and working, and the consideration of this question is immediately connected with the arrangement of single-line station yards. Before we discuss the simplifications and economies to be sought for in signalling and interlocking light-railway stations, it will be useful to describe as briefly as possible the functions of signals and the requirements of the Board of Trade on standard railways :

"Fixed signals consist of home, distant, starting, and siding signals.

"The home signal may be placed at a station (fig. 3, I., H. S., page 209), junction (fig. 3, II., Nos. 4, 6, 8, 10), siding, or signal-box, and is an absolute stop signal. It should be placed at a sufficient distance from the fouling point to allow some margin for accidentally drawing a little beyond the signal. No train must pass a home signal at danger, or foul the points or crossings which it protects, except as prescribed in the regulations-e.g., while shunting from one line to the other, or into or out of sidings; or where (at places other than junctions) starting signals are not provided, and it is necessary to bring the train under the protection of the home signal.

"The distant signal (as in fig. 3, I., D. S.) is fixed at a sufficient distance (say 1000 yards, or on a rising gradient 800 yards) from the home signal, and is not merely a repeater of the home signal, for when a driver sees the distant lowered, he knows that both the home and the starting signals have been lowered. When, however, the distantsignal is at danger, the driver must be ready to pull up at it, if necessary; but, if the road be clear, he may proceed cautiously (so that he may stop short of any obstruction) and bring his train to a stand as near the home signal as the circumstances of the case will allow. The distant signal should be distinguished by a fish-tail notch cut out of the end of the arm.

"Starting signals (at stations placed generally at the end of the platform) and advanced starting signals control the departure of trains into the section ahead, and must not be passed, when at danger, except where it is necessary to shunt over points and crossings or cross-over roads close by, when the signalman may allow the shunting to be carried out under his direction. The starting signal (fig. 3, I., S. S.) should not be lowered to allow a train to enter the next section until "line clear" has been received from the station in advance. But, where an advanced starting signal is provided, and the line is clear, the signalman may, if necessary, after bringing the train to a stand, lower the starting signal to allow such train to proceed to the advanced starting signal, and no further. The advanced starting signal thus marks the limit up to which a train may be drawn forward beyond the starting signal, in order to leave the platform line clear, or for shunting purposes, or other station duties. The advanced starting signal is generally placed (as in fig. 3, I.) 300 to 350 yards in advance of the

*Notes on Perman‍nt-Way Material, Platelaying, and Points and Crossings, by W. H. Cole, pp. 126 to 132 (E. & F. N. Spon).

cabin, so that a train of maximum length may clear the section in rear without entering the section ahead, and it should be clearly visible to the driver from the platform starting signal, as well as to the signalman in the cabin.

"Exit from a siding is controlled by a ground disc (fig. 3, I., G. D.) or dwarf semaphore siding signal. No train must leave the siding until such signal has been taken off,

"All signals should be on separate posts or on brackets. Where there is more than one arm on one side of a post, the first or top arm applies to the line on the left, the second arm to the line next in order from the left, and so on; but, if the main or important line be not the one on the left, the signals must be on separate posts or brackets.

"A distant signal must not back-lap a home or starting signal of a station in rear of it. If on the same post as a home or starting signal, its arm must be placed below, and be slotted with or controlled by the upper signal, so that it cannot possibly be pulled off when the latter is at danger. It is a general rule that lamps should be at least 7 ft. apart, so the distant should be 7 ft. below the home or starting signal. At a junction, all distant signals must be controlled by the respective home and starting signal.

"Every signal arm must be weighted, so as to fly to danger if the connection between arm and lever should break at any point.

"The front signal lights are red for danger,' and green for 'all right'; the back light (visible only when the signal is at danger) white. This is not obligatory on existing lines, or. on new lines run over by companies using a different system of lights. For the sake of distinction, the danger lights of bay starting and other minor signals are often purple instead of red.

"Signals are usually worked by wires, the 'slack' of which is better regulated by hand adjusters in the signal-cabin than by selfacting so called compensators.

"Having thus briefly described the functions of fixed signals, their approximate positions, and the requirements of the Board of Trade in regard to them, points and crossings in connection with them must be considered.

"Points must be worked or bolted by rods, the effect of varying temperature on rods of 100 ft. and upwards in length being corrected by self-acting compensators.

"Facing points should be avoided as far as possible. They must not be worked from a greater distance than 180 yards, and should be placed as near as practicable to the levers by which they are actuated. In the case of trailing points on the main line, or safety points of sidings, the limit of distance from the levers is 300 yards. This is the English practice, but on the Continent these limits are considerably exceeded, and with perfect safety.

"To secure facing points in their proper position they must be bolted by a locking plunger passing through the stretcher-bar; and, to prevent the signal from withdrawing the bolt while a train is pass

ing over the points, the plunger must be fitted with a locking-bar to suit the longest wheel-base of the rolling-stock. The plunger and locking-bar may be worked either by a separate lever or by the lever which also works the points.

"The first step towards the interlocking of points and signals is the concentration of the levers in one frame.

"The point and signal levers must be so interlocked—that a signal cannot be lowered for a train until the points have been properly set and locked; that any two signals which might lead to a collision cannot be exhibited at the same time; and that, after signals have been lowered for a train to pass, no points connected with, or leading to, the line on which the train is running can be moved. Home or starting signals, next in advance of trailing points, when lowered, must lock the points in either position, unless this locking will unduly interfere with the traffic.

"Points also, if possible, are to be so interlocked as to avoid the risk of a collision by over-running.

"A distant signal must not be capable of being lowered unless the home and starting signals in advance of it have been lowered.*

"Detectors must also be fitted, in order to ensure that the points are properly set before the signals are lowered, and to discover any failure in the connections between the levers and the points. Otherwise, if the rods were buckled or broken, a lever might be pulled over without any corresponding movement of the points.

"From the foregoing remarks-in which are included the present requirements of the Board of Trade-it will be seen that there are few absolute rules for the precedence of levers, etc. The interlocking is generally arranged to suit the requirements of the junction or station to which it is applied.

"Whenever it is possible, the interlocking of the point levers (independently of the signals) should be so arranged that the various switches may be set to form a trap or protection, when trains are backing or otherwise. The case of an ordinary double junction may be taken as an example (fig. 3, II., page 209).

"If a train from A on the main line is to proceed on the branch towards C over facing points 2, it is necessary, before making the road from main to branch, to turn over points 1, so that, if a train on the other line B B were backed over points 1, it would not foul the train from A when the latter was crossing the main line B B. The order of working would, therefore, be 1, 2, 3, 4, 5. The levers having been put back in reverse order, a train running over facing points 2 on the main line A A would require levers 3, 6, 7 to be pulled over in succession.

"For a train running on the main line B B over trailing points 1 the order would be 3, 10, 11, so that a train coming from the opposite direction on the other main line could not cross it. If, however, a

* In interlocking this means that the distant signal must also be put back to danger before the home and starting signals.

A passenger train going from A on the main line to C on the branch may be

train from D on the branch were entering the main line over points 1, it would be impossible to trap another train from the main line B B running in the same direction and over the same points. Nevertheless, an accident could only take place through disobedience of signals; for, when the road is made from branch to main line, signal 10 (and, therefore, 11 also) is locked at danger.

Again, where (as in fig. 3, III., page 209) we have a siding or slip road in a cross-over road, the cross-over points a should precede the siding points b, which in turn would precede the signal c.

"It is now required that the starting as well as the home or stop signal shall precede the distant, so that, should a driver approach a station or junction where the distant signal is down, he will know that not only is the station clear but the section in advance also.

"If the distant, however, be at danger, and the home signal only is lowered as described below, the driver will know that the station is clear but the section in advance is blocked, and that he must stop at the station until the starting signal is lowered. The rule is that, so long as the starting signal is at danger, the home and distant signals must be kept at danger, except on the near approach of a train which has to stop at the station, when, after the speed of the train has been reduced so as to admit of its entering slowly and being pulled up at the platform, the home signal may be taken off to admit the train, but the starting signal must be kept at danger until the section in advance is clear; in the case of a train not booked to stop, the home signal must not be lowered to admit the train until the train has been brought to a stand.

"Should the distant and home stand at danger, the driver will know that he must reduce his speed to enable him to stop at the latter.

"In all cases the lowering of the distant signal must backlock the home or starting signal levers, so that they cannot be put back until the distant signal has first been put to danger.

"In sections where the distance is so short that a distant signal is not required, the home or starting signal should be controlled from the station in advance. This is generally done on the signal itself, although there are cases, but very few, where, in mechanical boltlocking, the lever is governed or controlled.

"The general requirements of a good interlocking apparatus are"(1) That there shall be very close locking, i.e., the locking shall act as soon as the lever is moved, and the unlocking shall not be effected until the stroke has been completed;

"(2) That the locking shall be compactly arranged;

"(3) That the locking shall not occupy such space in front of the levers as will prevent the signalman from having the best possible view of the railway, nor such space at the back as will not allow him to stand well up to the levers;

stopped and made to wait for a goods train running on the other main line B B over points 1, as the former can be trapped and a collision averted if the driver over-runs signals, while the latter cannot.