y.

"What's that?" asked Jackson. "Knives, or some other weapons?"

"Neither," answered Tom. "It's a couple of files, and they've been used
lately. I can see something in the grooves yet and--"

Suddenly Tom ceased speaking and drew from his pocket a small but
powerful magnifying glass. Through this he looked at one of the files,
taking it out in front of the shack where the light was better.

"I thought so!" he cried. "Look here, Jackson!"

"What is it?"

"Another clew!" answered Tom.

CHAPTER XXIII

THE GOVERNMENT TEST

For a moment Jackson thought Tom had discovered a clew to, or evidences
of, some crime. He had an unpleasant suspicion, for an instant, that
there was blood on the files, and that it might prove to be the blood
of Mr. Nestor.

But the satisfaction that showed on Tom's face did not seem to indicate
such dire possibilities as these.

"What is it?" asked Jackson, unable to guess at what Tom was looking
through the powerful glass. "What do you see?"

"Metal filings on the grooves of these files," said the young inventor.
"And, unless I'm greatly mistaken, the particles of filings are from
the case of my aircraft silencer!"

"What!" cried the machinist. "Do you mean those are the files used in
weakening the outer case of your new machine, so that it burst a little
while ago?"

"That what I think," answered Tom. "I know it sounds pretty
far-fetched," he went on. "But take a look for yourself. If those
particles on, the files aren't exactly of the same color and texture as
the material of which the silencer case is made, I'll never build
another machine."

Jackson peered through the powerful glass moving out a little farther
from the shack, so as to get the best light possible on the subject of
his examination. It was fast getting dark, but there was enough glow in
the western sky for his purpose.

"Am I right?" asked Tom.

"You're right!" declared his helper. "This is exactly the same metal as
that of which your silencer case is made. It's a peculiar mixture of
aluminum and vanadium steel. I never knew it used in any shop but
yours, and these filings are certainly of that metal. It would seem,
Tom, that these were the files used to cut a crease in the case of your
silencer to weaken it so it would burst."

"My idea exactly!" cried Tom. "The spy, who got into my shop in some
undiscovered manner, did his work and then fled here to hide. He left
his files behind. Mr. Nestor must