“What chord?”

“That of vengeance!”

“Vengeance?—­against whom?”

“Against all those who have made themselves his enemies by discouraging him, by spurning him, expelling him, by constraining him to go a-begging from country to country with an invention of incontestable superiority!  Now all notion of patriotism is extinct in his soul.  He has now but one thought, one ferocious desire:  to avenge himself upon those who have denied him—­and even upon all mankind!  Really, Mr. Hart, your governments of Europe and America committed a stupendous blunder in refusing to pay Roch the price his fulgurator is worth!”

And Engineer Serko describes enthusiastically the various advantages of the new explosive which, he says, is incontestably superior to any yet invented.

“And what a destructive effect it has,” he adds.  “It is analogous to that of the Zalinski shell, but is a hundred times more powerful, and requires no machine for firing it, as it flies through the air on its own wings, so to speak.”

I listen in the hope that Engineer Serko will give away a part of the secret, but in vain.  He is careful not to say more than he wants to.

“Has Thomas Roch,” I ask, “made you acquainted with the composition of his explosive?”

“Yes, Mr. Hart—­if it is all the same to you—­and we shall shortly have considerable quantities of it stored in a safe place.”

“But will there not be a great and ever-impending danger in accumulating large quantities of it?  If an accident were to happen it would be all up with the island of——!”

Once more the name of Back Cup was on the point of escaping me.  They might consider me too well-informed if they were aware that in addition to being acquainted with the Count d’Artigas’ real name I also know where his stronghold is situated.

Luckily Engineer Serko has not remarked my reticence, and he replies: 

“There will be no cause for alarm.  Thomas Roch’s explosive will not burn unless subjected to a special deflagrator.  Neither fire nor shock will explode it.”

“And has Thomas Roch also sold you the secret of his deflagrator?”

“Not yet, Mr. Hart, but it will not be long before the bargain is concluded.  Therefore, I repeat, no danger is to be apprehended, and you need not keep awake of nights on that account.  A thousand devils, sir!  We have no desire to be blown up with our cavern and treasures!  A few more years of good business and we shall divide the profits, which will be large enough to enable each one of us to live as he thinks proper and enjoy life to the top of his bent—­after the dissolution of the firm of Ker Karraje and Co.  I may add that though there is no danger of an explosion, we have everything to fear from a denunciation—­which you are in the position to make, Mr. Hart.  Therefore, if you take my advice, you will, like a sensible man, resign yourself to the inevitable until the disbanding of the company.  We shall then see what in the interest of our security is best to be done with you!”