It was at a time when this state of affairs seemed seriously to threaten the safety of operation of great terminals that some genius invented the pneumatic control. Instead of a row of great levers requiring the strongest muscles, the towerman found himself confronting a battery of tiny ones, operated by the touch of a finger. And that finger-touch against the slender lever is instantly magnified to the pull of a giant arm against a switch half a mile or more away.
How? By a bewildering intricacy of cogs and valves, by the aid of the electric current and of compressed air, for, in order to perfect this mechanism, man has harnessed the whirlwind and the lightning. That finger-touch brings instantly an electric touch; the electric touch raises a valve which releases the compressed air from a cylinder into which it has been pumped; and the air thus withdrawn from the cylinder in the tower basement is also in the same instant withdrawn from a cylinder opposite the switch-point, by means of a slender pipe which connects the two; and a plunger in the cylinder at the switch moves the switch-point and the signals which protect it.
That seems enough for any mere machine to do—but it does much more. For, by a series of interlocking devices, the switches are so controlled by each other that no signal for a train to proceed can be given until all the other switches over which the train will pass have been properly set and locked, nor can any switch be moved as long as any signal is displayed which gives right of way over it. Thus was the margin of safety further broadened, and the control of a great terminal brought down to three men on each eight hour trick, representing the very cream of their profession.
Approaching trains announce their coming by ringing an electric gong, the chief towerman, of course, knowing just which train is due at that particular instant—knowing, too, if any train is late, and how late and with what other trains it conflicts. He must know the precise second of departure of each train from the shed, and every train must glide smoothly in and out without let or hindrance. He must know; he mustn’t merely think he knows, for this is one of the positions in which a man never has a chance to make two mistakes. For, while the tower machinery is wonderfully adapted to its purpose, it is, after all, the mind of the chief towerman which controls and directs it.
It was not by any means the first time that Allan West had sat watching this fascinating scene, but it had never grown uninteresting and he had never ceased to wonder at it.
“I used to think train-dispatching was a pretty nerve-racking business,” he remarked, after a while, “but it’s child’s play compared with this.”
“Well, I don’t know,” said Jim, his eyes on a through train threading its way cautiously out of the terminal and over the network of switches. “We don’t have to worry about big accidents up here—the interlocking takes care of that. We can’t have a head-end collision, for instance—at least, not while the signals are working properly. What we’ve got to look out for is tangles. If we have to hold one train two or three minutes, that means that two or three other trains will be held up, and before you know it, you’ve got a block ten miles long. Then’s when somebody up here has to do some tall thinking and do it quick. The only way to keep things straight is to keep ’em moving. Sixteen,” he added to his assistants, as the overhead bell rang.
They watched the train as it rolled in, saw it disgorge its load of passengers, saw the baggage and express and mail matter hustled off, saw the yard-engine back up and couple on to the rear coach, and slowly drag the train out from under the train-shed.
“I never watch that done,” added Jim, as the train disappeared down the yards, “but what my heart gets right up in my throat. You don’t know what a way those pesky little yard-engines have of jumping switches. Open sixteen, Sam,” he added, as the big engine which had brought the train in rolled sedately down the yards on the way to the round-house, to be washed out and raked down and coaled up. “Ring off thirteen, Nick,” he said, and Nick touches one of the little handles, a blade on a signal bridge opposite the end of the train-shed drops, there is a sharp puff, puff, of a locomotive, and another train starts slowly from the train-shed on its journey east or west, north or south, as the case may be.