navigation has been so little studied by those who have taken an interest in balloons. About 1863, M. Nadar, of Paris, a clever aëronaut, took a fancy that it was impossible to control the direction of balloons, on account of their lightness and large surface; and he considered that he had discovered an important scientific principle-namely, that" pour lutter contre l'air il faut être plus lourd que l'air." He wrote a book (the most readable and entertaining work on balloons ever written) for the purpose of publishing the principle, and he founded a society to carry it into practice, by constructing flying machines in which buoyancy would have no part. Some years later the same idea was given a much wider circulation, by being propounded in a well-known work entitled The Reign of Law," by the Duke of Argyll. The book contains a series of observations on the flying of birds, and the passage in question is as follows; the italics are mine :

"It is remarkable that the force which seems so adverse-the force of gravitation, drawing down all bodies to the earth-is the very force which is the principal one concerned in flight, and without which flight would be impos

sible. It is curious how completely this has been forgotten in almost all human attempts to navigate the air. Birds are not lighter than the air, but immensely heavier. If they were lighter than the air they might float, but they could not fly. This is the difference between a bird and a balloon. A balloon rises because it is lighter than the air, and floats upon it, consequently it is incapable of being directed, because it possesses no active force enabling it to resist the currents of the air in which it is immersed, and because, if it had such a force, it would have no fulcrum, or resisting medium against which to exert it. It becomes, as it were, part of the atmosphere, and must go with it wherever it goes. No bird is ever for an instant of time lighter than the air in which it flies; but being, on the contrary, always greatly heavier, it keeps possession of a force capable of supplying momentum, and therefore capable of overcoming any lesser force, such as the ordinary resistance of the atmosphere, and even of heavy gales of wind. The law of gravitation, therefore, is used in the flight of birds as one of the most essential of

the forces which are available for the accomplishment of the end in view."*

The effect of the ex cathedra dissemination of such opinions has been to discourage the study of aërial navigation

by balloons, and to turn attention rather toward the invention of flying machines.

Persons acquainted with the mechanics of fluids must be somewhat puzzled to understand how such strange ideas as those involved in the above extract can have come into being. I think they may perhaps be capable of some degree of explanation by two considerations. In the first place, good observers of flying, like the author of this passage, cannot fail to have remarked, particularly when watching the larger birds, the great use they make of momentum in their flying manœuvres. A bird will be often seen sailing along for great distances without a single impulsive movement of his wings; and as we are usually in the habit of measuring the mass of a body by its weight, many persons are led to confound one with the other, and to imagine that the gravity of the bird's body is the agent in this motion. But all mechanical students know that this is a mistake; the motion of the bird exactly corresponds with that of a cannon-ball or of a railway train when the steam is suddenly shut off. A quantity of "work" previously developed by a certain power has given motion to and becomes stored up in a certain mass of matter, and that mass will continue in motion, and will, if necessary, overcome resistance till the work stored up in it is exhausted, when the body will come to rest again. All this is totally independent of gravity, and would take place if the attracting earth were entirely All that the bird does in this away. passive motion is simply the result of active muscular power exerted previ ously.

Secondly, a case often occurs where the Duke of Argyll's theory is apparently true-namely, the case where the bird, being already at a high level, descends in flying. Here, undoubtedly, gravity is an active power which will aid the bird's flight, just as it would aid the passage through the air of a stone or any other body. Some observation of this effect has probably led to the inference that gravity was a flying power; but the observer so inferring would have forgotten that the bird, in order to raise himself to the elevated position, must have previously exerted an amount of muscular power or energy exactly equal to that

which is restored in his fall. So that gravity does not furnish the power, it only acts as a reservoir to store it up, just as power is stored up in the spring or weight of a clock, to be given out again at a future time. Thus gravity, like momentum, does nothing more than give the bird some facility for modifying his manœuvres. The only power used in flight is muscular force, and all resist ance must be overcome by that, and that alone. The idea that birds could not fly unless they were heavier than air is surely a hallucination; if it were true we ought to improve their flying by loading them, which would be an absurdity. On the contrary, commonsense tells us that gravity is the chief impediment to flying, and it is precisely by getting rid of it that the invention of the balloon has rendered aërial navigation practicable.

The passage in the extract which I have underlined referring to the balloon is altogether incomprehensible. A balloon is "capable of being directed;" and if we provide it with a screw, turned by steam or human power, it will "possess an active force, enabling it to resist the currents of the air in which it is immersed," or, in other words, giving it an independent motion; and when pro vided with such a force, it will have a "fulcrum or resisting medium against which to exert it"-namely, the inertia of the surrounding atmosphere. All this is dictated by common mechanics, and is confirmed by experience. Lavoisier saw and expressed it clearly a century ago, and M. Giffard and M. de Lôme have added the practical demonstration of it in our own time.

The fallacy of the argument will be glaringly apparent if it is applied to the analogous case of motion through water. Flying and swimming are identical actions, only differing according to the density of the fluid they have to be performed in. Fishes have, I believe, generally about the same specific gravity as

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water; and, therefore, gravitation gives them no aid; yet they swim about perfectly well. And suppose we were to apply to a rowing or steam boat the language that the Duke of Argyll applies to a balloon, A boat remains on the surface because it is lighter than the water, and floats upon it; consequently it is incapable of being directed, because it possesses no active force enabling it to resist the tides and currents of the water in which it is immersed; and because, if it had such a force, it would have no fulcrum or resisting medium against which to exert it. It becomes, as it were, part of the water, and must go with it wherever it goes.' And suppose on this sort of argument we were to exhort the world to abolish rowing and steam boats, and to substitute swimming machines "plus lourds que l'eau !"

Nadar's objection to dirigible balloons. was much more reasonable. He said that to get the requisite floating power we must have great bulk, which would offer corresponding resistance to motion. This is true enough in principle; but the amount has been much overrated. The resistance to M. Dupuy de Lôme's balloon was only 40 lbs. ; and though for our proposed 100-feet machine we have, at 30 miles an hour, 3,500 lbs. to overcome, this is a cheap price at which to purchase freedom from the necessity of lifting, by mechanical power, 35 tons into the air.

There is no occasion to discourage the attempts that are made from time to time to produce flying machines. The problem involves no impossibility, like the perpetual motion or squaring the circle; and if any mechanic can invent a motor, at once so powerful and so light as to be able to raise itself in the air, the thing is done. But we are a long, long way off that yet; and in the mean time we have actually got navigable balloons, which only want improving.Fortnightly Review.

I.

So many people seem to take a lively interest in balloons and ballooning, that perhaps it may be worth while to note down the following short account of some early experiences and first impressions with balloons before they fade away from the memory.

July 28.-This is the third day that we have been hard at work making gas for balloons in the Arsenal at Woolwich with an experimental apparatus. The process of manufacturing hydrogen by blowing steam through heated iron turnings presents no great novelty in principle, for the French used it for inflating their military balloons as long ago as the battle of Fleurus in 1794; and to judge by the meagre accounts which have reached us, they appear to have been very successful in the manufacture. In these days of competitive examinations and Staff College certificates the soldier has to use his pen as much if not more than his sword, and the military student of the future will be overwhelmed with records only too voluminous and elaborate of every detail of our military equipment. But in those days, under the stern régime of a revolutionary convention, the sword had decidedly the best of it, so no detailed records of the French and their work are available. We must be content to learn our experi ence from the beginning, and find out how to manufacture our hydrogen for ourselves. We are at 'present very new to the work, and we have to contend with many difficulties. Yet we do manage to make hydrogen. The worst of it is that when we have got it, it is very difficult to keep it, for it is the most subtle and difficult to retain of any gas which we could possibly use. So we cannot avoid a serious loss by leakage, though our light balloon fabric does retain it much better than might fairly be expected.

But to day being fine and favorable for ballooning, it is time to forsake the gas furnace, and get a little practical experience as an aëronaut. The Talis

man, as the balloon is named which we propose to employ, being already half full of hydrogen, is filled up completely with gas, and I first try a captive ascent.

A strong rope, perhaps 4000 feet long, is wound upon a large drum, whence it can be paid out or hauled in, as required, by means of a winch and brake. The end of the rope is carefully made fast to the Talisman's hoop. This is a strong circle of ash, to which all the terminal cords of the balloon netting above are fastened, and below which again the car is suspended by proper car-lines or connecting ropes. I get into the car. A sufficient number of bags of sand as ballast are introduced, to leave only a moderate lift or ascensional power in the balloon. The rope pays itself out readily from the drum as the Sapper in charge eases off the brake. The Talisman soars aloft, and whenever the pace is too rapid it is easily checked by a light application of the brake.

This is almost my first introduction to captive work, and the sensation is most decidedly not too pleasant or reassuring. The great balloon above tugs and struggles, as if perfectly conscious of a humiliating state of captivity, and longing to be free. This is especially the case whenever a gust of wind puts a considerable extra strain on the guy rope. The latter, as I have said, is fastened to the hoop above one's head. But it rides. against the light wicker-work of the car, which creaks and groans in response in a doleful and somewhat distressing manner. Were it not for a powerful spring of india-rubber, which checks the oscillations of the guy rope, and tends to steady the balloon, the effect on one's nerves might be much worse than it is.

But, fortunately, there is not too much time for noticing these matters, for there is a constant necessity for letting go ballast, to meet the continually increasing weight of suspended guy rope below, or the balloon would soon cease to rise. At last the ballast is all expended, and the guy rope is paid out no further. The wind has caused the balloon to drift off to a considerable distance horizon.

tally from the point of departure below, and she now settles into a condition of approximate equilibrium. The height above the ground is shown by the barometer to be about 1000 feet. The long guy rope hangs in a graceful curve below. The portion next the balloon, for hundreds of feet, is nearly vertical, and that near the ground almost horizontal. But of this I see little. One or two timid glances are quite sufficient, for one's head, naturally a very indifferent one where it is a question of looking down from giddy heights, is not yet acclimatized to the situation by practice in ballooning. So I cannot look at the ground under, or nearly under, the balloon without a shudder and a decidedly creepy sensation. Above all, one must avoid looking down the guy rope, for this, in its long catenary, extending far below, reach after reach, and ending almost in a vanishing point, gives a measure to the eye of the giddy height. And to look along it makes one's brain reel-far worse, as I afterward find, than looking down from thrice the height in a free trip where there is no guy rope.

For military purposes, for reconnoitring that is, there can be no question of the value of such a suspended point of observation as this. Every detail in the innumerable buildings below-the workmen going to and fro in their work, the ships passing and repassing on the Thames, the Beckton gas-works on the further shore and lower down the river, the artillery exercise ground on Woolwich Common, the Herbert Hospital and other buildings further away-everything is seen, and in the clearest possible manner. For there is a very sensible advantage in the clearness of view from a balloon as contrasted with that obtained at the ground level, even where the latter is perfectly free and unobstructed by obstacles. It is well known to astronomers, and to all who have to make careful observations of distant objects, that the vision in a horizontal or nearly horizontal direction is greatly interfered with by the unseen exhalations from the ground, and the varying density of the lowest strata of air at and near the ground. Whereas at a high angle, as here from the balloon, the rays of light have only to traverse a very limited amount of these disturbed strata, and NEW SERIES.-VOL. XXXIII., No. 3

are consequently much more unimpeded and reliable.

But the day is wearing on, and I want to get away as early as possible for a free run, so I signal with a flag to lower. The drum is set in motion, and the Sappers below apply themselves steadily to wind the Talisman down. This is rather a long business, and the oscillations of the rope which it causes give rise to sensations which remind me very unpleasantly of the rolling of a vessel at sea in a ground swell. It is not without much thankfulness that at last terra firma is reached.

The Talisman has lost some considerable amount of gas in the captive ascent, owing to the expansion due to the diminished barometric pressure at 1000 feet from the ground. This loss is quickly replenished, that the start may be made with a full balloon, and about 4 P.M. all is ready.

The getting away, or starting, in a balloon is always rather a delicate and critical operation, and far more ballooning accidents have occurred probably, in connection with it, than at any other period, for it is by no means easy to regulate the ascension or lift of the balloon. This must be sufficient to clear all obstacles on the ground, but if it be too great the balloon would be carried upward too fast and too far.

The case is rendered more difficult on this occasion by the circumstance that there are a set of telegraph wires close to the balloon ground, and down wind, which of course I must avoid. We make two or three false starts, to try the lift of the balloon, and haul her down again to alter the weight of ballast. But at last I am off safely with a moderate

ascension" at 4.15 P.M. I am quite alone, as before in the captive ascent, for the balloon is rather too small to carry two persons well, in addition to a sufficient quantity of ballast. Moreover, I shall learn my experience far better when thus left to one's own re

sources.

After noting with much satisfaction that we have cleared the telegraph wires, and are rising steadily at a moderate rate, so that there is time to attend to necessary matters, the first thing to be done is to see that the valve line is hanging ready to hand, and disentangled

21

from the other ropes, for it might easily have got foul of something in the sway ing and bumping of the balloon before she was set free. 1 glance upward at the same time to make sure that the "petticoat," or tail of the balloon, is freely open; for were this tied up in its normal condition on the ground, the expansion of the imprisoned gas on rising to any considerable height would infallibly burst the balloon. The next thing is to take the aneroid barometer from the case wherein it has hitherto lain, for protection from the shocks of starting, and fasten it up in a convenient position for observation on one of the side carlines.

I note while tying it up that it shows that we are rising steadily, but not too rapidly. Next the pilot line must be thrown overboard, and left hanging from the hoop. This is a strong cord measuring 100 feet, and its use is to guide the eye as to one's distance from the ground in descending. It has been lying in a rough coil at the bottom of the car, to prevent its getting entangled at starting. I now overhaul it and pay it out of the balloon.

The view of the ground below, which one gets while leaning over the side of the car, to see that the pilot line has not fouled in its extension, is the first look I have really had to see what we are doing and where we are going. These little necessary preliminary operations have taken up every instant of time, and have been done, if the truth must be told, with a considerable amount of nervous haste.

That steady coolness which would clearly be a most desirable element in ballooning is hardly forthcoming, for this is the first time that I have found myself thus alone in a balloon with the whole responsibility of its management. So I am nervous just at starting. By and by, with more experience, one may hope to get steadier.

About this time a strong smell of gas warns me that the balloon is overfilled by expansion, and it is time to let out gas at the top, if one does not mean to be choked by the downward rush from the opening at the bottom. One steady pull on the valve line, and a sufficient quantity escapes at the top of the balloon to provide for present security.

Now there is time to look around. Vertically below the balloon I dare not look, or only for a moment, my head not yet being educated to the required point. But looking over the side at a steep angle, the decks of the steamers far below are a curious and interesting study, with the long black tails of smoke, which they are apparently dragging after them, for we are passing over the Thames. It lies below in a broad silver sheet, with the sun shining upon it. On either side its numerous windings and snake-like folds are clearly visible, ending in a forest of innumerable masts and spires on the London side. Conspicuous therein are the transverse streaks representing the several bridges, and a few prominent buildings, such as the Houses of Parliament and St. Paul's Cathedral. Eastward, on the side of the sea, the tortuous folds lose themselves in the broad estuary which opens out toward the Nore.

Now we are on the Essex side of the river. The balloon has reached her equilibrium level at about 2000 feet, and for a short time she floats horizontally along. For a short time only-for the impossibility of keeping a balloon in such a continuous horizontal course is a leading difficulty in ballooning, although some approximation may be made to it by skilful and fortunate management. My balloon soon begins to settle downward again.

Were she left to herself she would tend to run down faster and faster, and soon reach the earth. I allow her to descend slowly, but I prevent any such acceleration by throwing small quantities of ballast at intervals, watching the barometer all the time for guidance as to the amount required. I am most careful not to throw too much ballast, otherwise she would turn upward again, and, unless checked by letting out gas with the valve, would run up higher than before. By watching carefully, and thus gradually drawing out the balloon's descending path into a line more and more nearly horizontal, I manage to get her on a horizontal course at length, and about 100 feet from the ground. Every time the pilot line-which is 100 feet long-drags on the ground I throw a little ballast, just enough to lift it clear again without giving the balloon any de