a number of strange machines.

"Yes--the very place where I was," answered Mr. Jenks, "and there is the
apparatus--the steel box--from which the diamonds are taken--now to see
how they make them."

Fascinated, the adventurers looked into the cave. The men there were
unaware of the presence of our friends, and were busily engaged. Some
attended to the grinding machine, the roar and clatter of which made
it possible for Tom and the others to talk and move about without being
overheard. Into this machine certain ingredients were put, and they were
then pulverized, and taken out in powdery form.

The power to run the mixing machine was a gasoline motor, which
chug-chugged away in one corner of the cave.

As the powder was taken out, other men fashioned it into small balls,
which were put on pan, and into a sort of oven, that was heated by a
gasoline stove.

"Is that how they make the diamonds?" asked Mr. Damon.

"That is evidently the first step," said Mr. Jenks. "Those balls of
powdered chemicals are partly baked, and then they are put into the
steel box. In some way terrific heat and pressure are applied, and the
diamonds are made. But how the heat and pressure are obtained is what we
have yet to learn."

He paused to watch the men at work. They were all busy, some attending
to the machines, and others coming and going in and out of the cave. In
one part a man was apparently getting ready a meal.

Suddenly there rushed into the cave a man who seemed much excited.

"Are you nearly ready with that stuff?" he cried. "There's a good storm
gathering on the mountain!"

"Yes, we'll be ready in half an hour," answered one of the men at the
mixing machine.

"Good. It will be flashing lightning bolts then, and we can see what
luck we have. The last batch was a failure." The man hurried out again.
Mr. Parker touched Tom and Mr. Jenks on their shoulders.

"What is it?" asked Tom.

"I know the secret of making the diamonds," said the scientist.

"What?" cried Mr. Jenks.

"It is by the awful power of the lightning bolts!" whispered Mr. Parker.
"Everything is explained now--the reason why they make diamonds in this
lonely place, near the top of the mountain. They need a place where the
lightning is powerful. I can understand it now--I suspected it before.
They make diamonds by lightning!"

"Are you sure?" cried Mr. Jenks.

"Positive."

"I agree with you," said Tom Swift. "I was just getting on that track
myself,