USRE11388E - Multiple switchboard - Google Patents

Description

M. G KELLOGG.. MULTIPLE SWITGHBOARD.

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MILO Gr. KELLOGG, OF-CHICAGO, ILLINOIS.

'MULTIPLE-SWITCHBOARD.

SPECIFICATION forming part of Reissued Letters Patent No. 1 1,388.,datedNovembe1 14, 1893.

Original No. 393, 508, dated November 27, 1888- Application for reissue filed January 23, 1891. Serial N0. 37B,853. Q

To all whom it may concern:

Be it known that I, MILO G. KELLOGG, formerly of Hyde Park, and now Of hicago, Illinois, have invented certain new and useful Improvements in Multiple Switchboards for Telephone-Exchanges, of which the following is a full, clear, concise, and exact description,

reference being bad to the accompanying drawings,'formin g a part of this specification. My invention relates to a metallic-circuit telephone exchange system; and it consists, first, in a system of testing at one board of a inultiple-switch-board system to determine whether a line is in use at another board, which system I shall hereinafter describe and claim in detail.

. describe and claim in detail;

It consists, thirdly, of certain apparatus for switching, answering, calling, and clearin g out subscribers lines, which I shall hereinafter describe and claim in detail.

Figures 1 and 1 of the drawings are front views of sections of two multiple switchboards to which the same wires are connected. Fig. 2 shows a complete diagram of the boards with their circuits, apparatus, and connections necessary to operate them according to my invention. Fig; 3 shows a diagram of the subscribers station apparatus used in the system.

In-my invention I place on each board for each line a spring-jack switch or suitable device connected to the lines and apparatus,

substantially as hereinafter described. For

each line I use, or may use, a calling aununciator in the central office, and these annunciators are distributed'amon'g the "different boards, so that the calls may be readily answered and attended to. The switching. ap-

paratus of a line on the board where its calls are to be attended to is different, and is connected differently from the switching apparatus of the line on the other boards. At this 5.5 boardthe line terminates on both sides in a double or loop cord and a double or loop plug. This plug is normally, or when the line is not switched for conversation, placed in a switching device, or otherwise placed so that one of 6c the sides of the line is grounded, and when the plug is withdrawn 'from the switching device or taken from its place the ground connection is removed from the line. This side of the line also passes through spring-jack or similar switches at all of the boards, these, switches being connected in the circuit between the switch-plug and the subscribers station, and so constructed and connected that when a switch plug is inserted into any switch-it disconnects the side heretofore mentioned from the ground and connects it to one ofthe contact pieces of the plug. The other side of the line isnormally open at the central office, and is connected at each board 7 5 to a contact piece suitably place'd and adapted to be brought into connection with aiest-plug, which forms the terminal of a test wire or circuit at that board grounded at its other end. In this test-wire is a test-receiving in-' 8% strument and a test-battery of suitable char acter.

The side of the line which is normally open at the central office is also connected at its switch at each board to a contact piece suitably placed and adapted to be brought into connection with the other con tact piece of the double plug when tiepiug is inserted into the switch. The contact-pieces to which the test plugs are to be applied and the switch con no tact-pieces last abovementioned maybe one. and the same piece, as shown in the drawings;

The calling-annunciator of a line is connected into the circuit of that side of the line which is grounded and is placed between the 9 5 plug and the switches of the line.

On each board I place in convenient positions one or more switching devices, cach hav- I ing two contact pieces, and adapted, at the will of the operator, to be brought into elec-. roo

trical connection with the two contact pieces, respectively, of any loop-plug located at the board. Ateach b ard '1 also placeinco nve'n ient positions switching devices adapted: to

loop a calliug-generator and an operators tele- In Fig. 2 ofthedrawing's two'inetal lic elf-- cuit lines are shown, andthey'areconnectedI to'the switches andappa-ratu's -2ojn the two boards shown in such a mauner'as' to allow all. to

the necessary operations of a 'tel'e'p'honejexchange system, and at thesame time show the principles of lnyinvention. 'Thetwo sides a plug is inserted into a switch,

of one line are marked Line' No. 1 and fLine No. 1. Line No. 1 is the side-.nor-- inally grounded at the. central oflice and line, No. 1 is the side normally open at the central ofiice. The sides of the other line are marked Line No. 2 and Line No. 2.'

rand r are the two spring-jack switches of line No. 1 at the two boards, and s and s'are: the two spring-jacks of line No. 2 at the two boards.-'

- g vg, &c are the springcoutact-pieces of the switches.

h h are the contact-pieces on which the springs normally rest.

jj, &c.,'are the contact-pieces of the'lines on the difierent boards to which the test-plugs may be applied. They are also the pieces which form the connection between one side of the plug and the open end of a line when 00,are switching devices, inwhich the plugs are normally placed, and which ground one side of a line attached to v a plug whenso placed, as shown and as heretofore indicated. 10 and w are calling-annunciators for the two lines, w being for line No. 1 and located at board A, where the double plug and cord of that line are also located and where its calls are to be answered, as being forlineNo.'2 and located at board A, where its double plug and cord are located and its calls are to be answered.

D and D are two loopplugs attached to double flexible cords, D being for line N 0'. 1

and D for lineNo. 2. Theplugs. D and D should normally be in switches o 0 at their respective boards in such a position that the sideof'their lines in whitlh are the switches and'annu'uciato'r of the lines is normally grounded.

Wand X are two looping-in switches'for the lines, counectedto their-circuits and the other apparatus, substantially as shown.

B B at the two boards are calling-generators or batteries, and t t are operators telephones. switch for each line, each at the board where the calls of the line are, to be, answered, and they should be connected to the operators telephone and generator of the operator who attends to the calls of the lines in the way substantially as shown and as will be apparent to those. skilled in the art.-.

' 'IT at the two boardsare test-plugsattached to flexible 'cords, and adapted 'to'be' brought indicated.

There should. be one 'lo'opingdn into connection with the pieces j j at their respective. boards. a

if t. are test-receiving instruments, and B B are test-batteries at thetwo boards.

Gin each case in the'drawings is a ground connection. r v

G C are switching devices at the two boards,

the contact-pieces c eot' each of which are connected to the two sides of the operators telephone at-itsboard,j andare adapted to be brought into connection, atthe will of the operator, with the two contact-pieces of any loop-plug located at the board. These switching. devices may be made as shown, or of other appropriate forms of construction.

The main line connections are substantially as shown'and as have Inthe subscribers station apparatus shown in Fig.3, (of. which there should be one at each subscribers station,) 1 is the telephonebeen heretofore Switch, 2 is the signal-bell, 3 is the callinggenerator, and4 is the subscribers telephone. These parts may be the usual forms of. apparatus, andrare connected as shown, or in other known ways. The calling-generator is, however, modified, as will hereinafter bedescribed. l

The generator has an automatic device,-

(shown in the drawings) by which, when the crank is not in motion, the wire of the armature is shunted and the line is disconnected from the ground at the subscribers station,

and when the generator is turned or operated the shunt is automatically removed and the line is temporarily connected to the ground.

The automatic device shown is a modification of a form very generally. used, the modificatiombeing' substantially in the arrangement of the contact points: It contains a V- shaped attachment to the hub of the drivingwheel, a pi-nin the shaft, which engages in --the V'-shaped arrangement, and a spring, which presses against the wheel and brings the pin normally in the center of the V arrangement. The contact-points are substan-- tially as shown, and as will produce the switching operations above described. This apparatus should-be connected in the circuit of'a liue in such a position that when the generator .isoperated the armature is in circnit' between the; ground then established at the-subscribers station and the central oflie ground of the line heretofore mentioned.

It will be seen that each of the looping-in switches wzandX have a pair of movable levers and three pairsof contact-bolts, on, which respectively, the lovers of the switch may be placed, and that each of these pairs of contact-bolts is connected by a loop. In one of the loops is acalling'generator or battery, and in another loop is an operators telephone.

The third loop contains nothing. The oper- V as desired, loop either the battery or theltelephone into the circuit with the line to which the switchbelongs,or connect the line through the switch without either instrument being in its circuit.

The operation of the system is as follows: Vtlien a subscriber operates .his generator to send in asignal, he grounds hisline with'its armature and the calling annunciator at thecentral'otfice in circuit between the oflice' ground and his own ground, thereby operating the annunciator. Thepperator then removes the plug which belongs to the line from its normal position, and, placing its two contact-pieces on the two contact-pieces of switching device 0 at her board, finds out what line is wanted. She then tests 'the line wanted to see whether it is in use at another board, and if it isnot in use she places the plug of the line calling into the switch of the line which is wanted,

and by operating the loop switch connected with the plug sends a calling signal through the circuit.- The two lines are thus disconnected from the ground and are connected together in metallic circuit for conversation, and the subscriber'who is wanted has been called. Clearing out signals now sent by either subscriber will be received on the calling annunciator of the linein which the call originated and whose double plug is being used for the connection. It will be noticed that when the lines are connected together, as indicated, the calling annunciator of the -line whose plug is in use is in their circuit and the annunciatorof the other line is not receiving instruments is broken.

in the circuit.

'Each of the metallic circuit lines is normally (or when the line is not switched for use) connected through one of its plug contacts with one side of each of the test-receivinginstruments at the several boards. When the line is temporarily switched for conversation, said connection of the line with the test- The other side of each test-receiving instrument is connected with a test-plug adapted to be brought into connection with any line at its board. In the circuit of the instruments, between their test-plugs and their normal connections with the lines, is a test battery, (or batteries.)

4 It will be apparent from this description that when a line is tested and is not switched. .there will be a complete circuit through the battery and the test-receiving instrument, and the latter would sound or respond and when the line is switched there will be no such complete circuit, and the instrument will not respond. In the organization shown the test battery is placed between the switch, testing plug and its ground connection, and this con- I stitutes another feature of my invention.

For convenience in carrying out the testing system, in connection with the calling and switching systems I employ, the test receiving instruments are normally connected on one side to the lines through the ground, and by the operation of switching the lines, as described, they are temporarily disconnected from the ground and thereforefrom the testreceiving instruments. In such a system, with such normal connection through the ground between the test-receiving instruments and the lines, broken when the lines are switched, it is imperative that the linesbe not grounded at any other point when they are switched. In order to obtain this, and at the same time operate the calling annunciators placed as described I employ the automatic attachment heretofore described for the generators, which temporarily ground the lines for signaling as described. V

The testing system is as follows: .Each line is normally grounded at the central ofiice only, and there as indicated. W hen a line is switched for conversation with another line, either by the use of its double plug or at one of its line-switches, as indicated, it is disconnected from the ground, and'when a test plug l, is applied to one of the pieces jot the line at either board when it is thus switched, the test-receiving instrument connected with the plug will not respond, because there is then no complete circuit. Theoperator will know by the instrument not responding that the line is in use. If, when she applies the test plug as above to the piecej of any-line and the line is not switched for conversation,

there is a complete circuit from the ground through the test-receiving instrument and battery to the test plug, and thence through the line tested to the ground connection of the line, the test-receiving instrument will then respond, indicating that the line is not in use.

I claim as my invention and desire to secure by Letters Patent 1. In a telephone-exchange system, metallic circuit telephone lines, line switching devices at the central oflice-one for each lineeach switch containing three contact pieces, two of which are normally in contact, one of said pieces which are normally in contact being connected with one side or branch of its line,

and the third contact piece being insulated from the others and connected to the other side or branch of its line, in combination with double or loop plugs with double flexible conductorsone for each line-the two conductors of each cord being attached to the two contact-pieces of its plug, respectively, and the other ends of the conductors being attached to the two sides or branches of their line, respectively, ground switching devices for said plugs, and calling annunciator-s for said lines, each of said plugs being adapted tobe inserted into any of said line-switches, and

when inserted to disconnect the two switch contact pieces which are normally in contact and connect the two contact-pieces of the plug with the two contact-pieces of the switch, re-

spectively, which are connected to thetwo sides or branches of the line,each of said plugs being normally in position with one of said ground switching devices, whereby one of its con tactpieces is-normally grounded, said two contact-- pieces of a switch which are normally incontact being in the circuit of its line between its subscribers station and the contact-piece I .Of its plug which is normally grounded, and

"-the annunciator of a line being in the circuit "of the line between said two normally-closed contactpieces of the switch and said normallygrounded contact-piece of its plug, substantially'as and for the purpose set forth.

j 2. Inatelephone-exchango system, metallic circuit telephonelines, multiple switch boards for said lines, line switchingdevices for said 1ines,one for each line on each board-each switch containing three contact-pieces, two of which are normallyin contact, the contactpieces of the switches of a line which are normany in contact. being in the circuit of one of the sides or branches of the line and the other contact pieces of the switches of a line being connected to the other side or branch of the line, in'combination wit-h double or loop plugs with double flexiblecords-one for each linethe plugs being distributed among the several boards, the two conductors of each cord being attached to the two contactpieces of its plug, respectively, ground switching devices at the several boards for said plugs, and callingannnnciators forsaid lines,

each of said plfugs being adapted to be inserted into any of said line-switches .at its board, and when inserted to disconnect the two switch contact-pieces which are normally in contact and con nect the two contact-pieces of the plug with the two contact-pieces of the switch, respectively, which are connected to the twosides or branches of the line, each of said plugs being normally in position with one of said ground switching devices, whereby one of its contact pieces is normally grounded, said pairs of contact pieces of. the switches of a line which are normally in contact being in the circuit of the line between-the subscribers station and the contact-piece of its plug which is normally grounded, and the 'annun'ciator of a'line being in the circuit of the line between the said pairs of contact pieces of its switches and said normally grounded contact-piece of its plug, substan: tially as and for the purpose set forth.

3. In a telephone-exchange system, metallic combination with double ,or loop plugs with double flexible conductors-one for *each linethe two conductors of each cord being attached'to the two contact-pieces of its plug, respectively, and the other ends of the conductors being attached to the two sides orbranches of their line, respectively, and

ground switching devices for said plugs,'each of said plugs, being adapted to be inserted into any of said line-switches, and when inserted to disconnect the two switch contactpieces which are normally in contact and concontact-pieces is normally grohndedandsaid plug for the line, a plug switching device in passing through said pair of switch contacts ively, which are connected to the two sides or branches of the line, each of said plugs being normally in position' with one of said ground switching devices, whereby one of its two contact-Pieces ofa switch which are norinally in contact being in the .circuit of its line between its subscribers station and the contact piece of its plug which is normally grounded, substantially as and for the purpose set forth.

4. Inatelephone-exchangesystem, metallic circuittelephone lines, multiple switch boards for said lines, line switching devices for said linesone -for each of said boardseach switch containing three contact-pieces, two of which' are -ncrmally in contact, the contactpieces of'the switches of a line which are normally in contact being in the circuit of one of the sides or branches of the line, and the other contact-pieces of the switches of a line being connected to the other side or branch of the line,'in combination with double or loop plugs with double flexible cordsoue for each nethe plugs being distributed among the. everal boards, the two conductors of'eachcord being attached to the two contact-pieces of its plug, respectively, and ground switching devices at the several boards for said plugs, each of said plugs being adapted to be inserted into any of said line-switches at its board, and when inserted to disconnect the two switch contact-pieces which are normally in contact and connect the two contact-pieces of the plug with the two contact-pieces of the switch, respectively, which are connected to the two sides or branches of the lingeach of said plugs being normally in position with one of said ground switching devices, whereby one of its contact-pieces is grounded normally, said pairs of contact pieces of the switches of a line which are normally incontact being in the circuit of the line between thesubscribers station and the contact-piece of its plug which is normally grounded,substantially as and for the purpose set forth. n5

5. In a telephone exchange system, .4. metal,

'lic circuit 1ine,,the two sides or branches of which are normally opento each other at the central office and one side or branch of which isnormally grounded there, in combination with a switch for the line adapted to receive the switch plugs of other lines,and comprising a pair of switch contacts normally closed but open while a plug is in the switch,'a switch which the plug is normally placed, and a pair of contacts which are closed while the plug is ,ivg'the switching device and opened by the hdrawal of. the plug from the device, said branch of the line which is normally grounded 13::

and-thencethrough said other .pair of contact s to ground, substantially asset forth.

6. In a telephone exchange systems metallic circuit line, the two sides or branches of which are normally open to each other at the central oflice and one side or branch of which is normally grounded there, in combination with a switch for the line adapted to receive the switch plugs of other lines, and comprising a pair of switch contacts normally closed but open while a plug is in the switch, aswitch plug for the line, a plug switching device in which the plug is normally placed, a pair of contacts which are closed while the plug is in the switching device and opened by the withdrawal of the plug from the device, said branch of the line which is normally grounded passing through said pair of switch contacts and thence through said other pair of contacts to ground, and the line annunciator in circuit between said pairs of contacts, substantially as set forth.

7. In a telephone-exchange system, a metal:

lic circuit line the two sides or branches of' which are normally open to each other at the central ofiice, and one side or branch of which is normally grounded there, in combination with switches for the line, one on eaclrof the multiple switch boards, each switch being adapted to receive the switch plugs of the other lines located at its board, and comprising a pair of contacts which are normally closed but opened while a plug is in the switch,a switch plug for the line, a plug switching device in which the plug is normally placed and a pair ofcontacts which are closed while the plug is in the switching device and opened by the withdrawal of the plug from the device, said branch of'the line which is normally grounded passing successively through said pairs of its 5 itch contact points, and thence through the other pair of contacts to ground, substantially as set forth.

8. In a telephone exchange system, a metallic circuit line, the two sides or branches of which are normally open to each other at the is normally grounded there, in com 'ination ,with switches for the line, one on each of the multiple switch boards, each switch being adapted to receive the switch plugs of the other lines, located at its board,and comprising a'pair of contacts which are normally closed but opened while a plug is in the switch, a switch plug for the line, a plug switching device in which the plug is normally placed, a pair of contacts which are closed while the plug is in the switching device and opened by the withdrawal of the plug from the device, said branch of the line which is normally grounded passing successively through said pairs of its switch contact points and thence through the other pairof contacts to ground, and the line annunciator in circuit between said pairs of switch contacts on the one hand, and said other pair of contacts on the other hand, substantially as set forth.

9. In a telephone exchange system, a metallic circuit line, the two sides or branches of which are normally open to each other at the central office and one side or branch of which is normally grounded there, in combination with a switch for the line adapted to receive the switch plugs of other lines, and comprising a pair of switch contacts normally closed but open whilea plug is in the switch,a switch plug for theline having a switch contact piece connected by a flexible conduct-or with said 5 normally grounded side or branch of the line, a plug switching device into which the plug is normally placed anda contact piece in said plug switching device which is connected with the ground and with which said contact piece of the plug forms contact when the plug is inserted intothe switchip g device, said pa r of switch contacts being in the circuit of the normally grounded branch of the line, between said contact pieceof the plug and the subsoribers station,substantially as set forth.

10.- In a telephone exchange system, a metallic circuit line, the two sides or branches of which are normally open to each other at the central office, and one side or branch of 1,: which is normally grounded there, in coinbination with switches for'th'e line, one switch on each board of the multiple switch boards, each switch being adapted to receive the switch plugs of other lines located at its t card, 5 I

and comprising a pair of contacts which are normally closed but open while a plug is. in the switch, a switch plug for the line having a switch contact piece connected by a flexible conductor with said normally grounded I00 side or branch of the line, a plug switching device into which the plug is normallyplaced and a contact piece in said plug switching device which is connected with the ground and with which said contact piece of the plug 5 forms contact when the plug is inserted into the switching device, said pairs of switch contacts being in the circuit of the normally grounded branch of the line between said a "contact piece of the plug and the subscribers no central office, and one side or branch, t which.

station,substantially as set forth.

11. In a telephone exchange system, a me tallic circuit line, the two sides or branches of which are normally open to each other at the central office, and one side or branch of :15 which is normally grounded there, in combination with switches forthe line, one switch on each board of the multiple switch boards, each switch being adapted to receive the switch plugs of other lines located at itsboard, i 20 and comprising a pair of contacts for each switch which are normally closed but open, while a plug is in the switch, a switch plug for the line having a switch contact piece connected by a flexible conductor with said norr25 mally grounded side or branch of the line, a plug switching device into which the plug is! normally placed, a contact piece in said plug switching device which is connected withthe 1 ground'and with which said=contact piece of 1'30 the plug forms contact when the plug is inscrted into the switching device, said pairs of switch contacts being in the circuit of the normally grounded branchof theline between [and contact piece'o'f thegp'lug and the sub- .scribers station,and the line annunciator in circuit between said pairs of switch'contact points and thecontactpiece of the plug,sub-

stantially as set forth.

12. In a telephone exchange system, metallic circuit telephone lines normally grounded at the central office and there only, line i the two conductors of each cord being attached to the two contact-pieces of its plug, respectively, and the other ends of the con- 4 ductors being attached to the two sides or branches of their line, respectively, and I I at the will 'of the operator, to connect the ground switching devices for said plugs, each i f saidplugs being adapted to be insertedinto any of said line switching devices, and

. when inserted/to disconnect the two switch contact-pieces which are normally incontact and connect the two contact pieces of theplug with the two contact pieces of the switch,

respectively, which are connected to the two SIdGB OI branches of the line, each. of said plugs being normally in position with client said ground switching devices, whereby one of its contact piecesv is normally grounded,

said two contact pieces of a switch which are normally in contact being-in the circuit of fts line,- between the subscribers station and t e contact piece of its plug which is normally I grounded, in combination with a test-receivinginstrument and abattery at the central olfice in a test wire or circuit grounded at 1 13; In atelephone-exchange system, metallie circuit telephone lines normally grounded at the central cities, and there only, multiple switch boards for saidvlines, line switching devices for saidlin'es-one for each line on each board-each switch containing three contact pieces, two of which are nor'mall-yin contact, the contact pieces of the switches of a line whichare normallyin'contact being in the circuit of oneofthe'sidesofbranches of the line and the other contect'pieceref the switches being, connected, tou-the'othe'r side or branch of the line doubleol" l v'byplngs with double flexible cord's one for-each 1inethe plugs being distributed .atno'ng'jthe co'nuected ou'its other side to a switch-testing plug' adapted, at the will of the operator, to. be brought into connection with said line when-it is not switched, and a. battery and test-receiving instrument in the test-circuit,

several boards, the two conductors-of -eacI i-"'v cord being attached to the twocjontact-pieces of its plug, respectively, andthe'bther ends;

of the conductors being attached tothe two sides or br nches of their line, respectively,'

to disconnect the two switch contact pieces which are normallyjin contact, and connect".

the two contact pieces of the plug with thetwo contact pieces of the switch, respectively, which are connected to the two sides or. branches of the line, each of said plugs being normally inposition with one of saint ground switching devices',-whereby'one of its contact pieces is normally grcunded, said pairs of contact pieces of the switches of a-liue which arenormally in contact being 'in the circuit and the contact piece of its plug which is normally grounded, in combination with a testof the line between the subscribers station 1 receiving instrument at. each board in a test wire or circuit grounded on one side, and

witha battery in said test wire or circuit, and

switch-testing devices at each board adapted,

' 14;. Ina-telephone exchange system,a metallic circuit line, thetwo sides or branches of '--which terminate in the two contact-pieces,

respectively, of aloopfswi'tch plug, a swi,tch-= i'ng device "for said plug in which it is nor-1 many-placed, said plug being adapted to be removed from .said switching device and placed in the board switch of another line, in

combination with a test circuitnormally connected (i. e, when the plug is'in its normal position in thej switchiug device) on one side to one of the contact pieces of he plug; and on the other side to a switch testing plug adapted at the will of the operator to be brought into connection with said line when it is not switched for conversatiomand a battery and test instrument or test device in the test circuit thus established, whereby when the switch-plug is in its'norzjnal position the test-instrument will'sound on the test being made, and when the" plug is removed from its normal position, the instrument will not sound; substantially as set forth. I 15.;In atelephone-exchange system, a metallic circuit line the two sides or branches of which terminate in the two contact-pieces, re-

anothr' ';line,'in combination with a test circnitconnected on' one side to a contact-piece of the switching device with which one of the contact-pieces of'the plug is in contact when ipsertcd into the device, said circuit being lye the instrument will not sound, substantially as set forth.

16. In a telephone-exchange system, two metallic circuit lines,'in combination with double or loop switch plugs,-one for each line-in the two contact pieces of which the two sides orbranches of the line respectively terminate, switches,one for each line-each switch having two contact-points normally in contact in the circuit of one of the sides or branches of its line, a switching device for each plug, in which the plug is normally placed, each switching device having a contact-piece which, when the plug is inserted into the device isin connection with that side or branch of the line in which are said con tact-points of its switch and then only, a testreceiving instrument and a battery in a testcircuit connected on one side of the instru- .ment and battery to said contact pieces of said switching devices, and a switch testing plug or device connected to said test-circuit on the other side of said instrument and battery, and adapted, at the will of the uPGIkttOl, to be brought into connection with either line when it is not switched, whereby, when the lines are in their normal condition, the testreceiving instruments will sound on a test being made, and when the lines are switched for conversation by the switch plug of one line being removed from its normal position and placed in the switch of the other line they are disconnected from the test-receiving instrument and it will not sound on atest being applied, substantially as set forth.

17. In a telephone exchangesystetmmetal- -lic circuit lines and double or loop plugs located at a central ofiice switch board,onev

plug for each line-in the two contact-pieces of which the two sides or branches ofthe line terminate, in combination with a switching device at the board containing two contactpieces connected to the two sides, respectively, of the operators telephone said contact-pieces of said switching device being adapted to have the two contact-pieces of any of said loopplugs applied to or brought into contact with them,respectively, whereby the operator may, by thus applyin g any loop-plug to said switching device, loop her telephone into the circuit of the line to which the plug belongs, substantially as set forth.

18. .In atelephone exchange system, metallic circuit lines each having a loop switch plug to the two contact pieces of which are connected respectively the two sides or branches of its line and which is adapted to be placed in the switch of either of the other lines and connect its two contact-pieces with the two sides or branches of such other line, in combination with an operators telephone and a switching device or apparatus foreach operator by which the operator may at Will (3011- nect the two sides of her telephone to the two sides or branches respectively, of either of saidlines, substantially as set forth.

19. In a telephone exchangesystem, metallic telephonelines, line switching devices at the central oflice,-one for each line-having contacts connected with the line, substantially as set forth, in combination with double or loop plugs with double flexible conductors being' attached to the two contact pieces of the plug, respectively-on'e for each line-, andthe opposite ends of the conductors being attached to. the two sides or branches .of

-'tl1eir line, respectively, and a switch W or X interposed between one of the plug-contacts and its side of the line, said switch having three sets of connections or contacts,-viz;- one making the circuit through a conducting loop, another through a calling battery, and another through a telephone, substantially as and for the purpose set forth.

20. In a telephone exchange system, a metallic circuit line normally connected with the ground at the central office, and disconnected from the ground while switched for'conversation, in combination with a test-receiving in strument grounded on one side, a switch-testing plug or device adapted, at the will of the operator, to be brought into connection with said line, and a battery in circuit'with the instrument between the ground and the switchtesting plug, substantially as set forth.

21. In a telephone exchange system, a metallic circuit line normally connected with the ground at the central otfice and switching apparatus to disconnect it from the ground while it is switched for conversation, tn combination with a' test receiving instrument grounded on one side, a switch testing plug ordevice connected to the other side of the instrument and adapted at the will of the operator to be broughtinto connection with said line and a battery in circuit with the instrument between its ground and the switch testing plug, substantially as set forth.

22. In a telephone exchange system,multiple switch boards, metallic circuit lines, each normally grounded at the central office and switching devices at each board to connect any two of said lines together for conversatween its ground and switch testing plug,

substantially as set forth.

23. In a telephone exchange system, multiple switch boards, metallic circuit lines normally disconnected from the ground at the subscribers stations and a switch on each board for each line, each switch containing a Ito tion and when they are thus connected todisswitches and Y120 a common ground wire or connection; and the other side or branch of each line being connected to said normally insulated" contact pieces of its switches, and loop switch plugs, one for each line in which the sides of theline terminate, each adapted to be insertedinto the switches and when one is inserted to disconnect the pair of contact points which are normally in contact and connect the two sides or branches of theline with the two contact pieces of the plug, respectively, in combination with test receiving instruments, one at each board, each instrument being grounded on oneside and connected on its other side'to a test plug or device adapted tohebronghtinto connection with any of the normally insulated contact pieces at its board and a batteryin the test circuit thereby established, substantially as set forth. i

24. In a telephone exchange system, two or more metallic circuit lines, a local test wire at the central otiice,on'e'side of which is normally connected to one side or branch of each of said lines, and theother side of which is connected to-a switch testing-deviceadapted;

at the will-of the operator, to bring said side into connection with the other side or branch of each of said lines and a hatteryin the test circuit thereby established, in combination with a switching device for eachline to break said normal connection between the line and said local test Wire and a test receiving in-. strument in said local test Wire, substantially as set forth. Y

Signed at New York, N. Y., this 16th day of January, 1891.

MILO G. KELLOGGQ Witnesses:

FRANK S. OBER, EDWARD C. DAVIDSON.

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