US852523A - Automatic telephone-exchange. - Google Patents

Description

fetmow.

Systems, Automatic,

Lockout, Central energy.

PATENTBD MAY 7, 1907.

J. G. ROBERTS.

AUTOMATIC TELEPHONE EXCHANGE.

APPLIGATION FILED PEB. E, 1906.

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arrangement whereby -when connection is;

UNITED srirrns PATENT onirica.

JOHN G. ROBERTS, OF CHICAGO, ILLINOIS, ASSIGNOR TO WESTERN ELECTRIC COMPANY, OF CHICAGO,-ILLINOIS, A CORPORATION lOF ILLINOIS.

c AUTOMATIC TELEPHONE-EXCHANGE.:

f No. 852,523.

l Specification of Letters Patent.

Patented May '7, 1907'.

'Application filed February 5, 1906. Serial No. 299,424. Y

I "i i To aZZ whom at may concern: i

Be it known that I, JOHN G. RonERTs, af citizen of the United States, residing at Chicago, in the county of Cook and State of Illi-v nois, have invented a certain new and-.useful Improvement in Automatic Telephone-Exchanges, of which the' following is a full, clear, concise, and exact description.

My invention relates to an automatic telephone exchange system of the central energy type, and has for its object to provide improved and efficient means for effecting the interconnection ofiany two subscribers in the exchange, while requiring the minimum amount of labor on `the part of the calling subscriber. i

A feature of my invention ,consists in the made with an idle called line, ringing current is automatically applied thereto to signal the called-party, said ringing current being automatically cut oif when the called subscriber responds. In case' the called subscriber does not respond after. thevringing current has been applied a predetermined length of time, the ringing current is automatically cut oif and a busy tone apparatus connected with the calling line.

Another feature of the inventionconsists in the manner of imposing interrupted current upon the line to operate the selector controlling mechanism without. the use ofa. ground connection at the substation, so

' avoiding trouble due to high potential grounded circuits:

Other features of the invention consist in the detailed structural arrangement to be described hereinafter.

' I will describe my invention more particularly by reference to the accompanying drawing, which is a diagrammaticrepresentation of asubstation single subscribers line, and its substation and central office equipment. v

The telephone line shown extends in two limbs L1, L2,'from the substation to the cen,-x tral ofiice, the battery b being included in a bridge A of the line at the central office. The line relay a is included in said bridge between the free poleiof the battery and the limb L1 of the line, while the impedance coil c .is included in said bridge between the grounded pole'o said battery and the limb L2 of the line. At the substation is provided an interrupter E, said interrupter'being pro- 55 vided with a ratchet wheel adapted to be operated by an arm E1 to make and break contacts 47 -which are included in a conductorr47'a extending from the limb L1 of the line to a Contact arm 48, which is adapted 6o when the arm E of the interrupter is away from normal position, to engage a' contact spring 8 and separate it from its anvil 1, said spring 8 being connected with line conductor L1. Thus normally the contacts 1, 8, are in- 6 5 eluded in conductor L1, but when the contactv arm is moved into position to operate lthe ratchet wheel, the contacts l, 8, are separated, and conductor 47a, including the conltactsl .4T operated by the ratchet wheel, is 7o substituted, and said ratchet wheel in mak-- ing and breaking said contacts 47 causes an interrupted or oscillating current to flow from battery b to relay a over limb Ll ofthe f' line, through 'the substation and back over 75 limb L2 ofthe line to the battery, in a complete metallic circuit. The use of a ground connection at the substation is thus avoided.

The relay a is provided with an armature 46 and a heavy suspended arm or lever m. 8o

The armature 46 of said relay is so designed as to be responsive to interruptions of the .current through the windings of the relay produced in the operation of selection, to be' described hereinafter, and to actupon the arm m to close contacts 5, the arm m being so pivoted, and ofsuch Weight and inertia as to e immovable under a temporary impact of armature 46 as the latter engages 1t in closing said contacts, said arm, however, re- 9o 4spondlng to a continuous pull of the armature resulting from a continuous flow of current through the relay a.

In order to render the arm m moresluggish, I may employ a spring 9 so applied as to9 5 I l exert its maximum force when the arm is in normal position, as shown, in which position an increasedrestoring force is more desirable, and to 'exertits minimum force when its arm is in its operative position, the reduc- 'roo ,y tion in the slprings'action being due tothe fact thatn its compressed condition its pressure is more nearlyL in lline withthe pivot 45 offsaid armm f:\'l`he contacts 5- control a local circuit AB extending fromnthe free pole of I battery -b.thro11gh-cntacts '11 of relayd,

stepping magnet c of the selector C, retaining magnet f of said selector, which is shunted by a non-inductive resistance g, contacts 7, nor

short circuited by the portion of conductor B controlled at contacts 7, this short circuit, however, being opened when the arm responds to the continuous current in relay a to permit the relay h to operate. It will thus e seen .that the relay z, will not be operated to extend the line to the contact brushes i, lc, `until after the interrupted current has been passed through relay a to advance the selector arm to the desiredfterminals, this being desirable in order that there may be no disturbance or confusion as the contact arms i, c, which are of the wiping type, advance over the line terminals of the selector.

The selector, while away from normal position, opens contacts 31, 34, disconnecting the line from its multiple terminals R, T, on the diiierent selectors in the exchanges A. conductor M extends from the busy tone a paratus B1 to a contact 35, which, when t e contacts 34 are se arated by the selector a'rm, engages the memilier of said contacts directly connected with the test terminals T of the calling subscribers line. Said arm, while away from normal position, also closes contacts 17, 18. The contacts 17 control a circuit E2 extending rom a grounded battery b1 through contacts 19 of a ulsator D1, magnets n, o, contacts 2O of re ay p, contacts 21 closed by armature h of the connecting relay h when energized, to earth. The magnets n, o, control the automatic ringing mechanism comprising a ratchet wheel g provided with a stepping pawl 22 operated by magnet o, retaining pawl 23 operated by magnet n, said ratchet wheel when advanced rotating a contact wheel 1' carrying a number of cams 24 which are adapted successively to operate a ringing key G and se arate contacts 16, 13, normally included inlline conductors L, L2, and connect the portions of said conductors leading directly to the vbrushes i, 7c, of the selector With contacts 26, 27, respectively, contact 26 beingconnected to earth by conductor G1, while contact 27 is connected by a conductor G2 with the contacts 28 of a pulsator F, said contacts being connected with the free pole of a grounded battery b2.

-A conductor H extends from line conductor L2 between the condenser 10 and con'- tacts 12 therein, through contacts 37 of relay p, winding of said relay p, contacts 18, to

I earth, relay 2g, in other words, bein included 1n a grounded leg from the contact rush 7c of the selector. This relay would be adapted to res ond to a potential at the terminal 30 of a cal ed subscriber, created upon the removal of the called subscribers receiver from its hook. Relay p, when energized, attracts its armature p1, opening contacts 20, and breaking the circuit of the automatic ringing magnets n, o. The armature 36 of relay p is connected by conductor I with the free pole of battery b, said armature when attracted separating contacts 37, engaging the contact thereof directly connected through the winding of relay p, through contacts 18, to earth, so locking up relay p until the conversation is completed.

The first cam 24 on wheel 1', if said wheel is allowed to continue its rotation, as when the called subscriber does not respond, is adapted eventually to close contacts 39, 40, contact 39 being connected by conductor K through the winding 41 of relay d to conductor D, which is connected to earth through contacts 5, while contact 40 is connected with conductor I, which leads to the free ole of battery b..

The armature dl of magnet when attracted, is adapted to open contacts 1 lincluded in the circuit of the selector magnets e, f, said armature being connected by a conductor d2 with conductor K, and being adapted to engage the member of contacts 11 which is directly connected with the Jree pole of battery b. The armature 25 of relay d is connected by conductor d3 with line conductor L1, a condenser 33 being included in said line conductor between the junction of conductor d3 with limb Ll and the substation. The contact 25*1 which the armature 25 engages when attracted, is connected with a busy tone apparatus B1.

The armature h2 of relay h, which,y when attracted, completes the continuity of line conductor L, 1s directly connected with a portion thereof leading to contact brush i, said armature when retracted engaging the contact 42 connected with a conductor L which leads through the winding 44 of relay d to contact 6 closed when the heavy arm m is operated by continuous current in magnet a. Thus if the line is busy a potential will exist at the terminal 30a of such line, producing a current to operate magnet d when the selector makes connection with the desired line before the sluggish magnet h has operated, and after the inertia arm m has o erated, so applying busy test current to t e circuit; or 1f the called party does not respond to the ringing current, relay d, when operated, also connects said busy tone apparatus with the calling subscribers line.

Operation.

Calling 'an' 'idle Ina-In establishing a connection, the calling subscriber iirst re- IOO IIS

moves his telephone from its hook, thereby completing the metallic line circuit from battery bthrough line relay a, limb L1 of the line, springs 1,' 8, of the interrupter, transmitter 2, contacts 3 closed by the sWitch hook, induction coil Winding 4, limb L2 of the line to the battery. The line circuit when thus completed effects the energization of relay c, which closes contacts 5 and 6 and opens contacts 7, thereby advancing the arms i, c, of the selector C through one step. This operation is,r however, incidental, since the first contact of the selector has no electrical connection. The calling party noW moves his interrupter arm E1 to the number of the desired subscriber, which operation, in addition to opening the line circuit, prepares the same for the operation of the selector by introducing the interrupter contacts 47 in the line circuit; separating, as before described, contacts 1, 8. The interrupter arm, when released from its advanced position, interrupts at contacts 47 the metallic circuit through the line relay a, and causes the same to close its contacts 5, in response to each impulse, the contacts 7 remaining closed, due to the inertia of armature m. Each closure vof contacts 5 completes the circuit D, including the stepping magnet e and retaining magnetf of the selector C, which magnets operate their respective paWls e1, f 1, causing the same to engage the ratchet Wheel l of the'selector. The ratchet Wheel Zis thus caused to advance the contact brushes fi, 7c, to the terminals of the desired line.

The interrupter arm having returned to its resting position after effecting the advance of the selector arm, the line relay ain response to the steady current now flowing therethrough, overcomes the inertia of the heavy arm m and the pressure of the spring 9, and opens contacts 7, closing contacts 6. The short circuit controlled vat contacts 7 about relay h is noW open, and said relay 71, is included in a circuit B-D, including battery b. Said sluggish relay ZL thereupon operates Ato extend the circuit of the line conductors L1, L2, to the contact brushes fi, c, of the selector. The extension of limb L1 leads through contact 15 and armature h2 of relay h, through contacts 16, to selector brush i, While the eX- tension of limb L2 leads through condenser 10, contacts 12 of relay h, contacts 13, contacts 14 of the selector to the brush c thereof.

The selector arm, While aWay from normal position, as beforev described, opens contacts 31, 34and disconnects the multiple terminals of the calling line therefrom. The selector arm, in opening contacts 34, connects the test terminals of the calling subscribers line by Way of conductor M, with the busy test apparatus B1. The contacts 17 closed by the selector arm While away from normal position now co-operate With the armature k1 and contact 21 of sluggish relay h to complete the circuit E2 from pulsator D1, through the retaining magnet n and stepping magnet o of the automatic ringing apparatus, through contacts 2O of relay p, to earth. The ratchet Wheel q is stepped forward by the operation of the stepping pawl 22 and is retained by the locking paWl 23, advancing in its movement the contact Wheel r. As the Wheel 1" advances, the cams 24 are brought consecutively into engagement With the ringing key to open contacts 16 and 13 and close contacts 26 and 27, thereby providing a circuit for ringing current from generator F. Ringing current thereupon flows from battery b2 through pulsating contacts 28, conductor G2, contacts 27, contacts 14, selector arm k, terminal 30 of the called subscribers line, through the called subscribers line wire L2, ringer S, condenser 32, interrupter contact 1, line Wire L1, condenser 33, terminal 30a of the selector, and from thence through brush i, contacts 26 to ground, by Way of conductor G1. At definite intervals, therefore, dependent upon the rate at which the ringing key G is actuated, the bell at the called subscribers station will be automatically rung. Obviously the opening of contacts 16 and 13 prevents any reaction of the ringing current u on the ear of the calling subscriber, who would at this time be'listenf the called subscriber responds promptly relay p of the calling subscribers line is energized, and operates instantly to open IOO contacts 20 and sever the circuit E2 for the magnets fn, o, of the automatic ringer. As before described, the relay p, when contacts 13 of the ringer G are closed, is included in a grounded leg from contact brush k, by Way of contacts 12 of relayv h, conductor Il, contacts 37 of relay p, Winding of said relay p, contacts 18, to earth. Wv hen the called subscriber responds to the call by removing his telephone from its hook, he raises the terminal 30 of his line to a potential equal to the drop in potential through the impedance c, which potential produces a current flowing from said terminal 30, contacts 14, 13, 12, 37, winding of relay p, contacts 18, to ground, thereby operatinr relay p, Which opens the contacts 20 of t e ringing circuit and completes at its armature 36 and one of the members of contacts 37 a locking circuit I-H, through contacts 18 to ground.

The opening of contacts 20 by breaking the circuit E2 releases the stepping and retaining pawls 22, 23, of ratchet g, allowing said wheel and its companion 1 to be restored to normal condition. It Will readily be understood that although the cam Wheel 1' `will in its restoration, as in'its advance, actuate the ringing key G, and thereby send impulses of ringing current over the called IIO restores its contacts to normal position.

subscribers line, said restoration may be easily made to occur in so short a time that the ringing impulses will have ceased and the called circuit be l'in a quiescent state beforethe called party will have had time to place his receiver to his ear.

Upon theresponse of the called subscriber, by the removal of his receiventhe talking circuit between the two stations is completed, consisting of the two lines, supplied through their respective bridged impedances a and c with current from central battery l).

When the calling subscriber replaces his receiver on the hook at the completion of a conversation, the line relay a of his line is de-energized, and its armature opens contacts 5 and 6 and closes contacts?. The closing of contact 7 re-establishes a short circuit about the sluggish connecting. relay 7L, which releases its armatures, and disconnects the extensions of line wires L1, L2, from the selector arms i, c, so that during the return of the selector arm, brushes i, k, will be dead. Contacts 5, when opened, sever the circuit B of stepping and retaining magnets e, f, of selector C, allowing the selector brushes i., f, to be restored b y the usual spring. The selector arm, when it resumes its normal position, breaks contacts 17 and 18 and 35, and closes contacts 31, 34, connecting the line with its multiple terminals. The opening of contacts 18 breaks the locking circuit I--H for relay p, which thereupon It will be. observed that the said restoration of the apparatus is made dependent upon the action of the calling subscriber. This ar rangement, however, does not prevent either party from disconnecting at any time and establishing other connections. In case the called subscriber, upon being signaled, fails to respond, the wheel 1a continues to advance until the first of its cams 24 engages spring 39 and forces the same into engagement with contact 40, thereby completing the circuit from the free pole of battery b, conductor 1,1 contacts 39, 40, conductorK, winding 41 of relay d, contacts 5 of relay a, to earth. Relay d is thereupon energized and attracts its armatures, armature d1 o ening contacts 11 included in the circuit o the retaining and stepping magnets of the selector, and completing a locking circuit for said winding 41 of relay d, from the free pole of battery b, conductor B, one ofthe members of contacts 11, armature d1, conductor d2, conductor K, winding 41, contacts 5 of relay a to earth. The armature 25 of said relay d when attracted, engages contact 25a and connects busy tone apparatus B1 with limb L1 of the line, by way of conductor d3. The calling subscriber, upon hearing the busy signal and hanging up his telephone, would de-energize relay a and break the locking circuitlof winding 41 of relay d.

Calling a busy hina-In case the called line were busy, the steps .before described would be proceeded with up to the point when the selector reached the terminals of the desired If the called 4line were busy a potential would be present at the terminal 3011 of such line, and when the selector brush i reached said terminal, and before had been operated, current would flow from said terminal through brush i, extension of line conductor L1, contacts 16, armature h2 of connecting relay L and its back contact 42, through conductor L, winding 44 of relay d, contacts 6 closed by arm m, contacts 5 of relay a, to earth. Relay d would thereupon be energized, drawing up its armature d1 to open the circuit of the stepping and retaining magnets of the selector and lock itself up until the calling subscriber hung up; armature 25 would operate to connect the busy tone apparatus with the limb L1 of the calling subscribers line. i

I claim:

1. The combination with a telephone line,

of a bridge of theline at the central oflice including a source of current, a magnet having a'winding included-in said bridge, an armature for saidl magnet, a lever engaged by said armaturein its attracted position, said lever possessing considerable inertia, whereby it is unresponsive to a momentaly impact of the armature but is responsive to a continuous engagement thereof, a circuit closed by the contacts of said armature and lever, a second circuit closed by said armature and lever when the lever is in itsresponsive' position, and switching mechanism at the subscribers station for either interruptedly or continuously closing the circuit of the line through saidA magnet..

' 2. In an automatic telephone exchange, the combination with a telephone line and a l selector therefor, of a bridge of the line at the central office including a battery, a magnet having a winding included in said bridge, an armature f or said magnet, a lever engaged by said armature in its attracted position, said lever possessing considerable inertia whereby it is unresponsive to a momentary impact of the armature but is responsive to a continuous engagement thereof, a local circuit having contacts controlled by said armature and lever, said circuit including electromagnetic means `for operating the selector and a relay for connecting the subscribers line to the terminals of said selector, a short circuit for said relay closed when the lever is in its normal position, and switching" mechanism and an interrupter at the subscribers station for closing the circuit and for producing an interrupted current through the magnet, respectively; whereby the selector is actuated to select the terminals of the called subscriber and the calling subscribers line is extended to said terminals.

the sluggish relay 7i IOO IIO

IIS

the combination selector therefor,

,L7 S 3. n an automatic telephone exchange,

with a telephone line and a of a bridge of the line at the central ofiice including a magnet and a source scribers station uous or intermittent currents in current, switching mechanism at the subfor producing either continsaid magnet,

means operated by an intermittent current in th the terminals of a called subscriber, a source necting the ringing current to the called sub# e magnet to actuate the selector to select ringing current, and means operated by a ntmuous current 1n said magnet for conscribers line and for connecting the calling i th subscribers line to the selected terminals.

4. In an automatic telephone exchange, e combination With a switching by the line relay for called subscriber and for connecting the line of the calling subscriber thereto, a source of ringing current, automatically operatedmeans for connectin circuit of the ringing scriber, and a relay e same to the terminal of the called subenergized upon the resubscriber to openl the current,

5. In an automatic telephone exchange, e combination with a telephone line and a onse of the called selector therefor having terminals for the several subscribers ing brushes adapted of a relay h adapted lines and an arm carryto engage the terminals, to connect the circuit of e calling subscribers line to the terminals his selector, a line relay a, means at the bstation for controlling said line relay, a

local circuit, controlled by relay a, in-

cluding Athe relay h and electromagnetic means for actuating the selector to select the terminals of the called subscriber, a short circuit of the relay h controlled by the line rel ay, a source of ringing current, and means automatically controlled by the relay h for selector therefor having nnecting the same With the selector arm after it has reached the selected terminals.

6. In an automatic telephone exchange, e combination with a telephone line and a terminals for the several subscribers lines and an arm carrying brushes adapted to engage the terminals, of a relay h adapted to connect the circuit of the CEL his selector,

to the terminals of a line relay a, means at the sublling subscribers line station for controlling said line relay, a local circuit, controlled by relay a, including the rel ayh and electromagnetic means for actuating the selector to select the terminals of the called subscriber, a

short circuit of the relay controlled by the line relay, a source of ringing current, mechanism for connecting the same W1th the selector arm, and a local circuit including electromagnetic means for actuating said mechanism, said circuit being controlled by relay 7L.

7. In an automatic telephone exchange,

.selector therefor, of a telephone line and a selector therefor, of a line relay, mechanism controlled selecting the line of a the cmbination With a telephone line and a bridge of the line at the central oiiice including a battery, aline relay a, having a Winding included in said bridge, switching mechanism and an interrupter at the substation for closing the circuit and producingan interrupted current through said relay, respectively, a local circuit controlled by said relay, includin(r electromagnetic means for operating the seIector to selectr the terminals of the called subscriber, and a shunt of said local circuit, includin a relay h, controlled by the line relay, said re ay h being adapted to connect the circuit of the line to the selected terminals.

8. In an automatic telephone exchange, the combination With a telephone line and a selector therefor, of a bridge of the line at the central oiiice including a battery, a line relay a having a Winding included in said bridge, switching mechanism and an interrupter at the'substation for closing the circuit and producing an interruptedY current through said i relay, respectively, a local circuit, controlled by said relay, includin electromagnetic means for operatin the se ector to select the terminals of the ca led subscriber, a shunt of ysaid local circuit including a relay h con# relay, said relay h being' trolled by the line adapted to connect the circuit of the line to the selected terminals, a source of ringing current and means controlled by the relay h for connecting the same to a selected terminal.

9. In an automatic telephone exchan e, the combination with a telephone line an a selector therefor, of a bridge of the line at the central office includinga battery, a line relay a having a Winding included in said bridge, switching mechanism and an interrupter at the substation for closing the circuit and producing an interrupted current through said relay, respectively, a local circuit, controlled by said relay, includin electromagnetic means for operatinfT the se ector to select the terminals of the called subscriber, a shunt of said local circuit including a relay h controlled by the line relay, said relay h being adapted to connect the circuit of the line to the selected terminals, a source of ringing current, mechanism for connecting the same to a selected terminal, and a local-circuit including electromagnetic means for actuatin said mechanism, said circuit being controlled by relay h.

10. In an automatic telephone exchange, the combination with a telephone line, of a bridge of the line at the central oflice including a battery, a line relay a having a Winding included in said bridge, switching mechanism controlled by thetline relay for selecting the line of the called subscriber, a relay h controlled by the line relay for connecting the circuit of the calling subscriber to the terminals of the called subscriber, a source of IOO IIO

ringing current, ringer mechanism for connecting the same to the selected terminal, a local circuit including electromagnetic means for actuating said ringer mechanism, said circuit being adapted to be closed by the relay h,A and a relay p adapted to be energized to open said local circuit upon the response of the called subscriber.

11. In an automatic telephone exchan e, the combination with a telephone line, of a bridge of the line at the central oflice includin a battery one pole of which is grounded, a ine relay al .having a winding included in said bridge, switching mechanism controlled by the line relay for selecting the line of the called subscriber, a relay h controlled by the line relay for connectingthe circuit of the calling subscriber tothe terminals of. the called subscriber, a source of ringing current, ringer mechanism for connecting the same to the selected terminal, a local circuit including electromagnetic means for actuating said. ringer mechanism, said circuit being adapted to be closed by the relay h, a relay p adapted-` to be energized to open said local circuit upon the response of the called subscriber, a test relay d having a winding included in a normally open circuit,ja contact device upon said ringer mechanism adapted to close the circuit of relay d after a predetermined time upon. the failure of the called subscriber to respond, and a busy tone a aratus adapted to be connected to the ca ing subscriber-s line by the test relay d.

12. In an automatic telephone exchange, a calling subscribers line and a. selector therefor, subscribers lines having terminals in said selector, means controlled by the calling subscriber to select the line of' a desired subscriber and to connect the line of the calling subscriber thereto, a source of ringin T current, ringer mechanism at the central station adapted to automatically connect said source of ringing current to the selectedline, a busy tone apparatus, and automatic mechanism, operated by said ringer mechanism after a predetermined time, upon the failure of the called subscriber to respond, for connecting said-busy tone apparatus to the calling subscribers line.

18.' In an automatic telephone exchange, the combination with a calling subscribers line and a selector therefor, of subscribers lines having terminals in said selector, means controlled by the' calling subscriber to actuate the selector to select the terminals of a desired subscriber, a busy tone apparatus, a

test relay having two windings, one of which is included in a circuit automatically closed upon the failure of the selected subscriber to respond in a predetermined time, the other winding of the test relay being included in a circuit closed when the called line is engaged, and switching mechanism operated by said test relay for connecting the busy tone apparatus to the calling subscribers line.

14. In an automatic telephone exchange, the combination with an electric circuit including a source of current, of a magnet having its windings included in said circuit, an armature for said magnet, a pivoted lever engaged by said armature in its attracted position, a spring engaging said lever and incre asing its inertia when said lever is at its normal position, whereby the lever is unresponsive to a momentary impact of the armature but is responsive to a continuous engagement thereof, and switching mechanism for either interruptedly or continuously closing the circuit through said. magnet.

15. In an automatic telephone exchange, the combination with an electric circuit including a source of current, of a magnet hav,

ing its Winding included in said circuit, an armaturefor said magnet, a lever engaged by said armature in its attracted position, said lever possessing considerable inertia whereby it is unresponsive to a momentary impact of the armature but is responsive to a continuous engagement thereof, and switching mechanism in said circuit for either interruptedly or continuously closing the circuit through said magnet. Y

16. In an automatic telephone exchan e, the combination with a. telephone line an a selector therefor, of a source of current and a magnet in the circuit of the line at the central office, switching mechanism at the substation adapted to be set by the subscriber, for automatically producing intermittent currents in saidmagnet, to actuate said selector and select the desired line terminals, and thereafter for producing continuous current in said magnet, asource of ringing current, and mechanism automatically operated by said continuous current in said magnet for connecting the rin ing current to the desired line terminals.

n IWitness whereof, I hereunto subscribe my name this 26th day of January A. D.,

l JGHN G. ROBERTS. Witnesses:

ROY. T. ALLowAY, E. F. BEAUBIEN.

IOO

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