When he arrived over North America he descended in a desolate spot in the Far West. There the engineer, keeping a profound incognito, learnt with considerable pleasure that the Weldon Institute was about to begin its experiments, and that the "Go-Ahead," with Uncle Prudent and Phil Evans, was going to start from Philadelphia on the 29th of April.

Here was a chance for Robur and his crew to gratify their longing for revenge. Here was a chance for inflicting on their foes a terrible vengeance, which in the "Go-Ahead" they could not escape. A public vengeance, which would at the same time prove the superiority of the aeronef to all aerostats and contrivances of that nature!

And that is why, on this very day, like a vulture from the clouds, the aeronef appeared over Fairmount Park.

Yes! It was the "Albatross," easily recognizable by all those who had never before seen her.

The "Go-Ahead" was in full flight; but it soon appeared that she could not escape horizontally, and so she sought her safety in a vertical direction, not dropping to the ground, for the aeronef would have cut her off, but rising to a zone where she could not perhaps be reached. This was very daring, and at the same time very logical.

But the "Albatross" began to rise after her. Although she was smaller than the "Go-Ahead," it was a case of the swordfish and the whale.

This could easily be seen from below and with what anxiety! In a few moments the aerostat had attained a height of sixteen thousand feet.

The "Albatross" followed her as she rose. She flew round her flanks, and maneuvered round her in a circle with a constantly diminishing radius. She could have annihilated her at a stroke, and Uncle Prudent and his companions would have been dashed to atoms in a frightful fall.

The people, mute with horror, gazed breathlessly; they were seized with that sort of fear which presses on the chest and grips the legs when we see anyone fall from a height. An aerial combat was beginning in which there were none of the chances of safety as in a sea-fight. It was the first of its kind, but it would not be the last, for progress is one of the laws of this world. And if the "Go-Ahead" was flying the American colors, did not the "Albatross" display the stars and golden sun of Robur the Conqueror?

The "Go-Ahead" tried to distance her enemy by rising still higher. She threw away the ballast she had in reserve; she made a new leap of three thousand feet; she was now but a dot in space. The "Albatross," which followed her round and round at top speed, was now invisible.

Suddenly a shout of terror rose from the crowd. The "Go-Ahead" increased rapidly in size, and the aeronef appeared dropping with her. This time it was a fall. The gas had dilated in the higher zones of the atmosphere and had burst the balloon, which, half inflated still, was falling rapidly.

But the aeronef, slowing her suspensory screws, came down just as fast. She ran alongside the "Go-Ahead" when she was not more than four thousand feet from the ground.

Would Robur destroy her?

No; he was going to save her crew!

And so cleverly did he handle his vessel that the aeronaut jumped on board.

Would Uncle Prudent and Phil Evans refuse to be saved by him? They were quite capable of doing so. But the crew threw themselves on them and dragged them by force from the "Go-Ahead" to the "Albatross."

Then the aeronef glided off and remained stationary, while the balloon, quite empty of gas, fell on the trees of the clearing and hung there like a gigantic rag.

An appalling silence reigned on the ground. It seemed as though life were suspended in each of the crowd; and many eyes had been closed so as not to behold the final catastrophe. Uncle Prudent and Phil Evans had again become the prisoners of the redoubtable Robur. Now he had recaptured them, would he carry them off into space, where it was impossible to follow him?

It seemed so.

However, instead of mounting into the sky the "Albatross" stopped six feet from the ground.