the signalman; the lever being so controlled mechanically that it is impossible for the signalman to lower the signals for a train travelling in the direction of the arrow on line "b," until the "points" or "switches" have been placed in their proper position, as at d. On the other hand, before the signal can be lowered for the line c the switches must be placed as at e.
Fig. 9 gives a view in perspective of a pair of switches, and shows the manner in which they are worked.
Fig. 8 is a view of an ordinary junction between a main line and a double branch line, with the signal cabin from which the points and signals are worked, and the home signals for the junction. The diamond crossings are marked b, and the nearest single crossing is marked a. This is a simple double junction; but where the running lines are duplicated, and there are numerous cross-over-roads and sidings connecting with the main lines, the arrangement of roads frequently becomes extremely complicated.
There is one important feature in the formation of a well-constructed permanent way, which is known as the super-elevation of the outer rail on curves. Any one who has witnessed the evolutions of a circus rider will have observed that both horse and rider, in order to maintain their balance, incline their bodies towards the centre of the ring, and the greater the speed, the greater is their deviation from the perpendicular. In order to enable a train to do by mechanical means what the rider does by muscular power—that is, to balance the centrifugal force of a train running round a curve—it is necessary for the outer rail on a curve to be raised somewhat above the inner rail, and the
