Chapter XIV. Mysterious Disappearances

There was a dull, muffled report, a sort of rumbling that seemed to extend away down under the earth and then echo back again until the ground near the mouth of the tunnel, where the party was standing, appeared to rock and heave. There followed a cloud of yellow, heavy smoke which made one choke and gasp, and Tom, seeing it, cried:

"Down! Down, everybody! There's a back draft, and if you breathe any of that powder vapor you'll have a fearful headache! Get down, until the smoke rises!"

The tunnel contractors and their men understood the danger, for they had handled explosives before. It is a well-known fact that the fumes of dynamite and other giant powders will often produce severe headaches, and even illness. Tom's explosive contained a certain percentage of dynamite, and he knew its ill effects. Stretched prone, or crouching on the ground, there was little danger, as the fumes, being lighter than air, rose. The yellow haze soon drifted away, and it was safe to rise.

"Well, I wonder how much rock your explosive tore loose for us, Tom," observed Job Titus, as he looked at the thin, yellowish cloud of smoke that was still lazily drifting from the tunnel.

"Can't tell until we go in and take a look," replied the young inventor. "It won't be safe to go in for a while yet, though. That smoke will hang in there a long time. I didn't think there'd be a back draft."

"There is, for we've often had the same trouble with our shots," Walter Titus said. "I can't account for it unless there is some opening in the shaft, connecting with the outer air, which admits a wind that drives the smoke out of the mouth, instead of forward into the blast hole. It's a queer thing and we haven't been able to get at the bottom of it."

"That's right," agreed his brother. "We've looked for some opening, or natural shaft, but haven't been able to find it. Sometimes we shoot off a charge and everything goes well, the smoke disappears in a few minutes. Again it will all blow out this way and we lose half a day waiting for the air to clear. There's a hidden shaft, or natural chimney, I'm sure, but we can't find it."

"Thot blast didn't make much racket," commented Tim Sullivan. "I doubt thot much rock come down. An' thot's not sayin' anythin' ag'in yer powder, lad," he went on to Tom.

"Oh, that's all right," Tom Swift replied, with a laugh. "My explosive doesn't work by sound. It has lots of power, but it doesn't produce much concussion."

"We've often made more noise with our blasts," confirmed Job Titus, "but I can't say much for our results."

They were all anxious, Tom included, to hurry into the tunnel to see how much rock had been loosened by the blast, but it was not safe to venture in until the fumes had been allowed to