It is frequently urged that the celerity with which mechanical gates can be swung round and closed across the public road, is in itself a source of danger, and that persons preparing to cross the line might be struck by a moving gate, unless they received a distinct warning that such closing was about to take place. There is no doubt persons have been struck by such gates when closing across the road, and heavy claims for injuries have been decreed against railway companies, who were unable to prove that the man in charge had called out or given warning before moving the gates. To ensure that due and undeniable warning shall always be given, a firm of signal-makers have patented an appliance by which a powerful electric gong, fixed on the top of a tall post close to the gates, is sounded automatically by the gate machinery itself, and before the gates actually commence to move. As previously described, the pulling over of the lever to lower the gate-stops is the first operation to be performed whenever it is necessary to change the position of the gates, and it is the pulling over of this lever which actuates the apparatus, by bringing two electric points into contact, and thus starting the ringing of the gong or alarm. The gong continues to sound until the gates are moved over, the gate-stops raised, and the stop-lever put forward again into its normal position. The arrangement is very simple and very effective, and being purely automatic must work as regularly as the stop-lever. The tone and volume of the gong can be varied to suit circumstances. The public soon become familiar with its sound, and recognize its meaning.
[Figs. 509 and 510] give sketch plan and elevation of a set of mechanical gates for a public road level crossing on a double line of railway. The signal-cabin should be placed within a few yards of the gates, to enable the man in charge to have a good view of the persons and vehicles passing over the roadway. The underground gearing for working the gates and stops, must be protected by iron or wooden casing. The swinging portion of the wicket gates is closed, and held by a separate lever. The gates shown on the sketch are for a crossing on the square, but
they can be equally well arranged for an oblique crossing, and of widths to suit the locality.
Block-Telegraph Signalling.—However complete the outdoor signals and interlocking at any station, they can only control the movement of trains within their range, and something more is requisite to ensure the safe working of the traffic over the long lengths of line between stations. For some years a time-interval was allowed for the working of trains following one another on the UP and DOWN lines of a double line railway, no train being allowed to leave a station sooner than a fixed number of minutes after a previous train had started in the same direction. With this system there was always the risk that the first train might be overtaken and ran into by the second, and especially in the night time, or when the atmosphere was at all foggy. The electric telegraph was then called in to assist in the train-working, and brief telegrams were passed between the stations announcing the departure and arrival of trains. The increased security and convenience thus obtained led to the introduction of special electric telegraph instruments, devoted to the exclusive duty of train-working. These instruments, termed block telegraph instruments, are now almost universally used on all double lines of railway, and have largely contributed to the safe and efficient working of an ever increasing traffic. They are made in various forms, but the object of each is to ensure that before any train is allowed to start from, or pass any station, the signalman at that station shall receive from the signalman in the cabin in advance a distinct visible signal that the line is clear, and free of any train up to the cabin in advance; and also that after the train has been despatched, the signalman in the rear shall be at once advised when the train has arrived at the signal-cabin in advance. [Fig. 511] is a sketch of one type of block-telegraph instrument, in which the leading feature is the miniature signal-post with its two arms, an arrangement which readily appeals to the eye of the signalman as being so similar in form and action to the fixed signals in the station. Each instrument is supplied with a bell or gong, by which the adjacent signalmen can communicate with each other, in accordance with a fixed code of signals which defines the relative numbers of strokes of the bell or gong, to represent certain regulation calls and answers. In the signal-cabins of the intermediate stations, two
block-telegraph instruments are required, one for the section of the line to the left hand of the cabin, and the other for the section to the right. At the terminal stations only one instrument is required.
In the instrument shown in [Fig. 511], the upper arm of the miniature signal-post is coloured RED, and is moved by electricity through the medium of the block telegraph instrument in the signal-cabin in advance; and until this RED signal be lowered to the line clear position by the signalman in the cabin in advance, no train must be allowed to start from or pass the cabin in the rear. The lower signal-arm coloured WHITE is lowered by the plunger A on its own instrument by the signalman in charge, and at the same moment lowers by electricity the upper or RED arm of the block-telegraph instrument in the signal-cabin at the other end of the section. The lower or WHITE arm is thus restricted to the signals sent away from the signal-cabin, while the upper or RED arm is restricted to signals received in the signal-cabin. In the centre there is a round handle B, which rotates a circular disc inside the instrument, and on this disc are painted three distinct train inscriptions, only one of which can be seen at a time through the glazed opening. One inscription has the words ALL CLEAR painted in black letters on a WHITE ground; another has the words TRAIN ON LINE painted in white letters on a RED ground; and the third has the words TRAIN OFF, BUT SECTION BLOCKED painted in black letters on a GREEN ground. The instrument is considered to be in its normal position when the GREEN inscription is in view, and both the miniature signal-arms raised to danger.
[Fig. 512] represents a portion of double line divided out into sections, or working blocks, between the stations B, C, and D. Each station is provided with the necessary block-telegraph instruments, and the usual distant, home, and starting semaphore signals.