US1312514A

US1312514A - Ptanoobaph co

Info

Publication number: US1312514A
Authority: US
Publication date: 1919-08-12
Anticipated expiration: 1936-08-12

Description

I. G. BLESSING.

TRUNK SELECTING SWITCH.

Anucmon man IAN 11. m2. RENEWED MAY 28. m1.

1,312,51 4. Patented Aug. 12,1919.

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l. G. BLESSING.

TRUNK SELECTING SWITCH. mwucmon 11120 11 1111111 1912. RENEWED MAY 28. 1911.

1 ,3 12,5 1 4. Patented Aug. 12, 1919.

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J. G. BLESSING. TRUNK SELECTING SWITCH. APPLICATIGN FILED mu. l1, m2. RENEWED MAY 23. Ian.

1 ,3 12,514. Patented Aug. 12,1919.

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UNITED STATES PATENT OFFICE.

JOHN G. BLESSIN G, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIG ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

Specification of Letters Patent.

Patented Aug. 12, 1919.

Application filed January 1'7, 1912, Serial No. 671,696. Renewed May 28, 1917. Serial Np. 171.583.

To all whom it may concern:

Be it known that I JOHN G. BLEBSING, a. citizen of the United tates of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Trunk-Selecting Switches, of which the following is a specification.

My invention relates to automatic or semi- I automatic telephone systems, and it relates more specifically to an improved construe tion of a non-numerical trunk-selecting switch for use in such systems.

My invention relates to a trunk-selecting switch or rotary line switch of the type in which the wipers never release and rotate backward to normal, but have motion in a forward direction only. Hcretofore, in switches of this type, the wipers of the line switch when idle remained in contact with the terminal of the trunk line which was last seized by the switch. In my improved construction, however, although the wipers of the switch never release back to normal position, they do not stand on bank contacts when idle. The bank contacts are separated by spacers wide enough to allow the wipers to rest between the ad] acent contacts without touching the same. When a connection is released, the wipers simply move one step forward, off the contacts with which they were in engagement, but not onto the next contacts. The next time the switch operates, the wipers make one more step onto this next set of contacts, and if these contacts are busy the wipers are rotated automatically until an idle trunk is found.

Switches of this type have the advantage that their wipers do not return to normal after each call, and are thus not likely to have to rotate over busy trunks when a call in initiated.

A further advantage of my improved form of switch .is the fact that the wipers do not normally stand on bank contacts, which makes it possible to simplify the construction of this type of switch. Heretofore, in line switches of this type, the wipers rested upon bank contacts all the time. It was therefore necessary to provide means for disconnecting the line relay from the line, and connecting the line with the wi ers when the line to which the switch be onged became a calling line, and to also provide means for disconnecting the line relay but not connect the line with. the wipers when the line became it called line. This differential operation, which was necessary in prior switches of this type, is unnecessary in my improved construction for the reason that since the wipers do not rest upon the contacts normally, it does no harm to connect the line with the wipers, and thus the cut-off relay can-operate 1n the same manner whether the line is being called or is calling.

These and other objects and features in my invention will be more readily and clearly understood by reference to the accompanying drawings, in which- Figure 1 is a plan view of my improved rotary switch.

Fig. 2 is a sectional view taken on the line 2-2 in Fig. 1 to show the construction of the wipers and banks.

Figs. 3 and 4 show a complete connection between a calling substation A and a called substation A in a system embodying the principles of my invention.

s shown in Fig. 1, the subscribers indi vidual switch comprises, among other details, a bank of contacts 2 and two sets of Wipers 3, 4, 5 and 6 and 3 4 5 and 6 and for wiping over and making contact therewith. Corresponding wipers of each set are electrically connected together, and the two sets are so arranged that as one passes off the last contact of the bank the other passes onto the first contact. The bank 2 com rises four circular rows of contacts secur between suitable clampin plates and are suitably insulated from sald plates and from each other. The wipers 3, 4, 5 and 6 and 3, 4, 5 and 6 are insulated from each other and fastened together and are secured to a toothed wheel 7 which is loosely mounted upon a pin 8 secured to the base plate 9. The in 8 is located at the center of curvature of t e bank 2, so that as the wheel 7 is rotated the wipers make successive contact with their respective contacts in the bank. Electrical connections are made with the wipers 3, 4, 5 and 6 and 3, 4*, 5" and 6 through the medium of stationary brushes 10, 11, 12 and 13, which brushes bear against the central portion of the wipers. The means for rotating the wipers over the bank contacts comprises the electromagnet 14 and the lever comprising the two arms 15 and 16 which is secured to the armature of the magnet and loosely mounted upon the pin 23. The arms 15 and 16 co-operate with the beveled teeth of the wheel 7 in such a mannor that the wheel is rotated at distance equal to half the pitch of the teeth each time the magnet is energized or deenergized. The contacts in the bank 2 are spaced apart so that when the magnet 1-'-l it dei ncrgized the wipers may rest between adjacent contacts without touching them. When the magnet is energized, the wipers are rotated onto the set of contacts before which they were stnnding when the magnet was dei nergized. The magnet 14 is provided with means for interrupting its own circuit, said means comprising the spring 17 and the contact screw 18. Just before the armature of the magnet reaches its fully attracted position, the bushing 19 forces the spring 17 out of engagement with the screw 18 and hows it out so that it remains out of contact with the screw until the armature is restored far enough for the bushing 20 to force it back to its original position. The power for restoring the armature of the magnet is furnished by a sprin 150. The circuits of the switch are control ed by the relays 21 and 22. 'lhcse circuits are represented at C in Fig. 3. As shown in this circuit, the wipers 3 and t are the line wipers and the Wiper 5 is the private or testin wiper. The relay 21 is the line relay an the relay 22 is the cut-oil or lineswitching rela One terminal of the relay 21 is connector to the battery lead 75, while the other terminal is connected to the line 64 through the normally closed contacts 69 and 70 controlled by the cut-ofi' relay 22. The cut-ofi' relay 22 is connected to battery in series with the magnet 14, the opposite terminal of this cut-off relay being connected to its own spring 72. The rivate wiper 5 is connected to the contact 9 contro led by the relay 21, while the contact 68 is connected to a point midway between the rela 22 and the magnet 14.

T- e telephone system represented in Figs. 3 and 4 is the well-known type of automatic telephone system embodying subscribers individual or preselector switches, so-called first seiectors, second selectors and connectors. In this system each subscribers line is provided at the central ofiice with an individual switch C of the type shown in Fig. 1. Corresponding contacts in the bank of a plurality of these switches are multiplied together and connected to trunk lines leading to first selectors E. In this manner a small number of first selectors are made accessible suitable common buttery type of sul'istation which is provided with a calling device of the proper character for controlling the central oflice :mpnratus shown herein. The substation A comprises the usual. receiver 25, transmitter 26, ringer 27 and switch hook 28. The automatic calling device may be of the type shown in the British patent to S. G. S. Dicker No. 29,651- o-f 1910, but is herein represented diagramanatically by a pair ol impulse springs 29 and 30 and a toothed impulse wheel 31. The impulse wheel 31 is assumed to be controlled by the calling subscriber through the medium of a dial (not shown) provided with finger holes. In order to call any digit with such a calling device, the subscriber inserts a finger in the hole of the dial corresponding to the di it to be called and rotates the dial until the finger strikes a suitable stop, whereupon the finger is removed and the dial allowed to return to its normal position. During the forward movement of the dial a number of teeth, corresponding to the digit to be called, on the wheel 31 are rotated past the end Of the spring, out of engagement with the spring 29.

The selector E is of the general type of selector switches disclosed in United States Letters Patent No. 815,321, granted to Keith, Erickson & Erickson March 13, 1906, the circuits being modified, however, as shown in British patent to T. Gr. Martin No. 1419 of 1910, in order 'to operate in a system in which the central ofiice apparatus is controlled by the calling subscriber over the two sides of the line in series.

The second selector F is essentially the same as the first selector E.

The connector H is of the general type of connector switches disclosed in United States Letters Patent No. 815,176, granted to Keith, Erickson & Erickson March 13, 1906, but, like the selectors, is modified to operate in a two-wire system. Like the selectors, the connector 13 provided with a shaft (not shown) earryin the wipers 52, 53 and 54; and controlled lay the vertical magnet 55 and the rotary ma et 56. The usual side switch is controll by the private magnet 57 in the usual manner. At 58 there is shown a ringing relay which is provided for the purpose of cnnnecting ringing current with the called line after the connection has been completed. The tailking circuit through the connector is divided into twosections inductively connected through the condensers 59 and 60.

The substation A and the line switch C are identical with the substation A and line swi-tol'i C, respectively. At R there is shown a ringing current generator and at M a busy signaling machine is represented. A battery B having one terminal grounded at G is shown for the purpose of providing ourto the battery lead 75.

rent for operating the switches and for talking purposes.

Having given a general description of the apparatus with which I have chosen to illustrate mty invention, as the operation of this type 0 system is well known it is not thought necessary to further describe its operation, except in so far as it relates to my improved line switch. The removal of the receiver at the substation A from the switch hook permits the springs 61 and 62 to come into contact, thereby bridging the talking circuit of the substation across the

line conductors

63 and 64, whereby a circuit is closed through the line relay 21 of the switch C. This circuit extends from ground G through the

springs

65 and 66, line 63, springs 61 and 62, 29 and 30, receiver 25, transmitter 26', line 64, springs and 69 and relay 21 to the battery lead and thence through the battery B to ground G. The relay 21, upon energizing, completes a circuit extending from ground Gr through the springs 76, interrupter springs 17 and 18 and the operating magnet 14 to the battery lead 7 5. As has been explained, the wipers of the switch normally rest between two successive sets of contacts in the bank of the switch. When the above circuit is closed through the ma net 14, said magnet energizes and rotates the wipers one step onto the contacts immediately in front of them. If the trunk line which is connected to this set of wipers is idle, the magnet 14 remains energized and the wipers remain rest-ing upon this set of contacts. If the -first trunk line engaged by the wipers is busy, however, the circuit of the magnet 14 is automatically interrupted at the springs 17 and 18 and the wipers are automatically rotated until they do reach the contacts of an idle trunk. The manner in which the wipers are brought to rest upon the contacts of an idle trunk is as follows: It will be seen that when a first selector E is idle, the private bank contacts of the trunk line leading to said switch in the banks of the line switch are grounded through the sprin s 77 and 78 of the relay 49 in the selector. bus, when the wiper 5 engages the contact of an idle trunk, a circuit is closed from ground Gr through the springs 78 and 77, wiper 5, springs 79 and 80 of the relay 21, springs 81 and 72, cut-ofi' relay 22 and the magnet 14 Since the magnet 14 is energized at the instant this circuit is closed by the wiper 5, said magnet remalns operatively energized in series with the cutoff relay 22, regardless of the interruption of its original circuit at the springs 17 and 18. The relay 22, which is included in the locking circuit of the magnet 14, is operatively energized and operates to disconnect the line relay 21 and ground G from the calling line and to extend the line connection to the first selector E, as represented b the heavy conductors in the drawings.

he relay 22, upon energizing, also completes a locking circuit for itself and the relay 14 independent of the ground G at the selector E. This circuit extends from ground G (which is permanently connected with all of the contacts which are engaged by the wiper 6) throu h the wiper 6, springs 73 and 72 and throng the relay 22 and the magnet 14 to the battery lead 75. When the line circuit is extended through to the selector E, its line relay 48 is energized over a circuit extending from ground Gr through the lower winding of said relay, side switch wiper 42, line switch wiper 4, thence over the heavy conductors to and through the substation A and back over the other side of the line, through the line switch wiper 3 and the side switch wiper 41 and the upper winding of the relay 48 to the battery lead 78. The relay 48, upon energizing, completes an energizing circuit through the slow acting relay 49. The relay 49, upon energizing, separates the springs 7 7 and 78 to disconnect ground G from the line switch private bank contacts of the seized trunk, so as to prevent another line switch from obtaining connection with the selector E while it is in use. The line relay 21., of course, decnergizes when it is disconnected from the line by the operation of the relay 22, whereupon the wiper 5 is connected to a point between the relay 22 and the magnet 14 through the springs 79 and 82 and the springs 68. The line relay 21 of the line switch C is preferably slightly slow acting, so that it will be certain not to complete the connection of the wiper 5 with the point between the relay 22 and the magnet 14 until after the relay 49 at the selector has had suflicient time to energize and thus disconnect ground G from said wiper. As soon as the line switch C has completed connection with an idle selector E, the connector private bank contacts of the calling line are provided with a guarding ground potential which extends from ground G through the wiper 6, springs 73 and 72 and the conductor 83 to said contacts. This guarding potential protects the calling line from being called while it is in use.

Connection having been extended to an idle first selector by the removal of the receiver at the calling substation, the calling subscriber now operates his calling device in accordance with the various digits of the number of the called line, so a to extend a connection to the called line in the manner well understood in the art. When connection is completed with the called line, the circuit of the cut-off relay 115 of its line switch C is closed. This circuit extends from ground G in the connector through the side switch wiper 114, springs 116 and 117, wiper 54, relay 115 and magnet 118 to the battery lead 75. The windings and resistances of the cut-off relays and motor magnets of the subscribers individual switches are so proportioned that the current which flows through the motor magnet in series with the cut-off relay is not suflicient to operate the motor magnet, but is sufficient to maintain the motor magnet in its operated position if it is in that position when the circuit through the cut-off relay is closed. The only result of the closure of the above circuit through the relay 11.5 and the magnet 118, therefore, is to operate the relay 115. The relay 115, upon energizing, disconnects the line relay 120 from the line. The relay 115, upon energizing, also con nects the called line with the wipers 121 and 122, but since the magnet 118 is not energized, these wipers are not standing upon any contacts. and the connection of the line therewith is, therefore, without any effect whatever.

Upon the completion of the conversation the entire connection is automatically released upon the hanging up of the receiver at the substation. During the time conversation is being carried on, the circuits of the release magnets of the switches E, F and H are maintained open by the relays 49, 91 and 101, which are energized over a circuit extending from ground G at the connector H through the spring 151 and its front contact, whence it branches, one branch passing through the relay 101, While the other branch extends through the side switch wiper 102, springs 103 and conductor 99 and thence to and through the relays 91 and 19 of the switches F and E. The hanging up of the receiver at the substation A separates the springs 62 and 61, thereby breaking the energizing circuit of the connector line relay 100. The relay 100, upon deenergizing, breaks the circuits of the relays 101, 91 and 49. These relays, upon deenergizing, complots the circuits of their respective release magnets 131, 133 and 46, which in turn, upon energizing, release their respective switches. The circuits of the release magnets are opened at the off-normal springs by the switch shafts when. they reach their lowest position in a well-known manner. The connector switch, upon releasing, also destroys the energizing circuit for the cut-off relay 115 of the switch C, which relay, upon de'elnergizin restores the individual switch of the calls line to normal condition. The relay 49 of the selector E, upon deenergizing, also extends a connection from ground G through the springs 78 and 77, private wiper 5 of the switch G, springs 79 and 82 and the springs 68 to a point between the relay 22 and the magnet 14. The connection of ound G: with this point shortcircuits si e relay 22, which thereupon deenergizes. The springs of the relay 22 should be so adjusted that as the relay deenergizes the springs 72 and 73 separate to disconnect ground G from the circuit of the relay 22 and the magnet 14 an instant before the springs 68 separate to disconnect ground U. 'lhercforc, when ground G is finally disconnected, there is no longer any circuit through the relay 22 and the magnet 14, and said relay and magnet finally deenergize. The magnet 14, upon dei ncrgiz- 111g, permits the wipers of the switch to mo e one step off the contacts of the trunk line with which it had made connection and come to rest between said contacts and the next succeeding set.

I'Vhile I have illustrated my invention in connection with one particular type of automatic telephone system, it will be readily understood that my improved line switch can be used in connection with any desired form of telephone system. whether automatic or semi-automatic. Likewise, it is not necessary that this line switch be used individual to a subscribers line, as this same switch might be employed in any other position in the system. Many other modifications and changes which come within the scope of my invention will likewise suggest themselves to those skilled in the art.

What I claim as my invention is 1. In a "telephone system, a line, a trunkselecting switch individual to the line comprising a series of contacts, a contact arm adapted to engage with said contacts, and means for normally maintaining said arm in a position between any two adjacent contacts.

2. In a telephone system, a line, a trunkselecting rotary switch individual to the line comprismg a series of contacts, a contact arm adapted to rotate over said contacts, and means for maintaining said contact arm in a position between any two adjacent c0ntacts when said switch is idle.

3. In a telephone system, a non numerical trunk-selecting switch, said switch comprising a series of contacts, trunks connected with said contacts, a contact arm adapted to be rotated over said contacts to select an idle trunk, and means for maintaining said arm between any two adjacent contacts when said switch is idle.

4. In a. telephone system, a non-numerical trunk-selecting switch, a series of contacts, trunk lines connected with said contacts, a contact arm adapted to rotate in but one direction over said contacts to select an idle trunk, and means for maintaining said arm in a position between any two adjacent contacts when said switch is idle.

5. In a telephone system, a trunk-selecting switch comprising a series of contacts, a contact arm, a magnet for moving said arm step by step over said contacts, means for moving said arm onto one of said contacts when the magnet is energized, and means for moving said arm. to a position between two adjacent contacts when said magnet is doenergized.

6. In a telephone system, a trunlcselecting switch comprising a Series of contacts, a contact arm, means for rotating said arm over said contacts, said means including a ratchet and pawl mechanism, and a magnet for operating said mechanism to move said arm in contact with one of said contacts when said magnet is energized, and to move said arm to a position between two adjacent contacts when said magnet is denergized.

7 In a telephone system, a subscribers line, a non-numerical trunk-selecting switch for said line, said switch comprising a series of contacts, an arm adapted to be rotated in but one direction over said contacts, means for normally maintaining said arm in a position between two adjacent contacts, a magnet for operating said arm, means for energizing said magnet from said subscribers line to move said arm onto one of said contacts, and means for automatically deenergized and again energizing the said magnet to move said arm to the next of said contacts provided said first-mentirmed contact is busy.

8. In a telephone system, a non-numerical trunk-selecting switch including a line relay, a cut-ofi relay, an operating magnet, means for energizing said cut-off relay and magnet in series during the time a connection is maintained, and means for shortcircuiting said cut-ofi' relay when said connection is released.

9. In a telephone system, a plurality of trunk lines, a non-numerical trunk-selecting switch for selecting an idle trunk for extending a connection to a second automatic switch, an operating magnet and a cut-off relay for said trunk-selecting switch, means for energizing said magnet and cut-ofl' rela in series when a connection is maintainer and means for short-circuiting said cut-oil relay by establishing a ground connection at said second automatic switch when a connection is released.

10. In a telephone system, a plurality of trunk lines, a non-numerical trunk-selecting switch for selecting an idle trunk to exten a connection to a second automatic switch, said trunk-selecting switch including a pair of line wipers and a third wiper, a cut-oil relay, an operating magnet, means for energizing said magnet and relay in series when a connection with said second switch is maintained through said line and third wipers, a connection from said third wiper to a point intermediate of said magnet and cut-ofl relay, and means for establishing a ground connection at said second automatic switch over said third wiper when said switch releases to thereby short-circuit said cutofi' relay.

11. In a telephone system, a plurality of trunk lines, a trunk-selecting switch for selecting an idle trunk for extending a connection to a second automatic switch, said switch comprising a pluralit of line wipers and a third wiper, a cut-ofl relay for said trunk-selecting switch, means for energizin said relay to extend a connection to said wipers, a locking circuit for said relay, and means for establishing a ground connection at said second automatic switch over said third wiper to short-circuit said cut-ofll relay when said second automatic switch releases.

12. In a telephone system, a plurality of trunk lines, a trunk-selecting switch for selecting an idle trunk for extending a connection to a second automatic switch, said trunk-selecting switch comprising a plurality of line wipers and a third wiper, a cutoil relay for said trunk-selecting switch, means for energizing said relay to extend a connection to said wipers, a locking circuit for said relay, an operating magnet connected in series with said relay when a connection with said second automatic switch is maintained, and means for establishing a ground connection at said second automatic switch over said third wiper to short-circuit said cut-ofl" relay when said second automatic switch releases.

13. In a telephone system, a plurality of trunk lines, a trunk-selecting switch for selecting an idle trunk for extending a connection to a second automatic switch, said trunk-selecting switch comprising a plurality of line wipers and a third wiper, a cutoff relay for said trunk-selecting switch, means for energizing said relay to extend a connection to said wipers, a locking circuit for said relay, means for establishing a ground connection at said second automatic switch over said third wiper to short-circuit said cut-ofi' relay when said second automatic switch releases, and means operated upon the deenergization of said cut-oil relay for opening said locking circuit and disconnecting said third wiper from the circuit.

14. In a telephone system, a plurality of trunk lines, a trunk-selecting switch for selecting an idle trunk for extending a connection to a second automatic switch, said trunk-selecting switch comprising a plurality of line wipers and a third wiper, a cutofl relay for said trunk-selecting switch,- means for energizing said relay to extend a connection to said wipers, a locking circuit for said relay, an operating magnet connected in series with said relay when a connection with said second automatic switch is maintained, means for establishing a ground connection at said second. automatic switch over said third wiper to short-circuit said cut-o-fl relay when said second automatic switch releases, and means operated upon the dci nergization of said cut-oft relay for opening said locking circuit and disconnecting said third wi icr from the circuit.

15. In a telephone system, an operating magnet, a cut-off relay, a circuit for energizing said magnet and relay in series, said circuit including a pair of contact sprmgs controlled by said cut-ofl' relay.

16. In a telephone system, an operating magnet, a cut-off relay, a circuit for energizing said magnet and relay in series, said circuit including a pair of contact springs controlled by said cut-off relay, and means for short-cincuiting said relay to thereby deenergize 'both said relay and magnet.

17 In a telephone system, a switch comprising a series of contacts, a contact arm adapted to engage with said contacts, means for normally maintaining said arm in a posi' tion between any two adjacent contacts, and a motor magnet for rotating said wipers one step upon energizing and another step upon dee-nergizing.

18. In a telephone system, a rotary switch comprising a series of contacts, a contact arm adapted to rotate over said contacts, means for maintaining said contact arm in a position between any two adjacent contacts when said switch is idle, and a motor magnet for rotating said wipers one step upon ener gizing and another step upon deenergizing.

19. In a telephone system, a non-numerical trunk-selecting switch, said switch comprising a series of contacts, trunks connected with said contacts, a contact arm adapted to be rotated over said contacts to select an idle trunk, means for maintaining said arm be tween any two adjacent contacts when said switch is idle, and a motor magnet for rotating said wipers one step upon energizing and another step upon denergizing.

20. In a telephone system, a non-numerical trunk-selecting switch, a series of contacts, trunk lines connected with said contacts, a contact arm adapted to rotate in but one direction over said contacts to select an idle trunk, means for maintaining said arm in a position between any two adjacent contacts when said switch is idle, and a motor magnet for rotating said wipers one step upon energizing and another step upon deenergizin 21. In a telephone system, a line, a trun a switch in the trunk and a switch in the line for connecting the line with the trunk, a line relay, a switching relay and a motor magnet in the line switch, an energizing circuit for the motor magnet and the switching relay controlled by the line relay and the switchin relay.

22. In a to e hone system, a pair of lines, means for esta lishing a talking circuit between said lines, said means including any one ot a plurality. of trunk lines, a switch having a progressively movable wiper included in the talking circuit, said switch having access to said trunk lines through said wiper, release means for said switch responsive to the opening of the talking circuit, and a plurality of positions in any one of which the said wiper may be held while the switch is released, said switch controlled over the two sides of the talking circuit in series.

23. In a telephone system, a pair of lines, means for establishing a talking circuit between said lines, said means including any one of a plurality of trunk lines, and a switch havin a progressively movable wiper inelude? in the talking circuit, said switch having access to said trunk lines through said wiper, release means for said switch responsive to the opening of the talking circuit, and a plurality of positions in any one of which the said wiper may be hold while the switch is released, one such position for each trunk line, said switch controlled over the two sides of the talking circuit in series.

24. In a telephone system, a pair of subscribers lines, a pair of talking conductors individual to each of said lines, a switch cont-rolled over said conductors in series for establishing a talking circuit between said lines, a contact arm for said switch, a group of trunk lines accessible to said switch through said arm, a magnet controlled by opening said conductors for releasing said switch, and a position individual to each of said trunk lines in which said arm stands after said switch is released from the trunk line last used.

25. In a telephone system, a' pair of subscribers lines, a pair of talking conductors individual to each of said lines, a switch controlled over said conductors in series for establishing a talking circuit between said lines, a contact arm for said switch a group of trunk lines accessible to said switch through said arm, a magnet controlled by opening said conductors for releasing said switch, and a position individual to each of said trunk lines in which said arm stands after said switch is released from the trunk last used, said arm remaining in said position until said switch is again brought into use.

26. In a telephone system, a pair of subscribers lines, a pair of talking conductors individual to each of said lines, a switch controlled over said conductors in series for establishing a talking circuit between said lines, a contact arm for said switch, a grou of trunk lines accessible to said switc through said arm, a magnet controlled by opening said conductors for releasin said switch from any one of said trunk lines, a position individual to each of said trunk lines, means for holdin said arm in any one of said positions a or said switch is released, and means for advancing said arm from the last released position when the switch is used for another call.

27. In a telephone system, a pair of subscribers lines, a pair of talking conductors individual to each of said lines, a switch controlled over said conductors in series for es- "tablishing a talking circuit between said 0 each of said trunk lines, and means for holding said switch in any one of said positions 5,

after said switch is released, said last mentioned means also for advancing said arm from the last released position when the switch is used for another call.

Signed by me at Chicago, Cook county, 20

Illinois, this 2nd day of January, 1912.

JOHN G. BLESSING.

Witnesses:

ARTHUR J. RAY, ALBERT ANDERSEN.

copies of this patent may be obtained for live cent: each, by addressing the "Commissioner of Patenh, Washington, D. 0."