No more sharks were to be seen, but I concluded that it would be as well to refrain from taking a bath in the lagoon for some days to come.

I now know exactly where the entrance to the tunnel is situated. The orifice on this side is only ten feet below the edge of the western bank. But of what use is this knowledge to me?

_August 7_.--Twelve days have elapsed since the Count d'Artigas, Engineer Serko, and Captain Spade put to sea. There is nothing to indicate that their return is expected, though the tug is always kept in readiness for immediate departure by Gibson, the engine-driver. If the _Ebba_ is not afraid to enter the ports of the United States by day, I rather fancy she prefers to enter the rocky channel of Back Cup at nightfall. I also fancy, somehow, that Ker Karraje and his companions will return to-night.

_August 10_.--At ten o'clock last night, as I antic.i.p.ated, the tug went under and out, just in time to meet the _Ebba_ and tow her through the channel to her creek, after which she returned with Ker Karraje and the others.

When I look out this morning, I see Thomas Roch and Engineer Serko walking down to the lagoon, and talking. What they are talking about I can easily guess. I go forward and take a good look at my ex-patient.

He is asking questions of Engineer Serko With great animation. His eyes gleam, his face is flushed, and he is all eagerness to reach the jetty. Engineer Serko can hardly keep up with him.

The crew of the tug are unloading her, and they have just brought ash.o.r.e ten medium-sized boxes. These boxes bear a peculiar red mark, which Thomas Roch examines closely.

Engineer Serko orders the men to transport them to the storehouses on the left bank, and the boxes are forthwith loaded on a boat and rowed over.

In my opinion, these boxes contain the substances by the combination or mixture of which, the fulgurator and deflagrator are to be made.

The engines, doubtless, are being made in an American foundry, and when they are ready, the schooner will fetch them and bring them to Back Cup.

For once in a while, anyhow, the _Ebba_ has not returned with any stolen merchandise. She went out and has returned with a clear bill.

But with what terrible power Ker Karraje will be armed for both offensive and defensive operations at sea! If Thomas Roch is to be credited, this fulgurator could shatter the terrestrial spheroid at one blow. And who knows but what one day, he will try the experiment?

CHAPTER XII.

ENGINEER SERKO'S ADVICE.

Thomas Roch has started work and spends hours and hours in a wooden shed on the left bank of the lagoon that has been set apart as his laboratory and workshop. No one enters it except himself. Does he insist upon preparing the explosive in secret and does he intend to keep the formula thereof to himself? I should not wonder.

The manner of employing Roch's fulgurator is, I believe, very simple indeed. The projectile in which it is used requires neither gun nor mortar to launch it, nor pneumatic tube like the Zalinski sh.e.l.l. It is autopropulsive, it projects itself, and no ship within a certain zone when the engine explodes could escape utter destruction. With such a weapon as this at his command Ker Karraje would be invincible.

_From August 11 to August 17_.--During the past week Thomas Roch has been working without intermission. Every morning the inventor goes to his laboratory and does not issue therefrom till night. I have made no attempt to stop him or speak to him, knowing that it would be useless to do so.

Although he is still indifferent to everything that does not touch upon his work he appears to be perfectly self-possessed. Why should he not have recovered his reason? Has he not obtained what he has so long sought for? Is he not at last able to carry out the plans he formed years and years ago?

_August 18_.--At one o'clock this morning I was roused by several detonations.

"Has Back Cup been attacked?" was my first thought. "Has the schooner excited suspicion, and been chased to the entrance to the pa.s.ses? Is the island being bombarded with a view to its destruction? Has justice at last overtaken these evil-doers ere Thomas Roch has been able to complete the manufacture of his explosive, and before the autopropulsive engine could be fetched from the continent?"

The detonations, which are very violent, continue, succeeding each other at regular intervals, and it occurs to me that if the schooner has been destroyed, all communication with the bases of supply being impossible, Back Cup cannot be provisioned.

It is true the tug would be able to land the Count d'Artigas somewhere on the American coast where, money being no object, he could easily buy or order another vessel. But no matter. If Back Cup is only destroyed before Ker Karraje has Roch's fulgurator at his disposal I shall render thanks to heaven.

A few hours later, at the usual time, I quit my cell. All is quiet at the Beehive. The men are going about their business as usual. The tug is moored near the jetty. Thomas Roch is going to his laboratory, and Ker Karraje and Engineer Serko are tranquilly pacing backwards and forwards by the lake and chatting. The island therefore could not have been attacked during the night. Yet I was awakened by the report of cannon, this I will swear.

At this moment Ker Karraje goes off towards his abode and Engineer Serko, smilingly ironical, as usual, advances to meet me.

"Well, Mr. Simon Hart," he says, "are you getting accustomed to your tranquil existence? Do you appreciate at their just merit the advantages of this enchanted grotto? Have you given up all hope of recovering your liberty some day or other?"

What is the use of waxing wroth with this jester? I reply calmly:

"No, sir. I have not given up hope, and I still expect that I shall be released."

"What! Mr. Hart, separate ourselves from a man whom we all esteem--and I from a colleague who perhaps, in the course of Thomas Roch's fits of delirium, has learned some of his secrets? You are not serious!"

So this is why they are keeping me a prisoner in Back Cup! They suppose that I am in part familiar with Roch's invention, and they hope to force me to tell what I know if Thomas Roch refuses to give up his secret. This is the reason why I was kidnapped with him, and why I have not been accommodated with an involuntary plunge in the lagoon with a stone fastened to my neck. I see it all now, and it is just as well to know it.

"Very serious," I affirm, in response to the last remark of my interlocutor.

"Well," he continues, "if I had the honor to be Simon Hart, the engineer, I should reason as follows: 'Given, on the one hand, the personality of Ker Karraje, the reasons which incited him to select such a mysterious retreat as this cavern, the necessity of the said cavern being kept from any attempt to discover it, not only in the interest of the Count d'Artigas, but in that of his companions--'"

"Of his accomplices, if you please."

"'Of his accomplices,' then--'and on the other hand, given the fact that I know the real name of the Count d'Artigas and in what mysterious safe he keeps his riches--'"

"Riches stolen, and stained with blood, Mr. Serko."

"'Riches stolen and stained with blood,' if you like--'I ought to understand that this question of liberty cannot be settled in accordance with my desires.'"

It is useless to argue the point under these conditions, and I switch the conversation on to another line.

"May I ask," I continue, "how you came to find out that Gaydon, the warder, was Simon Hart, the engineer?"

"I see no reason for keeping you in ignorance on the subject, my dear colleague. It was largely by hazard. We had certain relations with the manufactory in New Jersey with which you were connected, and which you quitted suddenly one day under somewhat singular circ.u.mstances. Well, during a visit I made to Healthful House some months before the Count d'Artigas went there, I saw and recognized you."

"You?"

"My very self, and from that moment I promised myself the pleasure of having you for a fellow-pa.s.senger on board the _Ebba_."

I do not recall ever having seen this Serko at Healthful House, but what he says is very likely true.

"I hope your whim of having me for a companion will cost you dear, some day or other," I say to myself.

Then, abruptly, I go on:

"If I am not mistaken, you have succeeded in inducing Thomas Roch to disclose the secret of his fulgurator?"

"Yes, Mr. Hart. We paid millions for it. But millions, you know, are nothing to us. We have only the trouble of taking them! Therefore we filled all his pockets--covered him with millions!"

"Of what use are these millions to him if he is not allowed to enjoy them outside?"

"That, Mr. Hart, is a matter that does not trouble him a little bit!

This man of genius thinks nothing of the future: he lives but in the present. While engines are being constructed from his plans over yonder in America, he is preparing his explosive with chemical substances with which he has been abundantly supplied. He! he! What an invention it is, this autopropulsive engine, which flies through the air of its own power and accelerates its speed till the goal is reached, thanks to the properties of a certain powder of progressive combustion! Here we have an invention that will bring about a radical change in the art of war."

"Defensive war, Mr. Serko."

"And offensive war, Mr. Hart."