EXPLORATIONS OF THE UPPER ATMOSPHERE. 31.1 



careiully repaired in the workshops of the central establishment for 

 aerostation, its net being entirely renewed, and M. Besan^on had added 

 to it an equatorial band which increased its volume to 480 cubic meters. 

 The ascension was fixed for February 18 at 10 a. m. 



Besides the barothermograph of Eichard, which was hung freely 

 within the protecting basket, the Aerophile carried a thermograph 

 suspended in the interior of the balloon and an apparatus for taking 

 in air which had been contrived with the greatest care by M. Cailletet. 

 This exploration, the seventh one made by the French in the higher 

 regions of the atmosphere, had for its sponsor on this occasion Prince 

 Eoland Bonaparte, who had assumed the entire cost of the enterprise. 



At 10,15 a. m.,' during cold and foggy weather, the cord attaching 

 the aerostat to the ground was cut, and in less than a minute it had 

 disappeared in a dense fog. There was no delay this time in getting 

 news from it, for about the middle of the afternoon a dispatch arrived at 

 Paris informing MM. Hermite and Besangon that their balloon had 

 descended near Chaulnes, at Meharicourt, in the department of the 

 Somme, 105 kilometers from Paris, at 12.30. But this time, also, the 

 material had been considerably damaged, having dragged nearly 5 

 kilometers over ground wet with rain. The silk was torn in several 

 places and the net frayed into shreds. Hapi)ily the diagrams were 

 intact. 



The scientific results of this experiment were as follows: 



The maximum height attained by the Aerophile was 15,500 meters, 

 as shown by the barogram. This height was reached at 11.30, about 

 an hour after the ascent from the gas works of La Villette. The 

 descent was effected very quickly, as was also the case at the noctur- 

 nal ascent of the 14th of November, and it is possible that this effect 

 was produced by a deposit, in the region of the cirri, of fine particles of 

 ice, which, accumulating on the dome of the aerostat, overcharged it 

 and caused its rapid fall. 



An examination of the curve traced by the style of the external ther- 

 mograph shows that the lowest range of temperature — 66O0., corre- 

 sponds not to the highest point of the ascent, but to a little before the 

 final descent; that is to say, to a pressure of 109 millimeters of mercury. 

 The curve of the registering thermometer hung within the balloon is no 

 less curious. It shows a rapid fall, as low as —22°, due to the simulta- 

 neous action of the expansion of the gas and the cooling of the exte- 

 rior. Then the temperature ascended during the descent of the balloon, 

 attaining -+-14° at the level of the ground. During the entire voyage, 

 therefore, the temperature of the gas was considerably above that of 

 the surrounding medium, and when the temperature of the outside was 

 at the minimum there was a difference of 46° C. between the air and 

 the interior of the Aerophile. This phenomenon was already known, 

 as we especially remarked it in our exi)eriment of August 12, 1896. 



The most important result of this experiment was the entire success 



