414 
POPULAR SCIENCE REVIEW. 
78 at 3,000 feet; decreased to 73 at 6,000 feet, and then 
gradually to 22 at 21,000 feet. The law of moisture shown in 
cloudy states of the sky, was therefore a slight increase from 
the earth, to 3,000 feet high ; then a slight decrease to 6,000 
feet, the degree of humidity at this elevation being nearly of 
the same value as on the ground — from 6,000 to 7,000 feet 
there was a large decrease, and then an almost uniform decrease 
to 11,000 feet. 
On the contrary, with a clear sky, on the ground the 
number found was 59, increasing to 71 at 3,000 and 4,000 feet ; 
then decreased to 50 at 9,000 feet high ; and much smaller on 
ascending higher, to 16 only at 23,000 feet. 
The law of moisture here showm, is a shght increase from the 
ground to 1,000 feet high, a considerable increase between 
1.000 and 2,000 feet ; a nearly constant degree of humidity 
from 2,000 to 5,000 feet, and then a gradual decrease to 
12.000 feet. At greater heights the air is very dry. 
By comparing the results as found from the two states of the 
sky together, the degree of humidity of the air, up to 1,000 
feet, was 15 less with a clear sky than with one covered by 
clouds ; from 2,000 to 5,000 feet it is from four to six less ; at 
6.000 feet the air with a clear sky is much dryer than at 5,000 
feet, 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. Above 12,000 feet the air, 
with clear skies, generally becomes very dry, but with cloudy 
skies frequently becomes more humid, as was to be expected 
from the presence of clouds at the height of three and four 
miles. 
In both states of the sky at heights exceeding four and five 
miles the air becomes very dry — the amount of water present 
being very small indeed ; but at the highest elevations I have 
been, there has always been some water present — I never 
found the air free from water. At the same elevations the 
results of experiments on different days were found to be 
very different ; and on the same day water was found to be 
very differently distributed, there having been met with several 
successive layers of dry and wet air placed one above the other. 
We do not profess in this article to go into minute details 
regarding all the subjects of research, because oim space is 
limited, and therefore pass several of the objects of inquiry 
to one of high interest. In the observations made on solar 
radiation, the sun is the great source of light and heat, and 
no observations ever had been made on the effects which the 
sun produces on black ened-bulb thermometers, freely ex- 
posed to his infiuence when beyond the influence of the 
earth. 
