US1545064A

US1545064A - Telephone system

Info

Publication number: US1545064A
Application number: US268116A
Authority: US
Inventors: Winfred T Powell
Original assignee: STROMBERG CARLSON TELEPHONE
Current assignee: STROMBERG CARLSON TELEPHONE; STROMBERGCARLSON TELEPHONE MANUFACTURING Co
Priority date: 1918-12-23
Filing date: 1918-12-23
Publication date: 1925-07-07
Anticipated expiration: 1942-07-07

Description

TELEPHONE SYSTEM INVENTOR Wl/V DTJPOQELL.

ATTORNEY Patented July 7, 1925.

VTINIGR-ED T. POl/VELL, OF RQCHESTER, NEW YQRK, ASSIGNORITO TI-IQE'STROMBERG- CARLSON TELEPHONE MANUFACTURING 'GOE'LEAJBTY.

A COJR/POR'A'I'ION.O33 NEW YORK.

To all whom itmay concern:

Be it knownthat I, lVINFnnD T. POWELL, acitiz'en of the United States, residing in Rochester in the county of Monroe and State of New Yorlnhave invented certain new and useful Improvements in Telephone Systems, of which :the. following is a full, clear, 7 concise, and. exact description.

This invention. relates to telephone exchange systems, and more particularly to systemsin which automatic switches are used in establishing connections-either wholly or inparts In suchsystems of the art with which I am acquainted, troubles have been encountered duetotheznecessity for marginal adjustments, particularly where dependence 1s placed upon the relative speed with which associated relaysrelease their armatures.

Also in other systemswherein these troubles are eliminated by .the use of a third conductoror ground conuectionat the substation sending.device,:the sending device is necessarily complicated in structure,thereby r being made expensive to manufacture and to maintain. Also in such systems, there have been other difliculties which by my 1mproved-i construction are obviated.

A principal object of my invention is to.

provide means whereby witha very simple form of substation sendingdevice, the cen tral'oi'lice switching mechanism may be operated under the controlof-the substation apparatus, includingthe-sending device, to

connect the line of the calling subscriber with that of the. called subscriber with a;

minimumof apparatus operating in a most positive way.

- It is another objectto accomplish this in a systen'rusing a third 01' groundconnection at the subscribers instrument withoutcom-.

the time in an idle orunused condition; and. l have furthermoreprovidedmeans to pre 'OE BOCI-IEETER, NEVI YORK,

TELEPHONE SYSTEM.

Application filed December 23, 193.8. Serial No. 268.116.

vent the extension of the calling line to a V busy one of said switching mechanisms, common to the. group of subscribers; and I furthermore provide means whereby when such an extension is made, other calling lines may not make connection with the selected switch mechanism.

restored to'normal, by the mere opening of the subscribefls line circuit caused by the replacing of the callingsubscribers receiver upon his switchhook, no use being made of the ground connection above referred to, to cause this release, the release being accomplished something after the manner of release us {1 in the so-called 2 wire automatic systems althoughinmy improved system the release is accomplished without any dependence upon the relative speed of fast and slow relays? An improved busy test circuit is also provided w1ll be seen'from the descriptlon whichifollows, in whichother objects of my invention willvbe made apparent.

Referring to the drawing accompanying this specification, at A and B. I show two substation instruments connected to telephonev lines extending fromthe substations to an exchange. At the exchange I show line switches, one for eachof the said substations L and L respectively.

In this description it will be assumed that the substation A is the calling substation, and the substation B isthecalled substation. Intermediate of the two line switches is shown. a connector switch G N which is one of a group of connector switches, common to a large group of telephone lines, and which may beseized by any calling line, such as the line having the substation A, and under the control of the substation apparatus at A to All extend a talking connection to the line of a called subscriber, such as the line having the substation B.

The substation apparatus consists of the usual talking units, such as the transmitter 2, receiver 1*, induction coil 2' and condenser k; and in addition has a sending device consisting, for instance, of the usual impulse contacts 00 and ca. Contacts 00 when the sending dial is operated, are rapidly operated to open the line circuit a given number of times. In the operation of the dial, the contacts at are arranged to be closed in the preliminary forward motion of the dial, and are adapted to be opened when the dial restores to normal, subsequent to the last interruption of the line circuit by the contacts c0; 7

The mechanical structure of such a dial sender is well-known in the art and, there fore, it is not necessary to illustrate the same in detail here, the contacts only being shown for purposes of description.

Associated with the individual line switch mechanism L, are a plurality of active switch wipers Q, R, S, T and REL, these normally resting upon one of a plurality of sets of passive contacts, which sets of passive contacts known as home point contacts are alternately arranged with other sets of passive contacts known as trunk point contacts, each set of trunk point contacts being connected to a separate trunk con nector switching mechanism, such as CN; the home point contacts being provided for the purpose of establishing a plurality of normal or resting positions for the wipers of the line switch L to which they proceed when an established connection is released. Such an arrangement is shown in my prior application, Serial No. 250,617, filed Aug. 19, 1918.

Controlling the movement of these switch wipers is an electromagnetic stepping mech anism ST, comprising an electromagnet 8 and normally made contact 7. Each is adapted to be operated from the central source of current supply BY to drive the wipers step by step and successively over the alternate trunk and home point contacts when a call is initiated, until a set of trunk point contacts is reached which belong to an idle or unused connector switch mecha-' nism. Control over the stepping mechanism ST is exercised by a pair of relays LR and CO, these relays being under the control of the substation apparatus of the calling subscriber, and under certain conditions of use when the line with which they are associated is a called line, a certain measure of control is exercised by a substation apparatus of another line circuit, which in this case would be a calling line circuit, through the controlled actuation of the mechanism of an intermediate connector switch mechanism, 7

such as the connector switch mechanisn'i CN.

The functions of these two relays LR and CO is to control in a local circuit the op eration of the stepping magnet, to control its circuit and to control the extension oi the line conductors of a calling line to a seized connector switch mechanism, such as CN, and under other conditions of: use when the line is a called line to prevent such extension. 7

In passing it may be said that I accomplish this without the use of any interlocking or mechanical connection between the two relays, which mechanical connec tions are a source of trouble due to the diiliculty of maintaining proper alignment of the parts, and due to the weight and inertia of the extra parts required in such prior art structures above referred to.

The passive contacts shown in the drawing to the right of the line switch wipers of the line switch L, are preferably arranged in vertical sets, there being in this embodiment of my invention twice as many sets of passive contacts as there are trunk connections available to the calling line. In the drawing the switch wipers are resting upon the first set of contacts and the four sets of contacts are illustrated therein. However, in practice the wipers would usually be adapted to engage many more than four sets of passive contacts, twenty or more sets being usually provided, and instead of the contacts in a given row adapted to be engaged by a given line switch wiper being shown in a straight vertical row, they usually are arranged in the arc of a circle which may be, if desired, a complete circun'iference, or by subdividing the switch wipers each by equivalent means known in the art only an arc of the circumference need be used, in which case the arrangement is such that the conductor leading to a given switch wiper is extended always to one of the said sets of passive contacts. Such a switch structure is shown, "for intance. in the British patent to Fairweather, No. 7998 of 1906.

Although my invention is by no means limited to such switch structures, 1 have chosen to illustrate the same herein in con ncction with a connector switch mechanism wherein called line terminals are arranged in horizontal rows, one above the other, the switch wipers by means of which connection is extended through the connector switch to a called line being moved upwardly step by step under the control of a first series of circuit interruptions oi the calling line circuit, and then subsequently moved in a horizontal direction under the control oi a second series ot'circuit interruptions until the terminals of the called-for line are reached, release of the switch being accomplished by the energizationof a-rele'asemagnet provided therefor.

ln'connection with this switch mechanism, a side switch is provided having a plurality of active switch contacts and four sets of passive contacts adapted-to be successively engaged by the active switch contacts, the shifting or change-over from one set of passive contacts to the next succeeding set being accomplished tollowinga given-series of line circuit interruptions underthe control of the calling subscriber's dial, a deenergizationot an escape magnet so-called, controlling the side switch wipers to escape from a preceding position to the next succeeding position whereby certain controlling circuits of the connector switch are'shi'tted This side switchthough it may be of various constructions, in this embodiment illustrated and indicated to represent such a switch is spring propelled by a spring inclividual to the side switch and restored when the main switch is restored against the power of its individual spring, by virtue of the power of a stronger spring, provided for the purpose of restoring the main connector switch mechanism. The escape magnet is shown at ESQ and theside switcn wipers are shown at 11, 12,13, 14: and 15, the mechanical structure being wellunderstooth'is not specifically illustrated. The connector switchhas a movable carriage adapted to, be operated in a step by step manner, first in a vertical and then in a. horizontal direction, as above mentioned, this carriage carrying three connector switch-wipers l6, l7 and 18. To the right of these wipers inthe drawing are terminals of one ,Oii a large number of lines,.these terminals being called, terminals and are indicated at 19, 20 and 21. Other setsoi" terminals forother lines would of course be provided in a complete switch structure, only oneset being required for the purposes o'l tlns description; this set being the set associated with the .line switch L which is individual to the called line having a substation B.

.i. ssociated with the connector switch mechanism (N are a pair of actuating magnets, the first PM being adapted to littthe Likewise associated with the connector.

lays AB. BX. and XYQhave two windings,

tandem wound, with respect to each other.

other, so that when both are energized by :the simultaneousflow ofcurrent through them, their resultant energizationequal in strength and opposite in their effect onthe relay core, will causea resultant effect upon the said relay core equal to no energization, but when either-one O'l-tlIO-WlHCl-IH 'S- are enline.

ergized-the armatures-of the relay will be attracted. Such a relay is known in the art as a differential relay, and will be so in order called.

The; relays CX, AX,'K and BX are adapted to be included in circuit with the sul scribe'r s telephone and the central ollice source otcurrent, the flow of current through their windings is adapted to be-directly in circuit with the calling telephone Under certain conditions ofuse and at certain periods of use, however, the relay BX is operated by current through one of its windings, which current flows in a circuit local to the connector switch.

Certain switch mechanismcontrolled contacts known as off-normalcontacts are shownat ON, these contacts being adapted to be operated when the swit'cii mechanism is moved from its normal position. All of the apparatus in the drawing is shown in its normal or tin-operated position.

To enable a better understanding of the inventionto be secured, a description of the operation of the same will now be had reference being madeto the drawing, andunder the assumption that thesubstation calling is the substation A and that the substation alled is the substation l3, and the first encountered terminals ot' a connector switch mechanism, common to the telephone lines and which is therefore used to extend the connection between the calling-and called lines, isthe connector switch mechanism CN.

Thesubscriber at substation A, upon re vmoving his receiver 1", closes-an energizing circuit for the line relay LR o1. theline switch L'as follows: ground at (hwinding of line relay LR; home point contact and wiper T, normally closed contact 5 otthe cut oil relay CO, line conductor T, impulse springs c0 of the substation, transmitter, hook, switch'contact 7t, primary induction coil i,.lineconductor R, normally closed contact t of the cuto'll relay CO, wiper and home point contact R,-resistance coil RES, to the source (it current BY.

The line relay LR operates and closes the following circuit: ground G, contact 22 of relay LB, home point contact and wiper ,EEL, winding 10 of relay CO to battery.

Contact 22 also extends this ground G by way of theQ; wiper to the multiple test terminal'31 appearing before all connectors,

such as CN, in the group having access to this line. This causes the calling line switch L to test busy to incoming calls as soon as the line relay operates.

Relay CO operates when the above traced circuit through its winding is closed and opens the normally made contacts 2, 4i, 5 and closes the normally open contact 3. Contacts .4 and 5 open the above traced circuit of the line relay LR, but a shunt circuit around these contacts 4 and 5 had previously been closed at contacts 23 and 2% when the relay LR operated. Thus the relay LR will be held up from the closed circuit of the substation A over this substitute path which is independent of the cut off relay CO.

Relay CC also opens contact 2, which does nothing at this time, and closes contact 3, which closes a circuit for the stepping magnet ST as follows: ground G, contact of relay LR, home point contact and wiper S, contact 3 01" relay CO, contact 7 of stepping magnet ST, winding 8 of magnet ST to battery. The magnet ST energizes, opens its own circuit at contact 7 and then the armature is retracted by spring power in the well-known way. Upon release of the armature of magnet ST, the wipers Q, R, T, REL, S are driven one step, i. e. from the first set of home point contacts to the first set of trunk point contacts.

Assumingthis first trunk to be busy because some other line switch is using it, then there will be a ground on the test terminal 26, which is mnltipled before this calling line switch L, and others in thesame group. The ground would be placed there from GA, contact 2 of relay C0 of the line switch, similar to L, which is holding the trunk busy. Now when the testing line switch wiper S contacts with this grounded terminal 26, ground will flow from the terminal 26, wiper S, contact 3 of relay CO, divide and flow by one path through winding 9 of relay CO, which keeps relay CO energized while the wipers are resting on the busy trunk, so that the connection holding this trunk will not be disturbed. The other path may be traced by way of contact 7 and winding 8 of stepping magnet ST to battery.

This circuit causes the stepping magnet CT to again operate and release, advancing the wipers Q, R, T, REL, S to the next point which is a home point. Here the first traced circuit from contact 25 ofrelay LR again causes the switch to step and also keeps the relay CO energized.

Assuming the next trunk to be idle, then there will be no ground on point 27 and relay CO will release, place a busy ground GA, contact 2 and wiper S on the test terminal 27 of this trunk so that other line switches similar to L will not stop here. Contacts i and 5 of relay CO also close and extend the line conductor R by way of wiper R to trunk RC and conductor T by way of wiper T to trunk TC leading to the connector CN.

The line relay LR remains energized after the connector CH has been seized because of the following circuit: ground G, winding of relay LR, contact 23 of relay LR, line conductor T, substation set A, line eonductor R, contact 4 of relay CO, wiper R, trunk wire RC, winding 28 of relay CX, contact 30 of relay BX, winding of relay K to battery.

Referring back to the point where ground was placed on the connector terminal 31 to cause the calling line to test busy to incoming calls. This ground was from G, contact 22 of relay LR and home point contacts of wipers REL and Q, which ground is disconnected from terminal 31 when the wipers are on trunk point contacts. However, wiper Q, when leaving its home points makes contact with terminals which are connected to ground GB at all trunk points, maintaining the busy potential on terminal 31 constantly during the time that line switch L is in use.

Condenser 6 connected between contact 7 of magnet ST and ground is the usual spark 'quencher for contact 7.

The circuit has now been traced up to the point where the closed circuit from substation A is extended to trunk wires RC and TC of connector CN. This closed circuit causes relays K and AX to operate and is traced as follows: ground GC, contact 32 of relay BX, contact 33 of AX, winding of vAX, winding 29 of relay CX, trunk TC,

closed circuit of substation A, trunk RC, winding 28 of relay CX, contact 30 of relay BX, winding of relay K to battery.

CX is a dilierential relay and will not pull up when an equal amount of current flows through both windings but at this time it will pull up because of the unbalanced circuit caused by relay LR being legged off the TC trunk to ground. This is of no consequence at this time. Contact 34 being closed energizes the escape magnet ESC, but, as is well known, switches of this type keep the side switch wipers mechanically locked in normal position until the switch shafts step away from normal. The other contact 36 of relay CX closes a circuit from ground GC, winding 38 of relay BX, contact 36 of relay CX, resistance coil RS to battery.

This causes relay BX to operate and prepare the circuit to the primary magnet PM, by way ofcontact 40 but because AX is at this time operated, battery for operating PM is open at contacts 33. In case relay CX pulls up before relay AX, when the connector CN is seized, the magnet PM will not be prematurely operated because BX canee-nose This ground is also transmitter 25, hook contact 72. and primary induction coil dand is heldthere as lon as the calling-device is-away from itsnormal position. The ground on the T-line conductor is interrupted by springs as the calling device returns, the number of interruptions corresponding turned.

As the calling device is pulled forward, relay LR of line switch L releases because coming from GD, contact ca,- contact- 00, lineT andcontact23. Relay LR can not again energizeduring this connect-ion because it is open both at contact 23 and at wiper T of the line switch L. Ground GD, contacts ca and cc of substation-A also flows overline conductor T, through line switch cut oil relay (CO) springs 5, Wiper T, trunlrlG, winding 29 of relay OX, winding of'AX, contact-36 or relay CX, resistance tothe numberit-is short circuited by a ground being on] both sides, one-,shown at (land the'othen coilRS to battery. This holds AX as lon as contact 00' at substation remains closed,

but as the calling device returns, contact- 00 will be niterinittentlyopened-and closed.

Each time contact 00' opens, the circuit to relay AX is broken and 1t releases.

As stated above,relay-BX was energized when both OX and AX operated and 1t,-to gether with CX and K are" held energized over the fol-lowing circuit:

when thecall ingdevice is away from norm' alf'ground GD, contact ca, transmitter t, 'switchhook contact 7t, induction coil 2', lineconductor R,

" contact 4: of line switch relay C0, wiper R,

trunk wire RC winding 28 0f connector relay CX, winding 39 of relay BX, windof relay K to battery. lVlien-tl 1e call-- ing device is normal the holding circuit t or these relays BX, CX andKis from ground GS, winding 38 of relay BX, winding or" AX, winding '29 of CK, trunk TC, jline switch 'wiperT, contact 5 of relay 00,- line conductor T. ii-npulse'springs 00, t *ansmitter t, hoolzswitch contact 71., induction-coil 2 line conductor 'R, contact lof relay CO, wiper R, trunkRC, winding 28 ot-relay CX, winding 39 of relay 'BX, windingo1 relay- K to battery.

Thus it will be seenthat when the calling device-is normal, the impedance of the circuitto batteryis equal for each side of R8 to battery.

Ifthe first digit of the called number is will be momentarily separated twice to thereby cause relay AX,- to be momentarily deenergized twice. -Eaclr time relay :AX falls back-it closes the, following circuit to the primary magnet of the connector: ground Glihside switch-wiper 14 and first positionthereof primary magnet PM; contact of relay BX, contact 33 of relay AX, contact 36 of relay OX and resistance coil lhus the primary magnet PM receives two impulses and operates to raise theconnector switch shaft and wipers 16, 1 7 18 two steps .toa position opposite" the second level or row of bank' cont-acts.

After the impulse springs 00 atsubstation' Ainake their last closure,springs-0a open, this happening just betorethe calling device reaches normal. Because the ground GD is taken off the line, relay CX gets an equal amount of current through each winding, causing it to release andopen the circuit of the escape magnet ESQ, which had been previously held'energized from grouncl-G-F,.

contact 3a of relay CX, point one and side switch 15, winding of magnet ESC, resistance coil ES to battery. -This allows the side switch wipers 11, 12, 13, 14-, 15 to move to the second position.

The calling device at substation A may now be operatedin accordancewith the second digit ot'the called number, resulting inthe energiZationof relay as the call' ing devic is pulled forward, because the ground GD short circuitsits winding Relay CX again closes battery tl'irough resistance coil RS and contact 86 to contact tr relay AX, and, asthe calling: device again returns, relay AX is momentarily deenergi'zed eight timesa i'f the second digit in the called line is eight. This time however the circuit of PM is open and SM is closed because side switch wiper 1%! is in position 2, therefore at each 'de'energization of relay AX, the secondary magnet SM operates to advance the wipers 16, ll", 18 to the particular contacts in the level previously selected, which correspond to the numher of the called line. i-ifter the last impulse. is delivered, the relay CX again falls down and opens the circuit-of-the escape magnet ESQ at contact 34 of relay CX. It the called line is idle, the escapeniagnet thereupon deenergizes and allows the side switch wipers 11, 12, 13, 14, to move to the third position. It the called line is busy, theside switch remains in the second posi tion and the calling party is giventhe busy the line, relay AX and winding 38 of relay BX from the T side and WindingSQ of relay BX, in series with relay K.

signal in the following manner: lVhenever a line is busythere is a guarding ground on the test terminal app aring before all con-- nectors which can select said line. This groundv is placed there if the line is busy because of an originating call, as previously" described, by way of wiper Q, If the line is busy because of a terminating call this ground is placed on the test terminal 21 by some connector similar to UN being in the third or fourth position, said ground coming from GG, side switch wiper l3 and test wiper 18. Consequently, when the test wiper 18 of the connector CN which is testing a busy line, contacts with the terminal 21, a ground is extended from said terminal 21, test wiper 18, side switch 13 and second point thereof, contact 41 of relay BT, winding of relay BT, contact 35 of relay CX (when the dial at substation A stops and relay CX releases), second point and arm of side switch 15, winding of escape magnet ESC, resistance coil ES to battery. The escape magnet ESC remains operated and the relay BT operates over the above traced circuit. Relay BT, upon energizing, closes contact 42 before opening contact 41 which opens the operating circuit above traced and. closes a locking circuit to ground at oil normal contacts ON thereby holding the side switch arms 11, 12, 13, 14, 15 in second position and holding relay BT energized until the connection is released. The calling party receives the busy tone over the following circuit: common busy wire BM, contact 43 of relay BT, condenser TK, trunk TC, line conductor T, substation A, line conductor R, trunk conductor RC, condenser RK, winding 44 of relay AB, through. the battery to ground which is the other side of the busy transformer BT. Relay BT also closes contacts 45 and 46 which places a short circuit around both windings of relay CX so it cannot operate and interrupt the circuit of the escape magnet or cause the switch to step around, if the calling party should again turn the dial without first releasing.

If the called line is idle, the side switch wipers 11, 12, 13, 14, 15 will be advanced to the third position as previously described. Side switch wiper 13 places a guarding ground on the test terminal 21 of the called line, said ground also being used to energize the cut off relay CC of the called line switch L2. This circuit is traced from ground GG, side switch wiper 13, connector wiper 18, terminal 21, home point contact and wiper QA of called line switch L2, windving 47 of relay CC to battery. The cut off relay CG operates and disconnectsthe battery bridge from the called line by means of contacts 48 and49.

Ringing is now applied to the called line over the following circuit: common generator GR, common interrupter I, common lamp L, winding of relay TR, third position and arm OfSlClB switch wiper 11, connector wiper l6, terminal19, called line conductor R, 'ringerri, condenser'clc and contact icof the called substation B, line conductor T,

terminal 20, connector wiper 17, third position and arm of side switch 14, ground GE, through the battery and resistance coil RE lg the other side of the ringing generator Connector switch CN with its side switch wipers 11, 12, 13, 14, 15 in the ringing or third position, maintains a circuit for holding the escape magnet ESC energized as follows: ground GF, contact 50 of relay KY (which is the release magnet of the connector switch CN), third position and arm of side switch wiper 15, winding of escape magnet ESC, resistance coil ES to battery.

Now when the called party removes the receiver at substation B to answer, a closed circuit is placed across the called line conductors T and R, over which the generator is being applied, as previously described. This closed circuit causes relay TR to operate TR and close its contact 51, said contact placing a short circuit around the es cape magnet ESC, causing it to release and allowing the side switch wipers 11, 12, 13, 14, 15 to move to the fourth or talking position. Talking battery is fed to the called substation through the two windings of relay AB, fourth position and arms of side switch wipers l1 and 12, connector switch wipers 1G and 17, by way of the called line conductors T and R. Talking battery is fed to the calling substation A through windings of relays K, BX, GK and AX as previously described. The two lines are linked together for the passage of voice currents by condensers TK and RK.

The release of the connection will now be described. As long as the receiver 1" at substation A is off the hook, current will flow through relay K as follows: ground GO, winding 38 of relay BX, winding of relay AX, winding 29 of relay OK (or contact 46 of relay BT if releasing from a busy connection), trunk TC, through the line switch L and substation apparatus A, trunk RC, winding 28 of relay CX (or contact 45 of relay BT if releasing from a busy connection), winding 39 ofrelay BX, winding of relay K to battery. Also during the timethat this circuit is open at contact 00 of substation A, relay 7K will get an energizing circuit as follows: ground GD at substation A, contact 0a, transmitter t, hook switch contact h, induction coil 2', line B, through line switch L, trunk RC. winding 28 of relay OX (01' contact 45 of relay BT if connector ON is on a busy connection), winding 39 of relay BX, winding of relay K to battery With relay K energized the circuit to the release magnet XY is open and when the receiver of substation A is placedzonthe hook, the circuit of relay K is openechallowing it toifall downand close. its contact 52. y

This causes the connector release magnet meanest XY to toperate over thef'followingcircuit:

ground GH, oif-normal contact ON, con-.

tact .52 Qf'r'elay K, winding53'ofrelease magnet XY to battery. 'In addition to causing the release of connector CN'in 'the' position byway. of=l0wwinding 54, until,

the linesswitch L isstepped away from this trunk to its next home point? contact. Relay C0, of theline switch L, when operated, closes the following circuit to cause the said line switch to step away from this trunk: ground GF, contact 56 of connector release magnet XY, connector trnnli CS, lineswitchwiper S, contact 3 ofdine-switch cut-01f relay CO, contact 7 and winding 8 of stepping magnet ST to battery. This ground GFybei-ng held ontrunk wire SC until both the connector CN and'the line switch L release, also serves to cause this trunk to test busy to other line switches during the time taken to release both the connector and line switch. lVhenthe line switch Lsteps awayfromthetrunk, winding=54 of release magnet XY is opened and when the connector switch shaft reaches normal and opens contact ON, winding 53 of release magnet'XY 1s opened. The con- 1 nector' GN is now ready to beagain seized and used for establishing another connection. Line switch L' -is also resting at a home =po1ntcontact ready to be again used by substation A in se'lecting; another i'dle V connector.

It will be noted that relay AB is provided with a make contact 57- whichis closed by a l slow operating armature when said *relay is energized. This co'nta ct and"reslstancecoil; RA are fo-r 'the -following purpose: If a calln'ig party removes lllS receiver, causes his line switch L'to select a'c onnector ON- and then hangs upwrthout turning the d1al,'

there would be no operation-ofthe connector releasemagnet XY to' 'cause the' release of the line-switch L. By using contact 57 of relay-AB this-'diiliculty is overcome by causing connector switch CN togo through the release operati'On' under the above mentioned condition and-itis accom-- phshed lliljlllSWtl): lVhen the line switch L seizes connector ON, the following circuit is closed to operate relay' AB z g-roui'id Gil-l, winding- 58 of relay AB, s1de switch wiper its "contact 57 does nothingat this time. If the dial'is tnrned, side switch'wiper 12 'will leave its first position and open this circuit of relay ABI 1 If the dial is not turned and the calling-party hangs up the receiver, relay K-will fall down and close the following circuit: ground through contact 57 of relay AB, contact 52 of rclay li, winding 53 of release magnet XY to bat tery. Tl'llS'CELHSQS a release operation of botli the connector CN-and the line switch L is-described above. hen the line switch steps away from this trunk the circuit of relay ABis opened at line switch wiper RLC 'and'saidrelay falls down, leaving the connector UN in its normalcondi'tion.

lVhat I claim is:

i. In a telephone system, the combination with' a plurality of telephone lines, substations for each ofthe saidlines, a pair. of in dividual line conductors for each ofthe said lines arranged to be serially included-in a conversational circuit leadingto the said substations, sending mechanism at each substation comprising a pair of contact sets, a central'ofiice switch adapted to "be controlled by a calling telephone linessending mechanism, means to operate the said switchin a primal direction in one plane, means to operate the said switch in a secondary movabledirection in aseeond plane, a third conductor common to all of the telephone lilies of a group, a circuit conductor normally brokenby one of the said pairs of contacts for each substation sending mechanism leading from the said third conductor through normally closed contacts of the otherconta-ot set of the said substation send, ingmechanisn'i to a line conductor of the associated telephone line, a substation switchhook having normally open contacts in the circuit of the other line conductor, relay mechanism under the joint'control of the said-sets of contacts to control the motion'of the said switch, means to operate the said switch under the control ofthe said relay mechanism by intermittently opening the second set ofcontarts a definite number 'oftimes to move'it in a-p-riinary direction,

means'l'o maintain the first set of contacts closed during the said interruptions by the second set of contacts, and -1neans responsive to a subsequent opening of the first-set of contacts to alter the'control xercised by the said relay mechanism over the said switching mechanism, whereby a. subsequent set of interruptions by the second set of contacts will operate the said switch in a on'dary direction.

2. In a telephone system, the combination with-a plurality of telephone lines, a pair of line-conductors for'each of the said lines, station apparatus for each of-the said-lines at which the said line conductors terminate, a lineiswitch individual to each ofthe said lfi) lili) operating means including an active con-V tact of the said line switch and passive contacts adapted to be traversed thereby, contacts of the said line relay controlling the initiation of the said switch operating means, means to continue the operation of the said switch including passive contacts, one for each busy switching mechanism, and means responsive to the electrical condition of a traversed passive contact of an idle switching mechanism to disable the said switch operating means, a station sender tor controlling the selected idle switching mechanism, and contacts afor the said station sender arranged for progressive and rectrograde movements operative when the said sender is operated, to restore the said line relay.

3. In a telephone system, the combination with a telephone line, a line switch individual to the said line, a plurality of switching mechanisms, means under the control of the said substation apparatus to cause the said line switch to make connection with one of the said switching mechanisms, a release circuit for the said line switch extending through contacts of the said line switch and controlling contacts in the selected switching mechanism, a release magnet for the said switching mechanism controlling the said controlling contacts, a pair of relays for the said switching mechanism, means to cause one of the said relays to operate when the switching mechanism is selected, means to operate the other relay over a circuit including the said substation apparatus through contacts of the said line switch, re-

tarding means for the armature of the firstna-med relay, and a circuit for the said release magnet including normally open contacts of the first named relay and normally closed contacts of the second relay, said cir cuit including a source of current.

4-. In a telephone system, the combination with a telephone line, a line switch individual to the said line, a plurality of switching mechanisms, means under the control of the said substation apparatus to cause the said line switch to make connection with one of the said switching mechanisms, a release circuit forthe said line switch extending through contacts of "the" said' line switch and controlling COlltZtCtS'lll tliesele'cted switching mechanism, a release magnet for the said switching mechanism controlling the said controlling contacts, a

pair of relays for the said switching mechanism, means to cause one of the said rclays to operate when the switching mecha nism is selected, means to operate the other relay over a circuit including the said substation apparatus through contacts of the said line switch, retarding means for the armature of the first named relay, a second telephone line, operating means for the said switching means to cause a telephonic connection to be extended "from the first tclephone line to the second telephone line, circuit conductors and switch contacts to in clude the said first-named relay in circuit with the said second telephone line, windings for the said first relay, and a source of current serially connected with the said windings in serial circuit with the substation instrument of the second telephone line and in bridge with the said telephonic connection circuit conductors to feed transmitter battery to the substation oi the second telephone line.

In a telephone system, the combination with a telephone line, substation apparatus for the said line, a line switch individual to the said line, a plurality of switching mechanisms, means under the control of the saic substation apparatus to cause the operation of the said line switch whereby the said line switch makes connection with an idle one of the said switching mecha-' nisms, a release circuit for the said line Hit) switch extending through a movable contact' thereof and a stationary contact thereof, which stationary contact is associated with the selected switching mechanism, a circuit conductor leading through the said stationary Contact through a winding, and a normally open contact of a release relay for the said switching mechanism, a second winding for the said relay and a circuit therefor includ ing a source of current and serially connected normally closed contacts of a first relay and normally open contacts of a second relay, means to cause the said second relay to operate responsive to the selcrtion of the switching mechanism, and means to cause the first relay to be operated responsive to the presence of the subscriberssulr station apparatus on the said line.

6. In a telephone system, the combination with a telephone line, substation apparatus for the said line, a line switch individual to the said line, a plurality of switching mechv ary contact is associated with the selected switching. mechanism, a circuit conductor leading through the said'stationary contact through a winding, a normally open contact' ot a release relay forthe saidswitching mechanism, a second winding for the said relay and a circuit therefor including a source of current and seriallyconnected normally closed contacts of the first relay and normally open contacts of a second relay, means to cause the said second relay to operate responsive to the selection ofthe switching mechanism, means to cause the first relay to beoperated responsive to the presence of the subscribers substation apparatus on the said line, and retarding means for the normally open contacts of the second relay toprevent a too rapid closure thereof. a

7. In a telephone system, the combination with a telephone line, substation apparatus for the said line, a line switch individual to the said line, a plurality of switching mechanisms, mean's'under the control of the said" substation apparatus to cause the op eration of the said line switch, whereby the said'line switch makes connection with an idle one of the said switching mechanism, are'lease'circuit for the said linc switch extending through a movable contact there- 05 and a stationary contact thereof, which stationary contact is associated with the selectedswitching mechanism, a circuit conductor leadingthrough the said stationary contact to a winding, and-a normally open contact of a release relay-fonthe said switching mechanisn'i, a second winding tor the said relay and a circuit therefor including a source of current and serially connected normally closed contactsvof the first relay and normally open contacts of a second relay, meansto cause thesaidsecond relay to operate responsive to the selection of the switching mechanism, means to cause the first relay to be operated responsive to the presence orthe subscribers substation apparatus on the said line, and retarding means for the normally open contacts of the second relay to prevent a: too rapidclosure thereof. r

8; In a telephone system, the combination witha plurality of telephone lines, line switches for the said lines. a group of switching mechanisms adapted each for the use of a calling one'o'fthe said lines, switch actuating means for each of the said line switches under the control ot a calling substation of the associatedv line, circuit connections for each of the s id switching mechanisms to cause continuance of the operation of an operating line switch when the said switcl'lin-g mechanism isbusy, and

tocause a d iscontinuance'ot the said operation when the said switching mechanism is idle, a pair 036 relays tor each: line sw tch controlling -its switch actuation means, means to actuate both of the said relays when a call is initiated by a callingsubstation of the line, means to-re tire one of the said relays when an idle switching mechanismis selected by the said line switch, and means to retire the second of the said relays by a subsequent operation of switching contacts associated with a calling substa tion prior to the termination of a call.

9. In a telephone system, the combination with a plurality of telephone lines, line switches for the said lines, a group of switching in chanisms adapted each for the use of a calling one of the said lines and releasing means for the same, switch actuating means for each of the said line switches under the control of a calling substation of the associated line, circuit connections for each of the said switching mechanisms to cause continuance of the operation of an operating line switch when the saidswitching mechanism is busy, and to cause a dis continuance oi? the said operation when the said switching mechanism is idle, a pair of relays for each line switch controlling its switch actuating means, means to actuate both of the said relays when a call is initiated by a calling substation line, means to retire one of the said relays when an idle switching mechanism is selected by the said line switch, and means to retire the second of the said relays by a subsequent operation of switching contacts associated with a calling substation prior to the release of said idle switching mechanism, said first relay interposing normally closed contacts in the circuit of the line conductors leading from the'line' substation apparatus to the line switch movable contacts.

10: In a telephone system, the combination with aplurality of telephone lines, line switches for the said lines, agroup of switching. mechanisms adaptedeach for the use of a calling: one of the said lines, switch actuatingmeans for each of the said line switches under the control of a calling substation of the associated line, circuit connections for each of the said switching mechanisms to cause'contin-uance of the operation of an operating line switch when the said switching mechanism is busy,- and to'cause a discontinuance of the said operation when thesaid. switching mechanism is idle, a pair of relays for each line switch controlling; its switch actuating means, means to actuate both of the said relays when a call initiated by a calling substation line, means to retire one of the said rclays when an idle switching mechanism is selected by the saidlineswitch, and means to retire the second'ol the said relaysby a subsequent operation of switching contacts associated with a calling. substation, said first relay interposing normally closed con llU ill

tacts in the circuit of the line conductors leading from the line substation apparatus to the line switch movable contacts, said second relay having normally open contacts interposed between the passive contacts of the said line switch and the substation apparatus oi the line.

11. In a telephone system, the combination with a plurality of telephone lines, line switches for the said lines, a group of switching mechanisms adapted each for the use of a. calling one of the said lines, switch actuating means for each of the said line switches under the control oi a calling substation of the associated line, circuit connections for each of the said switching mechanisms to cause continuance of' the operation of an operating line switch when the said switching mechanism is busy, and to cause a discontinuance of the said operation when the said switching mechanism is idle, a pair of relays for each line switch controlling its switch actuating means, means to actuate both of the said relays when a call is initiated by a calling substation line, means to retire one of the said relays when an idle switching mechanism is selected by the said line switch, and means to retire the second of the said relays by a subsequent operation of switching contacts associated with a calling substation, said first relay interposing normally closed contacts in the circuit of the line conductors leading from the line substation apparatus to the line switch movable contacts. the said second relay having normally open contacts interposed between the line conductors of the line and passive contacts of a set upon which the line switch wipers normally rest.

12. In a telephone system, the combina tion with a plurality of telephone lines, line switches for the said lines, a group of switcl'iing mechanisms adapted each for the use of calling one of the said lines, switch actuating means for each of the said line switches under the control of a calling substation oi? the associated line, circuit connections for each of the said switching mechanisms to cause continuance of the operation of an operating line switch when the said switching mechanism is busy, and to cause a discontinuance of the said operation when the said switching mechanism is idle, a pair of relays for each line switch controlling its switch actuating means, means to actuate both of the said relays when a call is initiated by a calling substation line, means to retire one of the said relays when an idle switching mechanism is selected by the said line switch, and means to retire the second of the said relays by a subsequent operation of switching contacts ssociated with a calling substation, said first relay interpos'ing normally closed contacts in the circuit of the line conductors leading from the line substation apparatus to the line switch movable contacts, the said second relay having normally open contacts interposed between the line conductors of the line and passive contacts of a set upon which the line switch wipers normally rest, the

said first-named relay having two windings, one to initially operate 1t, and the other to continue its operationuntil contacts of an idle switch mechanism are encountered.

13. In a telephone system, the combina tion with a calling telephone line, means to extend the circuit of the said calling line and a connector switch, directively operating means, a test relay for the said connector switch, a test wiper therefor, controlling contacts atthe substation of the said calling telephone line. to directively control the movement of? the said wiper to cause it to make contact with a passive contact of the saidconnector leading to apparatus of a called telephone line, a pair of relays for the said connector, each of which has a winding in circuit with the calling substation, one of the said relays having a single winding and the other relay having two differential Windings, means to continuously operate the said differentially wound relay during the operation of the controlling contacts of the calling substation, means to operate the other relay in unison with the operation of the said controlling contacts, said directively operating means being under the joint control ofthe two relays, and means to include the said test relay and a source of current in circuit with the said test wiper upon the retiring of the said differential relay at the end. of a series of operations of the said substation contacts.

1.4:. In a telephone system, the combination with a calling telephone line, means to extend the circuit of the said calling tele phone line and a connector switch, directively operating means, attestrelay for the said connector switch, a test wiper therefor, controlling contacts at the substation of the said calling telephone line to directively control the movement of the said wiper to cause it to make contact with a passive contact of the said connector leading to apparatus of a called telephone line, a pair of relays for the said connector, each of which has a winding in circuit with the calling substation, one of the said relays having a singlewinding and the other relay having two differential windings, means to continuously operate the said differentially Wound relay during the operation of the controlling contacts of the calling substations, means to operate the other relay in unison with the operation of the said controlling contacts, said directively operating means being under the joint control of. the two relays, meansto include the said test relay and, a source of current in circuit with the said test till wiper upon the retiring'ot the'said' 'difiieren tial relay at the end of a series of operations of the saidsubstatlon contacts, and a locking circuit to maintain the said test movement of the said wiper tocause it to make contact with a passive contact of the said connector leading to apparatus of a called telephone line, a pair of relays for the said connector, each of which has a winding in circuit with the calling substation, one oi the said relays havinga single winding and the other relay having two ditterential windings, means'to continuously operate the said differentially wound relay during the operation ofthe controlling contacts of the calling substation, means to opcrate the other relay in unison with the operation of the said controlling contacts, said directively operating'means being under the joint control ofthe two relays, means to include the said testrelay and a source of current in circuit with the said test wiper upon the retiring of the said differential relay at the endota seriesof'operations of the said substation contacts; and a locking circuit :lor the said t'est relay exclusive of the said circuit including the first test wiper.

16; In a telephone system, the combination-with a calling telephone line. means to extend the circuit of the said calling'line and a connector switch. directively operatingmeans, a test relay for the said connector switch, a test wiper therefor, controlling contacts at the suhstation ofthe said calling telephone line to (lirectively control the movement of the said wiper to cause it to make contact with a passive contact of the said connector leading to apparatus of a called telephone line, a pair ot'relays torthe said connector, each of which has a winding; in circuit withthe calling substation, one of the said relays having a single wind ing and the other. relay having'two differential windings. means to continuously operate the said differentially woundn'elay during the operation ofthe controllingcontacts ot the calling suhstation. means to operate the other relay in unison with the operation of the said controlling contacts: said di rectivel operating. means'being under the joint control of the two relays; means to include the. said test relay and a source of current in circuit with the said testwiper upon the retiring of the said differential relay at'the end of a seriesoit'operationsot the saidsubst'afioncontacts; and a locking circuit including oll normal'contacts of the said connector switch.

1'7. In a telephone system, the combination with a calling telephone line, means to extend the circuit ot the saidcalling line and a connector switch. direetively operatin g means, a test relay for the said conne: tor switch, a test wiper thereto-r, controlling contacts at the substation of the said calling telephone line to directively control the movement of the said wiper to cause it to make contact witha passive contact of the said connector leading to apparatus o-t' a called telephone line, a pair of relay-stoi' the said connector, each. of which has a winding in circuit with the calling substation, one of the said relays having a single winding andthe other relay having two ditferential windings, means to continuously operate the said difi erentiallv wound relay during the operation of thecontrolling'contactsot the calling substation, means to 0p eratethe other relay in unison-with the operation'ot the said controllingcontacts, said directively operating meansbeing under the joint control of the two relay-s; means to include the said test relay anda source of current in circuit withthesaid test wiper upon the retiring of the said (-litterential'relay at the end ot'aseries of operations of the said substation contacts; a locking circuit including ofli-normal contacts of the said connectorswitch. a side switch adapted to be advanced fronroneside switch position to a fi'irthcrsidc switch position upon successive de-energizations of the said (littere'ntial relay, and means under th control of'the said busy test relay when energized to prevent further operation oi" the said side switch.

18: In atelephone system, the-co1nbination with a-calling telephone line. means to extend the circuit of the said calling line and a connector switch, directively operating means, a-test relay for the said connector switch, a test wiper therefor, controlling contacts-at the substation otthe said calling telephone line to directivelv control the movement'oi the said wiper to cause it to make-contact with a passive contact of the said connector leading to apparatus of a called telephone line, a pair of relays for the said connector, each of which has a winding in circuit with the calling substation. one of the said relays havinga single winding and the other relay having two d-i-li'erentialwindings, means to continuously operate the said difl'erentially wound re lay'during the'operation of the controlling contacts of the calling substation, means-to operate the other relay in unison with the Kill operation of the said controlling contacts, said directively operating means being under the joint control of the two relays, means to include the said test relay and a source of current in circuit with the said test relay upon the retiring of the said differential relay at the end of a series oi? opcrations of the said substation contacts, a locking circuit including oil-normal contacts of the said connector switch, a side switch adapted to be advanced from one side switch position to a further side switch position upon successive de-energizations of the said ditlerential relay, and means under the control of the said busy test relay when energized to prevent further operation of the said side switch, said lastuiamed means including disabling means for the said dillerential relay.

19. In a telephone system, the combination with a calling substation, a telephone line leading therefrom to a main station, a connector switch at the main vstation associated with the said calling line, sending mechanism at the said substation adapted to send successive series of current impulses to the connector switch mechanism under the manual control of an operator, a pair of relays at the main station for the said connector switch in circuit with, he said substation sending mechanism, one of the said relays being a differential relay, controlling contacts for the said sending mechanism and circuit connections to cause the said differential relay to be continuously operated during the sending of a series of impulses by the said sending mechanism, circuit con nections to cause the other relay to be responsive to each impulse of every series of impulses, a called substation telephone line, switch actuating mechanism operated under the control of the said pair of relays to cause the said connector switch to make connection with the desired line, and changeover switching mechanism adapted to alter the control of the said sending mechanism over the said switch actuating mechanism after each operation of the said differential relay.

20. In a telephone. system,.the combination with a calling substation, a telephone line leading therefrom to a main station, a connector switch at the main station associated with the said calling line, sending mechanism at the said substation adapted to send successive series of current impulses to the connector switch mechanism under the manual control of an operator, a pair of relays at the main station for the said connector switch in circuit withthe said substation sending mechanism, one of the said relays being a differential relay, con trolling contacts for the said sending mechanism and circuit connections to cause the said differential relay to be continuously operated during the sending of a series of impulses by the said sending mechanism, circuit connections to cause the other relay to be responsive to each impulse of every series of; impulses, a called substation telephone line, switch actuating mechanism operated under the control of the said pair of relays to cause the said connector switch to make connection with the desired line, changeover switching mechanism adapted to alter the control of the said sending mechanism over the said switch actuatin mechanism after each operation of the sa1d differential relay, a test wiper for the said connector switch adapted to make contact with a test contact of the called telephone line, a test relay in circuit with the said test wiper and adapted to be responsive to a busy condition of the tested called line,

and means responsive to a deenergization of the said differential relay and a given stage of operation of the said change over switching mechanism to close the C11- cuit of the said busy relay whereby the said busy relay is operated.

21. In a telephone system, the combination with a calling substation, a telephone line leading therefrom to a main station, a connector switch at the main station associated with the said calling line, sending mechanism at the said substation adapted to send successive series of current impulses to the connector switch mechanism under the manual control of an operator, a pair of relays at the main station for the said connector switch in circuit with the said substation sending mechanism, one of the said relays being a differential relay, controlling contacts for the said sending mechanism and circuit connections to cause the said differential relay to be continuously operated during the sending of a series of impulses by the said sending mechanism, circuit connections to cause the other relay to be responsive to each impulse of every series of impulses, a ealled'substation telephone line, switch actuating mechanism operated under the control of the said pair of relays to cause the said connector switch to make connection with the desired line, changeover switching mechanism adapted to alter the control ofthe said sending mechanism over the said switch actuating mechanism after each operation of the said differential relay, a testwiper for the said connector switch adapted to make contact with a test contact of the called. telephone line, a test relay in circuit with the said test wiper and adapted to be responsive to a busy condition of the tested called line, means responsix e to a de-energization of the said differential relay and a given stage of operation of the said change-over switching mechanism to close the circuitof the'said busy relay whereby the said busy relay is operated and switch contacts under the control of the said busy relay to maintain it operated.

22. In a telephone system, the combination with a calling substation, a telephone line leading therefrom to a main station, a connector switch at the main station associated with the said calling line, sending mechanism at the said substation adapted to send successive series of current impulses to the connector switch mechanism under the manual control of an operator, a pair of relays at the main station for the said connector switch in circuit with the said substation sending mechanism, one of the said relays being a difierential relay, controlling contacts for the said sending mechanism and circuit connections to cause the said differential relay to be continuously operated during the sending of a series of impulses by the said sending mechanism, circuit connections to cause the other relay to be responsive to each impulse of every series of impulses, a called substation telephone line, switch actuating mechanism. operated under the control of the said pair of relays to cause the said connector switch to make connection with the desired line, change-over switching mechanism adapted to alter the control of the said sending mechanism over the said switch actuating mechanism after each operation of the said difierential relay, a test wiper for the said connector switch adapted to make contact with a test contact of the called telephone line, a test relay in circuit with the said test wiper and adapted to be responsiv to a busy condition of the tested called line, means responsive to a de-energization of the said differential relay and a given stage of operation of the said change.-over switching mechanism to close the circuit of the said busy relay whereby the said busy relay is operated, switch contacts under the control of the said busy relay to maintain it operated, additional switch contacts under the control of the said busy relay for preventing a further operation of the said clmngecver switching mechanism.

23. In a telephone system, the combination with a calling substation, a telephone line leading therefrom to a main station, a connector switch at the main station associated with the said calling line, a sending mechanism at the said substation adapted to send successive series of current impulses to the connector switch mechanism under the manual control of an operator, a pair of relays at the main station for the said con nector switch in circuit with the said substation sending mechanism, one of the said relays being a differential relay, controlling contacts for the said sending mechanism and circuit connections to cause the said ditferential relay to be continuously operated during the sending of a series of impulses by the said sending mechanism, circuit con motions to cause the other relay to be responsive to each impulse of every series oi impulses, a called substation telephone line, switch actuating mechanism operated under the control of the said pair of relays to cause thesaid connector switch to make connection witli the desired 'line, change-over switching mechanism adapted to alter the control of the said sending mechanism under the said switch actuation mechanism after each operation of the said differential relay, a test wiper for the said connector switch adapted to make contact with a test contact of the called telephone line, a test relay in circuit with the said test wiper and adapted to be responsive to a busy condition of the tested called line, means responsive to a deenergization of the said diilerential relay and a given stage of operation of the said change-own" switching mechanism to close the circuit of the said busy relay whereby the said busy relay is operated, switch contacts under the control of the said busy relay to maintain it operated, additional switchcontacts under the control of the said relay for preventing a further operation of the said change-oven switching mechanism, and means responsive to the operation of the said busy relay to project a busy tone back over the line of a calling subscriber.

24-. In a telephone system, the combination with a calling substation, a telephone line leading therefrom to a main station, a connector switch at the main station associated with the said calling line, a sending mechanism at the said substation adapted to send successive series of current impulses to the connector switch mechanism under the manual control of an operator, a pair of relays at the main station for the said connector switch in circuit with the said substation sending mechanism, one of the said relays being a differential relay, controlling contacts tor the said sending mechanism and circuit coi'inections to cause the said difi erential relay to be continuously operated during the sending of a series of impulses by the said sending mechanism, circuit connections to cause the other relay to be responsive to each impulse of every series of impulses, a called substation telephone line, switch actuating mechanism operated under the control of the said pair of relays to cause the said connector switch to make connection with the desired line, changeover switching mechanism adapted to alter the control of the said sending mechanism under the said switch actuating mechanism after each operation of the said differential relay, a test wiper for the said connector switch adapted to make contact with a test contact of the called telephone line, a test as a relay in circuit with the said test wiper and adapted to be responsive to a busy condition of the tested called line, means responsive to a de-energization of the said differential relay and a given stage of operation of the said change-0W1 switching mechanism to close the circuit of the said busy relay whereby the said busy relay is operated, switch contacts under the control 10 of the said busy relay to maintain it operated, additional switch contacts under the control of the said busy relay forpreventing a further operation of the said changeover switching mechanism, and disabling means for the said switch actuating means under the control of the said busy relay.

In testimony whereof, I hereunto sub scribe my name this 20th day of Dec, A. D.

VINFRED T. POlVELL.