Karl was the only one of the three who knew anything about a balloon, or the mode of inflating it. Had it been their intention of navigating the air, an apparatus would have been required to carry up a fire. This Karl could easily have contrived. A basket of wicker-work, as he had said, well lined with clay, would have answered the purpose after a fashion; but as they did not intend to use the balloon for any purpose beyond making the single ascent to lift them over the cliffs, a continuous fire would not be required. The first inflation would answer that end well enough; and therefore a grate or fire-basket was not thought of.
The car to carry the passengers—or boat, as it is sometimes styled: since, for reasons easily understood, it is usually a boat—was quite another affair; and had it been designed for more than a mere temporary use, would have taken a considerable time in the making; but for what they wanted almost anything would serve; and all that they intended employing was a sort of wicker basket, or deep hamper, suspended by stout ropes. This had been already prepared; and only needed to be attached to the bottom of the air-bag.
In the present case, the “bottom of the bag” is quite a figure of speech—lucus a non lucendo. Strictly speaking, it had no bottom; but, where this should have been, there was a round aperture, formed by a stout hoop of ringall bamboo, to which the skin covering was lashed, and to which, also, the cords intended to sustain the afore-mentioned basket, as also the stay-ropes, were to be attached.
The object of this aperture will be easily understood. It was by it that the hot air was to be admitted inside the balloon, for the purpose of inflating it.
And how was this hot air to be obtained? That was a question which Karl alone could answer. Of course, fire was to be the agent for producing it: but how was it to be got into the bag? Karl could tell that, and Karl only; and, now that the time had arrived for trying the experiment, he condescended to explain to his coadjutors how he meant to proceed.
The bag was to be propped up between tall stakes set in the ground; its bottomless bottom turned towards the earth, so that the aperture would be below. Under this a fire was to be kindled—not, however, until everything else should be ready; and the hot air rising up into the aperture would enter the balloon, and cause it to swell out to its full globular dimensions. 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. He knew that the atmosphere in such a situation would be extremely rarefied, and that a balloon, which might easily ascend many thousand feet into the air starting from the level of the sea, would not stir from the ground if carried to the top of a mountain ten thousand feet high. This was the circumstance which preyed upon the spirit of the young philosopher, and hindered him from entertaining any very sanguine hopes of success in the experiment they were making.
The philosophical truth had been before his mind from the first, and at times ............