US1277883A - Telephone system. - Google Patents

Description

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A. H. DYSON. TELEPHONE SYSTEM.

APPLICATION FILED OCR-H. um.

Patented Sept. 3,1918.

4 SHEETS-SHEET I.

Patented Sept. 3,1918.

4 SHEETSSHE ET 2- .z/W 1 Z n 1211 m;- 4 v fiZfiedfigysaz'z FZZnrrz y.

a lii lalalalaHw- A. H. DYSON.

' TELEPHONE SYSTEM.

APPLlCfKTION man OCT.1I. um.

Patented Sept. 3,, &918.

4 SHEETS-SHEET 4.

Jim/272521 Z/fwi ALFRED H. DYSON, OF CHICAGO, ILLINOIS, ASSIGNOR T0 KELLOGG SWITCHBOAR'D 8:

SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Sept. 3, 1918.

Original application filed March 19, 1906, Serial No. 306,817. Renewed April 17, 1912, Serial No. 691,505. Ifatent No. 1,208,718. Divided and this application filed October 11, 1911. Serial No, 653,990.

means employed for signaling a called sub scriber that his attention is wanted and for signaling the calling subscriber that the line wanted is busy, should such be the case.

The object of my invention is to provide a structure, capable of employment for party line service, in whose use the operator ma on learnin the called subscribers number, insert the calling plug immediately into the jack of the wanted line, without waiting to preliminarily test the line, and perform the switching operation for ringing the subscriber wanted, automatically controlled means being provided to render this act ineffective, should the line be busy,

and to extend -to the calling subscriber a busy sign-all I am aware that it IS not new to provide Imeans for automatically extending a calling .signal or a busy signal, the signal extended being determined by theengaged or disen- SO gaged condition of'the called line, but as far as I am aware, it is new to provide for the automatic extension of busy signals in com bination with structures employing manually operated party line ringing keys.

My invention involves primarily special apparatus connected with the operators cord circuits, and may be employed in connection with a plurality of known forms of line circuit arrangements without. change therein,

being thus adapted for ready installation ,in connection with existing telephone ex- {fcha'nge systems.

...The )resent application isa division of an application filed by me, for improvements in telephone systems, now issued as Patent No. 1,208,718, December 12, 1916.

.Referring to the drawings,

Figure 1 illustrates a Slde. View ofa key structure employed in connectionwith my invention; i 1

Fig. 2 is a left-end view thereof, omitting Qthelistening cam L and its springs and the ringingYsp -ings of'plungers I);

Fig. 4.- shows in perspective the upper portion of spring-lever 61.

Fig. 5 is a front view of arm 57 employed to actuate the spring-lever 61.

Fig. 6 shows the association of the circuit changing springs with spring lever 61 adapted for use in connection with the circuit of Fig. 9.

Fig. 7 illustrates two telephone lines and operators cord connecting apparatus arranged in accordance with my invention.

Fig. 8 shows the application of my invention to a varying form of telephone eX- change system.

Fig. 9 illustrates a modified form of operators link circuit adapted for use with a modified form of key.

The key structure shown in Fig. 1, comprises the usual listening cam L adapted, when thrown over, to connect the operators talking set with the cord strands. In addition, plunger-s b, e", (Z and etare providcd, as is usualin selectiveparty line ringing systems, each being adapted, when. operated, to cause the bell of one subscribers substation on the called line to ring, and of one only. Two magnets 21 and 26. are provided for controlling the operation of the plungcrs, magnet 21 being arranged to be operated when connection is made with it called line and to hold a depressed plunger in its ringing position until the called subscriber responds or the operator withdraws the plug from connection with his'line, a response-failing. The other magnet 26 is operated only in case the called line is busy, and when so operated prevents a depressed plunger, from assuming its ringing position,

so that interference with existing conver- ,terlocking with rocker arm 51 as shown in l igs l and 2. The said arm pivoted at upper edge of 51 engages the shoulders 60 of the plunger-s preventing their depression, until such time as magnet 21 becomes energized, which occurs as soon as connection is made with a called line, when spring 54 rocks arm 51, so that it disengages shoulders 60 while its pawls press against the plungers. This is to prevent the operator from depressing a plunger until connection has been made with the called line so that, should the line be busy, magnet2d willbe actuated in time to prevent a depressed plunger from assuming its ringing position.

Magnet 26, by its spring 55 (Figs. 1 and 2 fastened to its armature, interlocks with rocker arm 418, whose four pawlstwo being shown complete'in Fig. 1' and two as broken o1fare normally held disengaged from their respective plungers. -When 26 is actuated, spring 55 moves arm 48 about its pivots 4.9 and 50, so that the said pawls I press against their plungers. As shown in igs. 2 and 3, arms 48 and 51 are disposed on opposite sides of the plungers.

The plungers'and the parts individual to them being identical, but one, d will be specifically described. It is journaled to mounting plate 62 and support 63, and when depressed and released, its spring 59 tends to raise it to its normal position shown. In addition to shoulder 60 before referred to, shoulder 56 is provided, which descends below the pawls of arms 51 and 48 on depression of the plunger, whereby its ascent is rendered controllable first by magnet 26, and

thereafter by magnet 21. Fastened to the plunger is arm.57 whose T shaped extremity fitting into the I shaped orifice of spring lever 61, (Figs. 1, 4 and 5), on downward stroke of plunger (Z passes-on the left sideof 61, while on the upward stroke it passes on the right side of 61 to a position where it causes the closure of contact 44.45. This is the ringing position of the plunger, and in this position the plunger is held (provided the line wanted is idle) due to the energized condition of magnet 21 and the consequent engagement of arm 51 with shoulder 56, until, on the response of the subscriber, .21 is denergized.

The plunger also carries arm 58 which extends through the frame, as shown in Fig. When the lunger is fully depressed, 58, engaging its particular angular surface of rocker arm 67, pivotally connected to the vertical and pivoted supporting arms shown, it-inovcs the said arm 67 .to the right, which, by its extension 67, moves mechanically connected springs 36 and 37 to their alternatepositions. Should the called line 'be busy and magnet 26 therefore energized when the plunger is depressed, arm 48 by its pawl engages shoulder 56 and holds the plunger practically completely depressed, so that springs 36 and 37 continue. in their alternate positions, while arm 57 is prevented from assuming its ringing position.

Having described in detail the special mechanism employed in connection with my invention, I shall describe the circuit drawings, in which, for the sake of clearness, but few mechanical elements, and those in diagrammatic form, are shown, without cross references to Figs. 1 to 5, assuming that the mechanical combinations are borne in mind.

Similar parts, appearing in Fig. 7 and Figs.

1-5, have corresponding reference characters.

In Fig. 7, I have illustrated a telephone line extending from substation B to the exchange and there provided with a well known line circuit arrangement. The mechanism at B includes hook lever 1 normally maintaining the condenser and bell in bridge of'liinbs 2 and 3, and adapted on removal of the receiver to open the bell circuit and connect the transmitter and receiver with the line limbs.

The various ground connections illus trated at the exchange indicate connections to the grounded side of battery by the office return.

The line limbs 23 of substation B are connected to the opposite sides of battery 65,

the line relay 4, controlling line signal lamp 5, bein connected between 2' and the active side of battery. The cut-ofl" relay 6, connected from ground to the sleeve contacts 8 of the spring jacks, when actuated, by its armatures opens the normal connections of limbs 2 and 3 and connects them to jack contacts 8 and 7. 1

A second telephone line is shown, to which are connected substations B, C, D and E, to each of which the description of substation B also applies. The central oiiice circuit (1); this line is similar to that of the line of An operators cord circuit is shown including an answering plug havin tip and sleeve contacts 9 and 10, and a ca ling plug having ti) and sleeve contacts 11 and 12. Associated with the answering plug contacts are relays 13 and 14, jointly controllin the answering supervisory signal 15, whi e, in association with the calllng plug contacts,

Relay 19, having preferablya high 'resistare relays 16 and 19 controlling the calling causes springs 37 and 3(3 ternate positlons, the actuation of 36 uniting the plug and conductor (36,

ance winding, by its armature controls the circuit of key magnet 21 to eti'ect its energization as soon as the calling plug is inserted .in a line jack, whereby plungers b 0 0?, and e are unlocked. A depressed plunger to assume their altest relay with the sleeve contact 12 whereby it. becomes sensitive to the busy condition of a called line. By its armature 24, relay 22 controls the key magnet 26. Armature 23 controls the connection of busy machine 39 with the line of the calling subscriber.

The circuit of magnet spring 31 of relay 27 and its normal contact, which latter relay has an actuating winding 29, normally connected to tip contact 11 of and a locking winding 28 controlled by armature 30. ConductorCG is adapted for connection with any subscriber wanted.

of the ringing springs 40, 42, 4 c and'tti.

The generators rent of diticrent frequencies and the callbells at substations B, C, l), and E- are tuned so that each is responsive only to current of the fre uency delivered by the generator designated by thecorrespomling small letter. Such an harmonic selective ringing system is described in U. S. Letters Patent to lVm. 1V. Dean, title, larty line telephone system, No. 779,533, issued Jan. 10, 190:).

By means of the plungers b 0 (P, and 6 the operator can connect the proper generator with an idle called line to ring the lnterrupters b, c, d, and c are provided to alternately interrupt and close connection between springs 40,42, 44 and 46 and their associat d generators, whereby the substation bells are'intcrmittently caused'to ring. In addition to the two brushes effecting this v additional brushes, so arranged that conductor 6 is always grounded when one of springs 40, 42, 4t and 46 is connected to it,

in order to insure thatwhen the called subscriber removes his receiver, circuit will instantanemlsly be completed through relay 2?. whereby magnet 21 is dciinergized to disconnect the enerator. The remaining con nectioris wil be understood best from the description of. the operation.

()pemfirm F '7. Assuming that converse withisubscriber D, the removal of the receiver at substation ll completes circuit through line relay 4, the current traveling through hook lever 1 and its alternate contact. The attracted armature of relay 4 effects the display of lamp 5 to attract the operators attention. he inserts the answering plug into the jack of the calling line. closing contacts 7-9 and 8 10, which latter completes a circuit of battery 21 extends through b, c, (I, and c, deliver cur-.

are provided two subscriber B desires to through supervisory relay 14 and cut-ofi' relay 6 1n series. The attracted armatnres of relay-6 open the circuit of relay 4: (whose retracted armature renders signal 5 inert) and by engaging their alternate contacts, connect limbs 2 and 3 to contacts 8 and 7. Relay 14 attracts its armature, which would cause the display of supervisory signal 15 were this not prevented by the attraction of the armature of relay 13, now energized by current through its winding, contact 9-7, armature of relay 6, hook-lever 1,-returning through the other armature of relay 6, contact 8-1O and through relay 1a to battery.

The operator, ascertaining in the usual manner what subscriber is Wanted, inserts the calling plug into a multiple jack of the line connected to the said subscribers station closing contacts 11-7 and 12 -8. Current flows from ground, through cut-ofi relay 6 of the called line, Contact :8'12, its normal contact and spring battery 65. The attracted armature of relay 19 closes circuit from ground, through spring 3]. and its normal contact. key magnet 21 and to battery, whose actuation causes plungers b 0 (Z and e to be unlocked. The attracted armature of relay 19 also etiects the display of supervisory signal lamp 20.

The operator now depresses plunger (Z to its full extent, which throws over springs 37 and 36 to engage'their alternate contacts. To this point, the operation of the system is the same whether the called line is busy or idle.

The described movement of spring 36 connects the winding of test relay tact 12 with the sleeve contacts 8 of the spring jacks of the called line] The: actua tion described ot' springfi? disconnectstemporarily the sleeve strand of the cord from the active side of battery ()5 and completes a new path for current tln'oi'lgh relay 19 to ground.

Assuming first that the. called line is idle. it will be observed that the grounded winding of relay 22'is connected through contacts 38- -36, 12-8. to the grounded winding of cut-otl relay t) of the called line. No flow of current results through relay 22',and the depressed plunger ascendsto the ring ing position because. owing to the dci nergized condition of relay key magnet 26 remains inert. The-contact of springs 37 and 36 with their alternate contacts being in this case momentary only, they resume their normal positions, circuit being again completed from ground at the called line,

through cut-(zit relay (3, ('()lll;2\('l.s"8-l2, spring 37, rc|ay 19 to battery. 'attractcd armatures of cut-oti'rcla 37, relay 19 to 22 with the sleeve strand of the cord and through conthrou h windin 29 ot rela 27. its normal n 2 v I contact. and sprmg -l'-3. armature 2o ot re- ,lay 22, contact 11-7, the attracted armature of relay (3 limb 3, through the call bells and condensers of substations li. I.) and E in parallel, returning over limb the attracted armature of relay (3, contact S--l2. spring 37, relay 19, to battery. Due to the substation condenser the. relay 27 is not encrgized; and the frequency of current being out of tune with the call bells of all the substations other than D. the subscriber at that substation is alone signaled. By the removal of the receiver at substation D, circuit is instantly completed from ground at the exchange, through one or the other of the brush pairs of interrupter (1', contact M -l5, winding 29 and, following the before traced pat-h ot' ringing current, to battery 65. This being direct; current, relay 27 is energized, whose attracted armature 30, engaging spring 31, completes a locking circuit through winding 28 for relay 27 and immediately thereafter opens the circuit of key magnet 21, whose detinergization allows the return of plunger to its normal position. The attracted armature 32 of relay 27, engaging spring 33, completes the talking circuit of the tip strand of the cord circuit and thereafter opens the circuit of winding 29 of relay 27. On the closure of contact 3233, a path for the flow of can-rent was established through the grounded winding of relay 16, over the talking circuit as indicated by the heavy lines, to limb 3 of the line of subscriber I), returning over limb 2 and through relay 19 to battery. The at.- tracted armature 18 of relay 16 opens the circuit of supervisory lamp 20 which is thereby put out, notifying the operator that the response has been made. The attracted armature 17 of relay 16 completes the tall ing circuit of the sleeve strand of the cord circuit. and the two subscribers are now in conversation through condensers s and s, the talking circuit being indicated from substation B to substation D, through the exchange, by the heavily marked conductors, current for energizing their respective transmitters being supplied from battery through the sleeve. supervisory relays 14 and 19 respectively, the return path being traced through the relays 13 and 1G respectively.

\Vhcn subscriber ll replaces his receiver, circuit is opened through relay 13, whose retracted armature effects the display of lamp 15; and when D replaces his receiver, circuit is opened through relay Ill. whose. retracted arn'iature 1S closes circuit through lamp 20. The operator, observing the simultaneous display of the two supervisory signals, withdraws the answering plug from the calling line, effecting the detnergization of relays 6 and let, while the withdrawal of the calling plug interrupts circuit through relays 6 and l9. The ret'acted armature of relay 19 opens circuit through lamp 20 and also through the locking winding 28 of relay 27, whose retracted armature 30 allows spring ll to engage its normal contact, again placing key magnet 21 under the control of relav 19: while tne retracted armature 32 of relay 27 allows spring 23? to engage its normal contact. again placing conductor 36 in operative relation with tip contact 11 of the calling plug.

(/(IIIILGF/I'OII with 7111s line.

The insertion ol either an answering plug or a calling plug into the spring jack of a line causes a tlow of current from battery of, through the respective sleeve supervisory relay it or 19, to ground through the. cut-oil relay (S of the line. ()wing to the resistance of the cut-off relay winding, sleeve contacts 8 of the line spring jacks are, under this condition, of a potential other than that. of ground. Assuming that. when the opera tor inserted the calling plug into a spring jack of the line of subscriber D, the just described condition existed, upon the complete depression of plunger (Z throwing over springs 37 and 36 to engage their alternate contacts, the raised potential oi the sleeve contact 8 of the jack, into which the calling plug was inserted, would cause a flow of current through sleeve con act 12 of the calling plug now inserted in the busy line, through contact 3(338, the winding of test relay to ground. The attracted armature 2-l of this relay then completes circuit: through busy magnet 26, whose actuationprevents the. return of plunger to the ringing position by holding it practically fully depressed so that springs 37 and 36 are continued in their alternate positions. The. attracted armature 23 of relay i212 conni'letes circuit from interrupter I"), through the induction coil and condenser, through the sleeve strand condenser s and contact. 10-8 to the calling line, whereby the calling subscriber is notified that the line. wanted is busy. lle thereupon replaces his receiver, therebydisplaying supervisory signal 15- and advising the operator that the line should be disconnected. The witlulrawal ot' the calling plug opens thecircuit of test relay 22, whose rc tractcd armaturcs 23 and 1M disconnect. the busy machine 3!) and decnergizc key magnet 24;. whereupon plunger I]: ascends to a posi t'ion where springs 36 and S57 assume their normal positions. I As soon as 37 disengages its alternate contact, relay It becomes inert, and the. retracted armature opens the circuit of key magnet 21, whose deiiuergization alblows the return of plunger (5 to normal;

Fig. In Fig. 8, I have illustrated a telephone lows 3 exchange system of well known character,

employing three conductor spring jacks and,

, signals inert when the substation circuitsare completed by the removals of the receivers, render them inert by shunting them by resistances and respectively.

The two connected subscribers lines in 8 areinductively united for conversation by windings r, r, of a repeating coil, inst id of by condensers s, s, as shown in l? 1g, 7.

l h' ietiy, the operation of Fig. 8 is as fol- When subscriber B initiates a call, relay andjlanip 5 are energized. On the insertion of the answering plug into the jack of the calling line, the placing in series of the signal lamp 15 with cut-off relay 6 Would cause its display, were it not immediately shunted by resistance 15" on the attraction of the armature of relay 18, which relay is energized at once by current over the callin g line. The operator, learning in the usual manner whatsubscriber is wanted, assumed to be D, inserts immediately the calling plug in a spring jack of the called line, closing contacts 1i=*-7=, 12"83 and 12 8". Thereupon current flows "from ground, through cut-oil relay 6 (attracting its armatures),

contact ti -12", spring 37, signal 20 (disfit;

tractcd urinate S9 with the (railing line and cause the-iactua- 7,

pit-tying it), relay 19 to battery lhe attracted armature of relay 19 eii'ects energization of key magnet 21, releasing the key plungers and setting the ringing position pawl-s againstthe plungers. The operator, now ;le ressing plunger (1 causes springs 37 and 3b to enga their alternate contacts, the closi of contact placing test relay 2?- in operative relation with sleeve 12* of the calling plug. It the. plug of another cord is already connected to the called-tor line, contacts 8 and 12 will be at a potential other than ground, due to a how of current from the other cord, through the resistance of cut-0d relay (2 of the called line, to ground. ltela y 252 will therefore be energized, and its at- I will connect interrupter tion oi key magnet :26 rcspectivel y, to trans init the busy signal to subscriber B and prevent plunger (Z 't'roin assuming its ringposition. Subscriber B, replacing his reteiver, thereupon dc'eTnergizes relay 13,

whose retracted armature removes the shunt of 15 from signal 15. Both signals being displayed, the operator removes the 1 two plugs and the apparatus resumes its normal condition.

Should, however, the 8 and 12* will be at the potential of. ground,

called line be I relay 22 and magnet 26 remain deenergized,

and plunger d assumes its ringing position,

whereby contact 44%5 is closed and ring-x ing. current projected from generator d, through winding 29 of relay 27, overthecalled line to ring the bell of subscriber D,, as before'described. On the removal of the receiver at D, direct current flows from ground, through contact 4H5, winding; 29, contact 1l7, through lever 1 at D,, returning through'8 12, supervisory relay 16 to battery 65*. Arniatures 30 and 32 of relay. 27 operate to 21, to allow the return of plungeri'lfliaiid to complete the talking circuit of the tip cord strand. The attracted armature of relay 16 shunts signal 20 to render it ine'rt by means of resistance 20 I l/Vhen subscribers Bv and D replace their receivers, relays 13 and 16 are deenergizcd, and their retracted, arn'iatures remove the shunts of resistances 15 and 20 from about deenergize magnet r signals l5 rand 20, whose simultaneous-dis play notifies the operator to remove the answering and calling plugs, which causes the line circuits and the cord circuit-to resume their normal positions. InFig. 9 I show my invention carri in a form employing the polarized relay. 88 and adapted to be used in connection with the key structure of Figs. 1 to 5; with the exception that key magnet 26 and its lever 48 are not employed, while fastened to lever 61 of each plunger is to lie-provided an additional switch spring ,With its. associated contact 100, asv shown in ;Fig.; (3, adapted when a plunger position to connect interrupter 87-, (Fig. 9) with relay 86. )n connection made with an. idle line by the calling plug of; Fig. :9, armature contact 89, 90 of relay 88 is closed no energize relay 82 whose arn'iature Shoe ed out i is in its ringing i *tab'lishes a locking path for current 011,82 i

from the it volt battery switch springs, of relay 76 and the cut-off relay 6 of the called line which flow puts the busy potential on the sleeve contacts of the spring jacks. The attracted armature "S t 'of relay 82 closes circuit through lampQZO displaying it, a branch circuit through key tap, through the n'iagnet 21 being also established to actuate 21' which unlocks the plungers (see Figs. 1

land 2) and places the pawls of lever 51 in position to hold a depressed plunger in ring ing position. orator d.(l?ig. 9)

4-1, 45 and 99', 100, will be closed and current will intermittently flow from generator (23' through armature ofrelay 86, when re- Assuming the plunger ot'gen-i to be. depressed, contacts complete the talking circuit of the strand.

' connection of said link-circuit tracted, armature 78 of relay 76 to the called line. On the response of the subscriber, relay 16 is actuated by current assing through the immature of relay 86 W e'n attracted, armature 78 and over the called line. The attracted armature 18 of relay 16 puts out lamp 20 and establishes a flow of current to energize relay 21 Whose attracted armatures open circuit through key magnet 21 (allowing the return of 2% depressed plunger to normal, whereby contacts 44, 45 and 99, 100'are opened) and tip cord Should the called line, however, be busy when the calling plug of Fig. 9 is connected to a spring jack thereof, armature 89 of relay 88 engages contact 91, and relay 7 6 is energized, its contact 81 opening and preventing the energization of. magnet 21 so that the key plunger cannot be de ressed, The closing of alternate contact (9 establishes a locking circuit for relay 76 through the cut-01f relay of the called line and the closing of alternate contact 81 energizes relay 82 to light signal 20. Busy back 39 is connected through alternate contact 80 to the sleeve strand of the cord and thus over the calling line whereupon the calling subscriber replaces his receiver. The operator finding the plungers locked against depression need not wait for the dis play of signal lamp fore Without delay remove the plugs of the cord circuit from the jacks of the two lines, whereby the cord apparatus is restored to normal, the calling subscriber having meanwhile for a short period heard the busy signal in his-receiver.

It is not my intention to limit myself to the particular devices and arrangements herein shown and described, as the principle of my invention is capable of varying employments, and I aim to cover all such arrangements as come Within the spirit and scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A telephone system comprising a telephone line, a link-circuit for establishing connection with said line, a ringing current source, contacts for connecting said source to said line to transmit ringing current thcrcovcr, means normally operative to hold said contacts against operation, and means for freeing said contacts in response to the to said line.

2. A telephone system con'iprising a telc phone llll(,i a linlccircuit for establishing connection to said line, a ringing current source, contacts for connecting said source to said line to transmit ringing current thcreovcr, a stop for preventing the operation of said contacts, an: 'uctroi'nagnet for removing said stop flight preventing p0 15, and she may there sition, and circuit connections and a source of current for operating said magnet to remove said stop in response to the connection of said link-circuit to said line.

3. A telephone system comprising a telephone line, a link-circuit for establishing connection to said line, a ringing current source, a ringing key for connecting said source to said line to transmit ringing current thereover, a stop normally lying in the path of movement of said key to prevent its operation, an electromagnet for removing said stop from its normal position to permit the operation of said key, and circuit connections anda source of current for operating said magnet upon the connection of said link-circuit and line.

4. A telephone system comprising a telephone line, a link-circuit for establishing connection to said line,

said line to transmit ringing current thereover, means normally operative to hold said contacts against operation, and means for freeing said contacts by closing a circuit over a portion of the connected link-circuit and line.

5. A telephone system comprising a telephone line, a link-circuit for establishing connection to said line, a ringing current source, contacts to connect said source to said line to transmit ringing current thereover, a stop normally operating to prevent a ringing current source, contacts to connect said source to the operation of said contacts, electro-magnetic means for removing normal position in response to the connection of said link-circuit and line, and means responsive to the subsequent operation of said contacts to cause said stop to lock said contacts in their actuated position.

6. A telephone system comprising a telephone line, a link-circuit for establishing said stop from its connection to said line, a ringing current source, contacts to connect said source to said line to transmit ringing current there over. a stop normally operating to-prevent the operation of said contacts, electromagnetic means for removing said stop from its normal posi ion in response to the connection of said link-circuit and line, and means also controlled by said electro-magnetic means for locking said contacts in their actuated position.

7. A telephone system comprising a telephone line. a link-circuit for connection to said line, a source of ringing current, a key for applying current from said source to said line, and meansfor preventing the operation of said key until said link-circuit is connected to said line.

8. A telephone system comprising a telephone line, a link-circuit for establishing connection to said line, a source of ringing current, normally locked'ring'ing contacts 9. A telephone system comprising a telephone line, a link-circuit for establishing connection to said line, asource of ringing current, normally locked ringing contacts for applying current from said source to said line, means operated upon the connection otsaid link-circuit to said line to unlock said contacts, means responsive to such connection to lock said contacts when moved to their actuated position.

10. A telephone system comprising a tele' phone line, a link-circuit tor establishing connection to said line, a-source of ringing current, normally locked ringing contacts for applying current from said source to saidline, means for unlocking said contacts by completing a circuit over a portion of the connected link-circuit and line, and means responsive to the subsequent operation of said contacts to lock said contacts in their actuated position.

11. A telephone system comprising a telephone line, a link-circuit for establishing connection to said line, a ringing current.

source, contacts to connect said source to said line to transmit ringing current thereover, a stop normally operating to prevent the operation of said contacts, electromagnetic means for removing said stop from its nprmal position, means for actuating said clcctronnignetic means by closing a circuit over a portion of the connected linkcircuit and line, and means responsive to the subseouent operation of said contacts to cause said stop to lock said contacts in their actuated position.

12. A; telephone system comprising :1. called telephone line. a link-circuit for connecting to said line. a source of ringing current. normally locked ringing contacts for applying said source to the connected line, means dependent upon the connection of said link-circuit to said line to tree. said ringing contacts, means operated upon the subsequent operation of said contacts to lock said contacts in their actuated position. and means dependent upon the response oi the called party to again tree said contacts.

13. In a telephone system including telephone lines, signals therefor at the exchange. and operators link-circuits tor connecting said lines. thelcon'ibination, with a line. ot' a station connected thcreto,-an operato s link-circuit connected with said line negted with said line, a manually operated ringing key associated with said link-circuit adapted to be placed 111 ts ringing position ing ringing current to, the

by the, operator, and apparatus sensitive to the connection of said first link-circuit with said line to prevent the placing of said key in ringing position and to extend a signal.

14. A telephone system comprising a telephone line, a link-circuit, a mamiallycoperated key for applying ringing current to the line when connected to said link-circuit, a control relay normally interrupting the talking circuit of said link circuit, a second relay, a control circuit therefor connected as a branch of a talking strand of said linkcircuit, a switch for conductively uniting the telephondlinc limbs to operate said second relay; and means actuated by said second relay to o 'i'eratc said control relay to effect the continuity of the talking circuit of said link-circuit.

15. A telephone system comprising a telephone line, a link-circuit, means for applylinewhen connected to said link circuit; a control relay normally interrupting the talking circuit of said link circuit. a second relay therefor, a b 'anch circuit extending from a talking strand of the link circuit and including said second relay, a switch for conductively uniting the telephone line limbs to operate said second relay, and means actuated by said second relay to operate said control relay to ciiect the continuity of the talking circuit of said link circuit.

16. A telephonesystem coml'irising a called party telephone line, a link circuit connected thereto. ringing keys adapted to be operated for associating ringing currents of dittercnt character with said link circuit and line. a magnet common to said keys, mcans for energizing said magne, a relay and source of direct current in bridge of said line and link circuit, a switch at the called substation of said line adapted to be closed to cause operation of said relay by said source, and circuit connections effective. upon. such operation whereby said magnet is decnergized to release any actuated key from its ringing apparatus.

17. A telephone system comprising telephone lines terminating at an exchange, link circuits for interconnecting said lines, a source of signaling current. a key for each link circuit for applying current from said source to the associated link circuit and thus to the connected called lines. and means to prevent the operation ot said key and thereby prevent-the application of current to a link circuit until connection made/with an idle called line.

18. A telephone system comprising lines terminating at an exchange. link circuits for interconnecting said lines, a source of sig naling current. a key for each link circuit for applying current from said source to called lines, and means to prevent the oper- &

ation of a key until theassociated link cir cuit is connected to a called line.

19. A telephone system comprising tele phone lines terminating at an exchange, a plug ended link circuit of said lines as a called line, a source oi. signaling current, a key for said link circuit for applying current from said source to saidlink circuit, and means to prevent the Operation of a key until the plug is coiinected ,to a jack of the called line.

20. A telephone system comprising tele phone lines, an operators link circuit for connecting to any of said lines as a called line, a normally disconnected source of signaling current, akey for said link circuit for connecting said signaling current to the link circuit, and means to prevent the operation of said key until a called line is connected with.

21. A, telephone systcni comprising telephone lines, link circuits for interconnecting said lines, a key for each link circuit for connecting ringing current to the associated link circuit, and means to prevent the operation of the key unless a telephone line is coin'iec-tet'l with.

22. In a telephone exchange system including telephone lines, substations cons nected thereto, signals at the exchange adapted for display responsive to currents over said lines, multiple terminals associated with said lines and link-circuits for intercoi'inecting said lines, adapted for connection with said terminals to render them busy, the COITlblIlfltlOli with a link-circuit of a ringing key associated with said link circuit for actuation by the operator, means normally locking said key against actuation, an electroinagnet adapted for eiiergization on connection made with an idle line, and mechanism controlled thereby for unlocking said. key and for causing it when actuated to assume its ringing position.

23. In a telephone exchange system including telephone lines, substations connected thereto, signals at the exchange adapted for display responsive to currents over said lines, multiple terminals associated with said lines and link-circuits for interconnecting said lines adapted for connection with said terminals to render them busy, the combination with a link-circuit of a. ringing key associated with said link circuit for actuation by the operator, means normally locking said key against actuation,

an electro-inagnet adapted for energization on connection made with an idle line, mechanism controlledthereby for unlocking said key and for causing it when actuated to as sumo its ringing position, and means operative on a response at the called substation to.

cause the key to leave its ringing position.

24. In a telephone exchange system int'or connecting to any eluding telephone lines, substations connected thereto, signals at the exchange adapted for display responsive tocurrents over said lines, multipleterminals associated with said lines and link-circuits for interconnecting said lines, adapted for connection with said terminals to render. them busy, the combination with a link-circuit of a ringing key associated with said link circuit for actuation by the operator capable of being caused'to assume means normally locking said key against actuation by the operator, an electro-magnet adapted for actuation on connection made with a line, mechanism controlled thereby three positions,

for unlocking said key and for causing the actuated key to assume its ringing position, means operative on a response at a called substation to cause the key to leave its ringing position F, second electromagnet adapted for actuation when connection is made with over said lines, multiple terminals associated with said lines and link-circuits for interconnecting said lines, adapted for connection with said terminals to render them busy, the combination with a link circuit of a ringing key associated with said link circuit for actuation by the operator capable of being caused to assume three positions, means normally locking said key against actuation by the operator, an electi'oniagnet adapted for actuation on connection made with a line, mechanism controlled thereby for unlocking said key and for causing the actuated key to assume its ringing position, and means operative on a response at a called substation to its ringing position.

26. In a telephone exchange system includii'ig telephone lines, substations con nected thereto, signals at the exchange cause the key to leave adapted for display responsive to currents over said lines, multiple terminals associated' with said lines and link-circuits for interconnecting said lines, adapted for 00111160 tionwitli said terminals to renderthem busy, the combination with a link-circuit of a ringing key associated with said link circuit for actuation by the operator capable of. being caused to assume three positions, means normally locking said "key against ac itiation by the operator, adapted for actuation on connection inade with a line,andmechanisni controlled thereby for unlocking said key and for causing;

an electroinagnet 12a of said lines, link circuits for'interconnecting said lines, sources of signaling current, a key for each link circuit for applying current from said sources to the associated link circuit and thus to the connected called lines, and means to prevent the operations of said key until connection is made with an idle called line.

28. In a telephone system, a plurality oftelephone lines extending by their. limbs from substations to anexchange, a cord circuit at the central for connecting said' lines, a source of signaling current for signalin said substations, circuit connections therefor, normally connected to the calling end of the cord circuit, manually operated switching means for connecting said source to said circuit connections and supervisory means operating on connection of the switclnng mechanism to a busy line to automatically disconnect the source of signaling current and prevent ringing in the ear of a subscriber using the line. i

Signed by me at Chicago, county of Cook,

and State of Illinois, in' the presence of two Witnesses. I v y 4 v p ALFREDHJDY ON.

Witnesses:

Gnouen E. MUELLER," M. R. Roonronn,

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