Know, O reader, that the business of tunneling is one of the most hazardous and dramatic, albeit interesting, of all known fields of labor. It consists, in these latter days at least, in so far as under-water tunneling is concerned, of sinking huge shafts at either end or side of a river, lake or channel (one hundred feet, perhaps, within the shore line) to a depth of, say, thirty feet below the water level, and from these two points tunneling outward under the bottom of the river until the two ends meet somewhere near the middle. The exact contact and precise joining of these outer ends is considered one of the true tests of skilful engineering. McGlathery personally understood all this but dimly. And even so it could not cheer him any.
And it should be said here that the safety of the men who did the work, and the possibility of it, depended first on the introduction at either end, just at the base of the shafts and then at about every hundred or so feet, as the tunnel progressed outward, of huge cylindrical chambers, or locks, of heavy iron—air locks, no less—fifteen feet in diameter, and closed at each end by massive doors swinging inward toward the shore line, so that the amazing and powerful pressure of air constantly forced outward from the shore by huge engines could not force them open. It was only by the same delicate system which causes water locks to open and close that they could be opened at all. That is, workingmen coming down into the shaft and desiring to pass into the head of the tunnel beyond the lock, would have to first enter one of these locks, which would then gradually be filled with air compressed up to the same pressure as that maintained in the main portion of the tunnel farther in. When this pressure had been reached they could easily open the inward swinging door and pass into the tunnel proper. Here, provided that so much had been completed, they might walk, say, so much as a hundred or more feet, when they would encounter another lock. The pressure in the lock, according to who had last used it, would be either that of the section of the tunnel toward the shore, or of the section beyond, toward the centre of the river. At first, bell cords, later telephones, and then electric signals controlled this—that is, the lowering or raising of the pressure of air in the locks so that one door or the other might be opened. If the pressure in the lock was different from that in your section, and you could not open the door (which you could not), you pulled the cord or pushed the button so many times, according to your position, and the air in the lock was adjusted to the section of the tunnel in which you stood. Then you could open the door. Once in, as in a water lock, the air was raised or lowered, according to your signal, and you could enter the next section outward or inward. All these things had been adjusted to a nicety even in those days, which was years ago.
The digging of this particular tunnel seemed safe enough—for McGlathery at least, once he began working here. It moved at the rate of two and even three feet a day, when things were going well, only there were days and days when, owing to the need of shoring and timbering and plate setting, to say nothing of the accidental encountering of rock in front which had to be drilled away, the men with picks and shovels had to be given a rest, or better yet, set to helping the joiners in erecting those cross beams and supports which made the walls safe. It was so that Dennis learned much about joining and even drilling.
Nevertheless, in spite of the increased pay, this matter of working under the river was a constant source of fear to him. The earth in which he worked was so uncertain. One day it would be hard black mud, another soft, another silt, another sand, according as the tunnel sloped further and further under the bed. In addition, at times great masses of it fell, not enough to make a hole in the roof above, but enough, had it chanced to fall on one of the workers, to break his back or half bury him in mud. Usually it was broken by the beams overhead. Only one day, some seven months after he had begun and when he was becoming fairly accustomed to the idea of working here, and when his skill had increased to such an extent that he was considered one of the most competent workers in his limited field, the unexpected happened.
He had come down one morning at eight with the rest of his gang and was working about the base of two new supports which had just been put in place, when he noticed, or thought he did, that the earth seemed wetter than usual, sticky, watery, and hard to manage. It could not have been much worse had a subterranean spring been encountered. Besides, one of the gasoline lamps having been brought forward and hung close by, he noticed by its light that the ceiling seemed to look silvery gray and beady. He spoke of it to Cavanaugh, who stood by.
“Yis,” said his foreman dubiously, staring upward, “’tis wet. Maybe the air pumps is not workin’ right. I’ll just make sure,” and he sent word to the engineer.
The shaft superintendent himself appeared.
“Everything’s all right up above,” he said. “Two thousand pounds to the square inch. I’ll just put on a little more, if you say so.”
“Ye’d better,” replied Cavanaugh. “The roof’s not actin’ right. And if ye see Mr. Henderson, send him down. I’d like to talk to him.”