e to begin the generating of
the lifting vapor. To his surprise there was no corresponding hiss
that told of the gas rushing into the bag.

"That's odd," he remarked. "Ned, see if anything is wrong with that
machine. I'll pull the lever again."

The bank clerk stood beside the apparatus, while Tom worked the
handle, but whatever was the matter with it was too intricate or
complicated for Ned to solve.

"I can't see what ails it," he called to his chum. "You better have
a peep."

"All right, I'll look if you work the handle."

The passengers on the airship, which now rested in a little clearing
in the dense jungle, gathered at the engine room door, looking at
Tom and Ned as they worked over the machine.

"Bless my pulley wheel!" exclaimed Mr. Damon "I hope nothing has
gone wrong."

"Well something has!" declared the young inventor in a muffled
voice, for he was down on his hands and knees peering under the gas
apparatus. "One of the compression cylinders has cracked," he added
dubiously. "It must have snapped when we landed this last time. I
came down too heavily."

"What does that mean?" asked Mr. Durban, who did not know much about
machinery.

"It means that I've got to put a new cylinder in," went on Tom.
"It's quite a job, too, but we can't make gas without it!"

"Well, can't you do it just as well up in the air as down here?"
asked Mr. Durban. "Make an ascension, Tom, and do the repairs up
above, where we've got good air, and where--"

He paused suddenly, and seemed to be listening.

"What is it?" asked the young inventor quickly. There was no need to
answer, for, from the jungle without, came the dull booming of the
war drums of some natives.

"That's what I was afraid of!" cried the old elephant hunter,
catching up his gun. "Some black scout has seen us and is summoning
his tribesmen. Hurry, Tom, send up the ship, and we'll take care of
the savages."

"But I CAN'T send her up!" cried Tom.

"You can't? Why not?"

"Because the gas machine won't work until I put in a new cylinder,
and that will take at least a half a day."

"Go up as an aeroplane then!" cried Mr. Damon. "Bless my monkey
wrench, Tom, you've often done it before."

For answer Tom waved his hand toward the thick jungle all about
them.

"We haven't room to get a running start of ten feet." he said, "and
without a start the airship can never rise as a mere aeroplane. The
only way we can get up from the jungle is like a balloon,