was hung aft, an opening in it allowing
the screw or propeller to revolve.

The boys were lost in admiration of the wonderful airship. They were
consumed with curiosity as to how the machinery worked, and they thought
no more of their knocks and bruises than as if a mosquito had bitten
them. The professor watched their faces with delight. He loved boys and
mechanical apparatus.

"Now we will enter the _Monarch_," he said. "Turn on the lights,
Washington."

There was a click, and the cabin of the airship was flooded with a soft
glow of incandescent lamps.

"Come on!" called Mr. Henderson, leading the way. The boys followed,
marveling at the wonders on every side.

They found the cabin of the strange craft divided into three parts.
First came a sort of parlor, with a table and seats arranged on the
sides. In the front part of this was a passage leading to the conning
tower, or the place for the steersman. Behind the parlor came the
sleeping quarters and dining room combined. The bunks were arranged to
fold against the wall, and a table in the centre could be shut up when
not in use and hoisted to the ceiling, giving plenty of space.

Next came the engine room, and as they entered it the boys could hardly
restrain from giving cheers of delight. It was almost filled with
machinery, and occupied a little more than half of the whole boat, being
twenty-two by ten feet in size.

The two boys did not know the use of one quarter of the machinery and
apparatus they gazed on. There were electric motors, storage batteries,
two gasoline engines similar to those used in automobiles, pumps, large
and small tanks, instruments for measuring the electric current, for
telling the temperature, the amount of moisture in the air, the speed of
the wind, the speed of the ship, the height to which it went, besides
compasses, barometers, telescopes, and other instruments.

There were levers and wheels on every side, switches, valves, electric
plugs and handles. Lockers arranged close to the wall and along the
floor held supplies and materials. Everything was new and shining, and
the professor smiled with pride as he touched piece after piece of
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 ob