The above conversation took place as our friends lay securely bound in a small cave, or recess, opening from the larger cavern, where, about an hour before, they had been captured and made prisoners by the diamond makers.  Despite their struggles they had been overpowered and bound, being carried to the cave, where they were laid in a row on some old bags.

“It certainly is a most unpleasant situation, to say the least,” observed Mr. Parker.

“And all my fault,” repeated Mr. Jenks.

“Oh, no it isn’t,” declared Tom Swift, quickly.  “We were just as ready to follow you into that cave as you were to go.  No one could tell that the men would return so soon.  It’s nobody’s fault.  It’s just our bad luck.”

From where he lay, tied hand and foot, the young inventor could look out into the cave where he and the others had been caught.  The diamond makers were busily engaged, apparently in getting ready to manufacture another batch of the precious stones.  They paid little attention to their captives, save to warn them, when they had first been taken into the little cave, that it was useless to try to escape.

“They needn’t have told us that,” observed Tom, as he and the others were talking over their situation in low voices.  “I don’t believe any one could loosen these ropes.”

“They certainly are pretty tight,” agreed Mr. Damon.  “I’ve been tugging and straining at mine for the last half hour, and all I’ve succeeded in doing is to make the cords cut into my flesh.”

“Better give it up,” advised Mr. Jenks.

“We’ll just have to wait.”

“For what?” the scientist wanted to know.

“To see what they’ll do with us.  They can’t keep us here forever.  They’ll have to let us go some time.”  Following their capture, Folwell and Munson, the latter the stowaway of the airship, had been in earnest conversation regarding our friends, but what conclusion they had reached the adventurers could only guess.

“And we didn’t have time to examine the diamond-making machinery close enough so that we could duplicate it if necessary,” complained Tom, a little later.

“No,” agreed Mr. Jenks.  “There are certain things about it that are not clear to me.  Well, I don’t believe I’ll have another chance to inspect it.  They’ll take good care of that, though they seem to be getting ready to make more diamonds.”

“Perhaps they’re going to manufacture a big batch, and then leave this place,” suggested Mr. Damon.  “They will probably go to some other secret cave, and leave us here.”

“I hope they untie us before they leave, and give us something to eat,” remarked the young inventor.

For two hours longer the captives lay there, in most uncomfortable positions.  Then Folwell and Munson, leaving the group of diamond makers who were grouped about the machinery, approached the captives.

“Well,” remarked Munson, “we got ahead of you after all; didn’t we.  You thought you had our secret, but it will be a long while before you ever make diamonds.”