GAY-LUSSACS ASCENT. 



299 



descended, and disappeared in the clouds beneath. They made ether 

 experiments, but descended without having obtained as accurate results as 

 had been anticipated. 



On the next occasion, however, every care was taken, and on 

 the 1 5th of September the important ascent was made by Gay-Lussac 

 alone. He fixed hanging ropes to the balloon with the view to 

 check the rotating movements, and having provided himself with all 

 necessary apparatus and two vacuum flasks to bring down some of the 

 upper air, the young man started. The barometer marked 30*66, the 



Fig. 296. The Nassau balloon. 



Fig. 297. The " Giant" balloon of M. Naclar. 



thermometer 82 (Fahr.). At an elevation of 12,680 feet Lussac perceived 

 that the variation of the compass was the same as on land. Two hundred 

 feet higher up he ascertained that a key held in the magnetic direction 

 repelled with the lower, and attracted with its upper extremity the north 

 pole of a needle. This experiment was repeated with the same result at an 

 elevation of 20,000 feet, which shows how the earth exercises its magnetic 

 influence. The temperature of the air was found to decrease in proportion 

 as the ascent up to 12,000 feet, where the reading was 47*3. It then 

 increased up to 14,000 feet by 6, and then regularly diminished again 

 as the balloon rose, till at the greatest elevation reached, 23,000 feet, 



