But they had entertained the thought—at least, Karl had done so—and examined it in all its bearings. Caspar had permitted it to pass out of his mind, under the impression that they could not make a balloon; and Karl had arrived at the same conclusion; but only from a belief that they had not the materials with which to make one. Given the materials, Karl felt quite equal to the construction of a balloon—a rude one, it is true; but one which might have served the purpose for which they required it.
During the days when they had been occupied in making the paper-bird, he had given his thoughts a good deal to this subject; for, to say the truth, he had never been very sanguine about the success of the kite experiment. He had pondered long and patiently on the subject of balloons—endeavouring to recall to mind what little he had studied of aerostatics—and had mentally examined all the material objects within reach, in the hope of discovering some substance out of which one might be constructed.
Unfortunately, he had not been able to think of anything that appeared to be suitable. The daphne paper—even had it been in abundance—would not do: for paper of itself, however close in texture, is not strong enough to withstand the pressure of the outside air—that is, in a balloon of sufficient size to carry any considerable weight. But it was of no use to talk of paper: since there was not enough; and Karl had given over thinking of a balloon: because there was nothing within reach likely to serve for its construction.
He knew that that great sphere would require to be air-proof. He had thought of the skins of animals; but such of these as might have been obtained in sufficient quantity, were entirely too thick and heavy to make the covering of a balloon. The hemp, of which there was an abundance, might be woven into a cloth, and then coated over by gum obtained from some tree; for in the valley were several species of gum-exuding trees. But the question was, could they manufacture a cloth out of hemp that would be light enough when thus coated over? It was very doubtful whether they could—at all events they would have to practise the weaving trade for a long time, before they should arrive at a sufficient expertness to accomplish such a feat. The plan was too unpromising to be seriously entertained; and Karl had dismissed it, along with the whole subject of the balloon.
That had been previous to the experiment of the kite, and its unfortunate ending. But now that all hope from this quarter had been brought to an end, the balloon once more began to shape itself in his mind, as well as in that of Caspar; and for the first time they proceeded to talk over the subject together.
“Cords we could have in plenty,” remarked Caspar, “but they’d be of no use, without the stuff to cover the great globe. They make it of silk, don’t they?”
“Yes,” replied Karl, “silk is the best material for the purpose.”
“And why?” inquired Caspar.
“Because it combines the three properties of lightness, strength, and closeness of texture, in a greater degree than any other known substance.”
“Would nothing else do?”