304 EXPLORATIONS OP THE UPPER ATMOSPHERE. 



Besides obtaining the temperature of atmospheric spaces, it was con- 

 sidered desirable to bring down in a special receptacle a certain quan- 

 tity of air taken in at the highest point of the ascension, 12,000 to 15,000 

 meters. As early as the beginning of 1896, M. Hermite tried to solve 

 this difficult problem, and the Aerophile that was released on the 22d 

 of March from the gas works of La Villette and that landed near Cam- 

 brai, after having reached a height of 14,000 meters, and having been 

 subjected to a cold of —63° C, carried an automatic apparatus for taking 

 in air, which, unfortunately (probably because of the low temperature), 

 gave no result. The reservoir, in which a vacuum had been made pre- 

 vious to the ascent, was to have been opened at the highest point by 

 means of the action of sulphuric acid on chlorate of potash. The res- 

 ervoir once filled, a continuation of the same action was to hermetically 

 seal it by melting and closing the tube for ingress of air, and thus the 

 air of the higher regions might be brought down and analyzed. 



In succeeding experiments, following the advice of M. Cailletet, M. 

 Hermite changed the arrangement of his apparatus, and successively 

 used a cock moved by clockwork adjusted before the ascent, a mixture of 

 paraffin and glycerin, and finally closure by means of a ball valve of a 

 quite novel character. After many disappointments and difficulties suc- 

 cessively overcome by dint of ingenuity and i)erseverance, the physicist 

 attained his end, his apparatus worked admirable, and we have now 

 ascertained the nature of the air in the higher regions, as will be seen 

 later on. 



Another problem, likewise very important, is tlie determination of the 

 actual altitude to which the recording balloon rises with the attached 

 instruments, for it is evident that the basis of any serious study of the 

 higher atmosphere must rest upon a knowledge of the law of the decrease 

 of barometric pressure with increase of altitude, a law which, when 

 scrutinized closely, is an evident corollary to the law of universal 

 gravitation. 



As a micrometer telescope had not proved successful, it became nec- 

 essary to devise another method, and M. Hermite was led to contrive 

 another apparatus, based upon the principle already employed in geodesy 

 for measuring the height of clouds, and which consists in observing a 

 moving point by means of two theodolites set on a previously deter- 

 mined base. But in practice this proceeding has a serious inconven- 

 ience, for the rapid displacement of the object prevents the observer 

 who watches the balloon at the telescope of the theodolite from noting 

 the azimuth and zenith distances and the time. An aid is necessary 

 for each of these, and it will be easily seen that if the operators are not 

 very well drilled they will embarrass each other and the observations 

 will fail. 



Hermite's dromograph is a sort of registering theodolite, with which 

 one may obtain a continuous automatic registration of the position of 

 the balloon as long as it remains visible by observing it behind the 



