[Illustration: Entrance Gates at a Large Station.]
So it was delivered to No. 1, and that train left "H" at full speed, expecting to run thirty-five miles to "K" before meeting No. 2. There was no telegraph office at "I," and there were no passengers to get off or on, and it passed there without stopping, and three miles below ran into No. 2 on a curve.
By one of those strange impulses which seem to come from some unconscious cerebration, the train-despatcher meanwhile had a feeling that something was wrong, and looked again at the message received from "H" and discovered his mistake. But the trains were then out of reach. He still hoped that No. 2 might arrive at "I" first, or that they might meet upon a straight portion of road, and as the time passed he waited at the instrument in a state of suspense which may be imagined. When the news came he left the office, and never returned.
Double tracks make accidents of this character impossible; but introduce a new possibility, that a derailment from any cause upon one track may obstruct the other track so closely ahead of an opposing train that no warning can be given.
[Illustration: Central Switch and Signal Tower.]
Where trains become very numerous additional safeguards are added by multiplying telegraph stations at short intervals, and giving them conspicuous signals of semaphore arms and lanterns, until finally the road is divided into a number of so-called "blocks" of a few miles each; and no train is permitted to enter any block until the train preceding has passed out. And in the approaches to some of our great depots, where trains and tracks are multiplied and confused with cross-overs and switching service, all switches are set and all movements controlled by signals from a single central tower. Sometimes, by very expensive and complicated apparatus, it is made mechanically impossible to open a track for the movement of a train without previously locking all openings by which another train might interfere. The illustrations on pages 169, 171, and above will serve to give some general idea of these appliances.[17]
[Illustration: Mantua Junction, West Philadelphia, showing a Complex System of Interlacing Tracks.]
There remains one other branch of the duties of the master of transportation--the proper daily distribution of cars to every station according to its needs, and the keeping record of their whereabouts. And now that the gauges of all roads are similar, and competition enforces through shipments, roads are practically making common property of each other's cars, and the detail and trouble of keeping record of them become enormous.