These signal codes operate fundamentally in connection with the essential rules of schedule that we have already shown. Suppose now that we consider the workings of all this system as it comes down to actual practice in a single concrete instance. We are finding our way to a big terminal yard in all the murkiness and cloudiness of very early morning, and once again we hunt out that urbane soul, the yardmaster. He holds in his hand the yellow tissue of an order from the despatcher of the division. In the conciseness of telegraphy it tells him to start a third section of train 118--through freight--at 6:15 o'clock. Just back of his little grimy box of an office is the big sprawling roundhouse--a dozen freighters with banked fires standing in the stalls, awaiting summons to work. The twelve engines are divided into several classifications according to pulling strength and speed, but the despatcher has designated the particular engine he wishes for third-118, and he gets it--a big lanky puller--1847. She is chosen chiefly because she has had the longest roundhouse rest, having brought in a through freight from up the line, and having been received with engineer's report showing her to be in good running order, at five o'clock yesterday afternoon. Before the 1847 slipped from the turntable into the waiting stall, the hostlers and the wipers were at her. The hostlers had taken her over the cinder-pit and cleaned out the fire-box. Then they went over her, cleaning her, inch by inch, a mechanical inspector in their wake, testing and sounding and checking every item in the engineer's report which showed 1847 to be in good order at the end of his run with her. There was not much chance left for any shirking of responsibility, no matter what might arise upon the 1847 on any coming day. We turn and watch the yardmaster once again. He has the roundhouse foreman send one of the bright young boys who hang around his office night and day, and who dream of that coming hour when they will handle an 1847 for themselves, to call the engineer and fireman, whose names are posted "first out." Or perhaps the telephone has come into play--in these days in the smaller towns there is hardly a house too humble to have receiver and transmitter hanging somewhere upon its walls. In any event the engine-crew are supposed to stay home when off duty, unless especially excused, and to live within reasonable distance--say a mile--of the roundhouse.