“Planning something new?” asked Mr. Jenks, with an attempt at jollity, which, however, failed.  The man had a curious air about him, as if he was carrying some secret that was too much for him.

“Well, nothing exactly new,” answered Tom.  “At best I am merely going to try an experiment.”

“An experiment, eh?” resumed Mr. Jenks, “And might I ask if it has anything to do with rescuing us from this island?”

“I hope it will have,” answered Tom, gravely.

“Good!” exclaimed Mr. Jenks.  “Well, now I have a proposition to make to you.  I suppose you are not very wealthy, Mr. Swift?” He gazed at Tom, quizzically.

“I am not poor,” was the young inventor’s proud answer, “but I would be glad to make more money—­legitimately.”

“I thought so.  Most every one would.  Look here!”

He approached closer to Tom, and, pulling his hand from his pocket, held it extended, in the palm were a number of irregularly-shaped objects—­stones or crystals the lad took them to be, yet they did not look like ordinary stones or crystals.

“Do you know what those are?” asked Mr. Jenks.

“I might guess,” replied Tom.

“I’ll save you the trouble.  They are diamonds!  Diamonds of the very first water, but uncut.  Now to the point.  I have half a million dollars worth of them.  If you get me safely off this island, I will agree to make you a quarter of a million dollars worth of diamonds!”

“Make me a quarter of a million dollars worth of diamonds?” asked Tom, struck by the use of the work “make.”

“Yes, ‘make,’” answered Mr. Jenks.  “That is if I can discover the secret—­the secret of Phantom Mountain.  Get me away from the island and I will share my knowledge with you—­I need help—­help to learn the secret and help to make the diamonds—­see, there are some of the first ones made, but I have been defrauded of my rights—­I need the aid of a young fellow like you.  Will you help?  See, I’ll give you some diamonds now.  They are genuine, though they are not like ordinary diamonds.  I made them.  Will you—­”

Before Tom could answer, there came a warning rumble of the earth, and a great fissure opened, almost at the feet of Mr. Jenks, who, with a cry of fear, leaped toward the young inventor.

CHAPTER XIX

SECRET OPERATIONS

“Help me save this machinery!” yelled Tom, whose first thought was for the electrical apparatus.  “Don’t let it fall into that chasm!”

For the crack had widened, until it was almost to the place where the parts of the wrecked airship had been carried.

“The machinery?  What do I care about the machinery?” cried Mr. Jenks.  “I want to save my life!”

“And this machinery is our only hope!” retorted Tom.  He began tugging at the heavy dynamos and gasolene engine, but he might have saved himself the trouble, for with the same suddenness with which it opened, the crack closed again.  The shock had done it, and, as if satisfied with that phenomena, the earthquake ceased, and the island no longer trembled.