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vacuum. These articles, with two barometers, were the principal instruments which M. Gay-Lussac took with him.

On the 15th September, at 9.40 A.m., the scientific voyager ascended from the same place as before. The barometer then stood at 30.66 inches, the thermometer at 82° Fahr., and the hygrometer at 57£°. The sky was unclonded, but misty. Scarcely had the observer reached the height of 3,000 feet, than he observed spread below him, over the whole extent of the atmosphere, a thin vapour which rendered distant objects very indistinct. Having gained an altitnde of 9,950 feet, he set his needle to vibrate, and found it to perform twenty oscillations in 83", though it had taken 84".33 to make the same number at the surface of the earth. At the height of 12,680 feet, he discovered the variations of the compass to be precisely the same as below; but with all the pains he could take, he was unable to determine with sufficient certainty the dip of the needle. M. Gay-Lussac continued to prosecute his other experiments with the same diligence, and with greater success. At the altitnde of 14,480 feet he found that a key, held in the magnetic direction, repelled with its lower end, and attracted with its upper end, the north pole of the needle of a small compass. This observation was repeated, and with equal success, at the vast height of 20,150 feet; a clear proof that the magnetism of the earth exerts its influence at remote distances. He made not fewer than fifteen trials at different altitndes, with the oscillations of his finely suspended needle. It was generally allowed to vibrate twenty or thirty times. The mean result gives 4".220 for each oscillation, while it was 4".216 at the surface of the earth; an apparent difference so extremely small as to be fairly neglected.

During the whole of his gradual ascent, he noticed, at short intervals, the state of the barometer, the thermometer, and the hygrometer. Of these observations, amounting in all to twenty-one, he has given a tabular view. Leslie regrets that Gay-Lussac neglected to mark the times at which they were made, since the results appear to have been very considerably modified by the progress of the day. He also suggests that it would have been desirable to have compared them with a register noted every half-hour at the Observatory. From the surface of the earth to the height of 12,125 feet, the temperature of the atmosphere decreased regularly from 82° to 47.3° Fahr. But afterwards it increased again, and reached to 53.6° at the altitnde of 14,000 feet; evidently owing to the influence of the warm currents of air, which, as the day advanced, rose continually from the heated ground. From that point the temperature diminished, with only slight deviations from a perfect regularity. At the height of 18,636 feet, the thermometer subsided to 32.9° on the verge of congelation; but it sunk to 14.9° at the enormous altitnde of 22,912 feet above Paris, or 23,040 feet above the level of the sea, the utmost limit of the balloon's ascent.

Sir John Leslie thinks that from these observations no conclusive inference can be drawn respecting the

mean gradation of cold which is maintained in the higher regions of the atmosphere; because the several strata are during the day kept considerably above their permanent temperature by the hot currents raised from the surface through the action of the sun's rays. Leslie had caleulated that the diminution of temperature corresponding to the first part of the ascent, or 12,125 feet, ought have been 40°; but the temperature actually observed was 34.7°. In the next portion of the voyage, from the altitnde of 14,000 feet to that of 18,636 feet, or the breadth of 4,636 feet, the decrease of temperature was caleulated at 16i°, whereas it was 20.7°, a proof that the dinrnal heat from below had not yet produced its full effect at such a great height. In the last portion of the balloon's ascent, from 18,636 feet to 22,912, a range of 3,276 feet, the decrease of heat was caleulated at 15j°, and it was actually 18°, owing most probably to the same cause, or the feebler influence which warm currents of air from the surface exert at those vast elevations. Taking the entire range of the ascent, or 22,912 feet, the diminution of temperature according to Leslie's formula would be, for the gradation of temperature in ascending the atmosphere, 85.4°. The decrease actually observed would be 67.1°, which might be raised to 80° if we admit the very probable supposition, that the surface of the earth had become heated from 82° to 94.9°, during the interval between ten o'clock in the morning, and near three in the afternoon, when the balloon floated at its greatest elevation.

It appears then from these results, that the gradation of temperature in the atmosphere is not uniform, but proceeds with augmented rapidity in the more elevated regions.

The hygrometers during the ascent of the balloon held a progress not quite so regular, but tending obviously towards dryness. At the height of 9,950 feet they had changed from 57.5°, to 62°, from which point they continued afterwards to decline, till they came to mark 27.5°, at the altitnde of 15,190 feet. From this inferior limit the hygrometers advanced again, yet with some fluctuations to 35.1°, which they indicated at the height of 18,460 feet. Above this altitnde the variation was slight, though rather inclining to humidity. There can exist no doubt, however, that allowing for the influence of the prevailing cold, the higher strata of the atmosphere must be generally drier than the lower, or capable of retaining, at the same temperature, a larger share of moisture.

At the altitnde of 21,460 feet, M. Gay-Lussac opened one of his exhausted flasks; and at that of 21,790 feet, the other. The air rushed into them through the narrow aperture with a whistling noise. He still rose a little higher, but at eleven minutes past three o'clock, he had attained the utmost limit of his ascent, and was then 22,912 feet above Paris, being more than four miles and a quarter above the level of the sea. The air was now more than twice as thin as ordinary, the barometer having sunk to 12.95 inches. From that stupendous altitnde, ],600 feet above the level of the Andes, more elevated than the loftiest pinnacle of our globe, and Lir above the heights to which any mortal had ever soared, the aerial navigator calmly pursued his observations. During his former ascent, he saw the fleecy clouds spread out below him, while the canopy of heaven seemed of the deepest azure, more intense than Prussian blue. This time, however, he pereeived no clouds gathered near the surface, but remarked a range of them stretching at a very considerable height over his head; the atmosphere, too, wanted transparency, and had a dull, misty appearance. The different aspect of the sky was probably owing to the direction of the wind, which blew from the northnorth-west, in Ins first voyage, but in his second from the south-east.

While occupied with experiments at this enormous elevation, he began, though warmly clad, to suffer from excessive cold, and his hands, by continued exposure, grew benumbed. Ho felt, likewise, a difficulty of breathing, and his pulse and respiration were much quickened. His throat became so parehed from inhaling the dry attenuated air, that he could hardly swallow a morsel of bread; but he experienced no other direct inconvenience from his situation. He had indeed been affected through the whole of the day with a slight headache, brought on by the preceding fatigues and want of sleep; but though it continued without abatement, it was not increased by his ascent.

The balloon was now completely distended, and not more than 33 lbs. of ballast remained; it began

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to droop, and M. Gay-Lussae, therefore, only sought to regulate its descent. It subsided very gently, at the rate of about a mile in 8 minutes; and after the lapse of 34 minutes, or at three-quarters past 3 o'clock, i he anchor touched the ground, and instantly secured the car. The voyager alighted with great case near the hamlet of St. Gourgon, about 16 miles northwest from Rouen. The inhabitants flocked around him, offering him assistance, and eager to gratify their curiosity.

As soon as he reached Paris, he hastened to the laboratory of the Polytechnic School with his flasks containing air of the higher regions, and proceeded to analyse it in the presence of Thenard and Gresset. Opened under water the liquid rushed into them, and apparently half filled their capacity. The transported

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air was found, by a very delicate analysis, to contain exactly the same proportions as that collected near the surface of the earth, every 1,000 parts holding 215 of oxygen. From concurring observations, therefore, it may be concluded that the proportions of oxygen and nitrogen in the atmosphere are essentially the same in all situations.

Sir John Leslie remarks truly, that the ascents performed by MM. Biot and Gay-Lussac are memorable, for being the first ever undertaken solely for objects of science. It is impossible, he says, not to admire the intrepid coolness with which they conducted these experiments, operating while they floated in the highest regions of the atmosphere, with the same composure and precision as if they had been quietly seated in their cabinets at Paris. Since that time numerous ascents have been performed in different countries, generally by adventurers guided by no philosophical views, nor leading to any valuable results. We may, however, remark that in 1806, Carlo Brioschi, astronomer royal at Naples, made a balloon ascent in company with Andreani, the first Italian aeronaut. In attempting to rise to a greater height than Gay-Lussac had done, they got into an atmosphere so rare that the balloon burst from the great expansion of the gas. Its shreds served to check the velocity of their descent, and falling into an open space their lives were saved, but Brioschi contracted a disease which afflicted him till his death in 1833.

We must also notice the voyage performed by Messrs. Holland, Mason, and Green, in the year ] 836, as being the longest on record, the distance of about 500 miles having been performed in 18 hours. The balloon was one which had been built by the proprietors of Vauxhall Gardens. It was pear-shaped, and when inflated was 60 feet high, and about 50 feet in its largest diameter. It required 85,000 cubic feet of gas fully to distend it, and its ascensive force was about 3,000 lbs. after allowing for the weight of the machine itself and its accessories, which were estimated at l,000lbs. The car was of wicker-work, oval in shape, 9 feet by 4 feet. The aeronauts proposed to embark in this balloon, and to proceed On whatever course the winds might direct. They do not state how long they intended to remain in the air, but they took a fortnight's provisions, laid in a ton of ballast in bags, registered and marked, while all round the hoop, and in and about the car, were' suspended cloaks, carpet bags, barrels of wood and of copper to provide for their safety in case the balloon should descend into the sea, speaking trumpets, barometers, telescopes, lamps, wine jars, spirit flasks, and other articles. They also had a machine for warming coffee and other liquids by means of the heat developed in the process of slaking lime. This was intended to supersede the necessity of making a fire. They had, however, a lamp, the flame of which was properly protected, to be burnt at night.

In addition to the ballast, the balloon was also furnished with a guide-rope about 1,000 feet long, to be lowered from the car by means of a windlass, and passing through a pulley attached to the hoop above, thus to remain freely suspended in the air. The use of this guide-rope is thus stated:—As soon as any alteration takes place, whereby the specific gravity of the balloon is increased, causing it to descend, the lower portion of this rope becomes gradually deposited on the ground, and acting like a discharge of ballast keeps constantly abs tracting from her weight until her further descent is eventually checked, and she either continues to ad vancc at the level at which she is thus reduced, or should her buoyancy from any cause be increased, she slowly rises and takes up the additional weight of rope which had been deposited on the ground. Another advantage of the guide-rope is, that in

sailing by night the rope m trailing on the ground ■would give information to the aeronauts when the balloon was near the surface, and thus enable them to adjust the balloon to the required elevation by throwing out small portions of ballast.

Everything being got ready by 1.30 P.m. on the 7th November, 1836, the balloon rose slowly, and under the influence of a moderate breeze was borne away towards the south-east. At 2.48 they crossed the Medway, and at 4.15 saw the sea under the last rays of the setting sun. The cold caused the balloon to contract, and they descended into a current which bore them northward. As one of the objects of the expedition was if possible to get to Paris, they threw out ballast, and thus gamed a higher level. In a few minutes they came over Dover, and at 4.48 quitted the shores of England, and in an hour were hovering over the French coast. As night advanced the scene was very striking. "The whole plane of the earth's surface for many a league around, as far and farther than the eye could distinctly embrace, seemed absolutely teeming with the scattered fires of a watehful population, and exhibited a starry spectacle below, that almost rivalled in brilliancy the remoter lustre of the concave firmament above. Incessantly during the earlier portion of the night, ere the inhabitants had retired to rest, large sources of light, signifying the presence of some more extensive community, would appear just looming above the distant horizon in the direction in which we were advancing, bearing at first no faint resemblance to the effect produced by some vast conflagration, when seen from such a aistance as to preclnde the minute investigation of its details. By degrees, as we drew nigh, this confused mass of illumination would appear to increase in intensity, extending itself over a larger portion of the earth, and assuming a more distinct form, and a more imposing appearance, until at length, having attained a position from whence we could more immediately direct our view, it would gradually resolve itself into its parts, and shooting out into streets, or spreading into squares, present us with the most perfect model of a town, diminished only in size, according to the elevation from which we happened at the time to observe it." In the course of the night, one of these scenes was particularly striking. "Situated in the centre of a district which actually appeared to blaze with the innumerable fires wherewith it was stndded in every direction, to the full extent of all our visible horizon, it seemed to offer in itself, and at one glance, an epitome of all those charms which we had previously been observing in detail. The perfect correctness with which every line of street was marked out by its particular line of fires; the forms and positions of the more important features of the city, the theatres, and squares, the markets, and public buildings, indicated by the presence of the larger and more irregular accumulation of lights, added to the faint murmur of a busy population still actively engaged in the pursuits of pleasure or business, altogether combined to form a picture, which for singularity and effect certainly

could never have been conceived. This was the city of Liege, remarkable for the extensive iron works which, abounding in its neighbourhood, occasioned the peculiar appearance." (Fig. 12, page 17.) After leaving this fiery district the darkness gradually increased in intensity; it seemed to the aeronauts as if they were cleaving their way through an interminable mass of black marble in which they were imbedded, and which, solid a few inches before them, seemed to soften as they approached in order to admit them still farther within its cold and dusky enclosure. In this way they proceeded blindly, as it may well be called, until about 3.30 A.m. when in the midst of impenetrable darkness and profound stillness, an unusual explosion issued from the machine above, followed by a violent rustling of the silk, and aE the signs which might be supposed to accompany the bursting of the balloon. The car was violently shaken; a second and a third explosion followed in quick succession; the danger seemed immediate, when snddenly the balloon recovered her usual form and stillness. These alarming symptoms seem to have been produced by the collapsing of the balloon under the diminished temperature of the upper regions after sunset, and the silk forming into folds under the netting. Now, when the guide-rope informed the voyagers that the balloon was too near the earth, ballast was thrown out, and the balloon rising rapidly into a thinner air experienced a diminution of pressure, so that its gaseous contents would expand, and in doing so open the folds of the collapsed silk, and produce this snapping noise which had occasioned so much alarm.

The cold during the night ranged from a few degrees below, to the freezing point. As morning advanced the rushing of waters was heard, and so little were the aeronauts aware of the course which they had been pursuing during the night, that they supposed themselves to have been thrown back upon the shores of the German Ocean, or about to enter the Baltic, whereas they were actually over the Rhine, not far from Coblenz. At 5.10 A. M. they gained their greatest elevation, which was about 12,000 feet, from which objects were seen at a distance of 150 miles on every side. The view of this stupendous landscape was enjoyed for about an hour, and at 6.15 they had the satisfaction of seeing the sun rise, which still more enhanced the beauties of the scene. Shortly afterwards the balloon descended rapidly to a lower level, and all again was dark, and it was not until they had seen the sun set twice, and rise three times, that daylight was fairly established. Even then, they were not aware of their locality, and actually supposed themselves to be hovering over the "boundless plains of Poland, or the barren and inhospitable Steppes of Russia." As soon as the mist had cleared away they hastened to descend, and after many difficulties succeeded in doing so, and found themselves "in the Duchy of Nassau, about two leagues from the town of Weilburg!" This is certainly a very complete answer to those who still advocate the possibility of guiding balloons, when in

this, the grandest experiment in aerostation in modern times, the aeronauts were so completely at the mercy of the winds as not to know either the direction they had taken or the locality in which they had descended. Did they neglect to cany a compass with them?' ,

In this voyage all the resources of the aerostatic art were put into practice, and it will be seen how very small an advance has been made in it from the time when the first hydrogen gas balloon was launched into the air in 1783. The grandest improvement was in the use of coal-gas instead of the hydrogen, as previously obtained by a slow and costly process, an improvement which was first put in practice by Mr. Green, in his ascent from St. James's Park in 1820, at the coronation of George IV. The general introduction of coal-gas about this period, thus afforded a ready means for filling these aerial toys, which was speedily taken advantage of wherever gas-works were at hand. Coal-gas is between four and five times heavier than its own bulk of hydrogen, so that it would require about four or five times the quantity to produce the same effect; but this supposes the hydrogen to have been pure, which it never was; for not only was it loaded with moisture, but it quickly became contaminated with air; so that the balance in favour of pure hydrogen, without reference to its increased cost, cannot be very great. The specific gravity of the coal-gas of London is about 0.4, atmospheric air being 1.0; so that after allowing for the weight of the balloon, the car, the voyagers, the ballast, &c., there is still a sufficient amount of ascensional force to convey the machine and its freight into the upper regions. The ballast generally consists of bags of sand, which, on being shaken out, relieve the balloon of a portion of its load, and thereby increase the ascensional force. But as the balloon ascends, the atmospheric pressure diminishes, and causes the gas to expand, and it would in fact burst the envelope unless means were taken to allow a portion to escape. This is done by means of a safety-valve placed at the top of the balloon, and regulated by a cord passing down into the car. By this means, also, the aeronaut regulates his descent; for as the gas is allowed to escape, the weight of the machine gradually destroys the ascensional force, and the balloon descends. He still retains sufficient buoyancy to prevent the balloon from falling with a jerk, and when near the earth, a grappling-hook attached to one extremity of a rope is thrown out; when this has taken hold of the earth, the balloon is landed by drawing the rope in, and then all the remaining gas is allowed to escape.

Thus it will be seen that the only guiding power possessed by the aeronaut is that of ascent and descent within certain limits. By throwing out ballast he can ascend; by letting out gas he can descend.

(1) The details of this voyage, and a variety of particulars and speculations respecting balloons, are given by Mr. Monck Mason, in his very amusing work entitled "Aeronautica, or Sketehrs Illustrative of the Theory and Practice of Aerostation." London, 1S3S.

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lie is absolutely powerless in guiding the balloon horizontally; for there is no analogy between a balloon and a ship sailing in the water. In the ship the action of the water on the rudder is a guide to the impelling foree of the winds acting on the sails. No such regulator as the rudder can be applied to a balloon, because it is sustained in, as well as impelled by the air. It is stated, however, by Mr. Green, and Mr. Monck Mason, from their own aeronautic experience, that "in this country, whatever may be the direction of the wind below, within 10,000 feet above the surface of the earth, the direction of the wind is invariably from some point between the north and west." If this really be the case, the aeronaut has only to ascend to the height named, and he will find an upper current always ready to convey him in any direction between south and cast.

One of the chief dangers in aerial excursions arises from a rapid and premature descent. To guard, in some degree, against such an occurrence, the parachute, or guard for falling, was introduced. The parachute resembles a large umbrella, sufficiently strong to resist the action of a moderate wind, and sufficiently large to offer a resistance equal to the weight of the person descending in it, so that it may reach the earth with a velocity not exceeding that of the shock which a person can sustain without danger.

Blanchard was the first aeronaut who attached a parachute to a balloon. During the excursion which he undertook from Lisle, in August, 1785, when he traversed a distance of 300 miles without halting, he let down a dog from a vast height in the basket of a parachute, and the poor animal, falling gently througu the air, reached the ground unhurt. Another aeronaut, M. Garncrin, even ventured on many occasions to descend from the clouds in this frail machine. During the short peace of 1802, he visited London, and made two ascents with his balloon, in the second of which ho threw himself from an amazing elevation with a parachute. This consisted of 32 gores of white canvass formed into a hemispherical case of 23 feet diameter, at the top of which was a round piece of wood with a hole in its centre, admitting short pieces of tape to fasten it to the several gores of the canvass. About 4J feet below the top, a wooden hoop 8 feet in diameter, was attached by a string from each scam, so that when the balloon rose the parachute hung like a curtain from this hoop, as in No. 1 of Fig. 13. Below was suspended a cylindrical basket covered with canvass, about 4 feet high and 2} feet wide. In this basket the aeronaut, dressed in a close jacket, placed himself and ascended from an inclosure near North Audley Street, at 6 P.m. of the 2d September. After hovering 7 or 8 minutes in the upper region of the atmosphere, he cut the cord by which his parachute was attached to the net of the balloon. The balloon immediately ascended and was lost, but the parachute instantly expanded, as in No. 2, and for some seconds descended with an accelerating velocity, until it became tossed extremely, as in Nos. 4 and 5, and took such wide oscillations that the basket was sometimes

thrown into a nearly horizontal position, as in No. 3. At the same time being carried along by the wind, the parachute passed over Marylebonc and Somers Town, and almost grazed the houses of St. Pancras.

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At length it strack the ground in a neighbouring field, but with a shock so violent, that Garnerin was thrown on his face and injured. It appears that one of the stays of the parachute had given way and had thrown the apparatus out of its proper balance, thus threatening the aeronaut with destruction during the whole of his descent. •

Mr. Monck Mason states an interesting meteorological fact as having been established by aeronautic observation. It appears that whenever a fall of rain occurs, and the sky is at the same time entirely overcast with clouds, there will be found to exist another stratum of clouds at a certain elevation above the former. So also, when the sky is entirely overeast, and rain is altogether or generally absent, the aeronaut, upon traversing the canopy immediately above him, is sure to enter upon another hemisphere, either perfectly cloudless or nearly so. Mr. M. Mason states that this fact has been verified during many hundred ascents. For example, during an ascent on the 12th October, 1837, "the sky was completely overspread with clouds, and torrents of rain fell incessantly during the whole of the day. Upon quitting the earth, the balloon was almost immediately enveloped in the clouds, through which it continued to work its way upwards for a few seconds. Upon emerging at the other side of this dense canopy, a vacant space, of some thousand feet in breadth, intervened, above which lay another stratum of a similar form and observing a similar character. As the rain, however, still continued to ^iour from this second layer of clouds, to preserve the correctness of the observation a third layer should by right have existed at a still further elevation; which, accordingly, proved to be the case. On the subsequent occasion of the ascent of the same balloon, (October 17th,) an exactly similar condition

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