a term used by naturalists for caverns or reservoirs of air, supposed to exist in the bowels of the earth. Kircher speaks much of aerophylacea, or huge caverns, replete with air, disposed under ground; from whence, through numerous occult passages, that element is conveyed either to subterraneous receptacles of water, which, according to him, are hereby raised into springs or rivers, or into the funds of subterraneous fire, which are hereby fed and kept alive for the reparation of metals, minerals, and the like.
AEROSTATION
AEROLGY.
Oils and Salts, why they separate in vacuo, 7.
Olive oil, with whitening, yields inflammable air, 124.
Phlogisticated air, its properties, 99. Nitrous acid procured by means of it, 100. Mr Cavendish's opinions on its nature, 103.
Phlogistication of air, whether it produces any vitriolic acid, 76. Explained, 89.
Phlogiston, too great powers attributed to it, 90. Its existence denied by the foreign chemists, 91. Whether inflammable air is pure phlogiston or not, 133, 138. Contained in alkaline air, 147.
Plants purify air by their vegetation, 38.
Populus nigra, dephlogisticated air plentifully produced from water by means of its cotton-like substance, 46, 47.
Precipitate per se, yields no water on being revived into a metal, 73.
Priestley, Dr., discovers dephlogisticated air, 24. His first hypothesis concerning the component parts of dephlogisticated air, 63. Difference between some of his experiments and those of Lavoisier, 64. His opinion concerning the non-existence of nitrous acid in dephlogisticated air, 66. Difficulties arising from some of his experiments concerning the generation of water in deflating dephlogisticated and inflammable air, 85. His conjectures concerning the incondensible vapour of water, 87. His experiments on the composition of fixed air, 110. His opinion concerning the composition of phlogisticated air, 111. Experiment in favour of his hypothesis concerning phlogisticated air, 114. Putrefying substances emit fixed air, 182.
Raw-fish produces dephlogisticated air by means of water, 41. Various substances substituted for it, 45. Comparison between its surface and that of the cotton-like substance of the Populus nigra, 47.
Red-lead yields no dephlogisticated air when first prepared, and but little for some time after, 29. Gives a greater quantity by a sudden than a slow heat, 30.
Respiration, Mr Lavoisier's experiments on it, 91.
Retorts with long necks proper for distilling dephlogisticated air, 31.
Scales of iron the same with finery-cinder, 124.
Scheele discovers dephlogisticated air, 28. His experiments on its diminution by combustion, 59. On the component parts of the atmosphere, 24.
Sea-water contains pure air, 53.
Seltzer-water imitated by Mr Venel, 20.
Sheep's wool separates dephlogisticated air from water, 45.
Soot yields pure air by distillation, 87.
Sponge imbibes a great quantity of alkaline air, 146.
Span-glass, unsuccessful attempt to procure dephlogisticated air from water by its means, 49.
Steam, proportions of inflammable air obtained by its means from different substances, 125. Its influence on the production of inflammable air from charcoal, 132.
Stones sometimes dissolved by the air, 14.
Sulphureous vapours, their pernicious effects, 5.
Sulphur yields inflammable air with steam, 124.
Sulphurated inflammable air procured from manganese, 144. And from iron melted in vitriolic acid air, 145.
Thomson, Sir Benjamin, his experiments on the production of dephlogisticated air, 39 et seq.
Turpentine oil yields inflammable air, 124.
Vegetation will not go on in vacuo, and why, 12. Produces dephlogisticated air, 32. Improves noxious air, 33.
Experiments seemingly contradictory, 34. Dr Ingenhousz's experiments on this subject, 35.
Van Helmont's discoveries, 16.
Vegetable acid air phlogisticates common air, 174.
Vitriolic acid air, 165.
Volatile alkali produced from nitrous acid and iron, 149.
Water, quantity of it evaporated from the Mediterranean, 4. From an acre of ground, ibid. Why it boils violently in vacuo, 7. Produces dephlogisticated air, 36. Quantity of air yielded by it, with the mixture of various substances, 46. By water alone, 50. Formed by the deflagration of inflammable and dephlogisticated air, 71. Quantity produced in this manner, 72, 73. Cavendish's experiments on this subject, 75. Dr Priestley's experiments on the same, 80, 81. Experiments of the French philosophers and Mr Kirwan, 82, 83. Water previous to air, 98. Method of procuring inflammable air by its means, 124. Always necessary to the production of this kind of air, 128, 131. Attraction betwixt it and burning charcoal or iron, 132. Great propensity of inflammable air to unite with it, 137, 140. Its effects on nitrous air, 162.
Wines, proportions of fixed air in different kinds of them, 182. AEROSTATION
Is a science newly introduced into the Encyclopædia. The word, 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-balloon.
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.
In the year 1672, Bishop Wilkins published a treatise, intitled, 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 bras 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 relied 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, contemporary 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 metallic 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 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 Strange's letter published in France in 1784, a Portuguese proposal of projector, Friar Guzman, 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 show 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 Barcelos 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 Guzman, 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 air thought common air. Soon after which, it occurred to Dr of Dr 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 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 thinness of them, 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... ed no farther than blowing up soap-bubbles with inflammable air, which ascended rapidly to the ceiling, 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 makers 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 in 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 of 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 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 expense. In consequence of this invitation, he constructed, in a garden in the Fauxbourg de 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 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 some an- 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 Mr Pilatre their very gradual descent in falling to the ground, had de Rozier originally showed 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 de 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, ciphers 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 attended 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 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 shown, that the aerostatic machines might be raised or lowered at the pleasure of the 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. Everything 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 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 about 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 sponge, 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 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 caoutchouc; 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; infomuch, 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 No. 5.
fully inflated of itself during the night: but upon inquiry, it was found, that they had inadvertently left open a stop-cock connected with the balloon, by which manner the common air gaining access, had mixed itself with partly filled the inflammable air; forming a compound still lighter than the common atmosphere, but not sufficiently light itself, 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 found 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 power of the whole. When it was at last let at liberty, after being 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 made by Messrs Rozier and Arlandes, naturally suggested the idea of undertaking something of the same kind with a balloon filled with inflammable air, Charles and Roberts. The machine used on this occasion was formed of gores of silk, covered over with a varnish made of caoutchouc, 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 fort 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 filken 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 between 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 remains gravity of 147 for the weight of the latter; and this calculation makes it only 5½ times lighter than common air.
At the time the balloon left the ground, the thermometer stood at 9° of Fahrenheit's scale, and the quicksilver in the barometer at 30.18 inches; and, by means... 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 Pilette 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 filken 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. 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, though only for a short time. He saw, for a few seconds, vapours rising from the valleys 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 Etna. 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.
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 Attempts 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 inflicted, 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 acceded 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 through the atmosphere, were repeated in the month of April 1784 by Messrs Morveau and 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 46 feet long and 27½ inches 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 equilibrium 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 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 show, that far from going against the wind, as is laid 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, a deviation of 22 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 expense, by falling upon flammable 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 Voyage of the Duke de Chartres; who, on the 15th of July the Duke 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 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, attacked by a whirlwind, and beat it so about, that they were rendered incapable wind, 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 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.
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 into 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 imminent 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 buffeted 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' a great number of other expeditions through the atmosphere have taken place. But of all the voyages which had been hitherto projected or put into 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 10 o'clock, and, at three quarters after twelve, everything 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 10 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 an 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 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 cloths, 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 Guinnes, 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 our own or other countries: It appeared sufficient for the purpose of this article to notice those which were 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 Chester in Mr Lunardi's (a) 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 reascending, 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
(a) Of this gentleman's adventurous excursions most people have been witnesses; and therefore it appeared unnecessary to take up room with an account of them in this article. many of his observations; but the few following are 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 in 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, tufting 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 through 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. He endeavours to convey some idea of the scene by a figure; (and from which fig. 13. of 2d Plate II. is copied). A represents a circular view he had from the car of the balloon, himself being over the centre of the view, looking down on the white floor of clouds and seeing the city of Chester through an opening, which discovered the landscape below, limited by surrounding vapour, to less than two miles in diameter. The breadth of the outer margin defines his apparent height in the balloon (viz. 4 miles) above the white floor of clouds. Mr Baldwin also gives 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 disc, 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 item 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 reascending, 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 cracked 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 growing noise like millstones, but not near so loud. 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.
The frequency of aerial voyages, accompanied with uses of particular details of trifling and uninteresting circumstances, and apparently made with a view to promote the interest of particular persons, regardless of any advancement in knowledge, have now sunk the science of aerostation so low in the opinion of most people, that 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 final 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 abovementioned 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 these 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 these 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 marily..." 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.
"The philosophical uses, to which these machines may be subservient, are numerous indeed; and it may be sufficient to say, that hardly anything 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, 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 inflated. 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 shown 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 heated 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 space; 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 by every degree of heat, marked on Fahrenheit's thermometer, about \(\frac{1}{36}\)th part of the whole. By heating a quantity of air, therefore, to 500 degrees of Fahrenheit, we will just double its bulk when the thermometer stands at 54 in the open air, and in the same proportion we will 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 shown 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 will 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 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 constructed on Montgolfier's plan, it must be an advantage to have them as large as possible; because possible,