342 AERONAUTIC VOYAGES. 



at the height' of 7,016 meters. Thia was the minimum he observed. MM. 

 Barral and liixio 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 observa- 

 tion. The barometer for determining the height was of course furnished with 

 a thermometer intended to give the temperature of the mercury. This ther- 

 mometer 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 sup- 

 posed 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 ba- 

 rometer 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 meJ;eorolgy. The inventor had sent 

 one of his thermometers d minima with arbitrary divisions to our aeronauts, 

 and this was enclosed in a case with numerous holes to permit the circula- 

 tion of air. At the request of the two aeronauts, a seal was applied, and this 

 seal, which arrived untouched, was broken,/^ the College of France in the 

 presence of lilM. Regnault and Walferdin. Careful examination proved that 

 the minimum thermometer had sunk to — 39°. 7. After these precise obser- 

 vations 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 liugers 

 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 qualiiies it, whether by radia- 

 tion into space or from whatever other cause, to exhibit so prodigious a refrige- 

 ration ? It is a question Avhich at this moment we can do no more than pro- 

 pound. 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 1 The solution of these questions 

 is reserved for the future, which does not, however, at all diminish the import- 

 ance 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 Avith 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 



