US1909350A - Telegraph system - Google Patents

Description

y 1933.. H. H. HARRISON 1,909,350

TELEGRAPH SYSTEM Filed July 20, 1931 6 Sheets-Sheet l May 16, 1933. H. H. HARRISON TELEGRAPH SYSTEM Filed July 20, 1951 e Sheets-Sheet 2 May 16, 1933. H. H. HARRISON TELEGRAPH SYSTEM Filed July 20, 1931 6 Sheets-Sheet 3 RCI 1m Harfi P11151125 Harris an May 16, 1933. H. H. HARRISON 1,909,350

TELEGRAPH SYSTEM Filed July 20, 1931 6 =Sheets-Sheet 4 7 m PM *d)' RR I 9-H g 7 cor? Hazy Hij hes Harrison May 16, 1933. H. H. HARRISON TELEGRAPH SYSTEM Filed July 20, 1931 6 Sheets-Sheet 5 I'm H f-k hes Harmsun y 1933. H. H. HARRISON 1,909,350-

TELEGRAPH SYSTEM Filed July 20, 1931 6 Sheets-Sheet 6 Imp- I-fmi-j PEI-12s Harrisun Patented May 16, 1933 HARRY HUG-HES HARRISON, OF

TELEPHONE AND TELEGRAPH OF DELAWARE Application filed. July 20, 1931.

This invention relates to telegraph systems and is more particularly concerned with 1ntercommunication systems for print ng telegraphs of the start-stop type in which connections are set up by means of automatic switching of the telephone type using a'standard calling dial.

It contemplates small teletype exchange systems in which each line terminates 1n an individual switch.

It contemplates also the provision of switching apparatus, access to whlch is ob tained by a calling line through hunting preselectors, so that the switching units are less in number than the number of 1.111%. It provides the equivalent of dial tone signals at each switching stage and when one statlon is switched through to another a clear pa1r of lines, is furnished for two-way signalling.

It provides also for the practlcal case where a number of telegraph offices are connected by a line or lines to two central ofiices A and B which are in turn connected together by a 11mited number of trunk lines. As the trunk lines may at times be fully occupied, a station local to A or B may be given a busy's1gnalor, and this is preferred, the trunk lines may terminate in finder switches adapted to search for storage devices containing one or more messages, the storage device being provlded between he originating stationand the station where the traflic concentrates onto a limited number of trunks. I I

The invention will be better understood from the following description of certain methods of carrying it into effect which should be taken in conjunction with the accompanying drawings comprising Figs. 1-6.

Figs. 1 and 2 show one of the simplest arrangements in which the calling station is provided with a dial switch of the type used in automatic telephony by means of which it is enabled to operate a single level rotary switch shown in Fig. 2 to establish connection with a suitable set of receiving apparatus. Fig. 3 shows diagrammatically slight modifications to the arrangement of Figs. 1 and 2 whereby the caller is given a positive busy signal in case the receiving apparatus with which he has connected himself happens'to be LIVERPOOL, ENGLAND, ASSIGNOR TO ASSOCIATED COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION TELEGRAPH SYSTEM Serial No. 551,850, and. in Great Britain July 25, 19 30.

in use at that time. Figsf and 5 show amodified arrangement suitable'for a somewhat larger system in which a stage of preselection used, that is to say a switch such as that shown in Fig. 2 employed which is however arranged to hunt freely to find. an idle outlet and this is followed by a selecting switch of. the two-directional type arranged to respondto two digits. Switches of this type are well-known in automatic telephone practice and as ordinarily constructed provide for 100 outlets arranged in ten rows or levels of ten each. Fig. 6 shows a group selector suitable for inclusion in a still larger system. This switch is mechanically of the same construction as the switch shown in Fig. 5, but its functions and hence its circuits are different in that it is arranged to respond to oneseries of impulses onlyand thereafter to perform an automatic hunting operation to select afreeoutlet in the group chosen in response to the first digit. Such a switch it will be understood would be inserted between the, rotary switch of Fig. land the two directional switch of Fig. 5, or it might even be arranged to replace the rotaryswitch.

Considering first the operation of the switches shown in Figs. 1 and 2, it should be explained that the leads from banks 1 and 2 of the switch RLS, Fig. 2, are assumed to extend to a station which is in all respects identical with that shown in Fig. 1, and consequently no separate showing of this receiving station has been given. Sufficient apparatus for the purpose of the invention is shown of a -printing telegraph organization in which a single magnet SM controlled by a polarized line relay PR allows a yieldingly driven shaft to make one revolution during which the successive conditions, operated or non-operated, of the magnet determine the settingv of selective members in a printing telegraph receiver. The transmitting mechanism isv also provided with a yieldingly driven shaft and variably controls a single transmitting lever in accordance with the arrangement of combination bars set by a character lrey lever. Such mechanisms are well-known and will not be further described except in so far as is necessary for a clear description of the scope of the invention.

When the station shown in Fig. 1 desires communication with another station in the system, the key NLK which is of the nonlocking type is thrown whereupon a circuit 1s closed for relays SR and R1 by way of springs 3 of the key NLK and the impulse springs CD of the dial. Relay R1 operates and reverses the connections of the battery B to the line but this has no immediate effeet. Relay SR also operates and prepares a circuit for relay R2 which is completed at the off-normal springs DON S of the dial as soon as the finger plate is moved to transmit the required number. Relay R2 thereupon switches out the receiving apparatus and connects the battery B through to the lines L1 and L2 and the current flow therein is now in such a direction as to operate the neutral polarized relay NPR, Fig. 2, so that its tongue moves to the right. A circuit is thereupon completed for the guard relay GR which at springs 1 locks itself up dependent upon the release relay RR, at springs 2 connects positive to the guard wire so as to guard the calling station against any attempt to connect with it at this time and at springs 3 completes a circuit for relay R which energizes though without useful effect at the moment.

The calling station will now dial the number of the required station and each time the impulse springs CD open, relay R1 will deenergize and reverse the connection of battery B to the lines L1 and L2 so as to produce operation of the relay NPR, Fig. 2, in the opposite sense. Each time this occurs a circuit is completed for the driving magnet DM of the switch RLS in series with the low resistance relay SR which is provided with a copper slug on its core so as to enable it to hold up throughout the train of impulses. By the operation of magnet DM the wipers 15 of the switch RLS are advanced a number of steps corresponding to the digit sent, and when relay SR releases at the end of the train of impulses the test relay TR is connected to test wiper 4 and a circuit is completed from positive, both windings of relay TR in series springs l of relay SR, wiper 4 and the contact on which it is resting to negative by way of a resistance. If the line is free, relay TR now operates and at springs 4 short-circuits its high resistance lower winding so as to prevent the seized line being taken by any other switch. It will be understood that if the line had already been in use, positive from the comparatively low resistance upper winding of another relay TR would have been connected to the bank contact and accordingly relay TR of Fig. 2 would have been unable to operate. Relay TR also at springs 1 and 2 disconnects the polarized relay NPR and connects the lines board which through to springs 1 and 2 of relay R, at springs 5 connects positive to wiper 5 to operate the relay corresponding to COR associated with the receiving station and at springs 3 opens the circuit of relay R. Relay R is slow to release and while it holds up battery is reversed back over the lines L1 and L2, and since relay R2 will de-energize with the return of the dial .to normal, this battery connection is extended to the polarized relay PR of the receiver by way of the normal contact of the automatic send-receive switch SRS of the start-stop keyboard transmitter. Relay PR operates and closes the circuit of the magnet SM of the receiving portion of the printing telegraph receiver whereupon the motor-driven shaft will make one or more revolutions and owing to the action of the cam RC1, the trembler bell BL is caused to ring. This signal is an indication to the calling station that he has successfully established connection with the desired receiving station and he may then call up this station by depressing a key lever on his keywill cause the lever TL to send out a start pulse and this by operating the receiving relay at the distant station will energize the start magnet initially and thus cause the bell to operate. It will be noted that during the sending operation a clean pair of wires exists between the two stations except for a high resistance bridge comprising the resistance HR at the switching station.

When the calling station has cleared his traflic and assuming that the called station has no trafiic for him he presses the release key RK. The effect of this is to connect positive to the two lines L1 and L2 in parallel and a circuit is thus completed for the release relay RR which is connected to the midpoint of the high resistance bridge. Rela RR operates and locks itself up over its lower winding to the off-normal bank and wiper 3, and at springs 2 closes a self-interrupted circuit for the driving magnet DM whereupon the switch wipers are advanced to normal in which position this circuit is opened by the de-energization of relay RR. At springs 2 also the locking circuit of the guard relay GR is opened and the energizing circuit of relay TR is opened by the operation of relay SR in series with the magnet DM. Consequently all the apparatus is now restored to normal and the receiving station may be called by some other station as may also the calling station.

In the arrangement of Figs. 1 and 2 no definite provision is made for giving the calling station a busy signal, it being assumed that the absence of the bell signal indicating the successful establishment of the connection may be taken as a sufiicient indication of the fact that the wanted station is busy. comparatively slight modifications, however,

are necessary as shown in Fig. 3 to enable a positive busy signal to be given. In this case the polarized relay NPR at the station of Fig. 1 is of the three-position type having a neutral position to which the tongue returns when no current is flowing. The contact which is made when current flows in the opposite direction from that necessary to energize the start magnet is connected to a buzzer BZ which provides the busy signal. At the switching station an additional relay BB is provided which is arranged to be slightly slow to energize and this. relay on operation is arranged to apply battery to the lines L1 and L2 so as to cause current to flow in the opposite direction to that produced by the operation of relay R.

During the train of impulses relay SR. is energized as previously described and when the switch comes to rest, the usual circuit is completed for relay TR and also a circuit is completed for relay SR over wiper 6 and the off-normal bank. If the line is free, relay TR will energize before relay BR and will open the circuit of the latterrelay at springs 6. If the line is already in use however, relay TR will be unable to energize and after a slight pauserelay BR will energize and transmit a current over the line to operate the tongue of relay NPR to the left and thus sound the buzzer BZ. This signal will persist until the calling station operates his release key whereupon the connection will be cleared down as previously described.

To form a teletype exchange oi large capacity a preselecting stage and a double motion switch are employed, and one suitable arrangement is illustrated in Figs. 4: and 5. It is assumed that the switches there shown are arranged to work with a calling station such as that shown in Fig. 1, but that the switch in Fig. a hunts before any impulses are received and the switch Fig. 5 is subsequently set in response to two trains of impulses. Upon the original seizure of the hunting switch, the polarized relay NPR operates its tongue to the left, thereby completing a circuit for the guard relay GR which at springs 1 prepares a locking circuit for relay R, at springs 2 completes a locking circuit for itself, at springs 3 applies positive through a resistance to the guard wire to protect the line against intrusion and at springs l completes a circuit for the driving magnet DM in series with its interrupter contact. The magnet thereupon advances the wipers one step and the driving circuit is then made by way of springs 5 of relay TR and the homing plate associated with wiper 7. A circuit is now completed also for relay R which looks up, prepares a circuit for relay BR and opens a point in the initial circuit for the driving magnet. The switch continues to step until test relay TR which is connected to test wiper 4: encounters a contact whichis not busy as indicated by the connection of low resistance negative there.- to. Relay TR then operates, connects the lines through at springs 1 and 2, short-cin cuits its lower winding at springs 3 so as to mark the seized line engaged, at springs 4 opens the circuit of relay R. and at springs 5 opens the circuit of the magnet so as to bring the switch to rest. As long as relay It holds up, battery is applied to the lines to cause the receiver to make one or more revolutions and thus to operate the bell signal which is therefore the equivalent of dialling tone, in an automatic telephone system. Relay TR also at springs 5 connects positive to wiper 5 of the switch whence it is (BX-I tended to relay D, Fig. 5. In case no idle line is available relay-TR- will not .operate and the switch will return to its normal position and come to rest since the initial driving circuit is now open. In this position a circuit is completed for relay BR which thereupon applies reverse battery to the lines so as to sound the buzzer to indicate the busy condition. r

then the switch in Fig. 5 is taken into use, relay'D operates and completes a circuit for relay A which in turn completes a circuit for relay B. This relay at springs 1 opens the circuit of the release magnet ZM and prepares the impulsing circuit. For each impulse transmitted by the'dial, relay PR reverses its armature and, thus deenergizes relay A'which accordingly transmits an impulse over springs -1 of relay B and the offno-rmal springs N2 to the vertical magnet VM in series with slow relay C. The switch wipers are thereupon raised to the level corresponding to the number of impulses sent. As soon as the switch steps from its normal position, the oii-normal springs N2 are changed over and the circuit then extends over operatedsprings 1 of relay C. Atthe end oi the train of impulses relay C releases and transfers the impulsing circuit to the rotary magnet RM which is then energized intermittently in response to the succeeding train of impulses in series with relay E, which however remains energized continuously in consequence of the copper slug on its core. The rotary magnet advances the wipers of this switch into engagement with the wanted station, and relay E in addition to opening the circuits of relays TR and BB at springs 1 and 2 respectively closes at springs 3 the circuit of the slow relay F which thereupon prepares a circuit {or relay B. When relay E de-energizes at the end of the train of impulses for operating the rotary magnet, relay TB is energized if the wanted line is free and at springs 5 short-circuits its high resistance lower winding to prevent the intrusion of any other swtich. Relay TR also at springs 1 and 2 switches the lines through, at springs 3 completes a circuit for relay R, at springs. 4

opens the circuit of relay BR and at springs 6 connects positive over the fourth wiper of the switch to operate the cut-off relay COR associated with the called station. Relay R only remains energized during the slow release time of relay F and by connecting battery back over the line in the manner previously described transmits a signal to the calling station to indicate that the wanted station has been connected with. In case the wanted station has been busy, relay TR would have been unable to operate and thus the circuit momentarily completed for relay BR would have remained closed and permitted this relay to operate. This circuit it will be noted includes the normal rotary springs NR which are closed on the first rotary step of the switch. Relay BR in the usual manner applies battery in the reverse direction to the line so as to operate the polarized relay at the calling station in such a direction as to sound the buzzer and thus give a busy signal.

Release is effected as in the previous case by the operation of the rel-ease key RK which produces the operation of relay RR in Fig. 1. This relay at springs 1 locks itself up dependent upon the homing bank 3, at springs 2 opens the circuit of relay TR and at springs 3 opens the circuit of relay GR. The release of relay TR completes a homing circuit at springs 5 for the switch which thereupon rotates to normal position and also disconnects positive from wiper 5 and hence effects the deenergization of relay D, Fig. 5. Relays A and B are thereupon released in turn, but while relay B holds up for an instant an im pulse is sent to the rotary magnet RM and relay E is again operated and thereupon opens the circuit of relay TR. vVhen relay B finally de-energizes, a circuit is completed for the release magnet ZM and this restores the switch to normal in the usual manner, the springs Z carried by this magnet serving to prevent the re-operation of relay TR during the release movement. tacts N1 open when the switch reaches normal position and thus interrupt the circuit of the release magnet ZM.

Referring now to Fig. 6 which shows the circuit of a group selector, it will be assumed that this switch is taken into use from a nonnumerical switch similar to that shown in Fig. 4. As in the case of the switch shown in Fig. 5, the seizure is effected by the energization of relay D which thereupon completes a circuit for relay A, and this in turn energizes relay B.

No further changes take place until the calling station operates his dial whereupon relay PR responds to impulses in the manner previously described and relay A de-energizes correspondingly. Upon each de-energization a circuit is completed for relay C in series with the vertical magnet VM and the magnet operates to raise the wipers opposite The off-normal con-- the required level while relay C being slow remains energized throughout the train of impulses. Upon the first vertical step of the switch the off-normal contacts close and a circuit is thereupon completed for relay E by way of off-normal contacts N2, springs 1 of relay C and springs 1 of relay B. Relay E at springs 2 completes a locking circuit for itself dependent upon interrupter contacts RMl carried by the rotary magnet and at springs 1 prepares a circuit for this magnet. When relay 0 de-energizes at the end of the train of impulses, the rotary magnet circuit is completed in series with the slow relay F and it thereupon operates to advance the wipers into engagement with the first set of bank contacts. The interrupter springs RMl open at the end of the magnet step, and thus the locking circuit of relay E is opened and it de-energizes. If the line now connected with is busy, relay TR will be unable to energize and a circuit will be completed over springs 7 of relay TR for re-operating relay E which will therefore effect the operation of the rotary magnet again. This interaction between relay E and magnet RM continues until the test wiper engages an idle line whereupon relay TR operates to switch through the lines at springs 1 and 2, at springs 3 completes a circuit for relay R, at springs 24 opens a point in the circuit of relay BR, at springs 5 short-circuits its high resistance lower winding to guard the seized line, at springs 6 connects positive over the fourth wiper to operate the cut-off relay associated with the seized line and at springs 7 opens the energizing circuit of relay E so as to prevent the switch talzing any further steps. Relay F remains energized for a short intervalafter the operation of relay TR and therefore relay is operated during this interval and sends back the usual signal to indicate that further dialling may take place. This will operate a switch such as that shown in Fig. 5, the connection over springs 6 of relay TR Fig. 6 serving to operate the relay D in such a switch.

In case the group selector of Fig. 6 should rotate over the whole of the selected level without finding a free line, it would move to the eleventh rotary position and the cam springs usually provided on such a switch would be closed. Thereupon at springs CS1 the circuit of relay E is opened to prevent further operation of the rotary magnet and at springs CS2 a circuit is completed for relay BR which in this instance need not be made slow to operate, and this relay serves to give a busy signal in the manner previously described.

Release is effected by the operation of the release key as in the previous case, the deenergization of relay TR, Fig. 4, serving to release relay D, Fig. 6, and thus bringing down relays A and B. On the de-energization of relay B, the release magnet ZM is operated to restore the switch mechanism to normal and also at springs Z to open the circuit of relayTR which accordingly de-energizes. vThe circuit of the release magnet is opened at springs N1 when normal position is reached and springsNQ serve to release relay E which 'will have been venergized through without useful effect during the release operation. g

What I claim as new and desire to secure by Letters Patent is v -1. In a' telegraph system, stations each connected to an individual telegraph line, automatic switches forconnecting said stations together, a polarized relay in each switch for controlling said switches, an impulse sender at each of said stations, and meansresponsive to the operation of the impulse sender at a calling station for transmittinga series of reversed current impulses over the line to said polarized relay to operate it and control the corresponding automatic switch toestablish a connection with a called station, said means connected to the line only when said impulse sender is operating.

2. In a'telegraph system, stations, a line for each of said stations, automatic switches for connecting any of said stations together, a polarized relay in veach switch for controllingsaid switches, an impulse sender at each of said stations, an impulserelay responsive to theoperation of the impulse sender at a calling station for transmitting series of impulses comprising series ofreversals ofqcurrent over the associated line to intermittently operate said polarized relay and control the corresponding automatic switch to establish a connection with a called station, and means.

controlled by said impulse sender for connecting said impulse relay to the line only at the time the impulse sender is operating.

3. In a telegraph system, stations,-'a line individual'to each station, automatic switches for extending connections between the stations, a polarized relay in each switch for controlling said switches, an impulse sender at each station, an impulse relay having a pair of contacts for transmitting reversed current impulses to operate said polarized relay to control the corresponding automatic switch and establish a connection with a called line, said impulse send-er operating said impulse relay, and meanscontrolled by the impulse sender when it is moved from its normal position for connecting said pairof contacts in the line.

4:. In a telegraph system, stations each connected to a separate line, automatic switches for connecting said stations, a polarized relay in each switch normally connected in each line for controlling said automatic switches, an impulse sender for'each of said stations, means responsive to the operation of the impulse sender at a calling station for operating said polarized relay over the line to control the corresponding automatic switch in a manner to establish a connection with a called line, and means controlled by the switch after it has been fully operated for disconnecting said polarized relay from: the line.

5. In a telegraph system, stations, a line and. an automatic switch for each station, a.

polarized relay normally associated with each line: for controlling the corresponding automatic switch, an impulse sender at each station, means'respon'sive to the operation of the impulse sender at a calling: station for oper'- v ating the polarized relay to control the auto matic switch so as to establish a connection with :1 called station, and means controlled by the automatic switch after it has established the connection for disconnecting the polarized relay from the line. I

6; In a telegraph system, stations, a line for each of said stations, automatic switches for connecting said stations together, a polarized relay in each switch for controlling said switch, an impulse sender at each station for transmitting impulses over the line from a cal'ling'station to sai dpol arized relay to operate it and control the corresponding automatic' switch to establish a connection with a called station, means controlled by the switch after said connection is established for disconnecting said polarized relay from the line and connecting a high resistance across the line, and a release relay connected to the mid-pointof said resistance. p

7; In a telegraph system, stations each having a separate line, anautomatic switch for each: line for connecting thestations together, a polarized relay in the line for controlling the associated switch", an impulse sender at each station for transmitting impulses over the line ot a calling station to operate the polarized relay and control the automatic switch for establishing a connection with a called station, means-controlled by the switch after it has established the connection for disconnecting the polarized-relay from the line, a high resistance connected across the line by'the switch when the polarized relay is disconnected, and a release relay for releasing the automatic switch connected to the mid-point oi said high resistance.

8. Ina telegraph system, stations each having a separate line, an automatic switch for connecting said lines together, a high resistance'in: the switch, a polarized relay for controlling the automatic switch, an impulse sender at-a calling station for operating'said roo polarized relay to control the automatic at the calling station for operating said release relay through-saidresistance to release the switch.

Y 9. In a telephone system, stations each having aline, an automaticswitch individual to each line for connecting them together, a high resistance in the switch connected acrossthe line, a release relay connected to the midpoint of said resistance, means controlled from a calling station for operating-its automatic switch to establish a connection with a called station, means controlled by the switch after it has operated for connecting said high resistance across the established connection, and a release key at the calling station for operating said release relay over the line and through said resistance to release the automatic switch to normal position.

10. In. a telegraph'system, stations each connected to an individual line, a signalat each station, automatic switches in which said lines terminate, a polarized relay-in each switch for controlling said switch, an impulse sender for each station, meansresponsive to the operation of the impulse sender at a callingstation for operating said polarized relay over the line to control said correspond ing automatic switch to establish a connection with a calledstation, and means in said switch after the connection hasbeen established for disconnecting said polarized relay from the line and for transmitting a momentary current back over the line to the calling station to operate the signal thereat.

11. In a telegraph station, stations each connected to anindividual line, a signal at each station, an automatic switch for each line for connecting them together, a polarized relay in the line for controlling the automatic'switch, an impulse sender at each station, means responsive to the operation of the impulse sender at a calling station for operating said polarized relay to control said automatic switch to establish a connection with a called station, means controlled b said switch after it has established the connection for disconnecting said polarized relay from the line and for transmitting a momentary current back over the line to the calling station, and means atsaid station re-. sponsive to said current for operating the signal at said station to indicate the establishment of the connection.

12. In a telegraph system, stations each connected to a line, an automatic switch for each line for connecting the stationstogether, a polarized relay forcontrolling the automatic switch, an impulse sender at each station, means responsive to the operation of the impulse sender at a calling station for operating the polarized relay to control the automatic switch and establish a connection with a called station,means controlled by said switch after it has established the connection for transmitting a momentary current flow back over the line to the calling station to indicate that the connection has been established, and means controlled by said switch in case said called station is busy for transmitting a reversed current flow back over the line to the calling station to indicate the busy condition of the called station.

13. In a telegraph system, stations each connected to a line, an automatic switch for each line for connecting the stations together, a starting signaland a busy signal at each station, a polarized relay for controlling the automatic switch, an'impulse sender at each station, means responsive to the operation of the impulse sender at a calling station for operating the polarized relay to control the automatic switch and establish a connection with a called station, means controlled by the switch responsive to the establishment of the connection for transmitting a flow of current back over the line to the calling station to operate the starting signal thereat to indicatethat the connection is completed, and means controlled by said switch in case the called station is busy for transmitting a momentary flow of reversed current back over the line to the calling station to operate the busy signal thereat to indicate the busy condition of the called station.

14. In a telegraph system, a plurality of stations each connected to an individual line, an automatic switch for each line in which it terminates, an impulse sender at each of said stations, a starting signal and a busy signal at each station, a polarized relay for controlling said signals, means responsive to the operationof the impulse sender at a calling station for controlling the automatic switch to establish a connection with a called station, means controlled by said switch responsive to the establishment of the connection-for transmitting a flow of current back over the line to the calling station to control the polarized relay in a certain manner to operate the starting signal and indicate that the connection has been completed, and means controlled by said automatic switch in case the called station is in a busy condition for transmitting a reversed flow of current back over the line to control the polarized relay in a difi'erent manner to operate the busy signal to indicate the busy condition of the called station.

. 15. In a telegraph system, a plurality of stations each connected to an individual line, an automatic switch for each line in which it terminates, an impulse sender at each of said stations, a starting signal and a busy signal at each station, a polarized relay for controlling said signals, means responsive to the operation of the impulse sender at a calling station for controlling the automatic Switch to establish a connection with a called station, means .controlled by said switch responsive to the establishment of the connection for transmitting a flow of current back over the line to the calling station to control the polarized relay in a certain manner to operate the starting signal and indicate that the connection has been completed, means controlled by said automatic switch in case the called station is in a busy condition for transmitting a reversed flow of current back over the line to control the polarized relay in a different manner to operate the busy signal to indicate the busy condition of the called station, and a release key at the calling station for releasing said switch and dis connecting the polarized relay torestore the busy signal to normal.

16. In a telephone system, stations each connected to aseparate line, a non-numerical switch individual to each line, numerical switches common to all of said lines for connecting the lines together, an impulse sender at each station, a signal at each station, means controlled by a calling station upon taking its line into use for automatically operating said non-numerical switch to engage an idle one of said numerical switches, means in said non-numerical switch responsive to its engagement with the numerical switch for transmitting a flow of current back over the line to the calling station to operate said signal thereat to indicate that impulse sending can take place, and means responsive to the operation of said impulse sender for operating said numerical switch to establish a connection with a called line.

17. In a telegraph system, a plurality of stations each having a line, a non-numerical switch for each line, numerical switches common to said lines, an impulse sender and a signal at each station, a polarized relay in each numerical switch for controlling the said numerical switch, means controlled by a calling station upon taking its line into use for automatically operating the non-numerical switch to select an idle one of said numerical switches, means in said non-numerical switch responsive to said selection for transmitting a flow of current back over the line to operate said signal to indicate that said numerical switch is ready to be operated, and means responsive to the operation of the impulse sender for operating the polarized relay in the selected numerical switch to control said numerical switch in a manner to establish a connection with a called station.

18. In a telegraph system, stations each having separate line conductors, an automatic switch for connecting said stations together, a polarized relay for controlling said switch, an impulse sender at each station, means responsive to a calling station taking its line conductors into use for automatically seizing and engaging said switch over a connection independent of said line conductors, means responsive to the operation of the impulse sender at the calling station for operating said polarized relay over the line conductors to control said automatic switch in a manner to establish a connection with a called station, and meansfor holding said switch in its operated position over said independent connection.

19. In a telegraph system, stations each connected to separate line conductors, an automatic switch for connecting said stations together, an impulse sender at each station, means responsive to a calling station taking its line conductors into use for automatically seizing and connecting with said automatic switch over a connection independent of said line conductors, means responsive to the operation of the impulse sender for operating said switch over said line conductors to establish a connection with a called station, and means for holding said switch in its operated position over said independent connection.

20. In a telegraph system, a plurality of stations, a line for each of said stations, a non-numerical switch connected to each line, numerical switches common to all of said nonnumerical switches, an impulse sender at each station, a dialling signal, a busy signal, and a starting signal, said signals being at each of said stations,means responsive to a calling station taking its line into use for automatically operating the associated non-numerical switch to select an idle one of said numerical switches, means in said non-numerical switch responsive to said selection for operating said dialling signal to indicate that said numerical switch has been engaged and impulse sending can proceed, means responsive to the operation of the impulse sender at the calling station for operating said numerical switch to establish a connection with a called station, means in said numerical switch in case the called station is in a busy condition for operating said busy signal at the calling station to indicate the busy condition of the called station, andmeans in said numerical switch after the connection with the called station has been established for operating said starting signal at the calling station to indicate that the connection has been completed.

In testimony whereof I affix my signature.

HARRY HUGHES HARRISON.

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