322 RAILWAY CONSTRUCTION. 



an all-right signal for the 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 spec- 

 tacles 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. 



Ground or disc signals are fixed at the ground-level, and are 

 worked in conjunction with trap points or outlet switches from 

 sidings. In some cases they are worked direct by a connecting- 



