feet. When the gases cool down sufficiently, we can force them out with compressed air. So you see we can let the powder explode without injuring anybody except the magazine tender. But the men outside would not be in danger, and the busy city two hundred and fifty feet above would scarcely know that anything had happened.”
“But,” said Will, who had been by no means convinced, “I thought nothing could stand up against such a quantity of dynamite. I don't see how any door can hold it.”
“Do you know,” said Mr, Douglas, “there is more energy in a pound of gasolene than in a 
THE DOORWAY LEADING INTO THE DYNAMITE MAGAZINE. pound of dynamite? But here is the difference, gasolene combustion is comparatively slow, while the chief value of dynamite is the suddenness of its explosion. It is chiefly that first explosion wave that we must guard against, and so we make it dash itself against the rock walls until it is pretty well spent. This door here” (we had come to the end of the passageway by this time), “is made to stand twice the pressure that we estimate it will be subjected to. See, it is built of heavy steel I-beams, with oak timbers twelve inches square between them; and then the door-way is set in an enormous mass of concrete, Oh, no, it could not possibly give way.”
“But have you tried it?” asked Will,
“Oh, yes: we exploded half a dozen sticks just around the first bend, and it slammed the door shut, nicely, and the drain here—but I have n't shown you that yet.” here was a gutter running down the center of the rock floor of the passage to carry off any moisture that might seep in. “We have to run that drain through to the outside, and that ventilating pipe you see overhead also has to have some connection with the outside, and so we have an opening under that plate in the floor and a tapered plug hanging on a guide rod just in front of the opening. Well, as I was saying, when the powder went off, it drove that plug in the drain so hard that we had to use a hydraulic jack to force it out,”
“But,” persisted Will, “you have never exploded a full charge of one thousand pounds, have you?”
Mr, Douglas laughed. “Look here, young man, you would make a pretty good lawyer. No, we have never tried it here, but in Europe, where the idea originated, because they have to do so much mining right under large towns, fully as much powder as that was set off once without the slightest damage to anything outside, There was a small car in front of the door of the magazine, but it was not in the least affected by the explosion.”
It was wonderful, and I was glad we had seen it, but all the same it was a decided relief to step out of that deadly chamber.
Just as we emerged from the magazine, the lights in the tunnel began to wink slowly once, twice, three times.
“Hello!” exclaimed Mr. Douglas, “that is the signal to hunt for cover, They are going to shoot the heading in half a minute. We had hetter step into the magazine to be sure that no flying pieces of rock hit us,”
“The magazine!" I cried in astonishment. Of all places on earth that was the last I would ever seek as a refuge from a blast, but I was hustled into the place before I had time to make any protest.
When we got inside, I expected them to shut the door. In fact, Will and I both tried to shut the door because we knew there was no time to lose, as Mr. Douglas had said that the shot would be fired in half a minute after the signal. But he motioned to us to desist. “We never close that door. That counterweight is put there for the very purpose of holding the door open,” he said, pointing to a rope that ran from the top of the door over a pulley on the wall, and was attached to a heavy iron weight.
You can imagine our feelings. Forced to seek shelter in a cave charged with dynamite, a thousand pounds of it! What was to prevent the shock from setting it off? and then where would we be? A thousand thoughts chased through my brain in the brief moment before the explosion came.
It is a curious thing about blasting, that the sound travels through the rock much faster than it does through the air, and so there is always a warning crack an instant before the crash of the air wave reaches the ear. Just before the warning sound came, the superintendent shouted something that I did n’t catch; but I saw him grab at his hat, and I followed his example, not a moment too soon, The next instant, I was engulfed932
