CHAPTER XL

TELEPHONE TRAIN DISPATCHING[A]

It has been only within the past three few that the telephone has begun to replace the telegraph for handling train movements. The telegraph and the railroads have grown up together in this country since 1850, and in view of the excellent results that the telegraph has given in train dispatching and of the close alliance that has always naturally existed between the railway and the telegraph, it has been difficult for the telephone, which came much later, to enter the field.

=Rapid Growth.= The telephone has been in general use among the railroads for many years, but only on a few short lines has it been used for dispatching trains. In these cases the ordinary magneto circuit and instruments have been employed, differing in no respect from those used in commercial service at the present time. Code ringing was used and the number of stations on a circuit was limited by the same causes that limit the telephones on commercial party lines at present.

The present type of telephone dispatching systems, however, differs essentially from the systems used in commercial work, and is, in fact, a highly specialized party-line system, arranged for selective ringing and _many stations_. The first of the present type was installed by the New York Central and Hudson River Railroad in October, 1907, between Albany and Fonda, New York, a distance of 40 miles. This section of the road is on the main line and has four tracks controlled by block signals.

The Chicago, Burlington, and Quincy Railroad was the second to install train-dispatching circuits. In December, 1907, a portion of the main line from Aurora to Mendota, Illinois, a distance of 46 miles, was equipped. This was followed in quick succession by various other circuits ranging, in general, in lengths over 100 miles. At the present time there are over 20 train-dispatching circuits on the Chicago, Burlington, and Quincy Railroad covering 125 miles of double track, 28 miles of multi-track, and 1,381 miles of single track, and connecting with 286 stations.

Other railroads entered this field in quick order after the initial installations, and at the present time nearly every large railroad system in the United States is equipped with several telephone train-dispatching circuits and all of these seem to be extending their systems.

In 1910, several railroads, including the Delaware, Lackawanna, and Western, had their total mileage equipped with telephone dispatching circuits. The Atchison, Topeka, and Santa Fe Railroad is equipping its whole system as rapidly as possible and already is the largest user of this equipment in this country. From latest information, over 55 railroads have entered this field, with the result that the telephone is now in use in railroad service on over 29,000 miles of line.

=Causes of Its Introduction.= The reasons leading to the introduction of the telephone into the dispatching field were of this nature: First, and most important, was the enactment of State and Federal Laws limiting to nine hours the working day of railroad employes transmitting or receiving orders pertaining to the movement of trains. The second, which is directly dependent upon the first, was the inability of the railroads to obtain the additional number of telegraph operators which were required under the provisions of the new laws. It was estimated that 15,000 additional operators would be required to maintain service in the same fashion after the new laws went into effect in 1907. The increased annual expense occasioned by the employment of these additional operators was roughly estimated at $10,000,000. A third reason is found in the decreased efficiency of the average railway and commercial telegraph operator. There is a very general complaint among the railroads today regarding this particular point, and many of them welcome the telephone, because, if for no other reason, it renders them independent of the telegrapher. What has occasioned this decrease in efficiency it is not easy to say, but there is a strong tendency to lay it, in part, to the attitude of the telegraphers' organization toward the student operator. It is a fact, too, that the limits which these organizations have placed on student operators were directly responsible for the lack of available men when they were needed.

=Advantages.= In making this radical change, railroad officials were most cautious, and yet we know of no case where the introduction of the telephone has been followed by its abandonment, the tendency having been in all cases toward further installations and more equipment of the modern type. The reasons for this are clear, for where the telephone is used it does not require a highly specialized man as station operator and consequently a much broader field is open to the railroads from which to draw operators. This, we think, is the most far-reaching advantage.

The telephone method also is faster. On an ordinary train-dispatching circuit it now requires from 0.1 of a second to 5 seconds to call any station. In case a plurality of calls is desired, the dispatcher calls one station after another, getting the answer from one while the next is being called, and so on. By speaking into a telephone many more words may be transmitted in a given time than by Morse telegraphy. It is possible to send fifty words a minute by Morse, but such speed is exceptional. Less than half that is the rule. The gain in high speed, therefore, which is obtained is obvious and it has been found that this is a most important feature on busy divisions. It is true that in the issuance of "orders," the speed, in telephonic train dispatching, is limited to that required to write the words in longhand. But all directions of a collateral character, the receipt of important information, and the instantaneous descriptions of emergency situations can be given and received at a speed limited only by that of human speech.

The dispatcher is also brought into a closer personal relation with the station men and trainmen, and this feature of direct personal communication has been found to be of importance in bringing about a higher degree of co-operation and better discipline in the service.

Telephone dispatching has features peculiar to itself which are important in improving the class of service. One of these is the "answer-back" automatically given to the dispatcher by the waystation bell. This informs the dispatcher whether or not the bell at the station rang, and excuses by the operators that it did not, are eliminated.

Anyone can answer a telephone call in an emergency. The station operator is frequently agent also, and his duties often take him out of hearing of the telegraph sounder. The selector bell used with the telephone can be heard for a distance of several hundred feet. In addition, it is quite likely that anyone in the neighborhood would recognize that the station was wanted and either notify the operator or answer the call.

In cases of emergency the train crews can get into direct communication with the dispatcher immediately, by means of portable telephone sets which are carried on the trains. It is a well-known fact that every minute a main line is blocked by a wreck can be reckoned as great loss to the railroad.

It is also possible to install siding telephone sets located either in booths or on poles along the right-of-way. These are in general service today at sidings, crossings, drawbridges, water tanks, and such places, where it may be essential for a train crew to reach the nearest waystation to give or receive information.

The advantage of these siding sets is coming more and more to be realized. With the telegraph method of dispatching, a train is ordered to pass another train at a certain siding, let us say. It reaches this point, and to use a railroad expression, "goes into the hole." Now, if anything happens to the second train whereby it is delayed, the first train remains tied up at that siding without the possibility of either reaching the dispatcher or being reached by him. With the telephone station at the siding, which requires no operator, this is avoided. If a train finds itself waiting too long, the conductor goes to the siding telephone and talks to the dispatcher, possibly getting orders which will advance him many miles that would otherwise have been lost.

It is no longer necessary for a waystation operator to call the dispatcher. When one of these operators wishes to talk to the dispatcher, he merely takes his telephone receiver off the hook, presses a button, and speaks to the dispatcher.

With the telephone it is a simple matter to arrange for provision so that the chief dispatcher, the superintendent, or any other official may listen in at will upon a train circuit to observe the character of the service. The fact that this can be done and that the operators know it can be done has a very strong tendency to improve the discipline.

The dispatchers are so relieved, by the elimination of the strain of continuous telegraphing, and can handle their work so much more quickly with the telephone, that in many cases it has been found possible to increase the length of their divisions from 30 to 50 per cent.

=Railroad Conditions.= One of the main reasons that delayed the telephone for so many years in its entrance to the dispatching field is that the conditions in this field are like nothing which has yet been met with in commercial telephony. There was no system developed for meeting them, although the elements were at hand. A railroad is divided up into a number of divisions or dispatchers' districts of varying lengths. These lengths are dependent on the density of the traffic over the division. In some cases a dispatcher will handle not more than 25 miles of line. In other cases this district may be 300 miles long. Over the length of one of these divisions the telephone circuit extends, and this circuit may have upon it 5 or 50 stations, _all of which may be required to listen upon the line at the same time_.

It will be seen from this that the telephone dispatching circuit partakes somewhat of the nature of a long-distance commercial circuit in its length, and it also resembles a rural line in that it has a large number of telephones upon it. Regarding three other characteristics, namely, that many of these stations may be required to be in on the circuit simultaneously, that they must all be signaled selectively, and that it must also be possible to talk and signal on the circuit simultaneously, a telephone train-dispatching circuit resembles nothing in the commercial field. These requirements are the ones which have necessitated the development of special equipment.

=Transmitting Orders.= The method of giving orders is the same as that followed with the telegraph, with one important exception. When the dispatcher transmits a train order by telephone, he writes out the order as he speaks it into his transmitter. In this way the speed at which the order is given is regulated so that everyone receiving it can easily get it all down, and a copy of the transmitted order is retained by the dispatcher. All figures and proper names are spelled out. Then after an order has been given, it is repeated to the dispatcher by each man receiving it, and he underlines each word as it comes in. This is now done so rapidly that a man can repeat an order more quickly than the dispatcher can underline. The doubt as to the accuracy with which it is possible to transmit information by telephone has been dispelled by this method of procedure, and the safety of telephone dispatching has been fully established.

=Apparatus.= The apparatus which is employed at waystations may be divided into two groups--the selector equipment and the telephone equipment. The selector is an electro-mechanical device for ringing a bell at a waystation when the dispatcher operates a key corresponding to that station. At first, as in telegraphy, the selector magnets were connected in series in the line, but today all systems bridge the selectors across the telephone circuit in the same way and for the same reasons that it is done in bridging party-line work. There are at the present time three types of selectors in general use, and the mileage operated by means of these is probably considerably over 95 per cent of the total mileage so operated in the country.

_The Western Electric Selector._ This selector is the latest and perhaps the simplest. Fig. 475 shows it with its glass dust-proof cover on, and Fig. 476 shows it with the cover removed. This selector is adapted for operating at high speed, stations being called at the rate of ten per second.

The operating mechanism, which is mounted on the front of the selector so as to be readily accessible, works on the central-energy principle--the battery for its operation, as well as for the operation of the bell used in connection with it, both being located at the dispatcher's office. The bell battery may, however, be placed at the waystation if this is desired.

The selector consists of two electromagnets which are bridged in series across the telephone circuit and are of very high impedance. It is possible to place as many of these selectors as may be desired across a circuit without seriously affecting the telephonic transmission. Direct-current impulses sent out by the dispatcher operate these magnets, one of which is slow and the other quick-acting. The first impulse sent out is a long impulse and pulls up both armatures, thereby causing the pawls above and below the small ratchet wheel, shown in Fig. 476, to engage with this wheel. The remaining impulses operate the quick-acting magnet and step the wheel around the proper number of teeth, but do not affect the slow-acting magnet which remains held up by them. The pawl connected to the slow-acting magnet merely serves to prevent the ratchet wheel from turning back. Attached to the ratchet wheel is a contact whose position can be varied in relation to the stationary contact on the left of the selector with which this engages. This contact is set so that when the wheel has been rotated the desired number of teeth, the two contacts will make and the bell be rung. Any selector may thus be adjusted for any station, and the selectors are thus interchangeable. When the current is removed from the line at the dispatcher's office, the armatures fall back and everything is restored to normal. An "answer-back" signal is provided with this selector dependent upon the operation of the bell. When the selector at a station operates, the bell normally rings for a few seconds. The dispatcher, however, can hold this ring for any length of time desired.

The keys employed at the dispatcher's office for operating selectors are shown in Fig. 477. There is one key for each waystation on the line and the dispatcher calls any station by merely giving the corresponding key a quarter turn to the right. Fig. 478 shows the mechanism of one of these keys and the means employed for sending out current impulses over the circuit. The key is adjustable and may be arranged for any station desired by means of the movable cams shown on the rear in Fig. 478, these cams, when occupying different positions, serving to cover different numbers of the teeth of the impulse wheel which operate the impulse contacts.

_The Gill Selector._ The second type of selector in extensive use throughout the country today is known as the Gill, after its inventor. It is manufactured for both local-battery and central-energy types, the latter being the latest development of this selector. With the local-battery type, the waystation bell rings until stopped by the dispatcher. With the central-energy type it rings a definite length of time and can be held for a longer period as is the case with the Western Electric selector. The selector is operated by combinations of direct-current impulses which are sent out over the line by keys in the dispatcher's office.

The dispatcher has a key cabinet, and calls in the same way as already described, but these keys instead of sending a series of quick impulses, send a succession of impulses with intervals between corresponding to the particular arrangement of teeth in the corresponding waystation selector wheel. Each key, therefore, belongs definitely with a certain selector and can be used in connection with no other.

A concrete example may make this clearer. The dispatcher may operate key No. 1421. This key starts a clockwork mechanism which impresses at regular intervals, on the telephone line, direct-current impulses, with intervals between as follows: 1-4-2-1. There is on the line one selector corresponding to this combination and it alone, of all the selectors on the circuit, will step its wheel clear around so that contact is made and the bell is rung. In all the others, the pawls will have slipped out at some point of the revolution and the wheels will have returned to their normal positions.

The Gill selector is shown in Fig. 479. It contains a double-wound relay which is bridged across the telephone circuit and operates the selector. This relay has a resistance of 4,500 ohms and a high impedance, and operates the selector mechanism which is a special modification of the ratchet and pawl principle. The essential features of this selector are the "step-up" selector wheel and a time wheel, normally held at the bottom of an inclined track.

The operation of the selector magnet pushes the time wheel up the track and allows it to roll down. If the magnet is operated rapidly, the wheel does not get clear down before being pushed back again. A small pin on the side of the pawl, engaging the selector wheel normally, opposes the selector wheel teeth near their outer points. When the time wheel rolls to the bottom of the track, however, the pawl is allowed to drop to the bottom of the tooth. Some of the teeth on the selector wheel are formed so that they will effectually engage with the pawl only when the latter is in normal position, while others will engage only while the pawl is at the bottom position; thus innumerable combinations can be made which will respond to certain combinations of rapid impulses with intervals between. The correct combination of impulses and intervals steps the selector wheel clear around so that a contact is made. The selector wheels at all other stations fail to reach their contact position because at some point or points in their revolution the pawls have slipped out, allowing the selector wheels to return "home."

The "answer-back" is provided in this selector by means of a few inductive turns of the bell circuit which are wound on the selector relay. The operation of the bell through these turns induces an alternating current in the selector winding which flows out on the line and is heard as a distinctive buzzing noise by the dispatcher.

_The Cummings-Wray Selector._ Both of the selectors already described are of a type known as the _individual-call_ selectors, meaning that only one station at a time can be called. If a plurality of calls is desired, the dispatcher calls one station after another. The third type of selector in use today is of a type known as the _multiple-call_, in which the dispatcher can call simultaneously as many stations as he desires.

The Cummings-Wray selector and that of the Kellogg Switchboard and Supply Company are of this type and operate on the principle of synchronous clocks. When the dispatcher wishes to put through a call, he throws the keys of all the stations that he desires and then operates a starting key. The bells at all these stations are rung by one operation.

The dispatcher's sending equipment of the Cummings-Wray system is shown in Fig. 480, and the waystation selector in Fig. 481. It is necessary with this system for the clocks at all stations to be wound every eight days.

In the dispatcher's master sender the clock-work mechanism operates a contact arm which shows on the face of the sender in Fig. 480. There is one contact for every station on the line. The clock at this office and the clocks at all the waystation offices start together, and it is by this means that the stations are signaled, as will be described later, when the detailed operation of the circuits is taken up.

=Telephone Equipment.= Of no less importance than the selective devices is the telephone apparatus. That which is here illustrated is the product of the Western Electric Company, to whom we are indebted for all the illustrations in this chapter.

_Dispatcher's Transmitter._ The dispatcher, in most cases, uses the chest transmitter similar to that employed by switchboard operators in every-day service. He is connected at all times to the telephone circuit, and for this reason equipment easy for him to wear is essential. In very noisy locations he is equipped with a double head receiver. On account of the dispatcher being connected across the line permanently and of his being required to talk a large part of the time, there is a severe drain on the transmitter battery. For this reason storage batteries are generally used.

_Waystation Telephones._ At the waystations various types of telephone equipment may be used. Perhaps the most common is the familiar desk stand shown in Fig. 482, which, for railroad service, is arranged with a special hook-switch lever for use with a head receiver.

Often some of the familiar swinging-arm telephone supports are used, in connection with head receivers, but certain special types developed particularly for railway use are advantageous, because in many cases the operator who handles train orders is located in a tower where he must also attend to the interlocking signals, and for such service it is necessary for him to be able to get away from the telephone and back to it quickly. The Western Electric telephone arm developed for this use is shown in Fig. 483. In this the transmitter and the receiver are so disposed as to conform approximately to the shape of the operator's head. When the arm is thrown back out of the way it opens the transmitter circuit by means of a commutator in its base.

_Siding Telephones._ Two types of sets are employed for siding purposes. The first is an ordinary magneto wall instrument, which embodies the special apparatus and circuit features employed in the standard waystation sets. These are used only where it is possible to locate them indoors or in booths along the line. These sets are permanently connected to the train wire, and since the chances are small that more than one of them will be in use at a time, they are rung by the dispatcher, by means of a regular hand generator, when it is necessary for him to signal a switching.

In certain cases it is not feasible to locate these siding telephone sets indoors, and to meet these conditions an iron weather-proof set is employed, as shown in Figs. 484 and 485. The apparatus in this set is treated with a moisture-proofing compound, and the casing itself is impervious to weather conditions.

_Portable Train Sets._ Portable telephone sets are being carried regularly on wrecking trains and their use is coming into more and more general acceptance on freight and passenger trains. Fig. 486 shows one of these sets equipped with a five-bar generator for calling the dispatcher. Fig. 487 shows a small set without generator for conductors' and inspectors' use on lines where the dispatcher is at all times connected in the circuit.

These sets are connected to the telephone circuit at any point on the line by means of a light portable pole arranged with terminals at its outer extremity for hooking over the line wires, and with flexible conducting cords leading to the portable set. The use of these sets among officials on their private cars, among construction and bridge gangs working on the line, and among telephone inspectors and repairmen for reporting trouble, is becoming more and more general.

=Western Electric Circuits.= As already stated, a telephone train-dispatching circuit may be from 25 to 300 miles in length, and upon this may be as many stations as can be handled by one dispatcher. The largest known number of stations upon an existing circuit of this character is 65.

_Dispatcher's Circuit Arrangement._ The circuits of the dispatcher's station in the Western Electric system are shown in Fig. 488, the operation of which is briefly as follows: When the dispatcher wishes to call any particular station, he gives the key corresponding to that station a quarter turn. This sends out a series of rapid direct-current impulses on the telephone line through the contact of a special telegraph relay which is operated by the key in a local circuit. The telegraph relay is equipped with spark-eliminating condensers around its contacts and is of heavy construction throughout in order to carry properly the sending current.

_Voltage._ The voltage of the sending battery is dependent on the length of the line and the number of stations upon it. It ranges from 100 to 300 volts in most cases. When higher voltages are required in order successfully to operate the circuit, it is generally customary to install a telegraph repeater circuit at the center of the line, in order to keep the voltage within safe limits. One reason for limiting the voltage employed is that the condensers used in the circuit will not stand much higher potentials without danger of burning out. It is also possible to halve the voltage by placing the dispatcher in the center of the line, from which position he may signal in two directions instead of from one end.

_Simultaneous Talking and Signaling._ Retardation coils and condensers will be noticed in series with the circuit through which the signaling current must pass before going out on the line. These are for the purpose of absorbing the noise which is caused by high-voltage battery, thus enabling the dispatcher to talk and signal simultaneously. The 250-ohm resistance connected across the circuit through one back contact of the telegraph relay absorbs the discharge of the 6-microfarad condenser.

=Waystation Circuit.= The complete selector set for the waystations is shown in Fig. 489, and the wiring diagram of its apparatus in Fig. 490. The first impulse sent out by the key in the dispatcher's office is a long direct-current impulse, the first tooth being three or four times as wide as the other teeth. This impulse operates both magnets of the selector and attracts their armatures, which, in turn, cause two pawls to engage with the ratchet wheel, while the remaining quick impulses operate the "stepping-up" pawl and rotate the wheel the requisite number of teeth. Retardation coils are placed in series with the selector in order to choke back any lightning discharges which might come in over the line. The selector contact, when operated, closes a bell circuit, and it will be noted that both the selector and the bell are operated from battery current coming over the main line through variable resistances. There are, of course, a number of selectors bridged across the circuit, and the variable resistance at each station is so adjusted as to give each approximately 10 milliamperes, which allows a large factor of safety for line leakage in wet weather. The drop across the coils at 10 milliamperes is 38 volts. If these coils were not employed, it is clear that the selectors nearer the dispatcher would get most of the current and those further away very little.

A time-signal contact is also indicated on the selector-circuit diagram of Fig. 490. This is common to all offices and may be operated by a special key in the dispatcher's office, thereby enabling him to send out time signals over the telephone circuit.

=Gill Circuits.= The circuit arrangement for the dispatcher's outfit of the Gill system is shown in Fig. 491. This is similar to that of the Western Electric system just described. The method of operation also is similar, the mechanical means of accomplishing the selection being the main point of difference. In Fig. 492 the wiring of the Gill selector at a waystation for local-battery service is shown. The selector contact closes the bell circuit in the station and a few windings of this circuit are located on the selector magnets, as shown. These provide the "answer-back" by inductive means.

Fig. 493 shows the wiring of the waystation, central-energy Gill selector. In this case, the local battery for the operation of the bell is omitted and the bell is rung, as is the case of the Western Electric selector, by the main sending battery in the dispatcher's office.

The sending keys of these two types of circuits differ, in that with the local-battery selector the key contact is open after the selector has operated, and the ringing of the bell must be stopped by the dispatcher pressing a button or calling another station. Either of these operations sends out a new current impulse which releases the selector and opens its circuit.

With the central-energy selector, however, the contacts of the sending key at the dispatcher's office remain closed after operation for a definite length of time. This is obviously necessary in order that battery may be kept on the line for the operation of the bell. In this case the contacts remain closed during a certain portion of the revolution of the key, and the bell stops ringing when that portion of the revolution is completed. If, however, the dispatcher desires to give any station a longer ring, he may do so by keeping the key contacts closed through an auxiliary strap key as soon as he hears the "answer-back" signal from the called station.

=Cummings-Wray Circuits.= The Cummings-Wray system, as previously stated, is of the multiple-call type, operating with synchronous clocks. Instead of operating one key after another in order to call a number of stations, all the keys are operated at once and a starting key sets the mechanism in motion which calls all these stations with one operation. Fig. 494 shows the circuit arrangement of this system.

In order to ring one or more stations, the dispatcher presses the corresponding key or keys and then operates the starting key. This starting key maintains its contact for an appreciable length of time to allow the clock mechanism to get under way and get clear of the releasing magnet clutch. Closing the starting key operates the clock-releasing magnet and also operates the two telegraph-line relays. These send out an impulse of battery on the line operating the bridged 2,500-ohm line relays and, in turn, the selector releasing magnets; thus, all the waystation clocks start in unison with the master clock. The second hand arbor of each clock carries an arm, which at each waystation is set at a different angle with the normal position than that at any other station. Each of these arms makes contact precisely at the moment the master-clock arm is passing over the contact corresponding to that station.

If, now, a given station key is pressed in the master sender, the telegraph-line relays will again operate when the master-clock arm reaches that point, sending out another impulse of battery over the line. The selector contact at the waystation is closed at this moment; therefore, the closing of the relay contact operates the ringing relay through a local circuit, as shown. The ringing relay is immediately locked through its own contact, thus maintaining the bell circuit closed until it is opened by the key and the ringing is stopped.

As the master-clock arm passes the last point on the contact dial, the current flows through the restoring relay operating the restoring magnet which releases all the keys. A push button is provided by means of which the keys may be manually released, if desired. This is used in case the dispatcher presses a key by mistake. Retardation coils and variable resistances are provided at the waystation just as with the other selector systems which have been described and for the same reasons.

The circuits of the operator's telephone equipment shown in Fig. 495, are also bridged across the line. This apparatus is of high impedance and of a special design adapted to railroad service. There may be any number of telephones listening in upon a railroad train wire at the same time, and often a dispatcher calls in five or six at once to give orders. These conditions have necessitated the special circuit arrangement shown in Fig. 495.

The receivers used at the waystations are of high impedance and are normally connected, through the hook switch, directly across the line in series with a condenser. When the operator, at a waystation wishes to talk, however, he presses the key shown. This puts the receiver across the line in series with the retardation coil and in parallel with the secondary of the induction coil. It closes the transmitter battery circuit at the same time through the primary of the induction coil.

The retardation coil is for the purpose of preventing excessive side tone, and it also increases the impedance of the receiver circuit, which is a shunt on the induction coil. This latter coil, however, is of a special design which permits just enough current to flow through the receiver to allow the dispatcher to interrupt a waystation operator when he is talking.

The key used to close the transmitter battery is operated by hand and is of a non-locking type. In some cases, where the operators are very busy, a foot switch is used in place of this key. The use of such a key or switch in practical operation has been found perfectly satisfactory, and it takes the operators but a short time to become used to it.

The circuits of the dispatcher's office are similarly arranged, Fig. 495, being designed especially to facilitate their operation. In other words, as the dispatcher is doing most of the work on the circuit, his receiver is of a low-impedance type, which gives him slightly better transmission than the waystations obtain. The key in his transmitter circuit is of the locking type, so that he does not have to hold it in while talking. This is for the reason that the dispatcher does most of the talking on this circuit. Foot switches are also employed in some cases by the dispatchers.

=Test Boards.= It is becoming quite a general practice among the railroads to install more than one telephone circuit along their rights-of-way. In many cases in addition to the train wire, a message circuit is also equipped, and quite frequently a block wire also operated by telephone, parallels these two. It is desirable on these circuits to be able to make simple tests and also to be able to patch one circuit with another in cases of emergency.

Test boards have been designed for facilitating this work. These consist of simple plug and jack boxes, the general appearance of which is shown in Fig. 496. The circuit arrangement of one of these is shown in Fig. 497. Each wire comes into an individual jack as will be noted on one side of the board, and passes through the inside contact of this jack, out through a similar jack on the opposite side. The selector and telephone set at an office are taken off these inside contacts through a key, as shown. The outside contacts of this key are wired across two pairs of cords. Now, assume the train wire comes in on jacks _1_ and _3_, and the message wire on jacks _9_ and _11_. In case of an accident to the train wire between two stations, it is desirable to patch this connection with a message wire in order to keep the all-important train wire working. The dispatcher instructs the operator at the last station which he can obtain, to insert plugs _1_ and _2_ in jacks _1_ and _10_, and plugs _3_ and _4_ in jacks _3_ and _12_, at the same time throwing the left-hand key. Then, obtaining an operator beyond the break by any available means, he instructs him likewise to insert plugs _1_ and _2_ in jacks _9_ and _2_, and plugs _3_ and _4_ in jacks _11_ and _4_, similarly throwing the left-hand key. By tracing this out, it will be observed that the train wire is patched over the disabled section by means of the message circuit, and that the selector and the telephone equipment are cut over on to the patched connections; in other words, bridged across the patching cords.

It will also be seen that with this board it is possible to open any circuit merely by plugging into a jack. Two wires can be short-circuited or a loop made by plugging two cords of corresponding colors into the two jacks. A ground jack is provided for grounding any wire. In this way, a very flexible arrangement of circuits is obtained, and it is possible to make any of the simple tests which are all that are usually required on this type of circuit.

=Blocking Sets.= As was just mentioned, quite frequently in addition to train wires and message circuits, block wires are also operated by telephone. In some cases separate telephone instruments are used for the blocking service, but in others the same man handles all three circuits over the same telephone. The block wire is generally a converted telegraph wire between stations, usually of iron and usually grounded. It seldom ranges in length over six miles.

Where the block wires are operated as individual units with their own instruments, it is unnecessary to have any auxiliary apparatus to be used in connection with them. Where, however, they are operated as part of a system and the same telephone is used on these that is used on the train wire and message wire, additional apparatus, called a blocking set, is required. This blocking set, shown in Figs. 498 and 499, was developed especially for this service by the Western Electric Company. As will be noted, a repeating coil at the top and a key on the front of the set are wired in connection with a pair of train wire cords. This repeating coil is for use in connecting a grounded circuit to a metallic circuit, as, for instance, connecting a block wire to the train wire, and is, of course, for the purpose of eliminating noise. Below the key are three combined jacks and signals. One block wire comes into each of these and a private line may be brought into the middle one. When the next block rings up, a visual signal is displayed which operates a bell in the office by means of a local circuit. The operator answers by plugging the telephone cord extending from the bottom of the set into the proper jack. This automatically restores the signal and stops the bell.

Below these signals appear four jacks. One is wired across the train wire; one across the message wire; and the other two are bridged across the two pairs of patching cords on each side of the set. The operator answers a call on any circuit by plugging his telephone cord into the proper jack.

If a waystation is not kept open in the evening, or the operator leaves it for any reason and locks up, he can connect two blocks together by means of the block-wire cords. These are arranged simply for connecting two grounded circuits together and serve to join two adjacent blocks, thereby eliminating one station. A jack is wired across these cords, so that the waystation operator can listen in on the connection if he so desires.

In some cases not only are the telephone circuits brought into the test board, but also two telegraph wires are looped through this board before going to the peg switchboard. This is becoming quite a frequent practice and, in times of great emergency, enables patches to be made to the telegraph wires as well as to the telephone wires.

=Dispatching on Electric Railways.= As interurban electric railways are becoming more extended, and as their traffic is becoming heavier, they approximate more closely to steam methods of operation. It is not unusual for an electric railway to dispatch its cars exactly as in the case of a steam road. There is a tendency, however, in this class of work, toward slightly different methods, and these will be briefly outlined.

On those electric railways where the traffic is not especially heavy, an ordinary magneto telephone line is frequently employed with standard magneto instruments. In some cases the telephone sets are placed in waiting rooms or booths along the line of the road. In other cases it is not feasible to locate the telephone indoors and then iron weather-proof sets, such as are shown in Figs. 484 and 485, are mounted directly on the poles along the line of railway. With a line of this character there is usually some central point from which orders are issued and the trainmen call this number when arriving at sidings or wherever they may need to do so.

Another method of installing a telephone system upon electric railways is as follows: Instead of instruments being mounted in booths or on poles along the line, portable telephone sets are carried on the cars and jacks are located at regular intervals along the right-of-way on the poles. The crew of the car wishing to get in touch with the central office or the dispatcher, plugs into one of these jacks and uses the portable telephone set. At indoor stations, in offices or buildings belonging to the railroad, the regular magneto sets may be employed, as in the first case outlined.

On electric railway systems where the traffic is heavy, the train or car movements may be handled by a dispatcher just as on the steam railroad. There is usually one difference, however. On a steam road, the operators who give the train crews their orders and manipulate the semaphore signals are located at regular intervals in the different waystations. No such operators are usually found on electric railways, except, perhaps, at very important points, and, therefore, it is necessary for the dispatcher to be able to signal cars at any point and to get into communication with the crews of these cars. He does this by means of semaphores operated by telephone selectors over the telephone line. The telephone circuit may be equipped with any number of selectors desired, and the dispatcher can operate any particular one without operating any other one on the circuit. Each selector, when operated, closes a pair of contacts. This completes a local circuit which throws the semaphore arm to the "danger" position, at the same time giving the dispatcher a distinctive buzz in his ear, which informs him that the arm has actually moved to this position. He can get this signal only by the operation of the arm.

Each semaphore is located adjacent to a telephone booth in which is also placed the restoring lever, by means of which the semaphore is set in the "clear" position by the crew of the car which has been signaled. The wall-type telephone set is usually employed for this class of service, but if desired, desk stands or any of the various transmitter arms may be used.

It is necessary for the crew of the car which first approaches a semaphore set at "danger," to get out, communicate with the dispatcher, and restore the signal to the "clear" position. The dispatcher can not restore the signal. The signal is set only in order that the train crew may get into telephonic communication with the dispatcher, and in order to do this, it is necessary for them to go into the booth in any case.

[Footnote A: We wish particularly to acknowledge the courtesy of the Western Electric Company in their generous assistance in the preparation of this chapter.]

REVIEW QUESTIONS

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 11--68

* * * * *

1. What are the advantages of a common-battery system?

2. When is the local battery to be preferred to the common-battery?

3. Enumerate the different kinds of line signals.

4. Make a diagram of the arrangement of a direct line lamp signal.

5. What is a direct line lamp with ballast? Give sketch.

6. Describe a line lamp with relay.

7. What is a pilot lamp and what are its functions?

8. Sketch three different kinds of batteries applied to cord circuits.

9. What is a supervisory signal?

10. Make diagram of a complete simple common-battery switchboard circuit.

11. When will the supervisory signal become operative?

12. What is the candle-power of incandescent lamps used for line and supervisory signals?

13. At what voltages do they operate?

14. What are visual signals?

15. Describe the mechanical signal of the Western Electric Company.

16. Give a short description of the general assembly of the parts of a simple common-battery switchboard.

17. What is a transfer switchboard?

18. Outline the limitations of a simple switchboard.

19. Describe and sketch a plug-ended transfer line.

20. Why is the plug-seat switch not more widely adopted for use?

21. Make diagram of an order-wire arrangement.

22. What are the limitations of the transfer system?

23. What are the fundamental features of the multiple switchboard?

24. What is a multiple jack?

25. What is an answering jack?

26. Make a diagram showing the principle of multiple switchboards.

27. What is the busy signal?

28. What determines the size of a multiple switchboard?

29. What is the use of the intermediate distributing frame?

30. Make diagram of the series magneto multiple switchboard and describe its operation.

31. What are the defects of this system?

32. Give a diagram of the branch terminal magneto multiple switchboard.

33. Give a diagram and a short description of the Monarch magneto multiple switchboard.

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 69--134

* * * * *

1. Sketch and describe the line circuit of the common-battery multiple switchboard of the Bell companies.

2. Make a diagram of the cord circuit of the Western Electric standard multiple common-battery switchboard.

3. Describe the busy test in this system.

4. What is the function of the order-wire circuits?

5. What is jumper wire?

6. Give a short description of the relay mounting in the standard No. 1 relay board of the Western Electric Company.

7. What is the ultimate capacity of the No. 1 Western Electric switchboard?

8. What is the capacity of the No. 10 Western Electric switchboard?

9. How does this switchboard No. 10 differ from No. 1?

10. Give a diagram of the two-wire line circuit of the Kellogg Company.

11. What is the capacity of the condenser of the cord circuit in the foregoing system?

12. Give a complete diagram of the Kellogg two-wire board.

13. Describe the busy test in this system.

14. Give diagram of the Stromberg-Carlson multiple-board circuit.

15. What is the most important piece of apparatus in a multiple switchboard?

16. What is the spacing of the multiple jacks in the No. 1 Western Electric switchboard?

17. How do the relays of the Western Electric Company differ from those of other companies?

18. Describe the relay construction of the Monarch Telephone Company.

19. What is meant by inter-office trunking?

20. What is the present practice in America as to the capacity of multiple hoards?

21. What is the tendency in Europe regarding the capacity of multiple boards?

22. Discuss the preferences in American practice.

23. State the different methods of trunking between exchanges.

24. When are two-way trunks employed?

25. Make diagram of the Western Electric inter-office connection system.

26. Describe the standard four-party line trunk ringing key of the Western Electric Company.

27. Sketch and describe a keyless trunk.

28. Give diagram of the inter-office connection of the Kellogg system.

29. How does this system differ from the Western Electric in regard to the ringing?

30. Why are the A and B switchboards in large exchanges entirely separated?

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 135--226

* * * * *

1. What is the general object of automatic telephone systems?

2. What are the common arguments against these systems and how are they met?

3. Give the operations that the calling subscriber has to go through in any one of the successful systems.

4. During calling what is happening at the central office?

5. Describe the action of the Strowger or Automatic Electric Company selecting switch.

6. What is the function of a line switch?

7. Describe the Strowger scheme of trunking and illustrate its action by diagram.

8. Make a diagram of the sub-station apparatus and connections.

9. Make a diagram of the line switch unit.

10. Describe the action of the various guarding features necessary to protect a busy line.

11. Make a simple diagram of the circuits of the first selector.

12. Give the functions and operations of the connector.

13. Give a diagram of connecting circuits.

14. Tell all you can regarding the battery supply to the connected subscriber.

15. How are subscribers disconnected after they are through talking?

16. Describe a multi-office system.

17. Give a diagram of circuits of the trunk repeater.

18. Make a complete diagram of the connections between a calling and a called subscriber in an automatic system.

19. What is the rotary connector?

20. Describe the sub-station equipment of the Lorimer automatic system.

21. Describe the Lorimer central-office apparatus.

22. Give a description of the progress of a call from its institution to the final disconnection in the Lorimer system.

23. What is the automanual system?

24. Give general features of the operation in the automanual system.

25. Describe the automanual system subscribers' apparatus.

26. Give a description of the automanual central-office equipment.

REVIEW QUESTIONS

ON SUBJECT OF TELEPHONY

PAGES 227--270

* * * * *

1. What kinds of currents are employed?

2. What types of power plants are used?

3. Describe the sources of current supplied for the operator's transmitter current and ringing current.

4. Make a diagram of the Warner pole changer.

5. Make a diagram of pole changers for harmonic ringing.

6. What is a multi-cyclic generator set?

7. Make a diagram of governor for harmonic ringing generators.

8. Describe the various primary sources of power.

9. Make a diagram of the mercury-arc-rectifier circuits.

10. What provision against breakdown is made?

11. Tell all you can about the storage battery--its construction and its operation.

12. What is a pilot cell?

13. Describe the switches, meters, and protective devices used on the power switchboard.

14. Give a diagram showing a typical example of a common-battery manual switchboard equipment and circuits.

15. Give the main points concerning the construction of a central-office building.

16. What provision should be made for cable runways?

17. Make a sketch of a small central-office floor plan.

18. Describe the Western Electric main and intermediate frames. Give diagrams.

19. Give principal points regarding small office terminal apparatus.

20. Give types of line circuits.

21. Describe the typical equipment of a large manual office. Give floor plans.

22. Give floor plan of an automatic office.

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 271--320

* * * * *

1. What is a private-branch exchange?

2. What does "P. B. X." mean?

3. What is the function of the private-branch exchange operator?

4. Describe the key type of a small private-branch exchange switchboard.

5. Describe the different methods of supervision of private-branch connections.

6. Describe the automatic equipment of the common-battery type in private-branch exchanges.

7. How is secrecy of individual lines obtained in a private-exchange equipment?

8. What is an intercommunicating system?

9. Sketch a magneto intercommunicating system.

10. Sketch and describe a plug type common-battery intercommunicating system.

11. Sketch and describe the action of the push button in the Monarch system and in the Western Electric system.

12. Sketch and describe the Monarch intercommunicating system.

13. What is the office of the junction box in this system?

14. What is a long-distance message?

15. What is the function of the repeating coil in the long-distance line?

16. Which is the simplest form of long-distance switch?

17. What is a phantom circuit?

18. Under what control is the ringing of the subscriber in long-distance calls?

19. What is meant by ticket passing?

20. What particular advantage has a common-battery set on long-distance lines?

21. Give a typical load curve for telephone traffic.

22. Why is traffic a study of importance?

23. State the function of the intermediate distributing frame.

24. State the different methods of traffic study.

25. What is the trunking factor?

26. Define _trunking efficiency_.

27. Enumerate some of the elements upon which the quality of service in a manual system depends.

28. What is team work?

29. How does the cost of telephone service vary?

30. What two general methods of charging for telephone service are in use?

31. Describe a calculagraph and how is it used?

32. How are toll connections timed by the Monarch Telephone Company?

33. Sketch and describe the Western Electric Company line circuit and service meter.

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 321--358

* * * * *

1. Describe a phantom circuit with diagram.

2. Explain how two phantoms may be joined by a physical circuit.

3. Which are the better, phantom or physical circuits, and why?

4. Explain how the simplex circuit differs from the phantom telephone circuit.

5. Why are not telegraph wires as serviceable for telephone work as telephone wires are for telegraph work?

6. Give the names of the different parts of a railway composite set and explain method of operating.

7. State the causes of the introduction of the telephone into the train dispatching field and explain the advantages it has over the telegraph for this work.

8. In transmitting orders for train dispatching, how are mistakes avoided?

9. Describe the Western Electric selector and explain its use.

10. In what way does the Gill selector differ from the Western Electric?

11. What special feature does the multiple coil selector possess?

12. What special arrangement is provided for the train dispatcher in noisy locations?

13. How can a man on a wrecking train get connection with the train dispatcher?

14. What is the usual limit in length of a telephone train dispatching circuit and what is the largest number of stations at present existing on such a circuit?

15. What is the voltage of the sending battery for a train dispatcher's circuit and upon what is it dependent?

16. For what purpose is a repeater circuit used?

17. How is the noise caused by a high voltage battery absorbed so that the dispatcher may talk and signal simultaneously?

18. Draw a diagram showing the circuit arrangement for the dispatcher's outfit of the Gill system.

19. Explain fully the purpose of the retardation coil in connection with a waystation set.

20. In case of accident to a train wire between two stations, how can the connection be patched if the road is also equipped with a message circuit in addition to the train wire?

21. Why do some railroads have block wires in addition to train wires and message circuits?

22. If a waystation on a block wire is to be cut out for any length of time, by what method can the two adjacent blocks be connected, eliminating the station between?

23. What are some of the methods used for dispatching on electric railways where the traffic is not especially heavy?

24. On an electric road in case a car approaches a semaphore set at "danger," what must the crew of the car do?

INDEX

_The page numbers of this volume will be found at the bottom of the pages; the numbers at the top refer only to the section._

A

Automanual system 218 automatic distribution of calls 223 automatic switching equipment 222 building up a connection 224 characteristics of 218 operation 219 operator's equipment 220 setting up a connection 224 speed in handling calls 224 subscriber's apparatus 219

Automatic desk stand 158

Automatic Electric Company's telephone system 149 automatic sub-offices 201 connector 185 function of 185 location of 186 operation of 186 first selector operation 179 function of line switch 152 line switch 153, 163 bridge cut-off 173 circuit operations 167 guarding functions 173 line and trunk contacts 164 locking segment 172 master switch 171 relation of, to connectors 174 structure of 166 summary of operation 174 trunk ratio 165 trunk selection 165 multi-office system 196 party lines 202 release after conversation 196 rotary connector 202 second selector operation 182 selecting switches 153, 175 release mechanism 178 side switch 175 subdivision of subscribers' lines 152 subscribers' station apparatus 158 operation 160 bell and transmitter springs 160 ground springs 160 impulse springs 161 release springs 163 ringing springs 163 salient points 163 trunking 154 connector action 157 first selector action 156 line switch action 154 second selector action 156 two-wire automatic systems 203 two-wire and three-wire systems 157 underlying feature of trunking system 153

Automatic telephone systems 135 arguments against 135 attitude of public 141 complexity 136 expense 140 flexibility 140 subscriber's station equipment 142 automatic vs. manual 143 comparative costs 142 definition 135 methods of operation 143 fundamental idea 147 grouping of subscribers 145 local and inter-office trunks 148 Lorimer system 144 magnet vs. power-driven switches 144

Automatic telephone systems methods of operation multiple vs. trunking 145 outline of action 146 Strowger system 143 testing 148 trunking between groups 145

Automatic wall set 158

B

Blocking sets 355

Busy test 48 busy-test faults 50 potential of test thimbles 49 principle 49

C

Circuits 321 applications 322 composite 326 phantom 321 transmission over 324 transpositions 323 railway composite 327 ringing 327 simplex 324

Common-battery multiple switchboard 69 assembly 106 Dean multiple board 93 cord circuit 94 line circuit 93 listening key 94 ringing keys 94 test 94 Kellogg two-wire multiple board 84 battery feed 88 busy test 90 complete cord and line circuit 88 cord circuit 86 line circuit 85 summary of operation 91 supervisory signals 87 wiring of line circuit 92 multiple switchboard apparatus 97 jacks 99 lamp jacks 100 relays 101 Stromberg-Carlson multiple board 96 cord circuit 96 supervisory signals 97 test 97 Western Electric No. 1 relay board 69 capacity range 80 cord circuit 71 functions of distributing frames 77 line circuit 69 modified relay windings 79 operation 72 operator's circuit detail 75 order-wire circuits 78 pilot signals 79 relay mounting 80 testing--called line busy 75 testing--called line idle 74 wiring of line circuit 76 Western Electric No. 10 board 80 circuits 81 economy 84 operation 83 test 83

Common-battery switchboard 11 advantages of operation 11 common battery vs. magneto 12 cord circuit 20 battery supply 20 complete circuit 21 supervisory signals 21 cycle of operations 23 jacks 30 lamps 24 mounting 25 line signals 14 direct-line lamp 14 direct-line lamp with ballast 15 line lamp with relay 17 pilot signals 17 mechanical signals 27 Kellogg 28 Monarch 28 Western Electric 27 relays 28 switchboard assembly 31

Composite circuits 326

Connector 185

Cord circuit 20

Cord circuit battery supply 20 complete circuit 21 supervisory signals 21

Cord-rack connectors 66

Cummings-Wray selector 342

D

Dean multiple board 93

Dispatchers' keys 339

Dispatching on electric railways 356

G

Gill selector 341

H

Housing central-office equipment 249 arrangement of apparatus in small manual offices 252 combined main and intermediate frames 253 floor plans for 252 types of line circuits 255 automatic offices 267 typical automatic office 270 central-office building 249 fire hazard 249 provision for cable runways 251 provision for employes 251 size of building 250 strength of building 250 large manual office 256

I

Intercommunicating systems 282 common-battery systems 283 Kellogg plug type 284 Kellogg push-button type 285 Monarch system 287 Western Electric system 285 definition 282 limitations 282 for private-branch exchanges 290 simple magneto system 282

J

Jacks 30

K

Kellogg mechanical signal 28

Kellogg trunk circuits 125

Kellogg two-wire multiple board 84

Keyboard wiring 67

L

Lamp mounting 25

Lamps 24

Line signals 14 direct-line lamp 14 direct-line lamp with ballast 15 line lamp with relay 17 pilot signals 17

Line switch 163

Long-distance switching 293 definitions 293 center-checking 297 operators' orders 294 by call circuits 294 by telegraph 294 particular party calls 295 switching through local board 293 ticket passing 296 trunking 295 high-voltage toll trunks 295 through ringing 295 two-number calls 294 use of repeating coil 293 waystations 297

Lorimer automatic system 144, 205 central-office apparatus 208 connective division 210 sectional apparatus 209 switches 213 interconnector 214 interconnector selector 214 primary connector 213 rotary switch 213 secondary connector 214 signal transmitter controller 214 operation 215 subscriber's station equipment 206

M

Magneto multiple switchboard 53 branch-terminal multiple board 58 arrangement of apparatus 61 magnet windings 61 operation 60 field of utility 53 modern magneto multiple board 63 assembly 66 cord circuit 64 test 62

Magneto multiple switchboard series-multiple board 54 defects 57 operation 56

Measured service 310 local service 316 meter method 316 prepayment method 318 ticket method 316 rates 310 toll service 311 long haul 311 short haul 311 timing toll connections 312 units of charging 311

Mechanical signals 27 Kellogg 28 Monarch 28 Western Electric 27

Mercury-arc rectifier circuits 237

Monarch visual signal 28

Multi-office exchanges, necessity for 109

Multiple switchboard 43 busy test 48 cord circuits 46 diagram showing principle of 47 double connections 46 field of each operator 51 field of utility 43 influence of traffic 52 line signals 45 multiple feature 43

P

Phantom circuit 321

Pilot signals 17

Plug-seat switch 38

Pole changers for harmonic ringing 231

Power plants 227 auxiliary signaling currents 233 currents employed 227 alternating current 227 direct current 227 operator's transmitter supply 228 power plant circuit 248 power switchboard 246 meters 246 protective devices 248 switches 246 primary sources 234 charging from direct-current mains 234 charging dynamos 235 mercury-arc rectifiers 236 rotary converters 234 provision against breakdown 237 capacity of power units 238 duplicate charging machines 238 duplicate primary sources 238 duplicate ringing machines 238 ringing-current supply 229 magneto generators 229 pole changers 229 ringing dynamos 232 storage battery 239 initial charge 241 installation 240 low cells 244 operation 242 overcharge 243 pilot cell 243 regular charge 244 replacing batteries 245 sediment 245 types 227 common-battery systems 228 magneto systems 228

Power switchboard 246

Private-branch exchanges 271 with automatic offices 278 secrecy 279 battery supply 279 circuits, key-type board 276 definitions 271 desirable features 281 functions of the private-branch exchange operator 272 marking of apparatus 281 private-branch switchboards 273 common-battery type 273 cord type 275 key type 275 magneto type 273 ringing current 280 supervision of private-branch connections 277

R

Relays 28

Rotary connector 202

S

Selecting switches 175

Selector 175

Simplex circuits 324

Storage battery 239

Storage cell 240

Stromberg-Carlson multiple board 96

Strowger automatic system 143

Subscribers' board 259-261

Switchboard assembly 31

T

Table automanual system time data 225 automatic systems, messages per trunk in 305 calling rates 302 long-distance groups, messages per trunk in 305 manual system, messages per trunk in 304 out-trunking, effect of, on operator's capacity 303 subscribers' waiting time 226

Telephone traffic 298 importance of traffic study 300 methods of traffic study 301 observation of service 308 quality of service 305 accuracy and promptness 307 answering time 306 busy and don't answer calls 307 courtesy and form 307 disconnecting time 306 enunciation 308 team work 308 rates of calling 300 representative traffic data 302 calling rates 302 operators' loads 302 toll traffic 304 trunk efficiency 303 trunking factor 303 traffic variations 298 busy hour ratio 299 unit of traffic 298

Telephone train dispatching 333 advantages 335 apparatus 338 Cummings-Wray selector 342 dispatcher's transmitter 343 Gill selector 341 portable train sets 345 siding telephones 345 waystation telephones 344 Western Electric selector 338 blocking sets 355 causes of its introduction 334 Cummings-Wray circuits 350 on electric railways 356 Gill circuits 349 railroad conditions 337 rapid growth 333 test boards 353 transmitting orders 337 waystation circuits 348 Western Electric circuits 347

Telephone train-dispatching circuit Cummings-Wray 350 Gill 349 waystation 348 Western Electric 347

Test boards 353

Transfer switchboard 34 field of usefulness 41 handling transfers 38 limitations 40 plug-seat switch 38 transfer lines 35 jack-ended trunk 35 plug-ended trunk 37

Trunking in multi-office systems 109 classification 112 one-way trunks 103 two-way trunks 112 Kellogg trunk circuits 125 necessity for exchanges 109 Western Electric trunk circuits 116

W

Warner pole changer 230

Waystation telephones 344

Western Electric mechanical signal 27 selector 338 trunk circuits 116

Transcriber's Notes.

Spelling variants where it wasn't possible to determine the author's intent were left as is. These include: "clockwork" and "clock-work;" "doorkeeper" and "door-keeper;" "interrelation" and "inter-relation;" "multicyclic" and "multi-cyclic;" "redesign" and "re-design," along with derivatives.

Added closing double quote in Steinmetz entry in list of authorities: "Theoretical Elements of Electrical Engineering."

Changed "switch-hook" to "switch hook" on page 88: "the subscriber's switch hook."

Page 107 says there is room for 300 banks of 100 multiple jacks, but then says this allows for 3,000 multiple jacks in all, rather than 30,000. Based on the figure, 300 banks should be 30 banks, which would correct the arithmetic. However, I did not change this.

Changed "bi-paths" to "by-paths" on page 185: "circuits or by-paths."

Changed "appararus" to "apparatus" on page 209: "The sectional apparatus."

Changed "two number" to "two-number" on page 312: "the two-number calls are ticketed."

On page 333, a paragraph begins with "It has been only within the past three few." Perhaps the author meant "It has been only within the past three years" or "It has been only within the past few years." But since I didn't know, I left is as is.

Changed "them ain" to "the main" on page 333: "on the main line."

Changed "weatherproof" to "weather-proof" on page 357: "iron weather-proof sets."

Changed "interoffice" to "inter-office" three times on page 364, to match the spelling in the body of the document: "meant by inter-office trunking;" "inter-office connection system;" "of the inter-office connection."

Changed "break-down" to "breakdown" on page 367: "provision against breakdown."

Changed "way-station" to "waystation" twice on page 372: "with a waystation set;" and "a waystation on a block wire."

Changed "way stations" to "waystations" on page 375, in the entry for Long-distance switching.

Each page of the Index repeated this text: "Note.--For page numbers see foot of pages." They were removed.