it is scarce possible to talk of a paper kite, without thinking of that other and greater aerostatic contrivance—a balloon.

karl had thought of it, long before this time; and so had caspar, just as long: for the kite had suggested it simultaneously to the minds of both.

it may be asked why they had not entertained the thought, and endeavoured to carry it into practical effect: since a balloon would have been far more likely to have delivered them out of their “mountain prison” than a paper kite?

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?”

“oh, yes; many things would answer to make a balloon, that might carry up a certain amount of weight. even a paper balloon can be constructed to take up a few pounds—a cat, or a small dog; and people in many countries have been cruel enough to dispatch such creatures into the air, not caring what became of them.”

“very cruel indeed!” assented caspar, who, although a hunter, was far from having an unfeeling heart. “such people should be sent up themselves in paper balloons.”

“yes, if paper balloons would carry them; which, unfortunately for us, they wouldn’t. even if we had an unlimited supply of paper, it would be of no use to us. we require something stronger, and more tenacious.”

“can we not think of something? let us try, karl!”

“ah! dear brother, i have been trying for days, and in vain. there is nothing within this valley at all suitable for the purpose.”

“would canvas do? have you thought of that?”

“i have. it would be too coarse and heavy.”

“but, with great pains, could we not make it light enough? we might choose the finer fibres of the hemp; and spin and weave it with scrupulous care. ossaroo here is a perfect omphale in his way. i’ll warrant he could beat hercules with the distaff.”

“ho! brother!” exclaimed karl, a little astonished. “you are quite classical in your speech this morning. where learnt you the history of hercules—you who have never seen the inside of a university?”

“you forget, brother karl, that you yourself have been my instructor in these classical themes, as you call them. though i must tell you that, with the exception of their occasionally lending a little ornament to my speech, i have derived not the slightest advantage from them; nor is it likely i ever shall.”

“well, caspar,” answered the botanist, “i am not going to stand up for the classics, as you are well aware. although i have taught you a little of their lore, it was when i had nothing to do, and you were equally idle; otherwise i should have considered that both of us were wasting time. you already know my opinions on that subject—which are: that a knowledge of what is usually termed ‘the classics’ is of about as much use to a reasoning man as might be an equally profound knowledge of chinese mnemonics. the time i have spent in the study of the dead languages has been sheer waste; and all i have learnt wont raise us a foot higher here. my knowledge of jupiter and juno is not likely to gain us the means of getting out of our difficulty, no more than my acquaintance with mercury will help me to a pair of wings. so a truce to classical ideas, and let us see whether scientific ones may not serve us better just now. you have a quick invention, brother caspar; can you think of anything—i mean anything within our reach—that would make the air-bag of a balloon?”

“but could you make the balloon, if you had the stuff?” inquired caspar, still in doubt whether any other than an experienced aeronaut could construct so wonderful a machine.

“pooh!” replied the philosopher, “the making of a balloon is almost as easy as making a soap-bubble. any air-tight bag, filled with heated atmosphere, becomes a balloon. the question is, what weight it can be made to carry—including the materials out of which it may be constructed.”

“but how are you to get the heated air into it?”

“simply by making a fire under an aperture left open below.”

“but would not this air soon become cold again?”

“yes; and then the balloon would sink back to the earth from the air inside getting cooled, and becoming as heavy as that without. of course,” continued the philosopher, “you are aware that heated air is much lighter than the ordinary atmosphere; and that is why a balloon filled with the former, rises, and will continue rising, till it has reached that elevation, where the rarefied atmosphere is as light as the heated air. then it can go no further, and the weight of the balloon itself will bring it down again. a bladder of ordinary air sunk in water, or a corked bottle, will illustrate this point to your comprehension.”

“i comprehend it well enough,” rejoined karl, rather piqued at being treated too much à l’enfant by his learned brother. “but i thought that, in a balloon, it was necessary to keep a fire constantly burning—a sort of grate or fire-basket suspended below. now, even if we had the silk to make the great spherical bag, how could we make a fire-basket without iron?”

“we should not need the fire-basket you speak of. that is only required, when you design to keep your balloon some length of time in the air. if you only wish to make a short ascent, once filling the bag with hot air is sufficient; as it would be for us here. even if we wanted a suspended grate, surely, brother, you have enough ingenuity to get over such a trifling difficulty as that?”

“well, i’m not so sure that i could. how would you get over it?”

“why, by making a common basket, and lining it with clay. that would carry fire, as well as a vessel of either cast or wrought iron—at least sufficient to serve for a short excursion such as we should care to make. now-a-days, fire is not used for inflating balloons. inflammable gas has been found to be far superior for this purpose; but as we have no such thing in stock, we should have to proceed on the old original plan—that employed by the brothers montgolfier—the first inventors of the balloon.”

“you think, then, that the fire apparatus could be dispensed with, if we could only discover some material that would make the great globe-shaped bag to contain the heated air?”

“ay,” replied karl; “think of something to do that, and i promise to make you a balloon.”

thus challenged, caspar set his wits to work; and for a long while he sat in silence, as if buried in some very profound speculation. probably, there was no material substance in that valley that did not pass in review before the retina of his mental vision; and all were considered in turn.

“it must be light, air-tight, and strong?” asked he, at length, as if there was something in his thoughts possessing these three requisites.

“light, air-tight, and strong,” answered karl, simply repeating his words.

“the two last i am sure of,” rejoined caspar. “of the first only have i my doubts.”

“what is it?” asked karl, in a tone that betrayed his interest in what caspar had said.

“eel-skins!” was the laconic answer.