The only fault in the system--as in all systems--is that human beings are not infallible, and mistakes are sometimes bound to happen. The signals may be wrongly set, or when rightly set, may not be seen. Fog or smoke may obscure them, and the engineer rushes by, trusting that all is well. If he obeyed the rules, he would stop and make sure; but that would delay the train, perhaps needlessly, and trains must be run on time. The engineer who fails to run on time, either through timidity or overcaution, is very soon relegated to the work-train or the yard-engine--a humiliating fall for the master of the queenly flyer. As Byers was a junction, there were two signals there for the government of trains, one a train-signal on the front of the shanty, and the other a semaphore just outside the door. The train-signal was merely an arm or signal-blade, operated by a lever inside the shanty. Normally, this arm hung down in a perpendicular position and showed green, which meant proceed; but when the operator wanted an approaching train to stop, he pulled the lever, raising the arm to a horizontal position. At night, of course, it would not be possible for an engineer to see the position of this arm, so at the inner end of it was a large casting with two holes in it, one fitted with a green lens and the other with a red one. Behind this a lamp was placed, and when the arm hung down for safety, the light shone through the green lens. When it was raised, the red lens was thrown before the light and indicated danger. The semaphore was a tall pole just outside the door. At its top was a cross-arm, bearing at either end red lanterns at night, to indicate its position, and operated by a lever at the foot of the pole. When the arm at the top stood in a perpendicular position, displaying the signals one above the other, it indicated that P. & O. trains could pass; when the arm was thrown to a horizontal position, displaying the signals one beside the other, it cleared the track for the connecting road. A ladder on the side of the pole enabled the person in charge of it to mount and attach the lanterns at nightfall. He was supposed to take them down and fill and clean them sometime during the day. There is, it may be added, a semaphore at every railroad-crossing which is worked on just this principle. Allan had, of course, in preparing himself for the duties of operator, familiarized himself with all the signals used; and, as has been said, he stepped to the door of the shanty to assure himself that the train-signal was raised and showing red and that the lanterns on the semaphore were burning properly, so that the train which was almost due would stop to receive the orders intended for it. Then his heart gave a sudden sickening leap, for the light of neither train-signal nor semaphore was showing at all!