ON NINE BALLOON ASCENTS IN 1863 AND 1864. 297 



"With a clear sky, tlie degree of humidity was — 



On the ground 59 from 9 experiments. 



At 1000 feet 61 „ 14 



2000 „ 70 „ 17 



3000 „ 71 „ 23 



4000 „ 71 „ 19 



5000 „ 69 „ 17 



6000 „ 02 „ 15 



7000 „ 56 „ 16 



8000 „ 50 „ 14 



9000 „ 50 „ 9 



10,000 „ 46 „ 18 



11,000 „ 43 „ 10 



12,000 „ 35 „ 8 



13,000 , 37 „ 7 



14,000 „ 37 „ 7 „ . 



15,000 „ 44 „ 5 „ 



16,000 „ 40 „ 5 



17,000 „ 39 „ 4 



18,000 „ 21 „ 2 



19,000 „ 36 „ 2 „ 



20,000 „ 33 „ 1 



21,000 „ 32 „ 1 



22,000 „ 21 „ 1 „ 



23,000 ,, 16 „ 1 „ 



The law of moisture here shown is a slight increase to 1000 feet, a con- 

 siderable increase between 1000 and 2000 feet, a nearly constant degree of 

 humidity from 2000 to 5000 feet, and a gradual decrease afterwards to 12,000 

 feet ; at greater heights the numbers are less regular. The results wp to 

 11,000 feet are based upon experiments varying from 10 to 23, and are most 

 likely very nearly true normal values ; at heights exceeding 12,000 feet the 

 n\unber of experiments have varied from 1 to 8, and no great confidence can 

 be placed in them. 



By comparing the results from the two states of the sky, the degree of 

 humidity of the air up to 1000 feet high is 15 less with a clear sky than with 

 a cloudy ; from 2000 to 5000 feet it is from 4 to 6 less ; at 6000 feet the air 

 with a clear sky is much drier than at 5000, but with a cloudy sky it is 

 nearly of the same degree of humidity, so that the difference between the two 

 states is large, amounting to no less than 11 ; tliis difference decreases to 

 at 9000 feet, but increases to 4 at 11,000 feet ; at heights exceeding 11,000 

 feet the air with clear skies generally becomes veiy dry, but with cloudy skies 

 frequently becomes more humid, as was to be expected from the fact of the 

 presence of clouds at heights exceeding 3 and 4 miles. 



In both states of the sky at extreme elevations the air becomes very dry, 

 but, so far as my experiments go, is never free from water. 



