It was necessary to increase the ascensional power to prevent her falling into the sea.
When the look-out man had got clear of his gag and shouted, Robur and Tom Turner had rushed up to him and torn off his bandage.

The mate had then run back to the stern cabin.

It was empty! Tapage had searched Frycollin's cabin, and that also was empty.
When he saw that the prisoners had escaped, Robur was seized with a paroxysm of anger.

The escape meant the revelation of his secret to the world.

He had not been much concerned at the document thrown overboard while they were crossing Europe, for there were so many chances that it would be lost in its fall; but now! As he grew calm, "They have escaped," said he.