heavy trains may travel safely and smoothly at a high rate of speed, and with a minimum wear and tear and expenditure of motive power.
The intersection of one rail with another at any angle is termed a "crossing," and these crossings are so constructed with wing rails and check rails as to guide the flange of the wheel, and ensure its taking the required direction at the point of intersection. The simplest form of crossing is where the rails intersect each other at right angles (Fig. 7, No. 2), but such crossings are of rare occurrence. When the rails intersect at any other than a right angle, the crossings are of two types. When the external angle of intersection is acute (as at a, Fig. 7, Nos. 1 and 3), the crossing is known as a single or "V" crossing, but where the angle of intersection is obtuse (as at b, No. 3), it is called a "diamond" crossing. "Diamond" crossings occur only in pairs.
For "V" crossings, check rails are provided (m and n, No. 1, Fig. 7), which, by holding one wheel on an axle to its proper course, prevents the wheel at the other end of the axle from taking the wrong side of the point of the crossing between m and n. The check rail n guides the flange when a wheel is travelling from f to g, and the check rail m guides it in the directionh to k.
From an inspection of these diagrams (Fig. 7) it will be easy to trace the course of the wheel flange, which is always on the inner side of the wheel.
To turn a train off one line of railway and on to another which connects with it, a pair of tapered moveable rails, called "switches," or "points," are made use of (see Fig. 7, No. 4). These are connected by rods with a lever in the signal cabin, and worked by
