All attempts to run them to earth were vain. Terror and uneasiness having ceased with the danger, Ker Karraje's exploits soon began to be forgotten, even in the West Pacific.

This is what had happened--and what will never be known unless I succeed in escaping from Back Cup:

These wretches were, as a matter of fact, possessed of great wealth when they abandoned the Southern Seas. Having destroyed their ship they dispersed in different directions after having arranged to meet on the American continent.

Engineer Serko, who was well versed in his profession, and was a clever mechanic to boot, and who had made a special study of submarine craft, proposed to Ker Karraje that they should construct one of these boats in order to continue their criminal exploits with greater secrecy and effectiveness.

Ker Karraje at once saw the practical nature of the proposition, and as they had no lack of money the idea was soon carried out.

While the so-called Count d'Artigas ordered the construction of the schooner _Ebba_ at the shipyards of Gotteborg, in Sweden, he gave to the Cramps of Philadelphia, in America, the plans of a submarine boat whose construction excited no suspicion. Besides, as will be seen, it soon disappeared and was never heard of again.

The boat was constructed from a model and under the personal supervision of Engineer Serko, and fitted with all the known appliances of nautical science. The screw was worked with electric piles of recent invention which imparted enormous propulsive power to the motor.

It goes without saying that no one imagined that Count d'Artigas was none other than Ker Karraje, the former pirate of the Pacific, and that Engineer Serko was the most formidable and resolute of his accomplices. The former was regarded as a foreigner of noble birth and great fortune, who for several months had been frequenting the ports of the United States, the _Ebba_ having been launched long before the tug was ready.

Work upon the latter occupied fully eighteen months, and when the boat was finished it excited the admiration of all those interested in these engines of submarine navigation. By its external form, its interior arrangements, its air-supply system, the rapidity with which it could be immersed, the facility with which it could be handled and controlled, and its extraordinary speed, it was conceded to be far superior to the _Goubet,_ the _Gymnote_, the _Zede_, and other similar boats which had made great strides towards perfection.

After several extremely successful experiments a public test was given in the open sea, four miles off Charleston, in presence of several American and foreign warships, merchant vessels, and pleasure boats invited for the occasion.

Of course the _Ebba_ was among them, with the Count d'Artigas, Engineer Serko, and Captain Spade on board, and the old crew as well, save half a dozen men who manned the submarine machine, which was worked by a mechanical engineer named Gibson, a bold and very clever Englishman.

The programme of this definite experiment comprised various evolutions on the surface of the water, which were to be followed by an immersion to last several hours, the boat being ordered not to rise again until a certain buoy stationed many miles out at sea had been attained.

At the appointed time the lid was closed and the boat at first manoeuvred on the surface. Her speed and the ease with which she turned and twisted were loudly praised by all the technical spectators.

Then at a signal given on board the _Ebba_ the tug sank slowly out of sight, and several vessels started for the buoy where she was to reappear.

Three hours went by, but there was no sign of the boat.

No one could suppose that in accordance with instructions received from the Count d'Artigas and Engineer Serko this submarine machine, which was destined to act as the invisible tug of the schooner, would not emerge till it had gone several miles beyond the rendezvous. Therefore, with the exception of those who were in the secret, no one entertained any doubt that the boat and all inside her had perished as the result of an accident either to her metallic covering or machinery.