ON NINE BALLOON ASCENTS IN 1863 AND 1864. 



293 



before starting, the difference between that and the temperature of the air 

 being 17°, "which nearly gradually declined to 13° by the time 3000 feet 'was 

 gained. On descending the temperature was found to be nearly the same at 

 2300 feet as it was at 3000 feet ; the difference at the lower of these eleva- 

 tions was 14° ; on reascending the difference decreased till 3450 feet was 

 gained, then increased to 13° by 3540 feet ; on descending it remained nearly 

 the same ; on again ascending it differed very little also till 3050 feet was 

 reached, wliere it Avas also 13° ; the balloon then turned to make our down- 

 ward journey, when the difference decreased to 9° and to 8° by the time the 



ground was reached. 



Table VII. (continued.) 

 Twentieth Ascent. 



June 20. — The temperature of the dew-point was 55°-8 on the ground, 

 the difference between that and the temperature of the air being 10°-7, de- 

 clining very gradually till 4100 feet was gained, where the difference was 3g° ; 

 on descending it gradually increased to 2740 feet, it then being 4° ; on reiis- 

 cending the air again began to get moist, although at several points it seemed 

 inclined to get drier, but then went back to its moist state again ; at 4270 feet, 

 however, complete saturation was met with ; on descending it became drier in 

 the first 100 feet, remained about the same for 800 feet, then became moist 

 at 3200 feet ; became drier at 2700 feet, after which, with one slight exception, 

 it remained the same tiU the ground was reached, the difference then being 



June 27. — The temperatm-e of the dew-point was 46|° on the ground, 

 differed but little from 43° from 500 feet to 1500 feet high, was about 40|° 

 at 3000 feet, and 38° at 4000 feet; at about 4100 feet the air was more 

 moist, the difference between the temperatiires of the air and dew-point being 

 21° ; this difference increased till at SOOOfeet it was rather less than 4°, the hu- 

 midity being 86°. On descending the air became gradually drier, till at nearly 

 4500 feet the difference was 6°-2 ; the air then again became moist, for at 

 3600 feet it was 2|°, the air then began to get drier ; continuing to do so 

 tiU at 660 feet it was 10|° ; on reascending this difference very gradxially in- 

 creased till about 3650 feet, when it was 13° ; on reaching 3240 feet it had 



