1576

THEORY AND PRACTICE OF ENGINEERING.

Book II.

two classes of carriages, onefor passengers, and the otherfor goods, varying in speed,means must be provided toallow of their occasionallypassing each other, with-out which the passengers*carriage would be subjectto delay and obstructionfrom the one more heavilyladen.

As there is always somerisk in passing in and outof a line, it is advisableto have as few sidings aspossible: in the best con-trived crossings, trains ra-pidly passingmay meet withaccidents, if there be theslightest want of care andattention on the part of theattendants. Where there isa single line of railroad,either of the three methodsshown may be adopted, asthe carriages, travelling ineither direction, can pass bythe sidings without incon-venience to those going in anopposite direction. The firstis generally applied when thecarriages are all proceedingin the same direction, but

Fig. 2959.

Fig. 2960.

Fig. 2961.

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Fig.2962.

with a difference in the speed, a movable rail is alone required to divert them into thesiding, or a switch which is restored to its first position by the servant whose business itis to attend it: should carriages require to pass in an opposite direction, the switches aremoved so as to enable them to digress, and again enter the main line. Loaded carriages,invariably keep the line, and the empty ones take the sidings, the movable rail being onthe side towards which they pass.

In the second example, the movable switch is dispensed with, as the carriages can pass eachother without changing the rail: this arrangement is usually adopted in mines. The thirdexample allows the carriages both going and coming to diverge, and the main line to begained by both. Wherever the sidings are adopted, the oblique lines of rails should be laidat an angle that will prevent the carriages passing by them from having their wheels thrownoff the rails by the sudden change of direction, which angle must in some degree bedetermined by the speed: when this is not more than 8 miles an hour, it may be made atthat number of degrees ; but when at 20 or 30 miles 1^° or 2° should be the extent of theangle from the straight line.

Switches and their Movements _The point and switch rails are most commonly used

for sidings, and when worked by hand, they always remain open, so that if the trains arerequired to be moved into the siding place, this is effected by moving the switches : theyare sometimes kept shut by the application of a weight, which the loaded carriages can pushopen, but the empty ones cannot, so that they are obliged to pass by the siding. Theends of the point rails do not touch the continued line, and the space left between them is