US561335A - Telephone-exchange system - Google Patents

Description

(No Model.) 3 sheets sheet 1.

' K. B. MILLER. TELEPHONE EXCHANGE SYSTEM.

Patanted June 2, 1896.

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3 Sheets-Sheet 2.

(No Model.)

K. B. MILLER. TELEPHONE EXCHANGE SYSTEM.

* Patented June 2, 1896.

(No Model.) I 3 SheetsSheet s. K. B. MILLER.

TELEPHONE EXCHANGE SYSTEM. No. 561,335. Patented June 2 1896.

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TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 561,335, dated June 2, 1896.

Application filed February 18, 1896. Serial No. 579,795. (No model.)

To all whom it may concern:

Be it known that I, KEMPSTER B. MILLER, a citizen of the United States, residing at WVilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Telephone-Exchange Systems, of which the following is a specifi cation.

My invention relates to what are known as divided-board exchange systems, and has for its object a construction of less com plexity than those in use at present, which will nevertheless give quicker and more reliable service. In order to attain this object, I terininate the subscribers lines in spring-jacks arranged on divided boards. Connected to each line is an annunciator, also on the board. This annunciator not only serves to indicate calls, but also, after connections have been made, as a clearing-out signal.

I provide each board with a number of connecting-plugs arranged in two sets, each set intended to be manipulated by a different operator. These plugs form the terminals of trunlnlines extending between the boards. The plugs of the first set at each board which are to be manipulated by an operator, whom I shall designate the A operator, are to be used only to answer calls. The trunk-lines from the individual plugs of the first or A operators set at each board are distributed among all the boards, where they terminate in plugs of the second sets.

The second set of plugs at each board is under the control of an operator, whom Ishall designate as B operator. The B operator at each board is charged only with the duty of completing the connections which have been initiated by the A operator at her own or another board, and each B operator, therefore, has before her in the second set of plugs one or more trunk-terminals from each A operator. Thus the A and the B operator at any board are each able to reach and control the entire number of jacks on that board; but so far as the plugs are concerned each operator has to attend to those of her own set only.

In order that the greatest possible speed may be attained in their'respective duties, I provide the A operator with special means for listening in and for restoring the annunciators, adapted to be governed by the partial insertion or withdrawal of her plugs, and for the B operator special means for listening in, operated by simply grasping and slightly moving the plug with which she is to complete the connection. In addition I provide a signaling-circuit for each trunk-line, containing mutual signals for both operators. These signals are directly in the circuit, together with a generator, and this circuit is directly controlled by the manipulation of the respective operators plugs, without any intermediate apparatus and without the interposition of relays or subcircuits.

The means I prefer to use for restoring the annunc iators and connecting the A operators telephones by the insertion or withdrawal of their plugs consist of contact-springs connected to the restoring-coils and to the A operators telephones, respectively, lying adjacent to the 1ine-springs and alternate annular depressions and enlargements 011 the plugs so located as to interconnect the springs momentarily during their insertion in or withdrawal from a jack. In practical operation each A operator is to be provided with a dummy plug held in the left hand and provided with a proper surface to operate these springs. A call being received, her telephone is connected to the line and the annunciator restored by the insertion of the dummy plug. She ascertains the number desired and selects the terminal plug of the trunk-line leading to the board (whether her own or anothers) upon which the desired subscribers line terminates. As she removes this plug from its seat and inserts it in place of the dummy the signaling-circuit appropriate to the selected plug is automatically energized. As this trunk-line terminates at the board in which the called-subscribens line terminates in a B operators set the operator, noticing the signal, has only to grasp the corresponding terminal plug andtilt it slightly to connect her telephone through the trunkline to the calling-subscribers line and in her turn ascertain the number required, when nothing remains but to lift the plug she has already grasped, insert it in the proper jack, and depress the calling-generator key. The

act of lifting her plug from its seat changes the" I T resistance of the trunk-line signaling-circuit o shows a calling-plug, and Fig. 5 is a dummy and at central. Fig. 0

and operates the A operators signal, thus informing her that the desired connection is complete.

The 13 operators plugs will, of course, fit in the spring-jack of every line, but unlike the A operators plugs they lack the projection necessary to connect the operators telephone to line. They are provided, however, with the necessary projection to complete the annunciator-restoring circuits.

When the subscribers shall have rung off, the simple withdrawal of the plugs finally rcstores the annunciators, and their replacement in their seats finally deenergizes the signaling-circuit. If, however, one plug only is replaced, the corresponding signal only is actuated.

My invention is also equally applicable to small exchanges requiring but one board and one set of operators. 111 this case no dummy plug is required for ascertaining the number of the line desired, as the operator may insert the answering-plug of any pair not in use in the jack of the calling subscriber and ascertain the number wanted either by the use of the plug and spring-jack, already referred to in connection with the A operators sets in the divided-board system, or she may be provided with plug-seat switches like those forming the operatorsmeans of listening in in the divided-board exchange. In a single-board system of this kind the operator is therefore provided with a number of pairs of plugs and with either one of the two means for listening in described in connec tion with the divided-board exchange.

In carrying out my invention I employ detailed constructions of the various parts, which will be fully described hereinafter.

My invention is illustrated in the accompanying drawings, in which- Figure 1 is a diagrammatic viewof the central-ollice apparatus and circuits of an exchange having three divided boards, the circuits and mechanism pertaining to signaling between the operators being omitted. Fig. 2 is a diagram showing the circuits and apparatus of a lineboth at the subscribers station is a detail view of an answering-plug and line spring-jack. Fig. 4

plug. Fig. 6 shows the apparatus and circuits associated with the calling-plugs, and Fig. '7 shows a trunk-line signaling-circuit.

In Fig. 1 are shown three divided boards 1, 2, and 3, each containing, say, three hundred spring-jacks and their corresponding annunciators. Each of these jacks forms a terminal for a subscribers line. The subscribers lines are grouped according to greatest convenience, and each terminates in one jack only. Below each board are shown two sets of plugs, the answering or A operators plugs PA and the calling or B operators plugs PB. One A. operators plug (marked 1) at board 1 is shown connected by the trunk-line T T with a B operators plug at board 1. Another A operators plug (marked 2) at board 1 is connected bya similar trunk-line to a l3 operators plug at board 2, and still another A operators plug (marked 3) at board 1 is connected to a B operators plug at board 3. In like manner each A operator is provided with a set of answering-plugs, forming the ter1ninals of trunk-lines, each of which runs to a calling-plug in some one B operators set, so that each. A operator is connected by a separate trunk-line with each operator.

I have hereinafter termed the collection of trunk-lines running from any A operators set of plugs a set of trunk-lines. It will now be seen that each set of trunklines centers in some one A operators plugs, and from there the separate lines ra- (hate in a fan-like arrangement, each running to a plug at some B operators set.

For convenience and simplicity of illustration but one trunk-line is shown from each A operator to each 13 operator; but it will readily be understood that in practice several will be needed.

Each spring-jack J (see Figs. 2 and 3) is composed of two line-springs a and b and two auxiliary springs c and cl, all normally insulated from each other and mounted, as shown, on insulating-strips w, or in any other suitable manner. The springs to and b of each jack are connected, respectively, to the two limbs L and L of the line, as shown in Fig. 2. All the springs c of each board are connected bywire 5 to one side of the telephone tbelongin g to the A operator at that board, while all the springs d are connected by wire 6 to the other side of the same telephone.

As all the springs c at each board are permanently electrically united, and likewise all the springs d, it is advisable in practice to form them by laterally slotting a strip of brass corresponding in length to the length of a row of jacks, thus forming teeth like those of a comb. These teeth, which form the springs c and d, are so spaced as to over lie the line-springs of the separate jacks of a row.

The A operators plug PA consists of two cylindrical contact-pieces c and f, mounted in any well-known manner in a handle 9 of insulating material. The contact e'is substantially of the form shown, and consists of a balltip i and a neck he]? reduced diameter. The contact f has an annular depression 7;, so placed as to leave a port-ion 7; of greater diameter between it and the neck 7b of the contact 6. These enlargements and depressions are so spaced longitudinally with respect to the plug that when the plug is partially inserted in the jack J the line-spring a is pressed by the ball-tip 'i into contact with the auxiliary spring 0, and at the same time line-spring b is pressed by the enlargement 7t" into contact with the auxiliary spring d, thereby connecting the A operators telephone with the line. On pushing the plug home, however, springs a and I) fall into the depressions h and 70, respectively, thus breaking their contacts with springs c and (l, respectively, and disconnecting the A operators telephone.

The combined calling and clearing-out annunciators are of any of the well-known selfrestoring types and are each provided with an operating-coil m and a restoringcoil n. The coil m is of high resistance and impedance and is connected on oneside to the limb L of the line-wire and on the other side to ground at G. One side of the coil n is connected by wire 3 to the spring Z) of the springjack to which the particular annunciator belongs, while the other side is connected by the wires 4 and 0 with the auxiliary spring d of the same jack. The wire 4 contains a battery B or other source of our 'ent.

The annunciator is operated by calling-current coming from the generator at the subscribers station over the limb L of the line through the coil m and to ground.

\Vhen an operator inserts a plug in a jack for making a connection, spring 1) is pressed against spring d of that jack by the larger portion of the plug, thus completing the local circuit through coil 07. and battery B and restoring the annunciator. lVhen the plug is pushed entirely in, however, contact between springs Z) and dis broken, as before described, and the annunciator is left ready to serve as a clearing-out signal. After it has been so operated by the subscribers ringing off the simple withdrawal of the plug by the operator momentarily connects springs 19 and d, and the coil n is again energized to finally restore the signal.

In addition to the plugs PA each A operator is provided with a single plug PX, which I have termed a dummy plug, and which is preferably made entirely of insulating material, having no circuit connections whatever. This plug is of such a size that when inserted in a jack it presses springs a and Z) into contact with springs c and cl, respectively, just as is done by the larger portions of the plugs PA. It is carried by the A operator in her left hand, and is used in a manner hereinafter described.

The B operators plugs PB, Fig. 4, differ from those of, the A operator in that the enlarged ball-tip 1; is omitted, thus leavin g the whole tip of the same diameter as the neck 7L on the A operators plug. Thus the l'l operators plug when inserted in or withdrawn from a jack will restore the an nunciator-shutter by closing spring 1) against spring (Z, but will not connect the A operators telephone with the line, as would be the 'case were the tip of the plug large enough to press spring a against spring 0. The B operators plug is also fitted with a metallic heel n, which en ables the A and B operators to readily distinguish their own plugs when inserted in jacks on the same board. The

real function of this heel will, however, be referred to later.

The B operators plugs rest in sockets provided with three contact-springs q, r, and s, Fig. 6, each insulated from the others and so fastened together by insulating material as to move in unison. In the path of the springs q and r are placed two contacts q and r, with which these springs are normally out of engagement. A forward tilting of the plug PB While it rests in its socket presses the springs q and r into contact with their respective pins q and r. The springs q and r are permanently connected to the two sides, respectively, of the trunk-line of which their particular plug PB forms a terminal, while the contact-pins g and r form the terminals of the B operators telephone circuit. Consequently a B operator in order to connect her telephone to any trunk-line has only to tilt the plug of that line toward her without removing it from its socket. A knob Q is provided on the spring 8, so that in case the B operator wishes to listen in afterher plug has been removed from its socket she may do so by pulling forward on the knob, thus closing the pairs of contacts q q and r r. The 13 operators are also provided with calling-keys K, one for each plug. Each key when depressed disconnects the B operators plug from the rest of the trunk-line and at the same time connects its terminals with the calling-generator B in a wellknown manner.

In order that appropriate signals may be automatically transmitted between the two operators at both ends of each trunk-line, I provide a separate signal-oi rcuit S, Figs. 6 and '7, for each trunk-line, the signals in which are controlled by contacts in connection with the plug-seats of the trunk-line plugs. The sockets in which the A operators plugs normally rest are each provided with two contact-springs o and p, which are held apart by the plug while in its seat, but which make contact with each other as soon as it is withdrawn therefrom. These springs control the continuity of the signal-circuit S, of which they form a part.

The spring 3, already referred to as being a part of the B operators plug-seat mechanism, is connected. to the signal-wire S belonging to its particular trunk-line and the metallic portion 11 of the plu g-seat is grounded. Thus when a B operators plug is in its seat the signal-line is closed to ground through the spring .9, metallic heel u, and piece o. The contacts .9 and o are permanently connccted by a moderately-large resistance R, so that the si gnal-cirouit is never entirely broken at the B operators end. The removal of the plug PB simply introduces the resistance R into the circuit.

WV isa low-resistance signal in circuit at the A operators end of the signal-line, and X is a high-resistance signal in circuit at the B IIO operators end. so adjusted to the strength of the battery 133 that W will be excited only when the resistance R is short-circuited, while X is made so sensitive that it will be operated when the contacts 0 p are closed, whether or not the resistance R is in circuit.

when the A operator removes a plug PA from its socket, springs 0 and p of that plugs seat make contact, thus closing the signal-circuit and displaying both signals. The signal X thus informs the eorrespondin g B operator that her attention is desired on this trunk line. "When she in turn removes her plug, the connection between 5' and c is broken and the resistance R thereby introduced into the signal-circnit, thus diminishing the amount of current flowing from battery B5. The current now flowing is insufficient to keep signal IV displayed, and it becomes deenergized, thus informing the A operator that the Boperator has removed her plug for making the desired connection. It now on disconnecting the two lines the B operator replaces her plug in its socket before the A operator, signal IV is displayed, informing the A operator of the fact that the trunk-line is disconnected at the other end. Should the A operator replace her plug first, the B operator is informed of the fact by the deenergization of her signal X, owing to the break in the circuit between springs 0 and 1). Thus we see that the condition of signal X at plug PB depends on the open or closed condition of the contacts 0 p at plug PA, while the condition of signal IV at plug PA depends on whether the resistance R at plug PB is in or out of circuit.

The operation of my system is as follows: A subscriber desiring a connection operates his generator in the usual way, thus throwing down the annunciator A belonging to his line. The A operator at the board at which the line terminatesfor instance, at board 1-seeing the signal at once thrusts her dummy plug in the corresponding spring-jack. This connects her telephone 25A in the line-circuit and at the same time restores the line-annunciator in a manner already described. She ascertains the number of the subscriber wanted, which we will suppose is No. 620. She knows that line No. 620 terminates on board 3, so she picks up one of her plugs marked 3, which, as we have seen, is connected with a B operators plug at board 3, and inserts it in the calling-subscribers line in place of the dummy plug. The lifting of this A operators plug from its seat allows springs 0 p of that seat to come into contact, thus exciting both signals IV and X. The B operator seeing the signal X excited grasps the corresponding plug PB and tilts it in its socket, thus connecting her telephone in circuit with the trunkline and with the calling subscriber. There are now two ways in which the B operator can learn the number desired. The first of these is for the calling subscriber to repeat the The two signals V and X are number, in which case the circuit over which the voice-currents travel is from subscribers station over limb L of line, spring a,tip c of A operators plug, limb T, trunk-line, contacts q, B operators telephone, contacts 1" r, limb T of trunk-line, sleeve f of A operators plug, spring I), and back over limb L of the line to the subscribers station. The second way is for the A operator to repeat the number, in which case she only partially inserts her plug PA, so that springs a and 1) contact with springs c and 61, respectively. In this case the talking-circuit is traced from the A operators telephone over wire 5, spring 0, spring a, tip 6 of plug PB, limbT of trunk line, contacts q q, B operators telephone, contacts 7 r, limb T of trunk-line, sleeve f of plug PA, springh, spring d, and wire 6 back to telephone 15A. The B operator having received the order has only to raise the plug PB,already grasped,and insert it in the springjack of the desired subscriber, in this case subscriber No. 620. She then presses the calling-key K, belonging to the plug used, and sends calling-current to ring up subscriber No. 620 in any well-known manner. If at any time while two lines are thus connected for conversation the A operator wishes to listen in, she does so by simply withdrawing her plug part way when her telephone is bridged across the line, as already described. In like manner the B operator may bridge her telephone into the circuit by pulling forward on the knob Q.

lVhen the conversation between the subscribers has been completed, either may ring off by operating his generator in the same manner as for calling. The clearing-out current passes to ground through the annunciators of both connected subscribers,thus throwing them down as clearing-out signals at both the A and B operators boards. Each operator on seeing the signal withdraws her plug and replaces it in its normal restingsocket. As an additional safeguard to prevent the lines being left connected at one of the boards the plug which is first replaced in its socket automatically actuates the trunkline signal at the other board, thus insuring the prompt attention of the operator at that board.

In some cases it may be advisable for the annunciator of the calling subscriber only to be used as a clearing-out annunciator. The only change needed to bring about this result is to omit the depression on the B operators plug, thus leaving them of the general contour shown by dotted lines in Fig. 4. This change would cause the springs Z) and d of the called-subscribers jack to remain in contact as long as a plug PB remained inserted therein. This would keep thelocal circuit through the restoring-coil n of the annunciator closed and prevent the actuation of the annunciator by any clearing-out currents coming over the line from either subscribers station. As the calling-subscribers line is always connected up by an A operator the clearing-out signal would in this case attract the attention of the A operator only. Seeing it, she would withdraw her plug and replace it in its socket, which would automatically open springs 0 p of the trunk-line signal-circuit and effect the signal X,thu s notifying the B operator that disconnection was desired.

Two forms of single board systems readily uggest themselves to those skilled in the art and clearly lie within the scope of my invention. In the first of these the springjacks and answering-plugs are identically the same as those already described, while the callingplugs are similar to those represented by the dotted lines in Fig. at. The plug-seat mechanism of both plugs is of course omitted. The operator on receiving a call inserts one of the answering-plugs part way in the jack of the calling-line and inquires the number wanted, on receiving which number she pushes the answering-plug home and inserts the other plug of the pair in the jack of the called subscriber, when she has only to press the calling-key belonging to the pair of plugs used to operate the called-subscribers bell. The insertion of the answerin g-plug restores the annunciator of the callingline, thus enabling it to be used as a clearing-out signal. After it has been so actuated the withdrawal of the answering-plug again automatically restores it, leaving it ready to indicate subsequent calls. The insertion of the calling-plug in the jack of the called subscriber energizes the restoring-coil, thus holding it against actuation by clearing-out currents.

In the second arrangement of single-board systems the operator connects her telephone with the line by the plug-seat mechanism shown in Fig. 6. The spring 0 is omitted from the spring-jacks and the ball-tip 2' from the answering-plug. In this case an operator on receiving a call inserts an answering-plug in the jack of the calling-line. This restores the annunciator in the way already described. She then grasps'the remaining plug of the pair and tilts it toward her and receives the order, after which she has only to lift the plug already grasped, insert it in the jack of the called subscriber, and press the calling-key. After the subscribers have rung off the withdrawal of the answering-plug again restores the annunciator.

It is also obvious that many of the details herein described are applicable with advantage to multiple-switchboard exchanges.

I claim as my invention and desire to secure by Letters Patent 1. In a telephone system, divided boards and groups of subscribers lines each group terminating in a board, trunk-lines term1nat-- leading to plugs distributed in the second sets of all the boards, substantially as de-.

terminating in a board, trunk-lines terminating in plugs at both ends for interconnecting the boards, said plugs being arranged in two sets at each board, the trunk-lines from plugs of the first set at one board leading to plugs distributed in the second sets of all the boards, operators circuit-terminals adjacent to the line-terminals on each board and means operated by the insertion of plugs of the first sets only to connect the subscribers lines to said operators sets and the trunk lines, whereby connections can be originated only by operators on the first sets, substantially as described.

4:. In a telephone system, divided boards,

spring-jacks therein, and subscribers lines connected thereto, operators telephones at each board, trunk-lines divided into sets interconnecting the boards, means operated by the partial insertion of the terminal plugs of a set at one board, to connect an operators telephone to a subscribers' line or to the trunk-line or both, an independent switching means connected with the same set at all the boards to connect an operators telephone with any particular trunk-line of that set at said boards, substantially as described.

5. In a telephone system, divided boards, spring-jacks thereon, and subscribers lines connected thereto, trunk-lines terminating in plugs at both ends for interconnecting the boards, said plugs being arranged in two sets at each board, the trunk-lines from plugs of the first set at one board leading to plugs distributed in the second sets at all the boards, an answering-operators circuit-terminals adjacent to the line-terminals on each board and means operated by the partial insertion of plugs of the first sets only to connect the subscribers lines to said answering-operators telephone sets and the trunk-lines, a calling-operators circuit-terminals adjacent to the plug-sockets of the second set of each board and means operated by tilting said plugs of the second sets to connect said calling-operators telephones through the trunklines to the subscribers lines, substantially as described.

6. In a telephone system, divided boards, spring-jacks thereon, and subscribers lines connected thereto, trunk-lines terminating in plugs at both ends for interconnecting the boards, said plugs being arranged in two sets at. each board, an answering and a callingoperators telephone circuit-terminals at each board, means controlled by plugs of the first set only for connecting subscribers lines to said answering-operators telephone and to the trunk-lines,and means controlled by plugs of the second set only for connecting said calling operators telephone through the trunk-lines to subscribers lines, a self-restorin g annunciator having its actuating-coil connected to each subscribers line and its restoringcoil connected to a terminal on the board, and means carried by all the plugs of both sets for momentarily energizing said restoring coil during the insertion or withdrawal of said plugs, substantially as described.

7. In a telephone system, divided boards and subscribers lines terminating in jacks therein, trunk-lines and plugs interconnect in g the boards,and separate signaling-circuits also interconnecting the boards, means for en ergizing said signalin g-circuits by the removal of a trunk-plug from its socket, an operators telephone connected to each board an d means operated by the partial insertion of said plugs to connect the subscribers line to the operators set and to the trunk-circui t, substantially as described.

8. In a telephone system, divided boards, and groups of subscribers lines, each group terminating in a board, trunk-lines terminating in plugs at both ends for interconnecting the boards, said plugs being arranged in two sets at each board, an answering and a callin g operators circuit-terminals at each board, an independent signalingcircuit for each trunk-line, means controlled by plugs of the first set only for operating the signals in said signaling-circuits, and for connecting subscribers lines to answering-operators telephones and to the trunk-lines, and means controlled by plugs of the second set only for operating return-signals in said signaling-cir cuits and for connecting said calling-operators telephones through the trunk-lines to subscribers lines, substantially as described.

9. In a telephone-switchboard, insulatingstrips carrying rows of subscribers terminals, a single operators terminal carried upon and insulated from each row, and common to all the members thereof, plugs adapted to connect with any of the subscribers terminals, and alternate shoulders and depressions on said plugs, so proportioned that upon partial insertion thereof the subscribers terminals will be forced into engagement with the operators terminals, substantially as described.

10. In a telephone-switchboard, operators terminals; line-terminals underlying but normally out of contact therewith; a plug provided with insulated metallic portions adapted to make contact with said line-terminals only, said metallic portions on the plug being raised portion only having sufficient elevation to force the line-terminals into contact with the operators terminals, substantially as described.

11. A subscribers metallic circuit; a lineterminal connected to each side thereof, an operators metallic circuit and terminals connected to the respective sides thereof overlying the line-terminals; a plug provided with insulated metallic portions adapted to contact with the line-terminals only, said metallic portions on the plug being provided with advance annular shoulders and following annular depressions, said shoulders being so located and of such elevation as to simultaneously connect the operators terminals with the line-terminals during the insertion or withdrawal of the plug, but not at its complete insertion or withdrawal substantially as described.

12. In a telephone system, subscribers lines terminating in spring-jacks, operators telephone-circuit terminals and annunciator-restoring-circuit terminals adjacent to the linesprings in each jack, answering and calling plugs connected in pairs by cord-circuits, means carried by both plugs of a pair to actuate the annunciator-restoring terminals, and means carried by the answering-plugs only to actuate the operators telephone-terminals, substantially as described.

1 3. In a telephone-switchboard subscribers lines terminating in jacks thereon, an annunciator for each line, plugs and plug-circuits for interconnecting said lines, an operators telephone and means whereby the partial insertion of one of said plugs in, or its partial withdrawal from a jack restores the annunciator and at the same time connects the operators telephone to the line, substantially as described.

14. In a telephone system,a subscribers line and terminals therefor, a signal and signaloperating means under control of said line, a plug, and signal-restoring means energized momentarily at a certain point during the insertion or withdrawal of the plug, whereby while the plug is fullyinserted or withdrawn the signal will remain under control of the line substantially as described.

15. In a telephone system, a switchboard, terminals thereon, subscribers lines connected thereto, self-restoring annunciators normally under the control of, and plugs for interconnecting said subscribers lines, and means energized at one point during the insertion or withdrawal of the plugs for momentarily removing the annunciator from the control of the subscribers lines, by restoring the same and thereafter leaving the restored annunciators again under control of the subscribers lines, substantially as described.

16. In a telephone switchboard, springjacks thereon, and subscribers lines connected thereto, self-restoring annunciators having their actuating-coils connected to their respective lines, springs connected to the restoring-coils and arranged in juxtaposition to but insulated from the line spring of the jacks, and connecting-plugs each provided with one or more annular depressions and alternate elevations so located as to close the restoring-circuit momentarily during the insertion or withdrawal of a plug and thereafter leave the annunciatorunder the control of the line, substantially as described.

17. In a telephone system, a subseribers line terminating at a switchboard, a signal and operating means therefor connected to said line, a signal-restoring means also connected to said line and to a terminal on the board, an operators set also connected to said terminal, a plug, and means whereby on the partial insertion or withdrawal of said plug the signal is restored and the operators set connected to the line, substantially as de' scribed.

18. In a telephoneswitchboard a terminal plug and its seat, an operators telephone circuit and terminals therefor adjacent to said seat, and the arrangement being such that the tilting of said plug in its seat connects said terminals to the plug-circuit, substantially as described.

19. In a telephone-switchboard a plug and seat therefor recessed on one side, operators telephone circuit terminals adjacent thereto, contact-springs cooperating with said terminals and connected to the plug-circuit, and intermediate means whereby the tilting of the plug in its socket will close said contactsprings upon said terminals, substantially as described.

20. In a telephone-switchboard a plug-seat having a metallic portion, a contact-spring in juxtaposition thereto, a signaling-circuit including the metallic portion and said contactspring, and a plug having a metallic heel adapted to bridge across said seat and spring and so complete the signaling-circuit, an operators telephone-circuit terminals, a switch therefor with connections to the plug-circuit, and means whereby the tilting of said plug in its seat will actuate said switch to connect the operators telephone into the plug-circuit without altering the condition of the signaling-circuit, substantially as described.

21. In a telephone-switchboard a metallic plug-seat, a contaet-spring adjacent thereto, a signaling -circuit including said seat and spring, and a plug having a metallic heel adapted to bridge across the same, an operators telephone-circuit terminals, a switch therefor connected to the plug-circuit and an insulated mechanical connection between said switch and the aforesaid contact-spring, said mechanical connection carrying a projection whereby either the tilting of the plug in its seat or the retraction of the projection after the plug is removed will operate through the medium of the contaet-spring to actuate the telephone-switch, substantially as described.

22. A signaling-circuit, high and low resistance signals therein, said circuit being normally open at the low-resistance signal, a circuit-breaker and a resistance in shunt therewith adjacent to the high-resistanee signal to energize both signals, and means for operatin g the circuit-breaker adjacent to the highresistance signal, to increase the resistance of the circuit, and thereby deenergize the lowresistance signal, substantially as described.

23. In a signaling system a source of current, a low-resistance signal, a normally-open circuit-breaker adjacent thereto a high-resistance signal and a normally-closed circuitbreaker adjacent thereto; said source of current, signals and circuit-breakers being contained in series in a single circuit, and a resistance shunting said normally-closed circuit-breaker, the resistance of the shunt-circuit and that of the signals being so adjusted that the high-resistance signal will be dis played whenever the normally-open circuitbreaker is closed, and the low resistance signal will be displayed only when both circuit-breakers are closed, substantially as described.

24. In a signaling system a circuit containing a low-resistance signal, a normally-open circuit-breaker adjacent thereto,ahigh-resistance signal, a normally-closed circuit-breaker adjacent thereto, and a source of current; a resistance shunting said normally-closed cir cuit-breaker, said resistance and the resistance of the signals being so adjusted that the high -resistance signal is displayed on the closure of the normally-open circuit-breaker, and is unaffected by the condition of the normally-closed circuit-breaker, while the lowresistance signal is displayed only when both circuit-breakers are closed, substantially as described. KEMPSTER B. MILLER. Witnesses:

JAMES G. Sronnn, W. A. FERGUSON.

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