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 anticipated, 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 ashore 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 shell. 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 passes? 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.