In all systems in which the semaphore is employed, a horizontal position means that the block is occupied by a train and is equivalent to the order, *stop.* The roundel which in that position covers the lamp is red. In the two-position semaphore, the *block clear* sig nal is made by dropping the outer end of the blade to an angle of about 70 degrees below the horizontal. The roundel which corresponds to this position is, in most cases, white; but the larger railroads are, one by one, changing all *white* or *proceeds signals to green. In the three-position semaphore the horizontal posi tion of the blade means When the blade is dropped to an angle of 45 degrees, or, in some systems, raised to an angle of 45 de grees, the signal means *proceed with caution,* and its equivalent light at night is generally green, though by the new color plan it is a brownish-yellow, In the third position the blade is vertical — either upward or downward — signifying *block clear* or *proceed*; and in the older scheme the light at night is white and by the new color plan it is green. The doing away of the white light makes for a larger degree of safety, for it was not an un usual accident that the roundel should be broken and the light show white when it should have been red. Under the new color plan a white light will mean a broken roundel and hence *danger,' and will require a stop and exam ination as to the position of the semaphore blade.
In the more highly organized signal systems two sets of signals are used, the Thome* signal and the *distant* signal; the former name re lating to the signal at the entrance to the block, the latter to a signal which indicates the posi tion of the signal at the entrance to the next block. Both are usually on the same post. As a means of distinguishing them, the outer end of the semaphore blade is deeply notched, like a fish tail. It is generally set lower on the signal post. Or, in some systems the *distant* signal is shorter and narrower. The *distant* signal has only two positions — horizontal, meaning *caution* (when approaching entrance to the next block), and inclined, meaning that the next block also is clear. The colors of the lights displayed at night correspond to the *caution* and *clear* colors used on the sys tem. The *distant* signal, therefore, is only a preliminary indication of the signal at the next block and is merely designed to facilitate the operation of a fast train service.
Another signal system which has a large vogue uses the °disc* or 'banjos' device instead of the semaphore. The disc revolves on a pivot, so as to show the full face when at danger and only the edge of the disc when the block is clear. A lantern mounted on top of the disc carries two roundels of different colors, showing red when the disc presents a full face and white (or green) when the edge indicates a clear block A modification of the disc system is arranged so that the disc always presents a full face, with an opening in the centre. Across this opening are thrown col
ored roundels, red, green or yellow, as the case may be. This system is the one in use on nearly all subway and tunnel traffic and on many electric roads. On the last mentioned the Hall Automatic system, an electric block system, is in extensive use. The instrument which displays the signals is contained in a case mounted on an iron or wooden post, the length of which may be varied to suit condi tions. Within the case is mounted a disc of red silk, with a red glass on the opposite end of the arm carrying the disc. By day a white glass in the back of the home signal case is exposed through the glass-covered aperture in front so long as the large red disc is held out of sight. The front of the case being dark, the indication of safety is thus shown by a white disc in the centre of a dark ground. The falling of the large disc before the glass produces the danger signal, by showing red, and at the same time cuts off the strong con trast formed by the pure white light disc in the centre of the dark case. The front opening is larger than the disc proper, so that when the signal is at •anger' there is a band of white shown around the disc. At night the clear signal is obtained direct from a lamp, showing a white light through the small open ing in the top of the case. On the signal assuming the danger position, a ruby-glass lens is carried up before the small opening by grav ity, giving a red light. When desired, the night indication may be green instead of white. In this case the single glass disc is replaced by a double disc, one green, the other red, these being placed at right angles to each other. The distant signal is substantially of the same construction, but the disc is green, and the face of the case may be painted white, to distinguish this signal from the home sig nal. When at danger the green disc presents a strong contrast to the white surrounding case. At night a green (or orange) lens is used to indicate °caution.* At junctions, crossovers, sidings, etc., a switch instrument is used, which, through its electrical connections, causes the block signal to display °danger" when a switch is not set for the required movement. A vis ible indicator is placed at main-track switches to warn a trainman desiring to open a switch to let a train out on the main line. This indi cator will show 'danger)) if an approaching train shall have passed a point 1,000 feet or more in advance of the home signal next, back of the switch. If the main track is clear and the trainman therefore opens the switch, this operation sets at Manger)) the main-track home signal of the block in which the switch is situated.