Chapter XX. Suspicious Actions

The chase was kept up, and Tom, when he had a chance to look up at the speed register, as he labored frantically at the clogged gas machine, saw that they were rushing along as they never had before.

"Are we catching them, Ned?" he cried to his chum, who was not far away, playing the powerful light on the smugglers' craft.

"I think we're coming closer, but it's going to be a long chase. I don't see why we can't close up on 'em."

"Because they've got a very fast ship, Ned, and they are flying much lighter than we are. But we'll get 'em!"

"How are you making out with that gas machine?"

"Well, I'm doing all I can, but I can't seem to get the pressure down. I can't understand it. Some of the pipes must be clogged with a carbon deposit. I ought to have cleaned them out some time ago."

Ned gave a hasty glance at the gauge which showed the gas pressure. It registered six hundred pounds now, having risen a hundred in a short time.

"And she'll go up, sure, at eight hundred," murmured Ned, as he held the light steadily on the smugglers' aircraft. "Well, if Tom sticks to the chase, I will too, but I think it would be better to go down, open up everything, and let the gas escape. We could get the rascals later."

Tom, however, did not seem to think so, for he kept on with his task, working away at the pipes, trying to force the obstruction out, so that the gas from the generator would flow into the bag. At the same time he tried to shut off the generating apparatus, but that had become jammed in consequence of the pipe clogging, and the powerful vapor continued to manufacture itself automatically in spite of all that Tom could do.

The only safe way out of the danger, unless he could remove the obstruction, was to descend to earth, and, as Ned had said, open every outlet. But to have done that in mid-air would have been dangerous, as the large volume of gas, suddenly liberated, would have hung about the airship in a cloud, smothering all on board. If they were on the earth they could run away from it, and remain away until the vapor had blown off.

"Is Mr. Damon keeping her on the course, Ned?" asked Tom, pausing a moment to get his breath after a series of frantic efforts.

"Yes, and I think we're closing in on them a little."

"That's good. Are they still headed for the border?"

"Yes, I guess they're going to take no chances to-night. They're going right back to Canada where they came from."

"Well, we'll be hot after 'em. Whistle through the tube, and tell Koku to come here and give me a hand. He's with Mr. Damon in the pilot house."

Ned sent the message, and then gave his whole attention to the light. This was necessary, as the smugglers were resorting to dodging tactics, in an