machinery, and looked at the different instruments.

"Now we'll go out on the stern," he said.

The boys followed as he ascended the companion steps and emerged on a
small platform at the rear end of the cabin.

"Do you know what this is?" asked the professor, touching a long, thin,
round object.

"Looks like a gun," replied Mark.

"That's just what it is. It's a machine gun that will fire one hundred
shots a minute, and it can be turned in any direction, as it works on a
swivel. I don't know that we'll have any use for it, but I thought I'd
take it along."

Then the professor pointed out where the propeller shaft ran from the
engine room out through the stern, and showed how the rudder was worked
by wire ropes extending from it to the conning tower.

"In short we have everything necessary to successfully navigate the
air," he went on. "Not a thing has been overlooked. All I have to do is
to fill the big bag of oiled silk with a new gas I have discovered and
up we go. This is really the most important part of the invention.
Without this powerful gas the airship would not rise above the earth.

"But I have found this gas, which can be made in unlimited quantities
from simple materials that we can carry with us. The gas has enormous
lifting power, and if it was not for that I would not dare make such a