Eagerly the adventurers looked through the opening at the end of the passage into the larger cave. The men opened the small oven in which the balls of white chemicals and carbon mixed, had been baked, and a pile of things, that looked like irregularly-shaped marbles, were placed in the steel box.
This box, which was about the size of a trunk, was of massive metal. It was placed in a recess in the solid rock, and all about were layers of asbestos and other substances that were nonconductors of heat.
“That box becomes red hot,” exclaimed Mr. Jenks, in a whisper. “When things are in readiness, that lever is pulled and the diamonds are made. I pulled it once, but I did not then know the process involved. I supposed that the lightning had nothing to do with making the diamonds.”
“It has—a most important part,” said Mr. Parker. The hidden adventurers could talk in perfect safety now, for the men in the large cave were too excited to pay much attention to them. The muttering of the thunder grew louder, and at times a particularly loud crash told that a bolt had struck somewhere in the vicinity of the cave.
“But, bless my watch-charm!” exclaimed Mr. Damon, “I didn't know lightning made diamonds.”
“It does not—always,” went on the scientist. “But great heat and pressure are necessary to create the gems. In nature this was probably obtained by prehistoric volcanic fires, and by the terrific pressure of immense rocks. It is possible to make diamonds in the laboratory of the chemist, but they are so minute as to be practically valueless.
“However, these men seem to have hit upon a new plan. They utilize the terrific heat of lightning, and the pressure which is instantaneously obtained when the bolt strikes. I am anxious to see how it is done. Look, I think they are getting ready to make the gems.”
Indeed there seemed to be an air of expectancy among the diamond makers. The mixing machine had now been stopped, and, as it was more quiet in the cave, our friends, in their hiding-place, had to speak in mere whispers. All the men were now gathered about the great steel box.
This receptacle had been closed by a solid metal door, which was screwed and clamped tight. Then one of the men examined a number of heavily insulated electric wires that extended from the box off into the darkness where Tom and his companions could not discern them.
“That's Folwell—the man I befriended, and who got me into this game,” whispered Mr. Jenks. “He was also one of the first to turn against me. I think he's one of the leaders.”
Folwell came back, after having gone into a dark part of the cave. He went over to an electrical switch on one of the stone walls.
“It's almost time,” Tom heard him say to his confederates. “The storm is coming up rapidly.”
“Will it be severe enough?” asked one of the helpers. “We had all our work for nothing last time. The flashes weren't heavy enough.”
“These will be,” asserted Folwell. “The indicator shows nearly a million volts now, and it's increasing.”
“A million volts!” exclaimed Tom. “I hope it doesn't strike anywhere around here.”
“Oh, it will probably be harmlessly conducted down on the heavy wires,” said Mr. Parker. “We are in no danger, at present, though ultimately I expect to see the whole mountain shattered by a lightning bolt.”
“Cheerful prospect,” murmured Tom.
There was a terrific crash outside. The rocky floor of the cave trembled.
“Here she comes!” cried Folwell. “Get back, everybody! I'm going to throw over the switch now!”
The men retreated well away from the steel box. Folwell threw over the lever—the same one Mr. Jenks remembered pulling. Then the man ran to the electric switch on the wall, and snapped that into place, establishing a connection.
There was a moment's pause, as Folwell ran to join the others in their place of safety. Then from without there came a most nerve-racking and terrifying crash. It seemed as if the very mountain would be rent into fragments.
Watching with eager eyes, the adventurers saw sparks flash from the steel box. Instantly it became red hot, and then glowed white and incandescent. It was almost at the melting point.
Then came comparative quiet, as the echoes of the thunder died away amid the mountain peaks.
“I guess that did the trick!” cried Folwell. “It was a terrific crash all right!”
He and the others ran forward. The steel box was now a cherry red, 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.
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