US1315441A - Assicwob- to automatic electbic - Google Patents

Description

' A B. SMITH. I

AUTOMATIC TELEPHONE SYSTEM".

APPLICATION FILED MAY l0. ms.

1,315,441. PatentedSept. 9,1919. ya 7SHEETS-SHEETI.

A. B. SMITH.

AUTOMATIC TELEPHONE SYSTEM. APPLICATION FILED MAY 10. 1916.

1 ,3 1 5 414: 1 Patented Sept. 9, 1919.

A. B. SMITH AUTOMATIC TELEPHONE SYSTEM. APPLICATION 'HL ED MAY 10. 1915.

1 ,8 1 5,441 Patented Sept. 9, 1919.

' I 7 $HEET$$HEET 3- A. B. SMITH.

AUTOMATIC TELEPHONE SYSTEM. APPLICATION FILED MAY 10. 1916.

.1 3 1 5 44 1 PatentedS ept. 9, 1919.

7 SHEETS-SHEET A. B. SMITH. AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED MAY 10, I916.

Patented Sept. 9, 1919.

7 SHEET HEET Fi 5H.

A. B. SMITH. AUTOMATlC TELEPHONE SYSTEM.

APPLICATION FILED MAY 10. 1916. C 1 ,315,4%1 PatentedSept. J, 1919.

T SHEETSSHEET 6- A. B. SMITH.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED MAY 10. 1916.

1,315,441. Patented Sept. 9, 1919.

7 SHEETS-SHEET 7.

HZZUI may ARTHUR IBESSEY SMITH, 01F EVANSTON, ILLINOIS, ASSIGNOR T0 AUTOMATIC ELECTRIC COMPANY, A CORPORATION OF ILLINOIS.

Specification of Letters Patent;

Patented Sept. 9, 1919.

Application filed May 10, 1916. Seria1 No.'96,494.

To all whom it may concern Be it known that I, ARTHUR BnssnY SMITH, a citizen of the United States of America, and a resident of Evanston, county of Cook, and State of Illinois, have invented certain new and useful Improvements in Automatic Telephone Systems, of which the following is a specification.

While my invention relates ingeneral to automatic telephone systems, it is concerned chiefly with such systems as comprise a plurality of exchanges interconnected bytoll or long distance lines, and has particular reference to methods of automatic calling over toll lines upon which phantom circuits are superimposed. r

It is well known that in order to maintain quiet operation of a phantom circuit, all disturbancesor current changes in one physical lin which are not-compensated for by corresponding changes in the other physical linemust. be eliminated; or, in other words, the two physical circuits upon which the phantom is superimposed must be balanced in order to prevent current flow from one physical to the other via the phantom. Such conditions are difficult if not impossible of" attainment where the physical circuits are used separately as controlling circuitsfor automatic switches.

My pending application, Serial No; 86,596, discloses a. system of automatic calling'over phantome-d toll lines in which therequisite conditions for quiet operation are obtained, and in which automatic connections may be established over any two of the circuits in either direction. It is desirable, however, to be able to use all three of the circuits for automatic connections in either direction at the same time.

The principal object of the present in ventioh is to provide a new and efiicient method of automatic calling over toll lines having superimposed phantom circuits, whereby connections may be established antomatically over the physical circuits or over the phantom circuits without interference.

In carrying out my invention in connece tion with two toll lines having a superimposed phantom circuit, I employ preferably a so-called simplex operating circuit super-- imposed on the phantom circuit in well known manner; and, in addition, I employ alternating currents of different frequencies adapted to be separately or simultaneously included in the operating circuit, together with suitable alternating current relays each of which is soconstructed, or has its local circuit so arranged, that it will respond only to current of a. certain frequency.

Several son'icwhat dlfi'erent circuit ar raugements are available in accomplishing the foregoing general results, the two which I consider the most useful and practicable being illustrated and described hereinafter,

reference being had to the accompanying drawings.

For a clear'understanding of the drawings, Figures 1, 2 and 3 should be arranged in order with the lines at the sides thereof in alinement, Fig. 4 should be joined at its left hand end to the lower right hand corner of Fig. 3, and Fig. 5 should be placed as a continuation of Fig. 4. The apparatus shown in Figs. 1 and 2 is located in what I shall hereinafter designate as the. No. 1 exchange, while the apparatus shown in Figs. 3, 4, and 5 is located in what I shall hereinafter designate as the No. 2 exchange. Figs. 2 and 3 illustrate an alternative method of carrying out my invention which will be described later on.

When the drawings are properly laid out and joined together it will be seen that I have shown a toll line 10 1102 extending from'jack J 2 in the No.. 1 exchange to jack J in the No. 2 exchange; a second toll line extending from Jack J 4 in the No. 1 exchange to jack J 7 in the No, 2 exchange; and a phantom circuit superimposed in the reg ular manner upon the said toll lines and extending from jack J 3 in the No. 1 exchange to jack J 6 in the No. 2 exchange.

It will be shown hereinafterthat all three of the above lines are adapted for manual as well as automatic operation in both directions, as has been previously mentioned. In accomplishing the latter operation I employ, as before stated, a so-called simplex circuit superimposed on the phantom circuit in an obvious manner and evidently terminating turn terminate in three groups of apparatus indicated, respectively, by reference characters M M and M and which, in the case "of the No. 2 exchange, terminate in three similar groups of apparatus indicated, respectively, by reference characters M M, and'M The apparatus M ,.M etc, com-.

prises the means peculiar to my invention and will be fully described hereinafter.

To better facilitate the understanding of my invention I have elected to show a part of the apparatus in operated position where by a complete circuit connection has been established between a calling substation A (Fig. 1) and a called substation A (Fig. 5). The said connection has been established through the medium of multiple jack J, cord circuit P, jack J repeating coil R toll line 103104, repeating coil R, repeater E, selector switch F, and connector switch H.

The substation A (Fig. 1) may be of any suitable type or construction such, for example, as the type disclosed in British patent to T. G Martin, No. 1410 of 1010. As shown herein it comprises essentially the receiver 2, transmitter 3, switch book 4, ringer 5 and condenser (3. Being an automatic substation there is also provided a pair of impulse springs 7 and 8 controlled by the impulse wheel 0 through the medium of a finger hole dial (not shown).

The line conductors 12 and 13 of the substation A are connected at the No. 1 exchange to the individual line switch C which may be of the general type of line switch disclosed in British patent to R. \V. James, No. 20,301 of 1000; being, however, of the particular type shown in United States Letters Patent No. 1,078,090, granted Jan. 17, 1912, to Franl; Newforth. Since line switches of the above type are well known and form no part of my invention an extended description will not be given. It will suflice to say here that'through the medium of line switch C'the line of substation A is given access to a plurality of selector switches (not shown) which may be similar to the selector switch F to be mentioned hereinafter. trunk line which may be extended to one of these selector switches is indicated by reference characters 17, 18, and 19.

In additionto the line switch (1' there is also provided for the line of substation A a multiple ack J, which, as shown herein, is directly accessible to the toll operator. It is to be understood, however, that the toll operator may complete connection 10- cally by any other known method, the method shown having been chosen principally on account of its simplicity.

At P I have shown a toll operators cord circuit which may be of any suitable type or construction. As shown herein, it comprises among other details a bridged relay 36, which, in conjunction with sleeve relay 35, controls the supervisory lamp L; and the ringing up locking relay 37 which, in conjunction with sleeve relay 38, controls the supervisory lamp L. Keys K and K are ringing keys, while key K is a listening A three conductorkey, adapted, when operated, to bridge the operators head set across the two strands of the cord circuit.

The toll operator, besides having access to the local subscribers lines, has before her multiple jacks which are terminals of toll lines extending to other exchan es. The three jacks shown at the right of l ig. 1, that is, jacks J J, and J, are associated with toll lines extending to the No. 2 exchange, as has been previously stated. For each of these lines, including the phantom line, there is provided a group of apparatus, which in the case of the toll line 103-l(H is indicated as a whole by the reference character M". Considering the apparatus M more in detail, reference characters 02 and 50 indicate, respectively, a drop and cut-off relay. Reference characters and 52 indicate, respectivel y, an A. C. generator and a A. (J. relay. The A. C. relay 52, it will be observed, has its two windings connected in parallel with a condenser inseries with one of the windings in order to throw the currents in the two windings out of phase. Relay 51 is initially controlled by the key K and is adapted, when energized, to substitute the generator 80 for the relay 52 in the operating circuit associated with toll line 103104 which will be more fully described hereinafter. The key K also serves to insert the calling device S in this operating circuit, whereby impulses may be transmitted to the distant exchange. The calling device S may be of any suitable type, it being only required that the impulses produced in its operation shall cousist of interruptions of the circuit in which it is included. Such a calling device is shown in British patent to S. G. S. Dicker, No. 29,051 of 1910. The calling device S is not necessarily individual to the toll line 103104, but there may be one calling device for each operator. The reactance coil 57 and the condenser 50 constitute what I term a barrier and have a certain particular value of inductance and capacity depending on the frequency of current to which the associated A. C. relay 52 is adapted to respond as will be fully explained hereinafter.

A slight inspection of Figs. 2 and 3 will now show that the several groups of appara tus M M M, M, and M are each substantially like the group of apparatus .\l just described. Referring to the group of apparatus M (Fig. 3), a six conductor trunk line indicated by reference character 110 may be seen extending upward and to the right, where it terminates in the repeater E (Fig. 4). The trunk lines 105, 107, 100. 100. and 108, associated, respectively. with the groups of apparatus M M etc, are assumed to extend to similar repeaters, one

of these repeaters being in fact shown at E (Fig. 1).

While, as has been stated, the various sets of equipment ME M etc., are all substantially alike, this is strictly true only in so far as ei' uipmcnt at opposite ends of a particular line is concerned. For example, the apparatus shown at M may be exactly like that shown at M. The equipment M however, with the identical equipment M, and the equipment M with the identical equipment M", differ radically from equipment M in electrical characteristics, and these differences constitute the chief feature of my inveution. Briefly, the A. C. generators S0 and 180 deliver current of a frequency which is preferably somewhat higher than the highest commercial power frequency; A. C. generators 81 and 181 deliver current of a higher frequency than that delivered by generators 80 and 180; while generators 82 and 182 deliver current of a still higher frequency. I

sponding to any currents except those of the.

proper frequency can best be explained in connection with the detailed description of the operation.

Proceeding now with the description of the automatic apparatus, the repeater E may be of the general type of repeater disclosed in U. S. Letters Patent No. 1,136,912, granted April 20, 1915, to Talbot G. Martin, although the circuits are modified some-i what to enable the repeater to operate in conjunction with the equipment shown at M (Fig. 3). The operation and functions of the various relays of the repeater will be described fully in the detailed specification.

Directly connected with the repeater E is shown a. selector switch F, which may be of the general type of selector switch disclosed in U. S. Letters Patent No. 815,321, granted March 18, 1906, to Keith, Erickson, and Erickson; being, however, of the particular type disclosed in British patent to the Automatic Telephone Mfg. (10., No. 2,543 of 1914. Such a selector switch, as is well known, may be operated in response to the first digit of a called number to select one of a number of groups into which the lines of the No. 2 exchange are divided. For this purpose the selector F may be given access to a number of groups of trunk lines, the trunk lines of each group being extended to a group of connector switches. 7

One of these trunk lines is shown as extending to the connector H (Fig. 5), which may be of the general type of' connector switch disclosed in U. S. Letters Patent No.

815,176, granted March 13, 1906,..to Keith,

more nearly of the particular type disclosed in British patent to the Automatic Telephone Mfg. Co, No. 2,270 of 1914. The connector switch H has access to a single group of subscribers lines and may be operated in response to the last two digits in a called number to complete connection to a wanted line in the group.

One of the lines accessible to the connector H, comprising the conductors 12 and 13, is shown extending to the substation A, which may be similar to substation A (Fig. 1) already described. The line of substation A is provided at the No. 2 exchange with an individual line switch C which may be similar to the line switch C (Fig. 1). Conductors 1 1, 15, and 16 are assumed to extend to multiple jacks by which toll operators in the No. 2 exchange may be given access to the line of substation A.

While I have shown throughout the drawings a plurality of batteries, it is to be unvderstood that there are preferably but two of. these batteries, one for each exchange, and each having its positive pole grounded; Associated with the connector H I have shown a generator Gen for supplying ringingcurrent, an interrupter I for supplying intermittent ringing impulses, and a busy signaling machine Q.

Having given a general description of the apparatus, I will now proceed to a more detailed explanation of the operation of the same. Inasmuch as a great deal of the automatic equipment shown here is Well known and hasbeen described fully in the publications previously referred to, the operation of such apparatus will be described in a more or less general manner. I will first describe the operations which take place when establishing the complete connect-ion previously referred to between the substation A (Fig. 1) and the substation A (Fig. 5). The call is assumed to have originated with the subscriber at substation A and the connection is therefore handled by an op erator in the No. 1 exchange.

Referring now to Fig. l, the subscriber at substation A, in initiating a long distance call, must first get into communication with a so-called recording operator at the No. 1 exchange. Any approved method of accomplishing this object-will serve, but since the substation A is an automatic substation, it will be assumed that the operator has been called automatically as follows: Upon removing the receiver at substation A, the line switch C is operated to extend the line conductors 12 and 13 through to a selector switch, which may be the selector to which the trunk conductors 17, 18, and 19extend. After the line switch has operated, the calling subscriber may manipulate the finger hole dial of his instrument, thereby operating the selector switch to select a group of trunks extending to recording operat'ors positions; after which the selector operates antomatically to connect with an idle one of these trunks, all in a well known manner, as shown, for example, in the co-pending application of Talbot G. Martin, Serial No. 570,165, filed July 5, 1910. The calling subscriber upon hearing the operator respond, will give her the necessary information, such as thename and address of the person with whom conversation is desired, and also his own name and telephone number, and will then replace hisreceiver, thereby restoring his line switch and the selector switch to normal position. The recording operator in the meantime has written out the data received from the calling subscriber on a ticket, which is passed to a toll operator whose duty it is to complete the required connection.

In the case under consideration the wanted subscriber is located in the No. 2 exchange. The toll operator, therefore, having first tested the sleeve of jack J with the tip of her plug to determine its idle or busy condition and having found it idle, will insert, the calling plug of cord circuit P therein, thereby completing the following circuit; ground at G, winding of cut-off relay 50, conductor '71, contact springs 72 and 73 of repeater E, conductor 70, sleeve of jack J sleeve of plug, and winding of relay 38 to battery ll. Relay 38, upon energizing, extend ground to the armature of relay 37 and also disconnects the busy test conductor 21, from the upper strand of the cord circuit. The cut-oil relay 50. upon energizing, disconnects the drop '62 and the line conductors extending to repeater E from the tip and ring conductors of jack J in an obvious manner and in addition prepares a locking circuit for relay 51 which will be referred to later.

Since the connection is to be established automatically, the operator will now throw the calling device key K thereby inserting the calling device S in a circuit to be described presently, and at the same time completing a circuit for relay 51 as follows: ground at G contact springs 74 and 75, and winding of relay 51 to battery B. Relay 51, uponenergizing, completes a locking circuit for itself over the following path: ground at G contact springs 69 and 68, contact springs 63 and 64, and winding of relay 51 to battery B. As a further result of the energization of relay 51, contact spring 66 is separated from contact spring 67 and i shifted instead into engagement with contact spring 65, whereby is completed an operating circuit for the A. C. relay .152 at the distant exchange as follows: ground at G A. C. generator 80, non-inductive resistance 55, calling device S,contact springs 76 and 77 contact springs 65 and 66, reactance coil 57,

condenser 56, conductor 90, windings 113 and 1-1-1 of repeating coil R in parallel, winding 111, 112, 115, and 116 of repeating coils 1t and R in parallel, toll lines 101-102 and 103-401 in parallel, windings 1'17, 118, 121, and 122 of repeating coils R and R in parallel, windings 119 and 120 of repeating co l R in parallel, conductor 190, condenser 156, reactance coil 157, contact springs 196 and 167, and windings of A. C. relay 152 to ground at G. The reactance coils 57 and 157 and the condensers 5(3 and 156 are of such inductance and capacity, respectively, that the above circuit is resonant to the frequency of generator 80, whereby sufiicicnt current is permitted to flow to operate the A. t. relay 152. It will be observed that in addition to the path to ground by way of conductor 199, the e are four other possible paths to ground by way of which current from generator 80 might find its way back to ground at (1. These alternative or shunt paths may be easily traced by way of conductors 91 and 92 (Fig. 2) and 191 and 192 (Fig. 3). Each of these conductors is in series with a barrier comprising a reactauce coil and condenser similar to reactance coil 57 and condenser 56. The barriers in series with conductors 91 and 191 are tuned together with reference to the frequency of generator 81; while the barriers in series with conductors 82 and 182 are tuned together with reference to the frequency of generator 82. It will be clear from the foregoing that resonance will not, occur in any of the branch paths when in series with generator 80 and the barrier included in conductor 90, whence it follows that practically all the current flow is confined to the path traced via the A. C. relay 152. It follows, therefore, that while A. C. relay 152 is operated, the remaining A. C. relays 6., relays 53, 51, 153, and 154 receive Ver little current and do not respond.

lVhile the various barriers are themselves amply suflicient to direct the alternating current delivered 'by the several generators into the proper paths to operate the proper relays, it is possible to increase the sensibility of the relays somewhat by adjusting the local circuit of each relay with respect to the frequency on which the relay is intended to 0perate. For example, considering relay 152, the closed loop comprising the two windings and the condenser in series should be resonant to the frequency of generator 80.

To proceed with the operation, the A. C. relay 152, upon attracting its armature, completes a circuit including the line relays of repeater E (Fig. 4) over the following path: ground at G, winding of relay 211, conductor 179, contact springs 185 and 186, winding 123 of repeating coil R contact and armature of A. C. relay 152, winding 124 of repeating coil R contact springs 187,

188, and 189, conductor 178, and winding of 239. In this manner a guarding potential is,

relay 210 to battery B Upon energizing,

relay 210 closes a circuit for the slow. acting relay 213 as follows: ground at G flcontact V springs 217 and 218, and winding of relay 213 to battery 13*. Relay 213 attracts its armature, and by means of contact springs 232, 233, and 234 shifts the sleeve ofjack J from its normal connection by way'of conductors 170 and 171 to relay 150, to battery B by way of conductor 170 and resistance placed on the sleeve of jack J and, furthermore, should an operator disregard her busy test or plug into jack J accidentally I she will not release a connection already established automatically for the cut-ofl re-. lay 150 has had its circuit opened as explained. Relay 213 also prepares, by means of contact springs 237 and 238, an energizing circuit forrelay 214; and, by means of contact springs 235 and 236, a locking circuit for relay 212. i

Relay 211, upon energizing, closes a circuit for the line relay 250 of the selector F over the following path: ground at G",

lower winding of line relay 250, normally closed contacts of relay 253, conductor 243, contact springs 220 and 219, contact springs 230 and 231, winding of reactance coil 215, conductor 240,contact springs 226-and225,

conductor 242, normally closed. contacts of relay 253, and upper winding ofline relay 250 to battery 13. The line relay-250 energizes over the foregoing circuit and thereby closes an energizingcircuit from ground at G for the slow acting relay 251, which relay, upon energizing in turn, prepares circults 1n the well known manner for, the 7 vertical and rotary magnets 255 and 256.

The operator at the No. 1 exchange'may now proceed to dial the wanted numben.

Upon the operation of the calling device S in accordance with the first digit, the impulse springs of the calling device are separated momentarily a number of times interrupting each time the previously described circuit including the generator 80 and the A. C. relay 152. As a result of these 6' interruptions of its circuit, relay 152 de3 energizes a corresponding number of tlmes and at each deenergization breaks the circuit of relays 210 and 211 of the repeater E. Whence it will be seen that relays 210 and 211 will be decnergized a number of times corresponding to the first digit of the called numb At the first deiinergization of relay 210, a circuit is completed for the slow acting re lay 214 as follows: ground atv G contact springs 217 and 216, contact springs 238 and 237, and winding of relay 214 to battery B Relays 213 and 214 being slow acting, re-

tain their armatures 1n operated position durlng impulses, after which relay. 214 retracts its armature. Inits. energized; condition,

relay, 214 disconnects the conductors 243 from the conductors 240 and 241,. respectlvely, and from the normally bridged 24.2 and coil 215; substitutes for the lattera direct I path by way of contact springs 220 and 219 and contact springs 230 and 229; and com- .pletes an initial energizing circuit for relay 212 as follows': ground at G, winding of relayr212, and contactsprings 227 and 228 to'battery 13 Relay 212 looks itself in an obvious manner by closing contact springs 221 and 222; and also, by separating contact springs 223 and 224, opens the circuit by theline drop 162 (M Fig.3).

Relay 211, at each deenergization, breaks the circuit of the line relay 250 of the selector F; In response to these interruptions of its circuit, the line relay 250 is deenergized a corresponding number of times and sends at eachdeenergization' an impulse from ground at C to the slow acting relay 252 and the vertical magnet 255 in series. The vertical magnet, in response to these impulses, steps up the shaft until the wipers stand opposite the horizontal level which contains terminals oftrunk lines extending to the desired group. The relay 252, being slow acting, retains its armature during the series-of impulses and closes a circuit for the test rela 254, which latter relay, upon attracting 1ts armature, locks itself to ground at G" and also prepares a circuit for the: rotary magnet 256. At the end of the series of impulses the relay 252 deenergizes, thereby closing the aforementioned rotary magnet circuit, whereupon the wipers 260,

261 and 262 start rotating in search of an idle trunk line. As is well known, the ro tary magnet interrupts its own circuit and also'the locking circuit of the test relay254 at every energization, the contacts in the latter circuit, however, being short-circuitedthe test or private wiper 261 while passlng over busy or grounded test contacts. As soon, therefore, as the test wiper reaches an ungrounded test contact the armature of test relay 254 falls back and opens the rotary magnet circuit, thereby bringing the wipers to rest upon the contacts of an idle trunk line, assumed to be in this case thecontacts 263, 264, and 265. Upon deergizing, completes a holding circuit for the line switching relay 253 of the. selector F over the. 'l'ollowing path: ground at G, contact springs 320, bank contact 264, wiper 2131. contact springs of relay 251, and windingot" relay 253 to battery B The operator at the No. 1 exchange may now manipulate her calling device S in accordante with the. last two digits of the desired mnnber, resulting now in two series of ileiaiergizations of the .line relay 300 of the connector ll. Under the control of the line relay 300, the wipers 321, 322, and 323 are raised by the vertical magnet 307 and rotated by the rotary magnet 308 until they arrive at contacts which are terminals of the line of substation A. After each series of impulses the private magnet 311 is controlled through the medium of the slow acting relay 302 (in series with the operating magnets). whereby the side switch wipers 312. 313. 314, and 315 are advanced first to second position and finally to third position (it being assumed that the line of substation was idle when called).

As side switch wiper 315 comes into its third position, a circuit is completed from ground at (1 by way of wiper 322 and bank contacts 325 to the holding winding 330 of line switch t". Upon energizing, the holding winding operates the cut-off armature 331. whereby the line conductors of substation A are disconnected from their connections in line switch C. Ground from (l also extends to multiple contacts similar to contact 325 in the banks of other connectorsof the group, thereby making the line busy to other calls. By the advance of side switch wipers 312 and 313 to their third positions the connection is completed to the called line, relay 304 being denergized. By the advance of side switch wiper 314 to its third position a circuit is completed for the ringing relay 303, which is operated intermittently thereafter by the interrupter I to signal the. subscriber at substation A. \Vhen the called subscriber removes his receiver in response to the ringing of his bell a circuit is completed in the well known manner for the double wound back bridge relay 309 (ringing relay 303 being temporarily deenergized) which relay, upon energizing, reverses the incoming line conductors (of no particular consequence) and also completes a circuit for the ring cut oil relay 305. The ring cut-01f relay, upon attracting its armature, locks itself to ground at (F and at the same time opens the circuit of the ringing relay 303.

At the No. 1 exchange, when the operator has completed the dialing of the required number she may restore the calling device key K, thereby making the calling device S available for use in other connections. The connection with substation A may be completed at once or the operator may wait for the response of the called subscriber, the method adopted depending ordinarily upon whether it is only required to connect with a. certain substation in the No. 2 exchange or whether a certain particular person there is wanted. Assuming the latter to be the case, the operator first ascertains that the proper person is at the telephone in the distant exchange, then inserts the answering plug of the cord circuit P in jack J, and operates the ringing key K. By the insertion of the plug in jack J, a circuit is completed which may be traced from ground at G by Way of low resistance sleeve relay 35, sleeve of plug, sleeve of jack J, conductor 16, and cut-ofi' winding 48 of line switch C to battery B. The cut-ofl' armature 49 is thereby operated to disconnect the line conductors 12 and 13 from their connections in line switch C. A branch of the above circuit extends over conductor 20 to multiple contacts in the banks of connector switches having access to the line of substation A through the medium of normal conductors 21 and 22, thereby making the line of substation A busy to incoming automatic calls.

In response to the ringing of his bell the calling subscriber at substation A may now remove his receiver from the hook, when the required connection will have been completed. Current for the transmitter at the calling substation is supplied through the windings of the supervisory relay 36 of the cord circuit P, while current for the transmitter of the called substation is supplied through the windings of the double wound back bridge relay 309 of the connector H. The complete path for voice currents has been drawn in heavy lines and should be apparent without further explanation.

When the conversation is finished both subscribers will replace their receivers. Upon replacing the receiver at substation A the relay 36 is deenergized, thereby lighting the supervisory lamp L. By this means the operator is informed that the conversation is at an end, whereupon she may remove both plugs of cord circuit P from the jacks. The removal of the plug from jack J removes ground from conductor 16, wherebythe individual apparatus associated with substation A is restored to normal condition. The removal of the plug from jack J breaks the circuit of relay 50 Fig. 2). Relay 50, upon (leenergizing, breaks the locking circuit of relay 51, which relay, upon deenergizing in turn, disconnects the generator 80 from the circuit of the A. C. relay 152 (Fig.

3). The relay 152 thereupon retracts its armature and breaks the circuit of relays 210 and'211 of repeater E. By the (lechergization of relay 211 the circuitof the line relay 300 of the connector H is broken,

whereupon all the automatic switches are restored to normal position in the well known manner.

If the line of substation A had been busy when called, the connector H would have operated after the final series of impulses to connect a lead from the busy signaling machine Q with one side of the calling line, the side switch Wipers being held in the second position for this purpose and to prevent connection with the called line. Upon perceiving the busy signal, the operator at the distant exchange removes the plug from jack J 4 whereupon the apparatus is restored to normal as hereinafter described.

It is thought that the description which has been given will render the operation clear without further details. It should be mentioned. however, that the toll circuits shown in Figs. 2 and 3 are two way, i. 6., connections may be established in either direction. Since the equipment at one exchange is an exact duplicate of that at the other exchange, the manner of establishing a connection in the reverse direction will be l sufficiently obvious.

nections is absolutely prevented.

ation is well known. Assuming that the operator at the No. 1 exchange desires to establish a connection manually with the aid of the operator at the U0. 2 exchange, she will use the same cord circuit as before, but instead of throwing the calling device key K she will operate the ringing key K in her cord circuit. As a result, the drop 162 at the distant exchange is actuated, thereby signaling the operator at the No. 2 exchange, who will respond by inserting the plugof a cord circuit similar to cord circuit l in jack J The operators at the two exchanges now converse or establish a connection between local subscribers in their respective exchanges as desired. Interferenz e between manual and automatic con- \Vheneyer a plug is inserted in the jack of an idle toll line, the drop and the automatig v repeater associated therewith are discomnected. Conversely, whenever the repeater is operated from the distant end, a busy potential is placed on the sleeve of the jack and the cut-off relay is disabled, all as has been described. It is important to note in this connection that while the operator at the No. 2 exchange cannot interfere with automatic connections established byoperators in the No. 1 exchange to the extent of disconnecting such connections, she is enabled, nevertheless, to supervise such a onnection by simply disregarding the busy test and plugging into the jack. This feature is often a valuable one.

][ will now describe briefly an alternative method of carrying out m invention, or more accurately, a modification of the same. For this purpose Figs. 2 and 3 should be removed from the layout and Figs. 25 and 3 substituted therefor. The arrangement shown in Figs. 2 and 3 and already described may be termed a parallel arrangement, for the A. C. relays at each exchange are included in three parallel branches of the simplex operating circuit. The arrange ment shown in Figs. 2 and 3 diflers chiefly from the previous one in that itis a series arrangement, the A. C. relays at each ex change being all connected in series. A considerable portion of the apparatus shown in Figs. 2 and 3 is the same as the corre-' sponding parts in Figs. 2 and 3 and some of such apparatus has accordingly been in dicated by the same numerals.

As in the parallel arrangement the generators 80 and 180 deliver current of one frequency; generators 81' and 181 deliver current .of another frequency; while generators 82 and 182" deliver current of still another frequency. No barriers are used in connection with the A. C. relays but the. operation of these relays depends on local resonance. More specifically relay 152' (Fig. 3 is so designed that its local circuit including the two windings and the condenser in series will be resonant to the frequency of generator 80 (Fig. 2 The remaining A. C. relays are likewise so constructed that local resonance will occur with the proper frequency. A further requirement in the design of the A. C. relays is that they should have very low resistance in order that the local currents produced when resonance occurs will be much greater than the line currents.

The operation briefly is as follows: When the key K is operated a circuit including generator 80 is closed over the following path: upper terminal of generator 80, contact springs and 66, contact springs 77 and 76, calling device S, and primary winding of transformer T to the lower terminal of generator 80. An alternating current is now induced in. .the secondary winding of transformer T and takes the following path: ground at G, A. C. relay 52, secondary winding of transformer T, A. C. relay 53', secondary winding of transformer T, A. C. relay 5 secondary winding of T the simplex operating circuit to the No. 2 exchange, winding of transformer T, A. C. relay 1%, secondary winding of transformer TflA. C. relay 153, secondary winding oftransformer T and A. C. relay 152' to ground at G It will be noticed that the primary windings of the transformers T, T etc., are short circuited so that the secondary windings offer little impedance to current flow in the above circuit. 1

In. response to current flow in the above circuit, relays 52 and 152' attract their armatures. The operation of these relays is not directly due to the current in the line but is due principally to the local currents set up in the local circuits; for, it will be remembered, these relays are so constructed that resonance occurs with the frequency of current delivered by generator 80. The remaining A. C. relays, since their local circuits are out of tune with the frequency of current now on the line, are not operated, the retractile springs of their armatures being so adjusted that three or four times the line current produced by any one of the generators is required to overcome their tension.

It will be clear now that by operating the calling device S interruptions may be produced in the primary circuit of transformer T, whereby an interrupted alternating current is produced in the secondary winding and in the operating circuit including A. C. relay 152 at the distant exchange. The A. C. relay 152 is adapted to control the automatic switches shown in Figs. 4 and 5 through the medium of repeater E (Fig. 4:) whereby the required connection can be established substantially as previously de scribed. v

It will be seen from the foregoing that my invention provides a simple and efficient method by which a plurality of automatic switches may be controlled simultaneously over a single circuit through the medium of superimposed alternating currents of different frequencies, together with tuned alternating current relays responsive thereto.

While I have found it convenient, in explaining my invention, to show a certain specific embodiment thereof, I do not wish to limit myself to the precise forms shown, for modifications will no doubt be devised by persons skilled in the art. I desire, therefore, to include and have protected by Letters Patent all forms and modifications of my invention which may come within the scope of the appended claims.

What I claim as my invention is:

1. In combination, a circuit, a plurality of sources of current of different frequency, a plurality of relays in said circuit, a local circuit for each relay tuned for resonance to a particular frequency of current, and an automatic trunking switch associated with each relay, a series of line terminals for each switch arranged in a bank at each switch, lines terminating in said terminals, an impulse sending device associated with each source of alternating current and each provided with means for sending impulses from its associated source to operate the corresponding relay over said circuit to operate the correspondng trunking switch to establish a connection with any one of said lines in said series.

2. In combination,- a circuit, a plurality of sources of current of different frequency, a plurality of relays in said circuit, each relay having two windings connected in parallel to form a closed loop, a condenser in each loop whereby the several loops are each made electrically resonant to a different frequency of current, an automatic trunking switch associated with each relay, a series of line terminals for each switch arranged in a bank at each switch, lines terminating in said terminals, an impulse sending device associated with each source of alternating current and each provided with means for sending impulses from its associated source to operate the corresponding relay over said circuit to operate the corresponding trunking switch to establish a connection with any one of said lines in said series.

3. In combination, a plurality of circuits, a conductor common to said circuits, a source of current in each circuit, said sources delivering alternating currents of different frequency, a relay in each circuit, a capacity and an inductance in each circuit, whereby each circuit is tuned to the frequency of the current source included therein, and a local circuit for each relay including the windings of the relay and a condenser, each local circuit adjusted for resonance to the same frequency as its associated main circuit, an automatic trunking switch associated with each relay, a series of line terminals for each switch arranged in a bank at each switch, lines terminating in said terminals, an impulse sending device associated with each source of alternating current and each provided with means for sending impulses from its associated source to operate the corresponding relay over said circuit to operate the corresponding trunking switch to establish a connection with any one of said lines in said series.

4. In combination, a plurality of circuits, a conductor common to said circuits, a source of current in each circuit, said sources delivering alternating currents of different frequency, a relay in each circuit, a capacity and inductance in each circuit associated with the current source included therein, a capacity and inductance in each circuit associated with the relay included therein, whereby each circuit is tuned to the frequency of its associated current source, and a local circuit for each relay including the windings of the relay and a condenser, each local circuit adjusted for resonance to the same frequency as its associated main circuit, an automatic trunking switch associated with each relay, a series of line terminals for each switch arranged in a bank at each switch, lines terminating in said terminals, an impulse sending device associated with each source of alternating current and each provided with means for sending impulses from its associated source to operate the corresponding relay over said circuit to operate the corresponding trunking switch to establish a connection with any one of said lines in said series.

. 5. In combination, a plurality of circuits,

a conductor common to said circuits, a

windings of the relay and a condenser, each local circuit adjusted for resonance to the same frequency as its associated main circuit, an automatic trunkin switch associated with each relay, 2, series of line terminals for each switch arranged in a bank at each switch, lines terminating in said terminals, an impulse sending device associated with each source of alternating current and each provided with means for sending impulses from its associated source to operate the corresponding relay over said circuit to operate the corresponding trunking switch to establish a. connection with any one of said lines in said series.

6. In combination, a circuit, a plurality of sources of alternating current of different frequency, a plurality of parallel branches of said circu t, a relay 1n each branch, means for electrically tuning said branches whereby the relays included therein are each made responsive only to a particular frequency of current 'in said cir cuit, and a local circuit for each relay including the windings of the relay and a condenser, each local circuit adjusted for resonance to the same frequency as its associated main circuit, an automatic trunking switch associated with each relay, a series of line terminals for each switch arranged in' a bank at each switch, lines terminating in said terminals, an impulsesending device associated with each source of alternating current and each rovided with means for sending impulses rom its associated source to operate the corresponding relay over said circuit to operate the .cor-

responding trunking switch to establish a connection with any one of said lines in said series. I

7 In a telephone system, a 'lurality of automatic progressively movab e switches, controlling circuits for said switches having a common conductor, a source of current in eat-la circuit, saidsources delivering currents of different electrical character, and a controlling relay in eac circuit for the associated switch, said relays each responsive only to current from the particular source included in the same circuit.

8. In a telephone system, a plurality of automatic progressively movable switches, controlling circuits for said switches having a common conductor, a source of current in each circuit, said sources delivering alternating currents of difi'erent frequency, and a controlling relay in each circuit for the associated switch, said relays each responsive only to current of a particular frequency.

9; In a telephone system, a plurality of automatic progressively movable switches, controlling circuits for said switches having a common conductor, a source of current in each circuit, said sources delivering alternating currents of diderent frequency, a controlling relay in each circuit for the associated switch, and a capacity and an inductance in each circuit, whereby each circuit is tuned to the frequency of the current source included therein.

10. In a telephone system, a plurality of circuit for each relay including the windings of the relay and acondenser, each local circuit adjusted for resonance to the same frequency as its associated main circuit.

11. In a telephone system, a plurality of automatic progressively movable switches, controlling circuits for said switches having a common conductor, a source of cur rent in each circuit, said sources delivering alternating currents of different frequency, a controlling relay in each circuit for the associated switch, said relays each responsive only to current of a particular frequency, and a local circuit for each relay including the windings of the relay and a condenser, each local circuit adjusted for resonance to the same frequency as its associated main circuit.

12. In a telephone system, a plurality of automatic progressively movable switches,

13. In a telephone system, a plurality of automatic progressively movable switches, a common controlling circuit for said switches, a plurality of branches of said circuit corresponding in number to the number of said switches, a relay in each branch for ,controlling a particular switch, a plurality of sources of alternating current of different frequency, means for separately including said sources in said circuit, and means for directing the current from each source through a particular branch, whereby said switches may be operated independently through the medium of their controlling relays.

14. In a telephone system, a plurality of automatic progressively movable switches, a common controlling circuit for said switches, a plurality of branches of said circuit corresponding in number to the number of said switches, a relay in each branch for controlling a particular switch, a source of alternating current corresponding to each relay, said sources delivering currents of different frequency, an inductance and a capacity in each branch, whereby each branch is tuned to the frequency of the corresponding source, and means for including said sources separately or simultaneously in said circuit to operate the corresponding relays.

15. In an automatic telephone system, a first exchange, a second exchange, a pair of lines connecting said exchanges, a phantom line superimposed on said first lines, an automatic switch at the second exchange for each of said lines, a common controlling circuit for said switches superimposed on said phantom line, means at the first exchange for transmitting alternating cur rents of different frequencies over said controlling circuit, and controlling relays for said switches in said circuit at the second exchange, each of said relays responsive only to current of a particular frequency.

16. In an automatic telephone system, a first exchange, a second exchange, a pair of lines connecting said exchanges, a phantom line superimposed on said first lines, an automatic switch at the second exchange for each of said lines, a common controlling circuit for said switches superimposed on .said phantom line, means at the first exchange for transmitting alternating currents of different frequencies over said con trolling circuit, a plurality of branches of said cont-rolling circuit at the second exchange, each branch containing a relay for controlling a particular one of said switches, and means in each branch whereby said relays are each made responsive only to current of a particular frequency.

17. In an automatic telephone system, a first exchange, a second exchange, a pair of lines connecting said exchanges, a phantom line superimposed on said first lines, an automatic switch at the second exchange for each of said lines, a common controlling circuit for said switches superimposed on said phantom line, means at the first exchange for transmitting alternating currents of different frequencies over said controlling circuit, controlling relays for said switches in said circuit at the second exchange, each of said relays responsive only to current of a particular frequency, and means at said first exchange for intermittently interrupting the transmission of any of said currents, whereby said switches may be operated through the medium of their controlling relays.

18. In an automatic telephone system, a first exchange, a second exchange, a pair of lines connecting said exchanges, a phantom line superimposed on said first. lines, an automatic switch at the second exchange for each of said lines, a common controlling circuit for said switches superimposed on said phantom line, means at the first exchange for transmitting alternating cur rents of difl'erent frequencies over said con trolling circuit, a plurality of branches of said controlling circuit at the second exchange, each branch containing a relay for controlling a particular one of said switches, means in each branch whereby said. relays are each made responsive only to current of a particular frequency, and means at said first exchange for intermittently interrupt.- ing the transmission of any of said currents, whereby said switches may be operated through the medium of their controlling relays.

19. In an automatic telephone system, a first exchange and a second exchange, a pair of lines connecting said exchanges, a phantom line superimposed on said lines, a manual jack for each line in each exchange, an

automatic switch for each line at the second exchange, a controlling circuit for said switches superin'iposed on said phantom line, sources of alternating current of different frequency at the first exchange, controlling relays for said switches in said circuit at the second exchange, each of said relays responsive only to current of a particular frequency, means for including said sources separately or simultaneously in said circuit, and means for intermittently interrupting the flow of current from any source so included whereby to operate the corresponding switch at the second exchange.

20. In an automatic telephone system, a first exchange and a second exchange, a pair of lines connecting said exchanges, a phantom line superimposed on said lines, a manual jack for each line in each exchange, an automatic switch for each line at the second exchange, a controlling circuit for said switches superimposed on said phantom line, sources of alternating current of different frequency at the first exchange, controlling relays for said switches in said circuit at the second exchange, each of said relays responsive only to current of a particular frequency, means for including said sources separately or simultaneously in said circuit, means for intermittently inter 'upting the flow of current from any source so included whereby to operate the corresponding switch at the second exchange, and a cut-off relay for each line in the second exchange, each relay operated when manual connection is made with its associated line to disconnect the associated switch.

21. In an automatic telephone system, a first exchange and a second exchange, a pair of lines connecting said exchanges, a phantom line superimposed on said lines, a manual jack for each line in each exchange, an automatic switch for each line at the second exchange, a controlling circuit for said switches superimposed on said phantom line, sources of alternating current of different frequency at the first exchange, controlling relays for said switches in said circuit at the second exchange, each. of said relays responsive only to current of a particular frequency, means for including said sources separately or simultaneously in said circuit, means for intermittently interrupting the flow of current from any source so included whereby to operate the corresponding switch at the second exchange, and means associated with each switch for placing a busy potential upon the sleeve of the jack associated with the same line at the same exchange when such switch is operated.

22. In an automatic telephone system, a pair of lines connecting two exchanges, a phantom line superimposed thereon, a manual jack for each line at each exchange, an automatic switch for each line at each exchange, a controlling circuit for said switches superimposed on said phantom line, a source of current for each line at the first exchange, said sources delivering alternating currents of different frequency, similar sources for said lines. at the other exchange, a controlling relay in said circuit for each of said switches at the first exchange, said relays each responsive only to current of a particular frequency, similar controlling relays for the switches at the other exchange, means at each exchange for including the current sources thereat separately or simultaneously in said circuit, and means for intermittently interrupting the flow of current from any source so included whereby to operate the corresponding switch at the other exchange.

23. In an automatic telephone system, a pair of lines connecting two exchanges, a phantom line superimposed thereon, a manual jack for each line at each exchange, an automatic switch for each line at each exchange, a controlling circuit for said switches superimposed on said phantom line, a source of current for each line at the first exchange,

said sources delivering alternating currents of different frequency, similar sources for said lines at the other exchange, a controlling relay in said circuit for each of said switches at the first exchange, said relays each responsive only to current of a particular frequency, similar controlling relays for the switches at the other exchange, means at each exchange for including the current sources thereat separately or simultaneously in said circuit, means for intermittently interrupting the flow of current from any source so included whereby to operate the corresponding switch at the other exchange, and means associated with each switch for placing a busy potential upon the sleeve of the ack assoclated with the same line at the same exchan e when such switch is operated.

24:. In com ination, a plurality of sources of current of different frequency, a plurality of relays each having two windings, a main circuit including all of said relays in series and the two windings of each relay in parallel, means for including said sources separately in said circuit, none of said relays being directly responsive to the resulting current flow in the main circuit, and a closed local circuit for each relay including its two windings and a condenser of such capacity that the associated local circuit is made resonant to the frequency of a particular one of said current sources, whereby when any particular current source is included in the main circuit, local currents of greater value than the current in the main line will be caused to flow in the corresponding local circuit in order to operate the associated relay.

25. In a telephone system, a plurality'of automatic trunking switches, a series of line terminals for each switch arranged in a bank at each switch,lines terminating in said terminals, in combination with a plurality of sources of alternating current of different frequencies and a plurality of relays, a line common to said sources and relays, an impulse sender for each source of alternating current for sending impulses from its associated source over said common line to operate the corresponding relay, said relays being tuned each to respond to only one of the frequencies of said sources and each to a different one, and each relay having control of a different one of said automatic trunking switches whereby said switches may be operated by said calling devices one at a time or more than one at the same time without the impulses from one calling device and source interfering with the impulses from another calling device and source.

26. In a telephone system, a plurality of automatic trunking switches, a series of line terminals for each switch arranged in a bank at each switch. lines terminating in said terminals. in combination with a plurality of sources of alternating current of different frequencies and a plurality of relays, a line common to said sources and relays, an impulse. sender for each source of alternating current for sending impulses from its associated source over said common line to operate the corresponding relay, said relays being tuned each to respond to only one of thefrequencies of said sources and each to a different one, and each relay having control of a different one of said automatic trunking switches whereby said switches may be operated by said calling devices one at a time or more than one at the same time without the impulses from one calling device and source interfering with the impulses from another calling device and source, each relay having two windings connected in multiple, the two multipled windings of each relay connected in series with a portion of said common line, sald multipled windings of each relay forming a local closed series circuit.

27. In a telephone system, a plurality of automatic trunking switches, a series of line terminals for each switch arranged in a bank at each switch, lines terminating in said terminals, in combination with a plurality of sources of alternating current of different frequencies and a plurality of relays, a line common to said sources and relays, an impulse sender for each source of alternating current for sending "limpul'ses from its associated source over said common line to operate the corresponding relay, said relays being tuned each to respond to only one of the frequencies of said sources and each to a different one, and each relay having control of a different one of said automatic trunking switches whereby said switches may be operated by said calling devices one at. a time or more than one at the same time without the impulses from one calling device and source interfering with the impulses from another calling device and source, each relay having two windings connected in multiple, the two multipled windings of each relay connected in series with a portion of said common line, said multipled windings of each relay forming a local closed series circuit, and a condenser in said local closed circuit.

28. In a telephone system, a circuit, a source of alternating current and a reactance connected in series in said circuit, a relay, said relay having two windings connected in multiple with each other and the two multipled windings connected in series in said circuit with said current source and said reactance, said relay multipled windings forming a local closed series circuit tuned to the frequency of current from said source,

another circuit controlled by said relay, an impulse calling device for sending impulses over said first circuit from said source of current for controlling said relay, an automatic trunking switch, a series of lines terminating in a bank at said switch, said switch controlled by said relay over said circuit to extend a connection to any one. of said lines.

29. In a telephone system, a circuit, a source of alternating current and a reactauce connected in series in said circuit, a relay, said relay having two windings connected in multiple with each other and the two multipled windings connected in series in said circuit with said current source and said reactance, said relay multipled windings forming a local closed series circuit having a'condenser included therein tuned to the frequency of current from said source, another circuit controlled by said relay, an impulse calling device for sending impulses over said first circuit from said source of current for controlling said relay, an automatic trunking switch, a series of lines terminating in a bank at said switch, said switch controlled by said relay over said circuit to extend a connection to any one of said lines.

30. In a telephone system, a circuit, a source of alternating current, a relay, said relay having two windings connected in multiple with each other, thetwo multipled windings connected in series in said circuit, said relay multipled windings forming a local closed series circuit tuned to the frequency of current from said source, another circuit controlled by said relay, an impulse sending device for sending impulses over said first circuit from said source of alternating current for controlling said relay, an automatic trunking switch, a series of lines terminating in a bank at said switch, said switch controlled by said relay over said circuit to extend a connection to any one of said lines.

31. In a telephone system, a circuit, a plurality of sources of alternating current associated therewith, each source producing a current of different frequency, a plurality of relays associated with said circuit, each 1!- la v having two windings connected in multiple, and the two multipled windings of each relay connected in series with a portion of said circuit, said multipled windings of each relay forming a closed series circuit. each of which is tuned to a particular one of the frequencies produced by said sources, each of said relays controlling another circuit, an impulse sending device associated with each one of said sources of alternating current whereby impulses from any or all of said sources may be transmitted over said first circuit to said relays for controlling said relays, an automatic trunking switch in each one of the circuits controlled by each one of said relays, a difierent series of lines terminating in a bank at each one of said switches, each of said switches controlled :by its assoclated relay over the relay controlled by said circuit to extend a connection to any one of said lines.

32. In a telephone system, a second exchange, a pair of lines connecting said exchanges, a phantom line superimposed on said first lines, an automatic switch at the second exchange for each of said lines, a common controlling circuit for said switches superimposed on said phantom line, means at the first exchange for transmitting currents of different characters over said controlling circuit simultaneously, and means responsive to said currents at the second exchange for operating said switch at the same instant independently of each other.

33. In a telephone system, a first exchange, a second exchange, a plair of lines connecting said exchanges, a p antom line superimposed on said first lines, an automatic switch at the second exchange for each of said lines, a common controlling circuit for said switches superimposed on said phantom line, operator controlled means at the first exchange for intermittently transmitting currents of different characters over said controlling circuit simultaneously, and a plurality of relays at the second exchange responsive to a first exchange,

said currents one for each particular char- I actor of current, whereby the said switches are operated at the same instant independently of each other.

34. In a telephone system, a first exchange, a second exchange, a plair of lines connecting said exchanges, a p antom line superimposed on said first lines, an automatic switch at each exchange for each of said lines, a common controlling circuit for said switches superimposed on said phantom line, means at each exchange for transmitting a plurality of currents of different characters over said controlling circuit simultaneously, and means responsive at the second exchange to said current of one character and at the first exchange to said currents of a different character, for operating one of the said switches associated with each of said lines at the same instant independently of each other.

35. In combination with a talking circuit established between telephones, Whlch talking circuit has two parallel talking paths, a second circuit, one side of said second circuit having three sections in series, one of said sections having in multiple the parallel sides of said talking circuit, another one of said sections having an alternating current generator, and the third of said sections having an alternating current relay, said relay controlling the continuity of said talking circuit, said relay maintained energized by current from said alternating current generator while the conversation is going on between said two telephones for malntaining the continuity of the talking circuit.

Signed by me at Chicago, Cook county, State of Illinois, this 19th day of April,

ARTHUR BESSEY SMITH.

Images