RAILWAY CONSTRUCTION. 231 



according to circumstances. In station-yards it is usual to fill in 

 the ballast almost up to the level of the top of the rails for the con- 

 venience and safety of the men who are constantly moving about 

 marshalling the carriages and waggons. Out on the open line 

 between stations, the ballast on some railways is filled in up to 

 rail-level, while on others it is only filled in up to the tops of the 

 sleepers, leaving the rails and chairs quite clear of the ballast. 

 On others, again, the ballast is filled well up to the rails and 

 channelled in the centre, as shown on the sketches Figs. 336 and 

 337. Channelling the centre of the road reduces the quantity of 

 ballast per mile, ensures good drainage, and also stability by not 

 permitting any central support to the sleepers. By covering up 

 the lower table and sides of rails the noise is reduced to a 

 minimum, vibration is absorbed, and a more silent road is the 

 result. The contact with the ballast also preserves the rail from 

 the extremes of temperature. Where the ballasting is not 

 channelled there is some risk of the sleepers breaking in the 

 middle. The constant packing of the sleepers just under the 

 rails has a tendency to drift some of the ballast inwards towards 

 the middle of the sleeper, forming a hard compact mass, and this 

 mass, acting as fulcrum, throws considerable strain on the middle 

 of the sleeper when the trains pass over and depress the ends. 

 Where the ballast is filled in level with the rails on top of sleepers 

 it should be loosened occasionally in the middle to prevent it 

 becoming too hard. 



Connections with the rails of the main line will have to be 

 made in various forms to suit the circumstances of the joining 

 lines or sidings. 



Fig. 345 shows a simple double-line junction. 



Fig. 346 shows an example of what is termed a flying 

 junction, or a junction of two double lines arranged in such 

 a manner as to cause the least interruption to a constant train 

 traffic passing UP and DOWN over both lines. Upon referring to 

 Fig. 345 it will be seen that a train from F, turning off at the 

 points E and proceeding to G, must block, or close for traffic the 

 section ABC during its passage over that line towards Q. 

 With a crowded train-service the blocking of both UP and DOWN 

 main lines for the working of one train would cause much 

 interruption, and to obviate such delay the flying junction is 

 substituted. Fig. 346 shows how a train from F is turned off at 

 the points J and proceeds on to K, where by means of a bridge 



