it, or rather, don't hear it, and I think you'll agree
with me. Silent Sam for Uncle Sam!"

"Good!" cried Mr. Damon. "Bless my dictionary, but that's a good name!
Does it sail silently, Tom?"

"I'll let you judge presently. Silent Sam is all ready for his first
trial, and I'll be glad to have you with me. Now, I'll just--"

Tom suddenly ceased speaking and held up a hand to enjoin silence.
Then, while Mr. Damon watched, the young inventor began moving
noiselessly toward the rear of the big shed, inside which was his new
machine.

CHAPTER XVIII

SUSPICIONS

"Who's there?" suddenly called Tom, and in such a sharp voice that Mr.
Damon started, ready as he was for something unusual.

There was no answer and Tom suddenly switched on all the lights in the
shed. Up to then there had been only a few glowing--just enough for him
to show the new Air Scout to his friend.

"Who's there?" asked Tom again, sharply.

"Bless my opera glasses, Tom!" cried Mr. Damon, "but are you seeing
things?"

"No; but I'm hearing them," answered Tom with a short laugh. "Did you
think you heard some one moving around near the rudders of Silent Sam,
Mr. Damon?"

"No, I can't say that I did. Everything seems to me to be all right."

"Well, it doesn't to me," went on Tom grimly. "I think there is an
intruder in this shed, though how any one could get in when the doors
have been locked all day, is more than I can figure out. But I'm going
to have a look."

"I'll help you," offered Mr. Damon, and, in the bright glare from many
electric lights, the two began a search of the big hangar where the new
craft was kept.

But though the young inventor and his friend went around to the rear of
the aeroplane, walking in opposite directions, they saw no one, nor did
any one try to escape past them.

"And yet I was sure I heard some one in here," declared Tom, when a
search had revealed nothing. "It sounded as if some one were scuffling
softly about in rubber-soled shoes, trying to hide."

"Bless my suspenders!" cried Mr. Damon, "who do you think it could have
been, Tom?"

"Who else but some spy trying to get possession of my secrets?" was the
answer. "But I guess I was too quick for them. They couldn't learn much
from looking at the outside of my muffler, and it hasn't been
disturbed, as far as I can see."

"Who would want to gain a knowledge of it in that unlawful way?" asked
Mr. Damon.

"Perhaps some of the Universal crowd. They