in the atmosphere increases. They also reported that they had experienced much physical suffering, and observed physiological phenomena, such as the swelling of the lips and veins, the bleeding of the eyes, &c., which have not been uniformly verified in subsequent expeditions.

However this might be, the Academy of Sciences of St. Petersburgh determined on a repetition of the experiment to be made by Robertson himself, assisted by Sacharoff, one of its own members, distinguished both as a physicist and chemist. This second expedition took place June 30, 1804. The aeronauts ascended from St. Petersburgh at 7 hours 45 minutes p. m., and descended at 10 hours 45 minutes, near Sivoritz, at a distance of about 20 leagues. At the moment of departure the barometer stood at 30 inches, and the thermometer at 19° Reaumur; at the greatest elevation the two instruments indicated respectively 22 inches and 4°.5 Reaumur. We conclude from these observations that the barometric pressure and the temperature were, at the point of departure, 812.1 millimeters, and +23°.7; at the greatest elevation, 595.5 millimeters and+5°.6; and from this it results that the highest point reached was 2,703 meters. MM. Robertson and Sacharoff were not able to make regular magnetic observations, but they felt authorized to affirm that the needle of declination had ceased to be horizontal, and that its north pole was elevated about 10 degrees, its south pole having an inclination of the same amount towards the earth.

IV. VOYAGES OF BIOT AND GAY LUSSAC.

Saussure, after a series of observations made on the Col du Geant at a height of 3,435 meters, conceived it to be ascertained that at that height the magnetic intensity undergoes a sensible diminution, which he estimated at about one-fifth. This result appeared to be verified by the aeronautic voyages of Robertson, Lhoest, and Sacharoff, just spoken of. But the proofs of the fact were not given in a sufficiently decisive manner to secure it a definitive reception into science, and the question appeared important enough to the principal members of the Institute, Laplace, Berthollet, Chaptal, to justify a special experiment. This was intrusted to MM. Biot and Gay Lussac, who ascended from the garden of the Conservatoire des arts et metiers, August 24, 1804, provided with all the necessary instruments. The small dimensions of the balloon did not allow the two aeronauts to reach the height of more than 4,000 meters, and at that elevation the temperature, which had been+17°.5 on the earth, had only sunk to +10°.5. Leaving at 10 o'clock in the forenoon, they descended, about half after one, 18 leagues from Paris, in the department of Loiret. Taking advantage of the moments when the movement of rotation of the balloon in one direction stopped, being about to be resumed in the opposite direction, the learned physicists were able to determine the duration of five oscillations of the magnetic needle in different aerial strata, and they obtained the following results:

Thus the observations agree in giving 35 seconds for the duration of five oscillations, or at least the observed differences are too small to allow of any conclusion being drawn from them.

Under these circumstances it was evident that a new ascension ought to be undertaken. This time Gay Lussac ascended alone. He rose from the garden of the Conservatory, September 16, 1804, at 9 hours 40 minutes in the morning. He alighted at 3 hours 45 minutes, between Rouen and Dieppe, 40 leagues from Paris, near the village of Saint Gourgon.

The distinguished savant had furnished his aerostat with long cords, designed to moderate its movement of rotation, and he could consequently count more easily the oscillations of the magnetic needle; he obtained the following results:

From these observations, which do not present sufficiently appreciable dif ferences, Gay Lussac drew the conclusion that the magnetic force does not undergo sensible variations up to the greatest heights which we can attain. In regard to this he thus expresses himself: "The consequence which we have drawn from our experiments may seem a little too precipitate to those who remember that we have not been able to make observations on the inclination of the magnetic needle. But when it is remarked that the force which causes a horizontal needle to oscillate is necessarily dependent on the intensity and direction of the magnetic force itself, and that it is represented by the cosine of the angle of inclination of this last force, the conclusion which we have arrived at cannot fail to be drawn, that, since the horizontal force has not varied, the total force cannot have varied, unless one chooses to suppose that the magnetic force may vary precisely in an opposite direction, and with the same relation to the cosine of its inclination, which is not at all probable.. We have, moreover, in support of our conclusion, the experiment of the inclination which was made at the height of 3,902 meters, and which proves that at that elevation the inclination did not vary in a perceptible degree." This conclusion was logical at an epoch when it was not generally known that at a given place and under given circumstances the duration of the oscillations of a magnetic needle is influenced by its temperature. Now, the depression of the thermometer of Gay Lussac had been sufficiently considerable to produce noticeable changes in the magnetic needle. We see that, in the imperfect state of the instruments and the science in 1804, it was impossible to arrive at an exact solution of the problem which the Institute had in view. Even at present this problem is still unsolved.

The principal result of the aeronautic voyage of Gay Lussac relates to the constant composition of the atmospheric air to a height of 7,000 metres. The illustrious physicist had the good fortune to bring the first air from those high regions, and to give an analysis of it, whose accuracy has been uniformly verified by new experiments conducted with the improved processes which science has discovered during half a century.

Another fact, no less important, is the wide difference which Gay Lussac found between the temperatures below and at the great height to which he

ascended. At the moment of his departure the barometer registered 765.25 millimeters, and the thermometer +279.75; at the greatest elevation these instruments gave 328.8 millimeters for the pressure, and -9°.5 for the temperature. It results that Gay Lussac rose to the height of 7,016 meters above the mean level of the sea, and that he found himself exposed to temperatures differing by 37°.

I shall not speak of the hygrometrical observations, because it only results from them, as from the greater part of those which have been made to this day, that the dryness of the air becomes very considerable in high regions of the atmosphere. Hair hygrometers are instruments whose indica ions are so little comparable with one another that it is impossible to deduce precise conclusions from them.

Gay Lussac has reduced to their just value the recitals of physical sufferings which are supposed to be felt in very elevated strata of air; he expresses himself on this subject with perspicuity and simplicity: "Arrived at the highest point of my ascension, 7,016 meters above the mean level of the sea, my respiration was sensibly embarrassed; but I was still very far from experiencing a degree of inconvenience which could induce me to descend. My pulse and respiration were much accelerated; and, breathing thus rapidly in an air of extreme dryness, I could not be surprised at having the throat so dry that it was painful for me to swallow bread."

It is thus seen that the ascensions of Biot and Gay Lussac are the first which have been made with marked success as regards the solution of scientific questions.

V. VOYAGES OF BARRAL AND BIXIO.

MM. Barral and Bixio made two aeronautic voyages, by the last of which, especially, science was enriched with unforeseen results of great importance. In reporting to the Academy of Sciences an account of the first excursion of these intrepid physicists, I expressed myself in nearly the following terms: "MM. Barral and Bixio had conceived the idea of ascending to a great height in order to study, with the improved scientific instruments of the present day, a multitude of atmospheric phenomena still imperfectly known. It was proposed to determine the law of the decrease of temperature with the height; the law of the diminution of humidity; to ascertain whether the chemical composition of the atmosphere is the same throughout; the portion of carbonic acid at different elevations; to compare the calorific effects of the solar rays in the highest regions of the atmosphere with these same effects observed on the surface of the earth; to determine whether there arrives at a given point the same number of calorific rays from all points of space; whether the light reflected and transmitted by clouds is or is not polarized, &c.

The instruments necessary for so interesting an expedition had been prepared with great care and precision by M. Regnault. Never has the love of science been manifested with more disinterestedness. M. Walferdin furnished several of his ingenious thermometers. The explorers were, besides, provided with barometers very accurately graduated, for determining the height at which the different observations were made.

The aeronauts had intrusted the preparation of the balloon to M. Dupuis Delcourt, who had distinguished himself by twenty-eight aerial voyages. All the arrangements were made in the garden of the Observatory of Paris. The ascension took place Saturday, June 29, 1850, at 10 hours 27 minutes in the morning, the balloon having been filled with pure hydrogen gas procured by the action of chlorhydric acid on iron.

According to all previous calculation, the explorers might now have expected to rise to the height of 10,000 or 12,000 meters, supposing the upper strata of the atmosphere to correspond with received theoretical ideas.

At the moment of departure, however, it might easily be seen that in several respects the aerostatic apparatus was imperfect. The balloon, in consequence of the prevalence of high winds, had been torn at many points, and mended with too great haste; the rain fell in torrents. What was to be done? It had been most prudent, perhaps, not to ascend, but the aeronauts rejected the idea. They placed themselves in the car, and boldly launched into the air, without even taking the precaution, so violent was the wind, of determining with a balance the ascensional force of the aerostat. Their ascent was extremely rapid; the spectators compared it to that of an arrow; they very soon disappeared in the clouds, and it was above the curtain which thus shrouded them from the view of man that the stirring scenes took place which remain to be described.

The dilated balloon pressed with great force on the meshes of the netting, which was much too small. It expanded from above downwards; descended on the aeronauts, whose car was suspended by cords which were too short, and covered them in some sort like a hood. At this time the adventurers found themselves in a situation of the greatest difficulty; one of them, in his efforts to disengage the cord of the valve, caused an opening in the inferior prolongation of the balloon; the hydrogen gas, which escaped nearly on a level with their heads, almost suffocated them, and caused excessive vomitings and momentary syncope.

Consulting the barometer, they found that they were descending rapidly, and, in seeking to ascertain the cause of this unexpected movement, they discovered that the balloon was torn in the region of its equator to the extent of nearly 2 meters. They now perceived, but with a composure which merits admiration, that all they could hope was to escape with life. It is no little to say that the velocity of their descent was much greater than that of their ascent. They discharged all their remaining ballast, threw overboard even the coverings which had been provided against the cold, including their furred boots, but parted with none of the instruments of research.

They fell, at 11 hours 14 minutes, in a vineyard, the ground of which was fortunately soft, in the commune of Dampmart, near Lagny. The laborers and vine-dressers ran to their help, and found the two aeronauts clinging by the feet and hands to the stems of the vines, in order to counteract as far as possible the horizontal movement of the car. The most earnest assistance was rendered them.

From a voyage performed under such conditions it is evident that science could derive but a very small amount of information in comparison with what might have been expected; yet it is our duty to say that our two physicists established, by decisive experiments, that the light of clouds is not polarized, that the bed of clouds which they traversed was at least 3,000 meters in thickness, and that, notwithstanding the existence of this curtain between the earth and sky, the decrease of temperature was very nearly the same with that verified by Gay Lussac in his celebrated voyage performed in a perfectly cloudless sky. From the barometrical observations compared with those made at the Observatory of Paris, it is deducible that, in the region where the balloon was torn, the height attained was 5,900 meters, and from a similar computation that the upper surface of the cloud passed through was at the height of 4,200 meters.

The following numbers complete the details which I laid before the Academy: At the moment of departure the barometer of the Observatory, reduced to zero, marked 753 millimeters, and the exterior thermometer 30°.3; the direction of the wind was west-southwest, and the sky was completely covered. At 10 hours 29 minutes the voyagers penetrated into a cloud having the appearance of a dense mist, which deprived them of the sight of the earth. At 10 hours 47 minutes the barometer of the car, reduced to zero, marked 458.3 millimeters, and

the thermometer +7°; at the same instant the barometer of the Observatory indicated a pressure of 753.17 millimeters, and the thermometer + 19°.4. These numbers give, by calculation, the height of 4,242 metres above the mean level of the sea, and correspond with the moment at which the balloon emerged from the upper part of the clouds. The bed of clouds now below the observers presented the appearance of mamillary swellings, silver white in color, the light from which, examined with the polariscopic telescope, yielded no trace of polarization. Except a few clouds, which here and there rose high above the balloon, the sky was of a pale and dull blue. At 10 hours 59 minutes the barometer of the car indicated 373.4 millimeters, and the thermometer had sunk below zero. M. Barral was unable to make out the exact thermometric degree on account of a layer of hoar-frost deposited on the instrument, which he could not remove. The barometer was at this time in a state of oscillation, the mean height of its changes being represented by the number just mentioned. The balloon, which, notwithstanding the precise directions given, had been so constructed as not to leave sufficient room for the development incident to the natural dilatation of the hydrogen,* had now sunk down upon the excursionists; the valve provided for the escape of the gas was closed; a rent had taken place in the upper part of the balloon, and MM. Barral and Bixio fell to the earth after having traversed 5,800 meters in from four to five minutes.

They immediately commenced preparations for a new ascent, which took place a month after that of which an account has been given. They rose, as before, from the garden of the Observatory; and I was a witness of this, as I had been of their former ascension. I had taken part in all the deliberations which regarded the scientific purposes of the voyage. If the first one had been rendered, by unfavorable circumstances, almost entirely barren of results, beyond giving proof of the intrepidity of the two distinguished explorers, and initiating them in the dangers of an ascent through an atmosphere agitated by winds and turbid with thick clouds, it would be sufficient to read the journal of the second voyage to comprehend how fertile it was both in novelty and interest. The Academy of Sciences having judged it desirable that such a statement should be prepared as would enable those least familiar with these matters to appreciate the importance of the contribution made by MM. Barral and Bixio to meteorology, I yielded to the wishes of that learned body, and shall here reproduce, in nearly identical terms, the account of the voyage which I then submitted:

"The two scientific explorers having properly resolved to renew their enterprise under more favorable circumstances, and being no longer under a necessity of evincing their courage or punctuality, could afford to await patiently the day and the moment. M. Regnault took charge, with M. Barral, of the preparations, which is equivalent to saying that the utmost ingenuity and exactness presided over the construction and disposal of the instruments. No one, however, but an eye-witness, can appreciate the indefatigable zeal and devotedness which my distinguished colleague exerted day and night in this behalf.

"Everything was ready on Friday, July 26, 1850, but the weather was adverse. Saturday morning, the atmosphere having cleared up, the filling of the balloon was begun. The operation was tedious, and by the time it was finished, towards one or two o'clock, the sky was overclouded, and a deluge of rain was falling. The rain finally ceased, but the sky remained entirely overcast; it would have been only natural, under these circumstances, to

The difficulty of managing the balloon before its ascent was the reason why the length of the cords attaching the car was reduced. The wind was so violent that 120 soldiers could scarcely keep the balloon from being carried away.