could pick
out any certain one, though he had extraordinarily good eyesight.
However, the airship was now afloat and, starting the motor, Mr. Sharp
found that even with one propeller the Red Cloud did fairly well,
making good speed.

"Now for home, to repair everything, and we'll be ready for a longer
trip," the aeronaut said to the young inventor, as they turned around,
and headed off before the wind, while hundreds below them cheered.

"We ought to carry spare propellers if we're going to smash into school
towers," remarked Tom. "I seem to be a sort of hoodoo."

"Nonsense! It wasn't your fault at all," commented Mr. Sharp warmly.
"It would have happened to me had I been steering. But we will take an
extra propeller along after this."

An hour later they arrived in front of the big shed and the Red Cloud
was safely housed. Mr. Swift was just beginning to get anxious about
his son and his friend, and was glad to welcome them back.

"Now for a big trip, in about a week!" exclaimed Mr. Sharp
enthusiastically. "You'll come with us, won't you, Mr. Swift?"

The inventor slowly shook his head.

"Not on a trip," he said. "I may go for a trial spin with you, but I've
got too important a matter under way to venture on a long trip," and he
turned away without explaining what it was. But Tom and Mr. Sharp were
soon to learn.

Chapter 7

Andy Tries a Trick

Without loss of time the young inventor and the aeronaut began to
repair the damage done to the Red Cloud by colliding with the tower.
The most important part to reconstruct was the propeller, and Mr. Sharp
decided to make two, instead of one, in order to have an extra one in
case of future accidents.

Tom's task was to arrange the mechanism so that, hereafter, the rudder
could not become jammed, and so prevent the airship from steering
properly. This the lad accomplished by a simple but effective device
which, when the balloonist saw it, caused him to compliment Tom.

"That's worth patenting," he declared. "I advise you to take out papers
on that."

"It seems such a simple thing," answered the youth. "And I don't see
much use of spending the money for a patent. Airships aren't likely to
be so numerous that I could make anything off that patent."

"You take my advice," insisted Mr. Sharp. "Airships are going to be
used more in the future than you have any idea of. You get that device
patented."

Tom did so, and, not many years afterward he was glad t