AEROSTATION
, in its proper and primary sense, denotes the science of weights suspended in the air; but in the modern application of the term, it siguifies the art of navigating or floating in the air, both as to the practice and principles of it. Hence also the machines which are employed for this purpose, are called | aerostats, or aerostatic machines; and which, on account of their round and bell-like shape, are otherwise called air ballcons. Also aeronaut is the name given to the person who navigates or sloats in the air by means of such machines.
Principles of Aerostation. The fundamental principles of this art bave been long and generally known, as well as speculations on the theory of it; but the successful application of them to practice seems to be altogether a modern discovery. These principles chiefly respect the weight or pressure, and elasticity of the air, with its specific gravity, and that of the other bodies to be raised or floated in it: the particular detail of which principles may be seen under the respective words in this dictionary. Suffice it therefore in this place to observe, that any body which is specifically, or bulk for bulk, lighter than the atmosphere, or air encompassing the earth, will be buoyed up by it, and ascend, like as wood, or a cork, or a blown bladder, ascends in water. And thus the body would continue to ascend to the top of the atmosphere, if the air were every where of the same density as at the surface of the earth. But as the air is compressible and elastic, its density decreases continually in ascending, on account of the diminished pressure of the superincumbent air, at the higher elevations above the earth; and therefore the body will ascend only to such height where the air is of the same specific gravity with itself; where the body will float, and move along with the wind or current of air, which it may meet with at that height. This body then is an aerostatic machine, of whatever form or nature it may be. And an air-balloon is a body of this kind, the whole mass of which, including its covering and contents, and the weights annexed to it, is of less weight than the same bulk of air in which it rises.
We know of no solid bodies however that are light enough thus to ascend and float in the atmosphere; and therefore recourse must be had to some fluid or aeriform substance.
Among these, that which is called inslammable air is the most proper of any that have hitherto been discovered. It is very elastic, and from six to ten or eleven times lighter than common atmospheric air at the surface of the earth, according to the different methods of preparing it. If therefore a sufficient quantity of this kind of air be inclosed in any thin bag or covering, the weight of the two together will be less than the weight of the same bulk of common air; and, consequently this compound mass will rise in the atmosphere, and continue to ascend till it attain a height at which the atmosphere is of the same specific gravity as itself; where it will remain or float with the current of air, as long as the inflammable air does not escape through the pores of its covering. And this is an inflammable air-balloon.
Another way is to make use of common air, rendered lighter by warming it, instead of the inflammable air. Heat, it is well known, rarefies and expands common air, and consequently lessens its specific gravity; and the diminution of its weight is proportional to the heat applied. If therefore the air, inclosed in any kind of a bag or covering, be heated, and consequently dilated, to such a degree, that the excess of the weight of an equal bulk of common air, above the weight of the heated air, be greater than the weight of the covering and its appendages, the whole compound mass will ascend in the atmosphere, till, by the diminished density of the surrounding air, the whole become of the same specific gravity with the air in which it sloats; where it will remain, till, by the cooling and condensation of the included air, it shall gradually contract and descend again, unless the heat is renewed or kept up. And such is a heated air-balloon, otherwise called a Montgolfier, from its inventor.
Now it has been discovered, by various experiments, that one degree of heat, according to the seale of Fahrenheit's thermometer, expands the air about one five-hundredth part; and therefore that it will require about 500 degrees, or nearer 484 degrees of hent, to expand the air to just double its bulk. Which is a degree of heat far above what it is practicable to give it on such occasions. And therefore, in this respect, common air heated, is much inferior to inflammable air, in point of levity and usefulness for aerostatic machines.
Upon such principles then depends the construction of the two sorts of air-balloons. But before treating of this branch more particularly, it will be proper to give a short historical account of this late-discovered art.
History of Aerostation. Various schemes for rising in the air, and passing through it, have been devised and attempted, both by the ancients and moderns, and that upon different principles, and with various success. Of these, some attempts have been upon mechanical principles, or by virtue of the powers of mechanism: and such are conceived to be the instances related of the flying pigeon made by Archytas, the flying eagle and fly by Regiomontanus, and various others. Again, other projects have been formed for attaching wings to some part of the body, which were to be moved either by the hands or feet, by the help of mechanical powers; so that striking the air with them, aster the manner of the wings of a bird, the person might raise himself in the air, and transport himself through it, in imitation of that animal. But of these and various other devices of the like nature, a particular account will be given under the article artisicial flying, as belonging rather to that species or principle of motion, than to our present subject of aerostation, which is properly the sailing or floating in the air by means of a machine rendered specifically lighter than that element, in imitation of aqueous navigation, or the sailing upon the water in a ship, or vessel, which is specisically lighter than the water.
The first rational account that we have upon record, for this sort of sailing, is perhaps that of our countryman Roger Bacon, who died in the year 1292. He not only affirms that the art is feasible, but assures us that he himself knew how to make an engine, in which a man sitting might be able to carry himself through the air like a bird; and he farther affirms that there was another person who had tried it with success. And the secret it seems consisted in a couple of large thin shells, or hollow globes, of copper, exhausted of air; so that the whole being thus rendered lighter than air, they would support a chair, on which a person might sit.
Bishop Wilkins too, who died in 1672, in several | of his works, makes mention of similar ideas being entertained by divers persons. “It is a pretty notion to this purpose, says he (in his Discovery of a New World, prop. 14), mentioned by Albertus de Saxonia, and out of him by Francis Mendoza, that the air is in some part of it navigable. And that upon this statick principle, any brass or iron vessel (suppose a kettle), whose substance is much heavier than that of the water; yet being filled with the lighter air, it will swim upon it, and not sink.” And again, in his Dedalus, chap. 6, “Scaliger conceives the framing of such volant automata to be very easy. Volantis columbæ machinulam, cujus autorem Archytam tradunt, vel facillime profiteri audeo. Those ancient motions were thought to be contrived by the force of some included air: So Gellius, Ita erat scilicet libramentis suspensum, & aura spiritus inclusa, atque occulta consitum, &c. As if there had been some lamp, or other fire within it, which might produce such a forcible rarefaction, as should give a motion to the whole frame.” From which it would seem that Bishop Wilkins had some confused notion of such a thing as a heated air-balloon.
Again F. Francisco Lana, in his Prodroma, printed in 1670, proposes the same method with that of Roger Bacon, as his own thought.
He considered that a hollow vessel, exhausted of air, would weigh less than when filled with that fluid; he also reasoned that, as the capacity of spherical vessels increases much faster than their surface, if there were two spherical vessels, of which the diameter of one is double the diameter of the other; then the capacity of the former will be equal to 8 times the capacity of the latter, but the surface of that only equal to 4 times the surface of this: and the one sphere have its diameter equal to triple the diameter of the other; then the capacity of the greater will be equal to 27 times the capacity of the less, while its surface is only 9 times greater: and so on, the capacities increasing as the cubes of the diameters, while the surfaces increase only as the squares of the same diameters. And from this mathematical principle, father Lana deduces, that it is possible to make a spherical vessel of any given matter, and thickness, and of such a size as, when emptied of air, it will be lighter than an equal bulk of that air, and consequently that it will ascend in that element, together with some additional weight attached to it. After stating these principles, father Lana computes that a round vessel of plate brass, 14 feet in diameter, weighing 3 ounces the square foot, will only weight 1848 ounces; whereas a quantity of air of the same bulk will weigh 2155 2/3 ounces, allowing only one ounce to the cubic foot; so that the globe will not only be sustained in the air, but will also carry up a weight of 307 2/3 ounces: and by increasing the bulk of the globe, without increasing the thickness of the metal, he adds, a vessel might be made to carry a much greater weight.
Such then were the ingenious speculations of learned men, and the gradual approaches towards this art. But one thing more was yet wanting: although acquainted in some degree with the weight of any quantity of air, considered as a detached substance, it seems they were not aware of its great elasticity, and the universal pressure of the atmosphere; by which pressure, a globe of the dimensions above-described, and exhausted of its air, would immediately be crushed inwards, for want of the equivalent internal counter pressure, to be sought for in some element, much lighter than common air, and yet nearly of equal pressure or elasticity with it; a property or circumstance attending common air when considerably heated. It is evident then that the schemes of ingenious men hitherto must have terminated in mere speculation; otherwise they could never have recorded schemes, which, on the first attempt to put in practice, must have manifested their own insufficiency, by an immediate failure of success: For instead of exhausting the vessel of air, it must either be filled with common air heated, or with some other equally elastic and lighter air. So that upon the whole it appears, that the art of traversing the air, is an invention of our own time; and the whole history of it is comprehended within a very short period.
The rarefaction and expansion of air by heat, is a property of it that has long been known, not only to philosophers, but even to the vulgar: by this means it is, that the smoke is continually carried up our chimneys; and the effect of heat upon air, is made very sensible by bringing a bladder, only partly full of air, near a fire; when the air presently expands with the heat, and distends the bladder so as almost to burst it: and so well are the common people acquainted with this effect, that it is the common practice of those who kick blown bladders about for foot-balls, to bring them from time to time to the fire, to restore the spring of the air, and distension of the ball, lost by the continual waste of that fluid through the sides of it.
But the great levity of inflammable air, is a very modern discovery. As to the inflammable property of this air itself, it had been long known to miners, and especially in coal mines, by the dreadful effects it sometimes produces by its explosions. Among them it is sometimes vulgarly called sulphur, but more properly the fire damp, or inflammable damp, to distinguish it from the choak damp, and other damps, a species of air sometimes found in deep wells and mines, and which does not explode nor take fire, but presently extinguishes candles, and suffocates the persons who may happen to go into it. But it seems that it was Mr. Cavendish who first discovered with exactness the specific gravity of inflammable air; and his experiments and observations upon it, are published in the 56th volume of the Philosophical Transactions for the year 1766. Soon after this discovery of Mr. Cavendish, it occurred to the ingenious Dr. Black of Edinburgh, that if a bladder, or other vessel, sufficiently light and thin, were filled with this air, it would form altogether a mass lighter than the same bulk of atmospheric air, and consequently that it would ascend in it.
This idea he mentioned in his chemical lectures in the year 1767 or 1768; and he farther proposed to exhibit the experiment, by filling the allantois of a calf with such air. The allantois however was not prepared just at the time when he was at that part of his lectures, and other avocations afterwards prevented his design: so that, considering it only as an amusing experiment, and being fully satisfied of the truth of so evident an effect, he contented himself with barely mentioning the experiment from time to time in his lectures. About the year 1777 or 1778 too it occurred to Mr. Cavallo, | that it might be possible to construct a vessel, which, when filled with inflammable air, would ascend in the atmosphere: and there is no doubt but that similar ideas would occur to many other persons, of so evident a consequence of Mr. Cavendish's discovery.
But it seems to have been Mr. Cavallo who first actually attempted the experiment, in which however he succeeded no farther than in being able to raise soap bubbles of two or three inches diameter: a thing which had been done by children for their amusement time immemorial. These experiments Mr. Cavallo made in the beginning of the year 1782, and an account of them was read at a public meeting of the Royal Society on the 20th day of June of that year. From which it appears that he tried bladders and paper of various sorts. But the bladders, however thin they were made by scraping, &c, were still found too heavy to ascend in the atmosphere, when fully inflated with the inflammable air: and in using China paper, he found that this air passed through its pores, like water through a sieve. And having failed of success by blowing the same air into a thick solution of gum, thick varnishes, and oil paint, he was obliged to rest satisfied with soap-balls or bubbles, which, being filled with inflammable air, by dipping the end of a small glass tube, connected with a bladder containing the air, into a thick solution of soap, and gently compressing the bladder, ascended rapidly in the atmosphere, and broke against the ceiling of the room.
Here however it seems the matter might have rested, had it not been for experiments made in France soon after, by the two brothers Stephen and Joseph Montgolfier, upon principles suggested, not by the levity of inflammable air, which probably they had never heard of, but by that of smoke and clouds ascending in the atmosphere. These two brothers it seems were natives of Annonay, a town in the Vivarais, about 36 miles distant from Lyons; and that in their youth, Stephen, the elder, had assiduously studied the mathematics, but the other had applied himself more particularly to natural philosophy and chemistry. They were not intended for any particular way of business, but the death of a brother obliged them to put themselves at the head of a considerable paper manufactory at Annonay. In the intervals of time allowed by their business they amused themselves in several philosophical pursuits, and particularly with the experiments in aerostation, of which we are now to give some account. It would be perhaps impossible to know all the particular steps and ideas which finally produced this discovery: but it has been said that the real principle, upon which the effect of the aerostatic machine depends, was unknown even for a considerable time after its discovery: that M. Montgolfier attributed the effect of the machine, not to the rarefaction of the air, which is the true cause, but to a certain gas, specifically lighter than common air, which was supposed to be developed srom burning substances, and which was commonly called Montgolfier's gas. Be this however as it may, it is well known that the two brothers began to think of the experiment of the aerostatic machine about the middle or the larter part of the year 1782. The natural ascension of the smoke and the clouds in the atmosphere, suggested the first idea; and to imitate those bodies, or to inclose a cloud in a bag, and let the latter be lifted up by the buoyancy of the former, was the first project of those celebrated gentlemen.
Accordingly the first experiment was made at Avignon by Stephen, the elder brother, about the middle of November 1782. Having prepared a bag of sine silk, in the shape of a parallelopipedon, and of about 40 cubic feet in capacity, he applied burning paper to an aperture in the bottom, which rarefied the air, and thus formed a kind of cloud in the bag; and when it became sufficiently expanded, it ascended rapidly to the ceiling.
Soon afterwards the experiment was repeated with the same machine at Annonay, by the two brothers, in the open air; when the bag ascended to the height of about 70 feet. Encouraged by this success, they constructed another machine, of about 650 cubic feet capacity; which, when inflated as before, broke the cords which confined it, and after ascending rapidly to the height of about 600 feet, descended and fell on the adjoining ground. With another larger machine, of 37 feet diameter, they repeated the experiment on the 25th day of April, which answered exceedingly well: the machine had such force of ascension, that, breaking abruptly from its confinement of ropes, it rose to the height of more than 1000 feet, and then, being carried by the wind, descended and fell at a place about three quarters of a mile from the place of its ascension. The capacity of this machine was equal to above 23 thousand cubic feet, and, being nearly globular, when inflated, it measured 117 English feet in circumference. The covering was formed of linen, lined with paper; and its aperture at the bottom was fixed to a wooden frame, of about 4 feet square, or 16 feet in surface. When filled with vapour, which it was conjectured might be about half as heavy as common air, it was capable of lifting up about 490 pounds, besides its own weight, which, together with that of the wooden frame, was equal to about 500 pounds. With this same machine the next experiment was publicly performed at Annonay, on the 5th of June 1783, before a great multitude of spectators. The flaccid bag was suspended on a pole 35 feet high; straw and chopped wool were burned under the opening at the bottom; the vapour, or rather smoke, soon inflated the bag, so as to distend it in all its parts; and this enormous mas<*> ascended in the air with such velocity, that in less than ten minutes it reached the height of above 6 thousand feet; when a breeze carried it in an horizontal direction to the distance of 7668 feet, or near a mile and a half, where it descended gently to the ground.
As soon as the news of this experiment reached Paris, the philosophers of that city, conceiving that a new species of gas, of about half the weight of common air, had been discovered by Messrs. Montgolfier; and knowing that the weight of inflammable air was but about the eighth or tenth part of the weight of common air, they justly concluded that inflammable air would answer the purpose of this experiment better than the gas of Montgolfier, and accordingly they resolved to make trial of it.
A subscription was opened by M. Faujas de St. Fond, towards defraying the expence of the experiment. A sufficient sum of money having soon been raised, | Messrs. Roberts were appointed to construct the machine, and M. Charles, professor of experimental philosophy, to superintend the work. After a considerable time spent, and surmounting many difficulties in obtaining a sufficient quantity of inflammable air, and searching out a substance light enough for the covering, they at length constructed a globe of the silk called lutestring, which was rendered impervious to the inclosed air by a varnish of elastic gum or caeutchouc, dissolved in some kind of spirit or essential oil. The diameter of this globe was about 13 feet; and it had only one aperture, like a bladder, to which a stop-cock was adapted: and the weight of this covering, when empty, together with that of the stop-cock, was 25 pounds.
On the 23d of August 1783, they began to fill the globe with inflammable air; but this, being their first attempt, was attended with many obstructions and disappointments, which took up two or three days to overcome.
At length however it was prepared for exhibition, and on the 27th it was carried from the Place des Victoires, where it had been prepared, to the Champs de Mars, a spacious open ground in the front of the Military School, where, after introducing some more inflammable air, and disengaging it from the cords by which it was held down, it rose, in less than two minutes, to the height of 3123 feet: the specific gravity of the balloon, when it went up, being 35 pounds less than that of common air. At that height the balloon entered a cloud, but soon appeared again; and at last it was lost among other clouds. After floating about in the air for about three quarters of an hour, it fell in a field about 15 miles from the place of its ascent; where, as we may easily imagine, it occasioned great amazement to the peasants who found it. Its fall was owing to a rent in the covering, probably occasioned by the superior elasticity of the inflammable air, over that of the rare part of the atmosphere to which it had ascended.
In consequence of this brilliant experiment, numberless small balloons were made, mostly of goldbeater's skin, from 6 and 9 to 18 or 20 inches diameter; their cheapness putting it in the power of almost every family to satisfy its curiosity relative to the new experiment; and in a few days time balloons were seen flying all about Paris, from whence they were soon after sent abroad.
Mr. Joseph Montgolfier repeted an experiment with a machine of his construction before the commissaries of the Academy of Sciences, on the 11th and 12th of September. The machine was about 74 feet high, and 43 feet in diameter; it was made of canvass, covered with paper both within and without, and weighed 1000 pounds. It was filled with rarefied air in 9 minutes, and in one trial the weight of eight men was not sufficient to keep it down. It was not suffered to go up, as it had been intended for exhibition before the Royal Family, a few days after. By the violence of the rain, however, which fell about this time, it was so much spoiled, that he thought proper to construct another for that purpose, in which he used so great dispatch, that it was completed in the short space of four days time. This machine was constructed of cloth made of linnen and cotton thread, and painted with water colours both within and without. Its height was 60 feet, and diameter 43 feet. Having made the necessary preparation for inflating it, the operation was bègun about one o'elock on the 19th of the same month; before the king and queen, the court, and the inhabitants of the place, as well as all the Parisians who could procure a conveyance to Versailles. The balloon was soon filled, and in eleven minutes after the commencement of the operation, the ropes being cut, it ascended, bearing up with it a wicker cage, containing a cock, a duck, and a sheep, the first animals that ever ascended into the atmosphere with an aerostatic machine. Its power of ascension, or the weight by which it was lighter than an equal bulk of common air, allowing for the animals and their cage, was 696 pounds. The balloon rose to the height of 1440 feet; and being driven by the wind for the space of eight minutes, it gradually descended in consequence of two large rents made in the covering by the wind, and fell in a wood at the distance of 10,200 feet, or about two miles from Versailles. The animals landed again as safe as when they went up, and the sheep was found feeding.
The success of this experiment induced M. Pilatre de Rozier, with a philosophical intrepidity which will be recorded with applause in the history of aerostation, to offer himself as the first adventurer in this aerial navigation. For this purpose M. Montgolfier constructed a new machine, of an oval shape, in a garden of the fauxbourg St. Antoine; its diameter being about 48 feet, and height 74 feet. To the aperture in the lower part was annexed a wicker gallery about three feet broad, with a ballustrade of three feet high. From the middle of the aperture an iron grate, or brazier, was suspended by chains, descending from the sides of the machine, in which a fire was lighted for inflating the machine; and towards the aperture port-holes were opened in the gallery, through which any person, who might venture to ascend, might feed the fire on the grate with fuel, and regulate at pleasure the dilatation of the air inclosed in the machine: the weight of the whole being upwards of 1600 pounds. On the 15th of October 1783. the fire being lighted, and the balloon inflated, M. P. de Rozier placed himself in the gallery, and, to the astonishment of a multitude of spectators, ascended as high as the length of the restraining cords would permit, which was about 84 feet from the ground, and there kept the machine afloat about four minutes and a half, by repeatedly throwing straw and wool upon the fire: the machine then descended gradually and gently, through a medium of increasing density, to the ground; and the intrepid adventurer assured the admiring spectators that he had not experienced the least inconvensence in this aerial excursion. This experiment was repeted on the 17th with nearly the same success; and again several times on the 19th, when M. P. de Rozier, by a partial ascent and descent, several times repeted, evinced to the multitude of observers that the machine may be made to ascend and descend at the pleasure of the aeronaut, by merely increasing or diminishing the fire in the grate. The balloon having been hauled down, by the ropes which always confined it, M. Gironde de Villette placed himself in the gallery | opposite to M. de Rozier, and the machine being suffered to ascend, it hovered for about 9 minutes over Paris, in the sight of all its inhabitants, at the height of 330 feet. And on their descending, the marquis of Arlandes ascended with M. de Rozier much in the same manner.
In consequence of the report of these experiments, signed by the commissaries of the Academy of Sciences, it was ordered that the annual prize of 600 livres should be given to Messrs. Montgolfier for the year 1783.
In the experiments above-recited, the machine was always secured by long ropes, to prevent its entire escape: but they were soon succeeded by unconfined aerial navigation. For this purpose the same balloon of 74 feet in height was conveyed to La Muette, a royal palace in the Bois de Boulogne: and all things being got ready, on the 21st of November 1783, M. P. de Rozier and the marquis d'Arlandes took their post in opposite sides of the gallery, and at 54 minutes after one the machine was absolutely abandoned to the element, and it ascended calmly and majestically in the atmosphere. On reaching the height of about 280 feet the intrepid aeronauts waved their hats to the astonished multitude: but they soon after rose too high to be distinguished, and it is supposed they rose to more than 3000 feet in height. At first they were driven, by a north-west wind, horizontally over the river Seine and part of Paris, taking care to clear the steeples and high buildings by increasing the fire; and in rising they met with a current of air which carried them southward. Having thus passed the Boulevard, and finally desisting from supplying the fire with fuel, they descended very gently in a field beyond the new Boulevard, about 9000 yards, or a little more than 5 miles distant from the palace de La Muette, having been between 20 and 25 minutes in the air. The weight of the whole apparatus including that of the two travellers, was between 1600 and 1700 pounds.
Notwithstanding the rapid progress of aerostation in France, it is remarkable that we have no authentic account of any experiments of this kind being attempted in other countries. Even in our own island, where all arts and sciences sind an indulgent nursery, and many their birth, no aerostatic machine was seen before the month of November 1783. Various speculations have been made on the reasons of this strange neglect of so novel and brilliant an experiment. But none seemed to carry any shew of probability except that it was said to be discouraged by the leader of a philosophical society, expressly instituted for the improvement of natural knowledge, for the reason, as it was said, that it was the discovery of a neighbouring nation. Be this however as it may, it is a fact that the first aerostatic experiment was exhibited in England by a foreigner unconnected and unsupported. This was a count Zambeccari, an ingenious Italian, who happened to be in London about that time. He made a balloon of oiled-silk, 10 feet in diameter, weighing only 11 pounds: it was gilt, both for ornament, and to render it more impermeable to the inflammable air with which it was to be filled. The balloon, after being publicly shewn for several days in London, was carried to the Artillery Ground, and there being filled about three-quarters with inflammable air, and having a direction inclosed in a tin box for any person by whom it should afterwards be found, it was launched about one o'clock on the 25th of November 1783. At half past three it was taken up near Petworth in Sussex, 48 miles distant from London; so that it travelled at the rate of near 20 miles an hour. Its descent was occasioned by a rent in the silk, which must have been the effect of the rarefaction of the inflammable air when the balloon ascended to a rarer part of the atmosphere.
The French philosophers having executed the first aerial voyage with a balloon inflated by heated air, resolved to attempt a similar voyage with a balloon filled with inflammable air, which seemed to be preserable to dilated air in every respect, the expence of preparing it only excepted. A subscription was opened however to defray that expence, which was estimated at about ten thousand livres; and the balloon was constructed by Messrs. Roberts, of gores of silk, varnished with a solution of elastic gum. Its form was spherical, and it measured 27 1/2 feet in diameter. The upper hemisphere was covered by a net, which was fastened to a hoop encircling its middle, and called its equator. To this equator was suspended by ropes a car or boat, covered with painted linen, and beautifully ornamented, which swung a few feet below the balloon. To prevent the bursting of the machine by the expansion of the inflammable air in a rarer medium, or to cause the balloon to descend, it was furnished with a valve, which might be opened by means of a string descending from it, for discharging a part of the internal air, without admitting the external to enter: And the car was ballasted with bags of sand, for the purpose of lightening it occasionally, and causing it to ascend: so that by letting some of the air escape through the valve, they might descend; and by discharging some of their sand ballast, ascend. To this balloon was likewise annexed a long pipe by which it was filled. The apparatus for filling it consisted of several casks placed round a large tub of water, each having a long tin tube, that terminated under a vessel or funnel which was inverted into the water of the tub, and communicated with the long pipe annexed to the lower part of the balloon. Iron filings and diluted vitriolic acid being put into the casks, the inflammable air which was produced from these materials, passed through the tin tubes, thence through the water of the tubs to the inverted funnel, and so through the pipe into the balloon. When inflated, the weight of the common air which was equal in bulk to the balloon, was 771 1/2 pounds; also the power of ascension, or weight just necessary to keep it from ascending, was 20 pounds, and the weight of the balloon, with its car, passengers, and all its appendages, was 604 1/2 pounds, which two together make 624 1/2 pounds: and this taken from 771 1/2 pounds, the weight of common air displaced, leaves 147 pounds for the weight of the inflammable air contained in the balloon, and which is to 771 1/2 pounds, the weight of the same bulk of common air, nearly as 1 to 5 1/4; that is, the inflammable air used in this experiment was 5 1/4 times lighter than common air.
The first of December was fixed on for the display of this grand experiment; and every preparation was | made for conducting it with advantage. The garden of the Thuilleries at Paris was the scene of operation; which was soon crowded and encompassed with a prodigious multitude of observers. Signals were given, from time to time, by the siring of cannon, waving of flags, &c: and a small montgolsier was launched, for shewing the direction of the wind, and for the amusement of the people previous to the general display. At three quarters after one o'clock, M. Charles and one of the Roberts, having seated themselves in the boat attached to the balloon, and being furnished with proper instruments, cloathing, and provisions, left the ground, and ascended with a moderately accelerated velocity to the height of about 600 yards; the surrounding multitude standing silent with fear and amazement; while the aerial navigators at this height made signals of their safety. When they left the ground, the thermometer, according to Fahrenheit's scale, stood at 59 degrees; and the barometer, at 30.18 inches: and at the utmost height to which they ascended, the barometer fell to 27 inches; from which they deduced their height as above to be 600 yards, or one third part of a mile. During the rest of the vovage the quicksilver in the barometer was generally between 27 and 27.65 inches, rising and falling, as part of the ballast was thrown out, or some of the inflammable air escaped from the balloon. The thermometer generally stood between 53 and 57 degrees. Soon after their ascent, they remained stationary for some time: they then moved horizontally in the direction north-north-west: and having crossed the Seine, and passed over several towns and villages, to the great amazement of the inhabitants, they descended in a field, about 27 miles distant from Paris, at three-quarters past 3 o'clock; so that they had travelled at the rate of near 15 miles an hour, without feeling the least inconvenience.
The balloon still containing a considerable quantity of inflammable air, M. Charles re-ascended alone, and it was computed he went to the height of 3100 yards, or almost 2 miles, the barometer being then at 20 English inches: having amused himself in the air about 33 minutes, he pulled the string of the valve, and descended at 3 miles distance from the place of his ascent. All the inconvenience he experienced in his great elevation, was a dry sharp cold, with a pain in one of his ears and a part of his face, which he ascribed to the dilatation of the internal air: a circumstance that usually happens to persons who suddenly change the density of their atmosphere, either by ascending into a rarer, or descending into a denser one. The small balloon, launched at the beginning by M. Montgolfier, was found to have moved in a direction opposite to that of the aeronauts; from which it is inferred that there were two currents of air at different heights above the earth.
In the month of December this year, several experiments were made at Philadelphia in America with air balloons, by Messrs. Rittenhouse and Hopkins. They constructed and filled a great many small balloons, and connected them together; in which a man went up several times, and was drawn down again; and finally, the ropes being cut, he ascended to the height of 100 feet, and floated to a considerable distance; but, being afraid, he cut open the balloons with a knife, and so descended.
About the close of this year small balloons were sent up in many places, and were become very common in some parts of France and England. And in the beginning of the year following, their number and magnitude increased considerably; and some of the more remarkable ones were as follow:—On the 19th of January M. Joseph Montgolfier, accompanied by six other persons, ascended from Lyons with a rarefied air balloon, to the height of 1000 yards. This was the largest machine that had been hitherto made, being 131 feet high, and 104 feet in diameter: it was formed of a double covering of linen, with three layers of paper between them; and it weighed, when it went up, 1600 pounds, including the gallery, passengers, &c. It was at first intended for six passengers; but before it went up, it was not judged safe to freight it with more than three: however no authority nor solicitations could prevail upon any of the six to quit their place, nor even to cast lots which three should resign their pretensions: so that the spectators saw them all ascend with terror and anxiety; and to add to their distress, when the ropes were cut, and the machine had ascended a foot or two from the ground, a seventh person suddenly leaped into the gallery, and the fire being increased, the whole ascended together. To add to the terror of the scene, after being in the air about 15 minutes, a large rent of about 50 feet in length was made by the balloon taking fire, in consequence of which it descended very rapidly to the ground, though fortunately without injury to any of the aeronauts.
On the 22d of February an inflammable air balloon was launched from Sandwich in Kent. It was but a small one, being only 5 feet in diameter; but it was rendered remarkable by being the first machine that crossed the sea from England to France. It was found in a field at Warneton, about 9 miles from Lisle in French Flanders, two hours and a half after it left Sandwich, the distance being about 74 miles; so that it floated at the rate of about 30 miles an hour.
The chevalier Paul Andreani, of Milan, was the first aerial traveller in Italy. The chevalier was at the sole expence of this machine, but was assisted in the construction by two brothers of the name of Gerli. They all three ascended together near Milan on the 25th of February, and remained in the atmosphere about 20 minutes, when they descended, all their fuel being exhausted. This machine was a montgolfier, of a spherical shape, and about 68 feet in diameter. From calculations made on the power of this, and other machines of the same sort, it appears that the included air is raresied commonly but about one-third, or that the included warm air weighs about two-thirds of the same bulk of the external or common air.
The next aerial voyage was performed on the 2d of March 1784, by M. Jean Pierre Blanchard, a man who has since that time made more voyages than any other person, and who has rendered himself famous by being the first who has floated in the air over the channel from England to France. M. Blanchard it scems had sor many years been in pursuit of mechanical means for flying through the air; but on hearing of the late invented air balloons, he dropped | his former pursuits, and turned his attention to them. He accordingly constructed one of 27 feet diameter, to which a boat was suspended with two wings, and a rudder to steer it by, as also a large parachute spread horizontally between the boat and the balloon, designed to check the fall in case the balloon should burst. The machine being filled with inflammable air, he ascended, from the Champs de Mars at Paris, to the height of near ten thousand feet, or almost 2 miles; and after floating in the air for an hour and a quarter, he descended at Billancourt near Seve, having experienced by turns heat, cold, hunger, and an excessive drowsiness. It appears from his own account, and as might have been expected, that the wings and rudder of his boat had little or no power in turning the balloon from the direction of the wind.
In the course of this year, 1784, aerostatic experiments and aerial voyages became so frequent, that the limits of this article will not allow of any thing farther than mentioning those which were attended with any remarkable circumstances. On the 25th of April, Messrs. de Morveau and Bertrand ascended from Dijon, with an inflammable-air balloon, to the height of thirteen thousand feet, or near 2 miles and a half, where the thermometer marked 25 degrees. They were in the air 1 hour and 25 minutes, in which time they floated 18 miles.
On the 20th of May, four ladies and a gentleman ascended from Paris, in a large montgolfier, above the highest buildings, and remained suspended there a considerable time, the balloon being confined by ropes from flying away.
On the 23d of May, M. Blanchard, with the same balloon as before, ascended from Rouen, to such height that the mercury in the barometer stood at 20.57 inches, which on the earth had been at 30.16. It was observed that in this voyage M. Blanchard's wings or oars could not turn him aside from the direction of the wind.
On the 4th of June M. Fleurant and Madame Thible, the first lady who made an aerial voyage, ascended at Lyons in a machine of 70 feet diameter. They went to the height of 8500 feet, and floated about 2 miles in 45 minutes.
On the 14th of June, M. Coustard de Massi and M. Mouchet ascended at Nantes to a great height, with a balloon of 32 1/2 feet diameter, filled with inflammable air extracted from zink; and they floated to the distance of 27 miles in 58 minutes.
On the 23d of June, the first aerial traveller M. Pilatre de Rozier, accompanied with M. Prouts, ascended at Versailles, in the presence of the royal family and the king of Sweden, with a large montgolfier, whose diameter was 79 feet, and its height 91 seet and a half. They floated to the distance of 36 miles in three-quarters of an hour, when they descended, which is at the rate of 48 miles an hour. In consequence of this experiment the king granted to M. de Rozier a pension of 2000 livres.
On the 15th of July the duke of Chartres, the two brothers Roberts, and a fourth person ascended from the park of St. Cloud, with an inflammable-air machine, of an oblong form, its diameter being 34 feet, and its length, which went in a direction parallel to the horizon, was 55 1/2 feet; and they remained in the atmosphere for 45 minutes in the greatest fear and danger. The machine contained an interior small balloon, filled with common air, by means of which it was proposed to cause the machine to ascend or descend without the loss of any inflammable air or ballast: and the boat was furnished with a helm and oars, which were intended to guide it. Three minutes after ascending, the machine was lost in the clouds, and involved in a dense vapour. A violent agitation of the air, resembling a whirlwind, greatly alarmed the aeronauts, turned the machine three times round in a moment, and gave it such shocks as prevented them from using any of their instruments for managing the machine. After many struggles, with great difficulty they tore about 7 or 8 feet of the lower part of the covering, by which the inflamable air escaped, and they descended to the ground with great rapidity, though without any hurt. At the place of departure the barometer slood at 30.12 inches, and at their greatest elevation it stood at 24.36 inches; so that their ascent was about 5100 feet, or near one mile.
On the 18th of July, M. Blanchard, with a Mr. Boley, made his third voyage with the same balloon as he had before, and rose so high as to sink the barometer from 30.1 to 25.34 inches, answering to a height of about 4600 feet. In 2 hours and a quarter they floated 45 miles, which is at the rate of 20 miles an hour. In this voyage M. Blanchard pretended that he was able to turn the machine with his wings, and to make it ascend and descend at pleasure. After descending, it is said the balloon remained all the night at anchor full of air; and that the next day several ladies amused themselves by ascending successively to the height of 80 feet, the length of the ropes by which it was anchored.
In the course of this summer two persons had nearly lost their lives by ascending with machines of warmed air. The one in Spain, on the 5th of June, by the machine taking fire, was much burnt, and so hurt by the fall that his life was long despaired of. The latter having ascended a few feet, the machinery entangled under the eves of a house, which broke the ropes, and the man fell about twenty feet: the machine presently took fire, and was consumed. Other montgolfiers were also burned about London, by taking fire, through the defects of their construction.
The first aerial voyage performed in England was by one Vincent Lunardi, a native of Italy, who ascended from the Artillery Ground, London, with an inflammable-air balloon on the 15th of September. His machine was made of oiled silk, painted in alternate stripes of blue and red; and its diameter was 33 feet. From a net, which covered about two-thirds of the balloon, 45 cords descended to a hoop hanging below the balloon, to which the gallery was attached. The machine had no valve; and its neck, which terminated in the form of a pear, was the aperture through which the inflammable air was introduced, and through which it might be let out. The balloon was filled with air produced from zink by means of diluted vitriolic acid. And when the aeronaut departed, at 2 o'clock, he took up with him a dog, a cat, and a pigeon. After throwing out some sand to clear the houses, he ascended to a considerable height; and the direction of his motion at first was north-west by west; | but as the balloon rose higher, it came into another current of air, which carried it nearly north. In the course of his voyage the thermometer was as low as 29 degrees, and the drops of water which had collected round the balloon were frozen. About half after three he descended very near the ground, and landed the cat, which was almost dead with cold: then rising, he prosecuted his voyage, till at 10 minutes past 4 o'clock he landed near Ware in Hertfordshire. He pretends that he descended by means of his oars or wings; but other circumstances related by him, strongly contradict the fact.
The longest and most interesting voyage performed about this time, was that of Messrs. Roberts and M. Colin Hullin, who ascended at Paris, at noon on the 19th of September, with an aerostat, filled with inflammable air, which was 27 <*> feet in diameter, and 46 3/4 feet long, the machine being made to float with its longest part parallel to the horizon, and having a boat of near 17 feet long attached to it. The boat was fitted up with several wings or oars, shaped like an umbrella, and they ascended at 12 o'clock with 450 pounds of sand ballast, and after various manœuvres finally descended, at 40 minutes past 6 o'clock, near Arras in Artois, 150 miles from Paris, having still 200 pounds of ballast remaining in the boat. In one part they found the current of air uniform from 600 to 4200 feet high, which it seems was their greatest height, and the sall of the barometer had been near 5.6 degrees. They found that by means of their oars they could accelerate their course a little in the direction of the wind, when it moved slowly, which may be true; but there is great reason to doubt of the accuracy of their experiments by which they pretended to cause their path to deviate about 22 degrees from the wind, going with a considerable velocity.
The second aerial voyage in England, was performed by Mr. Blanchard, and Mr. Sheldon professor of anatomy to the Royal Academy, being the first Englishman who ascended with an aerostatic machine. They ascended at Chelsea the 16th of October, at 9 minutes past 12 o'clock. Mr. Blanchard having landed Mr. Sheldon at about 14 miles from Chelsea, re-ascended alone, and finally landed near Rumsey in Hampshire, about 75 miles distant from London, having gone nearly at the rate of 20 miles an hour. The wings used on this occasion it seems produced no deviation from the direction of the wind. Mr. Blanchard said that he ascended so high as to seel a great difficulty of breathing: and that a pigeon, which flew away from the boat, labou<*>ed for some time to sustain itself with its wings in the rarefied air, but after wandering a good while, returned, and rested on the side of the boat.
On the 4th of October, Mr. Sadler, an ingenious tradesman at Oxsord, ascended at that place with an inflammable-air balloon of his own construction and filling. And again on the 12th of the same month he ascended at Oxford, and floated to the distance of 14 miles in 17 minutes, which is at the rate of near 50 miles an hour.
The 30th of November this year Mr. Blanchard's fifth aerial voyage, still with his old machine, was performed in company with Dr. J. Jeffries, a native of America. Their voyage was about 21 miles; and it does not appear that the greatest action of their oars produced any effect in directing the course of the balloon.
On the 4th of January, 1785, a Mr. Harper ascended at Bitmingham with an inflammable-air balloon, and went to the distance of 50 miles in an hour and a quarter, and sussered no other inconvenience than a temporary deafness, and what might be expected from the changes of wet and cold. The thermometer descended from 40 to 28 degrees.
On the 7th of January, Mr. Blanchard, accompanied with Dr. Jeffries, performed his sixth aerial voyage, by actually crossing the British channel from Dover to Calais, with the same balloon which had sive times before carried him successfully through the air. They ascended with only 30 pounds of sand ballast, besides their provisions, some books, instruments, and other necessaries. The machine parted with the gas very rapidly, and their ballast was soon all exhausted; after which, from time to time they threw out every thing else in the boat, to prevent themselves from dropping into the sea. In this way they disposed of all their provisions, their books and instruments, and finally the most part of their very clothes themselves. This however bringing them near the French coast, they gradually ascended, cleared the cliffs and houses, and landed in the forest of Guiennes. It is remarkable that a bottle, being thrown out when they were in danger of falling into the sea, struck the water with sach force, that they heard and felt the shock very sensibly on the car and balloon. In consequence of this voyage the king of France presented M. Blanchard with a gift of 12000 livres, and granted him a pension of 1200 lives a year.
On the 19th of January, Mr. Crosbie ascended at Dublin in Ireland, with an inflammable-air balloon to a great height. He rose so rapidly that he was out of sight in 3 minutes and a half. By suddenly opening the valve he descended just at the edge of the sea, as he was driving towards the channel, being unprovided for properly passing over to England.
On the 23d of March, Count Zambeccari and Admiral Sir Edward Vernon ascended at London, and sailed to Horsham in Sussex, at the distance of 35 miles in less than an hour. The voyage proved very dangerous, owing to some of the machinery about the valve being damaged, which obliged them to cut open some part of the balloon when they were about two miles perpendicular height above the earth, the barometer having fallen from 30.4 to 20.8 inches. In descending they passed through a dense cloud, which felt very cold, and covered them with snow. The observatione they made were, that the balloon kept perpetually turning round its vertical axis, sometimes so rapidly as to make each revolution in 4 or 5 seconds; that a peculiar noise, like rustling, was heard among the clouds, and that the balloon was greatly agitated in the descent.
On May the 5th, Mr. Sadler, and William Windham, esq. member of parliament for Norwich, ascended at Moulsey-hurst. The machine took a south-east course, and the current of air was so strong that they were in great danger of being driven to sea. They had the good fortune however to descend near the con- | flux of the Thames and Medway, not a mile from the water's edge. By an accident they lost their balloon: for while the aeronauts were busied in securing their instruments, the country people, whom they had employed in holding down the machine, suddenly let go the cords, when the balloon instantly ascended, and was driven many miles out to sea, where it fell, and was taken up by a trading vessel. It was afterwards restored again, and another voyage made with it from Manchester to Pontefract, in which Mr. Sadler was still more unfortunate; for no person being near when it descended, and not being able to confine it by his own strength, he was dragged by it over trees and hedges; and at last was forced to quit it at the utmost peril of his life; after which it rose, and was out of sight in a few minutes. It was afterwards found near Gainsborough.
On the 12th of May Mr. Crosbie ascended, at Dublin, as high as the tops of the houses; but soon descended again with a velocity that alarmed all the spectators for his safety. On his stepping out of the car, in an instant Mr. M'Guire, a college youth, sprung into it, and the balloon ascended with him to the astonishment of the beholders, and presently he was carried with great velocity towards the channel in the direction of Holyhead. This being observed, a crowd of horsemen pursued full speed the course he seemed to take, and could plainly perceive the balloon descending into the sea. Lord H. Fitzgerald, who was among the foremost, instantly dispatched a swift-sailing vessel mounted with oars, and all the boats that could be got, to the relief of the gallant youth; whom they found almost spent with swimming, just time enough to save his life.
The fate of M. Pilatre de Rozier, the first aerial traveller, and his companion M. Romain, has been much lamented. They ascended at Boulogne the 15th of June, with intent to cross the channel to England: for the first 20 minutes they seemed to take the proper direction; when presently the whole apparatus was seen in flames, and the unfortunate adventurers fell to the ground from the height of more than a thousand yards, and were killed on the spot, their bones being broken, and their bodies crushed in a shocking manner. The machine in which they ascended, consisted of a spherical balloon, 37 feet in diameter, filled with inflammable air; and under this balloon was suspended a small montgolfier, or fire balloon, of 10 feet diameter; the gallery which suspended the aeronauts, was attached to the net of the upper balloon by cords, which were fastened to a hoop rather larger than the montgolsier, and descended perpendicularly to the gallery. The montgolfier was intended to promote and prolong the ascension, by rarefying the atmospheric air, and by that means gaining levity. It is not certainly known whether the balloon was actually set on fire by the montgolfier, or, being over-rarefied by the heat beneath, burst, and by that means the inflammable air was set in a blaze.
On the 19th of July, at 20 minutes past 2 o'clock, Mr. Crosbie ascended at Dublin, with intent to cross the channel to Holyhead in England. The usual form of the boat had been changed, for a capacious wicker basket, of a circular form, round the upper edges of which were fastened a great many bladders, which were intended to render his gallery buoyant, in case of a disaster at sea. About 300 pounds of ballast were put into the basket, but the aeronaut discharged half a hundred on his first rise. At first the current of air carried him due west; but it soon changed his course to nearly north-east, pointing nearly towards Whitehaven. At upwards of 40 miles from the Irish shore, he found himself within clear sight of both lands, and he said it was impossible to give any adequate idea of the unspeakable beauties which the scenery of the sea, bounded by both lands, presented. He rose at one time so high, that by the intense cold his ink was frozen, and the mercury sunk quite into the ball of the thermometer. He was sick, and felt a strong prepulsion on the tympanum of the ears. At his utmost height he thought himself stationary; but on liberating some gas, he descended to a current of air blowing north, and extremely rough. He now entered a thick cloud, and encountered strong blasts of wind, with thunder and lightning, which brought him rapidly towards the surface of the water. Here the balloon made a circuit, but falling lower, the water entered his car, and he lost his notes of observation. All his endeavours to throw out ballast were of no avail; the force of the wind plunged him into the ocean; and with much difficulty he put on his cork jacket. The propriety of his idea was now very manifest in the construction of his boat; as by the admission of the water into the lower part of it, and the suspension of his bladders, which were arranged at the top, the water, added to his own weight, became proper ballast; and the balloon maintaining its poise, it became a powerful sail, by means of which, and a snatch block to his car, he went before the wind as regularly as a sailing vessel. In this situation he found himself inclined to eat, and he took a little fowl. At the distance of a league he discovered some vessels crowding after him; but as his progress outstripped all their endeavours, he lengthened the space of the balloon from the car, which gave a check to the rapidity of his sailing, and he was at length overtaken and saved by the Dunleary barge, which took him on board, and steered to Dunleary, towing the balloon after them.
A similar accident happened to Major Money, who ascended at Norwich, on the 22d of July, at 20 minutes past 4 in the afternoon; when meeting with an improper current, and not being able to let himself down, on account of the smallness of the valve, he was driven out to sea, where, after blowing about for near two hours, he dropped into the water. Here the struggles were astonishing which he made to keep the balloon up, which was torn, and hung only like an umbrella over his head. A ship was once within a mile, but, he adds, whether from want of humanity, or by mistaking the balloon for a sea monster, they sheered off, and left him to his fate: but a boat chased him for two hours, till just dark, and then bore away. He now gave up all hopes, and began to wish that providence had given him the fate of Pilatre de Rozier, rather than such a lingering death. Exerting himself however to preserve life as long as possible, by keeping the balloon floating over his head, to keep himself out of the water, into which nevertheless he sunk gradually inch | by inch, as it lost its power, till he was at length breast deep in water, when he was providentially taken up by a revenue cutter, at half past eleven at night, but so weak that he was obliged to be lifted out of the car into the ship.
About the latter end of August, the longest aerial voyage hitherto made, was performed by Mr. Blanchard, who ascended at Lisle, accompanied by the Chevalier de L'Epinard, and travelled 300 miles in their balloon before it descended. On this occasion, as on some former ones, Mr. Blanchard made trial of a parachute, like a large umbrella, invented to break the fall in case of an accident happening the balloon: with this machine he dropped a dog from the car soon after his ascension, which descended gently and unhurt.
On September the 8th, Thomas Baldwin, Esq. ascended from the city of Chester, at 40 minutes past one o'clock, and descended at Rixton-Moss, at 25 miles distance, after a voyage of 2 hours and a quarter. The greatest perpendicular altitude ascended was about a mile and a half, and the aeronaut computed that in some parts of the voyage he moved at the rate of 30 miles an hour. Mr. Baldwin published a very circumstantial account of his voyage, with many ingenious philosophical remarks relating to aerostation, of which subject his book may be considered as one of the best treatises yet given to the public.
October the 5th, Mr. Lunardi made the first aerial voyage in Scotland. He ascended at Edinburgh, and after various turnings, landed near Cupar in Fife, having described a track of 40 miles over the sea, and 10 over the land, in an hour and a half. He said the mercury in the barometer sunk as low as 18.3 inches at his greatest elevation.
November the 19th the celebrated Blanchard ascended at Ghent to a great height, and after many dangers descended at Delft without his car, which he cut away to lighten the machine when he was descending too rapidly, and slung himself by the cords to the balloon, which served him then in the nature of a parachute. On his first ascent, when he was almost out of sight, he let down a dog, by means of a parachute, which came easily to the ground.
November the 25th Mr. Lunardi ascended at Glasgow, and in two hours it is said he described a track of 125 miles. It is further remarkable that, being overcome with drowsiness, he says he slept for about 20 minutes in the bottom of the car, during this voyage.
Many other voyages were made in different countries, and with various success. But since the year 1785, the rage for balloons has considerably abated, and we have gradually had less and less of these aerial excuisions, so that it is now become rather an uncommon thing to hear of one of them performed in any country whatever: which speedy decline in this new art is perhaps to be ascribed chiefly to the following causes; namely, a less degree of eagerness in people to pursue such experiments, from their curiosity having been satisfied; secondly, the trouble, danger, and great expence, attending them; and lastly, the want of the means of conducting them, and the small degree of utility to which they have hitherto been applied. The failure in the many attempts that have been made to direct balloons at pleasure through the air, cannot but be felt as a very discouraging circumstance: and it ito be feared that it will ever be felt as such, notwithstanding the pretensions of some persons on this head; for they never have caused, nor is it to be expected they ever can cause the machine to deviate sensibly from the course of the wind, except only in the case when this moves with a very small celerity. For when the current blows only at the rate of 10 miles an hour, which is but a very gentle wind, it may be shewn that a balloon of 50 feet in diameter will require a force equal to the pressure of 72 pounds weight, to cause it to deviate 30 degrees from the course of the wind; and a force equal to double or triple that weight, when the wind blows with a double or triple velocity, that is, at the rate of 20 or 30 miles an hour; and so in proportion. To obviate the danger of a fall, arising from any accident happening to the balloon, some experiments have been made with a parachute, chiefly by Mr. Blanchard, whose endeavours and perseverance it seems have continued longer than in any other person: we still hear of his excursions in different parts of Europe, and improvements of the parachute, wings, &c; and have just read accounts of two voyages lately performed by him; with which, being very curious, we shall conclude our narration of these aerial excursions. They will be best related in Mr. Blanchard's own words, taken from his letter, dated Leipsick, October the 9th, 1787, to the editors of the Paris Journal. “I did not mention,” says he, “in your interesting paper, my ascension at Strasburg on the 26th of last August: the weather was so horrible that I mounted only for the sake of contenting the astonishing crowd of strangers assembled there from all parts of the country. Every body seemed satisfied at the attempt, but I assure you, gentlemen, that I was far from being pleased with so common an experiment. The only remarkable thing that occurred at that time, was the following circumstance: At the height of about 2000 yards, or a mile and half a quarter, I let down a dog tied to the parachute, who, instead of descending gently, was forcibly carried, by a whirlwind, above the clouds. I met him soon after, bending his course directly downwards, and, as on recollecting his master, he began to bark a little, I was going to take hold of the parachute, when another whirlwind lifted him again to a great height. I lost him for the space of six minutes, and perceived him afterwards, with my telescope, as if sleeping in the cradle or basket belonging to the machine. Continually agitated, and impetuously tossed through every point of the compass, by the violence of the different currents of air, I determined to end my voyage on the other side of the Rhine, after having passed vertically over Zell. I descended at a small village, with an intention to be assisted a little, and about thirty men soon came within reach of the balloon very a-propos, and fixed me to the ground. The wind was so violent that anchors or ropes would have been of no service. I had however added to the large aerostatic globe a smaller one, of 60 pounds ascensional force, which would have contributed to fix me, when once I let it loose; but notwithstanding this precaution, the men's assistance was very necessary to me. The parachute was still wavering in the air, and did not come down till 12 minutes after.” |
“I performed my 27th ascension at Leipsick the 29th of September, in the midst of an incredible number of spectators, forming one of the most brilliant assemblies I ever beheld. The sky was as clear and serene as possible, and the air so calm that many of my friends, and multitudes of others, could follow me on horseback, and even on foot. I was sometimes so near them that they thought they could reach me, but I could soon find the means of rising; and once, when they had actually taken hold of the cords, to see me float with the strings in their hands, I suddenly cut them, and mounted again in the air. All these amusing evolutions were in sight of the town and its environs. At length I yielded to the earnest solicirations of the company, and entered the town triumphantly in my car, followed by a concourse of people transported with joy, and amidst the acclamations of thousands. The next day I emptied the inflammable air into another globe, with which I intended to try some experiments; and I let it off with a cradle, in which a dog was fixed. The balloon, having reached a considerable height, made an explosion in its under part, as I had imagined it would, having previously disposed it in a proper manner for that purpose; by which means the little animal fell gently to the ground.”
“The day before yesterday having repeated this experiment, at the town's request, I prepared the globe in such a manner as to cause an explosion in its upper part, and added a parachute with two small dogs fixed to it. They went so high that, notwithstanding the serenity of the sky, the balloon was lost in its immense expanse. Telescopes of the best sort became useless, and I began to be apprehensive for the death of the little animals, on account of the severity of the cold. They descended however about two hours after, quite safe and well, in the town of Delitzsch, three miles from Leipsick. I went yesterday to claim them, and found them again over the town in the air with the parachute. Such experiments had been already tried many times in the course of the day, and some officers had thrown them from the top of a steeple, in the sight of all the inhabitants of Delitzsch, from whence they descended safe.”
We have lately heard of Mr. Blanchard's 32d ascension at Brunswick in the month of August 1788, in which he much assisted his ascent by means of his wings.
Practice of Aerostation. The first consideration in the practice of aerostation, is the form and the size of the machine. Various shapes have been tried and proposed, but the globular, or the egg-like figure, is the most proper and convenient, for all purposes; and this form also will require less cloth or silk than any other shape of the same capacity; so that it will both come cheaper, and have a greater power of ascension. The bag or cover of an inflammable-air balloon, is best made of the silk stuff called lustring, varnished over. But for a montgolfier, or heated-air balloon, on account of its great size, linen cloth has been used, lined within or without with paper, and varnished. Small balloons are made either of varnished paper, or simply of paper unvarnished, or of gold-beater's skin, or such-like light substances.
With respect to the form of a balloon, it will be necessary that the operator remember the common proportions between the diameters, circumferences, surfaces, and solidities of spheres; for instance, that of different spheres, the circumferences are as the diameters; that the surfaces are as the squares of the diameters; and the solidities as the cubes of the same diameters: that any diameter is to its circumference as 7 to 22, or as 1 to 3 1/7; and therefore 3 times and 1/7 of any diameter will be its circumserence; so that if the diameter of a balloon be 35 feet, its circumference will be 110 feet. And if the diameter be multiplied by the circumference, the product will be the surface of the sphere; thus 35 multiplied by 110 gives 3850, which is the sursace of the same sphere in square feet. and if this surface be divided by the breadth of the stuff, in feet, which the balloon is to be made of, the quotient will be the number of feet in length necessary to construct the balloon; so if the stuff be 3 feet wide, then 3850 divided by 3, gives 1283 1/3 feet, or 428 yards nearly, the requisite quantity of stuff of 3 feet or one yard wide, to form the balloon of 35 feet diameter. Hence also, by knowing the weight of a given piece of the stuff, as of a square foot, or square yard, it is easy to find the weight of the whole bag, namely by multiplying the surface, in square feet or yards, by the weight of a square foot or yard: so if each square yard weigh 16 ounces or 1 pound, then the whole bag will weigh 428 pounds. Again, the capacity, or solid contents, of the sphere, will be found by multiplying 1/6 of the surface by the diameter, or by taking 11/22 of the cube of the diameter; which gives 22458 cubie feet for the capacity of the said balloon, that is, it will contain, or displace, 22458 cubic feet of air. From the content and surface of the balloon, so found, is to be derived its power or levity, thus: on an average, a cubic foot of common air weighs 1 1/5 ounce, and therefore to the number 22458, which is the content of our balloon, adding its (1/5)th part, we have 26950 ounces, or 1684 pounds, for the weight of the common air displaced or occupied by the balloon. From this weight must be deducted the weight of the bag, namely 428 pounds, and then there remains 1256 pounds levity of the balloon, without however considering the contained air, whether it be heated air, or of the inflammable kind. If inflammable air be used, as it is of different weights, from 1/4 to 1/10 or 1/12 the weight of common air, according to the modes of preparing it, let us suppose for instance that it is 1/6 of the weight of common air; then 1/6 of 1684 is 261 pounds, which is the weight of the bag full of that air; which being taken from 1256, leaves 995 pounds for the levity of the balloon when so filled with that inflammable air, or the weight which it will carry up, consisting of the car, the ropes, the passengers, the necessaries, and ballast. But if heated air be used; then as it is known from experiment that, by heating, the contained air is diminished in density about one-third only, therefore from 1684, take 1/3 of itself, and there remains 1123 for the weight of the contained warm air; and this being subtracted from 1256, leaves only 133 pounds for the levity of the balloon in this case; which being too small to carry up the car, passengers, &c, it shews that for those purposes a larger balloon is necessary, on | Montgolfier's principles. But if now, from the preceding computation, it be required to find how much the size of the balloon must be increased, that its levity, or power of ascension, may be equal to any given weight, as suppose 1000 pounds; then because the levities are nearly as the cubes of the diameters, therefore the diameters will be nearly as the cube roots of the levities; but the levities 133 and 1000 are nearly as 1 to 8, the cube roots of which are as 1 to 2, and consequently 1 : 2 :: 35 : 70 feet, the diameter of a montgolfier, made of the same thickness of stuff as the former, capable of lifting 1000 pounds.
On the same principles we can easily find the size of a balloon that shall just float in air when made of stuff of a given thickness or weight, and filled with air of a given density; the rule for which is this: from the weight of a cubic foot of common air, subtract that of a cubic foot of the lighter or contained air; then divide 6 times the weight of a square foot of the stuff, by the remainder; and the quotient will be the diameter, in feet, of the balloon that will just float at the surface of the earth. Suppose, for instance, that the materials are as before, namely, the stuff 1 pound to the square yard, or 16/9 ounces to the square foot, which taken 6 times is 32/3; then the cubic foot of common air weighing 1 1/5 ounce, and of heated air 2/3 of the same, whose difference is 2/5; therefore 32/3 divided by 2/5, gives 26 2/3 feet, which is the diameter of a montgolfier that will just float: but if inflammable air be used of 1/6 the weight of common air, the difference between 1 1/5 and 1/6 of it, is 1; by which dividing 32/3 or 10 2/3, the quotient is the same 10 2/3 feet, which therefore is the diameter of an inflammable-air balloon that will just float. And if the diameter be more than these dimensions, the balloons will rise up into the atmosphere.
The height nearly to which a given balloon will rise in the atmosphere, may be thus found, having given only the diameter of the balloon, and the weight which just balances it, or that is just necessary to keep it from rising: compute the capacity or content of the globe in cubic feet, and divide its restraining weight in ounces by that content, and the
| Height in miles. | Density. |
| 0 | 1.200 |
| 1/4 | 1.141 |
| 1/2 | 1.085 |
| 3/4 | 1.031 |
| 1 | 0.980 |
| 1 1/4 | 0.932 |
| 1 1/2 | 0.886 |
| 1 3/4 | 0.842 |
| 2 | 0.800 |
| 2 1/4 | 0.761 |
| 2 1/2 | 0.723 |
| 2 3/4 | 0.687 |
| 3 | 0.653 |
The best way to make up the whole coating of the balloon, is by different pieces or slips joined lengthways from end to end, like the pieces composing the surface of a geographical globe, and contained between one meridian and another, or like the slices into which a melon is usually cut, and supposed to be spread flat out. Now the edges of such pieces cannot be exactly described by a pair of compasses, not being circular, but flatter or less round than circular arches; but if the slips are sufficiently narrow, or numerous, they will differ the less from circles, and may be described as such. But more accurately, the breadths of the slip, at the several distances from the point to the middle, where it is broadest, are directly as the sines of those distances, radius being the sine of the half length of the slip, or of the distance of either point from the middle of the slip: that is, If ACBD be one of the slips, AB being half the circumference, or AE a quadrant conceived to be equal to AC or AD; then will CD be to a b, as radius or the sine of AC, to the sine of Aa. So that if the quadrant AE or AC be divided into any number of equal parts, as here suppose 9, then divide the quadrant or 90 degrees by the number of parts 9, and the quotient 10 is the number of degrees in each part; and hence the arcs AC, Aa, Ac, &c, will be respectively 90°, 80°, 70°, &c; and CD being radius, the several breadths ab, cd, ef, &c, will be respectively the sines of 80°, 70°, 60°, &c, which are here placed opposite them, the radius being 1. Therefore when it is proposed to cut out slips for a globe of a given diameter; compute the circumference, and make AE or AC a quarter of that circumference, and CD of any breadth, as 3 feet, or 2 feet, or any other | quantity; then multiply each of the decimal numbers, set opposite the figure, by that quantity, or breadth of CD, so shall the products be the several breadths ab, cd, ef, &c.
Various schemes have been devised for conducting balloons in any direction, whether vertical or sideways. As to the vertical directions, namely upwards or downwards, the means are obvious, viz. in order to ascend, the aeronaut throws out some ballast; and that he may descend, he opens a valve in the top of his machine by means of a string, to let some of the gas escape; or if it be a montgolfier, he increases or diminishes the fire, as he would ascend or descend. But to direct the machine in a side or horizontal course, is a very difficult operation, and what has hitherto not been accomplished, except in a small degree, and when the current of air is very gentle indeed. The dissiculty of moving the balloon sideways, arises from the want of wind blowing upon it; for as it floats along with the current of air, it is relatively in a calm, and the aeronaut feels no more wind than if the machine were at rest in a perfect calm. For this reason, any thing in the nature of sails can be of no use; and all that can be hoped for, is to be attempted by means of oars; and how small the effect of these must be, may easily be conceived from the rarity of the medium against which they must act, and the great magnitude of the machine to be forced through it. We can easily assign what force is necessary to move a given machine in the air with any proposed velocity. From very accurate experiments I have determined, that a globe of 6 3/8 inches in diameter, and moving with a velocity of 20 feet per second of time, suffers a resistance from the air which is just equal to the weight or pressure of one ounce Averdupois; and farther that with different surfaces, and the same velocity, the resistances are directly proportional to the surface nearly, a double surface having a double resistance, a triple surface a triple resistance, and so on; and also that with different velocities, the resistances are proportional to the squares of the velocities nearly, so that a double velocity produced a quadruple resistance, and three times the velocity nine times the resistance, and so on. And hence we can assign the resistance to move a given balloon, with any velocity. Thus, take the balloon as before of 35 feet diameter; then by comparifon as above it is found that this globe, if moved with the velocity of 20 feet per second, or almost 14 miles per hour, will suffer a resistance equal to 271 pounds; to move it at the rate of 7 miles an hour, the resistance will be 68 pounds; and to move it 3 1/2 miles an hour, the resistance will be 17 pounds; and so on: and with such force must the aeronauts act on the air in a contrary direction, to communicate such a motion to the machine. And if the balloon move through a rarer part of the atmosphere, than that at the surface of the earth, as 1/3, or 1/4, &c, rarer, and consequently the resistance be less in the same proportion; yet the force of the oars will be diminished as much; and therefore the same difficulty still remains. In general, the aeronaut must strike the air, by means of his oars, with a force just equal to the resistance of the air on the balloon, and therefore he must strike that air with a velocity which must be greater as the surface of the oar is less than the resisted surface of the globe, but not in the same proportion, because the force is as the square of the velocity.
Now suppose the aeronaut act with an oar equal to 100 square feet of surface, to move the balloon above mentioned at the rate of 20 feet per second, or 14 miles an hour; then must he move this oar with the great velocity of 62 feet per second, or near 43 miles per hour: and so in proportion for other velocities of the balloon. From whence it is highly probable, that it will never be in the power of man to guide such machine with any tolerable degree of success, especially when any considerable wind blows, which is almost always the case.
As some aeronauts have thought of using parachutes, made something like umbrellas, to break their fall, in case of any accident happening to the balloon, we shall here consider the principles and power of such a machine. Let us suppose a person wants to know what the size of a parachute must be, that he may descend with it at the uniform rate of 10 feet in a second, which is nearly equal to the velocity he acquires by falling or leaping from the height only of 17 inches, and which it is presumed he may do with safety. Now in order to descend with any uniform velocity, the resistance of the air must be equal to the whole weight that descends: then suppose the weight of the aeronaut to be 150 pounds, and that the parachute is flat, and circular, and made of such materials as that every square foot of its surface weighs 2 ounces, and farther that the weight increases in the same proportion as the surface; then the diameter of the parachute necessary to descend with the moderate velocity of 10 feet per second, must be upwards of 78 feet in diameter: but if the parachute be not a flat surface, but concave on the lower side, its power will be rather the greater, and the diameter may be somewhat less. If it be required to know the power of a flat circular parachute, or what resistance it meets with from air of a mean density, when descending with a given velocity; say as the number 800 is to the square of the velocity in feet, so is the square of the diameter in feet, to a fourth number, which will be the resistance in pounds. And hence, if it be required to know with what velocity a parachute will descend with a given weight; say as the given diameter is to the square root of the weight, so is the number 28 1/3 to a fourth term, which will be the velocity when the descent is in air of a mean density. So if the diameter of a balloon be 50, and its weight together with that of a man be 530 pounds, the square root of which is 23 very nearly; then as 50 : 23 :: 28 1/3 : 13, so that the man and parachute will descend with the velocity of 13 feet per second; which it is presumed he may safely do, as he would meet with a shock only equal to that of leaping freely from a height only of 2 feet 2 inches.
The methods of extracting inflammable air from various substances, for filling balloons, and for other purposes, may be seen under the words Air and Gas. And as to the methods of filling and constructing balloons, being matters merely mechanical, they are omitted in this place.
Ample information however on these, and many other particulars, may be met with in several books expressly written on the subject; as in Cavallo's History | and Practice of Aerostation, 8vo, 1785; in Baldwin's Airopaidia, 8vo, 1786; &c.
It has often been discussed, says the former of these gentlemen, whether the preference should be given to machines raised by inflammable air, or to those raised by heated air. Each of them has its peculiar advantages and disadvantages; a just consideration of which seems to decide in favour of those made with inflammable air. The principal comparative advantages of the other sort are, that they do not require to be made of so expensive materials; that they are filled with little or no expence; and that the combustibles necessary to fill them are found almost every where; so that when the stock of fuel is exhausted, the aeronaut may descend and recruit it again, in order to proceed on his voyage. But then this sort of machines must be made larger than the other, to take up the same weight; and the presence of a fire is a continual trouble, and a continual danger: in fact, among the many aerial voyages that have been made and attempted with such machines, very few have succeeded without an inconvenience, or an accident; and some indeed have been attended with dangerous and even fatal consequences; from which the other sort is in a great measure exempt. But, on the other hand, the inflammable air balloon must be made of a substance impermeable to the subtle gas: the gas itself cannot be produced without a considerable expence; and it is not easy to find the materials and apparatus necessary for the production of it in every place. However, it has been found that an inflammable-air balloon, of 30 feet in diameter, may be made so close as to sustain two persons, and a considerable quantity of ballast, in the air for more than 24 hours, when properly managed; and possibly one man might be supported by the same machine for three days: and it is probable that the stuff for these balloons may be so far improved, as to be quite impermeable to the gas, or very nearly so; in which case, the machine, once silled, would continue to float for a long space of time. At Paris they have already attained to a great degree of perfection in this point; and small balloons have been kept floating in a room for many weeks, without losing any considerable quantity of their levity: but the difficulty lies in the large machines: for in these, the weight of the stuff itself, with the weight and stress of the ropes and boat, and the folding them up, may easily crack and rub off the varnish, and make them leaky.
In regard to philosophical observations, derived from the new subject of aerostation, there have been very few made; the novelty of the discovery, and of the prospect enjoyed from the car of an aerostatic machine, have commonly distracted the attention of the aeronauts; not to remark that many of the adventurers were inadequate to the purpose of making improvements in philosophy, being mostly influenced either by pecuniary motives, or the vanity of adding their names to the list of aerial travellers.—The agreeable stillness and tranquillity experienced aloft in the atmosphere, have been matter of general observation. Some machines have ascended to a great height, as far, it has been said, as two miles; and they have commonly passed through fogs and clouds, above which they have enjoyed the clear light and heat of the sun, whilst the earth beneath was actually covered by dense clouds, which poured down abundance of rain. In ascending very high, the aeronauts have often experienced a pain in their ears, arising, it is supposed, from the internal air being not of the same density as the air without; but the pain usually went off in a short time: and it seems that this effect is similar to what is experienced by persons who descend by a diving-bell to considerable depths in the sea: I remember often to have heard the late unfortunate Mr. Spalding, the celebrated diver, speak of this effect, with a marked and philosophical accuracy: after descending two or three fathoms below the surface, he began to feel a pain in his ears, which gradually increased to a very great degree if the descent was too quick; his method was therefore to descend slowly, and to make a stop for some minutes at the depth of 5 fathom, which is equal nearly to the pressure of the atmosphere, and where consequently the air in his bell was of double the density of common air at the surface; after resting here awhile, his ears, as he expressed it, gave a crack, and he was suddenly relieved of the pain. He then descended 5 fathoms more, with the same symptoms, and the same effect: and so on continually, from one five fathoms to another, descending leisurely, and stopping a little at each stage, to give time for his constitution to adapt itself to the degree of condensation of the air; after which he felt no more inconvenience, till he came to ascend again, which was performed with the same caution and circumstances. One experiment is recorded, in which the air of a high region, being brought down, and examined by means of nitrous air, was found to be purer than the air below. The temperature of the upper regions too, it has been found, is much colder than that of the air near the earth; the thermometer, in some aerostatic machines, having descended many degrees below the freezing point of water, while it was considerably higher than that degree at the earth's surface.
ÆSTIVAL, see Estival.
ÆSTUARY, or Estuary, in Geography, an arm of the sea, running up a good way into the land. Such as Bristol channel, many of the friths in Sootland, and such like.
ÆTHER, see Ether.
