Half an hour later, with fast-beating heart, Allan dropped off the train at the little frame shanty which served as the operator's office at Byers Junction. The day operator had been compelled to work thirty-five minutes overtime, and was in no very genial humour in consequence, for if there is one point of honour upon which all operators agree, it is that they shall relieve each other promptly. So the day operator, whose name was Nevins, and who knew that his supper would probably be cold when he got to it, merely nodded to the boy when he appeared in the doorway, put on his coat and hat, picked up his lunch-basket, and went out without saying a word. Allan, his pulses racing, set his basket on the table, took off coat and hat, hung them on a nail near the window, and looked about the little room. The instrument was calling, but not for him, so he had leisure to examine the orders which fluttered from a hook on the wall near by. One was for a train which would be due in a few minutes, and Allan went to the door to see that the signals were properly set and burning. White is no longer a safety signal on any of the larger railroads. The colours now in use are red for danger, and green for safety. Under the old system, the red lens of the lantern might drop out or a tramp might smash it, leaving the lantern showing a white light past which the engineer would run, thinking everything all right. So green was substituted for white, and now white means danger just as much as red does. The only light past which an engineer may run is a green one. In fact, the first rule under the "Use of Signals" is that a signal imperfectly displayed, or the absence of a signal from a place where one is usually shown, must be regarded as a stop signal. The railroads are trying all the time to find some third colour which can be used satisfactorily in signalling. Red for danger and green for safety are very well, as far as they go; but a caution signal is badly needed--one which will not absolutely stop a train, but which will warn the engineer to get it under control and proceed carefully. No such signal which will do the work required of it under all conditions has as yet been devised, although yellow is now used on some roads for this purpose. Of course there are one or two other colours used. A combined green and white signal, for instance, is used to stop a train at a flag station; and a blue flag by day, or a blue light by night, displayed at one or both ends of an engine, car, or train, indicates that workmen are under or about it. When thus protected, it must not be coupled to or moved, and no man may remove these signals but the one who placed them there. This rule is enforced absolutely to safeguard, as far as possible, the lives of the employees of the road.