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buiar, with a bent tube, but in the form of a included air, or the diminished density of grotesque human figure, and the blast pro- the surrounding air, it becomes of the same ceeds from the mouth.
specific gravity with the air in which it ÆOLUS'S harp, or EOLIAN harp, a musi- floats; and without renewed heat, it will cal instrument so named from its producing gradually descend. If, instead of heating an agreeable harmony merely by the action common air inclosed in any covering, and of the wind. See ACOUSTICS.
thus diminishing its weight, the covering be ÆRA, a fixed point of time, from which filled with an elastic fuid, lighter than atany number of years is begun to bei reck- mospheric air, so that the excess of the oned. See CHRONOLOGY.
weight of an equal bulk of the latter above AEROSTATION, in the modern appli- that of the inclosed elastic fluid be greater cation of the term, signifies the art of navi- than the weight of the covering and its apgation through the air, both in its principles pendages, the whole mass will, in this case, and practice. Hence also the machines ascend in the atmosphere, and continue to which are employed for this purpose, are rise till it attains a height at which the surcalled aerostats, or aerostatic machines ; and rounding air is of the same specific gravity on account of their round figure, air balloons. with itself. Inflammable air, or, as it is called,
The fundamental principles of this art hydrogen gas, is a fluid of this kind. For have been long and generally known; al the knowledge of many of its properties we though the application of them to practice are indebted to Mr. Henry Cavendish, who seems to be altogether a modern discovery. discovered that, if common air is eight It will be sufficient, therefore, to observe, hundred times lighter than water, infiamin this place, that any body, which is spe. mable air is seven times lighter than com-cifically, or bulk for bulk, lighter than the mon air ; but if common air is eight hunatmospheric air encompassing the earth, dred and fifty times lighter than water, will be buoyed up by it, and ascend; but then inflammable air is 10.8 times lighter as the density of the atmospliere decreases, than common air. The construction of airon account of the diminished pressure of balloons depends upon the principles above the superincumbent air, and the elastic pro- stated; and they are of two kinds, as one perty which it possesses at different eleva. or the other of the preceding methods of tions above the earth, this body can rise preparing them is adopted. only to a height in which the surrounding In the various schemes that have been air will be of the same specific gravity with proposed for navigating through the air, itself. In this situation it will either float, some have had recourse to artificial wings; or be driven in the direction of the wind or which, being constructed like those of birds, current of air, to which it is exposed. An and annexed to the human body, might air-balloon is a body of this kind, the whole bear it up, and by their motion, produced mass of which, including its covering and either by mechanical springs, or muscular contents, and the several weights annexed exertion, effect its progress in any direction to it, is of less specific gravity than that of at pleasure. This is one of the methods of the air in which it rises. Heat is well artificial flying suggested by Bishop Wilknown to rarefy and expand, and conse kins, in the seventh chapter of his “ De. quently to lessen the specific gravity of the dalus, or Treatise on Mechanical Motions ;" air to which it is applied; and the diminu- but the success of it is doubtful, and expe. tion of its weight is proportional to the heat. riments made in this way have been few One degree of heat, according to the scale and unsatisfactory. Borelli having comof Fahrenheit's thermometer, seems to ex pared the power of the muscles which act pand the air about one four-hundredth part; on the wings of a bird with that of the and about 400, or rather 435, degrees of muscles of the breast and arms of a man, heat, will just double the bulk of a quan. finds the latter altogether insufficient to tity of air. If, therefore, the air inclosed produce, by means of any wings, that in any kind of covering be heated and motion against the air, which is necessary consequently dilated to such a degree, as to raise a man in the atmosphere. Soon that the excess of the weight of an equal after Mr. Cavendish's discovery of the spebulk of common air above the weight of cific gravity of inflammable air, it occurred the heated air, is greater than the weight to the ingenious Dr. Black, of Edinburgh, of the covering and its appendages, this that if a bladder, sufficiently light and thin, whole mass will ascend in the atmosphere, were filled with this air, it would form till, by the cooling and condensatiou of the a mass lighter than the same bulk of at
mospheric air, and rise in it. This thought in the experiment, broke the ropes that was suggested in his lectures in 1767 or confined it, and after ascending rapidly to 1768; and he proposed, by means of the the height of about 600 feet fell on the adallantois of a calf, to try the experiment. joining ground. With another machine, Other employments, however, prevented 35 feet in diameter, they repeated the expethe execution of his design. The possibi- riment in April 1783, when breaking loose lity of constructing a vessel, which, when from its confinement, it rose to the height filled with inflammable air, would ascend in of above 1000 feet, and being carried by the atmosphere, had occurred also to Mr. the wind, it fell at the distance of about Cavallo, about the same time; and to him three quarters of a mile from the place belongs the honour of having first made ex. where it ascended. The capacity of this maperiments on this subject, in the beginning chine was equal to about 23,430 cnbic feet; of the year 1782, of which an account was and when inflated, it measured 117 English read to the Royal Society, on the 20th of feet in circumference. The covering of June in that year. He tried bladders; but it was formed of linen lined with paper, the thinnest of these, however scraped and its shape was nearly spherical, and its apercleaned, were too heavy. In using China ture was fixed to a wooden frame about 16 paper, he found that the inflammable air feet in surface. When filled with vapour, passed through its pores, like water through which was conjectured to be about half as a sieve ; and having failed of success by heavy as common air, it was capable of liftblowing this air into a thick solution of ing up about 490 pounds, besides its own gum, thick varnishes, and oil-paint, he was weight, which, together with that of the under a necessity of being satisfied with soap- wooden frame, was equal to 500 pounds. bubbles, which being inflated with infiamma With this machine the next experiment was ble air, by dipping the end of a small glass performed at Annonay, on the 5th of June tabe, connected with a bladder contain- 1783, before a great multitude of spectaing air, into a thick solution of soap, and tors. The flaccid bag was suspended on a gently compressing the bladder, ascended pole 35 feet high; straw and chopped wool rapidly in the atmosphere; and these were were burnt under the opening at the botthe first sort of inflammable air-balloons that tom; the vapour, or rather smoke, soon inwere ever made. For balloons formed on a flated the bag, so as to distend it in all its larger scale, and on the principle of rarefied parts; and this immense mass ascended in air, we must direct our attention to France, the air with such a velocity, that in less than where the two brothers, Stephen and Jo- ten minutes it reached the height of about seph Montgolfier, paper-manufacturers at 6000 feet. A breeze carried it in an horiAnnonay, about 36 miles from Lyons, dis- zontal direction to the distance of 7668 feet; tinguished themselves by exhibiting the first and it then fell gently on the ground. M. of those aerostatic machines, which have Montgolfier attributed the ascent of the masince excited so much attention and as- chine, not to the rarefaction of the heated tonishment. The first idea of such a ma. air, which is the true cause, but to a certain chine was suggested to them by the natural gas or aeriform fluid, specitically lighter than ascent of the smoke and clouds in the at common air, which was supposed to be dismosphere; and the first experiment was engaged from burning substances, and which made at Avignon, by Stephen, the eldest has been commonly called Montgolfier's of the two brothers, towards the middle of gas, as baloons of this kind have been denoNovember 1782. Having prepared a bag minated Montgolfiers. As soon as the news of fine silk, in the shape of a paralelepipe. of this experiment reached Paris, the philodon, and in capacity about 40 cubic feet, sophers of the city, conceiving that a new be applied to its aperture burning paper, sort of gas, half as heavy as common air, bad which rarefied the air, and thus formed a been discovered by Messrs. Montgolfier; kind of cloud in the bag, and when it be- and knowing that the weight of inflammable came sufficiently expanded, it ascended air was not more than the eighth or tenth rapidly to the ceiling. Soon afterwards the part of the weight of common air, justly conexperiment was repeated by the two bro- claded, that inflammable air would answer thers at Annonay in the open air, when the the purpose of this experiment better than inachine ascended to the height of about the gas of Montgolfier, and resolved to make seventy feet. Encouraged by their success, trial of it. A subscription was opened by they constructed a machine, the capacity M. Faujas de St. Fond towards defraying of which was about 650 cubic feet, which, the expense of the experiment. A sufficient
sum of money baving been soon raised, minutes; and its force of ascension, when Messrs. Roberts were appointed to con inflated, was so great, that it raised eight struct the machine; and M. Charles, pro men who held it some feet from the ground. fessor of experimental philosophy, to super. This machine was so much damaged by the intend the work. After surmounting many rain, that it was found necessary to prepare difficulties in obtaining a sufficient quantity another for exhibition before the king and of intlammable air, and finding a substance royal family on the 19th. This new malight enough for the covering, they at length' chine consisted of cloth, made of linen and constructed a globe of lutestring, which was cotton thread, and was painted with waterrendered impervious to the inclosed air by a colours both within and without. Its height varnish of elastic gum, or caoutchouc, dis was near 60 feet, and its diameter about 43 solved in some kind of spirit or essential oil. feet. Having made the necessary preparaThe diameter of this globe, which, from its tions for inflating it, the operation was begun shape, was denominated a balloon, was about about one o'clock on the 19th of Septemthirteen feet, and it had only one aperture,' ber, before the king and queen, the court, like a bladder, to which a stop-cock was and all the Parisians who could procure a adapted: its weight, when empty, together conveyance to Versailles. In eleven miwith that of the stop-cock, was 25 pounds. nutes it was sufficiently distended, and the On the 23d of August, 1783, they began to ropes being cut, ii ascended, bearing up fill the globe with inflammable air ; but this, with it a wicker cage, in which were a being their first attempt, was attended with sheep, a cock, and a duck. Its power of asmany hindrances and disappointments. At cension, or the weight by which it was lighter last, however, it was prepared for exhibition; than an equal bulk of common air, allowing and on the 27th it was carried to the Champ for the cage and animals, was 696 pounds. de Mars, where, being disengaged from the This balloon rose to the height of about cords that held it down, it rose before a 1440 feet; and being driven by the wind, it prodigious concourse of people, in less than descended gradually, and fell gently into a two minutes, to the height of 3123 feet. It wood, at the distance of 10,200 feet from then entered a cloud, but soon appeared Versai'les. After remaining in the atmosagain; and at last it was lost among other phere eight minutes, the animals in the cage clouds. This balloon, after having floated were sately landed. The sheep was found about three quarters of an hour, fell in a feeding ; the cock had received some hurt field about 15 miles distant from the place on one of his wings, probably from a kick of of ascent; where, as we may naturally ima- the sheep; the duck was perfectly well. gine, it occasioned much astonishment to the The success of this experiment induced M. peasants. Its fall was owing to a reut, oc. Pilatre de Rozier, with a philosophical iocasioned by the expansion of the inflam- trepidity which will be recorded with apmable air in that part of the atmosphere plause in the history of aerostation, to offer to which it ascended. When the balloon himself as the first adventurer in this aerial went up, its specific gravity was 35 pounds navigation. Mr. Montgolfier constructed a less than that of common air. In conse new machine for this purpose in a garden in quence of this brilliant experiment, many the Fanxbourg St. Antoine. Its shape was balloons were made on a small scale; gold- oval; its diameter being about 48 feet, and beaters skin was used for the covering; and its height about 74 feet. To the aperture their size was from 9 to 18 icches in dia. at the bottom was annexed a wicker galmeter.
lery, about three feet broad, with a ballusMr. Montgolfier repeated an experiment trade about three feet high. From the with a machine of his construction before middle of the aperture was suspended by the commissaries of the Academy of Scien- chains, which came down from the sides of ces, on the 11th and 12th of September. the machine, an iron grate, or brazier, in This machine was 74 feet high, and about which a fire was lighted for inflating the 4S feet in diameter. When distended, it machine; and port-holes were opened in appeared spheroidical. It was made of the gallery, towards the aperture, through canvas, covered with paper both within and which any person, who should venture to without, and it weighed 1000 pounds. The ascend, might feed the fire on the grate with operation of filling it with rarefied air, pro- fuel, and regulate the dilatation of the induced by means of the combustion of 50 closed air of the machine at pleasure. The pounds of dry straw, and 12 pounds of weight of the aerostat was upwards of 1600 ehopped wool, was performed in abont nine ponnds. On the 15th of October, the fire
being lighted, and the machine inflated, M. fuel, they descended very gently in a field P. de Rozier placed himself in the gallery, beyond the New Boulevard, about 9000 and ascended, to the astonishment of a mul- yards distant from the palace, having been titude of spectators, to the height of 84 feet in the air about 25 minutes. The weight of from the ground and there kept the machine the whole apparatus, including that of the afloat during 4' 25", by repeatedly throwing two travellers, was between 1600 and 1700 straw and wool upon the fire: the machine pounds. Notwithstanding the rapid prothen descended gradually and gently, gress of aerostation in France, we have no tárough a medium of increasing density, to authentic account of the aerostatic experithe ground; and the intrepid adventurer
ments performed in other countries till assured the spectators that he had not ex about the close of the year 1783. The first perienced the least inconvenience in this
experiment of this kind, publicly exhibited aerial excursion. This experiment was re
in our own country, was performed in Lon. peated on the 17th and on the 19th, when don on the 25th of November, by Count M. P. de Rozier, in his descent, and in order Zambeccari, an ingenious Italian, with a to avoid danger by reascending, evinced to baloon of oil silk, 10 feet in diameter, and a multitude of observers, that the machine weighing 11 pounds. It was gilt, in order may be made to ascend and descend at the to render it more beautiful and more imperpleasure of the aeronaut, by merely increas- meable to the gas. This balloon, threeing or diminishing the fire in the grate. The fourths of which were filled with inflammable balloon having been hauled down, M. Gi- air, was launched from the Artillery-Ground raude de Villiette placed himself in the gal in the presence of a vast concourse of speclery opposite to M. Rozier; and being suf- tators, at one o'clock in the afternoon, and fered to ascend, it hovered for about nine
at half past three was taken up near Peta minutes aver Paris in the sight of all its in
worth, in Sussex, 48 miles distant from Lonhabitants at the height of about 330 feet. don; so that it travelled at the rate of nearly In another experiment the Marquis of Ar 20 miles an hour. Its descent was occasioned landes ascended with M. Rozier much in
by a rent, which must have been the effect the same manner. In consequence of the
of the rarefaction of the inflammable air, report of the preceding experiment, sigued
when the balloon ascended to the lighter by the commissaries of the Academy of
parts of the atmosphere. Sciences, it was ordered that the annual
Aerostatic experiments and aerial voyages prize of 600 livres should be given to Messrs.
became so frequent in the course of the year Montgolfier for the year 1783. In the ex
1784, that the limits of this article will not periments above recited the machine was
allow our particularly recording them. We secured by ropes; but they were soon suc
shall, therefore, merely mention those which ceeded by unconfined aerial navigation.
were attended with any peculiar circumAccordingly the balloon of 74 feet in height,
stances. Messrs. de Morveau and Bertrand above mentioned, was removed to a royal ascended from Dijon in April, to the height palace in the Bois de Boulogne: and all things being ready, on the 21st of November of about 13,000 feet, with an inflammable M. P. de Rozier and the Marquis d'Arlan, air balloon: the thermometer was observed des took their respective posts in the gallery, air during an hour
and 25 minutes, and went
to stand at 25 degrees. They were in the and at 54 minutes after one the machine was absolutely abandoned to the element, The clouds floated beneath them, and se
to the distance of about eighteen miles. and ascended calmly and majestically in
cluded them from the earth: and they the atmosphere. The aeronauts having reached the beight of about 280 feet, waved jointly repeated the motto inscribed on their
aerostat:-“Surgit nunc gallus ad aethera." their hats to the astonished multitude: but
In May, four ladies and two gentlemen asthey soon rose too high to be distinguished, cended with a Montgolfier at Paris above and are thought to have soared to an eleva
the highest buildings : the machine was contion of above 3000 feet. They were at first driven by a north-west wind horizontally in diameter. In a second voyage, performed
fined by ropes. It was 74 feet high, and 72 over the river Seine and over Paris, taking by Mr. Blanchard from Ronen in May, it care to clear the steeples and high buildings
was observed, that his wings and oars could by increasing the fire; and in rising met
not carry him in any other direction than with a current of air, which carried them southward. Having passed the Boulevard, that of the wind. The mercury in the baand desisting from supplying the fire with rometer descended as low as 20.57 inches ; VOL. I.
but on the earth, before he ascended, it stood which the inflammable air was introduced,