Fig. 486 is a sketch of an average sample of an ordinary single-arm wooden signal-post, with signal-arm, lamp, spectacles, ladder, and gearing complete for wire connection to signal-cabin. When the arm stands out in the horizontal position, representing the _danger_ or stop signal, the red spectacles will be in front of the lamps, and will show a red light to an approaching train. When the arm is lowered, as indicated by the dotted lines, the second spectacle will be in front of the lamps, and will show either a white or green light (according to the accepted code) as an _all-right_ signal for the 322 train to proceed. For many years a white light was adopted for the all-right signal, but latterly, to prevent confusion with other white lights about a station, there has been an increasing disposition to use a green light as an all-right signal. Several railway companies have already effected the change, and others have arranged to follow their example. The counter-weight W keeps the signal-arm to the danger position, except when it is raised by the pulling over of the signal-wire from the signal-cabin working over the pulley P. Should the wire break when being pulled, the weight W falls down to the stop-plate, and the signal-arm rises to danger. The signal-posts may be of wood, wrought-iron, steel lattice-work, or cast-iron. The arms of _distant signals_ should be cut to a fish-tail shape, as in Fig. 487, to distinguish them from other signals. Goods-line signals should have a thin sheet-iron ring, as in Fig. 488. Sometimes purple glass is used instead of red glass for the spectacles of goods signals. Letters or numbers may be attached to signal-arms to signify the lines or sidings to which they correspond. Special signals are sometimes made with the arm working on a centre pin, as in Fig. 489. At junctions or places where two or three signals have to be fixed near together, it is customary to carry them on a bracket signal-post, as in Figs. 490 and 491. The former represents the home signals at an ordinary junction, the taller signal being for the main line and the lower one for the branch line. Fig. 491 shows the home signals at a junction where there is one line turning out of the main line to the left and another to the right. The taller signal in this case also serves for the main line and the two lower signals for the branch lines. In important station-yards, where there are a large number of lines and sidings running side by side, it is not always convenient or possible to place the respective signal-posts in suitable positions between the lines. To overcome the difficulty, the signals are erected on light overhead lattice girders, as shown in Fig. 492. In some cases, for want of a better position, or to obtain a more comprehensive view of the lines and signals, the signal-cabin is built on lattice girders, as in Fig. 493.