However, a lot of things may happen ere then. I have learned one good thing from this conversation, and that is that if Thomas Roch has sold his explosive to Ker Karraje and Co., he has at any rate, kept the secret of his deflagrator, without which the explosive is of no more value than the dust of the highway.

But before terminating the interview I think I ought to make a very natural observation to Mr. Serko.

"Sir," I say, "you are now acquainted with the composition of Thomas Roch's explosive. Does it really possess the destructive power that the inventor attributes to it? Has it ever been tried? May you not have purchased a composition as inert as a pinch of snuff?"

"You are doubtless better informed upon this point than you pretend, Mr. Hart. Nevertheless, I thank you for the interest you manifest in our affairs, and am able to reassure you. The other night we made a series of decisive experiments. With only a few grains of this substance great blocks of rock were reduced to impalpable dust!"

This explanation evidently applies to the detonation I heard.

"Thus, my dear colleague," continues Engineer Serko, "I can assure you that our expectations have been answered. The effects of the explosive surpass anything that could have been imagined. A few thousand tons of it would burst our spheroid and scatter the fragments into space. You can be absolutely certain that it is capable of destroying no matter what vessel at a distance considerably greater than that attained by present projectiles and within a zone of at least a mile. The weak point in the invention is that rather too much time has to be expended in regulating the firing."

Engineer Serko stops short, as though reluctant to give any further information, but finally adds:

"Therefore, I end as I began, Mr. Hart. Resign yourself to the inevitable. Accept your new existence without reserve. Give yourself up to the tranquil delights of this subterranean life. If one is in good health, one preserves it; if one has lost one's health, one recovers it here. That is what is happening to your fellow countryman. Yes, the best thing you can do is to resign yourself to your lot."

Thereupon this giver of good advice leaves me, after saluting me with a friendly gesture, like a man whose good intentions merit appreciation. But what irony there is in his words, in his glance, in his attitude. Shall I ever be able to get even with him?

I now know that at any rate it is not easy to regulate the aim of Roch's auto-propulsive engine. It is probable that it always bursts at the same distance, and that beyond the zone in which the effects of the fulgurator are so terrible, and once it has been passed, a ship is safe from its effects. If I could only inform the world of this vital fact!

_August 20_.--For two days no incident worth recording has occurred. I have explored Back Cup to its extreme limits. At night when the long perspective of arched columns are illuminated by the electric lamps, I am almost religiously impressed when I gaze upon the natural wonders of this cavern, which has become my prison. I have never given up hope of finding somewhere in the walls a fissure of some kind of which the pirates are ignorant and through which I could make my escape. It is true that once outside I should have to wait till a passing ship hove in sight. My evasion would speedily be known at the Beehive, and I should soon be recaptured, unless--a happy thought strikes me--unless I could get at the _Ebba's_ boat that was drawn up high and dry on the little sandy beach in the creek. In this I might be able to make my way to St. George or Hamilton.

This evening--it was about nine o'clock--I stretched myself on a bed of sand at the foot of one of the columns, about one hundred yards to the east of the lagoon. Shortly afterwards I heard footsteps, then voices. Hiding myself as best I could behind the rocky base of the pillar, I listened with all my ears.

I recognized the voices as those of Ker Karraje and Engineer Serko. The two men stopped close to where I was lying, and continued their conversation in English--which is the language generally used in Back Cup.