More hot air being admitted, the cooler atmosphere within would be expelled, the balloon would become lighter than the surrounding air, and by the simple principle of atmospheric pressure it would ascend into the air.

It was expected it would do so--it was hoped it would.
To say the truth, the hopes of the engineer were far from being high-- his expectations anything but sanguine.

He had observed all along, that, notwithstanding the process employed for lightening the eel-skins, they were still far heavier than silk; and perhaps, after all, the experiment might not succeed.

There was another circumstance that had as much _weight_ on the mind of Karl as the eel-skins; and that was quite as likely to have a _bearing_ upon the balloon.

He had not overlooked the fact, that the spot, from which they proposed making the ascent, was nearly ten thousand feet above the level of the sea.