As Karl said this, he proceeded to the boiling spring, and plunged the eel-skin under the water. There it was permitted to remain for about half an hour, when it was taken out; and, after being scraped with the blade of a knife, was spread upon a rock, under the sun, where it would soon get thoroughly dry.
They all waited patiently for the completion of this process. The result was of too interesting a character to allow of their occupying themselves with anything else.
In due time the eel-skin had become sufficiently dry, to be submitted to examination; and Karl, once more taking it up, balanced it upon his palm.
Tested, even in this inexact fashion, it was evidently much lighter than before; and, by the gratified look with which the philosopher regarded it, he appeared to be much better satisfied with its weight. Still, however, he was not sanguine: as his words testified. They were almost a repetition of what he had said before.
“It may do—it is just possible. At all events, there can be no harm in trying. Let us try it, then.”
To say, “Let us try it,” meant the same as to say, “Let us make the balloon.” The others understood that; and of course acquiesced in the determination.
As there was nothing to interfere with the immediate commencement of the work, they resolved to set about it at once; and in fact did set about it without farther delay.
The number of eel-skins on hand, though very considerable, would not be near enough for covering a balloon; and therefore Ossaroo went to work with his hooks and lines to catch a few hundreds more. Karl was able to tell how many it would take; or he could at least make an estimate sufficiently exact for the purpose. He designed a balloon of twelve feet diameter: for he knew that one of less size would not have power enough to carry up the weight of a man. Of course, Karl knew how to calculate the surface of a sphere whose diameter should be twelve feet. He had only to multiply the diameter on the circumference; or the square of the diameter on the fixed number 3.1416; or find the convex surface of the circumscribing cylinder; or else find four times the area of a great circle of the said sphere. Any one of these methods would give him the correct result.
On making the calculation, he found that a sphere of 12 feet diameter would have a surface of 452 square feet, within a trifling fraction. Therefore 452 square feet of eel-skins would be required to cover it. In other words, that quantity would be required to make the balloon.
As the eels happened to be of large size—most of them being over a yard in length, and full four inches in average girth—the skin of one when spread out would yield about a square foot of surface. Taking large and small together—and allowing for waste, the heads and tails that would have to be chopped off—Karl calculated that he would get nearly a square foot each out of the eels; and that about five hundred skins would make the balloon bag. But as they would have to be cut occasionally with a slant, in order to get the globe shape, perhaps a few more would be needed; and therefore Ossaroo was to keep his baits in the water, until the requisite number of eels should be hooked out of it.