US775229A - Telephone-exchange system. - Google Patents

Description

PATBNTED NOV. 15, 1904.

E. e. WEBSTER.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED FEB.14 1903.

N0 MODEL.

UNITED STATES Patented November 15, 1904.

PATENT OEEicE.

HARRY G. IVEBSTER, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE STROM- BERG-CARLSON TELEPHONE MANUFACTURING- COMPANY, OF ROCHES- TER, NEIV YORK, A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 775,229, dated November 15, 1904.

Application filed February 14, 1903- Serial No. 143,307. No model.)

To (Ml whom it Hilly/011116776:

Be it known that I, HARRY G. \Vnesrna, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Telephone Exchange Systems, of which the following is a full, clear, concise, and exact description, reference be ing had to the accompanying drawing, forming a part of this specification.

My invention relates to telephonc-exchange systems, and more particularly to systems in which a common source of energy is located at the central station to supply talking-current to substation-transmitters.

My invention is particularly useful in conjunction with systems employing a so-called differential cut-ofi' relay, by means of which the use of the operators cord-circuit at the central station controls the line-signal to cause the extinction thereof upon the connection of cord connecting apparatus with a subscribers telephone-line.

The objects of my invention are to provide a system in which the apparatus employed may serve the double purpose of regulating and controlling the voice-currents transmitted from one line'to another and at the same time to effect the operation of suitable line and supervisory signals. I provide a system in which current for the substation-transmitters may be supplied entirely through linecircuit apparatus, as distinguished from those systems in which the substation transmittercurrent is supplied wholly or partially through cord-circuit apparatus.

My invention provides an improvement over other systems, in which the necessaryimpedance in the circuit supplying talking-current to the substation-transmitters is introduced by the provision of coils wound on iron cores on which there are short-circuited windings. These short-circuited windings tend to decrease the impedance.

In my improved system the impedance-coils are on the line and cut-off relays and serve other useful purposes in addition to that of providing the necessary impedance. The linecircuit arranged in accordance with my invention is adapted for use with instruments and connecting devices in which an alternating calling-current may be sent through a callbell at a substation over either the tip or the sleeve side of the telephone-line.

An improved ringing-circuit is one of the principal features of my invention.

The cord-circuit used in conjunction with my improved line-circuit may, if desired, be provided with two ringing'keys to correspond with lines some of which are operated with a calling-circuit over the sleeve side of the line and others in which there is a calling-circuit over the tip side of the line. Since the tall:- ing-current is supplied to the substation-transmitters through line-circuit apparatus rather than through the cord-circuit, itis possible to provide supervisory relays in the cord-circuit which are wound to comymratively high resistancefor instance, live hundred ohms whereby the operation of the supervisory signaling devices is made more sensitive and reliable.

In accordance with my invention 1 provide at the central station a suitable common battery, to the terminals of which are connected two limbs of a telephone-line leading to a substation. One of these limbs includes in its circuit the two differential windings of a cutoff relay and one winding of a line-relay. The other limb includes in its circuit a second cumulative winding of the line-relay. A 10- cal circuit jointly controlled by said line and cut-off relays affords current adapted to illuminate a line signaling-lamp. It will be apparent to those skilled in the art thatany other suitable form of line-signal may be employed in place of the well-known lamp and local circuit described herein. Cord connecting apparatus is provided for connecting lines for conversation, means being provided whereby the insertion of the plug of the cord connecting apparatus within a line-jack causes the closure of alow-resistance circuit through one winding of said cut-ofi' relay, whereby the same is given a net energization, and consequently actuated to discontinue or prevent the illumination of the line signal-lamp. A supervisory controlling-relay is provided and arranged to connect one battery-pole with suitable supervisory signaling apparatus upon the insertion of a plug of the cord-circuit within a line-jack.

My invention will be better understood by reference to the accompanying drawing, in which are illustrated at each of the substations A and B common-battery telephone sets, comprising in each instance a switch-hook 1,

serving when in its normal depressed position to connect the line-limb 2, through a condenser 3 and call-bell 4, with the ground. When relieved of the weight of the receiver 5, the switch-hook assumes its alternative upper position in which the line-limb 6 is connected, through the transmitter 7 and primary winding 8 of the induction-coil, with the linelimb 2. The secondary coil 9 of the induction-coil is connected with the receiver 5. The limbs 2 and 6 lead to the central station C, where they are connected with the terminals of the common battery 10, whose positive terminal is grounded, as shown. The limb 6 includes in its circuit the two difierential windings 11 and 12 of a differential cut-off relay 13 and a winding 14 of the line-relay 15. I have found it desirable to make each of the differential cut-ofi relay-windings 11 and 12 about one hundred ohms resistance and that of the winding 14 of the line-relay 15 of about one hundred ohms resistance. The limb 2 of the telephone-line is connected, through a twohundred-ohm winding 16 of the line-relay 15. The windings 1 1 and 16 of the line-relay are made cumulative in their efl'ects upon the relay-core.

The armature 17 of the line-relay and the armature 18 of the cut-off relay are included in a local circuit through a line signaling-lamp 19. The cut-off relay is provided with a second armature 20, adapted when in its attracted position to close a low-resistance circuit in shunt of the winding 11 of the cut-ofl relay. The telephone-lines are each associated with an answering-jack 21 and calling-jacks 22, the tip-contacts 23 of which are permanently connected to the limb 2 of the line, as shown. The sleeve-contacts, which may be in the shape of thimbles 24., are connected in parallel with the common terminal of the two windings 11 and 12 of the cut-off relay.

1 have illustrated cord connecting apparatus having an answering-plug 25 and a callingplug 26, the tip-contacts of which are connected by the tip-strand 27 and the sleevecontacts of which are connected by the sleevestrand 27, the continuity of the tip-strand being interrupted by the condenser 28. The usual listening-hey 29 is provided, adapted when manipulated to connect the operators telephone set 30 in bridge of the cord-circuit.

In the present embodiment of my invention I have shown two ringing- keys 31 and 32, the I ringing-key 31 serving when manipulated to connect the generator 33 between the ground and the sleeve-strand leading to the sleevecontact of the calling-plug 26, while a manipulation of the ringing-key 32 serves to connect the generator 34 between the ground and the tip-contact of the calling-plug 26. A supervisory controlling-relay 35 is connected between the grounded side of the common battery 10 and the sleeve-strand 27 of the cord-circuit. An attraction of the armature 36 serves to connect the positive terminal of the battery 10 with one terminal of each of the supervisory signalinglamps 37 and 38, whose circuits are further controlled by the armatures 39 and 10 of the supervisory relays .1 and 12, the relay 11 being connected in a circuit between the positive side of the battery 10 and the section of the tip-strand 27 of the cord-circuit leading to the tip-contact of the answering-plug and the supervisory relay 12- being connected in a circuit between the positive side of the battery 10 and a contact 13, which normally makes connection with the portion of the tip-strand 27 leading to the callingplug 26. An impedance-coil 14 is connected in a path between the contact of the listening-key and the negative pole of the battery 10. A condenser 16 is connected in the operators telephone-circuit between the contacts of the listening-key.

The operation of my improved system will now become apparent. A subscriber at substation A upon removing the receiver 5 from its switch-hook 1 closes a circuit between the limbs 2 and 6 of the associated telephone-line.

IOC

A circuit is thereby closed from the positive side of the battery 10 through the winding 16 of the line-relay, through the transmitter and primary winding 8, through the linelimb 6, the differential windings 11 and 12 of the cut-01f relay 13, and the winding 14: of the line-relay 15 to the negative pole of the battery 10. Current flowing over this circuit causes no net energization of the cut-off relay on account of the ditferential relation of the windings 11 and 12. The windings of the line-relay, however, are cumulative in their effects, and the line-relay is therefore actuated to cause the attraction of its armature 17. The armature 18 of the cut-off relay being in its normal unattracted position, a circuit is thereby closed through the line signalinglamp 19 to illuminate the same. The operator is thereby given a signal, to which she responds by the insertion of an answering-plug 25 of a cord-circuit within the answering-jack 21, associated with the calling telephone-line. The insertion of the answering-plug within the answering-jack closes the following circuit: from the positive pole of the battery 10, through the supervisory controlling-relay 35, to the sleeve-strand 27 of the cord-circuit, to the sleeve-contact 2 1 of the answering-jack, through the winding 12 of the cut-off relay and the winding ii of theline-relay, to thenegative ing substation, causes a current to tlow, side of the batteryll). The differential ett'ects ot' the windings 11 and 12 of the cut-oti' relay are thereby unbalanced and the relay-core is 5 given a net energization due to the excess current flowing through the coil 12 over that flowing through the coil 11. The cutoff-relay armatures are therefore attracted, the armature 18 serving to break the local circuit through the line signal-lamp 19 and the armature 20 serving to connect a low-resistance circuit in shunt of the winding 11 ot' the cutotl relay. At the same time the currenti'lowing through the supervisory controlling-relay causes the attraction of its armature 36 to connect the positive pole of the battery 10 with the supervisory signal-lamps 37 and 38.

A circuit through the supervisory relay *1 may be traced as follows: from the positive pole of the battery 10 to the tip-strand 27 of the cord-circuit, to the tip-contact 23 of the answering-jack 21, to the line-limb 2, through the switch-hook 1, the primary winding 8, the transmitter T, the line-limb 6, the low-re sistance slumt-circuit about the winding 11, the winding 12 ot' the cut-ott' relay, the winding ii of the line-relay, to the negative pole of the battery 10. The current flowing through the supervisory relay a1 causes the attraction of the armature 39 to break the otherwise completed circuit through the supervisory signal-lamp 37. The circuit through the supervisory signal-lamp 38 is completed by the armature it) of the supervisory relay 4E2, which makes connection with its back contact, as shown. The operator manipulates her listening-key to connect her telephone set in bridge of the cord-circuit and ascertains the number of the subscribers station with which the subscriber at substation A desires communication. Learning that substation B is desired, the operator inserts her calling-plug 26 within a calling-jack 22, associated with the called line to substation B. and thereupon manipulates her ringing-key 32 to connect the generator 54: with the tip-strand of the cord-circuit. The ringing-circuit may be traced t'rom the tip-contact of the callingjack 22 through the line-limb 2, the condenser the call-bell at, to the ground, with which one terminal of the ringing-generator is connected. Manipulation of the ringing-key also serves to connect the sleeve-strand 27, leading to the sleeve-contact ot' the callingplug 26, with the ground.

The insertion of the calling-plug 26 within a calling-jack 22 closes the following circuit: from the positive pole of the battery ll) through the supervisory controlling-relay 35, the sleeve-strand of the cord-circuit,the sleevecontact 2% of the calling-jack 22, the winding 12 of the cut-oti' relay, the winding 1* of the line-relay, to the negative pole of the battery ll). This circuit, similarly to that traced tor the apparatus associated with the callcausing the attraction ol the armatures l7 and 1b, the armature 18 serving immediately to open the circuit through the linelamp 19. The attraction of the armature 20 at once closes the low-resistance shunt-path about the winding ll of the cut-oil relay. The removal of the receiver at substation B from its switch-hook causes the closure of a circuit through the supervisory relay &2, whereupon its armature 4:0 is attracted to open the circuit through the supervisory lamp Upon the replacement of either of the receivers of the connected lines upon its switchhook the circuit through the associated super visory relay is opened, whereupon the supervisory lamp is caused to glow, thus indicating to the operator that the subscriber has linished with the desired conversation. She thereupon removes the plugs ol her cord-circuit from the line-jacks, whereupon the line-circuit apparatus is restored to its normal condition.

It will be apparent that by the arrangement of the resistances of the line and cut-oli relays as hereinbet'ore pointed out talking-current is applied from the battery it) to the substation-transmitter through limbs each of which includes an impedance-winding of two hundred ohms resistance. Since the batterycurrent is supplied to the transmitters through the apparatus of the line-circuit. it is possible to make the supervisory relays and the supervisory controlling-relay all of comparatively high resistance -lor instance, live hundred ohms. It will be seen that when the ringinggeuerator at the central station is connected with a line a circuit is closed through the melumdred-ohm winding of the line-relay to lock its armature in the attracted position. The ringing-current is transmitted to the call-bell at the substation past an impedance-coil having a resistance of two hundred ohms. It is seen that my invention provides for the necessary or desirable impedance in both limbs of the telephone-line without the introduction of auxiliary impedance-coils, which perform no other useful function than that ol choking the voice-currents between connected substations.

it is the practice in telephone systems to provide means whereby an operator may test the condition of a line before connecting the calling-generator therewith in order to ascertain whether such line is in use. The means provided in my improved system for such a test are as follows: It will be seen that the test-thimbles 2+ of an idle line are permanently com'iected, through the winding 12 ot' the cut-oil relay and the winding H of the linerelay, with the negative pole ol the battery 10. No current liowing through these windings, the test-thimbles are maintained at the potential ot' the negative side of thehatteigv. When, however, a plug of a cord-circuit has been inserted within any one of the line-jacks,

a circuit is closed through the winding 14 of the line-relay, the winding 12 of the cut-off relay, and the winding of the supervisory controlling-relay 35. The passage of current through this circuit to the positive side of the battery 10 causes a drop in the potential of the test-thimbles 24. It will be seen that the manipulation of the listening-key to connect the operators telephone set in bridge of the cord-circuit connects the contact 45 through the impedance-coil 4:4: with the negative side of the battery 10. This of course brings the tip of the calling-plug 26 to the potential of the negative pole of the battery 10. Thus when the tip of a calling-plug is applied to the test-thimble of an idle line no current will be caused to flow through the impedancecoil H, since the test-thimble and the tip of the calling-plug are at the same potential. WVhen, however, the potential of the test-thimbles has been reduced by connection with some other cord-circuit, a current will be caused to flow between the tip of the calling-plug and the test-thimble, this current passing through the impedance-coil 44., thereby causing a condenser-discharge which produces a click in the operators receiver, thereby notifying her of the busy condition of the tested line.

While I have herein shown and described one particular embodiment of my invention, it will be apparent to those skilled in the art that many modifications therein may be made without departing from the spirit of my invention. 1 do not, therefore, wish to limit myself to the precise disclosure herein set forth; but,

Having described my invention, I claim as new and desire to secure by Letters Patent 1. In a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two differential windings permanently serially included in the telephone-line circuit, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof.

2. In atelephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two differential windings serially included in the telephone-line circuit, a line signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation,

means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof and switching means adapted upon actuation of said cut-ofi relay to shortcircuit one winding thereof.

3. In atelephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two differential windings permanently included in the telephone-line circuit, a linesignal jointly controlled by said line and cutofi relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-oft relay to cause an actuation thereof.

4. In a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two difierential windings included in the telephone-line circuit, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof and switching means adapted upon actuation of said cut-0E relay to short-circuit one winding thereof.

5. In a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of cur rent to a substation, a line-relay having two cumulative windings and a cut-off relay having two differential windings permanently serially included in the telephone-line circuit, a line-signal jointly controlled by said line and cut-ofl relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay to destroy the substation control of the linerelay.

6. In a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two differential windings serially included in the telephone-line circuit, a line-signal 7. In atelephone-exchangesystem,the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two differential windings permanently included in the telephone-line circuit, a line-signal jointly controlled by said line and cut-ofi' relays, cord connecting apparatus forconnecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of' said cut-off relay to destroy the substation control of the line-relay.

8. In a telephone-exchange system, the combination with a source of current at the exchange, of' a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two difl'erential windings included in the telephone-line circuit, a line-signal jointly controlled by said line and cut-oti relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of' said cord connecting apparatus with said line causes an actuation of said cut-off relay to destroy the substation control of the line-relay and switching means adapted upon actuation of said cut-off relay to short-circuit one winding thereof.

9. In a telephone-exchange system, the combination with a source of current at the exchange, of' a telephone-line extending by its limbs from the terminals of said source of' current to a substation, a line-relay having two cumulative windings and a cut-off relay having two differential windings permanently serially included in the telephone-line circuit, a local signal-circuit jointly controlled by said relays, armatures for said relays adapted for serial inclusion in said local circuit with asignal, cord connectingapparatus for connecting said line with another for conversation, and

means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof.

11). In a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of' said source of' current to a substation, a line-relay having two cumulative windings and a cut-off relay having two differential windings permanently serially included in the telephone-line circuit, cord connecting appa "at-us for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay to destroy the substation control of' the line-relay.

11. In a telephone-exchange system, the combination with a source of' current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of' said line, a second cumulative winding of' said line-relay and the two differential windings of a cut-off relay pern'ianently serially included in a second limb of' said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-ofi' relay.

12. In a telephone exchange system, the combination with a source of' current at the central station, of' a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of alinerelay serially included in one limb of' said line, a second cumulative winding of said line-relay and the two ditlerential windings of a cutoff relay permanently serially included in a second limb of said line, a line-signal jointly controlled by said line and cutofi' relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of' said cord connecting apparatus with said line causes an actuation of said cut-ofi' relay.

13. In a telephone-exchange system, the combination with a source of' current at the central station, of a telephone-line extending by its limbs from the terminals of' said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of' said cord connecting apparatus with said line causes an actuation of said cut-otf' relay.

1%. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding ofa linerelay serially included in one limb of' said line, a second cumulative winding of said line-relay and the two differential windings ofa cutofi' relay serially included in a second limb of said TIO line, a line-signal jointly controlled by said line and cut-ofi relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay.

15. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the t vo differential windings of a cut-ofl' relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay, whereby the same is actuated to destroy the substation control of the line-signal.

16. In a telephone-exchange system, the combination with a source of current at the' central station, of a telephone-line extending by its limbs from the terminals of said source of current to asubstation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two' differential windings of a cut-off relay permanently serially included in a second limb of said line, a local signal-circuit jointly controlled by said relays, armatures for said relays adapted for serial inclusion 'in said local circuit with a signal, cord connecting apparatus forconnecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-ofl' relay.

1?. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said linerelay and the two difi'erential windings of a cutofl:' relay permanently serially included in a second limb of said line, a local signal-circuit jointly controlled by said relays, armatures for said relays adapted for serial inclusion in said local circuit with a signal, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay.

18. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cut-off relay serially included in a second limb of said line, a local signalcircuit jointly controlled by said relays, armatures for said relays adapted for serial inclusion in said local circuit with a signal, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay.

19. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line relay and the two differential windings of a cut-off relayserially included in a second limb of said line, a local signal-circuit jointly controlled by said relays, armatures for said relays adapted for serial inclusion in said local circuit with a signaL'cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay.

20. In a telephone-exchange system, the combination with a source of current at the central station, of atelephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cutofi' relay serially included ina second limb of said line, a local signal-circuit jointly controlled by said relays, armatures for said relays adapted for serial inclusion in said local circuit with a signal, cord connecting apparatus for connecting said line with another for conversation, and means whereby the con serially included in the telephone-line cir' cuit, a line-signal jointly controlled by said line and cut-ofi' relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-ofi' relay to cause an actuation thereof, and switching means adapted upon an actuation of said cut-otl relay to close a low-resistance path in shunt of one winding of said cut-ott' relay.

In a telephone-exchange system, the combination with a source of current at the exchange. of a telephone-line extending by its limbs from the tcrminalsot' said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two ditlerential windings included in the telephone-line circuit, a local line-signal circuit jointly controlled by said line and cutolt' relays. armatures for said relays adapted tor serial inclusion in said local circuit with a line-signal.cord connectingapparatus t'orconnecting said line with another for conversation. means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-otl' relay to cause an actuation thereof, and switching means adapted upon an actuation of said cut-ott' relay to close a low-resistance path in shunt of one winding of said cut-olt' relay.

2; In a telephone-exchange system, the combination with a source of current at the exchange. of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-otl' relay having two differential windings permanently serially included in the telephone-line circuit, a line-signal jointly controlled by said line and cut-otl' relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-otl' relay to destroy the substation control of the line-relay, and switching means adapted upon an actuation of said cut-ott' relay to close a low-resistance path in shunt of one winding of said cutotl' relay.

2%. In a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two tannulative windings and a cut-off relay having two ditlerential windings included in the telephone-line circuit. a local line-signal circuit jointly controlled by said line and cut-0t? relays, armatures for said relays adapted for serial inclusion in said local circuit with a linesignal, cord connecting apparatus for connecting said line with another for conversation. means whereby the connection of said 1 line I cord connecting apparatus with said ance path in shunt of one winding of said cutoff relay.

25. In a tclephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cuteotl' relay having two ditt'erential windings permanently se rially included in the telephone-line circuit, a local signal-circuit jointly controlled by said relays, armatures for said relays adapted for serial inclusion in said local circuit with a signal, cord connectingapparatus for connecting said line with another For conversation, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-otf relay to cause an actuation thereof, and switching means adapted upon an actuation of said cut-olf relay to close a low-resistance path in shunt of one winding of said cut-ofi relay.

26. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cun'iulative winding of said line-relay and the two ditt'erential windings ot' a cut-olt' relay permanently scrially included in a second limb of said line, a line-signal jointly controlled by said line and cut-01f relays, cord connectingapparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-ol'l relay, and switching means adapted upon an actuation of said cut-otl' relay to close a low-resistance path in shunt ol one winding of said cut-oll' relay.

2?. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a secondcumulative winding of said line-relay and the two ditferential windings ot a cut-oil relay permanently serially included in a sec ond limb of said line, a line-signal jointly controlled by said line and cut-ott' relays, cord connecting apparatus t'or connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-otl' relay, and switching means adapted upon an actuation of said cut-ott' relay to close a low-resistance path in shunt of one winding of said cutott' relay.

28. In a telephone-exchange system, the combination with a source ol currentat the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a Winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windversation, and meanswhereby the connecings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-ofl' relays, cord connecting apparatus for connecting said line witl another for conversation, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay, and switching mechanism adapted upon an actuation of said cut-ofi relay to close a low-resistance path in shunt of one winding of said cut-off relay.

29. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two difl'erential windings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-ofi relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay, and switching means adapted upon an actuation of said cut-ofl relay to close a low-resistance path in shunt of one winding of said cutofi relay.

30. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cut-01f relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-ofi' relay, whereby the same is actuated to destroy the substation control of the line signal, and switching means adapted upon an actuation of said cut-ofl relay to close a low-resistance path in shunt of one winding of said cut-off relay.

31. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two difijerential windings of a cut-off relay permanently serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for contion of said cord connecting apparatus with said line causes an actuation of said cut-off relay, the resistance of each winding of said cut-off relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

32. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a line-relay serially included in one limb of said line, a second cumulative winding of said linerelay and the two differential windings of a cut-off relay permanently serially included in a second limb of saidline, a line-signaljointly controlled by said line and cut-ofl' relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-ofi relay, the resistance of each winding of said cut-off relay and the resistance of said second winding of said linerelay being each substantially equal to onehalf the resistance of said first winding of said line-relay.

33. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay, the resistance of each winding of said cut-off relay and the resistance of said second winding of said line-relay being each substantially equal to one-h-alf the resistance of said first winding of said line-relay.

34:. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two diiierential windings of a cutoff relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-ofi' relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-otl' relay, the resistance of each winding of said cutoil relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said tirst winding of said line-relay.

35. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cuto'tl' relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-ofi' relays, cord connecting apparatus for connecting said line with another for conversation, and means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay, whereby the same is actuated to destroy the substation control of the line-relay, the resistance of each winding of said cut-off relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

36. In a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two differential windings permanently serially included in the telephone-line circuit, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-ofi' relay to cause an actuation thereof, and switching means adapted upon an actuation of said cut-oil relay to close a low-resistance path in shunt of one winding of said cut-oil relay, the resistance of each winding of said cut-ofl' relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said linerelay.

37. In a telephone-exchange system. the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cut-ofi' relay permanently serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-otl relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay, and switching means adapted upon an actuation of said cut-ofl' relay to close a low-resistance path in shunt of one winding of said cut-ofi relay, the resistance of each winding of said cut-off relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

38. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said linerelay and the two differential windings of a cut-ofi' relay permanently serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connectingsaid line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay, and switching means adapted upon an actuation of said cut-ofi' relay to close a low-resistance path in shunt of one winding of said cut-ofi' relay, the resistance of each winding of said cut-off relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

39. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cut-ofi relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-oil relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-ofl' relay, and switching mechanism adapted upon an actuation of said cut-oil relay to close a low-resistance path in shunt of one winding of said cut-off relay, the resistance of each winding of said cut-ofi' relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

40. In a telephone-exchange system, the combination with a source of current at the IOC central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said linerelay and the two differential windings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-ofi' relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cutoff relay, and switching means adapted upon an actuation of said cut-E relay to close a low-resistance path in shunt of one winding of said cut-off relay, the resistance of each Winding of said cut-ofi' relay and the resistance of said second Winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

&1. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said linerelay and the two ditferential windings of a cut-oif relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay, whereby the same is actuated to destroy the substation control of the line-relay, and switching means adapted upon an actuation of said cut-off relay to close a low-resistance path in shunt of one winding of said cut-off relay,

, the resistance of each winding of said cut-on.

relay and the resistance of said second winding of said line relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

12. 1n a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two difierential windings permanently included in the telephone-line circuit, a line-signal jointly controlled by said line and cut-ofl' relays, cord connecting apparatus for connect- 7 ing said line with another for conversation, a spring-jack having a test-contact permanently connected with the common terminal of the two windings of said differential cut-off relay, and means whereby the connection of said cord connectingapparatus with said line closes a circuit of decreased resistance through one winding of said cut-oil relay to cause an actuation thereof.

43. In a telephone-exchange system, the combination with a source of current at the exchange,'of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two diiierential windings permanently included in the telephone-line circuit, a linesignal jointly controlled by said line and cutoff relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a test-contact permanently connected with the common terminal of the two windings of said difierential cut-01f relay, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay to destroy the substation control of the line-relay.

44. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two difierential windings of a cut-ofl? relay permanently serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-off relay, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay.

45. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, asecond cumulative winding of said line-relay and the two differential windings of a cut-off relay permanently serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-off relay, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-oft relay.

46. In a telephone-exchange system, the

combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential w indings of a cut-oti relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cutott' relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connect- 1 ed with the first limb of said line and a test-conl tact permanently connected with the common terminal of the two di tlerential windings of said cut-ofi' relay, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-ofi relay.

U. in a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two ditierential windings of a cutofi' relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another t'or conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal ot' the two differential windings of said cut-ott relay, and means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-otl relay.

as. In a telephone exchange system, the combination with a source of current at the central station, of a telephoneline extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two ditferential windings ot' acutotf relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-otl' relays, cord connecting apparatus for connecting said line with another t'or conversation, a spring-jack having a contact permanentlydirectly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two difl'erential windings ofsaid cut-otl relay, and means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-otl' relay, whereby the same is actuated to destroy the substation control of the line-signal.

49. In a telephone-exchange system, the combination with a source ol current at the central station, of a telephone-line extending by its limbs from the terminals ol said source of current to a substation. a wii'idingot' a linerelay permanently serially included in one limb of said line, a second cumulative windingot said line-relay and the two ditlerential windings of the cut-off relay permanently serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-ofl' relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-off relay, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-ofi' relay, and switching means adapted upon an actuation of said cutoff relay to close a low-resistance path in shunt of one winding of said cut-ofi' relay.

50. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two ditferential windings of a eut-oti relay permanentlyserially included in a second limb of said line, a line-signal jointly controlled by said line and cut-otl relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a testeontaet permanently connected with the common terminal of the two differential windings of said cut-off relay, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-otf relay, and switching means adapted upon an actuation of said cut-off relay to close a low-resistance path in shunt of one winding of said cut-off relay.

51. In a telephone-exchange system, the

combination with a source of current at the central station, of a telephoneline extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two dillerential windings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-otf relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-ofi relay, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-off relay, and switching mechanism adapted upon an actuation of said cutoff relay to close a low-resistance path in shunt of one winding of said cut-01f relay.

52. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-ofi relay, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-elf relay, and switching means adapted upon an actuation of said cut-off relay to close a low-resistance path in shunt of one winding of said outoff relay.

53. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two diflierential windings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-ofli' relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two dilferential windings of said cut-off relay, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-01f relay, whereby the same is actuated to destroy the substation control of the line-signal, and switching means adapted upon an actuation of said cut-off relay to close a low-resistance path in shunt of one winding of said cut-off relay.

54:. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a windingof a linerelay serially included in one limb of said line,

a second cumulative winding of said line-relay and the two diflerential windings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-01f relay, and means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-ofl' relay, whereby the same is actuated to destroy the substation control of the line-relay, the resistance of each winding of said cut-0E relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said linerelay.

55. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of alinerelay permanently serially included in one limb of said line, a second cumulative Winding of said line-relay and the two differential windings of a cut-0H relay permanently s e rially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-off relay, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-ofi relay, and switching means adapted upon an actuation of said cutofl relay to close a low-resistance path in shunt of one winding of said cut-01f relay, the resistance of each winding of said cut-off relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

56. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in one limb of said line, a second cumulative winding of said line-relay and the two difierential windings of a cutoil relay permanently serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-off relays, cord connecting apparatus for connecting said line with another for conversation, at spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-oti' relay, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cutofi' relay, and switching means adapted upon an actuation of said eut-ofi relay to close a low-resistance path in shunt of one winding of said cut-ofi relay, the resistance of each winding of said cut-ofl relay and the resist ance of said'second winding of said line-relay being each substantially equal to one-half the resistance of said lirst winding of said linerelay.

57. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay permanently serially included in one limb of said line, a second cumulative winding of said line-relay and the two differential windings of a cutofi relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-ofl' relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-off relay, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-ofi' relay, and switching mechanism adapted upon an actuation of said outofi relay to close a low-resistance path in shunt of one winding of said cut-ofi relay, the resistance of each winding of said cut-off relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

58. In a telephone-exchange system, the combination with a source of current at the central station, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a winding of a linerelay serially included in onelimb of said line, a second cumulative winding of said line-relay and the two difi'erential windings of a cut-off relay serially included in a second limb of said line, a line-signal jointly controlled by said line and cut-ofl' relays, cord connecting apparatus for connecting said line with another for conversation, a spring-jack having a contact permanently directly connected with the first limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cutoff relay, means whereby the connection of said cord connecting apparatus with said line causes an actuation of said cut-01f relay, and switching means adapted upon an actuation of said cut-ofi' relay to close a low-resistance path in shunt of one winding of said cut-otl' relay, the resistance of each winding of said cut-off relay and the resistance of said second winding of said line-relay being each substantially equal to one-half the resistance of said first winding of said line-relay.

59. In a telephone-exchange system, the combination with a source of current at a central exchange, of a substation permanently connected therewith through the line-limbs, a line-relay having two windings one permanently included in each limb, and a cut-ofi relay for controlling said line-relay having two windings permanently included serially in one limb with the line-relay winding therein, the joint impedance of the windings in one limb being substantially equal to the impedance of the winding in the other limb.

60. In a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-0d relay having two differential windings permanently serially included in the telephone-line circuit, cord connectingapparatus for connectingsaid line with another for conversation, a springjack having a contact permanently directly connected with one limb of said line and a test-contact permanently connected with the common terminal of the two difi'erential windings of said cut-ofi' relay, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-off relay to cause an actuation thereof, and switching means adapted upon an actuation of said cut-ofi relay to close a low-resistance path in shunt of one winding of said cut-ol'l' relay.

61. In a telephone-exchange system, the combination with a source of current at the exchange, of a telephone-line extending by its limbs from the terminals of said source of current to a substation, a line-relay having two cumulative windings and a cut-off relay having two difi'erential windings permanently serially included in the telephone-line circuit, cord connecting apparatus for connecting said line with another for conversation, a springjacl: having a contact permanently directly connected with one limb of said line and a test-contact permanently connected with the common terminal of the two differential windings of said cut-off relay, means whereby the connection of said cord connecting apparatus with said line closes a circuit of decreased resistance through one winding of said cut-ofi' relay to cause an actuation thereof, and switching means adapted upon an actuation of said cut-ofl' relay to close a low-resistance path in shunt of one Winding of said cut-ofi relay, the resistance of each Winding of said cut-off relay and the resistance of said second Winding of said line-relay being each substantially equal to one-half the resistance of said first Winding of said line-relay.

In Witness whereof I hereunto subscribe my name this 5th day of February, A. D. 1903.

HARRY G. WEBSTER.

Witnesses:

LYNN A. VVILLIAMS, HARVEY L. HANSON.

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