US1601061A - Automatic telephone-exchange system - Google Patents

Description

Sept. 28, 1926. 1,601,061

B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Oct. 6, 1904 8 Sheets-Sheet 1 B. G. Dunkam,

J wmvmzg INVENTOR.

M15. W BY ATTORAEK Sept. 28 1926. 11,601,061

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A17 ORNEY.

Sept. 28 1926.

B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGE SYSTEM 6, 1904 8 Sheets-Shet .4

Filed Oct.

B. G. Dunk am 'INVENTOR. I

AJTORMY WITNESSES: dm @M Q. a /M Sept. 28 1926. Lfifllfifil B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Oct. 6, 1904;- 8 Sheets-Sheet 5 B.G'.Dun7zam,

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Sept. 28 1926. 1,601,061

B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Oct. 6, 1904 8 Sheets-Sheet '7 3; 5:, B. G. Dunizam, g WIMSSFS. .HVVEIVTOR. 6%, gm; C

ATTORNEY.

Sept. 28 1926.

B. G. DUNHAM AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Oct. 6, 1904 8 Sheets-Sht 8 l}. Ilunham nrngg- Patented Sept. 28, 1926.

UNITED STATES PATENT OFFICE.

BERT G. DUNHAM, O]? CHICAGO, ILLINOIS, ASSIGNOB, BY MESNE ASSIGNMEI ITS, T WESTERN ELECTRIC COMPANY, INCORPORATED, A. CORPORATION OF NEW YORK.

AUTOMATIC TELEPHONE-EXCHANGE SYSTEM.

Application filed October 8, 1904. Serial No. 227,462.

My invention relates to automatic telephone exchange systems-that is, those sys tems wherein the connection between any two lines is made by automatic switches at the central oflice, these being directed 1n their action by mechanism at the subscribers station under the control of the subscriber who desired to make a call.

In the most improved type of automatic telephone exchange systems prior to my invention, each subscribers line terminates at the central oflice in a switching device, known in the parlance of automatic exchange working, as a first selector switch. This device has, as its central moving feature, a vertical shaft capable of being lifted in steps by an electromagnet under the control of the subscriber, and after such lifting, of being rotated in an are, carrying with it contact brushes or wipers which make connection with circuits leading from the switch to other similar switches, one of which, having been selected by the operation of the first switch, may act, in its operation, se-

lecting a third and perhaps a fourth switch, and one of which, under similar control, will finally connect the line of the calling subscriber to that of the called subscriber.

In such a system as this, it is required that each subscribers line be provided with one first selector switch, and that it be of such size and provided with such an extent of vertical and rotary motion as to enable the calling subscriber to direct his line upon any one of ten series of trunk lines; each of the ten series of trunk lines requires to contain a considerable number of such accessible trunks, the number usually provided being ten, and in some instances economy L demands that each series contain more than ten. It is therefore necessary that each first selector be a mechanism capable 'of selecting any one from a number of 100 or more trunk lines. The resulting size and cost of the first selector switches, and the fact that one is required for each subscribers line, causes this portion of a central ofiice equipment of the automatic type to represent a very considerable investment. It is the ob- 5'o jectofmy invention to reduce this investment by providing each subscribers line with a relatively simple and inexpensive device, which by its operation will bring into action when needed, one of a group of first selectors, proceeding thereafter through the operation of that switch and others, to set up the desired connection. While my invention requires that each subscribers line be equlpped with such a device, and that each connection involves the use of this device to and a smaller number of switches similar to those used in previous systems, the number-of first selectors, which are expensive, is so much reduced as to render the whole installation of a given exchange much less costly. This reduction of cost results from obviating the necessity of providing a first selector for each line which the oflice contains, and of making it necessary to provide only such a number of first selectors as is required by the number of lines actually in operation at a time of maximum trafiic.

Furthermore in all of the systems of automatic exchange working which have been developed up to the time of my invention, in which the foregoing general principles have been used, each of the various switches involved in the establishment of a connection has been provided with a special device known as a side switch. The object of this feature of the mechanism is to enable the control of the motions of the selector or connector as to its vertical and rotary shaftmotions to be effected through the agency of simple current impulses over one or the other of the two wires of the line. Through the agency of this side switch one set of such current impulses over a given wire of the line may differ in result'from another set, the internal connections of the switch mech- 9o anism having been changed due to the action of the side switch. This side switch has been found reasonably efiective in operation, but is expensive to construct and maintain. My invention, therefore, has for its further object the elimination of this side switch device from some or all of the switches of automatic exchange systems, and the accomplishment of all the previously possible results in a simpler manner, with fewer elements of mechanism, and a consequently decreased, cost of installation and maintenance.

It is evident that to the end of accomplishing the advantages which I have first described herein as an object of my invention, with reference to reducing the total investment by providing each subscribers line with a new form of selector, those features of my invention which are pertinent to that object may be selected, and may be utilized without the necessity of combining them with exactly such other selector and connector switches as are described and illustrated herein. I do not desire therefore to limit myself to the relation which I show between a system involving such an individual selector for each line and other switches which are free from side switch mechanism.

It is further evident that the arrangement of selector and connector switches within themselves so as to accomplish their vertical and rotary operations without the use of side switches, is a useful result in itself, whether or not such switches form part of an installation in which each line is provided with a special individual selector. I do not desire therefore to limit my invention to a system in which both the existence of an individual selector, and'the absence of a side switch, are features, as it is of advantage to accomplish the elimination of the side switch whether or not the other advantage be adopted.

My invention is illustrated in the accompanying sheets of drawings which form a portion of this application, and in which Fig. 1 is a plan view of the subscribers individual selector;

Fig. 2 is an elevation of a part of that device viewed in the direction of the arrow on the line AA;

Fig. 2 is an elevation of another part of that device, viewed in the direction of the arrow on the lines BB;

Fig. 3 is a diagram of the circuits of the subscribers instrument adaptable for use with my invention;

Fig. 4 is a diagram of the circuits of the individual selector;

Fig. 5 is a diagram of the circuits of the first selector;

Fig. 6, of the circuits of the second selector;

Fig. 7, of the circuits of the conector, and Fig. 8, of the circuits of the individual selector of the subscriber who is being called. Figure 9 is a diagrammatic representation of the features of the side switch employed.

Figure 10 is a diagrammatic View showing the control of the rotary magnet armature over the private magnet armature.

Like characters refer to like parts throughout the several views.

Referring to Fig. 8, the operations performed by the subscriber in originating a call in the manner quite usual in the operation of automatic exchanges, can be understood. The talking apparatus, consisting of a receiver, transmitter and induction coil, may be connected between the vertical and rotary limbs of the lines, V and R, respectively, by the action of the hook switch, 3, in a manner well understood. Under normal conditions, that is, when the receiver is upon the hook, the bell orringer, 4, is connected between the two sides of the line, this connection extending throu h the spring, 5, and the arm, 6, of the hoo when the telephone is not in use. When the receiver is removed from the hook this connection is broken, and the talking contacts completed in an obvious manner. All ground connections at the subscribers station are primarily controlled at the pair of contacts, 7, these contacts bein held open as long as the receiver is on its hook, and after the receiver has been removed until the impulse transmitting device has been put in operation.

- The transmitting device acts by causing the springs 8 or 9, to engage the ground spring, 10, according to whether impulses are to be sent over the vertical or rotary sides of the line. That is, if six impulses are to be transmitted, the spring, 8, W111 be pressed against the spring, 10, six times, thus allowing that many impulses to flow from the central ofiice over the vertical side of the line to ground. It is obvious from the presence of the spring, 7, that no such impulse can take place unless the receiver has been removed from its hook, and the impulse transmitter operated, for only under these 95 conditions can the contact between springs, 7, be closed. In a similar manner an impulse over the rotary side of the line may be secured by pressing the spring, 9, against the spring, 10. It should be remembered that all selecting'is done over the vertical side of the line by sending a series of impulses corresponding to the digits belongin to the number of the subscriber wante Each series of impulses over the vertical 105 side of the line caused by the movements of the spring, 8, is followed by a single impulse over the rotary side of the line caused by the movement of the spring, 9.

When the hook, 3, is depressed at the no close of the conversation, its arm, 11, serves to press the springs, 12, 13 and 14, momentarily into engagement with each other, thereby grounding both the vertical and rotary sides of the line through the spring, 115 14, and the contact, 7. The mechanical arrangement of parts is such that the springs, 12, 13 and 14, are not brought into engagement with each other as the hook rises, or while it is either depressed or elevated.

15 is the spring actuated by the ringing button, this spring normally bearing against .spring, 16, and serving to hold closed the talking circuit. When, however, the ringing button is depressed, spring, 15, engages spring, 17 thereby grounding the vertical side of the line for the operation of the ringing relay in the connector switch.

The condenser, 19, is in series with the ringer, 4, with the result that the circuit through the subscribers telephone'from the wire, V, to the wire, R, is open to direct current, although closed to alternating current, during all the time the-receiver is upon its hook. Referring now to Fig. 4, the wires, V and R, from the subscribers station are seen entering at the left of the sheet. Upon the removal of the receiver from the hook at the instrument of the calling subscriber, current will flowthrough the following path, energizing the relay, L; from the undergrounded pole of the battery, B, through the winding, b, of the relay, L, to the contact, 21, upon which rests the wiper, 23, to the contact, 28, and spring, 29, of the relay, CO, the wire, R, to the subscribers instrument, through the receiver and the contact springs, 15 and 16, and the closed switch hook contacts to the vertical wire, thence to the central otlice, throu h the contact of springs, 30 and 31, the wiper, 22, and to ground at the contact, 32. As the relay, L, is energized, the attraction of its armature will break the contact between the springs, 33 and 34, and establish contact between 34 and 35. This contact establishes a circuit through the winding, a, of the relay, L, holding it energized by current from the battery, B, through that winding, the contact of 34 and 35, and to ground at contact of the wiper 24 upon 37. circuit is also established by this latter contact from the battery, B, through the rotary magnet, RM, its series contact, 36, springs, 35 and 34, the wiper, 24, and its grounded contact, 37., As the series contact,

36, is such a one as is broken by the stroke of the armature of the magnet, RM, the circuit which has resulted will cause a succes-* sion of strokes of that armature somewhat after the manner of the familiar vibrating bell. By means. of a pawl 162 best illustrated in Fig. 1 these armature motions will advance a ratchet 166 on the shaft, 38, turning the latter in such a way as to move the contact wipers, 22 to 27 inclusive, through an arc of contact pieces which also are best shown in Fig. 1. Each stroke of the armature of the magnet, RM, will "advance the wipers from one set of contacts to the next, and this stepping from set to set of the contacts will continue as long as the circuit conditions are found similar in the successive steps. A feature of the operation of my system throughout is that in order that a line or a trunk may be guarded from being connected with by any switch, while it is already occupied for conversation, a conductor associated with that line and terminating in a contact piece will control the circuits to prevent connectionof lines while it is grounded, but will allow them to operate to permit connection whenever .it is not grounded. The contacts associated with the wire, P, in Fig. 4, have such an oflice. At the first step of the shaft, 38, bringing the wiper, 24, upon a contact piece of the wire,

P, the ground at the contact, 37 would have been broken, and unless a ground had been found upon the contact of the trunk, P, the circuit of the magnet, RM, would have been opened and further rotation prevented. If. however, the contact of the wire, P, had been grounded, the rotary magnet would have executed another step, and step by step successively upon finding grounded contacts, would have passed to one which was not grounded, stopping the shaft as indicated. But at the same time the wiper, 26 would have left contact with 40, and would have engaged 43, which is an arc adapted to engage the wiper, 26, throughout all of its motion, except while in normal position.

. This engagement causes current to flow from the battery, B, through the cut-off relay, CO, the contact arc, 43, the wiper, 26, contact between springs, 35 and 34, to the grounds on contact pieces of the private wires of busy trunks. The effect is to operate the cut-ofi' relay, CO, during such time as busy trunks are engaged, and thus by the breakage of contacts between springs, 30 and 39, respectively, and points, 31 and 28, respectively, to disconnect the line composed of wires, V and R, from the wipers, 22 and 23. The line of the calling subscriber, therefore, is thus held open at the cut-off relay, during all the time in which the wipers, 22 and 23, are passing over occupied trunk conductors. As the continuity of this circuit depends upon the grounding of the wipers, 24, the cut-off relay will release as soon as a non-busy trunk is found, and thus the line conductors, V and R, will be extended as is required. Similarly, as the actuation of the relay, L, depends upon the wiper, 24, being grounded, it will release upon the finding of the nonbusy trunk. The release of its armature will break contact between springs, 35 and 34, and make contact between 33 and 34. This will ground the contact upon which the wiper, 24, rests thus making the wire, P, busy at all its contacts, and any other mechanism will be defeated from stopping with its wipers upon the trunk thus selected, be-- cause of this grounding of the private contacts. Likewise with reference to the possible stoppage of another switch upon the line composed of conductors, V and R, as they appear in connector switches, this line will be made busy by the presence of the wiper, 27 upon the arc, 44, similarin construction to the are, 43. This will place a ground upon the private wire, P, which accompanies the calling line in its appearances in connector banks, and accomplishes the protection required.

It will now be seen that the line composed of wires, V and R, is extended, without a. bridge upon it, to the wires, V and R, and in Fig. 5, these are seen entering at the left of the sheet. Similarly the wires, P and D enter, being continuations of those shown in Fig. 4. At the completion of the motion of the individual selector shown in Fig. 4, described as having selected the trunk which extends to the first selector, shown in Fig. 5, a ground was placed upon the conductor, P. In addition to guarding the selected trunk against the incursion of another switch, this ground acts, through the contact of springs, 45 and 46, of the offnormal switch, to energize the relay, L, by current flowing from the battery, B. The action of this relay places the relay, VR, in connection with the wire, V, and the relay, RR, in connection with the wire, R. This is by contact of the spring, 47 with 48, and 49 with 50.

As the previously described operations of the automatic selection of a trunk by the individual selector, and the just described association of the relays, VR and RR, with the two sides of the line, have taken place practically instantaneously, the result to this point is that the subscriber has under his control the succeeding operations of selecting the subscriber he desires by manipulating the instrument at his station. This he does in the usual manner, in which the first digit of the number is indicated by a succession of ground contacts upon the vertical wires This succession operates the relay, VR, in as many steps, due to current from the battery, B, through its winding, the contact of 48 with 47 over the wire, V, to the ground at the substation. The result of this relay operation is to make con tact between 51 and 52, causing current to flow from the battery, B, through the vertical magnet, VM, 51 and 52, to springs, 53 and 54, of the magnet, DM', and to ground. The vertical magnet will thus be operated a number of steps, acting through its pawl to lift the shaft, 55, stopping opposite one of the arcs of the contact bank with which the switch is equipped. As the act of the subscribers mechanism is to give one ground contact upon the rotary wire immediately after the series upon the vertical wire, such contact will cause current to flow from the, battery, B, through the relay, RR, in one impulse. This b closing its contact will cause current to ow from the battery, B, through the rotary magnet, RM, the spring, 56, t0 the contact, 52, and from 53 to 54 and ground. The action of the pawl of the rotary magnet will rotate the shaft, 55, one step, bringing its wipers, 57, 58 and 59 upon the first set of three contacts in the selected are of the bank. If there is no ground upon the private wire, PD, indicating that the trunk'of the wires, V and R is not busy, the shaft, 55, will make no further rotary motion, as its office has been fulfilled, and a trunk has been selected leading to the proper thousand, as indicated by the first figure of the called subscribers number. But if a ground is found upon the wire, PD, a further rotation of the shaft, 55, will ensue, resulting in the selection of a trunk which is not busy. This is accomplished by virtue of the control which the armature of the magnet RM has over the armature of the private magnet PM. This mechanical connection between the respective armatures is shown in Figure 10 where a suitable extension 6 upon the armature m of the rotary magnet RM engages the armature n of the private magnet PM. Thus, it will be seen that when the rotary magnet RM is energized, the armature n of the private magnet PM will operate precisely as if magnet PM had been energized. Thus, the springs controlled by the armature of the private magnet are moved when the rotary magnet is energized precisely as if the private magnet had been energized. As this occurred at the moment of making the rotary wire contact at the subscriber s station, a circuit was established from the battery, B, through the magnet, RM, through its contact, 60, springs, 61 and 62 to ground. Under these conditions, because the contact, 60, is such a one as will be broken by each stroke of the armature, rotation of the shaft would continue during the existence of those conditions. But another circuit is established at the same time from the battery, B, through the magnet, PM, contact 63, to spring, 64, thence through a low resistance relay, DR, to the wiper, 59; if this wiper is engagin successive grounded contacts of wires, as PD, belonging to trunk lines which are in use, the magnet, PM, will be energized during any such successive contact, holding the circuit of the rotary magnet, RM, closed for further rotation. Upon the engagement by the wiper, 59, of a nongrounded contact, the magnet, PM, will be released, breaking connection between 61 and 62, and stopping further action of the rotary magnet, RM.

The relay, DR, is wound of few turns, and relatively low resistance, a practical one being about ohm; and when in series with the winding of the magnet, PM, the relay, DR, will not be energized. The magnet, PM, may practically have a winding of 350 to 500 ohms.

It has been said that the actuation of the relay, L, was the result of a circuit extending through the off-normal switch springs, 45 and 46. The contact between 46 and 45 was broken at the time of the first vertical step of the shaft, 55, but contact was made at this time between 46 and 67 establishing a circuit from the battery, B, through the relay, L, springs, 46 and 67, 65 to 66,

and to ground by contact between 62 and 64 of the magnet, PM. At the beginning of the rotation of the shaft, this contact of 64 and 62 was broken, but at such a time the circuit of the relay, L continued to be establishcd to ground through successive ground contacts of the wiper, 59. It will thus be seen that the relay, L, has been actuated from the very beginning of the cycle until the stoppage of the wipers of the shaft, 55, upon the contacts of the selected idle trunk. At such time the relay, L, released its armature, causing the line composed of the wires, V and R, to be extended, free from bridge, to the wipers, 57 and 58.

The final release of the magnet, PM, at the stoppage of the rotation, restores contact between springs, 64 and 62, replacing a direct ground upon the conductor leading through the relay, DR, to the wiper, 59. This caused no action within the switch, but placed a condition of guard upon the private wire, PD, preventing an incursion of another switch upon the trunk line which has been selected.

Referring to Fig. 6, the wires, V, R and PD, the extensions of those similarly marked in Fig. 5, will be seen entering at the left of the sheet. Upon the placing of the described ground upon the wire, PD, by the wiper, 59, current was caused to flow from the battery, B, through the relay, L springs, 73 and 72, of the oft-normal switch, over the wire, PD, through the relay, DR, to ground at the contact of 64 with 62, in Fig. 5. The relay, DR, being as described of few turns, will not be actuated by the current which flows through relay, L which is of relatively high resistance; but the relay, U, will be operated by this current, resulting in the cutting off of the wires, V and R from extension to the wipers, 98 and 99, and also in the connection of the relays, VR' and RR to the lines Y and R respectively. Upon the subscriber actuating his telephone, therefore, relative to the second figure of the called number, contact with the vertical wire at the station will cause successive operations of the relay, VR', because of current from the battery, B, through the winding of this relay to the springs, 82 and 77, over the wire, V and its extension to the subscriber's instrument. The resulting action on the part of the relay, VR, will cause current from the battery, B, through the vertical magnet, VM, the contact of springs, 85 and 86, and the springs, 102 and 101, to ground. The vertical magnet, VM, will thus be actuated in as many steps as there are digits in the called'figure, and through its pawl will lift the shaft, 103, as many steps, stopping the wipers opposite the arcs of the contact bank containing points leading to the group of connectors in which the number of the called subscriber belongs. As a; rotary impulse always succeeds a series of vertical ones, such an impulse will now result and will operate the rotary relay, RR, by

current through the springs, 80 and 79, over the rotary wire to the'subscribers instru- -ment. The resulting contact of the rotary relay will cause current to flow from the battery, through the rotary magnet, RM, contact of 87 with 86, and through 102 and 101 to ground. The rotary magnet, RM will thusmake one stroke of its armature, and through its pawl will rotate the shaft, 103, one step, placing the wipers on the first trunk contacts of that are. If this trunk is not busy, and by virtue thereof no ground is,

upon its private wire, PD, no further action will result and the desired trunk will have" been selected. If, however, the trunk wire, PD, has a ground upon it, a further rotary motion will result, as-follows: Because of the operation of the rotary magnet, RM", and by reason of the mechanical extension on 1ts armature, the armature of the private magnet, PM, is also actuated quite as if its core had been energized. This acted to establish a circuit through the springs of the private magnet, PM, from the battery, B, through the magnet, RM its series contact, 89, springs, 90 and 91, to ground. This contact of the rotary magnet, which is wholly independent of the relay, RR, causes it to execute a succession of strokes, each stroke resulting to open the circuit, at 89, which causes it to execute another succession of strokes, quite after the manner of the familiar vibrating bell. Such strokes will succeed each other as long as the circuit conditions remain unchanged. That is, as long as the wiper, 100, continues to engage grounded private contacts of successive busy trunks. Another result of the mechanical actuation of the armature of the magnet, PM, is to extend a circuit from the battery, B, through the magnet, PM, and its sprlng, 93, to spring, 92, thence through the disconnect relay, DR, to the wiper, 100. As long, therefore, as the wiper, 100, makes successive contacts with grounded points of busy lines, the magnet, PM, will be actuated holding the circuit of the magnet, RM in rotative condition. Upon the wiper, 100, engaging a contact not grounded, themagnet. PM, will release its armature, interrupting the circuit of the magnet, RM, and stopping further rotation. By contact of 91 with 92, a ground is now placed upon the wiper, 100, through themagnet, DR, thus guarding the selected trunk against the incursion of another switch. The winding of the relay, DR, is of few turns, and low resistance, the latter being practical at about ohm, and the current received by this relay, while in series with the magnet, PM, is insulficient to operate it as the winding of the magnet, PM, is of relatively high resistance, say about 350 to 500 ohms.

At the first motion of this second selector,

guite as was described with reference to the rst selector, the spring, 73, of the off normal switch, disengages, 72 and engages 74-. As the relay, L is at this time operated, it is held operated through this new contact, and that of 75 with 76 to ground of 92 with 91, or of with a grounded contact polnt. By whichever of the three paths L is operated, it remains so until such time as a trunk is selected which is not busy, whereupon the final opening of its circuit allows its armature to fall away. This closes the wires, V and R through the wipers, 98 and 99, and places the line in condition for the next feature of operation.

Referring to Fig. 7, the wires, V, R and PD are seen entering at the left of the sheet, the relays, VR and RR, being bridged respectively between them and the battery. Upon the subscriber operating his instrument in reference to the third figure of the desired number, a succession of ground contacts will be made upon the vertical wire. The vertical relay responding by current from the battery, B, will make a succession of contacts between its springs, resulting in current from the battery, B, through the vertical magnet, VM the contact, 121, and the lever, of the side switch, the spr ngs, 116 and 117, of the magnet, PM springs, 107 and 106, to ground. The vertical magnet by its action will lift the shaft, 130, in as man vertical steps. The side switch which has n mentioned is a device composed of four levers, 120 to 120 inclusive, each adapted to make contacts, symmetrically with the others, upon one of three contact points. Fig. 9 illustrates diagrammatically the mechanical {features of a side-switch ada ted to carr out the operations attribute to it. In t is figure the same reference characters are used, where possible, as those used in the other figures. No attempt is made in this figure, however, to illustrate associated parts which are not directly concerned in the operation of the side-switch. Thus, for example, the private magnet, PM, is shown without the contacts 114, 115, 116 and 117 which, in fact, are associated with this magnet as shown, for example in Fig. 7. The rotatably mounted shaft, carries the side-switch levers 25", 25", etc. only two of which are shown, however. The associated contacts are shown at 26, 27", 28, and at 26", 27", and 28 The arm or lever, 202, having a triangular cross-section is rigidly mounted u on the shaft, 201. The private magnet P is provided with an armature, 203, pivoted at 204 and having an arm 205, extending toward the lever, 202. A spring, 211, co-operating with a spring arm, 212, tends to cause a rotation of the side-switch shaft and its switch arms in the direction of the arrow, 213. Thus upon the energization of the private magnet PM, the

arm 205, is depressed and this causes the tooth, 206 on the escapement arm to strike the top of the tooth, 210, on the spring member, 208, this member because of its springy characteristics being held by its on agement with lever 202 and not, therefore, mg effected by the movement of the armature 203. When the arm 205 is depressed to cause the tooth 206 thereon to strike the top of the tooth 210 on the sprin spring member is thus e actively forced out of engagement with the escapement arm, 202. The face of the tooth, 206, is only slightly to the left of the face of the tooth, 210, so that the substitution of the tooth, 206, to retain the escapement arm 202 in its position in place of the teeth 210 does not permit any material rotation of the sideswitch shaft due to the tension of the spring, 211. When, however, the de-energization of the private magnet, PM, permits retraction of the armature, 203, due to the influence of the spring, 214, the face of the tooth, 210, will not engage the front surface of the escapement arm, 202, and this arm and shaft will be permitted to turn to the left under the influence of the spring, 211, until it strikes the face of the tooth, 209. So, also, a subseqlgent ener ation of the rivatei magnet, M, will rst cause the toot 1, 207, to be substituted for the tooth, 209, to retain the side-switch shaft in its position, and then upon the de-energization of the private magnet the side-switch shaft will be caused to move a step further in advance. The wire, 215, which is connected with the arm, 212, passes through a hole in the rigidly supported guide, 216, and is provided with an adjustable stop, 217, by means of which the forward rotation of the side-switch shaft is limited.

The restoration of the side switches and the shaft upon which the are mounted to their normal position is brought about by the energization and subsequent de-energization of the disconnect-magnet, DM. In addition to the mechanism associated with this magnet for causing restoration of the shaft, 38, to its normal position, the armature, 218, of the magnet, DM, is provided with a catch, 219. The armature is pivoted at 220 and returned to its normal position by a comparatively stiff spring, 221. The wire, 215, which is quite splring is provided at its end with a very t in, exible plate, 222, this plate having a suitable opening at 223. The vertical magnet, VM, is equipped with an armature, 224:, pivoted at 225, and provided at its extremity with a catch, 226. The energization of this magnet, VM, raises the armature, 224, and by means of the catch, 226, it raises also the plate, 222, disengaging it from the restraining influence of the catch, 219, and making the rotation of the side-switch shaft, 201, subject only to the member 208, the

operation of the escapement associated with the private magnet, PM.

The restoration of the selector mechanism upon-the energization and de-energization of the disconnect-magnet, DM, restores the plate, 222, to the position shown in Flg. 7. When next this particular mechanism is called into service the first energization of vertical magnet, VM, immediately releases the plate, 222, from the catch, 219, and puts the side-switch under the control of the es- I springs, which act is at this time immaterial.

The important thing which happens is that the armature upon falling back moves the side switch levers as has been described to their second position. Upon the receipt of the fourth series of verticalimpulses caused by the subscriber operating his instrument relative to the fourth figure of the deslred number, the vertical relay will make contacts as before, but in this instance the result will be current through the rotary magnet, RM contact, 122 lever, 120, spr ngs,

116 and 117 of the private magnet, PM and springs, 107 and 106 to ground. This will actuate the rotary magnet, RM, and through its pawl the shaft, 130, in as many rotary steps, moving the wipers, 132, 133 and 134, in the arcs of the contact bank before which they had been placed by the vertical motions, stopping them upon the contact pleces of. the hne for which the call had been made. Upon the receipt of the single rotary impulse following the series of vertical impulses, current from the battery, B, through the private magnet, PM, to ground by contact of 108 upon 106, will actuate the side switch a second time, advancing its levers to their, third and extreme position. This serves to connect the wires, V and R serially through the condensers, 109 and 110, and the contacts of 131 with 125, and 126 with 124, of the calling relay, CR, to the wipers, 132 and 133.

Pressure of the ringing button at the subscribers station will place ground upon the vertical wire, V again operating the relay, VR current from the battery, B, will now flow to the calling relay, CR, contact, 123*, lever, 120, springs 117 and 116, and 107 and 106, to ground. The calling relay, CR, acts .to connect the terminals of the genthe line of the called subscriber.

erator, G, at 127 and 129, with the wipers, 133 and 132, respectively by contact of the former with 124 and 125 respectively. This will send ringing current over the called subscribers line, ringing his bell, and upon his response conversation may ensue.

The foregoingwith reference to the action of the connector shown in Fig. 7, has been terminated upon the assumption that the line of the called subscriber was not busy, and that connection with it was not defeated by that fact. If it had been busy, the operation of the connector would have been affected by the existence of ground upon the private wire, P associated with In such a case instead of the line of the calling subscriber having been extended through to that of the called subscriber by the. second motion of the side switch, the act of the last rotary impulse would have been to pass current from the battery, B, through the disconnect magnet, DM springs, 114 and 115, of the private magnet, which operated in response to that rotary contact, to contact, 122, and lever,-120 of the side switch to the wiper, 134, and thus to the ground upon the contact of the busy line. The disconnect magnet, DM by withdrawing its pawls from the vertical and rotary ratchets of the shaft, 130, would have permitted it to return to normal'position through the action of its springs and gravity.

But the calling subscriber would not have known that the connection had been defeated by these busy conditions, and would have pressed his ringing button, grounding the vertical wire. This would have operated the vertical relay, VH by current from the battery, B, to the substation ground on the vertical wire, and as the side switch levers had been returned to their normal position by the release of the connector switch, the result would have been current from the battery, B, through the vertical magnet, VM, and the described contacts, 117, 116, 107 and 106, operating to lift the shaft, 130, one or more Vertical steps, depending on the number of pressures of the ringing button. But the oil normal switch, composed of springs, '135 and 136, would be operated to close these contacts by this motion of the vertical shaft. Interrupted current induced by current from the battery B flowing through the interrupter I which is shunted by the condenser 137 would then flow through the lamp resistance K, the off- normal switch contacts 135 and 136, contact 121, the lever 120, over the rotary wire of the line to the ca1ling subscribers telephone, back to the central ofiice, over the wire, V and through the relay, VR again to the battery, B. The result is the announcement to the subscriber, by a tone in his receiver, that the called line is busy, he recognizing that tone to have that significance.

Returning to the assumption that the called line had not been found to be busy, and that conversation had ensued, the calling subscriber will restore his telephone to its hook at the close of the conversation. As described with reference to the substation instrument, the rotary and vertical wires will be simultaneously grounded. The relays, VR and RR will be actuated at the same time, connecting together their springs, 104 and 105, with the result that current from the battery, B, will flow through the disconnect magnet, DM springs 105, 104, to and through the wire PD, the wiper, 100, in Fig. 6; the relay, DR to ground at the springs, 92 and 91 of the private magnet, PM, in that figure. The operation of the magnet, DM in Fig. 7, will withdraw its pawls from the shaft, 130, allowing it to return to normal position. The operation of relay, DR, in Fig. 6, which will take place in series with the magnet, DM, in Fig. 7, because the latter is of relatively low resistance, say about 50 ohms, will close its contacts. The result will be current from the battery, B, through the disconnect magnet, DM contacts, 97 and 96, to and through the wire, PD, the wiper, 59, in Fig. 5, the disconnect relay, DR, and the ground through springs 64 and 62, of the private magnet, PM. The relay, DR, although of few turns, will operate in series with the disconnect magnet, DM, of Fig. 6, because the latter is of relatively low resistance, say about 50 ohms. The operation of the magnet, DM and the falling back of the armature, will release the second selector, allowing the shaft to return to normal position. The operation of the relay, DB, in Fig. 5, by closure of its contacts, will permit current to flow from the battery, through the disconnect magnet, DM, to ground at 94 and 95, disconnecting the shaft, 55, as soon as the magnet, DM, is de-energized, and allowing it to return to normal position. The operation of the disconnect magnet, BM in Fig. 5, and DM, in Fig. 6, to break contacts between their springs, 53 and 54, and 101 and 102, respectively, prevents false 0 erations of the vertical and rotary relays, %R and RR, and VR and RR, respectively, and permits the release to be absolute.

The contact closed by the relay, DR, which resulted in the disconnection of the first selector shown in Fig. 5, also permits current to flow from the battery B in Fig. 4 through the magnet DM, the wiper 25, wire D, and the springs 95 and 94 of the relay DR to ground, thus energizing the magnet and releasing the individual selector shown in Fig. 4. This restores the individual selector to its normal position, whereupon its wipers take up their normal contacts, and leave this selector in readiness to be again set in motion by the removal of the subscribers telephone from its hook.

If a called subscriber desires to disconnect his line from that of a calling subscriber at any time, he may do so by making one op eration of his instrument, as if to institute a call, and then hanging up his receiver. The first described motion acts to connect the springs, 7, as shown in Fig. 3, and the second to place a ground upon both the vertical and rotary wires. This by current from the battery, B, (Fig. 7) through the relay, BS, the lever, 120", the contact, 123', the springs, 131 and 125, the wiper, 132, and wire, V, to ground at the subscribers station will energize the relay, BS, and simultaneously over an analogous path will energize the relay, BR' The springs, 111, 112 and 113, will be crossed together, causing current from the battery, B, through the magnet, DM to the ground thus established to operate the magnet, DM, removing the pawls from the'vertical and rotary ratchets of the conductor shaft, 130, restoring it to its normal position through the agency of its spring and gravity.

Should this called subscriber desire to signal a toll operator who had called him through the agency of a built-up trunk, after the manner of a subscribers connection, and upon which trunk at the toll board there existed a signal associated with the rotary wire, such notice might be given by the called subscriber by pressure on his ringing button. This will energize the relay BS, and the springs 111 and 112 could be made to control a local circuit containing a signal or relay at the toll board which will, therefore, be actuated to notify the operator whenever the called subscriber presses his ringing button.

The path of the wires, V and R, to the called subscribers station, is by way of his individual selector, shown in Fig. 8. This is identical with the conditions of the individual selector shown in Fig. 4, but illustrates the path of the connection over the wires, V and R, to the called station.

In further particular reference to the individual selector as shown in Figs. 4 and 8, reference may be had to Figs. 1, 2 and 2, in which are shown in more exact detail the relations of parts.

Fig. 1, shows the assembly of the various elements making up the individual selector switch, and is a plan view. The ofiice of the relays, L and G0, has been described in the foregoing, and for the reason that Fig. 4, shows the circuit relation of these relays with reference to the magnets, RM and DM, and the other circuits involved in the system, connections by wires between the various parts of the selector switch have Ill been omitted from Figs. 1, 2 and 2. The shaft, 38, is carried in bearings formed of or mounted in the arm or bracket, 1-70, and a base, 181; the ratchet wheel, 166, is rigidly attached to the shaft, 38, by means of the screw or pin, 180, through its hub, and in engagement with the shaft. The shaft, 38, further carries the contact wipers, 22 to 27, inclusive. These are formed at their free ends in such manner as to engage the contact pieces yet to 'be described. Discs of rubber, fiber, or other insulating material, 182, separate the contact wipers from each other, and by suitable and usual formation insulate them also from the shaft, 38. By means of the nuts, 187, and the washers, 186, the wipers and their insulating bush ings are held firmly in place so as to be rotated with the shaft, and remain in alignment with each other. The upper end of the shaft, 38, has attached to it a coiled spring, 173, the remaining end of which is attached to the arm or bracket, 170, by means of the stud, 172. The effort of this spring is always to give the shaft, 38, a rotative tendency in a clock-wise direction, as

viewed in Fig. 1. Its motion in this direction is limited by contact of the projection, 167, of the ratchet wheel, 166; with the stud, 168, rising from the base plate, 181. Excess of motion in'the opposite direction by the actuation of the mechanism is limited by the projection, 169, of the ratchet wheel, 166, which in its turn engages the stud, 168.

The arcs of contacts which have been referred to in the description of Fig. 4, are best shown in mechanical detail in Fig. 2, in which the base plate, 181, by means of the studs, 177, carries this portion of the structure, drawn as if viewed, with other parts removed, in the direction of the arrow on the line AA in Fig. 1. The base, 181, carriesthe studs, 177. The plate, 175, is supported on the studs, 177, and the layers of insulating material, 176, supported thereon, include between them the six rows of contact pieces, of which 32, 21, 37, 42,

' 40 and 41,. are respectively the right hand cept the normal one.

pieces as shown in this view. With the exception of the arcs, 43 and 44, all of these contact pieces are of similar slze to the piece, 32, and are so shaped andspaced as to correspond/to the successive positions of contact of the wipers carried by the arm, 38. The arcs, 43 and 44, are of such length as to be engaged by their respective wipers, 26 and 27, when they are in any position ex- The top plate. 39, serves to bind the insulating pieces and the contact pieces in a rigid manner, between itself and the plate, 175, by means of the screws, 174. The whole group of parts forms a rigid unit, which has been referred to in the foregoing as a contact bank.

Referring to Fig. 1, the magnet, RM, controlling the armature, 150, is adapted to rotate the shaft, 38,- The winding of the magnet terminates at the studs, 147 of which there are two. The magnetic circuit is formed of thecore of the magnet, its pole p ece, 149, and armature, 150. The armature, 150, carries at one of its ends the pawl, 162; the latter is pivoted in the end of the armature, 150, and is adapted by the spring, 161, to be held in engagement with one or another toot-h of the ratchet, 166. The other end of the armature, 150, through the agency of the insulating stud, 190, bears upon the spr1ng, 152. The tension of this spring is such as normally to hold the armature, 150, away from the free end of the core of the magnet, and also to maintain the-contact between itself and the spring, 151, this contact being designated, 36. The springs, 151 and 152, separated by the bushmgs, 1523*, 153 and 153, are held in position upon the pole piece, 149, and therefore upon the structure of the magnet by the screws, 154. Actuation of the magnet results in drawing the pawl, 162, out of engagement with a given tooth of the ratchet, 166, and enables it to engage another. At the same time the contact, 36, is broken. Successive actuations of the armature, 150, by interrupted current or by current through its winding and the contact, 36, in series, thus causing interruptions in an otherwise continuous current, will advance the ratchet wheel, 166, tooth by tooth, as it is retained after each stroke by the engagement of the pawl, 165, which prevents its return to normal position. It is to be noted in this connection that it is the release of the armature, 150, which advances the ratchet wheel.

The magnet, DM, is formed similarly to the magnet, RM. Its pole piece, 158, forms with the core and the armature, 191, a magnetic circuit with but one gap. The armature, 191, pivoted to the pole piece'by the pin,-156,- carries at one free end a. pivoted pawl, 159. The spring, 157, attached to the pole piece, 158, bythe screws, 178, serves not only to hold the end of the armature normally away from the core, but to press the pawl, 159, into engagement with the stud, 160, carried by the base plate, 181. Uporf the energization of the core of the magnet, DM, through current entering at the terminals, 147, the pawl, 159, will be caused to engage the hook, 192, of the pawl, 162. Upon the release of the armature, 191, from the attraction of the magnet, the pawl, 162, will be drawn out of engagement with the ratchet wheel, and will, by engagement with the pawl, 165, release the ratchet wheel entirely; and by the action of the spring. 173, the ratchet wheel, the shaft, 38, and the wipers carried by it, will return to normal position, A

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In an automatic telephone system, a central office, a metallic circuit line leading therefrom to a substation, selecting switches at the central station, a switch actuated by taking'u the receiver at the substation to connect t 1e normally disconnected line with an idle selecting switch, and means controlled at the substation to actuate the selecting switch connected with said line.

2. In an automatic telephone system, a central ofiice, a metallic circuit line leading therefrom to a subscribers substation, a plurality of selecting switches, an individual switch for each line, trunk lines interconnecting said individual switch and said se-v lecting switches, and means automatically controlled by taking up the receiver at the substation to actuate said individual selecting switch to connect the calling l1ne with an idle trunk line.

3. In an automatic telephone system a plurality of metallic circuit telephone lines, an individual switch for each of said hnes, a plurality of secondary selecting switches, trunk lines for connecting said secondary selecting mechanism actuated upon the removal ot the receiver from thehook at a substation automatically to connect the switch arm of said individual switch with one of said secondary switches, and means controlled at the subscribers substation for actuating a secondary selecting switch after connection with a calling line.

4. In an automatic telephone system, a metallic circuit telephone line extending from a subscribers substation to a central oflice, selecting switch individual to said telephone line, secondary selecting switches and trunk lines interconnecting said individual switch and said selecting switches, and means whereby a single impulse sent over the line by the actuation of the substation switch-hook may cause the actuation of said individual switch to connect the calling line with an individual trunk line.

5. In an automatic telephone system the combination with a telephone line, of a subscribers substation, a central oiiice connected with said substation by said telephone line, a selecting switch individual to said line, secondary selecting switches, trunk lines leading from said individual selecting switch to said secondary selecting switches, and means automatically controlled by the initial operation of origlnating a call at the substation to actuate said individual selecting switch to connect the calling line with the first idle trunk line.

6. In an automatic telephone exchange system, a central ofiice, a subscribers sub station, a metallic circuit line connecting switches with subscribers lines,

said subscribers station with said central oflice, said line being normally open at the substation, a selecting switch at the central station individual to said line, waiting contacts in said selecting switch, trunk lines leading from said waiting contacts, secondary selecting switches connected with said trunk lines, and automatic mechanism actuated upon the closure of the line circuit at the subscribers substation to connect said individual selecting switch with an idle trunk line.

7. In an automatic telephone system, a. telephone line, contact wipers, aplurality of contact pieces, means adapting said contact wipers to engage said contact pieces, magnets adapted to control the engagement of said contact pieces, a magnet and associated mechanism adapted when said magnet is deenergized to connect said line to said contact wipers and to disconnect said controlling magnets from said line,' said mechanism adapted when the associated ma et is energized to disconnect said line from said wipers and to connect said controlling magnets to said line, substantially as described.

8. In an automatic telephone system, a telephone line, a plurality of contact pieces, telephone lines connected thereto, contact wipers, magnets controlling the making of contacts between said contact wipers and said contact pieces, a magnet and associated mechanism adapted when said magnet is de-energized to connect said line to said contact pieces and to disconnect said controlling magnets from said line, said mechanism adapted when the associated magnet is energized to disconnect said line from said contact pieces and to connect said controlling magnets to said line, and means adapted to energize said magnet when a call is originated on said line, and to de-encrgizc said magnet upon the engagement by said contact wipers of a set of said contact pieces connected to a non-busy line, substantially as described.

9. In a selecting switch for telephone lines, selecting contact pieces, a plurality of waiting contact pieces, lines lading from said waiting contact pieces. means for effecting engagement of said selecting contact pieces with certain of said waiting contact pieces, relays controlling said means for efiecting engagement, conductors connecting said line to said selecting contact pieces, a switch adapted to disconnect said line from the selecting contacts and to connect said line to said controlling relays'during the act of selection and to disconnect said line from said relays and connect it to said selecting contact pieces preliminary to conversation, substantially as described.

10. In an automatic telephone system, a telephone line, selecting contacts, a plurality of waiting contacts, trunk lines leading from said waiting contacts, means for efiecting the successive en agement of said selecting contacts with said waiting contacts, relays controlling said means, and a relay adapted to be energized upon the origination of a call upon said line, and upon such energization to connect said controlling relays to said'line, and

upon de'-energization to disconnect said controlling relays from said line, and to connect said line to said selecting contacts said relay being adapted to become de-energized upon the engagement of'said selecting contacts with the waiting contacts of a non-busy one of said trunk lines, substantially as described. f

11. In an automatic telephone system, a selecting switch, relays controllin said selecting switch, a telephone line, a rel a ed to be energized upon the origination of a call upon said line, and upon such energization to connect said controlling relays to said line, and to be (ls-energized to disconnect said relays from said line upon the selection of idle contacts in said selecting switch, substantially as described.

12. In an automatic telephone exchange system, a telephone line normally terminating in a selector switch at the exchange, means associated with the telephone line for operating such selector switch, and a plurality of circuits so connected to such selector switch that any one of them may be selected and connected to such telephone line by the operation of such selector switch, such selector switch consisting ,in a rotatable shaft. a' ratchet wheel mounted thereon, contact wipers carried by said shaft,}contact pieces adapted to be engaged by such wipers, an actuating magnet, a pawl engaging such ratchet wheel associated with said magnet, a pawl for normally preventing movement of said shaft in one direction, a disconnect magnet, and a catch pawl associated therewith for disengaging said pawls from said ratchet wheel.

13. In an automatic telephone exchange system, a telephone line normally terminating in a selector switch at the exchange, means associated with the telephone line for operating such selector switch, and a plurality of circuits so connected to such selector switch that any one of them may be selected and connected'to such telephone line by the operation of such selector switch, such selector switch consisting in a rotatable shaft, a ratchet wheel mounted thereon, contact wipers carried by said shaft, contact pieces adapted to be engaged by said contact wipers, spring means for drawing said shaft to a normal position, a pawl adapted to engage said ratchet wheel, an actuating magnet for said pawl adapted upon energization to advance said ratchet wheel, a second pawl for normally allowing rotation of said ratchet wheel inbut one direction, a disconnect magnet, and a catch paw'l therefor y adapt- 14. In an automatic telephone exchange It,

system, a telephone line, a rotatable sha contact wipers carried by said shaft, waiting contacts associated with said wipers, electro magnetic mechanism for causing a step by step rotation of said shaft, electromagnetic releasing mechanism, a restoring spring associated with said shaft, a relay associated with said telephone line and adapted to control the actuation of said electromagnetic rotating mechanism, and a switch mechanically actuated by the movement of said shaft {o disconnect said relay from the telephone ine.

15. In a telephone system, a substation telephone and a telephone line normally open therein, a source of current, a rotatable shaft, contact wipers carried thereon, contact pieces normally engaged by said con tact wipers, a relay normally connected to said line through the contact of said contact pieces and contact wipers, means adapting said relay to be energized by the closure of said line in said substation telephone, and to effect the rotation of said shaft, and means adapted to disconnect said relay from said line at the first step of the rotation of said shaft, substantially as described.

16. In a telephone system, a substation telephone and a telephone line normally open therein, a source of current, a lineselector, contact wipers in said selector normally connected to said line, magnets adapted to effect motions in said selector, a relay normally connected to said line and adapted to control one of said magnets, means for establishing motions of selection in said se lector upon the closure of said line in said telephone and for disconnection of said relay from said line at the first of said motions, and for continuing the motion after such disconnection, substantially as described.

17 In a telephone system, a substation telephone and a telephone line normally open therein, an individual selector, contact wipers normally connected to said telephone selector switch at the exchange, means associated with the telephone line for operating such selector switch, and a plurality of circuits so connected to such selector switch that any one of them may be selected and connected to such telephone line b the operation of such selector switch, suc selector switch consisting in a rotatable shaft and contact wipers mounted thereon, a magnet adapted to rotate said shaft, a spring adapted to return said shaft to a normal posltlon, a magnet adapted to effect the release of said shaft for return to a normal position, a switch adapted normally to connect said line to two of said Contact wipers, a magnet adapted to operate said switch to disconnect said line from said wipers during success ve engagements of said contact wipers with said contact pieces, and a relay normally connected to said line and adapted to control the rotation of said shaft and to be disconnected from said line at the first step of the rotation of said shaft.

19. In a telephone exchange. system, the combination with a metallic telephone line normally open at the substation of a trunk circuit at the central office common to a plurality of telephone lines, and a step-by-step rotary switch started upon the closure of the limbs of said telephone line for completing the circuit between said line and said trunk circuit, substantially as described.

20. In a telephone exchange system, the combination with a telephone line extending in two metallic limbs from the exchange to the substation, an idle trunk circuit at the exchange adapted to the use of any one of a plurality of telephone lines, and a stepby-step rotary device having contacts for connecting said trunk circuit and said line together and adapted to be started in rotation upon the completion of the circuit between the limbs of said line at the substation, substantially as described.

21. In a telephone system, the combination with a subscribers station, of a pair of normally open contacts at the subscribers station, closed during conversation to form a path for voice currents, a plurality of trunk circuits at the exchange and a step-by-step automatic selector switch at the central office adapted to be operated to connect said line with an idle trunk circuit when said contacts are closed to initiatea call, substantially as described.

22. In an automatic telephone system, the combination with a telephone line extending in two limbs from a substation to an exchange, of a selector switch at the exchange, a central source of current connected in a bridge of the telephone line through normal contacts of said selector switch, a locking relay in said bridge, said relay being adapted to beinitiall; actuated over the telephone line and thereafter actuated over the various busy contacts of the selector switch, whereby the selector switch is caused to rotate until an idle contact is reached, substantially as described.

23. In a telephonesystem, the combination with a telephone line of a line switch therefor individual to the line, a motor magnet for said line switch, a contact in circuit with the motor magnet and operated by the energization of the motor magnet, and means to complete a circuit through said motor magnet, and contacts for the'operation of said line switch, substantially as described.

2%. A step-by-step signal receiving device having a step-by-step element, a step-up pawl for said element, electromagnetic means to operate said pawl, a holding pawl for said element, both of said pawls being normally disengaged from said element, and both being brought into engagement with said elements upon the first actuation of said electromagnetic means and electromagnetic means to remove said holding pawl and said step-up pawl from said element.

25. In an automatic switch, the combination with a set of movable terminals, of an advancing magnet and a release magnet, a ratchet member attached to said movable contacts, a stepping pawl controlled by the advancing magnet, a retaining pawl adapted to be engaged by said stepping pawl, and a catch member carried by the armature of said release magnet and movable into engagement with said stepping pawl, the retraction of the armature of said release magnet bemg arranged to carry said stepping and retaining pawls out of engagement with said ratchet member.

26. In an automatic switching device, a step-by-step movable member having ratchet teeth thereon, a retaining pawl, an advancmg pawl normally engaging said retaining pawl, and a catch member normally engagmg said advancing pawl whereby the advancing and retaining pawls are both normally held out of engagement with said ratchet teeth, a stepping magnet and armature therefor connected with said advancing pawl, the first movement of said armature being arranged to disengage it from said catch member whereby the advancing and retaining pawls both engage the ratchet wheel teeth and a release magnet controlling the catch member.

27. In a switching device, the combination with movable ratchet teeth of a stepping magnet for controlling the movement of said teeth in one direction, and a release magnet for controlling the movement of said teeth in the other direction, a spring-pressed holding pawl, a spring-pressed stepping pawl having a portion adapted to engage said holding pawl to force the same out of engagement with said ratchet teeth, and a

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