Cyprian Arthur George Bridge, Allan Frederic Everett, Brahman Blanchard Adams, and Hugh Munro Ross

“ Distant signals are used to make it unnecessary for an engine- driver to slacken his speed in case the stop (home) signal is obscured by fog or smoke, or is beyond a curve, or for any reason is not visible sufficiently far away. Encountering the distant signal at a point 400 to 800 yds. before reaching the home signal, he is informed by its position that he may expect to find the latter in the same position; if it is " off " he passes it, knowing that the home signal must be in the same position, but if it is at danger he proceeds cautiously, prepared to stop at the home signal, if necessary. ”

“ Even when a satisfactory form of appliance has been discovered, the manner of using it is by no means simple. It is clearly no use placing such an apparatus im- mediately alongside a stop signal, as the driver would receive the intimation too late for him to be able to stop at the required spot. To place devices of this description at or near every stop signal in a large station or busy junction would involve a multiplication of wires or rods which is undesirable. Every such apparatus should certainly be capable of giving an " all-right " signal as well as a " danger " signal. ”

“ The arm of a distant signal usually has a fish-tail end. In Great Britain its colour indications are generally the same as for the home signal, but occasionally it shows yellow, and on some lines it is distinguished at night by an angular band of light, shaped like a fish-tail, which appears by the side of the red or green light. In America its night colour-indication is made different from that of the home signal. ”

“ If, however, the signal arm should be lowered to the "all-right " position before a train reaches it, the fogman should immediately remove the detonators and exhibit a green flag or lamp, replacing the detonators as soon as the signal is again raised to danger. As a rule the fogmen are drawn from the ranks of the permanent-way men, who otherwise would be idle. But if, as sometimes happens, a fog continues for several days, great difficulty is experienced in obtaining sufficient men to carry on this important duty without undue prolongation of their hours of work. ”

“ As soon as possible after a fog comes on, a man is stationed at the foot of each distant signal, and generally of each home signal also, who by means of detonators, red and green flags and a hand-lamp, conveys information to the driver of every train as to the position of the semaphore arm. ”

“ In America many block stations have only the home signal, even at stations where there are points and sidings, and on double-track lines the block telegraphing for both is done on a single Morse circuit. In the United Kingdom the practice is to have separate apparatus and separate wires for each track. ”

“ Some companies have adopted mechanical appliances, whereby a man can place a detonator upon a line of rails or remove it while standing at a distance away from the track, thus enabling him to attend to more than one line without danger to himself. The cost of detonators often amounts to a considerable sum; and an apparatus called an economizer has been introduced, whereby the explosion of one detonator removes the second from the rails before the wheels reach it. ”

“ Automatic signals are sometimes made to stand normally (when no train is in the section) in the " stop " position. The local circuit is connected with the rail circuit so that it is closed only when a train is approaching within, say, 1 m. With the rail circuit, distant signals are controlled, without a line wire, by means of a polarized relay. Each signal, when cleared, changes the polarity of the rail circuit for the next section in its rear, and inis, by the polarized relay, closes the local circuit of the distant signal, without affecting the home signal for that section. ”

“ At crossings at grade level of one railway with another, and at drawbridges, interlocked signals with derailing switches obviate the necessity of stopping all the trains, as formerly was required by law everywhere in America, and saving a stop saves money. The block system was introduced primarily for safety, but where trains are frequent it becomes also an element of economy. ”

“ Where more than two full-sized arms are used on a post, the custom in America is to have the upper arm indicate for the track of the extreme right, and the others in the order in which the tracks lie; in Great Britain the opposite rule prevails, the upper arm indicating for the extreme left. ”

“ Signalling is used on most campaigns to a large extent. In the Tirah expedition, 1897 and 1898, one signal station received and sent, between the 1st and 18th November, as many as 980 messages by heliograph, some of which were 200 to 300 words in length. It is often used as an auxiliary to the field telegraph, especially in mountainous countries, and when the wire is liable to be cut and stolen by hostile natives. ”

“ A motor, with gearing and cranks, is fixed to the sleepers at each pair of points, the power is conveyed from the cabin by underground wires, the locking is of common mechanical types, and, in general, the system is similar to pneumatic systems except in the source of power. By using accumulators, charged by dynamos run by gasoline engines, or by a travelling power-car, the cost of power is reduced to a very low figure, so that power-interlocking becomes economical at small as well as large stations. ”

“ In large city terminal stations, where additions to the space are out of the question, interlocking is necessary for economy of time and labour, as, indeed, it is in a less degree at smaller stations also; as a measure of safety, however, it is desirable at even the smallest, and the wise manager extends its use as fast as he is financially able. ”

“ Such inventions usually consist of two parts, namely (1) an inclined plane or block or trigger, placed on the permanent way alongside the track or between the rails, and working in connexion with the arm of the signal ; and (2) a
lever or rod connected with the steam-whistle, or an electric bell or indicator on the foot-plate, and depending from the under-side of the engine in such a position as to come in contact with the apparatus on the ground, when the latter is raised above the level of the rails. ”

“ The flags which constitute a signal are termed a " hoist." One or more hoists may be made at the same time. Although flag signalling is a slow method compared with others, a fair rate can be attained with practice. For example, a signal involving 162 separate hoists has been re- peated at sight by 13 ships in company in 76 minutes. Semaphore signals are made by the extension of a man's arms through a vertical plane, the different symbols being distinguished by the relative positions of the arms, which are never less than 45° apart. ”

“ In the electro-pneumatic system a full-size semaphore is used. Compressed air, from pumps situated at intervals of 10 to 20 m., is conveyed along the line in an iron pipe, and is supplied to a cylinder at each signal, exactly as in pneumatic interlocking, before described. The rail circuit, when complete, maintains pressure in a cylinder, holding the signal " off." On the entrance of a train or the failure of the current, the air is liberated and the signal arm is carried by gravity to the " stop " position. ”

“ To render the signals more conspicuous the signaller usually holds a small flag on a stick in each hand, but all ships are fitted with mechanical semaphores, which can be worked by one man, and are visible several miles. Flag signalling being comparatively slow and laborious, the ordinary message work in a squadron is generally signalled by semaphore. ”

“ Two lights for a single arm, giving their indication by position as well as colour, have been used to a limited extent for both home and distant signals. Dwarf signals (a in fig. 5) are used for very slow movements, such as those to or from a siding. Their blades are about 1 ft. long, and the posts about 4 ft. high; the lower arm on post c being for slow movements, is also frequently made shorter than the upper one. ”

“ Many attempts have been made to design a mechanical apparatus for conveying to a driver the requisite information as to the state of the signals during a fog, and for enabling the fogmen to be dispensed with. ”

“ The diagram (fig. 6) shows a section with a side view of one lever. A machine consists of as many levers, placed side by side, as there are points and signals to be moved, though in some cases two pairs of points are moved simultaneously by a single lever, and two or more separate arms on the same post may be so
arranged that either one of them will be moved by the same lever, the position of the point connexions being made to govern the selection of the arm to be moved. ”

“ A school of signal- ling was created at Chatham, and some time later all units of the line were directed to furnish men to be trained as signallers. At first a code book was used and the signals represented code words, but it was found better to revert to the telegraphic system of signalling by the Morse alphabet, amongst the unde- niable advantages of which was the fact that it was used both by the postal service and the telegraph units of Royal Engineers. Thenceforward, iA ever-increasing perfection, the work of signallers has been a feature of almost every campaign of the British army. ”

“ As the system only requires the exhibition of two elements it may be used in a variety of different manners with a minimum of material, namely, by waving the most conspicuous object at hand through short and long arcs, by exhibiting two different shapes, each representing one of the elements, or dipping a lantern in a bucket, and so on. ”

“ Automatic electric block signal, with rail circuit.
section the current is restored and the signals are forced back to show safety. The current used for the track circuit must be of low tension, because of the imperfect insulation, and as a rule the ballast must not be allowed to touch the rails and must be free from iron or other conducting substance. At each rail joint a wire is used to secure electrical continuity, and at the ends of each block section there are insulating joints in the track. ”

“ A switch rod would be connected to this lever at H; the lever K is for use where a signal is con- nected by two wires, as before described. The lever is held in each of its two positions by the catch rod V, which en- gages with notches in the segment B. When the signalman, preparatory to lowering a signal, grasps the lever at its upper end, he moves thisrodupwards, and in so doing actuates the interlocking, through the tappet N, attached at T. Lifting the tappet locks all levers which need to be locked to make it safe to move this one. ”

“ With the many private developments of such codes we are not here concerned, nor is it necessary to attempt an explanation of the systems of drum-taps, smoke-fires, &c, by which certain primitive peoples are supposed to be able to convey news over long distances with astonishing rapidity ”

“ In the simple block system it is clearly possible for a signal- man, through carelessness, forgetfulness, or other cause, and in disregard of the indications of his telegraph instruments, ft/ocfc"*" " so t0 l° wer his signals as to admit a second train into the block section before the first has left it, and that without the driver of either train being aware of the fact. ”

“ The fact that the heliograph requires sunlight, as mentioned above, militates against its employment in Great Britain, but where it is possible to use it it is by far the best means of signalling. Secrecy and rapidity are its chief advantages. An observer 6 m. distant would see none of its light if he were more than 50 yds. on one side of the exact align- ment, whereas a flag signal could be read from almost every ”

“ Moreover, a single lever will work two or more switches, locks, &c, simultaneously, where desirable. The absence of outdoor connexions above ground is also an advantage. Since about 1900 electric power has come into use for working both points and signals. ”

“ It is rarely possible in the field to work rapidly with less than five men at a trans- mitting and three at a terminal station. " Central " stations are manned according to the number of stations with which they communicate. ”

“ If tappet 2 were raised, its notch would come opposite dog J; and then the lifting of 1 would lock 2 by pushing J to the left. By means of horizontal rod R, the lifting of 1 also locks 4. If 4 were already up, it would be impossible to lift 1.
Switch and signal machines are sometimes worked by com- pressed air, or electric or hydraulic power. The use of power makes it possible to move points at a greater distance from the cabin than is permissible with manual locking. power. ”

“ To effect this result an electrical track circuit or rail circuit is employed, in conjunction with some form of power to put the signalling devices to safety. Live-wire circuits were formerly employed, but are now generally abandoned. The current from a battery b (fig. 9) passes along the rails of one side oi trie track to tine signal s and returns along the other tails through a relay. If the current through this relay is stopped in
Staff system. ”