AEROSTATION, in its primitive sense, denotes the science of suspending weights in the air: but, in its modern acceptation, it signifies aerial navigation, or the art of navigating through the atmosphere. Hence, also, the machines which are employed for this purpose are called aerostats, or aero­static machines; and, from their globular shape, air-balloons.

The romances of almost every nation have recorded instances of persons being carried through the air, both by the agency of spirits and by mechanical inventions: but, till the time of the celebrated Lord Bacon, no ra­tional principle appears ever to have been thought of by which this might be accomplished. Before that time, indeed, Friar Bacon had written upon the subject; and many had been of opinion, that, by means of arti­ficial wings, fixed to the arms or legs, a man might fly as well as a bird: but these opinions were thoroughly refuted by Borelli in his treatise De Motu Animalium, where, from a comparison between the power of the muscles which move the wings of a bird, and those which move the arms of a man, he demonstrates that the latter are utterly insufficient to strike the air with such force as to raise him from the ground. It cannot be denied, however, that wings of this kind, if pro­perly constructed, and dexterously managed, might be sufficient to break the fall of a human body from an high place, so that some adventurers in this way might possibly come off with safety; though by far the great­est number of those who have rashly adopted such schemes, have either lost their lives or limbs in the at­tempt.

[Page 4] In the year 1672, Bishop Wilkins published a trea­tise, entitled, The Discovery of the New World; in which he mentions, though in a very indistinct and confused manner, the true principle on which the air is navigable; quoting from Albertus de Saxonia and Francis Mendoca, "that the air is in some part of it navigable: and, upon this static principle, any brass or iron vessel, suppose a kettle, whose substance is much heavier than that of water, yet, being filled with the lighter air, it will swim upon it and not sink. So sup­pose a cup or wooden vessel upon the outward borders of this elementary air, the capacity of it being filled with fire, or rather ethereal air, it must necessarily, up­on the same ground, remain swimming there, and of it­self can no more fall than an empty ship can sink." This idea, however, he did not by any means pursue; but rested his hopes entirely upon mechanical motions, to be accomplished by the mere strength of a man, or by springs, &c. and which have been demonstrated in­capable of answering any useful purpose.

The only person who brought his scheme of flying to any kind of rational principle, was the Jesuit Francis Lana, cotemporary with Bishop Wilkins. He, being acquainted with the real weight of the atmosphere, justly concluded that if a globular vessel were exhaust­ed of air it would weigh less than before; and consi­dering that the solid contents of vessels increase in much greater proportion than their surfaces; he suppo­sed that a metalline vessel might be made so large, that, when emptied of its air, it would be able not only to raise itself in the atmosphere, but to carry up passengers along with it; and he made a number of calculations necessary for putting the project in execu­tion. But though the theory was here unexception­able, the means proposed were certainly insufficient to accomplish the end: for a vessel of copper, made so thin as was necessary to make it float in the atmo­sphere, would be utterly unable to resist the external [Page 5] pressure; which being demonstrated by those skilled in mechanics, no attempt was made on that principle.

In the year 1709, however, as we were informed by a letter published in France in 1784, a Portuguese projector, Friar Gusman, applied to the king for en­couragement to his invention of a flying machine. The principle on which this was constructed, if indeed it had any principle, seems to have been that of the pa­per kite. The machine was constructed in form of a bird, and contained several tubes through which the wind was to pass, in order to fill a kind of sails which were to elevate it; and, when the wind was deficient, the same effect was to be performed by means of bel­lows concealed within the body of the machine. The ascent was also to be promoted by the electric attrac­tion of pieces of amber placed in the top, and by two spheres inclosing magnets in the same situation.

These childish inventions shew the low state of sci­ence at that time in Portugal, especially as the king, in order to encourage him to farther exertions in such an useful invention, granted him the first vacant place in his college of B [...]celos or Santarem, with the first professorship in the University of Coimbra, and an an­nual pension of 600,000 reis during his life. Of this De Gusman it is also related, that in the year 1736 he made a wicker basket of about seven or eight feet diameter, and covered with paper, which raised itself about 200 feet in the air, and the effect was generally attributed to witchcraft.

In the year 1766 Mr. Henry Cavendish ascertained the weight and other properties of inflammable air, de­termining it to be at least seven times lighter than common air. Soon after which, it occurred to Doctor Black, that perhaps a thin bag filled with inflammable air might be buoyed up by the common atmosphere; and he thought of having the allantois of a calf prepa­red for this purpose: but his other avocations prevent­ed him from prosecuting the experiment. The same [Page 6] thought occurred some years afterwards to Mr. Cavallo; and he has the honour of being the first who made ex­periments on the subject. He first tried bladders; but the thinnest of these, however well scraped and prepa­red, were found too heavy. He then tried Chinese paper; but that proved so permeable, that the vapour passed through it like water through a sieve. His ex­periments, therefore, made in the year 1782, proceed­ed no farther than blowing up soap-bubbles with in­flammable air, which ascended rapidly to the cieling, and broke against it.

But while the discovery of the art of aerostation seemed thus on the point of being made in Britain, it was all at once announced in France, and that from a quarter whence nothing of the kind was to have been expected. Two brothers, Stephen and John Mont­golfier, natives of Annonay, and masters of a consider­able paper-manufactory there, had turned their thoughts towards this project as early as the middle of the year 1782. The idea was first suggested by the natural ascent of the smoke and clouds of the atmosphere; and their design was to form an artificial cloud, by inclosing the smoke in a bag, and making it carry up the cover­ing along with it. Towards the middle of November that year, the experiment was made at Avignon with a fine silk bag of a parallelopiped shape. By applying burning paper to the lower aperture, the air was rare­fied, and the bag ascended in the atmosphere, and struck rapidly against the ceiling. On repeating the experiment in the open air, it rose to the height of a­bout 70 feet.

An experiment on a more enlarged scale was now projected; and a new machine, containing about 650 cubic feet, was made, which broke the cords that con­fined it, and rose to the height of about 600 feet. A­nother of 35 feet in diameter rose about 1000 feet high, and fell to the ground three quarters of a mile from the place where it ascended. A public exhibition [Page 7] was next made on the 5th of June, 1783, at Annonay, where a vast number of spectators assembled. An im­mense bag of linen, lined with paper, and containing upwards of 23,000 cubic feet, was found to have a power of lifting about 500 pounds, including its own weight. The operation was begun by burning chop­ped straw and wool under the aperture of the machine, which immediately began to swell; and after being set at liberty, ascended into the atmosphere. In ten mi­nutes it had ascended 6000 feet; and when its force was exhausted, it fell to the ground at the distance of 7668 feet from the place from whence it set out.

Soon after this, one of the brothers arrived at Paris, where he was invited by the Academy of Sciences to repeat his experiments at their expence. In conse­quence of this invitation, he constructed, in a garden in the Fauxbourg of St. Germain, a large balloon of an elliptical form. In a preliminary experiment, this ma­chine lifted up from the ground eight persons who held it, and would have carried them all off if more had not quickly come to their assistance. Next day the expe­riment was repeated in presence of the members of the academy. The machine was filled by the combustion of 50 pounds of straw made up in small bundles, upon which about 12 pounds of chopped wool were thrown at intervals. The usual success attended this exhibi­tion: The machine soon swelled; endeavoured to a­scend; and immediately after sustained itself in the air, together with the charge of between 4 and 500 pounds weight. It was evident that it would have ascended to a great height; but as it was designed to repeat the experiment before the king and royal family at Versailles, the cords by which it was tied down were not cut. But in consequence of a violent rain and wind which happened at this time, the machine was so far damaged, that it became necessary to prepare a new one for the time that it had been determined to honour the experiment with the royal presence and [Page 8] such expedition was used, that this vast machine, of near 60 feet in height and 43 in diameter, was made, painted with water-colours both within and without, and finely decorated, in no more than four days and four nights. Along with this machine was sent a wicker cage, containing a sheep, a cock, and a duck, which were the first animals ever sent through the at­mosphere. The full success of the experiment was pre­vented by a violent gust of wind which tore the cloth in two places near the top before it ascended: How­ever, it rose to the height of 1440 feet; and, after re­maining in the air about eight minutes, fell to the ground at the distance of 10,200 feet from the place of its setting out. The animals were not in the least hurt.

The great power of these aerostatic machines, and their very gradual descent in falling to the ground, had originally shewed that they were capable of transport­ing people through the air with all imaginable safety; and this was further confirmed by the experiment al­ready mentioned. As Mr. Montgolfier, therefore, proposed to make a new aerostatic machine of a firmer and better construction than the former, Mr. Pilatre de Rozier offered himself to be the first aerial adven­turer.

This new machine was constructed in a garden in the Fauxbourg of St. Antoine. It was of an oval shape, about 48 feet in diameter and 74 in height; elegantly painted on the outside with the signs of the zodiac, cyphers of the king's name, and other ornaments. A proper gallery, grate, &c. were appended, in the man­ner afterwards described; so that it was easy for the person who ascended to supply the fire with fuel, and thus keep up the machine as long as he pleased. The weight of the whole apparatus was upwards of 1600 pounds. The experiment was performed on the 15th of October, 1783. Mr. Pilatre having placed himself in the gallery, the machine was inflated, and permit­ted [Page 9] to ascend to the height of 84 feet, where he kept it afloat for about four minutes and a half; after which it descended very gently: and such was its tendency to ascend, that it rebounded to a considerable height after touching the ground. Two days after, he repeated the experiment with the same success as before: but the wind being strong, the machine did not sustain itself so well as formerly. On repeating the experiment in calmer weather, he ascended to the height of 210 feet. His next ascent was 262 feet; and in the descent, a gust of wind having blown the machine over some large trees of an adjoining garden, Mr. Pilatre suddenly extricated himself from so dangerous a situation, by throwing some straw and chopped wool on the fire, which raised him at once to a sufficient height. On descending again, he once more raised himself to a proper height by throwing straw on the fire. Some time after, he ascended in company with Mr. Girond de Villette to the height of 330 feet; hovering over Paris at least nine minutes in sight of all the inhabitants, and the machine keeping all the while perfectly steady.

These experiments had shewn that the aerostatic machines might be raised or lowered at the pleasure of the persons who ascended: they had likewise discover­ed, that the keeping them fast with ropes was no advantage; but, on the contrary, that this was attend­ed with inconvenience and hazard. On the 21st of November, 1783, therefore, M. Pilatre determined to undertake an aerial voyage in which the machine should be fully set at liberty. Every thing being got in rea­diness, the balloon was filled in a few minutes; and M. Pilatre placed himself in the gallery, counterpoised by the Marquis d'Arlandes, who occupied the other side. It was intended to make some preliminary ex­periments on the ascending power of the machine: but the violence of the wind prevented this from being done, and even damaged the balloon essentially; so [Page 10] that it would have been entirely destroyed had not timely assistance been given. The extraordinary exer­tions of the workmen, however, repaired it again in two hours, and the adventurers set out. They met with no inconvenience during their voyage, which lasted about 25 minutes; during which time they had passed over a space of above five miles. From the account given by the Marquis d'Arlandes, it ap­pears that they met with several different currents of air; the effect of which was, to give a very sensible shock to the machine, and the direction of the motion seemed to be from the upper part downwards. It ap­pears also that they were in some danger of having the balloon burnt altogether; as the Marquis observed se­veral round holes made by the fire in the lower part of it, which alarmed him considerably, and indeed not without reason. However, the progress of the fire was easily stopped by the application of a wet spunge, and all appearance of danger ceased in a very short time.

This voyage of M. Pilatre and the Marquis d'Ar­landes may be said to conclude the history of those aerostatic machines which are elevated by means of fire: for though many other attempts have been made upon the same principle, most of them have either proved unsuccessful or were of little consequence. They have therefore given place to the other kind, filled with inflammable air; which, by reason of its smaller spe­cific gravity, is both more manageable, and capable of performing voyages of greater length, as it does not require to be supplied with fuel like the others. This was invented a very short time after the discovery had been made by M. Montgolfier. This gentleman had indeed designed to keep his method in some degree a secret from the world: but as it could not be conceal­ed, that a bag filled with any kind of fluid lighter than the common atmosphere would rise in it, inflammable air was naturally thought of as a proper succedaneum [Page 11] for the rarefied air of M. Montgolfier. The first ex­periment was made by two brothers, Messrs. Roberts, and M. Charles, a professor of experimental philoso­phy. The bag which contained the gas was compo­sed of lutestring, varnished over with a solution of the elastic gum called caoutch [...]u [...]; and that with which they made their first essay was only about 13 English feet in diameter. Many difficulties occurred in filling it with the inflammable air, chiefly owing to their ig­norance of the proper apparatus; insomuch, that, af­ter a whole day's labour from nine in the morning, they had got the balloon only one third part full. Next morning they were surprised to find that it had fully inflated of itself during the night: but, upon en­quiry, it was found that they had inadvertently left open a stop-cock connected with the balloon, by which the common air gaining access, had mixed itself with the inflammable air; forming a compound still lighter than the common atmosphere, but not sufficiently light to answer the purposes of aerostation. Thus they were obliged to renew their operation; and, by six o'clock in the evening of next day, they sound the machine considerably lighter than the common air; and, in an hour after, it made a considerable effort to ascend. The public exhibition, however, had been announced only for the third day after; so that the balloon was allowed to remain in an inflated state for a whole day; during which they found it had lost a power of ascent equal to about three pounds, being one seventh part of the whole. When it was at last set at liberty, after having been well filled with inflammable air, it was 35 pounds lighter than an equal bulk of common air. It remained in the atmosphere only three quarters of an hour, during which it had traversed 15 miles. Its sudden descent was supposed to have been owing to a rupture which had taken place when it ascended into the higher regions of the atmosphere.

The success of this experiment, and the aerial voy­age [Page 12] made by Messrs. Rozier and Arlandes, naturally suggested the idea of undertaking something of the same kind with a balloon filled with inflammable air. The machine used on this occasion was formed of gores of silk, covered over with a varnish made of [...], of a spherical figure, and measuring 27½ feet in dia­meter. A net was spread over the upper hemisphere, and was fastened to an hoop which passed round the middle of the balloon. To this a sort of car, or ra­ther boat, was suspended by ropes, in such a manner as to hang a few feet below the lower part of the bal­loon; and, in order to prevent the bursting of the ma­chine, a valve was placed in it, by opening of which some of the inflammable air might be occasionally let out. A long silken pipe communicated with the bal­loon, by means of which it was filled. The boat was made of basket-work, covered with painted linen, and beautifully ornamented; being 8 feet long, 4 broad, and 3½ deep; its weight 130 pounds. At this time, however, as at the former, they met with great difficul­ties in filling the machine with inflammable air, owing to their ignorance of the most proper apparatus. But at last, all obstacles being removed, the two adventu­rers took their seats at three quarters after one in the afternoon of the first of December, 1783. Persons skilled in mathematics were conveniently stationed with proper instruments to calculate the height, velocity, &c. of the balloon. The weight of the whole appa­ratus, including that of the two adventurers, was found to be 604½ pounds, and the power of ascent when they set out was 20 pounds; so that the whole difference betwixt the weight of this balloon and an equal bulk of common air was 624 pounds. But the weight of common atmosphere displaced by the inflammable gas was calculated to be 771 pounds, so that there remain 147 for the weight of the latter; and this calculation makes it only 5¼ times lighter than common air.

At the time the balloon left the ground, the ther­mometer [Page 13] stood at 9° of Fahrenheit's scale, and the quicksilver in the barometer at 30.18 inches; and, by means of the power of ascent with which they left the ground, the balloon rose till the mercury fell to 27 in­ches, from which they calculated their height to be about 600 yards. By throwing out ballast occasion­ally as they found the machine descending by the e­scape of some of the inflammable air, they found it practicable to keep at pretty near the same distance from the earth during the rest of their voyage; the quicksilver fluctuating between 27 and 27.65 inches, and the thermometer between 53° and 57°, the whole time. They continued in the air for the space of an hour and three quarters, when they alighted at the distance of 27 miles from Paris; having suffered no inconvenience during their voyage, nor experienced any contrary currents of air, as had been felt by Messrs. Pilatre and Arlandes. As the balloon still retained a great quantity of inflammable gas, Mr. Charles determined to take another voyage by him­self. Mr. Robert accordingly got out of the boat, which was thus lightened by 130 pounds, and of consequence the aerostatic machine now had nearly as much power of ascent. Thus he was carried up with such velocity, that in twenty minutes he was al­most 9000 feet high, and entirely out of sight of ter­restrial objects. At the moment of his parting with the ground, the globe had been rather flaccid: but it soon began to swell, and the inflammable air escaped from it in great quantity through the silken tube. He also frequently drew the valve that it might be the more freely emitted, and the balloon effectually pre­vented from bursting. The inflammable gas being considerably warmer than the external air, diffused it­self all round, and was felt like a warm atmosphere: but in ten minutes the thermometer indicated a varia­tion of temperature as great as that between the warmth of spring and the ordinary cold of winter. [Page 14] His fingers were benumbed by the cold, and he felt a violent pain in his right ear and jaw, which he ascribed to the dilatation of the air in these organs, as well as to the external cold. The beauty of the prospect which he now enjoyed, however, made amends for these in­conveniences. At his departure the sun was set on the valleys: but the height to which Mr. Charles was got in the atmosphere rendered him again visible, tho' only for a short time. He saw, for a few seconds, va­pours rising from the vallies and rivers. The clouds seemed to ascend from the earth, and collect one upon the other, still preserving their usual form; only their colour was grey and monotonous for want of sufficient light in the atmosphere. By the light of the moon he perceived that the machine was turning round with him in the air; and he observed that there were con­trary currents which brought him back again. He ob­served also, with surprize, the effects of the wind, and that the streamers of his banners pointed upwards; which, he says, could not be the effect either of his ascent or descent, as he was moving horizontally at the time. At last, recollecting his promise of returning to his friends in half an hour, he pulled the valve, and accelerated his descent. When within 200 feet of the earth, he threw out two or three pounds of ballast, which rendered the balloon again stationary: but, in a little time afterwards, he gently alighted in a field about three miles distant from the place whence he set out; though, by making allowance for all the turn­ings and windings of the voyage, he supposes that he had gone through nine miles at least. By the calcu­lations of M. de Maunier, he rose at this time not less than 10,500 feet high; a height somewhat greater than that of Mount AEtna. A small balloon, which had been sent off before the two brothers set out on their voyage, took a direction opposite to that of the large one, having met with an opposite current of air, probably at a much greater height.

[Page 15] The subsequent aerial voyages differ so little from that just now related, that any particular description of them seems to be superfluous. It had occurred to Mr. Charles, however, in his last flight, that there might be a possibility of directing the machine in the atmosphere; and this was soon attempted by Mr. Jean-Pierre Blan­chard, a gentleman who had, for several years before, amused himself with endeavours to fly by mechanical means, though he had never succeeded in the under­taking. As soon as the discovery of the aerostatic ma­chines was announced, however, he resolved to add the wings of his former machine to a balloon, and made no doubt that it would then be in his power to direct him­self through the air at pleasure. In his first attempt he was frustrated by the impetuosity of a young gentle­man, who insisted, right or wrong, on ascending along with him. In the scuffle which ensued on this occa­sion, the wings and other apparatus were entirely de­stroyed, so that Mr. Blanchard was obliged to commit himself to the direction of the wind; and in another attempt it was found that all the strength he could ap­ply to the wings was scarce sufficient to counteract the impression of the wind in any degree. In his voyage, he found his balloon, at a certain period, acted upon by two contrary winds: but, on throwing out four pounds of ballast, he ascended to a place where he met with the same current he had at setting out from the earth. His account of the sensations he felt during this voyage, was somewhat different from that of Mr. Charles; having, in one part of it, found the atmo­sphere very warm, in another cold; and having once found himself very hungry, and at another time almost overcome by a propensity to sleep. The height to which he arose, as measured by several observations with mathematical instruments, was thought to be very little less than 10,000 feet; and he remained in the atmo­sphere an hour and a quarter.

The attempts of Mr. Blanchard to direct his machine [Page 16] through the atmosphere, were repeated in the month of April, 1784, by Messrs. Morveau & Bertrand, at Dijon, who raised themselves with an inflammable air-balloon to the height, as it was thought, of 13,000 feet; pas­sing through a space of 18 miles in an hour and 25 minutes. Mr. Morveau had prepared a kind of oars for directing the machine through the air: but they were damaged by a gust of wind, so that only two of them remained serviceable; by working these, however, they were able to produce a sensible effect on the mo­tion of the machine. In a third aerial voyage perform­ed by Mr. Blanchard, he seemed to produce some effect by the agitation of his wings, both in ascending, de­scending, moving sidewise, and even in some measure against the wind. However, this is supposed, with some probability, to have been a mistake; as, in all his suc­ceeding voyages, the effects of his machinery could not be perceived.

The success of Messrs. Charles and Robert in their former experiments, encouraged them soon to repeat them, with the addition of some machinery to direct their course. Having enlarged their former balloon to the size of an oblong spheroid 46⅓ feet long and 27½ in diameter, they made it to float with its longest part parallel to the horizon. The wings were made in the shape of an umbrella without the handle, to the top of which a stick was fastened parallel to the aperture of the umbrella. Five of these were disposed round the boat, which was near 17 feet in length. The balloon was filled in three hours, and, with the addition of 450 pounds of ballast, remained in equilibrio with the at­mosphere. About noon, on the 19th of September, 1784, they began to ascend very gently in consequence of throwing out 24 pounds of ballast; but were soon obliged to throw out eight pounds more, in order to avoid running against some trees. Thus they rose to the height of 1400 feet, when they perceived some thunder-clouds near the horizon. On this they ascend­ed [Page 17] and descended, to avoid the danger, as the wind blew directly towards the threatening clouds; but, from the height of 600 feet to that of 4200 above the surface of the earth, the current was quite uniform and in one direction. During their voyage they lost one of their oars; but found that by means of those which remained they considerably accelerated their course. From the account of their voyage, it would seem that they had passed safely through the thunder-clouds; as we are informed, that, about 40 minutes after three, they heard a loud clap of thunder; and, three minutes after, another much louder; at which time the ther­mometer sunk from 77 to 59 degrees. This sudden cold, occasioned by the approach of the clouds, con­densed the inflammable air so that the balloon descend­ed very low, and they were obliged to throw out 40 pounds of ballast: yet on examining the heat of the air within the balloon, they found it to be 104°, when that of the external atmosphere was only 63. When they had got so high that the mercury in the barometer stood only at 23.94 inches, they found themselves becalmed; so that the machine did not go even at the rate of two feet in a second, though it had before gone at the rate of 24 feet in a second. On this they determined to try the effect of their oars to the utmost; and, by working them for 35 minutes, and marking the shadow of the balloon on the ground, they found in that time that they had described the segment of an ellipsis whose longest diameter was 6000 feet. After having tra­velled about 150 miles, they descended, only on account of the approach of night, having still 200 pounds of ballast left.

Their conclusion, with regard to the effect of their wings, is as follows:

"Those experiments shew, that, far from going against the wind, as is said by some persons to be possible in a certain manner, and some aeronauts pretend to have actually done, we only obtained, by means of two oars, [...] [Page 18] degrees. It is certain, however, that if we could have used our four oars, we might have deviated about 40 degrees from the direction of the wind; and as our machine would have been capable of carrying seven persons, it would have been easy for five persons to have gone, and to have put in action eight oars, by means of which a deviation of about 80 degrees would have been obtained.

"We had already observed," say they, "that if we did not deviate more than 22 degrees, it was because the wind carried us at the rate of 24 miles an hour; and it is natural to judge, that, if the wind had been twice as strong as it was, we should not have deviated more than one half of what we actually did: and, on the contrary, if the wind had been only half as strong, our deviation would have been propor­tionably greater."

Having thus related all that has been done with re­gard to the conducting of aerostatic machines through the atmosphere, we shall now relate the attempts that have been made to lessen their expence, by falling upon some contrivance to ascend without throwing out bal­last, and to descend without losing any of the inflam­mable air. The first attempt of this kind was made by the Duke de Chartres, who, on the 15th of July, 1784, ascended with the two brothers, Charles and Ro­bert, from the Park of St. Cloud. The balloon was of an oblong form, made to ascend with its longest dia­meter horizontally, and measured 55 feet in length and 24 in breadth. It contained within it a smaller balloon filled with common air; by blowing into which with a pair of bellows, and thus throwing in a consi­derable quantity of common air, it was supposed that the machine would become sufficiently heavy to descend, especially as, by the inflation of the internal bag, the inflammable air in the external one would be condensed into a smaller space, and thus become specifically hea­vier. The voyage, however, was attended with such circumstances as rendered it impossible to know what would have been the event of the scheme. The power [Page 19] of ascent with which they set out, seems to have been very great; as, in three minutes after parting with the ground, they were lost in the clouds, and involved in such a dense vapour that they could see neither the sky nor the earth. In this situation they seemed to be attacked by a whirlwind, which, besides turning the balloon three times round from right to left, shocked, and beat it so about, that they were rendered incapable of using any of the means proposed for directing their course, and the silk stuff of which the helm had been composed was even torn away. No scene can be con­ceived more terrible than that in which they were now involved. An immense ocean of shapeless clouds rolled one upon another below them, and seemed to prevent any return to the earth, which still continued invisible, while the agitation of the balloon became greater every moment. In this extremity they cut the cords which held the interior balloon, and of consequence it fell down upon the aperture of the tube that came from the large balloon into the boat, and stopped it up. They were then driven upwards by a gust of wind from below, which carried them to the top of that stormy vapour in which they had been involved. They now saw the sun without a cloud; but the heat of his rays, with the diminished density of the atmosphere, had such an effect on the inflammable air, that the balloon seem­ed every moment ready to burst. To prevent this they introduced a stick through the tube, in order to push away the inner balloon from its aperture: but the ex­pansion of the inflammable air pushed it so close, that all attempts of this kind proved ineffectual. It was now, however, become absolutely necessary to give vent to a very considerable quantity of the inflammable air; for which purpose the Duke de Chartres himself bored two holes in the balloon, which tore open for the length of seven or eight feet. On this they descended with great rapidity; and would have fallen into a lake, had they not hastily thrown out 60 pounds of ballast, which enabled them just to reach the water's edge.

[Page 20] The success of the scheme for raising or lowering aerostatic machines by means of bags filled with com­mon air being thus rendered dubious, another method was thought of. This was to put a small aerostatic machine with rarefied air under an inflammable air-balloon, but at such a distance that the inflammable air of the latter might be perfectly out of the reach of the fire used for inflating the former; and thus, by increa­sing or diminishing the fire in the small machine, the absolute weight of the whole would be considerably di­minished or augmented. This scheme was unhappily put in execution by the celebrated Mr. Pilatre de Ro­zier, and another gentleman named Mr. Romaine. Their inflammable air-balloon was about 37 feet in diameter, and the power of the rarefied-air one was equivalent to about 60 pounds. They ascended without any appear­ance of danger or sinister accident; but had not been long in the atmosphere when the inflammable air bal­loon was seen to swell very considerably, at the same time that the aeronauts were observed, by means of te­lescopes, very anxious to get down, and busied in pull­ing the valve and opening the appendages to the bal­loon, in order to facilitate the escape of as much in­flammable air as possible. A short time after this the whole machine was on fire, when they had then attained the height of about three quarters of a mile from the ground. No explosion was heard; and the silk which composed the air-balloon continued expanded, and seemed to resist the atmosphere for about a minute; after which it collapsed, and the remains of the appara­tus descended along with the two unfortunate travellers so rapidly, that both of them were killed. Mr. Pilatre seemed to have been dead before he came to the ground; but Mr. Romaine was alive when some persons came up to the place where he lay, though he expired immedi­ately after.

These are the most remarkable attempts that have been made to improve the science of aerostation; tho' [Page 21] a great number of other expeditions through the at­mosphere have taken place. But of all the voyages which had been hitherto projected or put in exe­cution, the most daring was that of Mr. Blanchard and Dr. Jeffries across the straits of Dover which separate Britain from France. This took place on the 7th of January, 1785, being a clear frosty morn­ing, with a wind, barely perceptible, at N. N. W. The operation of filling the balloon began at ten o'clock, and at three quarters after twelve every thing was ready for their departure. At one o'clock Mr. Blanchard desired the boat to be pushed off, which now stood only two feet distant from that precipice so finely described by Shakespeare in his tragedy of King Lear. As the balloon was scarcely sufficient to carry two, they were obliged to throw out all their ballast except three bags of ten pounds each; when they at last rose gently, though making very little way on account of there being so little wind. At a quarter after one o'clock, the barometer, which on the cliff stood at 29.7 inches, was now fallen to 27.3, and the weather proved fine and warm. They had now a most beautiful prospect of the south coast of England, and were able to count 37 villages upon it. After passing over several vessels, they found that the balloon, at 50 minutes after one, was descending, on which they threw out a sack and a half of ballast; but as they saw that it still descended, and that with much greater velocity than before, they now threw out all the ballast. This still proving ineffectual, they next threw out a parcel of books they carried along with them, which made the balloon ascend, when they were about midway betwixt France and England. At a quarter past two, finding themselves again descending, they threw away the re­mainder of their books, and, ten minutes after, they had a most enchanting prospect of the French coast. Still, however, the machine descended; and as they had now no more ballast, they were fain to throw away [Page 22] their provisions for eating, the wings of their boat, and every other moveable they could easily spare. "We threw away, says Dr. Jeffries, our only bottle, which, in its descent, cast out a steam like smoke, with a rush­ing noise; and when it struck the water, we heard and felt the shock very perceptibly on our car and balloon." All this proving insufficient to stop the descent of the balloon, they next threw out their anchors and cords, and at last stripped off their clothes, fastening themselves to certain slings, and intending to cut away the boat as their last resource. They had now the satisfaction, however, to find that they were rising; and as they passed over the high lands between Cape Blanc and Calais, the machine rose very fast, and carried them to a greater height than they had been at any former part of their voyage. They descended safely among some trees in the forest of Guiennes, where there was just opening enough to admit them.

It would be tedious as well as unnecessary to recount all the other aerial voyages that have been performed in different countries: It is sufficient to notice those which are most remarkable and interesting; and there­fore an account of the ingenious Mr. Baldwin's excur­sion from Chester, alluded to above, shall now close our enumeration.

On the 8th of September, 1785, at forty minutes past one P. M. Mr. Baldwin ascended from Chestenin Mr. Lunardi's balloon. After traversing in a variety of different directions, he first alighted, at 28 minutes after three, about twelve miles from Chester, in the neighbourhood of Frodsham; then re-ascending, and pursuing his excursion, he finally landed at Rixton moss, five miles N. N. E. of Wavington, and 25 miles from Chester. Mr. Baldwin has published his observa­tions and Remarks made during his voyage, and taken from minutes. Our limits will not admit of relating many of his observations: but the few following are [Page 23] some of the most important and curious. The sen­sation of ascending is compared to that of a strong pressure from the bottom of the car upwards against the soles of his feet. At the distance of what appeared to him seven miles from the earth, though by the ba­rometer scarcely a mile and a half, he had a grand and most enchanting view of the city of Chester and its adjacent places below. The river Dee appeared of a red colour; the city very diminutive; and the town entirely blue. The whole appeared a perfect plain, the highest building having no apparent height, but reduced all to the same level, and the whole terrestrial prospect appeared like a coloured map. Just after his first ascent, being a well-watered and maritime part of the country, he observed a remarkable and regular tendency of the balloon towards the sea: but shortly after rising into another current of air, he escaped the danger. This upper current, he says, was visible to him at the time of his ascent, by a lofty sound stratum of clouds flying in a safe direction. The perspective ap­pearance of things to him was very remarkable. The lowest bed of vapour that first appeared as cloud was pure white, in detached fleeces, increasing as they rose: they presently coalesced, and formed, as he expresses it, a sea of cotton, rufting here and there by the action of the air in the undisturbed part of the clouds. The whole became an extended white floor of cloud, the upper surface being smooth and even. Above this white floor he observed, at great and une­qual distances, a vast assemblage of thunder-clouds, each parcel consisting of whole acres in the densest form: he compares their form and appearance to the smoke of pieces of ordnance, which had consolidated as it were into masses of snow, and penetrated thro' the upper surface or white floor of common clouds, there remaining visible and at rest. Some clouds had mo­tions in slow and various directions, forming an appear­ance truly stupendous and majestic. Mr. Baldwin gives [Page 24] a curious description of his tracing the shadow of the balloon over tops of volumes of clouds. At first it was small, in size and shape like an egg: but soon in­creased to the magnitude of the sun's disk, still grow­ing larger, and attended with a most captivating ap­pearance of an iris encircling the whole shadow at some distance round it, the colours of which were remarkably brilliant. The regions did not feel colder, but rather warmer, than below. The sun was hottest to him when the balloon was stationary. The discharge of a cannon when the balloon was at a considerable height, was distinctly heard by the aeronaut; and a discharge from the same piece, when at the height of 30 yards, so disturbed him as to oblige him for safety to lay hold firmly of the cords of the balloon. At a considerable height he poured down a pint-bottle full of water; and as the air did not oppose a resistance sufficient to break the stream into small drops, it mostly fell down in large drops. In the course of the balloon's tract it was found much affected by the water, a circumstance ob­served in former aerial voyages. At one time the direction of the balloon kept continually over the wa­ter, going directly towards the sea, so much as to en­danger the aeronaut; the mouth of the balloon was opened, and he in two minutes descended into an under current blowing from the sea: he kept descending, and landed at Bellair farm in Rinsley, 12 miles from Chester. Here he lightened his car by 31 pounds, and instantly re-ascending, was carried into the interior part of the country, performing a number of different manoeuvres. At his greatest altitude he found his respiration free and easy. Several bladders which he had along with him crackled and expanded very considerably. Clouds and land, as before, appeared on the same level. By way of experiment, he tried the upper valve two or three times, the neck of the balloon being close; and re­marked, that the escape of the gas was attended with a growling noise like millstones, but not near so loud. [Page 25] Again, round the shadow of the balloon, on the clouds he observed the iris. A variety of other circumstances and appearances he met with, is fancifully described; and at 53 minutes past three he finally landed.

Before giving any account of the most proper method of constructing these machines, it may seem necessary to premise something concerning the uses to which they may possibly be applied. These, according to Mr. Cavallo, are the following.

"The small balloons, especially those made of paper, and raised by means of spirit of wine, may serve to ex­plore the direction of the winds in the upper regions of the atmosphere, particularly when there is a calm below: they may serve for signals in various circumstances, in which no other means can be used; and letters or other small things may be easily sent by them, as for instance from ships that cannot safely land on account of storms, from besieged places, islands, or the like. The larger aerostatic machines may answer all the above-mentioned purposes in a better manner; and they may, besides, be used as a help to a person who wants to ascend a moun­tain, a precipice, or to cross a river; and perhaps one of those machines tied to a boat by a long rope, may be, in some cases, a better sort of sail than any that is used at present. The largest sort of machines, which can take up one or more men, may evidently be subservient to various economical and philosophical purposes. Their conveying people from place to place with great swiftness, and with­out trouble, may be of essential use, even if the art of guiding them in a direction different from that of the wind should never be discovered. By means of those ma­chines, the shape of certain seas and lands may be better ascertained; men may ascend to the tops of mountains they never visited before; they may be carried over marshy and dangerous grounds; they may by that means come out of a besieged place, or an island; and they may, in hot climates, ascend to a cold region of the atmosphere, either to refresh themselves, or to observe the ice, which is never seen below; and, in short, they may be thus taken to several places, to which human art hitherto knew of no conveyance.

[Page 26] "The philosophical uses to which these machines may be subservient, are numerous indeed; and it may be suffi­cient to say, that hardly any thing which passes in the at­mosphere is known with precision, and that principally for want of a method of ascending into it. The forma­tion of rain, of thunder-storms, of vapours, hail, snow, and meteors in general, require to be attentively examined and ascertained. The action of the barometer, the refrac­tion and temperature of the air in various regions, the descent of bodies, the propagation of sound, &c. are sub­jects which all require a series of observations and experi­ments, the performance of which could never have been properly expected before the discovery of aerostatic ma­chines."

To those uses we may add the gratification of curiosity and pleasure as a very strong inducement to the practice of an art, in which, with any tolerable degree of cau­tion, there appears not to be the smallest danger. Every one who has tried the experiment testifies that the beauty of the prospect afforded by an ascent, or the pleasure of being conveyed through the atmo­sphere, cannot be exceeded. No one has felt the least of that giddiness consequent upon looking from the top of a very high building or of a precipice, nor have they any of the sickness arising from the motion of a vessel at sea. Many have been carried by bal­loons at the rate of 30, 40, or even 50 miles an hour, without feeling the least inconvenience, or even agi­tation of the wind; the reason of which is, that as the machine moves with nearly the velocity of the wind itself, they are always in a calm, and without uneasi­ness. Some have apprehended danger from the elec­tricity of the atmosphere; and have thought that a stroke of lightning, or the smallest electric spark, hap­pening near a balloon, might set fire to the inflamma­ble air, and destroy both the machine and the adven­turers. Mr. Cavallo has suggested several considerations for diminishing apprehensions of this kind. Balloons have been already raised in every season of the year, [Page 27] and even when thunder has been heard, without in­jury. In case of danger, the aeronauts may either de­scend to the earth, or ascend above the region of the clouds and thunder-storms. Besides, as balloons are formed of materials that are not conductors of electri­city, they are not likely to receive strokes, especially as by being encompassed with air they stand insulated. Moreover, inflammable air by itself, or unmixed with a certain quantity of common air, will not burn; so that if an electric spark should happen to pass through the balloon, it would not set fire to the inflammable air, unless a hole was made in the covering.

The general principles of aerostation are so little different from those of hydrostatics, that it may seem superfluous to insist much upon them. It is a fact universally known, That when a body is immersed in any fluid, if its weight be less than an equal bulk of that fluid, it will rise to the surface: but if heavier, it will sink; and if equal, it will remain in the place where it is left. For this reason smoke ascends into the atmo­sphere, and heated air in that which is colder. The ascent of the latter is shewn in a very easy and satis­factory manner by bringing a red-hot iron under one of the scales of a balance, by which the latter is in­stantly made to ascend: for, as soon as the red-hot iron is brought under the scale, the hot air being light­er than that which is colder, ascends, and strikes the bottom, which is thus impelled upwards, and the op­posite scale descends, as if a weight had been put into it.

Upon this simple principle depends the whole theo­ry of aerostation: for it is the same thing whether we render the air lighter by introducing a quantity of heat into it, or inclosing a quantity of gas specifically lighter than the common atmosphere in a certain spare; both will ascend, and for the same reason. A cubic foot of air, by the most accurate experiments, has been found to weigh about 554 grains, and to be ex­panded [Page 28] by every degree of heat, marked on Fahren­heit's thermometer, about 1500th part of the whole. By heating a quantity of air, therefore, to 500 de­grees of Fahrenheit, we shall just double its bulk when the thermometer stands at 54 in the open air, and in the same proportion we shall diminish its weight; and if such a quantity of this hot air be inclosed in a bag, that the excess of the weight of an equal bulk of com­mon air weighs more than the bag with the air con­tained in it, both the bag and air will rise into the at­mosphere, and continue to do so until they arrive at a place where the external air is naturally so much rare­fied that the weight becomes equal; and here the whole will float.

The power of hot air in raising weights, or rather that by which it is itself impelled upwards, may be shewn in the following manner: Roll up a sheet of paper into a conical form, and, by thrusting a pin into it near the apex, prevent it from unrolling. Fasten it then by its apex under one of the scales of a ba­lance by means of a thread, and, having properly counterpoised it by weights, put it into the opposite scale; apply the flame of a candle underneath, you will instantly perceive the cone to arise, and it will not be brought into equilibrium with the other but by a much greater weight than those who have never seen the experiment would believe. If we try this experi­ment with more accuracy, by getting proper recep­tacles made which contain determinate quantities of air, we shall find that the power of the heat depends much more on the capacity of the bag which contains it than could well be supposed. Thus, let a cubical receptacle be made of a small wooden frame covered with paper, capable of containing one foot of air; and let the power of a candle be tried with this, as above directed for the paper cone. It will then be found that a certain weight may be raised: but a much greater one will be raised by having a receptacle of the same [Page 29] kind which contains two cubic feet; a still greater by one of three feet; a yet greater by one of four feet, &c. and this even though the very same candle be made use of; nor is it known to what extent even the power of this small flame might be carried.

From these experiments it appears, that in the aero­static machines conducted on Montgolfier's plan, it must be an advantage to have them as large as possible; because a smaller quantity of fire will then have a great­er effect in raising them, and the danger from that element, which in this kind of machines is chiefly to be dreaded, will be in a great measure avoided. On this subject it may be remarked, that as the cubical con­tents of a globe, or any other figure of which balloons are made, increase much more rapidly than their sur­faces, there must ultimately be a degree of magni­tude at which the smallest imaginable heat would raise any weight whatever. Thus, supposing any aerostatic machine capable of containing 500 cubic feet, and the air within it to be only one degree hotter than the ex­ternal atmosphere; the tendency of this machine to rise, even without the application of artificial heat, would be near an ounce. Let its capacity be increased 16 times, and the tendency to rise will be equivalent to a pound, though this may be done without making the machine 16 times heavier than before. It is cer­tain, however, that all aerostatic machines have a ten­dency to produce or preserve heat within them, which would by no means be imagined by those who have not made the experiment. When Messrs. Charles and Roberts made their longest aerial voyage of 150 miles, they had the curiosity to try the temperature of the air within their balloon, in comparison with that of the external atmosphere; and at this time they found, that, when the external atmosphere was 63°▪ the ther­mometer within the balloon stood at 104°. Such a dif­ference of temperature must have given a machine of the magnitude which carried them a considerable ascend­ing [Page 30] power independent of any other cause, as it amount­ed to 41 grains on every cubic foot; and therefore in a machine containing 50,000 such feet would have been almost 200 pounds. Hence we may easily ac­count for what happened at Dijon, and is recorded by Mr. Morveau:

"A balloon, intended to be filled with inflammable air, being completed, was, by way of trial, filled with com­mon air, and in that state exposed to the atmosphere. Now it was observed, and indeed a similar observation had been made before, that the air within the balloon was much hotter than the circumambient air: the thermome­ter in the former stood at 120°; whereas in the latter, even when the sun shone upon it, the thermometer stood at 84°. This shewed a considerable degree of rarefaction within the balloon; and consequently it was suspected, that, by means of this rarefaction alone, especially if it were to increase a little, the balloon might ascend. On the 30th of May, about noon, the wind being rather strong, agitated the balloon so that two men were employed to take care of it: but, notwithstanding all their endeavours, it escaped from its confinement, and, lifting up about 65 pounds weight of cords, equatorial circle, &c. rose many feet high, and, passing over some houses, went to the distance of 250 yards, where at length it was properly secured."

This difference between the external and internal heat being so very considerable, must have a great in­fluence upon aerostatic machines, and will undoubtedly influence those filled with inflammable air as well as the other kind. Nor is it unlikely, that the short time which many aerial voyagers have been able to continue in the atmosphere, may have been owing to the want of a method of preserving this internal heat. It may naturally be supposed, and indeed it has always been found, that balloons, in passing through the higher re­gions of the atmosphere, acquire a very considerable quantity of moisture, not only from the rain or snow they sometimes meet with, but even from the dew and [Page 31] vapour which condense upon them. On this an eva­poration will instantly take place; and, as it is the pro­perty of this operation to produce a very violent cold, the internal heat of the balloon must be soon exhausted in such a manner as to make it become specifically hea­vier than the common atmosphere, and consequently descend in a much shorter time than it would have done by the mere loss of air. To this, in all probability, we are to ascribe the descent of the balloon which car­ried Messrs. Blanchard and Jeffries; and which seemed so extraordinary to many people, that they were ob­liged to have recourse to an imaginary attraction in the waters of the ocean in order to solve the pheno­menon. This supposition is rejected by Mr. Cavallo; who explains the matter, by remarking, that in two former voyages made with the same machine, it could not long support two men in the atmosphere; so that we had no occasion to wonder at its weakness on this occasion.

"As for its rising higher," says he, "just when it got over the land, that may be easily accounted for. In the first place, the two travellers threw out their cloaths just about that time; secondly, in consequence of the wind's then increasing, the balloon travelled at a much greater rate than it had done whilst over the sea; which increase of velocity lessened its tendency to descend: besides which the vicissitudes of heat and cold may produce a very con­siderable effect; for if we suppose that the air over the land was colder than that over the sea, the balloon com­ing into the latter from the former, continued to be hotter than the circumambient air for some time after, and con­sequently it was comparatively much lighter when in the cold air over the land than when in the hotter air over the sea. Hence it floated easier in the former than in the latter case."

It seems indeed very probable, that there was some­thing uncommon in the case of Mr. Blanchard's balloon while passing over the sea: for, as it rose higher after reaching the land than in any former period of the [Page 32] voyage, and likewise carried them to the distance over land more than half of that which they had passed over water, we can scarce avoid supposing, that it had a tendency to descend when over the water more than when over land, independent of any loss of air. Now, it does not appear that the air over the sea is at all warmer than that above land; on the contrary, there is every reason to believe, that the superior reflective power of the land renders the atmosphere above it warmer than the sea can do: but it is very natural to suppose that the air above the sea is more moist than that above land; and, consequently, by letting fall its moisture upon the balloon, must have occasioned an e­vaporation that would deprive the balloon of its inter­nal heat, which it would partly recover after it entered the warmer and drier atmosphere over land.

We shall now proceed to the construction of aero­static machines; of which the smaller are only for a­musement, or some slight experiments, and are very easily made. As in all of them, however, it is of the utmost consequence to have the weight as little as pos­sible, the shape becomes an object of great considera­tion. For this purpose a spherical figure has been ma­thematically demonstrated to be the best, as capable of containing a greater quantity under a smaller surface than any other.

For experimental purposes, both the inflammable and rarefied air-balloons may be made of paper; the former being made of that kind called thin-post, var­nished over with linseed oil; the latter either of that or any other kind, without varnish. In order to avoid the danger of burning, however, it has been proposed to impregnate the paper of which these small rarefied air-balloons are made with solution of sal-ammoniac, alum, or some other salt: but this does not seem to be necessary. Those filled with inflammable air have been made of gold-beater skin or peeled bladders: but the cheaper material of paper is undoubtedly preferable.

[Page 33] For aerostatic machines of a large size, the material universally employed is varnished silk▪ and for those of the rarefied-air kind, linen painted over with some size colour, or lined with paper.

The car or boat is best made of wicker-work, cover­ed with leather, and [...] painted or varnished over; and the proper method of suspending it, is by ropes pro­ceeding from the net which goes over the balloon. This net should be formed to the shape of the balloon, and fall down to the middle of it, with various cords proceeding from it to the circumference of a circle about two feet below the balloon; and from that circle other ropes should go to the edge of the boat. The circle may be made of wood, or of several pieces of slender cane bound together. The meshes of the net may be small at top, against which part of the balloon the inflammable air exerts the greatest force; and increase in size as they recede from the top. A hoop has sometimes been applied round the middle of the balloon to fasten the net. This, though not absolutely necessary, is best made of pieces of cane bound together, and covered with leather.

It now only remains to give some account of the method by which aerostatic machines may be filled with their proper gas, in order to give them their power of ascending into the atmosphere; and here we are enabled to determine with much greater precision concerning the inflammable air-balloons than the others. With regard to them, a primary consideration is, the most proper method of procuring the inflammable air. It may be obtained in various ways. The most advanta­geous methods are, by applying acids to certain metals; by exposing animal, vegetable, and some mineral sub­stances, in a close vessel, to a strong fire; or by trans­mitting the vapour of certain fluids through red-hot tubes.

1. In the first of these methods, iron, zinc, and vitriolic acid, are the materials most generally used. [Page 34] The vitriolic acid must be diluted by five or six parts of water. Iron may be expected to yield in the com­mon way 1700 times its own bulk of gas; or one cubic foot of inflammable air to be produced by 4½ ounces of iron, the like weight of oil of vitriol, and 22½ oun­ces of water. Six ounces of zinc, an equal weight of oil of vitriol, and 30 ounces of water, are necessary for producing the same quantity of gas. It is more proper to use the turnings or chippings of great pieces of iron, as of cannon, &c. than the filings of that metal, because the heat attending the effervescence will be diminished; and the diluted acid will pass more readily through the interstices of the turnings when they are heaped together, than through the filings which stick closer to one another. The weight of the inflammable air thus obtained by means of acid of vi­triol, is, in the common way of procuring it, gene­rally one-seventh part of the weight of common air; but with the necessary precautions for philosophical experiments, less than one-tenth of the weight of common air. Two other sorts of elastic fluids are sometimes generated with the inflammable air. These may be separated from it by passing the inflammable air through water in which quicklime has been dissol­ved. The water will absorb these fluids, cool the in­flammable air, and prevent its over-heating the bal­loon when introduced into it.

2. Inflammable air may be obtained at a much cheaper rate by the action of fire on various substances; but the gas which these yield is not so light as that produced by the effervescence of acids and metals. The substances proper to be used in this way are pit-coal, asphalt [...]m amber, rock-oil, and other minerals; wood, and especially oak, camphor-oil, spirits of wine, ether, and animal substances, which yield air in different de­grees, and of various specific gravities: but pit-coal is the preferable substance. A pound of this exposed to a red heat, yields about three cubic feet of inflammable [Page 35] air, which, whether it be passed through water or not, weighs about one-fourth of the weight of common air. Dr. Priestley found that animal or vegetable substances will yield six or seven times more inflammable air when the fire is suddenly increased than when it is gently raised, though it be afterwards made very strong.

3. The last method of obtaining inflammable air was lately discovered by Mr. Lavoisier, and also by Dr. Priestley. Mr. Lavoisier made the steam of boiling wa­ter pass through the barrel of a gun, kept red-hot by burning coals. Dr. Priestley uses, instead of the gun­barrel, a tube of red-hot brass, upon which the steam of water has no effect, and which he fills with the pieces of iron which are separated in the boring of can­non. By this method he obtains an inflammable air, the specific gravity of which is to that of common air as 1 to 13.

The conduct of balloons, when constructed, filled, and actually ascending in the atmosphere, is an object of great importance in the practice of aerostation. The method generally used for elevating or lowering the balloons with rarefied air, has been the increase or di­minution of the fire; and this is entirely at the com­mand of the aeronaut, as long as he has any fuel in the gallery. The inflammable air-balloons have been ge­nerally raised or lowered by diminishing the weight in the boat, or by letting out some of the gas through the valve: but the alternate escape of the air in de­scending, and discharge of the ballast for ascending, will by degrees render the machine incapable of float­ing; for in the air it is impossible to supply the loss of ballast, and very difficult to supply that of inflammable air.

These balloons will also rise or fall by means of the rarefaction or condensation of the inclosed air, oc­casioned by heat and cold. It has been proposed to aid a balloon in its alternate motion of ascent and de­scent, by annexing to it a vessel of common air, which [Page 36] might be condensed for lowering the machine, and ra­refied again, by expelling part of it, for raising the machine: But a vessel adapted to this purpose must be very strong; and, after all, the assistance afforded by it would not be very considerable. M. Meunier, in or­der to attain this end, proposes to inclose one balloon filled with common air in another filled with inflam­mable air: as the balloon ascends, the inflammable air is dilated, and of course compresses the internal balloon containing the common air; and, by diminishing its quantity, lessens its weight. If it should be necessary to supply this loss, he says it may be easily done by a pair of bellows fixed in the gallery. Others have pro­posed to annex a small machine with rarefied air to an inflamable-air balloon by ropes, at such a distance that the fire of the former might not affect the inflammable air of the latter: the whole apparatus, thus combined, of balloons formed on the two principles of heated and inflammable air, might be raised or lowered by merely increasing or diminishing the fire in the lower balloon.

Wings or oars are the only means of this sort that have been used with some success; and, as Mr. Cavallo ob­serves, they seem to be capable of considerable improve­ment. Although great effects are not to be expected from them, when the machine goes at a great rate, the best methods of moving these wings are by the hu­man strength applied similarly to the oars of a water­man. They may be made in general of silk stretched between wires, tubes, or sticks; and when used, must be turned edgewise when they are moved in the direc­tion in which the machine is intended to be impelled, but flat in the opposite direction.

The wing constructed by Count Zambaccari, con­sists of a piece of silk stretched between two tin tubes set at an angle, but these wings are so contrived as to turn edgewise by themselves when they go on one di­rection. Other contrivances have been made to direct aerostatic machines, but they have mostly been invent­ed [Page 37] to effect a power upon them as upon a ship. It ap­pears, however, that they can have no effect when a ma­chine is only moved by the wind alone, because the cir­cumambient air is at rest in respect to the machine. The case is quite different with a vessel at sea, because the water on which it floats stands still whilst the vessel goes on; but it must be time and experience that can realize the expectations suggested by these contrivances.