d slowly back and forward. It seemed to be covered with
a net-work of cords. On the ground beneath it was what seemed to be a
good-sized boat, with a large cabin amidships.

"What in the world is it?" cried Jack.

"It's my airship!" exclaimed Professor Henderson. "The only successful
airship ever invented. It is the electric _Monarch_!"

"What is it for?" asked Mark.

"To navigate the realm of the stars and moon!" cried the old man. "With
that I will rival the eagles in their flight!"

The boys were a little alarmed. The professor was strangely excited. His
eyes sparkled in the reflected light of the lamp. Jack and Mark thought
they might have been brought to the abode of a madman. They shrank back
a little. But they were reassured a moment later when, with a pleasant
laugh, the old man said:

"Don't be frightened, boys. I know what I am talking about. Here,
Washington, more light! We will show them what we have done, hidden away
from the sight of the curious, unbelieving world. Let them see my
_Monarch_!"

"We'll illuminationness dis abode like it was de orb ob day shinin'
heah!" exclaimed the negro, as he started several more lamps aglow.

"Are the shutters closed?" asked Mr. Henderson, anxiously.

"Tight as a drum-head," was the reply.

"Now look!" exclaimed the inventor, turning to the boys.

They were more than astonished at what they saw. They had no idea that
the rough shed held such a perfect piece of machinery.

Up near the roof of the place, which was quite high, there swayed an
immense bag of oiled silk. It was shaped like a cigar, big in the middle
and tapering at both ends. The bag was enclosed in a net of ropes which
extended down to the lower part of the airship.

This lower part, as the boys could see, was just like a steam launch in
shape, only much lighter in weight. It had a sharp bow, and a blunt
stern. From the stern there extended a large propeller, the blades being
made from sheets of aluminum.

The main part of the ship proper, or the part suspended from the gas
bag, was covered by a closed and roofed cabin about forty feet long, ten
feet wide, and extending five feet above the gunwale of the ship. The
cabin had four windows on each side, a companionway fore and aft, and a
sort of look-out or conning tower forward, which, the professor
explained, was the place for the steersman.

"Because this ship can be steered wherever you want to go," he said,
pointing to the big rudder that