WITHIN an hour the wondering inhabitants of Alexandria saw the Russian fleet rise a thousand feet into the air and form in two columns of line ahead. Then the Aerian fleet ranged itself in two long lines five hundred feet outside them and a thousand feet above them. A time-shell from the _Ithuriel_ gave the signal to start, and the two fleets leapt forward to the south-east at a speed of a hundred miles an hour, and in a few minutes had vanished over the desert. The speed was quickly increased to two hundred miles, and so they sped on all day and through the next night--the Russian ships being forced to show their lights while the Aerians remained in darkness--until, when morning dawned and Olga and her captains looked for Alan’s fleet they found that it had vanished, and that they were floating alone over the solitudes of the Southern Ocean. They had been escorted like offending school children out of harm’s way, and then left to their own devices. It was a bitterly humiliating ending to an expedition which had really produced such important results, but there was no possibility of present revenge, and so Olga gave the order to proceed straight to Mount Terror, intending to begin there and then the working out of her part of the compact that she had made with the Sultan. This arrangement was briefly to the following effect:--Olga placed at Khalid’s disposal all the necessary plans for the construction of both air-ships and submarine vessels, and also supplied members of her own immediate retinue, well skilled in the work, to supervise the building, which was, of course, to be carried out with the utmost secrecy and speed, so as to guard, as far as practicable, against the possible destruction of the factories and dockyards by the Aerians. The Sultan had engaged to find money and material for building a thousand air-ships, and the same number of submarine cruisers, within the year, and these were to be supplied with motive power at conversion-stations established at the dockyards under the exclusive control of certain of Olga’s lieutenants. The secret of this motive power, which was identical save for slight differences in the process of conversion with that possessed by the Aerians--that is to say, electrical energy derived directly from atomised carbon and vaporised petroleum--was retained in her own keeping by Olga, who had simply promised that an unlimited supply of it should be forthcoming as it was wanted. She had insisted on a strict engagement that no one not authorised by her should even approach the conversion-stations, and she had given the Sultan and his ministers distinctly to understand that any attempt to discover the secret of the process would terminate the alliance, and expose the cities of the Moslem empire to destruction.