When a long length of permanent way has been linked in, rails spiked to gauge, and fish-plates bolted together, the platelayers can proceed to the final adjustment to line and level in accordance with the stakes and pegs provided for their guidance. The setting to exact line is effected by means of long pointed round iron crowbars, which are struck forcibly into the ballast alongside the rails, and serve as powerful hand-levers to pull or push the rails to the right or left as directed by the foreman standing some distance back at one of the line-stakes. The men with the crowbars pass from rail-length to rail-length, until a long stretch of road has been pulled into correct line. The adjustment to rail-level is done by first packing up the sleepers to the correct height at the various level-pegs, and then packing up the intermediate sleepers so that the surface of the top of the rails forms one uniform even line from level-peg to level-peg. On new lines it is usual to pack a little high in the first instance to allow for the subsidence or compression which invariably takes place on the passage of heavy trains over fresh ballast. The form or contour line of the top ballast will vary according to 231 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 convenience 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.