US424310A - Multiple switch-board - Google Patents

Description

(No Model.) l 2' Sheets- Sheet 1. M. G. KELLOGG.

MULTIPLE SWITCH BOARD.

Patented Mar. 25, V1,890.

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(No Model.) 2 Sheets-Sheet 2.

M. G. KELLOGG. MULTIPLE SWITCH BOARD.

No. 424,310. Patented Mar. 25, 1890.

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UNITED STATES PATENT OFFICE..

MILO G. KELLOG 1i, OF HYDE PARK, ILLINOIS.

MULTIPLE SWITCH-BOARD.

SPECIFICATION forming part of Letters Patent No. 424,310, dated March 25, 18970.

Application iiled December 8, 1887. Serial No. 257,317. (No model.)

To aller/71,0711, t may concern.-

Be it known that I, MILO Gr. KELLOGG, of'

Hyde Park, Illinois, have invented certain new and useful Improvements in Multiple Switch-Boards for Telephone-Exchanges, of which the following is a full,'clear, concise, and exact description,reference being had to the accompanying drawings, forming a part of this specification. p

It is well known that multiple switch-board systems and apparatus as at present constructed and arranged become very expensive per line or subscriber where a very large number of subscribers lines are operated in one multiple switch-board exchange. In these systems there is now provided one switchboard for about every one hundred and iifty subscribers lines. The number of boards required may be more or less, according to the rapidity of the system used, the expertness of the operators, and the average use which subscribers make of their telephone-lines. On each board, as the multiple systems are at present organized and worked, there is one spring-jack or similar switch foreach subscribers line whichbelongs to the exchange. It is therefore evident that, as the number of boards used in an exchange is increased as the number of subscribers lines is increased, the number of switches for each line is correspondingly increased, and consequently the cost of the switches for a line is correspondingly increased. The number of switches used in an exchange of tive thousand subscribers lines will be four times the number of switches used in an exchange of twentyfive hundred subscribers lines, and the lnumber used in an exchange of ten thousand lines will be four times as great as the number used in an exchange of live thousand lines and sixteen times as great `as the number used in an exchange of twenty-live hundred lines. lVhere more lines are used, the number of switches used per line will increase in like ratio. The number of lines which can be operated in one multiple switch-board exchange is, moreover, limited by the number of the spring- ,jack or similar switches which may be grouped on one board within convenient reach of an operator. -It may be stated, approximately, that as the systems are at present constructed the number of lines which can be operated in tatus is devised and employed which will provide quick and satisfactory service to all, and the charges can be made reasonable by keeping within reasonable limits the cost of the plant and the service.

In my improvement in multiple switchboards, which I shall now describe, I reduce byon e-half then n mber of spring-jack switches which are required at each board, and at the same time I practically retain all the advantages which have heretofore been obtained in he multiple switch-board systems employed.

I therefore reduce approximately `by onehalf the cost of spring-jack or switch appa- `ratus required for a given number of lines, and double the number of lines which can be successfully operated at one exchange.

In carrying out my invention I divide the subscribers lines which center at an exchange into two divisions or classes, which, for convenience, I designate Class A and Class B. The lines which belong to Class A, I will designate Line A, Line A2, the., or A, A2, rbc. The lines which belong to Class B, I will designate Line B, Line B2, duc., or B, 132, dac.' The switch-boards at the exchange I also divide into two divisions. Those boards which belong to one division I will designate as Section A, and thosewhich belong to the other division I will designate as Section B.

On each board of Section A, I place a springjack or similar switch for each line of Class A, and on each board of Section B, I place a similar switch for each line of Class B. These switches are intended to be used when the line to which the switch belongs is asked for at the board where the switch is located. The line asked for is to be connected to the line which asks for the connection by means of a switch-plug or other suitable switching device connected to the line which asks for the connection.

On one of the boards of each of the two sections I place for each line of the exchange a signal-receiving instrument, whereby the operator at the board may know that the subscriber which belongs to thelinehas signaled distributed among the several boards.

fer to have the subscribers signal apparatusY 35 her, and `switching apparatus whereby 4she may connect her'telephone with his linemay connect the line for conversation with any line belonging to her class by means of the switch of the line called for and the plug connected to the line which asks for the connection, and may signal to the line called for, receive clearing-out signals, &c. On each board I also provide test circuits and apparatuswherebythe operator may knowwhether any line Which belongs to the class to which ller board belongs is switched for conversation at any other board ct the exchange. Vhen the signal has come to her from aline, she does not need to test that line, as the fact that the subscriber has called shows her that the line is not in use at anotherboard. She needs testing apparatus only to test the lines which may beY called for at her board, and consequently only for the lines which belong to her class.

I would divide the lines into approximately two equal classes. It is evident that with the organization I have described approximately only one-half the switches and only one-half the testing apparatus will be required for each line which is required in the usual or-- ganization.

AThe signal receiving and switching apparatus heretofore mentioned as provided for each line on two boards of the exchange, one board of each section, may be conveniently I preand the signal-receiving apparatus4 of his line at the two boards so constructed and placed with reference to each other that the subscriber may signal to either board at will without attracting the attention of the operatorat the other board. t

My invention as a whole is applicable to the various systems of lines and of testing which may be employed in multiple switchboard systems. The systems of lines and testing which I have shown in the drawings, and which I will now describe in detail, are a system of single-circuit lines, normally grounded at the central office, and a system of testing which now seems to me, all things considered, the most applicable for such lines.

In the drawings, Figures 1, 12,and 1b represent `front views of sections of three multipleswitch-boards of an exchange, Figs. lnl and l?? representing boards belonging to Section A of the exchange and Fig. lb representing a board belonging to Section B of the eX- change. Fig. 2 shows a complete diagram of thel boards, with all the central-office apparatus, circuits, and connections necessary to illustrate my invention. Fig. 3 shows in detail the calling-annunciators used in the ccntral office. Fig. 4 shows in diagram the subscribers station apparatus. Fig. 5 shows a modification of the subscribers signaling apparatus. Fig. Gis an end View of the generator-shaft at the subscribers station, with two contact-spr1ngs, bear1ng one on each side .one above the other, as shown.

of the shaft, and of the insulated contactpiece of the shaft.

In the drawings like part-s and apparatus are indicated by the sameletters of reference. G in each case represents the ground-connection.

In Fig. 2, A is a sectional view of the switch-board shown in Fig. la', A2 is a sectional view of the switch-board shown in Fig. if, and -B is a sectional view of the switch-board shown in Fig. lb', each as indicated by the line CZ c.

c c c represent rubber strips on which the metal parts of the spring-jacks are mounted. These strips may be long enough to receive any convenient number of spring-jack parts.

Z Z are the rectilinear holes through the fronts and at the edges of the strips adapted to receive the switch-plugs. The contactsprings g g are mounted to the rear of and 'are parallel to the holes Z Z to which they belong, as shown. The contact-points ZL Zt, on which the contact-springs or spring-levers g g normallybear, pass through the rubber strips, as shown. The contact-points have each a connecting-piece h', and also a contact-piece or extension ZL, as shown, along to the front of the-point and along the lower face of the hole. Toward the front of the switch-holes and along their lower faces I place the contact-pieces t' t', as shown. These pieces come in proximity with but do not touch the contact-pieces Zt, and extend far enough to the front of their respective holes, so that testplugs may be applied to them. The switchplugs are substantially as shown and as will ICC the hole from the contact-point on which it normally bears, and the iiexible cord of thev plug is connected with the spring-lever, while the contact-point and the contact-piece are electrically connected through the medium of the piece m' of the switch-plug, which then touches both t' and h of the switch.

Each section of the rubber strip, with its spring lever, contactpoint, contact pieces, and t-he hole, all arranged and operating as above and as shown, may be called a springjack switch. The rubber stripsI are placed The lower edge of one strip therefore provides the upper edges of the holes in the strip which is below it. The holes may be of any convenient shapeadapted to the shape and arrangement of the parts used.

Spring-jack switches are provided and distributed among the differentl boards of the exchange, as heretofore indicated.

The calling-annunciators or signal-receiving instruments located at the central office,A

one for each line in each of the two sections` of the'exchange, are marked w in the drawings, and those which are shown are located IIO IZO

at the boards where the calls of the lines are to be answered. The annunciators are polarized annunciators, and their construction is shown in greater detail in Fig. 3. Each of these annunciators responds or indicates when one polarity of current passes over its line, and does not respond when the other polarity passes over the line. The two annunciators of any given line, one in each section of boards, are so constructed 'and con` nected into `the circuitof their line that one of them will respond to one polarity of current and the other will respond to the other polarity.

In order to carry out the operation of the exchange system, I provide for each line at each board whereits calls are to be answered a switch-plug with flexible cord adapted to be inserted into the spring-jack switches at the board where it is located. These plugs are marked D.

m m are the metal pieces of the plugs, adapted to come into contact with andmove the spring-levers g g of the switches into which they are inserted and connect them with the cords of the plugs. m m are contact-pieces of the plugs, adapted to be incontact with the pieces h andV c' of a switch when the plug is inserted and connect them together. Y

n n are the rubber insulations of the plugs. I also provide for each line at each board where its calls are tobe answered a switching device in which the plug of the line at that board is normally placed, and which completes the circuit ofthe line to the ground when the plug is in its vnormal position, and

. which disconnects the line from the ground when the plug is withdrawn and at the same time closes a test-connection which forms a part of the general test system of the line and of the exchange. One of these switching devices ofa line (that one which, when the line is connected through to ground, is nearest the ground-connection) may also have contact-points which will shunt'or switch the annunciator of the line in the other sect-ion from the circuit when the plug is Withdrawn from the device. The reason for this will appear hereinafter. o o', dro.,` represent these devices, o being the device which has the contact-points last mentioned. In these devices g g represent contact-springs, lwith which the metal pieces m of the plugs are normally in contact7 and 7L 7L represent contact-points on which the springs g g rest when theplugs are withdrawn.

In the devices, o g represent a second spring insulated from the other, and whichl comes in `contact with the insulated piece j when the plug is withdrawn from the device, but is otherwise disconnected from it.

Inrthe diagram of the subscribers station apparatus shown in Fig. 4, 1 is the telephoneswitch, 2 is the signal-receiving bell, 3 is the calling generator, 4 is the operators telephone, and 7c 1 are two calling-keys. The

generator is constructed with the usual automally open, as shown.

matic device, whereby it' is shunted or switched from the line-circuit while not operated. lThe insulated contact-pieceon the shaft of the armature,` to which is connected one end of the armature-wire, and which conducts theV generated current to line through the stationary spring contact (or contacts) provided for it is a half-circle, the remaining part of the circle being an insulation. I provide two stationary spring contact-pieces 5 5, as shown, each bearing on the diametricallyopposite part of the circle of the shaft of which said insulated contact-piece is a part. In'to the circuit with each of said springs is the calling-key 7o or la.

The circuits from the Atwo springs, after passing through their respective keys, unite, as shown. The circuit of the line while the generator is being operated of the armature'and a current of the other.

polarity is generated during the other half of the revolution of the armature. It is evident,

therefore, that the subscriber 1n ay at will send currents of either polarity to his line by depressing either one or l the other of his calling-keys when he operates his generator. Vhen his line is provided with two callingannunciators which respond to currents of opposite polarity and are located at two .dif-` ferent boards, as heretofore indicated, he can therefore at will call the operatoriat either board and not disturb the other operator.

A Various other arrangements may be employed whereby the subscriber may at will signal to either operator without disturbing the other. In Fig. 5 is shown an electric battery for signaling, with a pole changing switchwhereby the Asubscriber may send currents of either polarity to line,

It ispreferable touse a signal-receiving lbell at the subscribers station, which will respond to either polarity of current. `ing such a bell the 'subscribercan tellwwhethcr By havor not he has Sent a signalingcurrent over his line. Thiswill be a reminder should hc forget to press one of the keys while signaling. Y

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battery. The test-receiving instruments may be the ordinary hand-telephones.

In Fig. 2 t t represent the test-receiving instruments. T T represent the test-plugs, and B B represent the test-batteries.

In the drawings I have illustrated the central-office apparatus and circuits necessary to connect'the operators telephones and calling-generators into the Various line-circuits.

Well-known apparatus and methods of connection may be employed for this purpose.

I have represented the-main line and testconnections for one line only, and that for a line which belongs to what I have designated Class A. From this the connections of the other lines of the exchange, as also the con` nections to all the boards of the exchange which may be employed, will be apparent to those skilled in the art.

The line represented as connected is marked A. After entering the ofrice it passes t-hrough its several spring-jack switches on the several boards of section A, as shown. From thence it passes through its annunciator located at one of the boards of section A, and thence to its flexible cord and plug located at that board. When the plug is in its switching device 0, the circuit continues from the plug through the spring g of that device, and thence to its annunciator located on a board y in the other section, and through it to its flexible cord and plug located at that board. When the plug is in its switching device 0 located at that board, the circuit continues from the vplug through the spring of the device to the ground. All the contact-pieces t' t' ot the switches of the line are connected with each other and with the contact-pieces h h of the two switching devices 0 o of the line, as shown. The contact points or pieces g and f of the switching device o of the line are connected to the circuit of the line, one on one side ofthe line-annunciator located at the board which belongs to its class and the other on the other side of the annunciator, as shown.

The annunciators which are located in one section of the 4exchange may be all so constructed and connected as to be operated by the same polarity of current passing over their lines, and the annunciators in the other section to be operated by the other polarity.

The calling-keys at the subscribers stations may be marked with the designations of the sections whose annunciators will be operated when they are depressed and their generator is operated-as, for example, A and B.

In the catalogue or list of the exchange may be placed each subscribers name and opposite it the number of his line, with the letter orA designation which indicates to what class lhis line belongs-as, for example, John Adams, A15 W1n.Andrews,BG. The subscriber who wishes to talk with John Adams will, when in calling, press on his key marked A, and when the operator answers him at the E board located in section A, state that he Wishes A1. v'see if line Al is busy, and if it is not she completes the connection desired. If the sub- 3 scriber, by mistake, presses on his calling-key 3marked B, and asks for A1, the operator at Q section B receiving the call will at once notice the mistake and inform the subscriber of it, gwho will then send the proper signal.

The operator will then test-to It will be seen that when an operator at any board takes a switch-plug from its norlmal position and places it in the spring-jack switch of any line at her board, she has dis- Iconnected both lines from the office-ground l and has connected the two lines together for conversation. It will also be noticed that when she has so connected them the annunciator located at her board of the line in which the call originated is in the united circuit for clearing-out purposes, and that none test-pieces t' t' of its switches is connected with the local office-ground and with the testreceiving instruments connected therewith,

plug to a test-piece t of a line and it 'is switched, there is a complete local office-test circuit, as indicated and shown, and the testreceiving instrument will respond. If the line is not switched at any place when the test is made, the instrument will not respond.

When a plug is withdrawn from a switching device for switching, the test-wire is connected with the ground-connection by means of the spring-lever g of the switching device coming in contact with the point h. When a plug is inserted in the switch of a line, the test-wire of the line is connected with the ground-connection by means of the contactpiece m ot' the plug pressing on both contact-pieces t' and h of the switch, the latter piece being connected with the office-ground through the main-line connections. Sincethe f test-circuits for the subscribers lines are local to the exchange-office and are not through the circuits of the lines, as is usually the casein exchanges where the multiple system is required, considerably less testing-battery is required and the uniformity and certainty of the test is greater. The telephone-exchange lines of a given exchange may vary in length from several hundred feet to many miles. A battery which gives a clear and satisfactory testsignal over a short line may not be strong IOO IIO

- cure by Letters Patentenough to give a clear signal over the long line; and if it is strong enough to give a clear signal over the long line,'it may give too loud a signal over the short line. It is desirable to have the test-signals of the various lines of the exchange come as nearly uniform as possible, and all of them clear and distinct; otherwise the operator, in the rapidity of her work, may mistake the signals.

In the apparatus and system which I have described the test-circuits will not greatly Vary and they are not greatly subject to in- 'duction and other extraneous interferences 3' hence the test-signals will come clear, distinct, and uniform. l

In my applications Serial No. d38,728, filed May 19, 1887, and Serial No. 278,423, filed June 28, 1888, I have shown arrangements similar to part of the organization herein disclosed,

and I disclaim herein any subject-matter claimed in said prior applications.

I claim as my invention and desire to sel. In atelephone-exchan'ge system, the coinbination of telephone-lines divided in'to two classes, multiple switch-boards for said lines divided into two sections, the switches for said lines, one switch for each line ot one class on eachboard of one section and one switch for,

each line of the other class on each board of the other section, annunciators for said lines,

two for each line, one annunciator being located at a board of one section and the other annunciator being located at a board ot the other section, and switching apparatus at each of the boards, whereby the operator at the board may connect anyline which has its annunciator at her board with any line which has its switch at her board, substantially as set forth. g

2. In atelephonelexchange system, the combination of telephone-lines divided into two classes, switch-boards for said lines divided into two sections, the switches for saidlines, one switch for each line of one class on eachboard of one section and one switch for each line of the other class on each board ot the other section, signaling apparatus whereby any subscriber, may at will signal to either of the operators at two boards of the exchange, one'board of each section, and switching apparatus at each of the two boards, whereby the operator at the b oard may connect the line of the subscriber with any linefwhich has its switch at herboard, substantially as setforth. l 3. In a telephone-exchange system, the cornbination of telephone-lines divided into two classes, multiple switclrboards for said lines divided into two sections, signaling apparatus whereby a subscriber may at will signal to the operatorat either of two boards, one boardl ot" each section, and switching apparatus whereby the operator at one of said boards may connect the line of the subscriber with anyiline of one of the classes and the operator at the other of said boards may connect the line with any line of the other class, substantially as set forth.

i 4: Inatelephone-exchange system, the combination of two switch-boards, one board havin g switches for making connections with part of the lines of the exchange when wanted and with them only, and the other board having switches for making connections with other lines of the exchange when wanted and with them only, a telephone-line connected with the two boards, and switching apparatus at ea-ch board,whereby the operator at the board may connect said line with any line having a switch at her board, substantially as set forth.

5. In a telephone-exchange system, two switch-boards, a telephone-line connected with said boards, two polarized annunciators in the circuit of said line, one annunciator be- Ving located at each board, one annunciator indicating' when a current of one polarity passes through it and the other indicating when a current of the other polarity passes, a signaling-generator vat the subscribers station, switching apparatus whereby the subscriber may at will send a current ot either polarity to his line, and switching apparatus at, each board, whereby the operator at the board may connect said line with other lines of the exchange, substantially as set forth.

In a telephone-exchange system, the coinbination of telephone-lines divided into two classes, multiple switch-boards for said Alines divided into two sections, the switches for said lines, one switch foreach line of one class on each board of one section and one switch for each line of the other class Ion each board of the other section, two polarized annunciators in the circuit of each line, one annunciator being located at aboard of one section and the other located at a board of the other section, one annunciator indicating when a current of one polarity passes through it and the other indicating when a current of the other polarity passes, a signaling-gen-- erator ateach subscribers station, switching apparatus whereby the subscriber may at will send a current of either polarity to his line, and switching apparatus for each line at each board where one of its annunciators is located, whereby theoperato'r at the board may con nect the line with any line which has its said switches at her boards, substantially as set forth.

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7. In atelephone-exchange system, the com` `each board ot the other section to make con-A nections with the lines of the other class-when wanted, callaeceiving apparatus for each-line at twoboards ofthe eichange, one -boardof each section.' the' call-receiving apparatus of the lines being distributed among the several boards of the exchange, and switching apparatus at each board, whereby the operator at the board may connect any'line which has its call-receiving apparatus at her board with any line which has its connecting-switch at her board, substantially as set forth.

8. In a telephone-exchange system, the coinbination of two switch-boards, one board having switches for making connections to part of the lines of the exchange when wanted and with them only, and the otherboard having switches for making connections to other lines of the exchange when wanted and with them only, a telephone-line connected to the Itwo boards, an d signaling apparatus whereby the subscriber may at will signal to the operator at either board, substantially as set forth.

9. In atelephone-exchange system, the combination of two switch-boards, a telephone-line connected to the two boards, a polarized annunciator in the circuit of the line at each board, one annunciator responding to a current of one polarity and the other an nu nciator responding` to a current of the other polarity passing through the line, a signaling-generator at thesubscribers station, and switching apparatus for sending currents of either polarity through the line at the will of the subscriber, whereby the subscriber may at will signal either operator, substantially as set forth.

10. In a subseribers station apparatus, a magneto-bell generator, two contact-springs for said generator, said springs bearing on diametrically-opposite segments of the armature-shaft, an insulated contact-piece on said shaft, on which said springs alternately bear when `the generator is operated, and to which one end of the armature-wire is attached, two circuit-wires connected together at one end and connected at their other ends to the two contact-springs, respectively, and two normally-open keys, one in the circuit of each wire, in combination with a shunt-circuit which shunts the circuit in which is included the generator and keys, and a switching device with a pair of contact-points operated by the generator to open said shunt-circuit when the generator is operated and to close it when the generator is not operated, substantially as set forth.

Il. In a telephone-exchange system, the two classes of lines and the two sections of switch-boards, in combination with the two calling-annunciators in each line, onein each section of the boards, the two annunciators being operated by oppositepolarities of current, an electric calling-generator, and two keys at each subscribers station to be used in calling for the two classes of lines, said keys on being depressed sending opposite polarities of current to line and being so marked or designated that the subscriber may know which key is to be used in calling for either class of lines, substantially as set forth.

l2. In a telephone-exchange system, telephone-lines normallyv passing successively through their spring-jack switches on the boards of their section, (part of the lines having their switches in one section of the boards and the rest in the other section) and thence through switch-plugs with cords and switching devices on two boards of the exchange, one plug with its cord and switching device on a board in each sectionv and to ground, each plug being adapted to be withdrawn from its switching device and placed in any spring-jack switch atits board, substantially as set forth.

13. In a telephone-exchange system, telephone-lines normally passing successively through their spring-jack switches on the boards of their section, (part of the lines having their switches in one section of the boards and the rest in the other section,) and thence through calling annunciators and switch plugs with cords -and switching devices on two boards of the exchange, one annunciator and one plug with its cord and switching device on a board in each section and to ground, the switching device nearest tothe ground having a pair of contact-points in a circuit which shunts the annunciator at the other board, said points being normally open, but closed when the plug is Withdrawn from the device, each plug being adapted to be withdrawn from its device and placed on any spring-jack switch at its board, substantially as set forth.

14. In a telephone-exchange system, two

multiple switch-boards, a telephone-line nor-- Vmally grounded at the central office, springjack switches for said line, one on each board, each switch containing a pair of contact-points in the circuit of the line, one of said contact-points of each switch being connected to the line when switched, and which therefore may be designated as the line contact-point of the switch, and the other contact-point being connected to theA normal ground when switched, and which therefore may be designated as the ground contactpoint of the'switch, test contact-pieces, one for each switch, the two test, contact-pieces being connected together and normally insulated from the line and the other switch contact-points and switch-plugs, each with two insulated contact-pieces and a flexible conducting-cord, said cord being attached to one of said plug contact-pieces and said plugs being adapted to be inserted into said switches, and when a plug is inserted into aV switch to open the pair of contact-points of the switch to connect the cord with the line contact-point of the switch and to connect the ground contact-point of the switch with its test contact-piece through the contact-piece of the plug which is not connected with the flexible cord, in combination with a test-receiving instrument at each board, each instrument being grounded on one side and connected on its other side to a test-plug IIO IZO

adapted to be brought into contact with the test contact-piece at its board, and a battery in the test-circuit between said plug and said test contact-piece, substantially as set forth.

15. In a telephone exchange system, the switch-boards of the exchange divided into sections and the lines of the exchange dvided into classes, each line of one class being connected to each board of one section and to a board of the other section, and each line of the other class being conected to each board of said other section and to a board of said first-mentioned section, in combination with switching apparatus for said lines at the boards to which they are connected, whereby the operators of the exchange may connect any two of said lines together for conversation, substantially as set forth.

16. In a telephoneexchange system, the switch-boards of the exchange divided into two sections and the lines of the exchange divided into two classes, each line of one class being connected to each board of one section and to a board of the other section and each line of the other class being connected to each board of said other section and to a board of said first-mentioned section, and switching apparatus for said lines at the boards to which they are connected, whereby the operators of the exchange may connect any two of said lines together for conversation, in combination with electric apparatus whereby an operator at any board may determine whether any line which is connected to all the boards of the section to which her board belongs is switched for conversation at any board of the exchange, substantially as set forth.

17. In a telephone-exchange system, the switch-boards of the exchange divided into two sections and the lines of the exchange divided into two classes, each line of one class having a switch on each board of one section and each line of the otherclasshavinga switch on each board of the other section, each switch being adapted to receive a switch-plug connected with a iexible ccnductingcord and when the plug is inserted into the switch to connect the line to which the switch belongs with the conducting-cord to which the plug belongs, in combination with switch-plu gs,

' two for each line, each plug being connected with its line by its flexible conduct1ngcord,

of one line into a switch of another line con-V nect any two lines together for conversation, substantially as set forth. p

1S. In a telephone-exchange system, the switch-boards of the exchange divided into two sections and the lines of the exchange divided into two classes, each line of one class having a spring-jack switch on each board of one section and each line of the other class having a spring-jack switch on each board of the other section, each switch having two contact-points, which are normally in contact and adapted to receive a switch-plug connected with a exihle conducting-cord and when a plug is inserted into a switch to disconnect the contact-points of the switch, which are normally in contact and connect one of them with the fiexible conducting-cord to which the plug belongs, in combination with switchplugs with flexible conducting-cords, two for each line, the plugs of a line being located at boards in the two sections, and switching devices, one for each plug, and located at the board where the plug is located, each switch* ing device being adapted to receive its plug, and when the plug is inserted to connect its conducting-cord with a contact-piece of the switching device, each line normally passing successively through each pair. of contactpoints of its switches, in each case going first to that contact-point of the switch which is in connection with the flexible cord when a plug, is inserted, said' line also normally passing successively through its two flexible conducting-cords with plugs and said contact-pieces of vtheir switching devices (into which the plugs are normally placed) and thence to ground,whereby the operators of the exchange may, by the withdrawal of a plug of one line from its switching device and its insertion into a switch of another line, disconnect any two lines from the office-ground and connect them together for conversation, substantially as set forth.

MIL() G. KELLOGG.

Witnesses: CALVIN DE WOLF, MILTON HEAD.

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