The balloon itself is composed of very fragile materials. It is merely a gas-holder, and is nowadays almost invariably made of fine cambric well varnished. Silk was the first-used material, but it is a needless expense. Thus it will be seen that the balloon itself has practically no strength in it whatever. All the space, however, and the pressure of the gas, are held in by a netting, which covers the whole of the balloon, to which it is fitted exactly, being shaped from the original pattern gore of the balloon itself—to be fully described hereafter.
Just below the neck of the balloon is a HOOP, to which all the netting lines are fastened. This hoop is made of ash, and is about three feet in diameter, all the strain of the balloon being concentrated at this point.
Below the hoop is attached the CAR, which is a large wicker basket suspended from the hoop by eight cords—technically termed car lines; and fastened to the hoop is a strong rope, generally made of flax, about 100 feet in length, which carries the anchor, or ‘grappling-iron,’ as it is called by aëronauts. This ‘grapnel’ differs in appearance from an ordinary anchor in that it has five prongs instead of only two. Inside the car are placed several canvas bags containing sifted sand, which is used as ballast, to regulate the ascending power of the balloon. The car also contains a few other requisites, notably a ‘liberating iron’ for letting the balloon go when all is reported ready, and an aneroid barometer, to show the altitude attained, &c.
Before entering upon the detailed description of how to make your model balloon, I think it will be well to give some idea of what an ordinary ascent really is, for it is of importance that we should realise what we are about before we proceed to construct the machine which is to carry us from the nether atmosphere into unknown regions miles above the earth, whether the ascent is to be made for scientific purposes or merely for amusement. I do not think there are many living men who can give better instruction on this point than myself, seeing that I have already made no less than eighty-four ascents, while I hope to make as many more before old age and infirmity put a stop to my ballooning career.
Balloons constructed to carry passengers vary very much in size, the smallest being of 18,000 cubic feet capacity, capable of raising two people only—the aëronaut and one passenger. This, or a little larger, is the size of the balloon now generally used, larger balloons being made principally for scientific purposes. Such a one was the celebrated ‘Mammoth,’ supplied by Mr. Coxwell for the memorable investigations by Mr. Glaisher about the year 1863, of which I suppose you may probably have heard, and concerning which it may interest you to learn that on two of their ascents I had the honour of accompanying those famous aëronauts, the ascents taking place on both occasions from the Crystal Palace, and the descents once at Singlewell, near Gravesend, and once near Woking.
The gas with which an ordinary balloon is filled is the gas supplied by the gas companies for street and house lighting, which is called carburetted hydrogen. Pure hydrogen is seldom employed for balloon inflation, though it may be interesting to state that the big captive balloon at the Paris Exhibition was initiated with pure hydrogen, manufactured with sulphuric acid, zinc, and water. This is called sulphuretted hydrogen, and possesses nearly double the lifting power of coal-gas. A balloon held down by a rope requires great ascending power, therefore all captive balloons should be inflated with pure hydrogen. The very great expense of this gas, however, prevents its use in ordinary cases.
The balloon being filled with gas, the aëronaut and his passenger take their seats in the car, ready to ascend. The first thing to be done is to untie the neck of the balloon, which has been fastened up with a piece of string or a handkerchief since the hose-pipe was removed, when the balloon was quite inflated. The object of having the neck of the balloon wide open is this: Directly the balloon rises expansion takes place, owing to the rarefied state of the atmosphere, and the higher it ascends the more rarefied the air becomes, and consequently the less atmospheric pressure is there upon the balloon, the natural result being that the gas expands, and makes its way by degrees out of the neck. If there were no such escape, the balloon would burst. When the neck is wide open, those in the car can see into the middle of the balloon, which has a very curious appearance.
We are now supposed to be ready for starting, there having been placed at the bottom of the car several more bags of ballast than are known to be required. These are handed out, one by one, until the weight in the car is about equal to or a little lighter than the ascending power of the balloon. Then the aëronaut, feeling himself master of the situation, calls out in a loud voice, ‘All hands off!’ At the word of command the assistants, who have been keeping the car down, leave go their hold, and the balloon rises slowly and majestically into the air. (Please now to put yourself into the place of the passenger making his first ascent, with eyes and ears open to take in all the instruction that can be conveyed to him.)
When about fifteen feet in the air the passenger, who has by this time probably worked himself into a somewhat feverish state of excitement, is astonished and considerably alarmed by a sudden jerk or shock, and the equally sudden arrest of the balloon in its upward journey. The fact is that we had not finally left our mother earth, but have been pulled down again by a rope, held by the assistants, which was attached to the hoop by an instrument called the ‘liberating iron.’ The aëronaut himself lets the balloon take its final departure when he touches a lever attached to the liberating iron, and we are being pulled down again on the present occasion because it is found that we have too much ascending power, and can take in another half bag ballast; and the more ballast a balloon can carry the better, as sometimes ballast is found to be worth its weight in gold—or rather, worth as much more as life is worth more than the most precious of all earthly possessions. At the risk of fatiguing you by a digression, I will explain how this is.