for it was cooling. Folwell threw back the lever, and another man
disconnected the switch. There was a period of waiting until the box was
cool enough to open. Then the heavy door was swung back.

With a long iron rod Folwell drew something from the retort. It was the
tray which had held the white balls. But they were white no longer, for
they had been turned into diamonds. From their hiding-place Tom and the
others could see the flashing gems, for, in spite of the fact that the
diamonds were uncut, some of them sparkled most brilliantly, due to the
peculiar manner in which they were made.

"We have the secret of the diamonds!" whispered Mr. Jenks. "There must
be a quart of the gems there!"

The men gathered about Folwell, uttering exclamations of delight. The
diamonds were too hot to handle yet.

"That's going some!" exclaimed the chief of the diamond makers. "We have
a small fortune here."

The was a sudden commotion at one end of the cave. A man rushed in. At
the sight of him Tom stared and uttered an exclamation.

"Munson--the stowaway!" he whispered.

"Hello!" cried Folwell, as he saw his confederate. "I thought you were
East, keeping Jenks away from here."

"He got the best of me!" cried Munson, "he and that Tom Swift! I stowed
away on their airship, but they found me out by a wireless message,
and marooned me in the woods. I've been trying to get here ever since!
Didn't you get my messages of warning?"

"No--what warnings?" cried Folwell.

"About Jenks, Tom Swift and the others. They're here--they must be on
Phantom Mountain now. In fact, I shouldn't be surprised if they were in
this cave. I traced them to their camp, but they're gone. They may be
among us now--in some of the secret recesses!"

For an instant Folwell stared at the bearer of these tidings. Then he
cried out:

"Scatter men, and find these fellows! We must get them before they
discover our secret!"

"It's too late--we know it!" exulted Tom Swift. Then he whispered to
the others to hurry to the part of the cave where Bill Renshaw had first
hidden them.

CHAPTER XXII--PRISONERS

"Do you think there is any danger of them finding us?" asked Mr. Damon,
as he hurried along beside Tom.

"I'm afraid so," was the answer. "I've been worried ever since we saw
Munson heading this way. But we couldn't do any differently."

"Perhaps Bill Renshaw may be able to conceal us," suggested Mr. Jenks.
"Very likely he knows that Munson is o