renounce the proposed ascension. I made, in the presence of the two aeronauts, the observation that it might be very useful to know the decrease of the atmospheric temperature with the height when a continuous screen of clouds shuts from us the view of the sky.* Now it sometimes happens that the sky becomes clear of a sudden; in this case there must remain in the atmosphere traces more or less marked of the abnormal decrease of temperature of which the presence of the cloud had been the cause. The observations made in aerostatic ascensions, performed during clear weather, are not completely applicable to this special case. Besides, there are numerous occasions when we observe through openings in the clouds. When MM. Barral and Bixio arrived at the conclusion, from these considerations and others which it would be superfluous to mention, that their voyage might prove useful, they placed themselves in the car and launched into the air.

"All the details of this ascension are scrupulously given in the journal written at the time by the aeronauts, and the calculations were compared by M. Regnault with the indications of the sealed instruments carried in the expedition. I shall only advert here to the fact that at their greatest elevation our explorers experienced no uneasiness or embarrassment in their respiration; and that M. Bixio, who had suffered in his first voyage from acute pain in the cars, guarded against that annoyance by simply counterfeiting from time to time the act of deglutition, by which the air within and without the organ was maintained in a state of equal pressure. It may be added, that they encountered a mass of cloud of more than 5,000 meters in thickness, that they did not succeed in rising entirely above it, but at the height of about 7,000 meters (22,960 feet) were forced to commence an involuntary descent, the effect of a rent in the lower part of the balloon. They might, perhaps, by throwing out the last of their ballast, have prolonged their stay at the height which they had reached, but circumstances no longer permitting them to gather useful indications for science, they thought best not to struggle against the downward tendency of the apparatus.

"Let us speak now of the observations which they had an opportunity of making. When they had attained their highest station in the immense bed of cloud, an opening took place in the vaporous mass which surrounded them, through which the blue sky was apparent. The polariscope, directed towards this region, showed an intense polarization; on the contrary, there was none at all, when the instrument was pointed aside beyond the opening. This should not be regarded as a repetition of the experiment made in the first voyage, for then they observed the light reflected by the clouds, while now it was in the transmitted light that they verified the absence of all polarization.

"An interesting optical phenomenon was exhibited during this ascension. Before attaining the highest limit, the bed of cloud which enveloped the balloon, having diminished in thickness or become less dense, the sun appeared weak and quite white; at the same time there appeared, below the horizontal plane of the car, at an angular distance from that plane equal to the angle formed by the sun's height, a second sun similar to one which might have been reflected from a sheet of water situated at that elevation. It is natural to suppose, with our aeronauts, that the second sun was formed by the reflection of the luminous rays on the horizontal faces of crystals of ice floating in that vaporous atmosphere.

"We now come to the most striking and wholly unexpected result furnished by the thermometrical observations. Gay Lussac, in his ascension in clear or rather slightly vaporous weather, had found a temperature of 9°.5 below zero

*The refractions at moderate heights depend on the law according to which this decrease is effected.

at the height of 7,016 meters. This was the minimum he observed. MM. Barral and Bixio encountered this same temperature in the cloud at the height of about 6,000 meters; but from this point, through an extent of some 600 meters, the temperature varied in a manner the most extraordinary, and beyond all anticipation. Lest the number which results from the observations should strike the reader with a feeling of incredulity, it is proper to say that proof of its exactness will be promptly submitted. At the height of 7,049 meters, at some distance from the upper limit of the cloud, MM. Barral and Bixio saw the centigrade thermometer descend to 39 degrees below zero. It is 30 degrees lower than the number observed by Gay Lussac at about the same height, but when the weather was clear.

"I hasten to prove that this surprising result is affected by no error of observation. The barometer for determining the height was of course furnished with a thermometer intended to give the temperature of the mercury. This thermometer had been graduated to 37 degrees below zero. It was thought that these 37 degrees ought to suffice for the greatest heights to which it was supposed explorers could ascend. But the mercury had descended below this 37th degree, though it had not shrunk entirely within the reservoir. By an estimate which could hardly be inexact when made by such a physicist as M. Regnault, the mercury had descended 2 degrees below 37. The thermometer of the barometer marked, therefore, 39 degrees.

"M. Walferdin has invented very ingenious self-registering thermometers, which give the maxima and minima of temperature to which they have been exposed. The one for maxima is frequently used; it is desirable that the second, which is less known, should be generally adopted by physicists. It is capable of being of great service to meteorolgy. The inventor had sent one of his thermometers á minima with arbitrary divisions to our aeronauts, and this was enclosed in a case with numerous holes to permit the circulation of air. At the request of the two aeronauts, a seal was applied, and this seal, which arrived untouched, was broken at the College of France in the presence of MM. Regnault and Walferdin. Careful examination proved that the minimum thermometer had sunk to -39°.7. After these precise observations it is scarcely necessary to say that the proof of an extraordinary depres sion of temperature is to be found in the impossibility which the aeronauts experienced of reading the indications of several thermometers, the fluid of which had sunk as low as the stopper of cork which supported them. Every attempt to remove this obstruction was frustrated by the stiffening of the fingers with cold. This nearly instantaneous depression of the temperature in the cloudy mass is a discovery which interests meteorology in the highest degree. What is the special constitution of a cloud which qualifies it, whether by radia tion into space or from whatever other cause, to exhibit so prodigious a refrigeration? It is a question which at this moment we can do no more than propound. Can this abnormal constitution play a part in the formation of hail? Is it, perchance, the cause of the considerable changes of temperature which are suddenly experienced at a given place? The solution of these questions is reserved for the future, which does not, however, at all diminish the importance of the observation.

“In the journal of the voyage the temperatures observed were rendered by thermometers having an arbitrary graduation; the aeronauts did not know what the numbers signified which they read and registered; the real temperatures were afterwards determined by M. Regnault, and the heights calculated by M. Mathieu. We may thus rely with perfect confidence on the results. From these we deduce that the height attained was 7,049 meters, taking into account the diminution of weight at those great elevations and the influence of the hour of the day on the barometric measurement of heights; this is 33 meters higher

than Gay Lussac had ascended. It is proper to observe that the formulas used in calculating heights proceed upon the hypothesis of a nearly uniform decrease of temperature, and that, in this instance, a change of elevation which may be estimated at 600 meters, was attended by a variation of temperature of about 30 degrees, while, in an unclouded atmosphere, the variation would have been but from 4 to 5 degrees.

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The important discovery made in this aeronautic voyage shows what science may expect from like expeditions when they shall be confided, as at that time, to intrepid, careful, exact, and candid observers."

The following is an extract from the journal kept by the two accomplished physicists during the voyage:

"The graduated instruments which we carried with us had been constructed by M. Fastré, under the direction of M. Regnault. The tables of graduation had been prepared in the laboratory of the College of France, and were known only to the last mentioned-savant.

"The balloon is the same which served for our first ascension; it is formed of two hemispheres of a radius of 4.8 millimeter, separated by a cylinder 3.8 millimeter in height, having for its base a great circle of the sphere. The total volume of the balloon is 729 cubic meters. A lower orifice, intended to give issue to the gas during its dilatation, is terminated by a cylindrical appendage of silk, 7 meters long, which is left open to permit the free escape of the gas during the period of ascent. The car is suspended at about 4 meters below the orifice of the appendage, so that the balloon may float at the distance of 11 meters from the car, and in no respect interfere with the observations. The instruments are fixed around a large cast-iron ring which is attached to the usual wooden circle for securing the cords of the car, and is of such a form that the instruments may be within convenient distance of the observers.

"It was our intention to set out at about 10 o'clock a. m., and measures had been taken for commencing the inflation of the balloon, an operation with which MM. Veron and Fontaine were charged, at 6 o'clock. Unfortunately, circumstances beyond our control, and arising from the necessity of thoroughly washing the gas in order to guard against its action upon the tissue of the balloon, occasioned delay, and it was 1 o'clock before the arrangements were completed. The sky, which had been quite clear till noon, became covered with clouds, and soon a deluge of rain was falling upon Paris. This continued until 3 o'clock. The day was then too far advanced, and the condition of the atmosphere too unfavorable, for us to hope that we could carry out the programme we had proposed. But the aerostat was ready, great expense had been incurred, and it was possible that observations in this troubled state of the atmosphere might lead to useful results. We decided, therefore, to ascend. Our departure took place at 4 o'clock. Some difficulty was occasioned by the narrowness of the space which the garden of the observatory afforded for the evolution of ascent. The balloon, as has been seen, was at a considerable distance from the car, and, swept forward by the wind, got the start of the frail skiff in which we were embarked, so that it was only through a series of oscillations, sufficiently divergent on either side from a vertical line, that we attained a state of tranquil suspension from the aerostat. We came in contact with trees and a pole, by which one of the barometers and the thermometer with a blackened surface were broken, and these were left behind. We shall here transcribe the notes taken during our ascension.

4h 3m. Departure. The balloon ascends at first slowly, taking a direction towards the east. The movement of ascension becomes more rapid after the discharge of some kilograms of ballast. The sky is completely covered with clouds, and we presently find ourselves in a light mist.

“Above us there extends an uninterrupted bed of clouds; below we perceive here and there detached clouds which appear to float over Paris. The wind is fresh.

"The cloud which we enter presents the appearance of an ordinary dense fog. The earth is no longer discernible.

"A few solar rays become perceptible through the clouds. "The barometer oscillates from 366.99 millimeters to 386.42 millimeters; the thermometer marks -9°.0; calculation gives from 5,911 to 5,492 as the height reached at this point of time.

"The balloon is entirely inflated. The appendage, compressed till now by the external atmosphere, is at present distended, and the gas escapes by its lower orifice under the form of a whitish trail; we perceive its odor very distinctly. We discover in the balloon, at the distance of about 1.5 millimeter from the insertion of the appendage, a rent, which affords issue to a greater amount of gas, without diminishing, however, in any important degree, the ascensional force of the aerostat.

"An opening in the cloud enables us vaguely to perceive the position of the

sun.

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The balloon resumes its ascendant movement after a new discharge of ballast.

66

4h 25m-Oscillations of the barometer between 347.75 millimeters and 367.04 millimeters indicate a new station of the balloon; the thermometer varies

*All the barometric heights taken have been reduced to the temperature of 0° by calcula tion. By means of the barometric and thermometric observations, made at the observatory and in the car, the heights of nineteen stations above the observatory and above the sea were calculated, increasing them by 65 meters. But the three heights, 6,512, 7,049, and 6,765 meters, where the temperature had sunk to -35°, -36°, and -390, were obtained by cal culating, not from the observatory, but from the intermediate station of 5,902 meters, where the temperature was -90.8, and the pressure 367.04 millimeters. There results 7,004 for the highest station. But it is still necessary to add a correction of 12 meters, due to the height (5,902 meters) of the inferior station of comparison, and 33 meters on account of the influence of the hour of the day, as was justly remarked by M. Bravais, which makes in all 7,049 meters.

from -10°.5 to -9°.8; the height we have reached varies from 6,330 to 6,902

meters.

"The fog, much less dense, permits our secing a white and feeble image of the sun.

"A renewed discharge of ballast occasions a new ascension of the balloon, which attains a new stationary position, indicated by renewed oscillations of the barometer. We are covered with small particles of ice, in the shape of extremely fine needles, which accumulate in the folds of our clothing. While the barometric oscillation is descending, and the movement of the balloon is consequently ascensional, these particles fall upon our open note-book in such quantity as to produce a sort of crepitation. Nothing similar is observed while the barometer is rising and the balloon, of course, descending.

"The horizontal glass thermometer indicates -4°.69; the silver-plated thermometer -8°.95.

"We distinctly see the disc of the sun through the frozen mist; but at the same time, in the same vertical plane, we perceive a second image of the sun, almost as intense as the former. The two images appear symmetrically disposed above and below the horizontal plane of the car, each making with this plane an angle of about thirty degrees. This phenomenon is apparent for more than ten minutes.

"The temperature lowers rapidly. We prepare to make a complete series of observations on the thermometers of radiation and those of the psychrometer, but the mercurial columns are hidden by the stoppers, inasmuch as no such rapid fall in the temperature had been anticipated. The thermometer with concentric envelopes of tin gives-23°.79.

"We open a cage in which two pigeons are confined, but they refuse to escape. We cast them off into space, when, spreading their wings and wheeling in large circles, they sink downwards and are soon lost to sight in the mist which surrounds us. We cannot perceive the anchor which is suspended below, at the end of a cord 50 meters long.

4h 32m-We discharge ballast and rise still higher. The clouds separate above, and we see in the sky a space of bright azure blue, similar to that seen on earth in clear weather. The polariscope indicates no polarization, in any direction, on the clouds immediately around or remote from us. The blue of the sky, on the contrary, is strongly polarized.

"The oscillations of the barometer indicating that we have ceased to ascend, we throw out ballast, and obtain a new ascensional movement.

"Our fingers are stiffened with cold, but we experience no pain in the ears, nor is respiration at all embarrassed. The sky is covered anew with clouds, but the sun, though veiled, is still seen, as well as its image. We think it would be interesting to find if the cold will still increase on ascending yet higher. We throw out ballast, which determines a further ascension.

"4h 50m-The barometer marks 315.02 millimeters. The extremity of the column of the thermometer of the barometer is lower by about two degrees than the last division marked on the instrument. This division is 37°; the temperature, therefore, was about-39°; the height, consequently, which we had attained is 7,039 meters.

-

"The barometer oscillates from 315.02 millimeters to 326.20; hence the balloon oscillates from 7,039 to 6,798 meters. There are only four kilograms of