And upon no one is this backing-out process more wearing than on the towerman, for the trains must be handled twice over the same track, and of course the track must be kept clear until the train is out again and safely on its way. Now there is never any surplusage of tracks in a terminal. Indeed, as one sees the tracks narrow and narrow as the terminal is approached, until they are merged into those which plunge beneath the train-shed, one is apt to think they are all too few. Yet their number has been calculated with the greatest care; there is not one more than is needed by the nicest economy of operation—nor one less. The number is just right for the station’s needs—so long as the towerman knows his business and keeps his head. And now to return to the glass-enclosed perch where, for eight hours of every day, Jim Davis and his two assistants send the trains in and out over the network of tracks. That long row of little handles is the last word in switch-control. Time was—and is, in all but the most important stations—when the towerman opened or closed the yard-switches by means of great levers. To throw one of these levers was no small athletic feat, especially if the switch it controlled was at some distance, and to keep at it eight hours at a time reduced the strongest man to mental and physical exhaustion. When the towerman left his work at the end of his trick, he was, in the expressive parlance of the day, “all in.” Now when men are “all in,” they are very apt to make mistakes, hence in a busy terminal under the old system, accidents more or less serious were of almost every-day occurrence. Besides which, the number of levers which one man was physically able to operate was comparatively small, so that there must be many men and a consequent divided responsibility and opportunity for confusion. The tower itself had been an evolution, for, at first, these yard-switches had been controlled by a brigade of switchmen, each of whom had two or three under his supervision, which he turned by hand whenever he saw a train coming his way. Then the hand switchmen were supplanted by a cluster of levers in a tower, operated by a single man. The tower was so located that its occupant had a general view of the yards, and the levers were connected by steel rods with the switches and signals which protected them. For every switch must have its signal—that is, a device by which the engineer of the approaching train may see whether the switch is properly set—the old standards showing yellow when the switch was open and red when it was closed—and since replaced by arms, or semaphores, which hang down when the train may pass and bar the way when it must stop.