RAILWAY CONSTRUCTION. 321 



Fig. 484 is a diagram sketch of the arrangement, in which the 

 main-line points are indicated by the letter A, and the trap 

 points by the letter B ; one series of rodding actuated by one 

 lever in the signal-cabin works both the main-line points and 

 the trap points at the same time and by the same movement. 

 The connections are so made that when the points A are set 

 for the passage of trains on the main line, the trap points B are 

 set open to throw off on to the ballast, as shown in Pig. 484 ; and 

 when the main-line points A are set to allow a train to pass 

 from the siding on to the main line, the trap points B are closed, 

 as shown on Fig. 485. A disc or other signal, worked or inter- 

 locked with the points, is placed near B to notify the engine- 

 driver when he may pass out of the siding on to the main line ; 

 but should he from any cause proceed before the points are 

 properly set and the corresponding signal given, his engine 

 would run off at the ends of the rails C, C, and be derailed on to 

 the ballast. The inconvenience caused by such derailment would 

 be trifling compared with what might result from a collision 

 with a train standing or passing on the main line. In some 

 cases the siding is continued onwards for a considerable distance 

 from the trap-point rails C, C, as indicated by the dotted lines 

 D D, and terminates with a dead end. When this arrangement 

 can be adopted, derailment is obviated, and the engine is brought 

 to a stand by a buffer-stop at the end of siding. On no account 

 should trap points be placed close to the top edge of a high 

 embankment, or up to the abutment or wing walls of an under- 

 line bridge, where an engine running through them accidentally 

 might fall down a considerable height, and cause serious results. 

 All sidings joining on to main lines should be trapped as above 

 described, and when properly signalled and interlocked in the 

 .signal-cabin, the traffic- working can be carried on with increased 

 facility and security. 



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 traia 

 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 



