“Everything.  I guess.” answered Mr. Anderson.

Tom looked to the motor, saw that it was in working order, and shoved over the lever of the gas machine 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, and without the gas—­”

He paused significantly.  The sound of the war drums became louder, and to it was added a weird singing chant.

“The natives!” cried Mr. Anderson.  “They’re coming right this way!  We must fight them off if they attack us!”