CHAPTER IV.

THE SECOND DIFFICULTY: THE GAS-VESSEL-ITS STIFFNESS.

THE stumbling-block of the threshold which has been discussed in the last chapter-the loss of force exerted in the boat hanging from the gas-vessel-is very closely connected with another difficulty, the apparent necessity of overcoming which in a particular manner has thrown the inventors upon the former obstacle.

The resistance of the air is supposed to be the aeronaut's greatest enemy. This is a very great mistake. I hope to show that it is his best friend and very ground of hope. But this much is certain, it is a friend that must be discreetly treated. It is then necessary that the form of the gas-vessel must be that best suited to humour the resistance of the air. What this form is, has never been determined. It has only been shown that the sphere, or balloon, is a very bad and there is not much reason for supone, posing that the eggoon is very greatly better. I am not about to consider, in this place, what the form should be, but to show into what dilemma the aerial navigators have been cast, in their endeavours to adapt to their purpose the best forms they could get. It was agreed by all, that the form must be a long one of some kind-a cylinder terminated by hemispheres or cones, a long egg shape, a fish shape, a 'prolate spheroid,' a 'lenticular ellipsoid,' according to fancy-but it must be long; but not, it appears, very long. There are two objections to this. One of these, which refers to the difficulty of keeping long figures poised in a horizontal direction without upsetting, I shall have to consider hereafter. The other objection is a very obvious one- -the difficulty of keeping firm and stiff, long figures of flexible materials. It is

Fig. 11.

quite evident that, if a moderately long bag be filled with light gas, and have a weight suspended beneath its middle as in fig 11, it may rise and retain its shape, so long as it be so full of gas as to keep its surface stretched and tense. But the envelope will not always be full enough to keep it tight; for instance, by loss of gas it may become flaccid, and this will sometimes be inevitable,

or it may be required to charge it incompletely, which will be advisable if it be desired to rise a great height in the air, with a load lighter than the full tonnage of the vessel. Now in such a case it is clear that, if the weight be suspended from the middle of the gas-vessel, and if the ends are free, they will turn up, by reason of the rising of the light gas (like a certain ill-looking black beetle which turns up its tail with a spiteful air if you touch it), and the apparatus will assume some such form as that represented in fig. 12. Now the necessity of having a more or less elongated form was undoubted, and therefore this difficulty was to be got over. Now, one means of remedying it was so obvious, that indeed it perhaps was adopted instinctively by the first persons who substituted an eggoon for a balloon, without the difficulty itself

Fig. 12.

Fig. 13.

which would have attended its omission ever presenting itself to their minds. And this is the more likely to have been the case, as the method alluded to is, in fact, nothing but the adaptation to the egg-shape of the appliances already in use with the original globe. It is the enclosing, or at least the covering, the envelope with a netting, from which, at points all round the horizontal section of the gas-vessel, cords are brought to the boat. By this means the weight

of the man-vessel is distributed over the whole upper surface of the envelope, ends as well as middle, and the cords A B, CD, and those near them, act as stays, to prevent the turning up of the head and tail of the gas-vessel.

Fig. 14.

B

The netting and its ropes have been looked upon as a sort of inalienable appurtenance to the balloon; which, like a membrane investing the egg contents, has clung most pertinaciously to the hatching chick, and clogged all its struggles for free life. There has scarcely been one aerial schemer who has ventured to try to rid himself of its meshes. The net sprung at once, with the valve and ballast, from the fertile brain of M. Charles,1 as the complete rigging of the balloon and car. These three contriv

ances were found to answer all the purposes for which they were designed, and have kept their place ever since, as the sacred implements of aeronauts, of which it seems a kind of treason to doubt the efficacy and necessity. But, whatever may be the utility of the other adaptations made by this most ingenious man, I have no hesitation in asserting that aerial navigation can never advance one step, till net, waste valve, and waste ballast are, if not utterly discarded and left to the balloon, at least reserved for other and secondary purposes, and no longer relied upon as the essential agents of equilibrium. At any rate, it is this traditional adherence to the net and cords which has placed aeronautic inventors in the first chief difficulty which I have been discussing at length. It relieved them at once from the one horn of the dilemma (the upturned ends), and has left them hanging ever since on the other and more perplexing alternative (the tilting tendency of the force in the car). In short, these very cords, which seemed so necessary to keeping the gas-vessel in shape,

Pour cette première ascension Charles créa, tout d'un coup et tout d'une pièce, l'art de l'aérostation. En effet, c'est à ce sujet qu'il imagina la soupape qui donne issue au gaz hydrogène et détermine la descente lente et graduelle de l'aérostat-la nacelle où s'embarquent les voyageurs; le fillet qui supporte et soutient la nacelle; le lest qui régle l'ascension et modère la descente; l'enduit de caoutchouc appliqué sur le tissu de ballon, qui rend l'enveloppe imperméable et prévient la déperdition du gaz; enfin l'usage de baromètre qui sert à mesurer les hauteurs, que l'aéronaute occupe dans l'atmosphère.'-Revue des Deux Mondes, tom. viii, p. 207.

and which, with the aid of the net, answer that purpose so well when the eggoon is not a long one, is pretty well full, and is not disturbed by any horizontal force in the boat, are the very causes (as has been shown above) of the loss of power in twisting the system out of horizontal position, as soon as propulsion is attempted.

Fig. 15.

Again not only is there this fatal objection to the net and converging cords, as the means of suspension, but the use of them alone is sufficient to put a limit to the horizontal length of the gas-vessel, for it is quite evident that if the attenuation of the supporting vessel be carried far, and if it remain flexible, it would be bent, or even doubled up, as in fig. 15, as soon as the weight was thrown more upon one end than the other. And this unequal distribution of the weight would be the immediate consequence of the tilted position, which, as has been shown, is the inevitable result of propulsion from

the boat when thus attached to the gas-vessel. Now, as I shall have presently to state more fully, the endeavour of the aerial architect must be to build his craft as long and narrow as possible, on the finest lines that are consistent with strength and stiffness. This, then, is another reason of itself sufficient for the rejection of this mode of rigging the air-craft.

The consideration of the object sought to be attained by the use of these cords diverging to the head and tail of the gas-vessel -of this martingale rig as it might be called-has led us to a second essential requisite in aerial gas-craft, viz.: That the gasvessel must be kept perfectly stiff, so that it shall neither turn up nor be bent down at the ends, but shall keep its form under all varying conditions of load from below, and of gas-charge within.

I am not aware of any attempts that have been made to ensure this object, except the almost universal one just treated of, viz. that of tying down the ends by stays to the boat, and the few cases in which it has been proposed to make the gas-vessel of some but slightly elongated shape, and to stiffen it by means of a backbone or equatorial framework, with which the car is to

be either in rigid or flexible connection. Instances of this latter endeavour are the devices of Scott, Génet, Partridge, Sanson and Sadd, referred to at pp. 44-6. There are objections to each of these, some of which I have noticed already in the four first examples; others are either not worth mentioning on account of the absurdity of the errors, or would be out of place in this part of the subject. But the chief points in which they fail as regards the conditions of length and stiffness, which we are now considering, is that none of the forms of the gas-vessel proposed by the designers are long enough in proportion to their thickness to enable them to be propelled with any useful speed; and that if they were made sufficiently elongated, the method of stiffening proposed for them by their authors would be inadequate to maintain their shape.

Perhaps one other method might be mentioned, which has been frequently proposed, and by which, if it were successfully applied with a proper method of suspension, this object of rigidity for the gas-vessel would be in some degree attained. I refer to the proposal to keep the gas-vessel perfectly filled with gas somewhat condensed by pressure. The increased elasticity of the contents of the envelope would, by stretching and tightening it, confer on it a certain amount of stiffness. But this has not been the chief aim of those who have suggested it, and its consideration naturally following in this connection belongs rather to the discussion of the special object for which it has been proposed, and which I shall next proceed to treat.

It does not then appear to me that any method has yet been proposed for keeping the gas-vessel inflexible, which will fulfil that condition when the envelope is of proper form, and the usual vicious mode of suspension is discarded. I shall hope to show hereafter by what means this essential requisite may be completely satisfied.