US766224A

US766224A - Selective signaling system.

Info

Publication number: US766224A
Application number: US15124903A
Authority: US
Inventors: William M Davis
Original assignee: Stromberg Carlson Telephone
Current assignee: Stromberg Carlson Telephone Manufacturing Co
Priority date: 1903-04-06
Filing date: 1903-04-06
Publication date: 1904-08-02
Anticipated expiration: 1921-08-02

Description

No. 766,224. PATENTED AUG. 2, 1904. W. M; DAVIS.

SELECTIVE SIGNALING SYSTEM.

APPLIOATION FILED APR. 6, 1903.

NO MODEL.

UNITED STATES Patented August 2, 1904.

ATENT Orrrcs.

WILLIAM M. DAVIS, OF CHICAGO, ILLINOIS, ASSIONOR TO STROMBERG- .ROC HICSTER,

SELECTIVE SIGNALING SYSTEM.

SPECIFICATION forming part of Letters Patent No. 766,224, dated A g s 2, 1904:.

Application filed April 6, 1903. Serial No. 151,249. No model.)

To [all 'uJ/mm/ '1"! Ill/(1y (v/warn:

Be it known that I, \VILLIAM M. .DAVIS, a citizen of the United States, residing at Chicago, in the county of Cook-and State of Illi- 5 nois, have invented a certain new and useful Improvement in Selective Signaling Systems, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part r of this specification.

My invention relates to selective signaling systems, and is particularly well adapted for use in connection with so-called party-line telephone systems.

The invention herein described and claimed is closely allied to an invention described in my copending application, Serial No. 149,786, tiled March 27, 1903.

The principal objects of my present invention are to provide a system similar to that described in my said copending application except that I herein disclose means for balancing a telephone-line on which the number of substations connected between one of the two metallic line limbs and ground is not equal to the number of substations connected between the other metallic line-limb and the ground.

A further object of my invention is to pro- 0 vide for a balanced party telephone-line in which there shall be no continuous current leakage.

My invention relates to a system of that type in which the selective apparatus at a number of stations is permanently connected and at all times similarly connected with an electric circuit and in which the signaling apparatus at any one of the substations may be actuated independently of the signaling 4 apparatus at all the other substations connected with the same line.

The selective signaling devices employed are adapted to be actuated each by electric currents of a certain given peculiar nature.

Thusl provide one signaling device adapted to be actuated only by an alternating current. A second signaling device is provided which is adapted to be actuated only by a direct ourrent in one direction----:t'or instance, the positive direction and a third signaling device 5 is provided adapted to be actuated only by a direct current in the reverse or negative direction. Thus upon a single electric circuit there may be connected three signaling devices, each of which will be actuated by a suitable electric current independently of the other signaling devices connected with the same circuit.

A preferred embodiment of my invention comprises an arrangement in which the lirst 6o signaling device consists of a polarized telephone-ringer serially connected with a condenser in bridge of the electric circuit employed. The second signaling device desirably consists of a polarized ringer in which a front contact of the ringer-armature when engaged by the armature when in its attracted position serves to close a low-resistance path in shunt of the ringer-coils, whereby the same are deenergized to permit the retraction of the ringer-armature. This rheotome-bell, adapted to be actuated by a direct current, may be polarized, if desired, in order that it may be actuated only by the passage of a direct current in a certain given direction. Serially connected with such a rheotome signal-bell in bridge of the line-circuit there is provided an impedance-coil adapted to check and largely prevent the flow of alternating currents through this signal-bell. It will be seen that the condenser associated with the lirst aforesaid signaling device prevents the passage of direct current through its associated bell-coils. A third signaling device may comprise apparatus similar to that de- 5 scribed for the second signaling device except that in the case of the third instrument the armature is oppositely polarized, whereby the third signal-bell is actuated only by the passage of a direct current in the opposite direction to that adapted to actuate the second signal-bell.

It is now common practice in telephone installations to provide bimetallic circuits to each of the subscribers substations. In con nection with the use of bimetallic lines I lind it desirable to connect substation signaling apparatus between the ground and each of the bimetallic line-limbs. An operator at the central station by connecting between either of the line-limbs and the ground the terminals of a source of current adapted to supply either an alternating current or a direct current in either of two directions may signal any one of the substations whose signaling apparatus is connected with either of the bimetallic line-limbs. In signaling any one of these substations the apparatus at the other substations will not be affected to produce a signal.

My invention will be more clearly understood by reference to the accompanying drawings, in which I have illustrated two bimetallic telephone-

lines

90 and 120, to each of which there are shown connected four substations, those connected with the line 90 being lettered A, B, C, and D and those connected with the line 120 being lettered E, F, G, and H. At each of the substations there is provided a telephone switch-hook 1, which when relieved of the weight of the receiver 2 causes the closure in bridge of the telephoneline of a circuit through a battery-transmitter 3 and the primary A of an induction-coil, whose secondary 5 is connected with the receiver 2. In addition to the telephone instruments each substation is'provided with signaling apparatus, the signaling apparatus at substations A, B, E, and F being identical. The signaling apparatus at substations A and F are connected between the line-limbs 6 and ground, while those at substations B and E are connected between the line-limbs 7 and ground. The signaling apparatus at each of the substations A, B, E, and F comprises a well-known telephone-ringer 8, the alternative energization of whose electromagnetcoils 9 9, due to the passage of an alternating current therethrough, causes the vibration of the polarized armature 10 and the attached bell-clapper 11. There is included in the circuit through the coils 9 9 a condenser 12. This condenser is for the purpose of preventing the passage of direct currents through the electromagnet-coils 9 9. At substation C in addition to the telephone apparatus there is provided a call-bell 13, which comprises electromagnet-coils 14c let and a polarized armature 15, adapted to be actuated thereby.

'In shunt of the coils 14 M there is a low-resistance circuit adapted to be closed upon the attraction of. the armature 15 into contact With the front contact 16. A retractingspring 1'7 serves normally to retain the armature 15 in the position shown. This circuit also serially includes the impedance-coil 18, adapted to check and prevent the passage of alternating currents through the ringer 13. The polarization of the armature 15 prevents its attraction by the electromagnet-coils 14 1A except upon the passage of a current in one of the tWo directions. Thus the bell 13 may be supposed to be actuated only upon the passage of a direct current in the positive direction therethrough. The signaling apparatus at the substation D may be identical With that at the substation C except that its armature 15 is oppositely polarized, whereby the signaling apparatus at the substation D may be actuated by a current in the reverse direction from that necessary to actuate the signaling apparatus at the substation (J. The signaling apparatus at substations G and H is identical, With the exception that the ringer-armatures are oppositely polarized. At each of these substations there is provided a ringer 13, which comprises electromagnet-coils 14' 14 and a polarized armature 15, adapted to be actuated thereby. The circuit through the coils 14 14 includes the armature 15 and a back contact 16 therethrough. A retractingspring 17 serves normally to retain the armature 15 in contact With the back contact 16. This circuit also serially includes the impedance coil 18, adapted to check and prevent the passage of alternating currents through the ringer 13. The polarization of the armature 15 at substation G may be supposed to be such that it will be actuated only upon the passage of a direct current in the positive direction, while the armature 15 at substation H may be polarized in such a way as to be actuated only upon the passage of a direct current in a negative direction.

It will be apparent that by connecting the terminals of a source of alternating current between the line-limb 6 of line 90 and ground the call-bell 8 at substation Awill beactuated. The bells 13 at the substations C and D will not be actuated, however, due to the prevention of the flow of the alternating current therethrough, dueto the impedance of the coils 18. The connection of the terminals of a source of direct current between the linelimb 6 of line 90 and ground will When connected in one directioni'or instance, the positive directioncause the actuation of the signaling-bell 13. at the substation C. The connection of a source of direct current between the line-limb 6 of the line 90 and ground in the reverse direction will similarly cause the actuation of the signal-bell at the substation D. The connection of a source of direct current between the line-limb 6 and the ground will not cause the passage of any current through the bell 8 at the substation A, due to the interruption of the continuous circuit through the coils 9 9 by the, condenser 12. In the same manner the connection of a source of alternating current between the line-limb 7 and ground will cause the actuation of the signal-bell at substation B. As it is possible and sometimes desirable to connect substations having signaling apparatus of any or all of the three types hereinbefore described connected between either of the line-limbs and ground, ltind it desirable to provide at the central station means whereby the terminals ol a source of alternating current or the terminals ot a source of direct current in either direction may be connected between either line-limb and the ground.

In an installation such as that herein described in wlnch there is connected between 1 one of the line-limbs and the ground three sets of signaling apparatus and between the other line-limb and ground only one set of signaling apparatus 1 lind it desirable to provide means for electrically and telephonically balancing the two line-limbs. may be balanced by connecting between the limb with which there is connected the-smaller munber ot' signalingapparatus and the ground an impedance or impedance-coils. Thus I have shown connected between the line-limb T of line 91) and the ground two impedancecoils 100 and lol. In this instance the impedance-coils may be located at points on the metallic line at substantially the same distance from the central station as the corresponding signaling apparatus are connected. Between the line-limb T of line .120 and the ground I have shown connected an impedance-coil 102, whose impedance may be varied by a suitable movement in or out of the winding of the core 103'. This impedance-coil is shown located at the central station, and its impedance may be varied to balance that of the instruments connected with the line-limb.

Aside from the provision of means where- I by the sign-allng-currents of proper character may be connected with the line-circuits the central station apparatus may be identical with that employed in a great many systems now well known to those skilled in the art, and herein lies one of the principal advantages of my selective signaling system, that it may be employed in conection with any of the well-known exchange systems now in use.

,In order to illustrate the method of associatmg my improved selective signaling system 9 with a telephone system, I. have shown line-' limbs (:3 and T for each of the telephone-lines 90 and 12a leading to the central exchange K, where they are respectively connected with tip and sleeve springs and 19 ot' the lineiacks 21. (.ontacts 22 and 25,) normally make connection with the jack-springs l9 and 20 and with suitable comluctors, connectinglinelimb 4' directly to the positive pole of the common battery it. The line-limb 6 connected. through a line-relay 25, with the negative pole of the common battery Ql. This line-relay controls by its armature 26 a local circuit through the line signaling-lamp 27, the operatlon ot' wlnch will be well understood by those skilled in the art.

The operators cord-circuit may comprise the usual zmswering-plug 28 and the callingplug 2%), whose tipcontacts are normally connected through the tip-strand 30 and whose The line-limbs sleeve-contacts are normally connected through the sleeve-strand 31. There are preterably included in the tip-strand circuit the supervisory signaling-

relays

32 and 33, these relays being shunted by the condenser 34:, 3 whereby the transmission o'tvoice-currents is improved. The usual operators telephone set 35 may be included in bridge of the cordcircuit by manipulation of the listening-key 36. The supervisory relays 32 and 33 control, respectively, the-armatures 37 and 38,

which in turn control local circuits through l the supervisory signaling-lamps 39 and ll). The continuity of the local circuits for the l lamps 39 and a0 is controlled by a plug-seat switch 4C1, adapted upon the removal of the plug 28 from its seat to connect the positive pole of the battery 2% with one of the terminals of each of the lamps 39 and {0. The common terminal of the

relays

32 and 33 is connected, as shown, with the negative pole of the battery 2%. I have illustrated a series of six ringing-keys L2, 4?), 4st, 4C5, lli, and 47, each adapted to connect the terminal of a suitable source of current with one of the

linelimbs

6 or 7 within the jack 21, associated with which the plug 29 has been inserted. The manipulation of the key l2 serves to connect a terminal of the alternating-currentgenerator %8 with the tip-strand of the cord-circuit leading to plug 29. The manipulation of the key 43 connects a terminalt'or instance, the positive terminal of the direct-cur rent generator 49 with the tip-strand. The manipulation of the key ll serves to connect the negative terminalot' the generator50 with the tipstrand. A manipulation of the key 45 connects one terminal of the alternating-current generator 51 with the sleeve-strand 31, leading to the plug 229. A manipulation of the key 46 connects the positive terminal of a direct-current generator 52 and with the sleeve-strand. and a manipulation of the key 47 connects the negative terminal of the direct-current generator 53 with the sleevestrand. The other terminals of these various sources of current may be permanently connected with the ground, as shown. I [hid it desirable also to provide contacts on the ringing-keys, whereby the limb of the line which is not utilized for the transmission of a signaling-current may be connected with the ground. Thus thelowcrcontaets tor the keys 2, l3, and 4st are connected with ground, while the upper contacts of the keys "T5, 46, and H are connected with ground. An impedance-coil 5% is connected between the positive pole of the battery 24 and the sleevestrand 31.

The operation of a telephone system employing my invention may be described as follows: Any one of the subscribers t'or instance, the subscriber at substation B on line I 90--upon removing his receiver from the l switch-hook -auses the closure of a circuit,

which may be traced as follows: from the positive pole of the battery 2 1 through the linelimb 7, the switch-hook 1, a primary coil 4: at

substation B, the transmitter 3, the line-limb 6, the line-relay 25, to the negative pole of the battery 24. The consequent energization of the relay 25 causes the attraction of its armature 26, whereby a local circuit is established to illuminate the line signal-lamp 27. The central operator answers the line-signal by the insertion of her answering-plug28 within a line-jack 21, associated with the line 90. The insertion of the plug 28 within the jack causes a spreading of the

springs

19 and 20, whereby the closed circuit through the line-relay 25 is interrupted to cause its deenergization and a consequent extinction of the line signal-lamp 27. It will be seen that the removal of the answering-plug 28 from its seat will have caused the closure of the plug-seat switch 4:1, whereby the positive pole of the battery will be connected with terminals of the lamps 39 and 4:0. The armature 37 will have been attracted, however, by the energization of the supervisory relay 32 due to the flow of current through a circuit which may be traced as follows: from the negative pole of the battery 24:, through the supervisory relay 32, the tip-strand 30 of the cord-connecting apparatus, the tip-spring'19 of a line-jack 21, line-limb 7, the subscribers telephone apparatus,theline-limb 6,the sleevespring 20, sleeve-strand 31,and the impedancecoil 54, to the positive pole of the battery 2&. The attraction of the armature 37 interrupts the otherwisecompleted local circuit through the supervisory signal-lamp 39, whereby the same is not illuminated. The supervisory signal-lamp 40, however, is illuminated, due to the flow of current through the armature 38, which has not been attracted by its relay 33. The operator communicates with subscriber at substation B on the line and a'scertains the number of the subscribers substation with which he desires communication. Assuming this to be substation G on line 120, she inserts her calling-plug 29 within one of the line-jacks 21, associated with line 120. She thereupon manipulates her ringing-key 13 to connect the terminals of the direct-current generator 49 with a circuit including the line-limb 7 and a ground-return. Current then flows from this generator over the line-limb 7 to ground, there being one path through the signaling apparatus at substation H. This signaling apparatus at substation H, however, is polarized in such a direction that the-positive current from the generator 49 does not affect the actuation of the signal-bell 13. The inclusion of the condenser 12 in circuit with the bell 8 prevents the passage of a direct current from the line-limb 7 to ground through this bell. There is another path for the currentfrom the generator 19 through the bell 13 at substation G to ground. This hell, it will be remembered,

is polarized in such a direction that the passage of a positive current causes the actuation of the armature 15. Thus the signaling apparatus at substation Gr on line 120 is actuated to call the subscriber to his telephone. Answering the call the subscriber removes his receiver from the switch-hook, thereby establishing a circuit through the supervisory relay 33 to cause the attraction of the armature 38, whereupon the supervisory signaling-lamp 40 is extinguished.

The replacement of the receivers either at substation B on line 90 or at substation G on line 120 causes an interruption of the circuit through the

supervisory relay

32 or 33, respectively, whereby the associated supervisory signaling-lamp is illuminated to indicate to the .operator that the connected subscribers have finished their conversation. She thereupon removes the cord-connecting plugs from the line-jacks, whereupon the apparatus is restored to its normal condition. It will be apparent that if another of the subscribers connected with line 120 had been desired by the calling subscriber the manipulation of the proper ringing-key, as hereinbefore described, would have caused the signal at the proper substation. In like manner the rheotome signaling-bells, such as illustrated at substations C and D, may be energized and actuated by a direct current of suitable polarity controlled from the central station.

Unless the impedance between each linelimb and ground is perfectly balanced the telephonic conductivity and efficiency of the system will not be perfect, and interference will result from noises due to the unbalanced ground connections. As there are an unequal number of substations connected with each limb of a line, as herein described, such interference would result if provision were not made to balance the system, and the impedance-coils 100 and 101 are of such strength and placed at such a position as to balance the impedance between the line-limbs and ground, thus preventing disturbances to telephonic currents, also to prevent leakage from the battery 21 to ground through theimpedancecoils connected therewith from both linelimbs. Condensers 103 and 104: are serially inserted in circuit with the impedance-coils and 101, respectively, and serve in the same manner as the condensers 12 at substations A andB to prevent direct currentflow. Instead of using the impedance-coils at various parts of the line, impedance-coil 102 may be.

and I do not, therefore, wish to limit myself i retm'n-path, an impedance connected between to the precise disclosure herein set forth; but,

I-Iavmg described my invention, I. claim as new and desire to secure by Letters Patent 1. In a party-line telephone-exchange system, the combination with a central station, of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs, a common return-path to the central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and said return-path, a rheotome signal- I l i i the other line conductor and said returnpath E to balance telephonically the bimetallic line,

and means lo ated at the central station adapted to connect the ternnnals ot' a source of alternating current between either of said line bell in a circuit of high impedance connected 1 bridge of said metallic line-limbs, a common 3 return-path to the central station, a polarized between one of said line conductors and said return-path, a variable impedance connected between the other line conductor and said return-path to balance telephonieally the bimetallic line, and means located at the central station adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path and adapted to connect the terminals of a source of direct current between the returnpath and that line conductor to which said rheotome signal-bell is connected.

2. In a party-line telephone-exchange system, the combination with a central station, of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs, a common return-path to the central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and said return-path, a rheotome signalbell in a circuit of high impedance connected i between one of said line conductors and said return-path, a variable impedance connected between the other line conductor and said return-path, and means located at the central station adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path and adapted to connect the terminals of a source of direct current between the returnpath and that line conductor to which said rheotome signal-bell is connected.

3. In a party-line telephone-exchange system, the combination with a central station, of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs, a common return-path to the central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conducbell in a circuit of high impedance connected between one of said line conductors and said l conductors and said return-path and adapted to connect the terminals of a source of direct current between the returnpath and that line conductor to which said rheotome signal-bell is connected.

4. .In a party-line telephone-exchange system, the combination with a central station, of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in signal-bell and a serially-connected condenser connected between each of said line conductors and said return-path, a rheotome signalbell in a circuit of high impedance connected between one of said line conductors and said return-path, an impedance connected between the other line conductor and said return-path, and means located at the centralstation adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path and adapted to connect the terminals of a source of direct current between the return-path and that line conductor to which said rheotome signal-bell is connected.

5. In a party-line telepllone-exchange sys: tem, the combination with a central station, of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs, a common return-path to the central station, a polarized signal-bell and a seriall \'-connected condenser connected between each of said line conductors and said return-path. a rheotome signalbell in a circuit of high impedance connected between one of said line conductors and said return-path, an impedance-coil connected between the other line conductor and said returnpath, the ii'npedanceot' said coil being substantially equal to the impedance of the circuit 1 through said rheotome signal-bell between the line conductor and the return-path, and means located at the central station adapted to connect the terminals of a source of alternating currentbetwecn said line conductors and said return-path and adapted to connect the terminals of a source of direct current between the return-path and that line conductor to which said rheotome signal-bell is connected.

6. In a partv-line telephone-exehange system, the combination with a central station, of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs, a common return-path to the central station,.a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and .said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a positive direction connected between one of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a negative direction connected between the same line conductor and said return-path, a variable impedance connected between the other line conductor and said return-path to balance telephonically the bimetallic line, means adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path, means adapted to connect the terminals of a source of direct current in apositive direction between said return-path and that line-limb to which said polarized rheotome signal-bells are connected, and means adapted to connect the terminals and the source or direct current in a negative direction between said return-path and that line-limb to which said polarized rheotome signal-bells are connected.

7 In a party-line telephone-exchange system, the combination with a central station, of a bimetallic telephone-line extending from said central-station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs, a common return-path to the central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a positive direction connected between one of said line conductors and said return-path, a

polarized rheotome signal-bell in a circuit of highimpedance adapted to be actuated by a di.

rect current in a negative direction connected between the same line conductor and said return-path, a variable impedance connected between the other line conductor and said returnpatlnmeans adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path, means adapted to connect the terminals of a source of direct current in a positive direction between said return-path and that linelimb to which said polarized rheotome signalbells are connected, and means adapted to connect the terminals of a source of direct current in a negative direction between said rcturn-path and that line-limb to which said polarized rheotome signal-bells are connected.

8. In a party-line telephone-exchange system, the combination with a central station,

of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limb, a common return-path to the central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high'im pedance adapted to be actuated by a direct current in a positive direction connected between one of said line conductors and said return-path, a polarized rheotome signal-bell in a circuitof high impedance adapted to be actuated by a direct current in a negative direction connected between the same line conductor and said return-path, an impedance connected between the other line conductor and said return-path to balance telephonically the bimetallic line, means adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path, means adapted to connect the terminals of a source of direct current in apositive direction between said return-path and that linelimb to which said polarized rheotome signalbells are connected, and means adapted to connect the terminals of a source of direct curvrent in a negative direction between said return-path and that line-limb to which said polarized rheotome signal-bells are connected.

9. In a party-line telephone-exchange system, the combination with a central station, of a bimetallic telephone-line extending from said central station to a series of substations,

subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs, a common v return-path to the central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a positive direction connected between one of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a negative direction connected between the same line conductor and said. return-path, an impedance connected between the other line conductor and said return-path, means adapted to connect the terminals of a source of alternating current between either of said line conductorsand said return-path, means adapted to connect the terminals of a source of direct current in a positive direction between said return-path and that linelimb to which said polarized rheotome signalbells are connected, and means adapted to connect the terminals of a source of direct current in a negative direction between said return-path and that line-limb to which said polarized rheotome signal-bells are connected.

ll). ln a party-line telepllone-exchange svsl of said metallic line-limbs a common return- 3 path to the central stat ion, a polarized signal tear, the combination with a central station, ot' a bimetallic telephone-line extending from said central station to a series of substations, subscriberstelephone instruments at each of said substations adapted to be connected in bridge of said metallic linelimbs, a common returnpath to the central station. a polarized signal-bell and a seriaILv-connected condenser connected between each of said line conductors and said return-oath, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a positive direction connected between one of said line coi'iductors and said return-path, a

bell and a seriall,v-connected condenser connected between each of said line comluctors and said return-path, a rheotome signalbell in a circuit of high impedance connected between one of said line conductors and said returnpath, a variable impedance and a condenser connected between the other line conductor and said return-path to balance telephonically the metallic line, and means located at the central station adapted to connect the terminals of i a source of alternating current between either polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a negative direction connected between the same line conductor and said returnpath, impedance connected between the other line conductor and said I'O'CUI'H-ptttll to balance telephonicallv the bimetallic line, means adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path,

m ans adapted to connect the terminals of a source of direct current in a positivedirection 1 between said return-path and that line-limb to which said polarized rheotome signal-bells are connected, and means adapted to connect the terminals of a source of direct current in a negative direction between said return-path and that linelimb to which said polarized rheotome signal-bells are connected.

'11. In a party-line tele 'ihone-exchange system, the combination with a central station, of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge path to the central station, a polarized signalbell and a serialtv-connected condenser connected between each ot sald line conductors and said return-path, a polarized rheotome signal -bell in a circuit of high impedance adapted to be actuated by a direct current in a positive direction connected between one of said line comluctors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a negative direction connected between the same line conductor and said return -path, impedance connected between the other line conductor and said return-tutti, said impedance being substantially equal to the circuit of said rheotome signal-bells between the connected line conductor and the return-path.

12. In a party-line telephone-exchange s vscm, the combination with a central station of a-bimetallic telephone-line extendingt'rom said of said line,,conductors and said return-path and adapted to connect the terminals of a source of direct current between the returnpath and that line conductor to which said rheotome signal-bell is connected.

13. In a party-line telephone-exchange system, the combination withs central station of a bimetallic telephone-line extending from the central station to a series of substations, subcentral station to a series of substations, subed to connect the terminals of a source ot discribcrs' telephone instruments at each of said substations adapted to be connected in bridge scribers telephone instruments ateach of said substations adapted to be connected in bridge of said metallic line-limbs a connnon returnpath to the central station, a polarized signalbell and a serially-connected condenser connected between each of said line conductors and said return-path, a rheotome signal-bell in a circuit of high impedance connected between one of said line conductors and said return-path, an impedance and a serially-connected condenserconnected between theother line coruluctor and said return-path to balance telephonically the bimetallic line, and means located at the central station adapted to connect the terminals of a source of alternating current between eitherot' said line conductors and said return-path, and adapted to i connect the terminals of a source of direct of said metallic line-limbs, a common ret-urncurrent between the returnpath and that line conductor to which said rheotome signal-bell is connected.

1-1:. In a party-line telephone-exchangc s,vstem, the combination with a central station of a bimetallic telephone line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be. connected in ln-idge of said metallic line-limbs a common return-path to the central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and said return-path, a rheotome signalbell in a circuit of high impedance connected between one of said line conductors and said return-path, an impedance and a condenser serially connected between the other line conductor and said return-path, means located at the central station to connect the terminals of a source of alternating current between either of said line conductors and said return-path, and means located at the central station adaptrect current between the return-path and that line conductor to which said rheotome signalbell is connected.

15. In a party-line telephone-exchange system, the combination with a central station of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at eachoi' said substations adapted to be connected in bridge of said metallic line-limbs a common return-path to the central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and said return-path, a rheotome signalbell in a circuit of high impedance connected between one of said line conductors and said return-path, an impedance-coil and a condenser serially connected between the other line conductor and said return-path, the-impedance of said coil being substantially equal to the impedance of the circuit through said rheotome signal-bell between the line conductor and the return-path, means located at the central station adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path, and means located atthe central station adapted to connect the terminals of a source of direct current between the returnpath and that line conductor to which said rheotome signal-bell is connected.

16. In a party-line telephone-exchange system, the combination with a central station of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs a common return-path to the central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and said common return-path, a polarized rheotome signal-bell in a circuit of high im pedance adapted to be actuated by a direct current in a positive direction, connected between one of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a negative direction, connected between the same line conductor and said return-path, a variable impedance and a condenser serially connected between the other line conductor and said return-path to balance telephonically the metallic line, means adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path, means located at the central station adapted to connect the terminals of a source of direct current in a positive direc tion between said common return-path and that line conductor to which said rheotome signal-bells are connected, and means located at the central station adapted to connect the terminals of a source of direct current in a {negative direction between said return-path and that line conductor to which said rheotome signal-bells are connected.

17. In a party-line telephone-exchange system, the combination with acentral station of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs a common return-path to the central station, apolarized signal-bell and aserially-connected condenser connected between each of said line conductors and said returnpath, a polarized rheotome signal bell in a circuit of high impedance adapted to be actuated by a direct current in a positive direction connected between one of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a negative direction, connected between the same line conductor and said return-path, a variable impedance and a condenser serially connected between the other line conductor and said return-path located at the central station, means adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path, means located at the central station adapted to connect the terminals of a source of direct current in a positive direction between said return-path and that line conductor to which said rheotome signalebells are connected, and means located at the central station adapted to connect the terminals of a source of direct current in a negative direction between the return-path and that line con ductor to which said rheotome signal-bells are connected.

18. In a party-line telephone-exchange system, the combination with a central station of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs a common return-path to a central station, a polarized signal-bell and a serially-connected condenser connected between each of said line conductors and said return-path, a polarized rheotome signal bell in a circuit of high impedance adapted to be actuated by a direct current in a positive direction connected between one of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a negative direction, connected between the same line conductor and said return-path, an impedance and a convalternating current between either of said line conductors and said return-path, means adapted to connect the terminals of a source of direct current in a positive direction between said return-path and that line conductor to which said rheotome signal-bells are connected, and means adapted to connect the terminals of a source of direct current in a negative direction between said return-path and that line conductor to which said rheotome signalbells are connected.

19. In a party-line telephone-exchange system, the combination with a central station of a bimetallic telephone-line extending from said central station to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs a common return-path to the central station, a polarized signal-bell anda serially-connected condenser connected between each of said line conductors and said common return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a positive direction connected between one of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a negative direction connected between the same line conductor and said return-path, impedance serially connected through a condenser between the other line conductor and said return-path to balance telephonically the bimetallic line, means adapted to connect the terminals of a source of alternating current between either of said line conductors and said return-path, means adapted to connect the terminals of a source of direct current in a positive direction between said return-path and that line conductor to which said rheotome signal-bells are connected, and means adapted to connect the terminals of a source of direct current in a negative direction between said return-path and that line conductor to which said rheotome signal-bells are connected.

20. In a party-line telephone-exchange system, the combination with a central station, of a bimetallic telephone-line extending therefrom to a series of substations, subscribers telephone instruments at each of said substations adapted to be connected in bridge of said metallic line-limbs, a common return-path to the central station, a polarized signal-bell, and a serially-connected condenser connected between each of said line conductors and said return-path, a polarized rheotome signahbell in a circuit of high impedance adapted to be actuated by a direct current in a positive direction connected between one of said line conductors and said return-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a negative direction connected between the same line conductor and said rcturn-path, and a variable impedance connected between the other line-limb and said returnpath, said impedance being adjustable by the station operator to balance the impedance of the telephonic circuit.

21. In a party-line telephone-exchange system, the combination with a central exchange, of a bimetallic telephone-line extending therefrom to a series of substations, a source of current at the exchange normally connected between the limbs of said telephone-line, a polarized signal-bell connected between each of said line-limbs and ground, a condenser included serially in circuit with each of said signal-bells to prevent the passage to ground from said source of current at the central exchange, polarized rheotome-bells permanently connected between one line-limb and ground through a path of high impedance, and means connected with the other limb of said line for balancing the impedance of the telephonic circuit and for preventing current-flow to ground from said source at the central exchange.

In witness whereof I hereunto subscribe my name this 2d day of April, A. I). 1903.

\VlLLlAM M. DAVIS.

\Vitnesses:

LYNN A. WVILLIAMS, IIARVEY L. HANSON