Home >> Engineer's And Mechanic's Encyclopedia >> A Vacuous Space In to And Saw Mills Saws >> Air Balloon_P1

Air Balloon

gas, filled, parachute, feet, ascended, heated, cords, hydrogen, ascend and gravity

Page: 1 2

BALLOON, AIR. A bag made of silk, paper, or other light material, for containing heated air, or gas, of less specific gravity than the atmosphere. If the weight of the balloon, and of the heated air or gas which it contains, be less than that of an equal bulk of atmospheric air, the balloon will ascend in con sequence of the equilibrium of atmospheric pressure being disturbed; the pressure of the column of which the balloon forms a part, being less than that of the ordinary atmosphere. The ascending, or upward pressure, therefore, carries the lighter body up until it arrives at a more attenuated medium, which is of the same specific gravity. After the discovery of hydrogen gas, the lightest of all ponderable substances, it occurred to Dr. Black, that a thin bag filled with this would ascend in the air. He suggested the employment of the allantois of a calf for this purpose, but Mr. Cavallo, who performed various experiments on this subject, found that this, and the lightest bladders he could procure, were all too heavy. Chinese paper was also tried, but the gas escaped rapidly through it. By filling soap-sud bubbles with hydrogen gas be succeeded, and these balloons rapidly ascended to the ceiling. Within these few years small experi mental balloons have been formed of the crop of a turkey, which, when the fat, &c. have been separated, are sufficiently light to ascend if filled with hy drogen gas, although some of them do not contain more than a pint. At about the same period of time, two brothers, named Montgolfier, natives of Annonay, in France, were trying experiments with balloons filled with heated air, the specific gravity of which is less than that of air at the ordinary temperature. They were led to these experiments by observing the rapid ascent of smoke from chimneys, and imagined that if the smoke were confined in a large and light bag, it would be borne upwards. A bag of fine silk, in the shape of a paral lelopiped, was constructed, and burning paper was held under the aperture, until the balloon contained a sufficient quantity of rarefied air to carry it up to the ceiling of the apartment. When this experiment was repeated in the open air, the vessel ascended to an altitude of about 70 feet. Other balloons on a larger scale were constructed, and a public exhibition of one containing 23,000 cubic feet was made at Annonay, on the 5th of June, 1783. This was formed of linen lined with paper, and when filled with heated air, was capable of raising 500 lbs. appended to the extremity. One of the Montgolfiers shortly after this visited Pans, and as the affair bad excited much attention, he was invited by the Academy of Sciences to repeat the experiment at the expense of the Society. A large balloon, of elliptic shape, was filled with heated air, in the presence of the members, and in this state it would have ascended with a weight of 500 lbs. if the cords which prevented it had been liberated. As it was intended to exhibit the ascent before the king of France and his court, this was not done, and the balloon was subsequently so much damaged by wind and rain, that it became necessary to construct another. This was nearly 60 feet in height, and 43 in diameter, and a wicker cage was attached to it, containing a sheep, a cock, and a duck. The balloon, when duly prepared, ascended with these to an altitude of about 1,400 feet, and would have ascended to a greater height had not a violent gust of wind torn the cloth, and permitted the heated air to escape. The facility of ascending in the atmosphere being thus fully established, Pilatre de Rozier offered personally to ascend in another balloon, to be constructed by Montgolfier. Accordingly another balloon was completed, of enormous meg nitude. The height was 74 feet, and the diameter 48; and its weight, including the car and necessary fuel for continuing the fire, was 1600 lbs. By this the intrepid Pilatre de Rozier made several ascents to an altitude of from 200 to 330 feet, but in these preliminary attempts the balloon was confined by cords. Subsequently lie ascended in company with the Marquis d'Arlandes, with the balloon unrestrained, and they continued in the air about 25 minutes, and descended at a distance of about five miles from the place of their departure. The difference between the specific gravity of air heated by the means employed, and that of air at ordinary temperatures, not being very considerable, the buoyant power of a balloon thus filled, was comparatively small, and therefore it was indispensable to employ a large quantity, and, consequently, a large machine to contain it. To double the volume of air by heat, requires a temperature' of nearly 480° Fehr. Messrs. Charles and Roberts therefore tried the experiment of filling a silk bag only 13 feet in diameter, with hydrogen gas, which is only the weight of ordinary air. The experiment was perfectly successful. This small balloon was capable of raising 35 lbs., and on being liberated, it ascended to a considerable height, and after remaining three-quarters of an hour in the air, descended at a distance of fifteen miles from the spot where it had ascended. A balloon formed of silk, and varnished with a solution of Indian rubber, was then constructed, which was filled with hydrogen gas. The diameter was 271 feet, and it was covered with a net-work, to which a car, capable of holding two persons, was attached. Messrs. Charles and Roberts ascended from Paris in this, in December 1783, and after remaining in the air an hour and three quarters, they alighted at a distance of 27 miles without accident. A sufficient quantity of gas still remained in the balloon to carry up one person, and Mr. Charles again ascended alone, and attained an altitude of more than 10,000 feet. Shortly after this successful effort, attempts were made to guide or impel a balloon in any required direction ; and if this could have been accomplished, the invention would have introduced a new era in science. Mr. Blanchard applied a species of wings to the car, but was unsuccessful in his attempt to travel against the direction of the wind; nor was Morveau more fortunate with large oars or sails, introduced with the same design. Numerous contrivances have been since adopted, but all have been ineffectual in practice ; and, indeed, when the great extent of surface which a balloon presents to the impulsive force of air in motion is duly considered, the probability of overcoming that force by any means which can be commanded by the aerial voyager, seems very remote. Endeavours have also been made to economize the gas which the balloon contains. A much larger quantity than is necessary to create the

buoyant power required to carry up the voyagers, is introduced, and to occasion the descent of the machine, the gas is permitted to escape by a valve ; but if the aeronaut require again to ascend in consequence of the unfavourable nature of the ground on which he is likely to descend, or from any other cause, be must part with ballast, which may be essential to his safety. The Duke de Chartres, accompanied by Charles and Roberts, ascended in a balloon filled with hydrogen gas, which contained a smaller within it, to be filled with common air, by means of a pair of bellows, as occasion might require. By inserting common air into the small balloon, the specific gravity of the machine would be increased, and it would descend without loss of gas, and reascend by with drawing the common air. However ingenious the contrivance, it was not found successful in practice, chiefly, perhaps, on account of the unfavourable state of the wind, which was tempestuous when the experiment was made. Pilatre de Rozier and Mr. Romaine, with the same design introduced a bal loon filled with heated air below the ordinary balloon containing hydrogen gas. The buoyant power of the heated-air balloon was equal to about 60 lbs. ; and by removing the source of heat, the specific gravity of the whole machine was increased, so that it was not necessary to part with any gas during a voyage. The attempt to carry this plan into execution was fatal to both voyagers. The upper balloon, by means unknown, took fire, and the intrepid De Rozier and his companion were precipitated to the earth and killed. It is not our purpose to describe the various attempts that have been subsequently made to improve the construction of balloons, or to render them subservient to scientific purposes, since little has been effected towards accomplishing these objects. We cannot, however, omit a description of an addition to the balloon, called a parachute, which was first employed, with daring courage, by M. Garnerin. fhe balloon was of the usual form, made of oiled silk, and filled with inflam mable gas ; it was covered, as represented in the annexed engraving, with a netting, from which cords proceeded that were tied together at a few feet below the balloon ; the several cords thus collected were then twisted so as to form a single rope, which was passed through the parachute, and fastened to the car, or basket. The real structure of the parachute is best seen in its expanded state, as shown in the descent, forming a near resemblance to a large umbrella; it was made of canvass, and about thirty feet in diameter; it had no ribs, the figure of its dome being preserved by the surrounding cords. The length of these cords, or ropes, from the edges of the dome of the parachute, to where they are connected together, was about 30 feet; and from this point of connexion, other shorter ropes proceeded, which were attached to the edges of the circular basket in which the aeronaut was situated. In the place of the handle of a com mon umbrella, a long tin tube was fixed in the parachute, through which the single rope before-mentioned was passed, to prevent its becoming entangled, and to allow it to slip away with certainty when severed for the purpose of de scending. The ascent took place on the 21st of September, 1802, from St. George's Parade, North Audley-street. The balloon began to be filled about two o'clock; 33 casks filled with diluted sulphuric acid, together with a quantity of iron filings, were employed for the production of the hydrogen gas. These communicated with three other casks, or general receivers, to each of which was affixed a tube that emptied itself into the main tube connected to the balloon. At six o'clock the balloon was completely filled ; when it rose with its long appendage of the parachute, the aeronaut in the little basket closing the train. Thousands of acclamations rent the air, while the eyes of tens of thousands of spectators were fixed in astonish ment and admiration at the gallant adventurer ; feelings which could be only surpassed by the most intense and painful anxiety for his safety. The weather was beautifully fine, with scarcely any wind. For eight minutes this intrepid man continued to ascend, till be arrived at such an immense height as to be scarcely visible, when he cut away the balloon. The parachute did not expand imme diately, and he fell with great velocity for a short space of time; when it opened, and his descent became gradual, but attended with a remarkable oscillation, like the pendulum of a clock, to that degree, at one time, that the parachute, cords, basket, and aeronaut, appeared to be stretched in an horizontal line. At length, as he approached the earth, these vibrations were less extended, and continued to diminish till he reached the ground, which he did without any injury to him self, or the apparatus, which he brought down with him, in a field near the Small Pox Hospital, at Pancras. The balloon was observed to ascend rapidly after separation from the parachute, and was soon out of sight. It has been ted to combine the parachute with the balloon so as to add nothing to the suggested but little to the weight of the machine ; it is as follows :—The band which divides the upper hemi sphere of the balloon from the lower one, is to be formed of a wooden hoop, to which the net-work which covers the upper hemisphere, is to be firmly attached ; the cords• which descend from this hoop, are to be fastened together in the usual manner, below the balloon, but not attached to the lower hemisphere ; now, if the upper hemisphere of the balloon should burst, the gas would escape, the balloon would begin to fall, and the lower hemisphere would immediately fall into the direction here re presented, lining the upper one, and forming a complete parachute. Should the lower part burst, the escape of the gas would not be so sudden as in the former instance ; but when it had escaped, and the balloon began to fall, it would immediately form itself into the same shape as before : in this latter ease, it would, perhaps, be better to open the valve at the top, by which means the balloon would sooner be formed into the shape of aute. This plan has, perhaps, these advantages over the common parachute; viz. 1st. That of taking up less room : 2d. Being less weighty : and 3d. Not being subject to that great and sudden fall which must render the use of the common parachute not only unpleasant, but extremely dangerous.

Page: 1 2