338 AERONAUTIC VOYAGES. 



ascended. At the moment of his departure the barometer registered 765.25 

 millimeters, and the thermometer +27°. 75; at the greatest elevation these 

 instruments gave 328.8 millimeters for the pressure, and —9°. 5 for the tem- 

 perature. It results that Gay Liissac 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. Plair hygrometers are instruments whose indica ions are so little 

 comparable with one another that it is impossible to deduce precise conclu- 

 sions 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 him- 

 self 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 respi- 

 ration was sensibly embarrassed ; but I was still very far from experiencing a 

 degree of inconvenience Avhich 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 impoi'tance. 



In reporting to the Academy of Sciences an account of the first exciirsion 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 pro- 

 posed to determine the law of the decrease of temperature with the height ; the 

 law of the diminution of humidity; to ascertain whether the chemical composi- 

 tion 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 sur- 

 face 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 I'ght reflected 

 and transmitted by clouds is or is not polarized, &;c. 



The instruments necessary for so interesting an expedition had been pre- 

 pared 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 Avere 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 ];rocured by 

 f 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. 



