US1394189A - Repeater-controlling system for four-wire circuits - Google Patents

Description

C. S. DEMAREST. REPEATER CONTROLLING SYSTEM FOR FOUR-WIRE CIRCUITS.

APPLICATION men rEa.24, 1919.

1,394,189. Patented Oct. 18, 1921.

6 SHEETS-SHEET INVTOR. C S flew/6w BY A TTORNEY C. S. DEMAREST. REPEATEH CONTROLLING SYSTEM FOR FOUR-WIRE cmcuns.

APPLICATION FILED FEB. 24, 1919.

Patented 0013. 18, 1921.

6 SHEETS-SHEET 2.

- INVEN TOR. B Sfimmmsti ATTORNEY C. S DEMAREST. REPEATER CONTROLLING SYSTEM FOR FOUR-WIRE CIRCUITS.

APPLICATION FILED FEB. 24. 1919.

1,394,189. Patented Oct. 18, 1921.

s SHEETS-SHEET s. w v T" K -L I N V EN TOR. 6, 61 Dalila/w! W A TTORNEY C. S. DEMAREST. REPEATER CONTROLLING SYSTEM FOR FOUR-WIRE CIRCUITS.

APPLICATION FILED FEB. 24, I919.

Patented Oct. 18, 1921.

6 SHEETS-SHEET 4.

61 Jffiammsl BY M IN VEN TOR.

ATTORNEY C. S. DEMA REST. REPEATER CONTROLLING SYSTEM FOR FOUR-WIRE CIRCUITS.

APPLICATION F|LED FEB. 24, 1919.

1,394,189, Patented Oct. 18, 1921.

6 SHEETS-SHEET 5.

INVEN TOR.

BY 8 Sflwmwesi g l ATTORNEY C. S. DEMAREST. REPE ATER CONTROLLING SYSTEM FOR FOUR-WIRE CIRCUITS.

V APPLICATION FILED FEB. 24, I919- 1,3 94,189.

R 6 SHEETS-SHEET 6.

IN V EN TOR. 6i (fie/Wm BY- wlp/gl V A TTORNEY Patented Oct. 18, 1921.

UNlTED STATES PATENT OFFICE.

CHARLES S. DEMAREST, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

REPEATER-CONTROLLING SYSTEM FOR FOUR-WIRE CIRCUITS.

Specification of Letters Patent.

Application filed February 24, 1919. Serial No. 278,945.

T 0 all whom it may concern Be it known that 1, CHARLES S. DEMABEST, residing at New York, in the county of New York and State of New York, have invented certain Improvements in Repeater-Controlling Systems for Fourire Circuits, of which the following is a specification.

This invention relates to telephone transmission systems and more particularly to means for controlling the connection of telephone repeaters to a four-wire telephone transmission circuit, and for testing the efficiency of such type of circuit.

Heretofore it has been customary to connect the repeaters into the four-wire repeater circuit, and to maintain such connection permanently, regardless of the nature of the circuit that may be connected with each end of the said four-wire circuit. The telephone repeaters connected with a four-wire circuit are usually designed and operated to give an amplification that will compensate not only for the loss inthe four-wire circuit itself, but also for the losses in the telephone 2 5 trunk lines that may ordinarily be connected with the said four-wire circuit. vVhen such a circuit is completely connected from subscriber to subscriber, the repeater is halanced and will operate satisfactorily, that is, without singing. It has been found that whenever an operator connects her telephone set with such circuit for the purpose of supervising such connection, an unbalanced condition is created and the repeaters begin to sing, thereby impairing the transmission over the circuit.

One of the objects of this invention is to provide means, whereby the repeater which is normally effectively disconnected from a repeater trunk circuit nay be effectively connected to the said circuit only when the repeater trunk circuit is connected in both directions to telephone circuits of the type with which it is intended that it should be associated, and when the keys of all associated cord circuits are in their normal, nonoperated positions.

A further object of this invention is to provide means for controlling the connections between the filament heater batteries and the filaments of thermionic repeaters whereby the said batteries will be connected with the filaments only when the repeaters are effectively connected into the repeater trunk circuit.

Another object of this invention is to pro vide a testing circuit the function of which is to determine whether the repeaters are operating properly so as to produce the desired transmission gain.

In order to show more effectively the nature of the invention a telephone transmission circuit is shown complete from one subscribers station to another. Figure 1 shows a subscribers line connected at its exchange with a trunk extending to one toll office. Fig. 2 shows a cord circuit at the aforementioned toll ofiice to connect the incoming trunk circuit with the four-wire repeater trunk shown in Fig. 3, which for purpose of description, is assumed to extend between two toll offices. Fig. 4 shows a cord circuit at the other of said toll ofiices to connect said repeater trunk with the trunk circuit shown on Fig. 5, which terminates in the ofiice in which the other of said subscribers lines also terminates. The complete circuit may be clearly seen by arranging all the figures subsequent to Fig. 1 so that the bottom edge of each figure coincides with the top edge of the preceding figure.

Fig. 6 shows a testing circuit by means of which-the repeaters shown in Fig. 3 may be tested. The circuit arrangements shown on these figures will be better understood from the following detailed description of the figures.

In Fig. 1 is shown a standard subscribers line A terminating at its exchange in the jack J,. C is a cord circuit of the usual subscribers type, having a plug 1?, adapted to be inserted in the jack J, and a plug P adapted to be inserted in ack J 2 of a ring down trunk D which extends from the said exchange to a toll board at the toll ofiice E terminating therein in a jack J Fig. 2 shows the cord circuit at the toll board E terminating in a plug P adapted to be inserted in the jack J of the ringdown trunk shown in Fig. 1 and also in a plug 1?, adapted for in ertion in either jack J or jack J of the toll board E shown in Fig. 3.

Fig. 3 shows a four-wire repeater trunk circuit extending between two toll offices, designated in and F, and terminating at each of these offices in two acks. The four-wire circuit is of the usual type, having two twowire branches which are electrically related by means of the hybrid repeating coils X Patented Oct. 18, 1921.

and Y. Associated with coil X are two networks N and N the former being adapted ofthe fourwire circuit has associated with it a group of relays controlled by the circuits connected with said jacks and adapted to control relays and 26 of the repeater circuit which, in turn control the connection of the repeaters tothe branches of the fourwire circuit, and the connection of the heater batteries with the filaments. 7

Figs shows a cord circuit located at the toll office F terminating in two plugs P and P P being adapted for insertion in jacks J and J of the four-wire trunk circuit and plug P being adapted for insertion in jack J of the circuit trunk shown in Fig. 5. 1

Fig. 5 shows a circuit trunk terminating in the jack J at the toll ofiice F and in the plug P, at the exchange H in which the subscribers line B also terminates, the said insertlon in the ack plug being adapted for J of the said subscribers line.

Fig. '6 shows the repeater testing equipment which is preferably located in the same office in which the repeater shown in Fig. 3 is located and is connected by means of ring-down trunks with the switchboards at the toll oflices E and F terminating therein in jacks J and J respectively. This circuit and the method of its operation will be described more fully hereafter.

If'the subscriber at substation A, which is located in a territory in which toll line service is furnished by the toll oflice E, desires to communicate with the subscriber at B, which is in a territory in which toll line service is furnished by the toll oflice F, the method of establishing the line of communication is as follows WVhen the subscriber at A removes his receiver 1 from the switch hook 52, causing the operation of relay 3 and the lighting of the lamp 4 the operator at the exchange C inserts plug P of the cord circuit in the jack J thereby operating relay 5 and extinguishing the lamp 4. When the operator at C 'ascertains from the subscriber at A that the subscriber desires to communicate with a subscriber B in the territory controlled by the toll oflice F, the operator inserts the other plug P of the cord circuit in jack J of thering-down trunk connecting exchange C with the toll office E. The operator at C applies ringing current to the trunk by operating key 6 which causes relay 7 to operate,

scriber 13 whose line is in the territory served I fore described.

thereby lighting the lamp 8 which is associated with jack J The operator at the toll oilice E answers this call by inserting plug P, of the cord circuit in jack J which operates relay 9, thereby opening the circuit of relay 7 which is normally bridged across the trunk. When the operator at toll oflice E ascertains that communication is desired with sub by toll board F, she inserts plug P, of the cord circuit in either jack J or J and depresses the ringing key K of the cord circuit which causes the lamp l0 atthetoll office F to light The operator at toll oflice F inserts the plug P of the cord circuit in so. the jack J, or J and operates the talking key K, of the cord circuit. The selection of v the proper jack at ofiice E or F in which the plugs 1? and P respectively, are to be inserted depends upon the characteristics of the trunk circuit with which the four-wire "trunk circuit is to be connected. Thebasis of selection will be fully explained hereafter. v y

vVhe-nthe operator at office E takes'up the call over trunk D by inserting the plug P in jack J a circuit is established over the sleeve contacts of the plug and the jack from the grounded battery 11 of the. cord circuit, windings of relays 12 and 9 thereby 9 operating both of said relays. The result ofthe operation of relay 9 has been heretos By the opening of the normal contact of relay12 a ground is removed from conductor 13. 'lVhen' plug P, was in serted in jack J a circuit was established over the sleeve contacts of thisplug and jack from the rounded battery 14, through resistance 10 in parallel with a short circuiting strap through contact 16, winding of relay 17, sleeve contacts oftheplug P and jack J windings of relays 18 and 19 to ground, operating relays 17, 18 and 19. The operation of relay 17 closes contact 20, thereby connecting grounded battery through winding ofrelay 21 to conductor 13. If conductor 13 is not grounded at any point relay 21'remains inoperative and contact 16 remains closed thereby maintainingoa low .thence through relay 25 to the grounded bat tery. The operation of relay 25 applies a ground to a part of the repeater control circuit but it does not effect the connection of the repeater .to this branch of the circuit until relay 26 is operated which will'now be described :-e

When the operator at toll oflice F inserts the plug P in the ack J 5 a circuit is established over the sleeve contacts of the plug and jack from the grounded battery 27. of the cord circuit through resistance 28 in parallel with the short circuiting strap through contact 29, thence through windings of relays 30, 31 and 32 to ground, thereby effecting the operation of relays 30 and 31. When relay 30 operates it closes contact 33, thereby establishing a circuit from grounded battery, through the winding of relay 34, over conductor 35 and contact 36 of relay 37 to ground, thereby causing relay 34 to operate which opens contact 29 of relay 34 and opens the short circuit around resistance 28. As a result of the removal of this short circuit, the amount of current that flows through relay 32 and the other relays in series therewith is limited by resistance 28 to such an extent that relay 32 which is marginal will not be operated; consequently, relay 26 remains unoperated and neither repeater will be connected into the four-wire circuit. Therefore the toll operators may use this circuit to establish the proper connections free from the annoyance caused by the singing of the repeaters. When the operator at toll ofiice F has learned the number of the desired subscribers line and has restored the talking key K, to its normal position she transmits the number over an order wire circuit (not shown) to a trunk operator at H and she inserts plug P in jack J, of the proper circuit trunk eXtending from the toll ofiice F to the exchange H at which the'subscribers line of the desired subscriber terminates. When the plug P is inserted in jack J a circuit is established over the sleeve contacts of the plug and jack from the grounded battery 38, through relays 39 and 37 and the 500 ohm winding of relay 40, causing relay 40 to operate which bridges the winding of relay 41 across the circuit trunk. Relay 37 is operated thereby which removes the ground from conductor 35 by opening contact 36 but relay 39 is marginal and does not respond when the 500 ohm winding is in series. However, as soon as relay 41 operates and connects the 150 ohm winding in parallel with the 500 ohm winding to ground, relay 39 operates closing contact 42, thereby grounding conductor This therefore maintains a closed circuit through relay 34 which keeps open the short circuit around resistance 28 and thereby prevents the operation of the marginal relay 32 which controls the connection of therepeaters.

When the operator at exchange H has been advised over the said order wire circuit by the operator at the toll ofiice F the number of the desiredsubscriberrthe operator at H inserts the plug P into the jack J, of the desired subscribers line, thereby establishing a circuit over the sleeve contacts of the plug and jack from the grounded battery 43, relay 44 and cut off relay 45 to ground, thereby operating relays 44 and 45. When plug P was inserted in jack J, and the winding of relay 41 was bridged across the trunk, relay 46 was thereby operated closing a contact to ground, thereby operating relay 47 which closed through the two sides of the trunk circuit to a subscribers station B. Vhen the subscriber at station B removes his receiver from the hook, relay 48 is thereby operated by the closing of the circuit at the hook switch and thereby disconnects relay 46 from the trunk circuit. Relay 41 which depends upon relay 46 for its energization is thereby released, opening its contact 49. This removes the ground from the 150 ohm winding of relay 40 leaving the 500 ohm winding in series with relays 37 and 39. Relay 39 which is marginal does not receive sufficient current under this condition to energize it and therefore it is released, causing the opening of contact 42 and thereby removing the ground from the conductor 35. It should be noted that relay 37 receives sufficient current to remain in its operated position thereby maintaining contact 36 in its open position and removing the ground from conductor 35. Furthermore, if all of the keys of the cord circuits at the toll stations E and F are in their normal positions, relay 34 will be unoperated, contact 29 will remain closed and the marginal relay 32 of the four-wire trunk circuit will receive suflicient current to eil'ei-t its operation. When relay 32 operates a circuit is established from ground through conductor 50 to the midpoint of coil 51, thence over the two wires in parallel of one branch of the tour-wire circuit to the midpoint 01 one of the windings of coil 52, over conductor 53, relay 26 to the grounded battery 54, thereby operating relay 26. As will be recalled relay 25 was operated when the telephone circuit was completely established from the subscribers station at A to the jack J of the four-wire trunk circuit at the toll oifice E, and when all of the keys of the cord circuit at the toll ofiiceE were in their normal non-operated positions. Nhen relays 25 and 26 are simultaneously operated, relays 55, 56, 57 and 58 will operate, thereby removing the short circuit around the repeaters 59 and 60 and efiectively connecting these repeaters into the two branches of the four-wire trunk circuit. Also relay 61 is operated as a result 01 the operation of relays 25 and 26, thereby connecting the filament heater batteries 62 and 63 in series with the filaments of the thermionic repeaters 60 and 59, respectively.

If the operator at either of the toll ofiices operates any of the keys except the monitoring keys K of the cord circuit with which said keys are associated or if she removes either of the plugs of either cord circuit from its associated jack, the winding of either relay 21 or relay 34 will be grounded thereby operating either of said relays and causing the marginal relays 19 or 32 to release. This will, in turn, release either relay 2501' 26 and will effect the disconnection of the repeaters 59 and 60 from the four-wire trunk circuit, thereby preventing the singing of the repeaters.

If the subscriber at station B restores his receiver to the hook, relay 48 will be deenergized, thusreconnecting relay 46 across the trunk circuit which again energizes relay 41. This will effectively connect the two windings of relay 4:0 in parallel to ground and will permit sufficient current to flow. through the marginal relay 39 to effect its operation. lVhen relay 39 operates a ground is thereby placedupon conductor 35 whichcauses relay 34; to operate which, in turn, results in the operation of marginal relay 32, thereby disconnecting the repeaters 59 and 60 from the trunk circuit.

If the subscriber at station A restores his receiver to the hook the operator at the exchange C, will receive a disconnect signal and Will remove the plugs P and P of the cord circuit from the associated jacks. When the toll operator at the oiiice E receives the disconnect signal she removes plug 7 P from jack J 3 of the trunk circuitthereby releasing relay 12 and grounding.conductor 13. Relay 21 is thereby energized opening contact 16 in the short circuiting strap around resistance 15., Under this condition the marginal relay 19 Will not receive sufficient current to maintain it in its operated position, and consequently it will release,

thereby removing the ground from con ductor 22 and releasing relay 25. As a result,.the repeater switching relays are deenergized and the repeaters are effectively dismnnected from the trunk circuit.

Mention has been made heretofore of a plurality of jacks in which the four-wire repeater trunk circuit terminates at the toll ofiices E and F, and of the necessity for making a selection among said jacks in or,- der to establish the proper connection between the subscribers stations A and B. It will be noted that in addition to the two balancing networks N and N associated with the hybrid repeating coils X and Y respectively of the repeater circuit, two other networks N, and N are connected with the repeater circuit, N being adapted to be associated with N and N with N These networks are provided to render it practicable to equalize the transmission equivalents of all through telephone connections that are completed over this four-wire division depending ,upon'whetherithey are above or below a certain predetermined transmission equivalent. Networks N and N are designed to have electrical characteristics substantially similar to those of one of said groups of trunks, and the combination of networks N andN or of net'- works N and N substantially similar to ing low transmission equivalent so that when,

connected with the repeater it would give a better grade of transmission than was attainable on circuits of the other group, she

will insert the plug P in the jack J thereby 7 connecting into the circuitithe network N which in addition to network N will give satisfactory transmission for this type of trunk circuit. In like manner, if the operator at F finds that it is necessary in order to complete the call to use a trunkhaving lowtransmisslon equivalent, she will insert plug P in the jack J which connects the network N in the circuit, in addition to 7 network N thereby establishing the proper grade of transmission for this connection.

If on the other hand, the operator at E receives a call over-a trunk that-has a high transmissionequivalent she will insert the V plug P in the jack J thereby operating relay 63. Thisin turn will effect the operation of relay 64, thereby disconnecting the network N and will leave'the networkN connected with-the circuit which permits the desired of circuit Likewise, if the operator at the toll .oflice F finds that, in order to establish the desired connection, it is necessary to use a trunk having high transmission equivalent, she inserts plug P. in-the jack J thereby operating relay 65 and in turn relay 66. The network N 4 is disconnected from the four-wire circuit, leaving the network Y associated therewith, which gives the desired, grade of transmission for this type of trunk.

In order to determine whether the four-V wire repeater trunk circuit is in proper opcrating condition a testingcircuit is provided a central testing arrangement which preferably is located in .the same office in which grade of transmission for this type as shown in Fig. 6; This consists in e therrcpeaters and 60 are located, and

connected by means of the trunks 67 and G8 with the toll offices E and F,- respectively, terminating thereinv in the jacks J and J respectively.

The central testing arrangement consists of an oscillator or vibrator 70 adapted to give an electromotive force of approximately telephonic frequency. A receiver 71 with which is associated a receiver shunt 73 is adapted to be connected across the end ofthe repeater circuit opposite to that end with which the oscillator 70 may be connected. The artificial line 72, which is of the well known type, has the same transmission equivalent as the four-wire circuit has when the repeaters are disconnected. A switch 7a is provided for connecting the oscillator 70 with either end of the repeater circuit or of the artificial line 72. A switch 7 5 is provided to connect the oscillator and the receiver alternately with the transmis sion circuit and with the artificial line.

In order to test the repeater, plug P is inserted in jack J and plug P in jack J Plug P is inserted in jack J at the toll office Rand plug 1? is inserted in jack J, at toll ofiiceF. Relay 12 of the cord circuit at oflice E and relay 37 of the cord circuit at of'fice F will be operated if the keys in both cordcircuits are normal and if plugs P and P are inserted in jacks J 4 and J respectively. If key 74 of the testing circuit is operated in the left hand direction an alter nating electromotive force will be applied over contacts of keys 74 and 76, tip and ring contacts of plug P and jack J trunk 67, over the tip and ring conductors of the cord circuit at ofi ice E, through branch 77 of the four-wire repeater circuit including the repeater 59, over the conductors of the cord circuit at oflice F and the conductors of trunk 68, tip and ring contacts of jack J and plug P right hand normal contacts of switches 76 and 74, through receiver shunt 73 to the receiver 71. Switch 7 5 is now operated, thereby causing the operation of. relays 79 and 80, which disconnects the source of tone from the trunk circuits 67 and 68, respectively, and connects said source of tone to one end of the artificial line 72, and the receiver 71 to the other end of said artificial line.

The receiver shunt 7 3 is gradually varied until the volume of tone received in the receiver 71 when the receiver is connected across the artificial line is the same as when it is connected across the trunk leading to one end of the four-wire repeater circuit.

If the switch 74 is thrown in the right hand direction the source of alternating electromotive force 70 will be applied to the trunk 68 and the receiver 71 will be connected across the end of trunk 67 thus establishing the circuit from vibrator 70, right hand contacts of switch 74, tip and ring contacts of plug P and jack J trunk 68, conductors of the cord circuit at oflice F, conductors 78 and repeater 60, forming one side of the four-wire circuit, conductors of the cord circuit at office E, trunk 67, contacts of jack J and plug P left hand contacts of switches 7 6 and 74:, receiver shunt 73 to receiver 71. By operating switch 75 in the manner heretofore described the vibrator 70 and the receiver and receiver shunt are alternately connected with the four-wire circuit and with the artificial line, and shunt 73 'is varied until the volume of tone in the receiver 71 when the receiver is connected with the artificial line is the same as when connected with the four-wire repeater circuit. The reading upon the scale of the receiver shunt represents the transmission gain due to the presence of repeater 60 in the circuit.

From the foregoing description of the apparatus in which this invention is embodied and of its mode of operation, it will be seen that this invention provides simple and effective means for controlling automatically the connection of the telephone repeaters with the trunk circuit, so that the said repeaters will be connected into the circuit only when it is necessary to have such repeaters connected thereto in order to produce the desired grade of transmission. This invention furthermore provides a simple and efficient method for determining the improvement in transmission due to the connection of the repeaters in the four-wire transmission circuit. Although this invention is shown as embodied in the single form, it is apparent that it is capable of embodiment in other and varied forms without departing from the spirit ano scope of the appended claims.

VVhat is claimed is:

1. In a telephone system the combination of two subscribers circuits, trunk circuits adapted to connect each subscribers circuit to a toll oflice, a four-wire repeater trunk circuit extending between said toll orhces', telephonic repeaters adapted to be connected with said four-wire circuit, link circuits adapted to connect said subscribers circuits with said trunk circuits and said trunk circuits with said repeater trunk circuit, and means associated with said repeater trunk circuit whereby the said telephonic repeaters may be effectively connected into said repeater trunk circuit when a talking connection is established between the two subscribers circuits.

2. In a telephone system the combination of two telephone lines, each consisting of a subscribers line connected with a trunk line, a four-wire repeater trunk circuit, telephonic repeaters adapted to be connected therewith, link circuits adapted to connect said telephone lines to the opposite ends of the said repeater trunk circuit and controlling means associated with said lin-k circuits and said repeater trunk circuit whereby the said telephonic repeaters may be effectively conj when the normal'conditions for a through nected with said repeater trunk circuit only telephone conversation exist.

3. In a telephone system the combination of two telephone lines, each consisting of a subscribers line connected with a trunk line, a four-wire repeater trunkcircuit having telephonic repeaters associated therewith, link circuits adapted to connect said telephone lines with said repeater trunk circuit and means associated with said link circuits and said repeater trunk circuit whereby the said repeaters Will be disconnected from said transmission circuit whenever any switch other than the monitoring switch associated with said link'circuits remains in its operated position.

effectively disconnected from said toll line so long as either of said link circuits remains disconnected from its associated telephone line. V i i 5. In a telephone system a combination of two telephone lines, each consisting of a subscribers line connected with a trunk line, a toll line having thermionic repeaters associated therewith, link circuits adapted to connect each of said telephone lines to the opposite ends of said toll line and means associated with the said toll line and con- .trolled by said link circuits whereby the said repeaters may be effectively disconnected from the said toll line and the filament heating batteries disconnected from the filaments of said repeaters when ever either of saidlink circuits'is disconnected from the line.

6. In a telephone system a combination of two telephone lines, each consisting of a subscribers line connected with a trunk line, a

toll line having thermionic repeaters associated therewith, link circuits adapted to connect each of said telephone lines to the oppositeends of said tolllin e and means associated with the said toll line and controlled by said link circuit whereby the saidrepeaters may be effectively disconnected from the said toll line and the filament heating batteries disconnected from the filaments of said repeaters. whenever any switch other than the monitoring switch associated with either of said link circuits remains in its operated position. v

7. In a telephone system, the combination of a four-wire repeater trunk circuit, telephone circuits adapted to beconnected with each end of said four-wire circuit, thermionic repeaters adapted for connection with either branch of said four-wire circuit, a plurality of filament heating batteries and means controlled by the connection of said telephone circuitswith said f0ur-wire circuits wherebythe filaments of said thermionic repeaters will be energized by said .bat- I teries simultaneously with the effective con-.

nection or" said repeaters with the four-wire circuit.

' 8. In a telephone system, the combination of a four-wire repeater trunk circuit terminating at each end in a plurality of jacks, a plurality of groups of telephone lines adapted for connection with said four-wire circuit, each of said groups having electrical characteristics differing from the others, a plurality of electrical networks adapted to be associated so as to have the same characteristics as said groups and to be connected with said founwire circuit to balance electrically the telephone circuit connected thereto and aplurality of telephone repeaters adaptedto be connected effectively with said four-wire circuit whenever said telephone lines are properly connected with the fours wire circuit.

In testimony whereof, I have signed my.

CHARLES S. DEMAREST.

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