US1306825A - Telephone district exchange system - Google Patents

Description

B. D. WILLIS AND T. G MARTIN. TELEPHONE DISTRICT EXCHANGE SYSTEM. APPLICATION mm AUG. :1. Hi3, mmuw AUG. 3. ma.

1 06,825 Patented June 17, 1919.

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Patented June 17. I919.

6 SHEET5-SHEET 2- Mvwvzaszrs B. D. WILLIS AND I. G. MARTIN.

TELEPHONE DISTRICT EXCHANGE SYSTEM. APPLICATION FILED AUG. l1v nus, RENEWED nus.a.191s.

1,306,825. Patented June 17, 1919.

6 SHEETS-SHEET 3.

L fiWE/W'ORJ h [I @WM/- "rTOR/VEmi B. D. WILLIS AND T. G. MARTIN. TELEPHONE DISTRICT ELXCHANGE SYSTEM. APPLICATION man AUG. :1. m3. nzniwmnus. 3, ma.

1 ,306,825. Patented J 11110 17. 1919.

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T Q llllllllllllHlv Patented June 17, 1919.

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fiWE/VTORS pm *4 if 211 A fi 97'0RNEK5 flu B. D. WILLIS AND T. G. MARTIN.

TELEPHONE DISTRICT EXCHANGE SYSTEM.

APPLIC AT|0N FILED MIC-2.11.1913. RENEWED AUG-3,1918.

SEU E Patented June 17, 1919.

5 SHEETS- SHEET 6- UNITED STATES PATENT OFFICE.

BERNARD D. WILLIS AND TALBOT G. MARTIN, OF CHICAGO, ILLINOIS, ASSIGNORS TO AUTOMATIC ELECTRIC COMPANY, OF CHIOAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE DISTRICT EXCHANGE SYSTEM.

Application filed August 11, 1913, Serial No. 784,111.

To a Il /101M it may concern:

Be it known that we, BERNARD D. WILLIS, and Tanner G. MARTIN, both citizens of the United States of America, and residents of Chicago, Cook county, Illinois, have invented certain new and useful Improvements in Telephone District Exchange Systems, of which the following is a specification.

)ur invention relates to a telephone exchange system which is divided into a certain number of districts or main offices, and sub-divided into a number of branch offices which have access to a certain number of the main oliices. ilnsuch a system the main office of each district is connected by trunk lines with the main oflice of each of the other districts, while the branch offices of each district are connected by trunk lines with the main office oi their own district only. Calls from one main office to another main office pass direct from the main office in which the call originates to the main office in which the called subscriber is located. Any call to or from a branch office must pass through the main office to which that branch oflice belongs.

In systems of this character it has heretoioro been necessary when one subscriber of a branch office called another subscriber of the same office that the connection first had to be trunked from the branch office to the main office and then back from the main office to the branch office. Thus, although both the lines of the calling and the called subscribers terminated in the same branch office, two trunk lines between the main and branch offices were included in the connection between the two lines.

It is an object of our present invention to provide means whereby connections between two subscribers of the same branch oflice may be confined entirely to local apparatus in the branch office and thereby avoid the use in such connections of any trunk lines extending between the main and branch offices.

It is a special object of our invention to accomplish this without in any way disturbing the general trunkin scheme, or requiring the subscribers of a branch office to call any special numbers or perform any other acts other than to call the regular directory number of the subscriber desire-d.

A further special object of our invention is the provision of a repeater at a branch office w ich operates to repeat impulses cor atented Julie 17, 1919.

Renewed August 3. 1918. Serial No. 248,222.

responding to the various digits of the called number to switches located at the same branch office or main office until it is definitely determined that the call is to extend to another subscriber of the same branch office. This repeater then operates to out off and release all switches which have been previously operated, and to extend the connectioir directly to other switches in the same branch office, through which last-mentioned switches the call is then completed to the desired line.

In order that our invention may be more clearly understood, we have illustrated in the accompanying drawings an automatic district telephone system in which automatic switches of various well-known types are employed in combination with the novel features of our invention. It is, of course, understood that if desired our invention can be employed with switches of other types without departing from the spirit of our in vention.

In the accompanying drawings- Figure 1 represents diagrannnatically the lay-out of a multi-ofiice telephone system embodying the principles of the invention disclosed herein.

Fig. 2 is a diagram showing more in detail the trunking arrangement of a portion of the system shown in Fig. 1.

Figs. L), 4, 5 and 6 show a complete con nection between a calling telephone T and a called telephone T in the system shown.

Fig. 7 shows the circuit of an additional apparatus which is employed in the system.

Figs. 8, 9 and 10. are diagrams representing the connections of the contacts of the selector-repeater L to meet various requirements.

Fig. 11 represents a selective signaling ring-back device for use in connection with party lines.

As shown in Fig. 1, the system represented herein is a, multi-oflice or district system comprising a pluralitv of exchange oflices A, B, G, D, A. A B, B etc. With re spect to the trunk connections between offices, these offi es are divided into two classes. The offices A, B, C and I) are each connected with each of the others by a separate set of trunk lines, and for convenience these offices will be designated as main offices. The offices A, A B, B etc, are each connected by trunk lines to only the nearest main ofiice A, B, C or D, as the case may be. These others A. A Ii, ll, elta, will be tenmcd branch olliccs. In a system of this character, when a slrbscriber whose lino terminates at one ot the main oliices (office A, for example) wishes to communicate with a sa l)- scribor whose line terminates at one of the other main ollices (ollicc (I, for example), the calling subscrilu-r s line is connected tin-(nigh the medium of suitable apparatus at his own ollice (ollirc A) to a trunk line leading directly to the office of the called subscriber (office at which oilice said trunk line is connected tl'irough the mediun'i of SlllttlblO apparatus with the line of the called sutbscriber. If a subscriber of one of the branch offices (otiice A, for example) wishes to call a subscriber of some other otlice, he must first obtain connection with a trunk linc leading to his main oifice (office A). At this office (onnection may then be made with a trunk line leading to the office of the called subscriber, providing the called sulwcribers line terminate in one of th" main offi es, or in another branch office (such as office 1V) which is connected to the same main oilice the calling subscriber. It the called subscribefs line terminates at a branch office (office C, for example) of a second main Office (oflicc C), the calling sulr scriiber, after having obtained connection over a trunk line with apparatus in his own. main office (oflice A), must then obtain connection with a trunk line leading to said second main office (office 0), and then, through the medium of appara tus at said second office. be connected with a trunk line leading to the branch office (olfice U) oi the called subscriber, where the connection is finally completed. Following out this general plan, if a subs ribmof a branch office. desired to obtain connection with a second subscriber of the same branch office, it was heretofore necessary that, he first obtain connection with a trunk line leading to a main office to which his branch office is connected, and would then obtain connection with a second trunk line leading back from the main ofiice t0 the branch ofiice, from which second trunk line connection would finally be completed to the called subscriber. It; is the object of our present invention, however, to provide means whereby the trunk lines leading from the branch office to the main office and; back from the main office to the branch office may be excluded from connections between the subscribers of the same branch office.

Referring to Fig. 2, the method of carry ing out the invention is, in general, as follows: The apparatus inclosecl within the dotted lines represents the apparatus of a branch office, while the remaining apparatus is assumed to be located at a main oifice. There are shown in this figure two groups oi subscribers substations T and T the line conductors of each of which terminate in an individual trunit-selecting or presclector switch E at the branch office. For the purpose of being called these lines terminate in the banks oi a plurality of commctor switches I". These connector switches are represented herein by small circles, three parallel lines underneath the same represent.- ing the multiple bank contacts which are assumed to be arranged in horizontal rows or levels. The individual switches lil oi each of the groups of subscribers substations T and T have access to a group of trunk lines 1 which lead to so-callcd secondary trunk-selecting switches H. The switches H have access to trunk lines I?" which lead to first selectors I in the main oiiice. Associated with the main office there are shown three groups of subscribers substations T T" and T each of which groups is pro- \idcd at the central otlicc with a group 01' prcsclccting or line switches E for calling purposes, and with connections in the banks of a group of connector switches I for be ing called. Each of the groups of line switches E have access to a group of first selector switches I, which first selectors in turn have access to second selectors J, which second selectors in turn have. access to third selectors K. Although the bank contacts of all the first selectors shown in Fig. 1 are represented as being nmltipled together, it is to be understood that this figure is only diagrammatic, and: any known or desired mnltipling arranpgenientv of the selectors may be employed. As shown herein, the first level of the first selectors has access over trunl; lines to second selectors J in the same exchange. The remaining two levels shown are assumed to have access to groups of trunk lines and 1 leading to other main offices, where said trunk lines would terminate in second selectors. In like mair nor, the main office shown would be provided with groups of second selectors which are accessible to the first selectors of the other main offices in the system. The first level of the group of second selectors J has access to a group of third selectors K, the first two levels of which have access to trunk lines leading to connector switches F which have access to the subscribers groups T and T in the branch office, while the remaining: level (or levels) of the same group of third selectors has access to connectors belonging to the subscribers group T 5 in the main office. The remaining groups of third selectors may have access to connectors all of which are situated in the main office, or some of which are situated in a branch oilice and some in the main office, or in any manner desired. In each of the trunk lines it which lead from the subscribers individual is a switching device L which, under certain conditions, may operate to connect the trunk line which has been seized by a subscribers individual switch to a secondary switch M, which secondary switch has access to a con nector in one or the other of the groups of connectors which have access to the branch oliicc subscriber groups T and T The secondary switches M are arranged to have individual terminals in the banks of the switching devices L so that a switching device L always uses the same secondary in extending a connection to a line in a particular group. If a call is directed to a line in another group another secondary switch M may be used which is also individual to the same device L.

In general the operation of the system shown in Fig. 2 is as follows: Upon the re moval of the receiver by the subscriber of one of the branch oflice groups, his individual line switch E operates to select a trunk line leading to a secondary switch H which in turn operates to select an idle first selector 1. The subscriber operates his calling device to cause the selected first selector to extend connection to an idle second se lector in the section or division of the exchange to which the called subscriber belongs. The selected second selector is then operated to extend connection to a third selcctor which has access to the next smallest subdivision of the exchange towhich the called subscriber belongs. This third selector is then operated to establish connection with an idle connector switch which has access to the group of subscribers to which the called subscriber belongs, which connector is then operated to establish connection with the called subscriber. Assume now that the called subscriber is in the same branch efiice as the calling subscriber. Under these conditions, when the calling subscriber operates his callin device to cause the third selector to estab ish connection with a connector switch, the switching apparatus L in the trunk line which has been seized by the calling subscribers line switch operates to extend the connection directly through one of the secondary switches M and ever a trunk line t directly to one of the connectors having access to the groups of subscribers T or T, depending upon the group in which the called subscriber is situated. In other Words, when the trunking has progressed to the stage of eliminating all the sections except the section to which the call is to revert, then the switchin ap paratus L is in order to cut off the ba anee of the system by switching to the local apparatus M. \Vhen the apparatus L thus opcrates to extend a connection by way of one of the secondary switches M, it causes the secondary switch H which was previously selected, as well as all the selectors which have been operated in the main ofliee, to be released and the connection is thereafter confined solely to the branch office.

The apparatus with which we have chosen to illustrate our invention is of a wellknown type and is shown in patents of the prior art, and it is therefore thought necessary to show only such details of construction as are necessary to bring out the novel features.

The telephone substation T (Fig. 3) coinprises the usual transmitter 2, receiver 3, swit-h hook 4, ringer 5 and condenser 6. Being an automatic substation it is also provided with a suitable calling device or impulse transmitter which is represented herein by a pair of impulse springs 7 and 8 and a toothed impulse wheel 9, which latter may be operated by the calling subscriber through the medium of a finger hole dial (not shown) to cause the impulse springs to be opened a number of times corresponding to any dig'it which it is desired to call.

The subscribers individual switch E (Fig. 3), which may represent any one of the switches E shown in Fig. 2, is of the general type of switches disclosed, for example, in British Patent to R. W. James No. 26,301 of 1906, being of the more particular form shown in British Patent to A. E. Keith No. 1421 of 1910. This line switch, as is well known, is provided with a movable plunger which, when idle, is always main tained opposite the bank terminal of an idle trunk line by a so-ealled master switch, and upon the operation of said line switch this plunger is forced into the terminal springs of said trunk line to connect the subscribefis line therewith. The master switch N which is shown herein differs somewhat from that shown in said British Patent No. 1421 of 1910. The usual plunger guide shaft 9 is connected with a rotary shaft 10 in such a manner that as the shaft 10 is rotated back and forth the plunger shaft 9 is caused to oscillate about said shaft 10 as an axis. The power for rotating the shaftlO in one direction is furnished by a spring 11, while the power for rotating it in the other direction and for restoring tension to the spring 11 is furnished by a solenoid 12. Secured to the shaft 10 there is a cam member 13 which is provided along its outer edge with a plurality of notches 14, one for each trunk line to which the line switches have access. The shaft 10 is normally locked against rotation in either direction by the engagement of the lever 15 with one of the notches 14. A small governor 17 is provided for controllingthe speed of operation of the master switch. The master switch is also provided with the usual bank of contacts comprising a common segment 24 and an individual contact a for each trunk line. The usual wiper 25 serves to keep the common segment 24 in electrical contact with the individual con- (acts of the trunk line before which the plungcrs of the idle line switches are resting.

Allotted to the calling subscriber-s line there is also a call register or meter 26 which is operated by a double-wound magnet 27, which magnet is so wound and a-djustial that it requires the cnergization of both windings in the saute direction to cause the meter to be operated.

The apparatus shown at L is one of the switching devices shown at l; in the diagrammatic Fig. 2. This device performs two functions. In a call from the branch ofiice to the main oflice it operates as an ordinary repeater to repeat the impulses from the calling substation around the condensers 23 and 29 to the branch conductors 30 and 31. In a local connection this device operates to free the trunk line leading to the main otlice and to divert the call to the proper local switches for completii'ig the dc sired connection. This SWit-Clllflg repeater comprises a vertically and rotatably movable switch shaft (not shown] which carries the wipers 3U, 37, 33 and 39 and is controlled by the soculled vertical and rotaiy magnets it) and ll in the manner shown in United States Letters Patent No. 815,176, granted March 13, 1906, to Keith, Erickson and Erickson, for connector switches. There is a single row or level of bank contacts for each wiper and the shaft is preferably arranged to be capable of making twenty l'0- tary steps. The switch shaft may be operated in response to the first three digits of the called number, the impulses for the first digit o-peratin to raise the shaft vertically and the impuics for the second and third digits operating to rotate it. The rows of contacts are placed so as to be engaged by their respective wipers only when the switch shaft has been raised a number of steps cor responding to the first digit of the subscribers numbers in the branch otlice. For example, if the numbers in the branch oflicc begin with the digit 1, whenever the dial is operated for the first digit 1 the wipers will be raised to a level of contacts, and if the first digit called by the first operation of the dial is greater than 1, the wipers will obviously be raised above the levels of contacts, making it impossible for a reverting call to result with any number the first digit of which is any higher than 1 in unit value. In the row of cont-acts which are engaged by the wiper 38 one contact is connected to ground through one winding of a double-wound relay 43. The position of this contact is determined by the units value of the second digit of the subscribers numbers in the branch oflice. For example, when the second digit of the subscribers numbers in. the branch oflice is 1., the connection to round through the relay 43 will be from tie first contact (Fig. 8); but if the second digit contacts are connected by means of trunk conductors, such as 2-H), 24 i. and 2+2, to secondary switches, such as the switch M (Fig. 7), which corresponds to one of the switches M (Fig. 2). The contacts which are thus connected, as will be shown, do not coincide with the position oi the contact which is connected to ground through the relay 43, but are always displaced to the right (Fig. 3). The amount of this displacement varieshowever. For example, if the third digit of any subscribers numbers in the branch ollicc is 1, the contacts which are displaced only one step will be connected to a secondary switch; it the third. digit of any of the branch otlice numbers is 2, the contacts which are displaced two steps will be connected. etc. In other words, the contacts which are connected to the secoi'idary switches M are the ones which are engaged by said wipers 35, 3b and 37 when the switch shaft has been rotated a mnnber of steps equal to the sum of the second and third digits of: the subscribcrs numbers in the branch ofiiee. The contacts in the row which is engaged by the wiper 39, to which wires are connected, coincide in position with the similar ones in the levels of wipers 35, 36 and 37. Furthermore, these wires are all multipled (Fig. 8) and are connected to one of a normally open pair of contact springs 171 of the relay 43. Since it is assumed that the repeater L is adapted to be used in a branch oflice in which all subscribers numbers begin with either 1l1 or l-1-2, the rows of contacts are placed so that the wipers reach a position opposite them on the first vertical step of the shaft. The first contact in the row which is engaged by the wiper 33 is connected to the relay 43, and in the rows which are engaged by the wipers 35, 36 and 37 the second and third sets of: contacts are connected to the switches M. Since in this instance it is assumed that the number of the subscriber who is actually being called at the branch is 11220, in the drawings the third set and this set of contacts only are actually connected, while stub conductors indicate similar connections from the second set of contacts, which would be used if lllXX were being called. With this arrangement it is evident that when a subscriber of a branch ofiice is calling another subscriber of the same ofiice, when the second digit is called the wiper '38 willbe brought into engagement with a contact which is connected with the winding of the relay 43, via, the first contact, and when the third digit is called this wiper, together with the others, will be carried on past the first position and the wipers 35, 36 M37 will be brought into engageluent with a set of contacts (the set in third position) which are connected to a trunk line leading to the secondary switch M.

The switching repeater L is also provided with a so-called side switch similar to that shown in said coi'inector Patent No. 815,176, which, however, comprises but a single wiper l-land is controlled by an escapement magnet -13 in the usual manner. The magnet -16 is the usual release magnet for restoring the switch shaft and side switch to normal position upon the release of the. connection. The operation of the selector-repeater is lontrolled through the medium of a doublewound line relay 33, which is connected with the line conductors through the springs of a reversing relay 31. The relay $31 is doublewound and is so adjusted that it is operas tivcly energized only when both windings are energized in the same direction. The talking circuit through the repeater, before reaching the condensers 28 and 29, passes through normally closed contacts of a switching relay 47, to the normally open springs of which are connected the wipers 35 and 36. The relays 48 and 19 are slow acting-41ml: is, relays that deenergize slowly after their energizing circuits have been broken.

T he secondary switches H (Fig. 4) and i (Fig. 7), which correspond respectively to one of the switches H and M (Fig. "2) are the same in principle as the subscribers individual switch E, being somewhat simplilied. however, in that they are provided with no line or cut-off relay armatures. Each of these switches belongs to a group which is controlled by a master switch similar to the master switch H (Fig. 3), there being shown, however. only the master switch N which controls the switch H.

The selector switches I, J and K, which may represent any one of the respective switvhes I, J or K (Fig. 2), are of the eneral type of selector switches disclose in United States Letters Patent No. 815,321, granted .hlai'ch 1.3, 1906, to Keith, Erickson and Erickson, being somewhat modified, however, as shown in British Patent No. 1421 of 1910, hereiuabove referred to, so as to operate in a two-wire system. Referring to the selector 1, each of these switches comprises a bank of contacts arranged in rows or levels and adapted to be engaged by a set of wipers 51, 5:2 and 53 which are carried by a vertically and rotatably movable shaft (not shown) which is controlled by the usual. vertical and rotary magnets 54 and 55. The usual side switch comprising the wipers 5(3, .37, 58 and is controlled by the private magnet 60 in the usual and well-known manner. The usual release magnet 61 is adapted to release the switch shaft immediately upon euergization, rather than by the decuergizatiou thereof as shown in said solector patent. lhe relays G2 and G3 are slow acting.

The connector switch F Fig. ('3, which may correspond to any of the switches F Fig. 2), is of the general type of connectors shown in said United States Letters Patent No. 815,176, previously referred to, being modified, however, in order to operate in a two-wire system. In this figure, 61, G5 and G6 are the usual shaft wipers. which are carried upon the vertically and rotatably movable shaft which controlled by the vertical and rotary magnets 67 and 68. The usual side switch is (ontrolled by the private magnet (39 in the welldmowu manner. At 70 there is shown the usual release magnet and at 71 the ringing relay is represented.

The telephone substation T and individual switch E are in all respects the same as the telephone substation T and switch E (Fig. 3).

At 0 (Fig. 6) there is represented a ringing current generator. At Q and Q (Figs. 8 and 6) there are represented two busy sig' naling machines. There are shown throughout the drawings a plurality of batteries X for supplying current for operating the central ottice apparatus and for talking purposes. There need, however, be but one battery, or, preferably, one battery in each exchange.

Having given a general description of the system and apparatus in connection with which it has been chosen to illustrate the invention disclosed herein. there will now be. given a more or less detailed description of the operations by which the connections are established between the various subscribers. Since the apparatus shown herein is in general well known in the art and is fully described in the publications herein referred to, it is not thought necessary to describe its operation in detail herein. It will first be explained how a connection is extended from the telephone substation T of a branch office to a telephone substation T of another b-ranch office, or of some main office. The number of the calling substation will be assumed to be 111.10 and the number of the called substation will. be assumed to be 22220.

Upon the removal of the receiver at the calling substation a bridge is closed across the calling line through the tral'ismitter 2 and receiver 3 by the closure of the hook switch contact 73, whereby an energizing circuit is closed through the line winding 71 of the subscribers switch E. The winding 74, upon energizing, attracts the. armature 75, whereby a circuit is closed through the pull-in winding 76, which operates to attract the plunger arm 77 and cut-off armature 278. The plunger arm 77, upon being attracted, thrusts the plunger into its bank of contacts, whereby the line circuit is me tended through the springs TH and 7t) and H0 and H1 to the seleetor-re u-ater 11, while the aruuiturc 2T8 operates to disconnect the winding 71 from the line. When connection is extended to the repeater L a circuit is closed through its line relay 33, said circuit extending from ground G through the lower winding of said relay, springs 82 and 83 of the relay 34, back contacts of the spring 81 of the relay 17, line switch bank.s)rings 81 and 80, line 85 of the telephone line 80, left-hand winding of the meter magnet 2?, bank springs 78 and 79, back contact of the spring 87 of the relay 4? and springs 88 and 89 of the relay 31 and upper wind ing of the relay 33 to the battery lead 90, and thence through the battery X to ground ti. The relay 33, upon energizing, closes a circuit from ground (t through the front contact of the spring 91 and relay 4 to the battery lead 0. One result oi the energization of the relay -18 is the closure of a circuit extending from ground G through the springs 02, t and 01- and line switch bank springs 95 and and winding 97 of the line switch E to the battery lead 90. The winding 97, upon energizing, serves to hold the switch E in its operated position after the line winding has been disconnected from the line and permitted the circuit of the winding 70 to be broken. A further result of the energization of the relay 48 of the repeater L is the closure of a circuit from ground l through the springs 92 and 93 and the lower winding of the relay 34 to the battery lead 90. A third result of the energization of the relay the closure of a circuit extending from ground (-1 through the springs 92 and 93, contact 98 of the relay 17, and thence over the trunk conductor 32 and through the winding 99 of the switch H (Fig. 4) and springs 100 and 102 and contact. 108 in the master switch N to the battery lead 90. The switch H thereupon operates to extend the connection through the contacts 101 and 105 to the first selector 1, while at the same time, by the shifting of the springs 100, 101 and 102, the winding 99 is connected to the battery lead through the high resistance winding 107, so as to reduce the holding current of the switch H. A further result of the energization of the line relay 33 of the selector-repeater L when connection is first extended thereto is the closure of a bridge across the trunk conductors 30 and 31, whereby, as soon as connection is extended to the first selector 1, as above described, an energizing circuit is closed for its line relay 109. This circuit extends from ground G at the selector through the lower winding of said relay 109, side switch wiper 59, trunk conductor 110, contact 105, conductor 31, contact 111 of the repeater line relay, upper winding of the 1 ,sca ses relays 112 and 21 1 in series, conductor 30, contact 101, side switch wiper Fit) and the upper winding of the selector line relay 101) to the battery lead 115. The relay 10$), upon energizing, closes the circuit of the slow act ing release relay 1113, At the selector-rcpeater L the current flowing through the upper winding of the relay Ill" in the circuit last traced is opposed by the current in the lower winding, and said relay is not opera-- t'ively energized. The current flowing in the upper winding of the relay 112, however, causes said relay to be operated to open the contact 117 to prevent the application of busy signaling current to the calling line in a manner which will be explained hereinafter. it will be reiueniherml that when connection was first extended to the repeater 11 its line relay was included in an energizing circuit which included the left-hand winding oi the subseril eus meter magnet 27. The current in this latter winding, hmu ever, is opposed at this time by current flow ing in the right-hand winding over a circuit extending from ground (it at the relay 1H t in the repeater L to the line switch bank springs and 90, as has previously been traced, thence through the right-hand winding of the magnet 27 and contact 121 to the battery lead 90. The magnet 27 therefore not operatively energized at this time.

The closure of the contact 122 by the operation of the subscribers switch E conipletes a circuit extending from ground G through said contact, master switch bank contact 123, wiper 25 (which is assumed to be resting upon said contact at the tiinel segment 24 and the relay 12-1 to the battery lead 90. The relay 121, upon energizing, closes the circuit of the relay 10, which withdraws the locking member 15 from the cam 13 and permits the idle plungers to be moved away from the trunk line seized by the switch E. When the wiper 25 engages the non-grounded contact of the first idle trunk line, the relays 124 and 16 denergize and the locking member 15 is permitted to drop back into the cam 13 and bring the plungers to rest in front of said idle trunk line. Vyhen the plungers in their search for an idle trunk line pass beyond the last trunk, the arm 22 closes the contact 23,whereby the circuit of the relay 18 is closed, said circuit extending from ground G through the springs of the relay 124 (which is energized at the time), contact 23, relay 18 and the contact 125 of the relay 16. (which is also energized at the time) to the battery lead 90. The relay 18, upon energizing, becomes locked in its operated position by the engagement of the spring 19 with the detent on the spring 20, and closes an energizing circuit for the solenoid 12 and a locking circuit for the relay 124 independent of the master switch bank. The solenoid, upon energizing, ro-

tatcs the plungcrs back past all the trunk lines to their starting positions, whereupon the arm 21 releases the spring 19 from the spring 20 and the plunger-s again come under the control of the master switch bank and come to rest upon the first idle trunk line. Upon the closure of the contact 106 (Fig. 1), the master switch N operates in the same manner as explained for the master switch N to select an idle trunk line for the idle switches of the group to which the switch H belongs.

The foregoing operation takes place immediately upon the removal of the receiver from the switch hook at the calling su-bsta tion. The calling subscriber now operates his calling device in the usual manner for the first digit 2 of the called number, whereby the substation impulse springs 7 and S are separated twice momentarily. Each time the substation impulse springs are separated, the line relay 33 of the repeater L is momentarily deencrgized. The breaking of the contact 111 each time the relay 33 deenergizes opens the bridge across the trunk conductors 30 and 31, thereby momentarily breaking the energizing circuit of the line relay 109 of the first selector 1'. The relay 48 in the repeater being slow acting does not deenergize during the momentary interruption of its circuit by the line relay 33, and therefore each time the spring 91 engages its back contact, an impulse is transmitted over the circuit extending from ground G? through the back contact of the spring 91, contact 126 of the relay 48, vertical magnet 41) and side sw itch wiper it in multiple with the relay -19 to the battery lead 90. The vertical magnet 40 receives two impulses over this circuit and operates to raise the switch shaft two steps. This operation of the switch shaft results in raising the wipers above the level of the bank contacts, as it has been assumed that the calling subscriber is not calling another subscriber in his own branch office. The slow acting relay 49 is energized by the first impulse transmitted through it and remains in its operated position until after the last impulse is delivered for the digit. In its operated position the relay 49, by shifting the spring 127 out of engagement. with its back contact and into engagement with its front contact, opens one side of the talking circuit through the repeater and short-circuits the upper winding of the relays 112 and 34:, so as to remove their resistance from the circuit of the line, relay of the selector I while impulses are being transmitted throughit. The closure of the contact 129 by the relay 49 completes an energizing circuit for the escapement magnet 45. Upon the breaking of this latter circuit, when the relay 19 deenergizes after the last impulse for the digit is delivered from the substation, the escapementmagcuits.

net 15 tie-energizes and permits the side switch wiper H to pass from first to second position. The two impulses which are transmitted to the line relay 109 of the first selector 1 by the relay 3" of the repeater L cause two lll'lPHlSUS to be transmitted through the vertical magnet 51 oi the selector in series with the slow acting private magnet relay U3, whereby the wipers of the said switch are lifted two steps. The private magnet relay (33, in its energized position, closes the circuit of the private magnet (30, which, after the last impulse for the digit is transmitted, denergizes and permits the side switch to pass to second position. The rotary magnet 55 thereupon begins to operate in a well-known manner and rotates the wipers 51, 52 and 53 onto the contacts of a trunk line leading to an idle second selector J, after which the side switch passes to third. position and through the medium of its wipers 56 and 59 completes the connection between the calling line and said second selector over the heavy conductors shown in the drawings.

The substation calling device is now operated for the second digit 2, whereby the repeater L is caused to operate in the same manner as for the previous digit to repeat two impulses to the second selector J which latter operates in the same manner as explained for the first selector 1' to extend connection to an idle third selector K. Since the side switch wiper H of the repeater L is in second position when the second digit is called, its rotary magnet 4-1, instead of the vertical magnet 40, is operated, which operation merely rotates the shaft of the repeater without carrying the wipers onto any cir- The escapement magnet is operated in the same manner as for the previous digit and causes the side switch wiper 4+1 to pass to third position after the last impulse is delivered. In third position the side switch wiper 44 connects the switching relay 4? with the battery lead 90. This, however, does not affect the relay 47, since its other terminal is connected to the wiper 39 and therefore terminates in an open circuit, the wiper 39 being now in the second level and out of engagement with its bank contact. When the substation calling device is operated for the third digit 2, the repeater L operates to repeat the two impulses to the third selector K, which operates in the same mannor as the previous selectors to extend the connection over the conductors 133 and 134 to an idle connector F, whereupon the line relay 136 of said connector becomes energized and closes a circuit through the slow acting release relay 137. \Vhen the substation calling device is operated for the fourth digit 2, the repeater line relay 33 operates to momentarily interrupt the circuit of the connector line relay 136 twice, whereby two impulses are transmitted through the vertical magnet 67 in series with the slow acting private magnet relay 138. The vertical magnet operates in response to these im pulses to raise the switch shaft two steps, while the relay 138 operates in the usual manner to cause the private magnet 69 to release the side switch from first to second position after the last impulse for the digit is delivered to the vertical magnet. Upon the operation of the substation calling device for the last digit 0, ten impulses are re peated by the repeater relay 33 to the connector line relay 136. Since the side switch of the connector is now in second position, the operation of the connector line relay 136 for this digit causes ten impulses to be transmitted through the rotary magnet 68 and res lay 138. The rotary magnet 68 operates in response to these impulses to rotate the wipers 64, 65 and 66 onto the contacts of the called line, after which, if said line is idle, the side switch passes to third position. It the called line is busy, the side switch is locked in second position and the calling subscriber is given a busy signal from the busy signaling device Q. in the well-known manner. It will be assumed that the called line is idle and that the side switch passes to third position. The engagement of the side switch wiper 140 with its third-position contact point extends a guardingpotential from ground G through said side switch wiper and shaft wiper 66 to the connector private bank contacts of the called line and completes an energizing circuit for the cut-off winding 141 of the called subscribers individual switch E The winding 141, upon energizing, is not strong enough to attract the plunger arm 142 from its normal position, but attracts the cut-off armature 143, whereby the switch is disconnected from the line and the contact 144 in the talking circuit is closed. The side switch wiper 145, upon passing to third position, completes a circuit for the ringing relay 71, which circuit extends from ground G9 through the interrupter 146, relay 71, back contact of the spring 147 of the relay 148 and through the side switch wiper 145 to the battery lead 115. The relay 71, upon energizing, disconnects the calling line from the called line and connects the ringing current generator 0 With the latter to signal the called subscriber. Since the circuit of the relay 71 includes the interrupter 146, said relay is energized only intermittently so as not to ring the called subscriber continuously. When the called subscriber removes his receiver from the switch ho0k,or assoon thereafter as the relay 71 denergizes, if it is energized at the time, the called substation is provided with talking current which flows over a circuit extending from ground G8 at the connector switch through the said .switch wiper 140,

1 ,aoaaea the lower winding of the back-bridge relay 14$ ringing relay springs 150, side switch wiper 151, shaft wiper 65, thence over the line circuit to and through the substation T back over the other side of the line, through the contact 144 at the switch E connector wiper 64, ringing relay springs 153, contact 254, upper winding of the relay 149 and side switch wiper 145 to the battery lead 115. The relay 1451, upon energizing, closes a circuit extending from ground G through the side switch wiper 140, reversing relay 148 and the contact 154 to the battery lead 115. The relay 148, upon energizing, by shifting the spring 147 out of engagement with its back contact and into engagement with its from contact, interrupts the circuit of the ringing relay 71 and forms a locking circuit for itself. The shifting of the springs 155 and 156 out of engagement with their back contacts and into engagement with their "front contacts transposes the connections be tween the windings of the line relay 136 and the trunk conductors 133 and 134, whereby the direction of current flowing in said conductors and in the bridge comprising the upper windings of the relays 34 and 112 at the repeater L is reversed. The reversal of current in the upper windin of the relay 34 causes said relay to assist t 1e lower winding of the same and said relay is operatively en ergized. The relay 34, upon operating, reverses the current in the calling line, whereby the left-hand winding of the subscribers meter magnet 27 is caused to assist the righthand winding and said magnet is operatively energized to advance the meter 26 one step to register the call. Upon the energiza' tion of the magnet 27, the contact 157 is closed, whereby the left-hand winding of said magnet is short-circuited and the magnet is thereafter maintained in its operated position by the right-hand winding alone.

Upon the completion of the conversation the entire connection is automatically released by the hanging up of the receiver at the calling substation. When said receiver is hung up, the circuit of the repeater line relay 33 is permanently broken. The opening of the contact 111 by the de'nergization of the relay 33 at this time permanently breaks the circuit of the connector line relay 136. The relay 136, upon deenergizing, breaks the circuit of the release relay 137, as well as the holding circuits of the release relays 160, 161 and 116 of the selectors K, J and I, the circuits of which relays are maintained closed solely by the connector line relay 136 after the side switch Wiper 162 passes to third position. The relays 137, 160, 161 and 116, upon denergizing, close the circuits of their respective release magnets 70, 163, 164 and 61, which, upon energizing, im mediately restore their switch shafts and side switches to normal position and. the circuits of the release magnets are finally broken at the oft-normal contacts when the switch shafts reach their lowest positions. At the repeater L a further result of the decnergization of the line relay 33 is the break ing of the circuit of the relay 48, which, upon deenergizin breaks the circuit of the relay 118, holding winding of the switch E and windings 99 and 107 of the switch H (Fig. 4). The relay 118, upon deenergizing, closes the circuit of the release magnet 46, which circuit extends from ground G through the back contact of the spring 166,

off-normal contact 167 and release magnet 46 to the battery lead 90. The magnet 46, upon energizing, restores the shaft and side switch of the repeater to normal position, and when the shaft reaches its lowest position it opens the circuit of the magnet 40 at the contact 167. The breaking of the holding circuits of the switches l and H permits said switches to be restored to normal position and all the apparatus employed in the connection is left in readiness for another call.

It will now be explained how a subscriber of the branch ofiice may obtain connection with another subscriber of his own branch office withont monopolizing the trunks leading to the main office. For instance, it will be assumed that the subscriber at the substation T (whose number is 11110) desires to call subscriber N 0. 11220, who, it will be assumed, is connected to the same branch oflice. Upon the removal of the receiver at the calling substation, the switch E, the repeater L and the switch H operate in the same manner as heretofore described to connect the calling line with an idle first selector I in the main oflice. The calling subscriber now operates his calling device for the first digit 1, whereby the first selector in the main oflice is operated to extend connection to an idle second selector connected to its first level in the usual manner, and the wipers of the repeater L are raised one step, which, in the case assumed, brings said wipers to a position opposite their respective rows or levels of contacts. The side switch wiper 44 of the repeater L passes to second position in the usual manner after this first digit is called. The calling subscriber now operates his calling device for the second digit 1, whereby the second selector which has been selected in the main ofiice is operated in the usual manner to select an idle trunk line connected to its first level. At the repeater L the impulse for this second digit causes the shaft of said repeater to be rotated a single step, whereupon the wiper 38 engages the contact 168, which is connected to the upper winding of the relay 43. A circuit is thereupon completed from ground G through the upper winding of said relay, contact 168, wiper 38 and the es capement magnet 45. The closure of this circuit energizes the relay 43 and provides a locking circuit for the escapement magnet 45 to prevent said magnet from detinergizing and permitting the side switch to pass from secoinl to third position, when the relay 49 deelnergizes after the last impulse for the second digit is delivered. The closure of the contact 169 of the relay 43 forms a locking circuit for said relay, said circuit extending from ground G at the relay 48 through the springs 92 and 93, contact 170 of the relay 118, contact 169 and the lower winding of the relay 43 to the battery lead 90. The closure of the contact 171 upon the energization of the relay 43 connects ground G with the contacts 173 and 174 in the row which is engaged by the wiper 39. When the subscribers calling device is operated for the third digit 2, the selected third selector in the main otiice will be operated in the usual manner to select an idle trunk line in its second level, which, in the case as sumed, would be a trunk line leading hack to a connector switch in the same exchange as the calling subscriber. At the repeater L, since the side switch did not pass to third position after the second digit was called, the shaft and wipers will be rotatedtwo more steps by the impulses for this third digit 2, whereby the wipers 35, 36, 37. 33 and 39 will be brought into engagement with the contacts 175, 176, 177, 178 and 174, respectively. The engagement of the wiper 37 with the contact 177 completes a. circuit ex tending from ground G at the relay 48 through the springs 92 and 93, contact 170, wiper 37, conductor 242 and winding 179 oi the secondary switch l\l[ to the battery lead 90. Upon the energization of the winding 179, the switch M operates in the same manner as explained for the switch H in the previous connection to extend the connection from the trunk conductors 240 and 241 to an idle connector switch in the branch office which has access to all the subscribers lines whose numbers begin with 112. The engagement of the wiper 39 at the repeater with the contact 174 completes a circuit extending from ground G at the relay 43 (which is locked in its operated position) through the contact 171. contact 174. wiper 39, relay 47 and side switch wiper 44 (which passed to third position after the third digit was called) to the battery lead 90. The relay 47, by shifting the springs 37 and 84 out of engagement with their back contacts and into engagement with their front contacts, disconnects the calling line from the line relay 33 of the repeater L and extends the line connection through the wipers 35 and 36 and contacts 171) and 176 to the trunk conductors 240 and 241, which, as has been explained, are now connected to an idle connector switch which has access to the lines of the desired subscriber. hen the line is disconnected from the line relay ol' the repeater Ii by the relay 47, said line re-- lay deiinergizcs and destroys the energizing circuit for the line relay of the connector to which the connection has been extended by the selectors in the main ottice, whereby said selectors are permitted to release in essen tially the same manner in which the selectors were released by the deenergization of the line relay of the connector F when the subscriber at substation T was called. The breaking of the contact 98 by the energization of the relay 47 at the repeater L de stroys the holding circuit of the secondary switch II (Fig. 1), whereby said switch is released and frees the trunk line leading to the selector 1. It will thus be seen that when the subscriber calls the third digit, not only is all the apparatus in the main ollice released. but also the trunk line leading from the branch otilcc to the main ol'lice. The opcrations of the switches in the main ottice in connection with this call are merely inci' dental and have no direct function in the establishment of the connection. The subscribers line conductors are. new extended from the line switch E through the contacts of the relay -17, thence through the wipers 35 and 36, conductors 240 and 211, secondary switch M and over the trunk conductors 180, 181 and 182 to a connector switch which has access to the line of the desired subscriber. which connector may in all respects be the same as the connector F (Fig. 6). \Vhen connection is extended to this connector its line relay energizes and provides a holding circuit for the switches M and E and for the relays 13 and 118 of the repeater L. Said circuit extends from a ground at the connector which corresponds to ground G (Fig. 6) through the side switch wiper 162, contact 183, thence to the trunk-release conductor, such as the conductor 135 in Fig. 6 or the conductor 182 in F ig. 7, contact 185, thence one branch passes through the windings 179 and 186 of the switch M to battery, While another branch passes back over the conductor 242 to the contact 177 and wiper 37 (Fig. 3), where it again branches, one branch passing back to and through the holding winding 97 of the switch E. while another branch passes through the contact 169 of the relay 43, (which, as before explained, is now energized} and through the lower winding of said relay to the battery lead 90. A third branch of this circuit extends from the Wiper 37 through the contact 170 and winding of the relay 118 to the battery lead 90. This circuit serves to maintain the various relays and magnets included therein in an energized position after their original energizing circuits have been broken by the denergization of the slow acting relay 48 at the repeater L, which occurs shortly alter the circuit of said relay is broken by the drainer-- gizatiou of the repeater line relay 33.

The calling subscriber now operates his calling device for the last two digits of the number of the called subscriber, which causes the selected local connector to establish connection with the desired line in the same manner as explained for the connector F (Fig. (3), when the subscriber at substation T was called. After the conversation is completed, the connection is released. by the hanging up of the receiver at the calling substation in the usual n1anncr-that is, when the receiver is restored to the switch hook, the line relay of the connector switch denergizes and releases the connector in the manner hereinbefore described and lelllth'ts the ground connection from the conductor 182 (Fig. T). This destroys the holding circuits of the switches l\1 and F. and oi tlic relays 43 and 118 of the repeater L. The switches 1W and E are thereupon restored to their normal positions. The relay 13, upon deenergizing, breaks the energizing circuit of the relay -17 of the repeater L. The relay 118, upon denergizing, closes the circuit of the release magnet 46 in a inanner which has previously been described.

whereby the shaft and side switch of said repeater are restored to normal position.

In the seleotorrepeater L there are provided means for giving the calling subscriber a busy signal in case all the trunk lines leading from the secondary switch H to the main exchange are in use when the call is initiated. This means comprises the double-wound relay 112 in the selector-repeater. The upper winding of the relay 112 is bridged across the trunk conductors 3t) and 31 by the closure of the line relay springs 111 when the call is initiated. If any of the trunk lines to which the switch H has access are idle, a connection will be extended to said trunk line and the relay 112 will be energized, as has heretofore been ex plained, and will open the contact 117. It, however, all the trunk lines to which the switch H has access are busy, its master switch N will be operated continuously and the contact 103 will be open. Therefore, the switch H will not be operated when connection is extended to it through the repeater L by the subscribers individual. switch E. This being the case, the relay 112 in the repeater will not be energized. It will thus be seen that as soon as the relay 118 is energized a circuit is closed extending from ground G through the spring 166 and its front Contact springs 117 and the lower winding of the relay 112 to the busy signaling machine Q. The busy signaling current flowing through the lower winding of this relay induces a corresponding current in the upper winding, which, being bridged across the subscribers line, transmits a signal to the calling subscriber.

1n the foregoing description it has been assumed that the selector-repeater is used in a one hundred thousand line system, or a systen'l in which the subscribers numbers comprise fire digits. It has also been assumed that the branch offices have a capacity of less than a. thousand lines. In Fig. 8 there is represented the manner in which the contacts of the selector-repeater F would be connected up in a branch ofiice of four hundred line capacity. Assuming that the wipers normally rest one step below their re spective rows, the branch oflice numbers with the connections as shown would be 111XX, 112XX, 11'4XX and 115XX. The second digit of all these numbers 1, which is indi cated by the fact that the first contact in the. row 0 which is engaged by the wiper 38 is connected to the relay 43. The third digit may be either 1, 2, 4 or 5, which is indicated by the fact that the contacts in the row I) which are connected to the contact 171 of the relay 43 are the first, second, fourth and fifth contacts, which are engaged by the wiper 39 after the wiper 38 leaves the contact in the row 0 which is connected to the winding of the relay 13. If there were only one hundred-group in the branch oflice, only one contact in the row 3) would be connected to the contact 171, and only one set of contacts in the rows. (Z, 6 and f would be connected to a secondary switch M, or, if desired, the conductors leading to the switch M (conductors 240 and 241, Fig. 3) could be permanently connected to the conductors i275 and 276, and the wipers 35 and 36 and contacts c and f entirely dispensed with in this particular case. If there are more than four hundred-groups in the branch oliice, more than four contacts in the row I) would be connected to the contact 171. If the capacity were increased to one thousand lines, ten of the contacts could thus be connected and the connections handled in the same manner as hereinabove described. If an entire thousand numbers be allotted to the branch office, the connections, however, could be taken care of in a much simpler manner. Assuming that a thousand numbers are assigned to the local oflice, it is evident that it is determined whether or not the calling subscriber intends to call back into his own oflice as soon as he calls the second digit. This being the case, the connection could be switched to the local switch as soon as the second digit was called. In this case the connection would be switched to a secondary switch M which has access, not to connector switches, but to selector switches, which would operate in response to the impulses for the third digit in the same manner as the third selectors in the main office to select an idle connector, through which connection could be con'ipletei'l with the desired line. If there were more than one complete thousand numbers in the branch other, a plurality of trunk lines would be connected to the contacts which are engaged by the wipers 35, 36 and 37, and each of these trunks would lead to a switch M which had access to selector switches, which latter in turn had access to different groups of connector switches. In Fig. 9 there are represented the connections of the banks of the selector-repeaters in a branch office to which are assigned four thousand numbers. Since in this case the selector-repeater operates in response to only two digits, there is no need of a wiper corresponding to the wiper 38, or a relay corresponding to the relay 13. In the row I) which is engaged by the wiper 39 the contacts which correspond to the groups of lilies in the branch otlice are permanently grounded. Therefore, assuming that the wipers in Fig. 9 normally rest one step below their respective rows of contacts. the connections in this figure are arranged for a branch oi lice in which the subscribers numbers are llXXX, l'lXXX, ll-XXX and 15XXX. In this instance it would be necessary for the shaft of the selector-repeater to have only ten rotary steps. This arrangement of the selector-repeater is also adapted for branch ofiices of one thousand lines, or smaller capacity, in a ten thousand line system. In such a system the connections, as shown in Fig. 9, would be suitable for an oflice to which were allotted the numbers llXX, 12XX, 14XX and loXX.

In case all the numbers which begin with any certain digit are allotted to one branch oilice. then the. switching repeater should be arranged to switch to the local switch only when one digit is called, and the secondary switches M would have access to selector switches which could perform the function of second selectors in an ordinary system. The selector-repeater may be arranged to switch on the first digit by giving the switch shaft rotary motion only and giving the side switch Wiper 44 only two positions, the contacts of which wiper would be connected in the same manner as the contacts for the second and third'positions of the wiper H in Fig. 3. The vertical magnet would be dispensed with and there would be no need for contact in the side switch wiper corresponding to the first position contact point of the wiper 44 (Fig. In Fig. 10 there is represented the connections of the contacts of a selector-repeater arranged for use in a branch office to which are allotted the numbers IXXXX and :ZXXXX in a one-hundred thousand line system, or num bers lXXX and QXXX in a ten-thousand line system.

It will be seen that the switching relay -17 in the repeater L is placed in front of the line relay, as Well as in front of the condensers 2s and :20. it is thus seen that not only are the two impedance bridges 01' the repeater excluded from the local connections, but there is also a coiuluctively continuous circuit from the calling line through the ondary switch M to whatever additional s itclu-sv are employed in the local connections. This exclusion of the repeater from the local connections has especial advantage in case party lines are used in the system. Although in the system shown herein the act of signaling the called subscriber is accomplished automatically without the control of the calling subscriber after connection is completed between two lines, with most methods of signaling back on the call ing line, in case of a reverting call on a party line, the application of the ringing current to the line must be ci'mtrollcd by the calling subscriber. This control may be acromliilishcd much more simply if no con densers are included in the line between the substation and the signaling apparatus than it condensers are included. To illustrate this feature of the invention, we have shown in Fig. 11 a so-called ring-back device for use in signaling called subscribers in reverting calls on party lines. One or more of these ringback devices may be placed in the branch otiice and made accessible through secondary switches M which are connected to some particular contacts in the switching repeaters L. Each partydine subscriber would then :be informed that in order to call any other subscriber on his own line he must call a special number corresponding to the contact in the repeaters L to which the secondary switches M, which have access to the ring-back devices, are connected. The ring-back device shown in Fig. 11 is similar to that shown and described in British patent to S. G. S. Dicker No. 1423 of 1910, and comprises essentially a pair of wipers 201 and 202 carried upon a rotary shaft (not shown) which is adapted to be rotated step by step by a driving magnet 211 and released to normal position by a release magnet 225. The wipers 201 and 202 are adapted to contact with a plurality of pairs of stationary contacts which form the terminals of a plurality of ringing current generators O, 0 each of which is adapted to produce ringing current of a proper character for operating the ringer of some one substation on each of the party lines. The ring-back device is also provided with a two-position auxiliary or side switch comprising the wipers 203, 204 and 214, and which is controlled by an escapement magnet 218 in the same manner in which the private magnets of the selector and connector switches control their side switches. In order to call a substation on his own line, a calling subscriber, after removing his re ceiver, first operates his calling device lolthe proper digits to cause the selector-repeater to extend connection through one o l' the secondary switches M to one of these ring-back devices in the same manner in which connection is extended to a. connector switch by the secondary switch M (Fig. 7 in the connection heretofore ex jdained. When the connection is extended to the ringback device, its line relays 210 and 209 become energized in the same manner in which the line relay of the connector is energized when connection is extended to it. The relay 210, upon energizing, closes the circuit of the relay 217, which in turn connects ground to the holding trunk 255 to furnish a holding circuit for the preceding apparatus in the connection. The calling subscriber must now operate his calling device for one more digit to cause the wipers 201 and 202 to be brought into contact with the proper generator for ringing the station desired. The relays 210 and 200 respond in the usual manner to the operation of the calling device for this digit, the relay 210 operating to transmit one or more impulses over the circuit extending from ground Gr through the contacts 262 and 264, relay 212, stepping magnet 211 and the side switch wiper 201 to the battery lead 90. The magnet 211 operates in response to these impulses to move the wipers 201 and 202 onto the desired contacts, while the relay 212 operates in a wellknown manner to cause the escapement magnet 213 to advance the side switch to its second position after the last impulse for the digit is transmitted. In passing from first to second position the side switch wiper 203 cuts off the line relay 210 and substitutes therefor the relay 218, which operates to maintain the circuit of the relay 217 closed. In order to cause the selected ringing current generator to be connected. with the line, the calling subscriber depresses a button at his telephone, such as the button 265 (Fig. 3), for example. The depression of this button inserts an additional resistance in the line circuit, whereby the current in the line is reduced sufficiently to cause the relay 209 (Fig. 11) to allow its armature to drop back, while the relay 218 remains in its energized position. The relay 209, upon deenergizing, completes a circuit extending from ground Gr through the interrupter 220, contact 272, ringing relay 219 and the side switch wiper 204 to the battery lead 90. The relay 219 is intermittently energized over this circuit and in its energized position operates to disconnect the relay 209 from the line to substitute therefor a connection to ground through the resistance 221 to maintain the circuit of the relay 218, and also connects the selected ringing current generator with the calling line. Ringing current will continue to be periodically supplied to said line until either the calling subscriber releases his ringing button, or until the called subscriber answers, in either of which cases the relay 20!) will again be supplied with suiticient current to be operatively energized to break the circuit of the ringing relay. l/Vhen both; subscribers hang nip their receivers after the conversation is completed, both the relays 218 and 209 deenergize. The relay 218, upon deenergizing, breaks the circuit of the relay 217, which in turn, upon deiinergizin g, closes the circuit of the release magnet 225. This circuit extends from ground G through the contact 262 of the relay 210, contact 279, magnet 225 and the contact 224 to the battery lead 90. The magnet 225, upon energizing, immediately re stores the wipers 201 and 202 to normal position, whereupon the shaft-controlled contact 224 is opened and the magnet 225 permitted to dei nergizc. The apparatus through which connection is extended to the ring-back device released in the manner heretofore explained when the holding ground is removed from the conductor 255 by the relay 217.

In the above description it is seen that in order to cause the ringing current to be applied to the line the calling subscriber must in some manner decrease the current flowing in the relay 209 of the ring-back device. If there are no condensers between the calling line and said device, as in the present case, this may be done by simply inserting a resistance in the line at the substation, as has been explained, while if the condensers of the repeater were included in this connection additional means would have to be supplied by which this control of the ring-back device could be accomplished.

It will thus be seen that we have devised a very eflicient arrangement for district telephone systems. That as soon as it is determined by a process of elimination that the called subscriber is in the same branch office as the calling subscriber, then the connection which has heretofore been established to the main office is released and the connection completed over connections local to the branch oflice. In other words, the connec tion is first extended over two parallel paths and then at a certain point, when it has been determined that the connection is a local connection, one path is cut oil and the connection completed over the other path.

\Vhile We have illustrated and described our invention in connection with an automatic telephone system of a particular type, it will be understood that in its broader as pect our invention is capable of use with other automatic systems, or in semi-automatic systemsthat is, systems in which a manual operator is employed for setting up certain parts of a connection. Various modifications in the repeater which: is ems ployed to repeat the impulses from the branch to the main oliice will likewise readily suggest themselves to those skilled in the art but come within the scope of our invention.

What we claim as our invention is 1. In a telephone system, a plurality of branch exchanges, subscribers lines connectcd with said branch exchanges, means for establishing a connection between two of said subscribers lines, said means including a trunk line having a terminal in a branch exchange, a branch for said trunk extending toward the main exchange, a local branch for said trunk normally disconnected therefrom, and means for connecting the local branch when a call is made by a sub scriber in the same branch exchange, and for disconnecting the main branch during talking.

2. In a telephone system, subscribers lines divided into groups, a trunk having a sin gle terminal at one end thereof, a branch normally connected to said teri'ninal and extending toward a plurality of said groups. a second branch normally disconnected from said trunk and extending toward other of said groups, and means for disconnecting said normally connected branch and connecting said other branch when it is desired to extend a connection to the particular groups to which said other branch is connected.

3. In a telephone system, a switch, a plurality of trunks leading therefrom, an automatic means associated with said switch for automatically switching a connection from a given trunk to another, automatic apparatus associated with said given trunk, and means in said switch for initiating a release of said automatic apparatus.

4. In a telephone system, main and branch exchanges, subscribers lines connected to said branch exchanges, trunking apparatus at said exchanges, means whereby a sub scriber in making a call operates said apparatus to first determine the main exchange and then the branch exchange with which the desired called subscribers line is connected, a trunk leading to the trunking apparatus in one exchange, a second trunk leading to the trunking apparatus in another exchangc, and means at one of the exchanges for initiating and causing a release of the trunking apparatus in the other ex change when the trunking operations have reached a stage of eliminating said exchange, which trunking apparatus was brought into use over said trunk.

5. In a telephone system, main and branch exchanges, subscribers lines connected with said branch exchanges, trunking apparatus at said exchanges, means whereb a subscriber in making a call operates said apparatus to first determine the main exchange and then the branch exchange. with which the desired 'alled subscriber is connected, a trunk at a branch exchange leading to the trunking apparatus at a main exchange, a second trunk in the same branch exchange leading to trunking apparatus in that exchange and normally t lisconnected' from said trunking apparatus, means whereby a subscriber at said branch exchange, when initiating a call, first extends a connection over the trunk extending to said main exchange, and means for then breaking said connection and extending the connection over said local trunk when it is determined that the call is for a subscriber in the same branch exchange.

6. In a telephone system, main and branch exchanges, subscribers lines connected with said branch exchanges, trunking apparatus at said exchanges, means whereby a sub scribcr in making a all operates said ap paratns to first determine the main exchange and then the bench exchange with which the desired called subscriber is connected, a trunk at a branch exchange leading to the trunking apparatus at a main exclu'inge, a second trunk in the same branch exchange leading to trunking apparatus in that exchange and normally disconnected from said trunking apparatus, means whereby a subscriber at said branch exchange, when initiating a call, first extends a connection over the trunk extending to said main exchange, means for then breaking said connection and extending the connection over said local trunk when it is determined that the call is for a subscriber in the same branch ex change, and means for releasing the switching apparatus at the main exchange when the connection is shifted to the local trunk.

T. In a telephone system, a trunk line having a single terminal at one end thereof and a pair of branches, one normally connected with said terminal and the other normally disconnected therefrom, a repeating mechanism in said normally connected branch, means controlled by said repeating mechanism for repeating impulses received over said terminal, and means controlled by said repeater for disconnecting said normally connected branch from said terminal and connecting said normally disconnected branch thereto when a particular sequence of impulses is received by said repeater.

8. In a telephone system, a trunk line having a single terminal at one end thereof and a pair of branches, one normally connected with said terminal and the other normally disconnected therefrom, switching mechanism associated with said trunk, a pair of line wipers and a pilot wiper for said switching mechanism, means for transmitting a plurality of series of impulses over said trunk to operate said mechanism, and means controlled by said mechanism when said pilot wiper has been moved in response to certain combinations of il'npulses to shift the connection of said terminal to the normally disconnected branch ot the trunk.

ll. In a telephone system, a trunk line having a single terminal at one end thereof and a pair of branches, one normally connected with said teiniinal and the other normally disconnected therefrom, a repeats ing mechanism in said trunk, said repeating mechanism including line and pilot wipers, means for operating said repeating meehanism by impulses received over said trunk to move said wipers, means controlled by said repeater for repeating in'ipulses over one branch of the trunk, and n'ieans controlled by said pilot wiper, when it has been moved in response to a certain sequence of impulses, to switch the connections from said trunk tern'linal to the normally discon ncctcd branch 01" the trunk.

10. In a telephone system, trunk lines having a single terminal at one end thereof and, a pair of branches, one normally connected with said terminal and the other nor mally disconnected therefrom, a switching meclmnism in said trunk, line and pilot wipers controlled by said mechanism, bank contacts with which said wipers are adapted to engage, a relay operatively connected with certain of the contacts in the bank engaged by said pilot wiper, means for energizing said relay when said pilot wiper comes in contact with said contacts, means operated by the energization of said relay for shifting the connection of said trunk terminal to the normally disconnected branch, of the trunk, and means controlled by said switching mechanism for repeating the impulses, received over said trunk terminal, over the normally connected branch of the trunk.

11. In a telephone system, a main exchange, a branch exchange, subscribers lines terminating at said branch exchange, a trunk line having a terminal adapted to be connected with said subscribers lines and provided with two branches, one extending toward the main exchange and the other extending toward switching mechanism in said branch exchange, impulse-transmitting devices on said subscribers lines, a repeater in said trunk for repeating impulses over said trunk toward the main exchange, said repeater including a pair of line wipers and a pilot wiper, means for transmitting a plurality of series of impulses over said trunk to operate said repeater, and means controlled by said repeater when said pilot wiper has been moved in respon% to cer-- tain combinations of impulses to shift the connections of said trunk terminal from the branch extending toward the main exchange.

152. In a telephone system, a main exchange, a branch exchange, subscribers lines

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