tor, who, in her cousin's small boat, the Dot, was having trouble
with the engine, and you shall hear more of Miss Nestor presently, for
she and Tom became quite friendly. Events so shaped themselves that
Andy Foger was glad to loan Tom the Red Streak in which to search for
the stolen Arrow, and it was in the later craft that Tom, his father
and Ned Newton had a most thrilling adventure.

They were on their way down the lake when, in the air overhead they saw
a balloon on fire, with a man clinging to the trapeze. They managed to
save the fellow's life, after a strenuous endeavor. The balloonist,
John Sharp, was destined to play quite a part in Tom's life.

Mr. Sharp was more than an aeronaut--he was the inventor of an
airship--that is, he had plans drawn for the more important parts, but
he had struck a "snag of clouds," as he expressed it, and could not
make the machine work. His falling in with Mr. Swift and his son seemed
providential, for Tom and his father were at once interested in the
project for navigating the upper air. They began a study of Mr. Sharp's
plans, and the balloonist was now in a fair way to have the difficulty
solved.

His airship was, primarily an aeroplane, but with a sustaining aluminum
container, shaped like a cigar, and filled with a secret gas, made
partly of hydrogen, being very light and powerful. It was testing the
effect of this gas on a small model of the aluminum container that the
explosion, told of in the first chapter, occurred. In fact it was only
one of several explosions, but, as Tom said, all the while they were
eliminating certain difficulties, until now the airship seemed almost a
finished thing. But a few more details remained to be worked out, and
Mr. Swift and his son felt that they could master these.

So it was with a feeling of no little elation, that the young inventor
followed Mr. Sharp into the shop. The balloonist, it may be explained,
had been invited to live with the Swifts pending the completion of the
airship.

"Do you think we'll get on the right track if we put the needle valve
in?" asked Tom, as he noted with satisfaction that the damage from the
explosion was not great.

"I'm sure we will," answered the aeronaut. "Now let's make another
model container, and try the gas again."

They set to work, with Mr. Swift helping them occasionally, and Garret
Jackson, the engineer, lending a hand whenever he was needed. All that
afternoon work on the airship progr