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The great railways of to-day are provided with a wonderfully complete system of safety devices that make travelling by rail, even at the highest speeds, as free from danger as human ingenuity can secure. Signalling methods have reached a very remarkable degree of perfection and trains are shepherded from starting point to destination with unceasing watchfulness. Signal boxes are placed at various points along the line, and from them the signals and points are operated by specially trained signalmen. As everyone knows, the signals themselves are in the form of semaphore arms fixed on high posts by the side of the line. These signal posts are usually placed at the left-hand side of the line of rails to which they refer, and the signal arms are on the left-hand side of the posts as seen by the driver of an oncoming train. There are thus separate sets of signals for both "up" anddown" lines, the "up" line being as a rule the line for trains going towards London. The front of the signal arms, that is the side seen by the engine driver, is painted red with a white stripe, and the back is painted white with a black stripe. Each signal post is also fitted with a lamp that is kept burning continuously, requiring to be replenished with oil only about once a week. Coloured glasses, called "spectacles," are attached to the signal arms, and through there the engine driver views the light at night. |
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The normal position of a signal arm is horizontal, signifying "danger," and when the arm is in this position a red glass covers the light, also signifying danger. The" line clear," or" all right," indication is given by lowering the arm to an angle of about 60 degrees, and in this position a green or blue glass is in front of the light. At one time a white light was used for this purpose, but its use proved to be dangerous. Drivers found it extremely difficult to decide whether a particular light was their signal or not, and there was always the possibility of a light in the window of a house close to the line being mistaken for a signal, with possibly disastrous consequences. Yet another danger was always present, namely, that a red "spectacle" glass might be broken, with the result that a white " line clear" signal might be given while the signal arm was actually at "danger." Signals are also provided with a small white light showing at the back which is obscured by a mask when the signal is lowered. These " back-lights" are for the purpose of enabling the signalman to tell at night whether the lamps of his signals are burning and also whether the signal arms are working correctly, in cases where his signals are in such positions that he cannot see the red and green lights. As we have already seen, the normal position of a signal arm is at danger, and the arm is balanced in this position by the spectacle portion and by a weighted lever placed close to the foot at the post. Connection between the lever and the arm is made by means of an iron rod. Should the rod break -which is unlikely- the weight of the spectacle would prevent the arm from falling to the "clear" position. |
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Before the arm can be lowered the weighted end of the lever must be raised, and this is done by the movement of a lever in the signal box, which pulls a wire connected to a chain attached to the weighted lever at the opposite end to the weight. If the chain or the wire should break while the signal is in the " all right" position, the weight on the lever will automatically raise the arm, thus preventing the possibility of the signal continuing to show "all right" if the signalman does not notice the breakage. Signal arms are made either with square ends or "fish-tailed " ends. The square-ended arm is a stop signal and the fish-tailed arm is a "distant" or cautionary signal. The first signal seen by the driver of a train approaching a signal box is the fish-tailed "distant" signal, so called because it is the signal at the furthest distance from the box. "Distant" signals were introduced about 1846 as the result of the increased weight and speed of trains, which made it difficult for a driver to pull up quickly at a "stop" signal, on account of not receiving sufficient warning. The object of the "distant "signal is to warn the driver when the next or" home "signal is likely to be at danger, and thus give him time to reduce the speed of his train to be ready to stop at the " home signal if necessary.
As a train is likely to be travelling at a high speed when the driver first sees the distant" signal, it is clearly necessary that this signal should be sufficiently far in advance of the
"home" signal to allow the driver to pull up at the latter if required. The standard distances from "distant" to ‘ home" varies from 600 yds. on a rising gradient to 1,000 yds. on a falling gradient. As long as a "home" signal is at danger the preceding" distant" signal also is kept at "danger" and the driver slows down and proceeds cautiously towards the "home" signal. If the latter is at "danger" when he reaches it, he must stop dead and must on no account go on until the signal is lowered to the "all right" position. At night the fish-tail shape of a "distant" signal cannot be seen, and formerly there was no difference between the red light of a distant" signal and that of a "stop" signal. It is becoming more general practice, however, to use an orange light too indicate the danger position on distant signals and in some cases a special arrangement is in use whereby an illuminated fish-tail is indicated at the side of the lamp. Similarly, to aid in its identification by day, the arm is painted yellow witha black stripe in addition to the fish-tailed end. Apart from such distinguishing features the drivers usually know the "distant" signals by their position. The third signal to be reached is the "starting" signal, the function of which is to prevent a train that has passed the "home" signal from starting away until the line ahead is known to be clear. Sometimes there is a crossover road or a siding connection ahead of the starting" signal. In such cases a fourth signal is necessary and this is called an "advanced starting" signal. The shape of "starting" and "advanced starting" signals is similar to that of "home" signals. Sometimes signal boxes are not far enough apart to allow the "distant" signal to be placed at the standard distance from |
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the "home" signal, and where that is the case the "distant" is placed on the same post as the "advanced-starting," "starting" or "home" signal of the previous box, its position always being below the other signal. Junctions are usually protected by two "distant" and two home" signals. The two signal arms are arranged on a "bracket," the left-hand and right-hand arms applying respectively to trains proceeding to the left or to the right at the junction. One of the arms is generally placed higher than the other, the higher arm applying to the more important line. In addition to the signals already described there are many others employed for special purposes, such as shunting, backing, etc. The approaches to and the exits from important stations present a bewildering array of lines, points and crossings, and at such places sets of signals are often carried over the rails on a sort of bridge called a "gantry." |
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Tapper bell used by signalmen to communicate with each other by means of a code of rings. |
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"train on line". In this case signalman No. 2 pegs his instrument to show "line clear" and so causes the "line clear" indication to appear on a similar but keyless instrument on box No. 1. This gives signalman No. 1 permission to send forward the train and he lowershis "starting signal" and his "advanced starting signal" if there is one, and the train moves forward into the next section. Immediately after lowering his signals, the man in No. I box signals two beats on the bell signifying train entering section," and this signalman No. 2 acknowledges by repeating it, at the same time altering his key-disc instrument and consequently the keyless instrument in box No. 1 to "train on line." As soon as the train has passed the No. 1 box the No. 1 signals are restored to the normal danger" position. The signalman in box No. 2 does not wait for the train to arrive, but immedi ately calls the attention of the signalman in box No. 3 by giving one beat on the bell, and the process just described is repeated. In this way the train is passed along to box No. 3, and so on from one box to another throughout its journcy, each step in its progress being |
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painted red and at night shows a red light. The L.M.S.R., however, use tail lamps painted aluminium colour to enable them to be more readily seen against the dark mass of the train. The bulb or light is, of course, red as usual. When a signal man sees this lamp at the rear of the train he knows that the train is complete, but if he does not see the lamp he assumes that some portion of the rear of the train has broken away and is left somewhere in the section. He then takes. immediate steps to prevent any other train entering this section and at the same time he signals to the box ahead: "Train passed without tail lamp" -nine consecutive beats- and accordingly the train is stopped at the next box and held up until the matter is investigated. If a signalman gives four beats on the bell, inquiring if the line is clear, and receives no response, he repeats his four beats at intervals until the man in the next box gives them back to show that the line is clear. |
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