he was building his airship. He and Washington were on hand when the
wreck occurred and they took the senseless boys to the airship shed.

The boys, after their recovery, accepted the invitation of the professor
to go on a search for the north pole. As the airship was about to start
Andy Sudds, an old hunter, and two men, Tom Smith and Bill Jones, who
had been called in to assist at the flight, held on too long and were
carried aloft.

Somewhat against their will the three latter made the trip, for the
professor did not want to return to earth with them.

The party had many adventures on the voyage, having to fight savage
animals and more savage Esquimaux. They reached the north pole, but in
the midst of such a violent storm that the ship was overturned, and the
discovery of the long-sought goal availed little. After many hardships,
and a fierce fight to recover the possession of the ship, which had been
seized by natives, the adventurers reached home.

Since then a little over a year had passed. The professor, having found
he could successfully navigate the air, turned his attention to the
water, and began to plan a craft that would sail beneath the ocean.

To this end he had moved his machine shop to this lonely spot on the
Maine coast. The two boys, who had grown no less fond of the old man
than he of them, went with him, as did Washington White, the negro, who
was a genius in his way, though somewhat inclined to use big words, of
the meaning of which he knew little and cared less.

Andy Sudds, the old hunter, had also been induced to accompany the
professor.

"I hunted game up north and in the air," said Andy, "and if there's a
chance to shoot something under the water I'm the one to do it."

Needing more assistance than either the boys, Andy or Washington could
give, the professor had engaged two young machinists, who, under a
strict promise never to divulge any of the secrets of the submarine, had
labored in its building.

Now the queer craft was almost finished. As it rested on the ways in the
shed, it looked exactly like a big cigar, excepting that the top part
was level, forming a platform.

The ship, which had been named the _Porpoise_, was eighty feet long, and
twenty feet in diameter at the largest part. From that it tapered
gradually, until the ends were reached. These consisted of flattened
plates about three feet in diameter, with a hole in the center one foot
in size.

Weary months of labor