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· MAP OF SOUTH AMERICA ,
54 32 52 23 51 25 50 5-2 49 46 47 32 46 59 4 25 43 41 38 20 37
1 37 15 36 43 33 2 29 2 28 27 27 20 22 30 18 29 17 1 13 44 12
4 7 29 7 3 6 50 4 20 3 4 2 12 1 4 0 39 N. 3 50 5 24 7 52 8 13
73 16 74 56 75 31 75 32 75. 46 7 70 28 74 0 71 20 71 5 73 41 73 29 73 8 71 40 71 39 71 14 71 6 70 6 70 16 720 76 13 77
6 79 28 80 41 80 48 81 7 SO 79 40 80 43 79 52 76 55 77 16 77 52 78 40
7 2+ 1 23 56 23 18 22 57 23 1 17 21 16 27 12 49 10 29 S 21 8
1 5 28 2 25 2 24 1 28 0 0 1 51 N. 3 57 5 56 7 32 8 11 10 45 10 13 10 37 10 30 11 9 12 11 1: 20 12 11 11 15 11 5 3 31
48 40 46 30 45 30 45 17 42 45 42 3 39 12 39 3 38 37 36 23 34 57 34 51 35 17 44 4 44. 23 48 30 50 0 50 9 51 14 55 15 58 49 60 3 62 46 64 48 67 1 68 8 68 32 TO 9 71 50 72 15 at 17 74 47
an elevation of temperature, for then the elasticity ON PHYSICS, OR NATURAL PHILOSOPHY. held in solution increases. No. XX,
Equilibrium at different Temperatures.-Equilibrium can only
exist in the same fluid, whether liquid or gaseous, so long as (Continued from page 280). Laws of the Mixture of Gases and Liquids.-- Water and several
Fig. 89. other liquids possess the property of absorbing gases; but under the same conditions of temperature and pressure, the same liquid does not absorb equal quantities of different gases. For instance: at an ordinary temperature and pressure, water absorbs .025 or one-fortieth of its volume of nitrogen, .046 or about one-twenty-second part of its volume of oxygen, a volume equal to its own of carbonic acid, and 430 times its volume of ammonia. Mercury appears incapable of absorbing gases. It has been proved experimentally that the mixture of ages and liquids takes place according to the three follow ing laws:
1st, The weight of a gas absorbed by a liquid at a given temperature is proportional to the pressure; or, the density of the gas absorbed is in a constant ratio to that of the same gas not absorbed.
2nd. The quantity of a gas absorbed increases as the temperature diminishes ; that is, as the elastic force of the gas diminishes.
3rd. The quantity of a gas absorbed by a liquid, is independent of the nature and quantity of other gases whieh the liquid may hold in solution.
Thus, if in place of a single elastic fluid, the atmosphere above a liquid contains several elastic fluids, it is ascertained that each of these gases, whatever may be their number, is the pressure is constant on all the points of each horizontal
rbed in the same proportion as if it were single, the pres- straiun; neither can it exist unless the density be the same sve which is proper to it being taken into considera- everywhere in the stratum; otherwise, the lighter particles tion. For example: oxygen forming only about part of the would rise in the fluid mass, like floating bodies, and the more
air, water in an ordinary state absorbs precisely the same dense particles would sink in the same. Now, gases and quantity of oxygen as if the atmosphere were entirely com- / liquids being very liable to expansion under the action of heat, posed of this gas, under a pressure equal to } part of that of the density diminishes when the temperature increases. the atmosphere. According to the first law, when the pres. Consequently, in order that a fluid mass may remain in equisure diminishes, the quantity of gas absorbed must decrease. librium, it is necessary that the temperature should be the This fact is verified by placing a gaseous solution under the same at all the points of every horizontal stratum of the receiver of an air-pump, and forming a vacuum; the gas is observed to act by its expensive force, and to disengage itself Moreover, in order that the equilibrium may be stable, the from the liquid in bubbles. The same effect is produced by | Auid strata must be arranged in the order of their density. , .
Still this condition does not require that the upper strata shall he never made the experiment, considering it only as an be more heated than the lower strata ; for the latter being amusing remark. Cavallo, in 1732, had communicated to the more compressed by the superincumbent mass, tend to become Royal Society of London some experiments which he had more dense; it is sufficient, therefore, if the density increases made, and which consisted in filling soap-bubbles with hydromore by the effect of pressure, in the lower strata, than by gen, which spontaneously rose in the atmosphere, the
with that of the diminution of the temperature; and this is gene- which they were filled being lighter than the air. But the rally the case in the atmosphere. The currents which arise in brothers Montgolfier knew nothing of the experiments of a fluid mass, in consequence of the differences of temperature Cavallo, nor of the lectures of Dr. Black, when they made their in the same horizontal stratum, are shown in the draught of discovery. As they employed heated 'air only to fill their chimneys and in the apparatus for warming by means of hot balloons, the name of Montgolfiers was given to such balloons, water. These applications will be considered in the sequel. in order to distinguish them from those filled with hydrogen,
which are the only kind employed in the present day. AEROSTATION
M. Charles, Professor of Natural Philosophy at Paris, who Quaquaversal Pressure of Gases.-The pressures produced by died in 1823, was the first who substituted hydrogen for gases, in consequence of their elastic force, are equally trans- heated air in the construction of balloons. On the 27th of mitted in all directions; this has been proved
in the case of August, 1783, a balloon inflated with this gas was launched air by means of the Magdeburg hemispheres. From this it is into the airy element from the Champ-de-Mars at Paris. In evident that what has been formerly stated regarding bodies reference to its appearance, Mercier thus writes : “Never was immersed in liquids, is equally applicable to air and gases, and a lesson in Natural Philosophy given before a more numerous that bodies immersed in elastic fluids lose a part ofitñeir weight and attentive audience." On the 21st of November, 1783, equal to the weight of the quantity of air or gas which they Pilatre de Rozier undertook, in company with the Chevalier displace. This loss of weight in air is proved by means of the d’Arlandes, the first ærial voyage in a balloon made to ascend baroscope (from the Greek, a wright-mark), an apparatus which by heated air. The ascent took place from the garden “ de la consists of a beam, having at one end a hollow brass sphere Muette,” near the wood of Boulogne. The æronauts kept up, four inches in diameter, and at the other a small loaden under the balloon, a fire of damp straw, in order to preserve weight as a counterpoise, fig. 89. In air, the two bodies, the the expansion of the air in its interior; thus the fire was in sphere and the weight, balance each other ; but if we place danger of being communicated at every instant to the balloon. the apparatus under the receiver of an air-pump, and exhaust Ten days after, MM. Charles and Robert ascended from the it of the air, the beam will lean to the side of the sphere, as garden of the Tuilleries at Paris, in a balloon filled with hyshown in the figure, which indicates that in reality the sphere drogen. On the 7th of January, 1785, M. Blanchard, in is heavier than the leaden weight, since they do not experience company with Dr. Jeffries, made the first passage from Dover any pressure from the air, but are only acted on by gravity. to Calais. The two æronauts reached the coast of France with It therefore follows, that in the air the sphere loses a certain very great difficulty, and only after having thrown their clothes part of its weight. If we wish to prove, by means of the into the sea, in order to lighten the balloon. Since that period, same apparatus, that this loss is nearly equal to the weight of a very considerable number of ascents in balloons have been the air displaced, we measure the volume of the sphere, which performed. The ascent which was made by M. Gay-Lussac is about 333 cubic inches; and as this volume of air weighs in 1804, was the most remarkable for the facts which it added about 11 grains, we attach this weight to the leaden weight at to science, and for the altitude which this celebrated philo. the end of the beam. The equilibrium which previously ex- sopher reached, being 23,019 feet above the level of the sea. isted between the leaden weight and the sphere, when placed Lastly, Mr. Green has risen to a greater height. At that in the air, is now destroyed; but as soon as the apparatus height, the barometer fell to about 13 inches, and the centiis placed in the exhausted receiver, we find that it is re- grade thermometer, which stood at 31° (that is, 870.8 stored.
Fahrenheit) on the ground, was then at—90(that is, 159.8 The principle which Archimedes discovered, as belonging Fahrenheit), being 5 degrees below zero or the freezing point. to liquids, being thus found true for bodies immersed in air, On the occasion of a recent ascent, a much lower temperature we can now apply to them all that has been formerly said re- was observed at the same height. In these elevated regions garding bodies immersed in liquids. Hence, when a body is of the atmosphere, the dryness was such, on the day of Gayheavier than the air, it falls in consequence of the excess of Lussac's ascent, which was in July, that hygrometric subits weight above the upward pressure or buoyancy of the fluid. stances, such as paper, parchment, &c., were dried and twisted If it be of the same density as the air, its weight and the up- as if they had been put before a fire. Respiration and the ward pressure are balanced, and the body floats in the atmo- circulation of the blood was accelerated in consequence of the sphere. But, if the body be lighter than the air, the buoyancy great rarefaction of the air. M. Gay-Lussac found that his carries it upwards, and the body rises in the atmosphere until pulse beat 120 times in a minute, instead of 66 times, the it reaches air of the same density as itself. The force of usual number when on the ground. At this great height, the ascension is then equal to the excess of the buoyancy above sky was of a very deep-blue colour, approaching the aspect of the weight of the body. This is the cause of the ascent of night; while an absolute and solemn silence surrounded the smoke, vapours, clouds, and balloons in the atmosphere. æronaut. Having ascended from the court of the “ Conserva
toire des Arts et Metiers" at Paris, Gay-Lussac descended
near Rouen, after an ærial voyage of six hours, having travelled Discovery of Balloons Balloons, as their name denotes, are about 90 miles. round or globe-shaped bodies,'made of a light material imper- Construction of Balloons.—The globe of balloons is pearmeable to air, and filled with heated air or hydrogen gas, which shaped, and made of long stripes of silk sewn together and rise in the atmosphere in consequence of their relative light- covered with varnish or a solution of caoutchouc, to render the ness. Their invention is due to two brothers, Stephen and silk impermeable to the air. At the top of a balloon is placed Joseph Montgolfier, paper-makers in the small town of a valve which is kept shut by a spring, and which the wronaut Annonay, in the department of Ardèche, in France, where can open at pleasure by means of a cord. A light wicker car, their first attempt was made on the 5th of June, 1783. Their in which several persons may be seated, is suspended from the first balloon was a globe made of linen, and lined with paper, balloon by the net-work which surrounds the pear-shaped about forty yards in circumference, and weighing about five globe, see figs. 90 and 91. A balloon of ordinary dimensions, cwt. Being epen below, it was inflated with heated air, by which can easily lift three persons, is about fifty feet in burning under it paper, wool, and wet straw. The academician height, and thirty-six feet in diameter; and its volume, when Lalande wrote thus on the occasion :-"At this news, we all completely inflated, is upwards of 24,000 cubic feet. The said : Such must be the case; how was it never thought of globe weighs about two cwt., and the appendages about one before?" It had been thought of; but there is a difference cwt. Balloons are inflated either with pure hydrogen, or with between the conception of an idea, and its realisation. Dr. carburetted hydrogen, such as is used for the purpose of lightBlack, Professor of Chemistry in the University of Edinburgh, ing shops and streets. Although the latter gas is more dense had stated, in his course of lectures in 1767, that a bladder filled than the former, it is now generally employed, because it is with hydrogen would naturally rise in the atmosphere; but I cheaper and more easily procured than pure hydrogen. It is
only necessary to place the balloon near a gasometer, and fill the excess of the weight of the air displaced above the whole it by means of a connecting-pipe.
weight of the apparatus, be about ten pounds. It is to be In og. 90 is represented the mode of filling a balloon with observed that this force remains constant so long as the pure hydrogen. On the right of the figure is shown a series balloon is not completely inflated by the expansion of the
interior gas. For, if the atmospheric pressure be reduced to *Fig. 91.
one-half, the gas in the balloon, according to Mariotte's law, is increased to double its volume.' Whence it follows, that the volume of air displaced is itself doubled, and its density is reduced to one-half; therefore its weight, and consequently its upward pressure or buoyancy are still the same. But as soon as the balloon is completely inflated, if it continue to rise, the force of ascent diminishes; for the volume of air displaced remaining the same, the density diminishes. Accordingly, the balloon will ere long reach a point where the upward pressure
Consequently, the balloon can only take then & horizontal direction, being carried by the currents of air which exist in the atmosphere.
The indications of the barometer are the most certain means by which the æronaut knows when he is ascending and when he is descending. In the former case, the column of mercury falls; in the latter, it rises. By the assistance of the same instrument, he is enabled to ascertain the height which he has reached. A long streamer fixed to the car, fig. 91, also indicates, by the position which it takes above or below the car, whether he is ascending or descending. When the æronaut wishes to descend, he draws the cord which opens the valve placed at the upper part of the balloon ; the hydrogen mixes with the exterior air, and the balloon descends. On the contrary, in order to slacken his descent when it is too rapid, or to re-ascend if placed in a perilous situation, the æronaut
mpties bags full of sand, a sufficient quantity of which had been placed in the car for this purpose. Thus lightened, the balloon rises again, in order to descend in a more suitable place. The descent is facilitated by suspending an anchor to the car by means of a long cord. When this anchor has taken hold of a proper obstacle on the ground, the car and balloon are lowered by gently drawing the cord.
Balloons have not as yet received any important applications.' At the battle of Fleurus, in 1794, a balloon, retained by a cord, was employed to discover the movements of the enemy, which were made known to the army by signals made by an observer seated in the car. Several ascents have also been undertaken with the view of making meteorological observations in the higher regions of the atmosphere.. But balloons will only become of real utility when the power of directing them has been attained. The trials hitherto made for this purpose have completely failed. At present, we can only rise in the atmosphere until we meet a current of air which will carry us in
the direction answerable to the end we have in view. of casks, which contain iron filings, water, and sulphuric acid,
The Parachute.-The object of the parachute (from the French, substances necessary for the preparation of the hydrogen a guard from falling) is to enable the æronaut to leave his balFrom each cask, the gas is conveyed to a central cask, open at loon, by giving him the means of slackening the velocity of this bottom, and immersed in a butt full of water. The gas, after descent. This apparatus is composed of a large circular sail, passing through this water, is conveyed into the balloon by a fig. 92, of about five or six yards in diameter, which, by the long canvas pipe, fixed at one end to the central cask, and at effect of the resistance of tắe air, expands and forms a huge the other to the bottom,
umbrella which slowly descends to the ground. On its edges In order to facilitate the filling of the balloon, two masts are fastened cords, which support a car, in which the æronaut are erected, having at their top pulleys traversed by a rope, is seated. In the centre of the parachute, there is an opening which passes through a ring fixed at the top of the valye. By for the escape of the air which is compressed by the effect of this means, the balloon being at first raised about a yard above the descent; without this, the air would produce oscillations the ground, the gas is admitted; then, in proportion as the on the parachute, which would be communicated to the car balloon is filled, it is raised a little higher, and it is allowed to and render the position of the wronaut perilous. In fig. 91 is expand more and more, until it frees itself from this apparatus. shown, on the side of the balloon, a parachute folded and It is now necessary to oppose the force with which it begins to attached to the netting, by means of a cord passing over a ascend. For this purpose, a number of men are employed to pulley and fixed to the car. By loosening this cord, the hold it down by means of cords fixed to the netting. When parachute is placed in the power of the wronaut. M. J. the balloon is completely filled, it is then necessary to remove GarneriuTas the first who descended in a parachute; but the pipe which conveyed the gas, and to attach the car to the M. Blanchard appears to have been the inventor. net-work. These different preparatory operations require at Weight required to raise a Balloon. In order to calculate the least two hours. The æronaut is then seated in the car, and weight required to raise a balloon of given dimensions, when at a given signal, the cords are loosed, and the balloon ascends it is supposed to be perfectly spherical, the following formula with a velocity in proportion to its lightness as compared with is employed : v=RD!, which represents geometrically the the air which it displaces.
volume of a sphere, whose diameter is D, a being the ratio of It is important to observe that a balloon should not be com- the circumference to the diameter, or 3.1416 nearly. Thus, pletely inflated; for the atmospheric pressure diminishing in if a balloon of thirty-six feet in diameter were completely proportion to the height of the ascent, the interior gas expands filled with hydrogen, its volume would be about 24,430 cubic in consequence of its elastic force, and tends to make the bal- feet. But in general, the balloon, when it begins to ascend, is loon burst. It is sufficient that the force of ascent; that is, only about half filled, whence its volume may be assumed at