 is provided with a lateral flange 38 that engages a correspondinglateral flange89 upon the release spring 37 which, as the switch-hook descends, forces the said spring 87 to crowd the three release springs into electric contact. When the switch-hook ascends, however, the flange 38 engages the flange 39 on the opposite side, so that the spring 37 is not pressed onto the spring 36 upon the upward motion of the switch-hook. A somewhat similar provision is made for the vertical and rotary impulse springs 16 and 18. The former is provided with a flange 40 which is engaged by the vertical impulse teeth 15, and the latter, namely the rotaryimpulse spring 18, is provided with a corresponding flange ll which is engaged by the rotary impulse tooth 17 The first-selector switch shown at A (Fig. 1) is an improved form of this type of selector. It embodies among other details the following: The switch-shaft 42 is a well known and essential element of the switch and carries the vertical, rotary and private wipers 43, 44. and 45, respectively; Another element of. the switch, which is also wellknown, is the side switch N. In the selector this side switch usually has four wipers only; but in the improved selector A it comprises five, namely the side switch wipers 46, 47,

4L8, 19 and 50. The wiper 46 performs a new function which will be described. I The said side switch, during the operation of the switch, passes through three successive positions commonly known as the first, second and third positions of the side switch. This operation is controlled by the private magnet 51. The said wipers are, of course, rigidly connected together, and in the first position occupy, respectively, the contact points 53, 54:, and 56; in second position they occupy the contact points 57, 58, 59, 60 and 61; and in third position they occupy the contact points 62, 63, 64, 65 and 66. Through the medium of the vertical and rotary line relays 67 and 68 the subscriber succeeds in operating the switch A before the side switch passes to third position, the operation of which switch is accomplished through the medium of the vertical and rotary magnets 9 and 70. The vertical and rotary line relays (ST and G8 are used by the subscriber during the same period if he desires to energize the release magnet 71; but if the side switch passes to third position the control of the switch attained through the medium 'tion.

of the back release relay 72, which relay is included in the so-calledtrunk release circuitthat comprises the private wiper 45. Among. the improvements in the selectorswitch A are the line switching bridge-cuto'tt relay 73 and the private normal relay "-4. When a manual subscriber calls the subscriber H, for instance, the line switching bridge-outed relay'73 pulls up and connects the line conductors 75 and 76 leading to the substation H with the jack normal conductors '77 and 7 8 that lead to the manual operators position. Said relay also at the same time breaks the connection between the vertical and rotary line relays 6'? and (38, opening up the bridge across the line. lVhen an automatic subscriber calls the automatic subscriber H the said relay T3 pulls up for the purpose of removing the bridge from across the line. The private normal relay 7%. is used, when a manual subscriber calls an automatic subscriber, for putting a guarding potential on the private normal conductor of the switch A, so that an automatic subscriber will not be able to establish connection with the line. Said selector A, in addition to the mechanismthus far described, is provided with a shaft cam 79 for limiting the motion of the side switch when the side switch passes from first to second posi- The longitudinal teeth 80 are enr ployed by the rotary magnet 70 for rotating the shaft, and the circular teeth 81 are used by the vertical magnet 69 for giving the shaft a vertical movement. The switchshaft 49, is normally under the control of the coiled spring 82, which spring has one terminal fixed to the shaft and the other to the normal post arm 83. The switch-shaft carries, in addition, a normal post arm 84 for controlling the oft-normal springs 85 and 86 which are comprised in a supervisory circuit that passes through the supervisory lamp 87. If by accident the switclrshaft 42 is raised and retained raised, the lamp 8? continues to burn, so that the switch at tendant can recognize the trouble at a glance and take steps toward restoring the switch to its normal condition, incidentally investigating the cause of the irregularity. The selector-switch is, of course, suitably provided with a line and private bank 88 and 89, respectively, with which the line and private wipers are respectively adapted to engage. V

The second-selector E (Figs. 4 and 7) is in general the same asthe first-selector A,

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with the exception that it has no line switch- The similar parts of the selectors A and E are similarly represented. Said selector E The secondselector has only-four side switch wipers;

has, of course, its vertical and rotary lino relays 90 and 91 and private magnet 92, vertical magnet 93, rotary magnet 94:, release magnet 95, and back-release relay 179.

The connector C (Figs. 2 and 7) is of the general well'known type, but is adapted for common battery work, as here shown. It has the usual switch-shaft 97, switch- shaft wipers 98, 99 and 100, private and line banks 101 and 102, shaft cam 103, longitudinal teeth 104, circular teeth 105, coiled spring 106 for normally controlling the shaft, normal post arm 107 and switch-shaft springs 108i and 109. In addition there are the vertical and rotary line relays 110 and 111, vertical magnet 112, rotary magnet 113, private magnet 11 1, release magnet 115 and the ringer relay 116, and also the back- bridge relays 117 and 118. For adapting the said switch to common battery work there is provided a differential relay 119 having two windings 120 and 121 for controlling certain circuits to be pointed out. The said switch'is, of course, provided with the usual side switch 0 and with the double dog 122. I

The connector-switch l3 (Figs. 3 and 5) is provided with the same details as the connector C (Fig. 7 with the exception that it has no private bank. It is of the commonbattery type, and although the circuits are somewhat different the relays and mechanical details are, with the exception of the private bank, exactly the same in both switches. It will therefore only be necessary to refer to each part of the connector B as they become involved in the circuits that follow. The main exchange is provided with a ringer generator 123 for furnishing ringing current to the automatic and manual departments of the main exchange. Since many of the features of the manual cord circuits that are used in this system are'well known in the art, it will not be necessary to describe them in detail, since they will be understood when reference is made to them during the description of the circuits to follow. A better understanding of the system may behad by following the operations of the subscribers in calling each other. It will be noticed upon referring to the banks of the selector A (Fig. 5) that the different levels of the said banks are used for difierent connections. As indicated, the second level is used by the automatic subscribers for establishing connections with the manual subscribers, thesixth level to call automatic subscribers of the main exchange, and the ninth level is used for establishing connections with the manual subscribers of the subexchange. There are a number of levels from which no trunk conductors are shown leading. These levels may be used for any desired purpose.for example, for further enabling connections between automatic and automatic subscribers, or between automatic and manual subscribers, as the business of the exchange may require. The arrangement of the bank levels, as shown, is notnecessarily confined to the banks of the firstselectors. The bank levels of the secondselectors may be so used if it is advantageous in any way. Assuming that the subscriber at substation H (Fig. 5) wishes to call the subscriber at substation I (Fig. 7) whose substation number, it will be assumed, is 6220,- he will proceed to operate his dial four times, first in accordance with the digit 6, then in accordance-with the digit 2, then 2, and finally in accordance with the cipher or last digit. In each case the vertical line conductor 75 is grounded a number of times, corresponding to the numerical value of the particular digit to which the operation corresponds, and then the rotary line conductor 76 is grounded once, as is well known. The operation of the dial, according to the digit 6, operates the selector A (Fig. 5) to the sixth level, from which level a trunk line is selected to some idle second-selectorfor example, the second-selector E (Fig. 7), to which the subscribers lines are then extended. The second operation of the dial raises the wipers of the second-selector E to the second level, from which level an idle connector is selected to which the subscribers lines are thenceforth extendedfor ex ample, the connector C. The connector C is then, as is well known, operated in accordance with the last two digits, so that connection is established with the desired substation #6220, if the said substation is not busy. If it is busy the connector-shaft is released and a busy signaling circuit is set up between the said connector and the call-' ing substation. In either case-that is, whether a busy line is found or where the connection is fully establishedthe switching apparatus employed is restored to normal condition by the calling subscriber when the latter hangs up his receiver and grounds both line conductors simultaneously. If the automatic subscriber at substation H wishes to call a manual subscriber at substation M, the numberof which station it will be assumed is 2220, the selector A is first operated to the second level, and then the subscribers line conductors are placed in connection with a second-selector E. The said selector is in turn operated into connection with a connector B which, last of all, is carried into connection with the desired line; or if the line is busy the usual busy signaling circuit is established upon the busy release of the connector-switch shaft. If the subscriber at substation H wishes to call the subscriber K at the sub-central office (Fig. 8), he operates his dial to raise the wipers of his selector to the ninth level; the repeater F is then seized, and a signal is transmitted to the trunking operator at D (Fig. 8). The said operator then comes in on the lineand learns from the calling subscriber the number he desires, and then connects him directly to the line called forin this case with the line leading to the substation K. It the manual subscriber at station L of the main exchange (Fig. 6) wishes to call the automatic subscriber at substation H, he removes his receiver and signals the operator at G. She comes in on the line by inserting her plug into jack (1, at which time the calling sub scriber informs her of the line desired. She then plugs the other end of the cord circuit (1' into the jack 1), thus completing a connection between the two subscribers as soon as the line switching relay 73 pulls up. If the subscriber at substation K (Fig. 8) wishes to call the subscriber H (Fig. 5), he signals his operator at D, who then signals the trunking operator at D, informing her that the substation K wishes to connect with the substation H, The operator at D inserts the answering end of her cord "circuit 1) into the jack and, at the sametime, signals the manual operatorat G over an order wire, which operator then answers by inserting the-answering end of the cord circuit G- into the jack d. The said operator then inserts the calling end of said cord circuit G into the jack Z), establishing the desired connection. In any case where connection is established between automatic and manual subscribers, since the connection is made through cord circuits having front and back supervisory signals, as soon as either or both subscribers leave the line the operator becomes aware of the fact and destroys the connection in the usual manner. In this system means are provided whereby calling and called automatic subscribers have guarding potentials provided at their jacks b, so that the operator at G may make the usual busy test. Also, when an automatic subscriber calls through the repeater F the trunk jacks d are made busy to the operator at G, and vice versa-that is, if the operator at G calls the sub-central station by using the ack d a guarding potential is provided at the selector banks A, so that an automatic subscriber may not be able to come in on the line and interfere. This latter provision, of course, provides protection not only on connections between the main manual exchange (Fig. .6) and the sub central (Fig. 8), but also for connections from the said subcentral to the main manual department (Fig. 6).

The repeater F is a very simple switching device having any suitable base. It has no such movable parts as switch-shafts and sliding contacts which characterize the stepby step switches. It is provided with vertical and rotary line relays 124: and 125, a differential relay 126 with windings 127 and 128, auxiliary relay 129, and a retardabusy trunk lines.

tion-coil 130 and private trunk relay 131. The circuit that passes through said repeater is divided into two sections by the condensers 132 and 133. A feature to which special attention is called is the following: Assuming that ten trunk lines are provided between the main exchange and the subeentral exchange, one will lead from each of the selector-bank contacts. To each of said trunks there is one. jack similar to the jack d (Fig. 6). There is also a repeater similar to the repeater F for each trunk line, the jack and the repeater being in multiple, as shown in Figs. 5, 6 and 8. Where the repeaters are all arranged to lead from the contacts of the ninth level, for instance, of the selector line banks, the jacks and the selector bank contacts are arranged in reverse order, as indicated in Fig. 9. Insaid Fig. 9 the contacts of the ninth level of the line bank 88 of Fig. 1 are arranged from left to right in the order 6 6 etc), and the jacks from left to right are arranged in the order (Z (Z etc. For example, the first bank terminale or the ninth level of the selector line bank 88 (Figs. 1 and 9) is connected with the jack al and the jack d is connccted with the bank-.terminal e lVith such an arrangement, and if the manual op erator always selects thetrunkconnections from leftto right, there will be a minimum loss of time from coming in contact with The same. will be true with respect to the selector A and all other selectors whose bank contacts are in multiple with'the bank contacts of said selector A.

More inv detail, the establishment of the connections between subscribers. is as follows:

To call the automatic subscriber #6220 the subscriber at substation'H operates his dial for the digits 6, 2, 2 and 0, as already explained. 7

The first digit being 6 the vertical line conductor 7 5 is grounded six times and then the rotary line conductor 76 is grounded once. Grounding the said vertical line conductor energizes the vertical line relay 67 of the selector A six times, once each time that the impulse teeth press the impulse spring 1 16 onto the ground post 25. The magnetizing current flows from the substation ground G through the groundsprings 21 and 2 1 to the ground post 25, thence to the vertical impulse spring 16, vertical line conductor 75, side switch wiper 49, contact point 55, conductor 134, line switching relay springs 135 and 136, conductor 137 to the vertical line relay 67, thence to the battery lead 138 and from battery B to ground G. The vertical line relay upon pressing the line relay springs 139 and 140 into contact operates the vertical magnet 69 by sending a flow of current from the substation ground Gr through the springs139-and let), conductor 141, private springs 142 and 1&3 to the vertical magnet 69, thence through the battery lead 138 and from battery B to ground G. The vertical magnet 69 then operates to raise the shaft 42 six steps, carrying the line and private wipers 48, :1, and Opposite the first contact of the sixth level of the line and private banks 88 and 89. The ground impulse to the rotary line conductor 76 that follows immediately after energizes the first-selector rotary line relay 68. The current passes from substation ground G to the rotary impulse spring 1S, thence through the rotary line conductor 7 (3, side switch wiper 50, contact point 56, conductor 14 1;, line switching relay springs 145 and 146, rotary line relay 68 to the battery lead, 138, thence through battery B to ground G; The rotary line relay upon closing connection between the line springs 147 and 139 ener izes the private magnet 51, which magnet then operates to release the sides'witch N from first to second position. The,magnetizing current forthe private magnet f ows from ground G through the springs 139 and147, conductor 148, pri vate magnet 51 to the battery lead 138 and through battery B to ground G. As soon as the side switch passes to second position the side switch wiper 47 passes onto the grounded contact point 58, whereby the energizing circuit for the rotary magnet is completed from ground G tl'irough the saidside switch wiper 4.7,. conductor 1 19,

' through one coil of the rotary magnet 70,

interrupter springs 150, through the second coil of said rotary magnet 70, to the battery lead 138, thence through battery B to ground G.

The rotary magnet then operates to'rotat-e the shaft one step, carrying the wipers into engagement with the first contact. If the private wiper 45 finds the first contact grounded-that is, if the first trunk line is bury the private magnet 51 again energizes before the-side switch has time to leave the second position, locking the side switch in said second position until the private wiper is carried beyond the last busy contact by the interrupted operations of the rotary nu {net 70. The energizing circuit for the pro a e m g et in this in t n e extends from the grounded private bank contact to the private wiper a5, thence through the conductor 151,. back release relay 72 can (latt 2, side switch wipe .8; Contac point .59, conductor 15.3 to the private magnet 51, thence to the battery lead 138 and from battery B to ground G. Assuming that all thetrunk lines are busy except the last one on thesixth leveL- the rotary magnet 70 continues to rotate the shaft until the line wipers are carried onto the trunk con- C G PS 1 a and 155 that lead t h se nd- EiCl E t h Saint time the 7 private contact of the sixth level of the priprivate wiper 45 is carried into engagement with the trunk release conductor 156. lVhen the private magnet 51 and the rotary magnet 70 tie-energize at the same time the side switch is then permitted to pass to third position, whereby the subscribers line conductors and 76, by way of the conductors 157 and 158; are placed in connection with the trunk conductors 154; and 155, respectively. At the same time a guarding potential is established at the private wiper 45 when the side switch wiper 18 engages the grounded contact point 64. Said guarding potential is then applied to the tenth rate bank 89 for protecting the seized trunk line from interference. The circuit over which the said guarding potential is established extends from ground G at the side switch N of the selector A to the side switch 80 wiper 4S, thence through the back-release relay 72 and conductor 151 to the private wiper 45, and to the engaged contact. The guarding potential is established, from the same ground G, at the connector private bank contacts by way of the private normal conductor 159, so that no calling subscriber may call in uponthe callingline until after the switches are restored. It will be noticed that the jack sleeve 160 of the jack (Figs. 1 and 6) is normally connected, through the private normal relay 74; and the side switch wiper 46, with the grounded contact: point, 52, whereby when the operator plugs in at the jack 1) the private normal relay 7st is energized from main battery B (Fig. 6) to the ground terminal G The said private normal relay 74 then causes the energizing of the line switching relay 7 3 from ground G by way of the side switch wiper 48 to battery B, for purposes heretofore explained. But when the side switch wiper 46 passes to third position the potential or polarity of the jack sleeve 160 is changed frompositive to negative, whereby the operator may receive the busy test indicating that the line of the substation H is busv. This gi iarding potential is set up over the following circuit: from the said jack sleeve 160 through the private normal relay 74 to the sideswitch wiper 1-6, thence to the con.- tact point 62 and through the line switching relay 78 to the negative or 11()l1- 51'1'0L1Il(l(3l terminal of battery B. After the selector A has thus been operated by the first operation of the dial the second operation is directed to the second-selector E. The relays 74 and 73 do not of course, energize when the operator tests for busy, 5; ".ce the said relays are respectively. five hundr-z-n l and thirteen hundred ohms. more or less. The second digit being 2 the subscr grounds the vertical line conductor in i e and the rotary line conduct-or 7 6 once. The i1 p..lscs to the vertical. line conductor 75 energize the vertical line relay 90 of the second-selector E. In the energizing circuit the current passes from. the substation ground G to the vertical line conductor 7 5, thence through the side switch wiper 49 of: the first-selector A (Figs. 1 and 5) to the contact point 65, thence over the conductor 157, vertical line wiper 43 to the vertical trunk conductor 154, thence to the side switch wiper 161 of the second-selector E (Figs. 4 and 7) to the contact point 162-, thence through the vertical line relay 90 to the battery lead 138 and through battery B to ground G. The vertical line relay 90 upon pressing the springs 163 and 164 together sends energizing current through the vertical magnet 93 from ground Gr through the said springs 163 and 164 and through the private springs 165 and 166 to the vertical magnet 93, thence to the battery lead 138 and from battery B to ground G. The vertical magnet 93 operates to raise the switch-shaft 1167? two steps, carrying the line and private wipers 168, 169 and 170 opposite the first contact of the second level of the line and private banks 171 and 172, respectively. After the vertical line conductor 75 is thus grounded to operate the switch-shaft 167 of the second-selector E vertically, the grounding of the rotary line conductor 76 brings about the rotation of said sha'i't by energizing the rotary line relay 91-at the selector E. The energizing current passes from ground G at the sub station (Fig. to the rotary line conductor 76, thence to the side switch wiper 50 of the first-selector A, through said side switch wiper to the contact point 66, thence over the conductor 158 to the rotary line wiper 44 and to the rotary trunk conductor 155. The current then continues to the side switch wiper 173 of the second-selector E, and through said wiper to the contact point 174, thence through the rotary line relay 91 to the battery lead 138 and through battery 13 to ground G. The rotary line relay then operates to close connection between the line relay springs 175 and 163 forenergizing the private magnet 92. conducting the magnetizing current extends from ground l through the said springs 163 and 175 to the private magnet 92, thence to the battery lead 138 and through battery B to ground G. The operation of the private magnet permits the side switch of the second-selector E to pass to second position, as described in connection with the first-ea lector A, whereby the. side switch wiper 176 passes into engagement with the grounded contact point 177, closing the energizing circuit for operating the rotary magnet 94. The said circuit is established from ground G through the contact point 177 and side switch wiper 176 to the rotary magnet 94 and through the interrupter spring 178 to The circuit for the battery lead 138 and through battery B to ground G. The rotary magnet then opcrates torotate the switch-shaft until the wipers are carried beyond all busy trunk lines, during which time the private magnet 92, as already explained, locks the side switch in second position. As in the firstselector the energizing circuit for the private magnet 92, while the side switch is in second position, extends from the grounded private bank contact to the private wiper 170, thence through the back-release relay 179 and side switch wiper 180 to the contact point 181, thence through the private magnet 92 to the battery lead 138 and through battery B to. ground G. Assuming that the wipers are carried to the tenth contact of the second level the line wipers 168 and 169 are, therefore, respectively connected with the vertical and rotary trunk conductors 181 and 182 that lead to the connector C. At the same time the private wiper 170 is placed in engagement with the trunle release conductor 183 that also leads to said connector C. The subscribers line conductors being thus extended to the connector C the next operation of the subscribers dial is directed to said switch.

The third digit being 2 also, the vertical and rotary line conductors 75 and 76 are grounded, the former twice and the latter once. The impulses to the former operate the line relay 110 of the connector C, together with the diiterential relay 119 of said connector (Figs. 2 and 7), since the said vertical line relay and one of the windings of the differential relay are connected in series. This energization of said differential relay does not play any part in the switch operations. The energizing circuit, however, extends from the substation ground G (Fig. 5) to the vertical line conductor 75, thence through the side switch wiper 49 oi the first-selector A to the vertical trunk conductor 154 and to the side switch wiper 161 of the second-selector E, thence to the contact point 184, conductor 185 and vertical line wiper 168 to the vertical trunk conductor 181 and to the vertical line relay 110 of the connector C, thence through said relay and through the winding 121 of the differential relay 119 to the battery lead 136, and through battery B to ground G. The said vertical line relay upon acting establishes a circuit through the vertical magnet 112 from the ground G when the springs 186 and 187 are carried into contact. The current flows from the said ground G- through the said springs 186 and 187, and through the private springs 188 and 189 to the conductor 190, thence to the side switch wiper 191 and contact point 192 to the vertical magnet 112, thence to the battery lead 138 and through battery B toground G. The v rtical mag t 141.2 perates-t0 raise the switch-shaft 97 two steps, carrying the. line wipers 98 and 99 and the private wiper 100 opposite the first contact 01 the second level of the line and private banks 102 and 101, respectively. The ground impulse to the rotary line conductor .7 6, following the impulses to the vertical line conductor is received by the rotary line relay 111 of the connector C and bythe diiterential relay 119, botii of which relays operate, but the latter to no effect. The circuit begins with the substation ground G and extends over the rotary line conductor 76 to the side switch wiper 50 of the selector A, thence to the rotary trunk conductor 155 and tothc side switch wiper 173 of the second-selector E, contact point 193, conductor 194, rotary line wiper 169 to the rotary trunk conductor 182,. thence through the rotary line relay 111 a'ndwinding 120 of the differential relay 119, conductors 195 and 196, springs 197 and 198 of the rotary back-bridge or pole-changing relay 118 to the battery lead 138 and through battery 13 to ground G. The rotary line relay 111, therefore, operates to press the spring 199 onto the ground spring 186 for energizing the privatemagnet 11 1. The current through said private magnet extends from ground G through the said springs 186 and 199 to the private magnet 114-, conductors 200 and 201 to the pole-changing relay springs 197 and 198 to the battery lead 138 and through battery B to ground G. The private magnet 11st upon operating permits the side switch 0 to shift to sccondposition. The movement of the side switch carries the side switch wiper 191 onto the side switch contact point 202, there-by substituting the rotary magnet 113 in place of the vertical magnet 112 to the control of the vertical line relay 110.

The fourth digit being 0 the subscriber operates to ground the vertical line conductor ten times and the rotary line conductor 7 6 once. Since the side switch wiper 191 is shifted as dcscribed,the ground impulses to the vertical line conductor 75 which, of course, operate the vertical line relay 110, as already explained-cause the step-by-step operation oi the rotary magnet 113. The said rotary magnet is energized each time that the vertical line relay 110 presses the line relay springs 186 and 187 into contact. The current-flow may traced from ground Gr through the said springs to the side switch wiper 191, thence through the contact point 202 of the side switch. to the rotary magnet 113, thence through battery lead 138 and through bat tery B to ground G. The rotary magnet being operated ten times, the line wipers 98 and 99 are carried into engagement with the normal conductors 203 and 204;, respectively, and the private wiper into engagement with the private normal conductor 205, The

76, after the connector wipers are carried into engagement 'with the desired line, causes either of two operationsthe final establishment of a connection, or the busy release oi the connector-switch shaft it the called line is busy. For the present it will be assumed that the connection is established and that the side switch O of the connector passes to third position. This, of course, occurs when the rotary line relay 111 operates and in turn energizes the private magnet 114, as already explained. The shifting of the side switch to third position accomplishes the following results: First, the subscribers extended line conductors 181 and 182 between the second-selector E and the connector "C are placed in connection with the normal conductors 203 and 20 1 The former (namely the conductor 181) is placed in connection with the normal conductor 203 through the condenser 206, ringer relay springs 207 and 208, side switch wiper 209, contact point 210, conductor 211, vertical line wiper 98 to the vertical line conductor 203. The conductor 182 is placed in connection with the rotary normal conductor 204; through the condenser 212, ringer relay springs 213 and 214, side switch wiper 215, contact point 216, conductor 217 and rotary line wiper 99.

To signal, the connection being est-ab- .lished, the calling subscriber presses'his signaling button 31, thereby grounding the vertical line conductor 7 5 and'energizing as a result the vertical line relay 1.10 oi the con nector C. The energizing circuit extends from the substation ground G through the ground springs 21 and 24 to the contact point 3 1, thence through the signaling button spring 32 and primary circuit springs 29 and 28 to the vertical line conductor 75, thence through the vertical line rclav at the connector C and windin 121 of the differcntial relay 119 to the battery lead 138, 110

arating the spring 218 from the spring 219 and carrying it into engagement with the spring 220. The combined operations of said line and ditl'erential relays establish an energizing circuit through the ringer relay 116 from the connector ground G through the line relay springs 186 and 187. private magnet springs 188 and 189 to the side switch wiper 191, thence to the contact point 221 and to the ringer relay 116, thence through the differential relay springs 220 and 218 to 139 Therefore, when the sub- 115 thebattery lead 138 and through battery B to ground G. The ringer relay operates to disconnect the calling subscribers line from the called subscribers line by separating the respective springs 208 and 214 from the springs 20? and 213 and carrying the l'orn'ier into engagement with the springs 222 and 223. The said springs 222 and 223 constitute the terminals of the ringer generator 123 (Fig. 5), while the springs 208 and 214 constitute the terminals of the called subscribers line. 1'1 ringing current is sent over the called line from the ringer generator 123 to the conductor 223, the ringer relay springs 222 and 208 to the side switch wiper 209, contact point 210, vertical line wiper 98, vertical normal conductor 203, vertical line conductor 224, condenser 225, ringer 226, springs 227 and 228, rotary line conductor 229, rotary normal conductor 204, rotary line wiper 99, side switch contact point 216, side switch wiper 215, ringer relay springs 214 and 223 to the conductor 214 and back to the ringer generator 123.

The called subscriber upon answering bridges his transmitter 230 and primary winding 231 across the line and establishes a circuit comprising the back- bridge relays 118 and 117 of the connector C and the transmitter 230 of the substation I in series. This circuit is made possible from the tact that the side switch wiper 232 is now in third position and in engagement with the contact point 233 and the ground G -The energizing current that is thus supplied is utilized for talking purposes at the substation, and for switching purposes at the connector 0, through the medium of the polechanging relay 118. The current flows from ground G to the contact point 233, thence to the side switch wiper 232, pole-changing relay 118, ringer relay springs 213 and 214, side switch wiper 215, contact point 216, rotary line wiper 99, rotary normal conductor 204, rotary line conductor 229, and through the primary winding 231 and transmitter 230 to the vertical line conductor 224, thence to the vertical normal conductor 203, vertical line wiper 98, contact point 210, side switch wiper 209, ringer relay springs 208 and 207, vertical. back-bridge coil 117, and

through the differential relay springs 219 and 218 to the battery lead 138, thence through battery B to ground G. The called subscriber is thus furnished with-talking battery current for his transmitter, which current, asalready stated, at the same time operates the pole-changing relay 118. The said pole-changing relay thus shifts the spring 197 away from the spring 198 onto the ground spring 235. The shifting of said spring 197 closes the circuit through the transmitter 8 of the substation H (Fig. 5) as follows: from ground G at the conside switch wiper 232, pole-changing relay springs 235 and 197 to the rotary line relay 111, thence through said relay to the rotary trunk conductor 182, rotary line wiper 169 of the second-selector E, side switch contact point 193, side switch wiper 17 3, rotary lrunk conductor 155 to the rotary line wiper 44 of the selector A, side switch contact I), contact point 184, vertical line wiper 168,

ertical trunk conductor 181, vertical line relay 110 of the connector C, winding 121 of the differential relay 119 to the battery lead 138 and through battery B to ground ti. The two subscribers, being thus provided with talking battery current, will converse .over the circuits through which the said talking current is flowing, which circuits are, of course, connected by the condenser 206 on one side of the battery and the condenser 212 on the otherside of the battery, as clearly shown in Fig. 7. While the subscribers are thus connected they are protected from interference by any other automatic subscriber who may try to establish connection with the already called subscriber by a guarding potential that appears at the private wiper 100, and at the engaged private contact, when the side switch wiper 232 engages the grounded contact point 233. This guarding potential is established from the connector side switch ground G through the side switch wiper 232 to the private wiper 100, and thence to the engaged contact; but not only does this guarding potential protect against interference by automatic subscribers, but also from interi'erence by the manual subscribers, through the medium of the following arrangement: The establishment of the guarding potential at the private wiper 100 of the connector 0' furnishes current for energizing the bridgecut-o1l' line switching relay 236 of the firstselector A from the private wiper 100 to the private .normal conductor 205, conductor 237, side switch wiper 239, contact point 240, conductor 241 to the line switching relay 236, thence to the battery lead 138 and through battery B to ground G. lVhen the line switching relay 236 pulls up, the springs 242 and 243 are then pressed together, so that the sleeve 244 of the jack f (Figs. 7 and 6) allotted to the line of thesubstation -;6220 is connected to the negative terminal 01' the battery B.

In that case the operator at the manual department will get a busy test by applying her plug-tip to the sleeve 244 of the nector side switch 0 to the contact point 233,jack 7'. It will be seen, therefore, that when an automatic subscriber calls another automatic subscriber, as explained in the foregoing, the calling subscriber makes his line busy when the side switch wiper 4-8 of his selector A passes to third position; and the side switch wiper 48 in passing to third position connects the private normal conductor 159 with the side switch ground G establishing connection between the side switch ground G and the connector private bank contacts that correspond to the substation H. The called line is protected by a guarding potentially established at the private wiper-100 of the connector C (Figs. 2 and 7) when the connector side switch wiper 232 engages the side switch ground contact 233 that connects with the ground G and the said called line is protected against calls from the manual subscribers by a guarding potential established at the sleeve 2441 of the jack f allotted to the substation #6220,(Figs. 6 and 7) when the line switching relay 236 of the called sele tor A (F 7) presses the line switching relay springs 243 and 242 into contact. It will be understooch of course that the calling subscriber has such control over the switching apparatus that he may release said apparatus either while the called subscribers receiver ison the hook or wiile it is ofl the hook. It will be well to consider first the circuits that are involved in the release if the calling subscriber hangs up his receiver while the called subscribers .re-

ceiver is on the said called subscribers swlteh-hook.

The release wh1le the called subscriber's receiver is on the switclrhook occurs when the calling. subscriber restores the receiver ously, The'verticaland rotary line conductors 75 and 76 are therefore grounded simultaneously from the substation ground G to the ground release spring 37, thence through the springs 36 and to the vertical and rotary line conductors and 76. The vertical and rotary line relays 110 and 111 of the connector C energize simultaneously, pressing the trunk release springs 2 15 and 24-6 into engagement, while at the same time the differential relay 119 energizes, since the current is flowing through bothot the windings 120 and 121 in parallel, ma'ntaining the said ,diflerential relay energized. The engagement of the trunk release springs 2 15 and 246 sets up an energizing circuit for magnetizing the connector release magnet 115 in series with the second-selector backrelease relay 179. The connector release magnet 115 upon energizing attracts the release armature 2.47, which armature operates-to restorethe double dog 122 to normal position. The energizing circuit for the said release magnet 115 and the backrelease relay 179 extends from ground Gr at the side switch of the second-selector E to the side switch wiper 180, thence to the back-release relay 179 to the private wiper 170, and to the trunk release conductor 18 3, thence to the trunk release springs 245 and 2 16 of the connector C to the release magnet 115 and through the ditlcrential relay springs 220 and 218 to the battery lead 138, thence through battery B to ground G. As a result the switch-shaft 9'? falls to normal position by well known means and the side switch is driven to first or normal position by the double dog arm 2 1 8 acting upon the side switch link 249. 01 course, the line relays 111 and 110 of the connector remain energized as long as the substation release springs 36 and 37 remain together, and consequently the release magnet 115 of the connector C and back-release relay 179 of the second-selector E will remain magnetized during the same interval. The energization of the back-release relay 179 of the second-selector E causes the closure of contact between the back-release relay springs 250 and 251 whereby an energizing circuit is established through the release magnet 95 of the second-selector E and the bachrelease relay 72 of the first-selector A in series. The energizing circuit through said release magnetand back-release relay (Figs. 1 and 4 or 5 and 7) extends from the side switch ground G at the first-selector A to the contact point 64-, side switch wiper 48, back-release relay 72, conductor 151, private wiper 45, trunk-release conductor 156 to the .prings and 250 of the second-selector E, thence through the rel .ase magnet 95 to the battery lead 138 and throughbattcry 15" to ground G. The release magnet upon magnetizing attracts its armature 251, thrusting the release link 252 over the lug 253 of the double dog 254-, placing the mechanism in readiness to restore the switch as soon as the energizing circuit opens and the substation release springs 35 36 and 37 disengage. The back-release relay 7 2 of the first-selector A upon energizing presses the springs 255 and 256 into contact, closing in turn the energizing circuit of the release magnet 71 ot' the first-selector A from ground G through the said springs and 256 and through the release magnet 71 to the battery lead 138, thence through batter B to ground G. The said release magnet 71 also attracts its armature 257, which lat ter then causes the release link 258 to engage the lug 259 of the double dog 260, placing the mechanism in readiness to i'estore the selector-switch. As soon as the subscribers switch-hook descends sufficiently to vpermit the substation release springs 35, 36 and 37 to separate, the energizing circuits through the line relays 110 and 111 of the connector C are then destroyed, so that the said relays permit the trunk-release springs 245 and 246 to separate. The separation of said release springs 245 and 246 destroys the energizing circuit through the connector release magnet 115 and back-release relay 179 of the connector O and selector E. The connector C is thus fully restored and the selector E is also fully restored as latter produces a full restoration of the switch. It will be evident, therefore, that by thus hanging up his receiver the calling subscriber restores all of the switching apparatus that he temporarily monopolized, restoring said switches at the same time to normal condition. If the automatic subscriber at substation H desires to call the manual subscriber #2220 (Fig. 6) he operates his dial in the same manner as if he were calling the subscriber #6220, with the exception that now the operations correspond to the digits 2, 2, 2, and 0.

The release after the called subscriberanswerst-hat is, while the receiver of the called subscriber is off the switch-hookoccurs in a manner different from the release while the said receiver is on the switchhook. In the former case the calling subscriber proceeds as usual by hanging up his receiver, and the switch-hook upon descending presses the release springs 35, 86 and 37 into contact, grounding the vertical and rotary line conductors and 7 6 simultaneously. Attention has vbeen called to the fact that the called subscriber upon removing his receiver energizes the pole-changing relay 118 of the connector C (Fig. 7), which pole-changing'relay then operates to I shift the rotary side of the line to ground by carrying the pole-changing relay spring 197 into engagement with the spring 235 while the connector side switch is in third position. Evidently, therefore, the inside terminal of the line that passes through the rotary line relay 111 of the connector (l, and through the winding 120 of the differential relay, is grounded at the connector side switch ground G Consequently, the result of grounding the subscribers rotary line conductor 76' at thesubstation H shortcircuits the said line relay 1.11- and the winding 120 of the differential relay 119 through ground. The effect of thus shortcircuiting the said relay coils is to cut short the flow of current through them. The primary effect of the cessation of the flow of current through this section of the circuit is to cause the dilferential relay 119 of the connector C (Figs. 2 and 7) to energize, since the flow of energizing current through the winding 121 of said differential relay is still maintained. In this instance the-current flows from the substation ground G to the ground release spring 37, thence to the release spring 36 and to the vertical line conductor 75, and by paths already described through the vertical line relay 110 and through the said differential winding 121 to the battery lead 138, thence through battery B to ground G. The differential relay upon energizing causes a separation of the springs 218 and 219 and the engagement of the spring 218 with the spring 220. The separation of said springs 218 and'219 destroys the circuit that provides the called subscribers transmitter with talking battery current through the vertical and rotary back- bridge coils 117 and 118. Evidently,

then, the rotar back-bridge relay 118 will de-energize wit the result that the spring 197 leaves the ground spring 235 and returns into normal engagement with the spring 198 that connects with the nongrounded terminal. of the battery B, thus restoring the connection between the release magnet 115 and the non-grounded terminal of battery B. The energizing of the differential relay 119 follows the de-energization of the rotary line relay 111, and

the consequent separation of the trunk-release springs 245 and 246; but the de-energization of the pole-changing or rotary back-bridge relay 118 that immediately follows, as described, removes the short-circuit through the rotary line relay 111 and winding 120 of the difi'erential relay 119, and reverses the connection so that a flow of current is now established through said winding 120 and rotary line relay, causing the rotary line relay to pull up again and establish connection between the trunk-release springs 245 and 246, the current in the winding 120 further strengthening the differential relay 119 which. is already ener gized. Eventually, then, the trunk release circuit is again established that comprises the release magnet 115 of the connector G and the back-release relay 179 of the second-selector E. The result is that the connector-switch shaft 97 and side switch 0 are restored, as already explained, whereby the connecting circuit with the called line is destroyed as soon as the line wipers leave ed, the torn'ier twice and the latter once,

whereby the vertical and rot line relays 6i" and 68 of the selector A are operated to raise the shatt 4-2 of the selector A two steps, carrying the line wipers 43 and it and the private wiper to opposite the first contact of the second level of their respective banks .88 and 89. Thenthe switchshalt is rotated automatically, carrying the wipers into engagement with some idle trunk line leading to a selector 1*). illthough the second-selector E shown in Fig.

5 is represented leading from the second level, and the selector E shown in F 1g. 7 is represented leading from the s xth level, still for convenience of illustration it will he assumed that both selectors are identical. Therefore, the trunk conductors of both views will be given the same reference characters. In actual practice it is customary to give each terminal in each level a special switch. Assuming that the first-selector A automatically rotates the line wipers 4b and 44 onto the tenth contact of the second level of the line bank 88, and that it establishes connection with the trunk conductors 154'. and 155 when the switch comes to a standstill, the subscribers line conductors and 76 will then be extended to the second-selector E, after receiving the impulses corresponding to the second digit of the number, 2220. v

The second digit being 2 the vertical and rotary line conductors 7 and 76 are grounded, twice and once respectively, and the vertical and rotary line relays and 91 of the secondselector E operate to raise the second-selector line and private wipers 168, 169 and 170 to the second level, after which operation they are then automatically rotatedonto anidletrunk line leading to some connector. It is assumed that the trunk line thus seized leads to the connector B. the selector E automatically rotating the shaft 167 until the line wipers 168 and 169 are carried into engagement with the trunk conductors 181 and 182, and the private wiper 170 into engagement with the private normal conductor 183. The subsorihers line conductors are, therefore, extended -to the connector B which now receives the impulses corresponding to the third and fourth digits of the desired ninuher (Figs. 3 and The third (ll lt l-Klllil' 2 the vertical and rotary line conductors if; and 76 are grounded, twire and once respea-twelv.

wherel the vertical and rotary line relays 261 and 262 of the connector ll are operated. The energiz ng circuit tor perating the vertical line relay 261 extends from the substation groundtrlto the vertical line conductor 75, thence through the side switch wiper at!) of the first-selector A to the contact point 65, vertical l ne wiper 43, vertical trunk conductor 1:34, side switch wiper I61 oi the second-selector lr'l, contact point L84, vcrt cal line wiper i568, vertical trunk conductor 18L to the vertical :line relay 261, thence through the winding 162 of the ditlerential relay 1.6 3 to the battery lead 138, and through battery ill to groundG. The (lilierei'itial relay 163, duriug'the impulse tor thethird digit, encrgizes in series with the vertical and rotary line relays 251 and 262, hut with no result oi. ('OIISfllllOilCG. The vert' ad line relay 261 upon pressing the line relay springs 264. and 265 into contact causes the operation of the cal magnet over the tollowing cir- From ground G through the springs 265 and 264, private springs 267 and 268 to the vertical magnet 266, side switch contact point'2ti9, side switch wiper 270 to the battery lead i338, and through battery 13 'to ground G. he vertical magnet, thereiore, operates to raise the shaii't- 271 .two steps, carryin the line wipers 272 and 273 opposite the first contact of the second level of the line bank 274. The ground impulses to the rotary line conductor 76 operate the rotary l ne rel-av 262 of the connector B over a circuit extending from ground G at the substation H to the rotary line conductor 76, thence to the side switch wiper 50, contact point (56, rot: line wiper 44, rotary trunk conductor 15:"), side switch wiper 173 of the second-selector E, contact point 193, rotary line'wiper 169, rotary trunk conductor 182 to the rotary line relay 262, thence through the winding 275 of the differential relay 163 and through .the ringer relay springs 276 and 277 to the battery lead 138, thence through battery B to ground G. The rotary line relay 262 upon energizing carries the spring 278 onto the ground spring 265, energizing the private magnet 259 by a flow of current from ground G through the springs 265 and 278 to the private magnet 279, thence through the ringer relay springs 276 and 277 to the loattery lead 138, and through battery B to ground G. The operation of the private magnet 279 causes the side switch P of the connector to pass from first to second position. The passage of the side switch from first-to second position carries thesideswitch wiper 270 onto the contact point 280, substi-

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