344 
CLINE. 
Ferrel,* and others we have learned that saturated air 
while ascending cools at the rate of about one degree Fahren¬ 
heit in each four hundred feet elevation f instead of one de¬ 
gree in about one hundred feet, as is the case with dry air. 
The reduction of temperature in ascending moist air is com¬ 
pensated about one-half by the heat liberated in the con¬ 
densation of moisture resulting from cooling in the ascent. 
According to Dr. Hann,t one-half of the vapor of the at¬ 
mosphere is below an elevation of 6,000 feet and eight-tenths 
is below 15.000 feet; hence we can readily see how small 
an amount of moisture can be retained by the atmosphere 
after crossing a mountain range with an altitude of 10,000 
to 15,000 feet. The Central Pacific railroad officials have 
kept records of the precipitation along the main line of their 
road from Sacramento to the summit pass for several years. 
On the result of these records it is stated § that the annual 
precipitation increases at the rate of one inch for every one 
hundred feet altitude; that at the summit pass the mean 
annual precipitation exceeds ninety inches, and that it is 
not improbable that this amount is considerably exceeded 
along the crest of the range. Eight tenths of the moisture 
of our atmosphere is below the crest of those mountains, 
and air in passing over them loses a large percentage of 
this moisture. This dry air, in descending over the eastern 
slope, after having dissipated the cloud carried over, gains 
temperature dynamically nearly twice as rapidly, in a cor¬ 
responding distance, as it cooled in ascending the western 
slope. In moving toward the low pressure area this dry air 
takes up the circulation around that area, is carried over 
* Recent advances in meteorology; being Appendix 71 to Annual report 
of the Chief Signal Officer. 8°. Washington, 1886; part 2. 
f This is the rate when pressure = 30 inches and temperature = 67° ; 
or p = 25 inches and t = 60°; or p = 20 inches and t = 53°. 
X Distribution of Aqueous Vapor of Atmosphere with Increase of Alti¬ 
tude. Zeitschrift Oest. Met. Gessell., 1874, pp. 193 to 200, IX. 
$By Capt. C. E. Dutton, in American Journal of Science. 8°. New 
Haven, 1881; October; no. 130; 3d series, vol. 22, p. 248. 
