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whose effect on temperature and evaporation, as already noticed, fs 
so marked, are of such peculiar nature as to demand our especial ex- 
amination. They are the same as the Chinook winds of Montana and 
the Foebn wind of Switzerland, and similar currents are found on the 
leeward sides of all extensive mountain ranges. Starting, if may be, 

— from the surface of the Pacifie, or in the warm valleys of the western 
r slope, this aerial current is cooled and more or less completely deprived 
i of its moisture while climbing the mountains; and in sliding rapidly 
_ down on the other side, it becomes gradually warmed by compression, 
~ amounting to six or seven degrees for each thousand feet, and arrivesat 
the foot even warmer than it started. The direct effect of this higher 
i temperacure is to increase its capacity for holding moisture, and having 
_ no means in its descent of regaining what was lost in the cool, rarefied 
region above, it is intensely dry and parched, increasing evaporation to 
— such an extent as to dry up small ponds and streams, and cause the 
snow to literally fade away. These winds are only noticed in cold 
- weather, for when the air is already warm, the change in temperature on 
_ their account is not appreciable. Their effect on climate is to make the 
region they frequent of higher average winter temperature than in the 
_ center of the continent, as may be seen by the isothermal lives of any 
 ¢limatie map of the United States. : 
‘ Their deleterious effect upon trees, besides the sudden changes of 
_ temperature, is more especially from their extreme dessicating power, 
which increases to an intense degree all the evils already described 
of rapid evaporation, acting on vegetation like fire. The barreness 
and somber appearance of the eastern slopes of the Rocky Mountains, 
_ as compared with the western, is caused partly by the blasting, secorch- 
ing effect of these winds on many of the native trees, not vigorous 
enough to stand the sudden drain on their vital forces. They also, 
ho doubt, play an important part in the treelessness of the western 
plains. 
In general it is found that they harden and dry the fruit on the side 
exposed to them, blacken, char, and curl up the young and tender 
_ leaves, cnt off the fragrance of odorous plants, and kill young sprouts 
_ in a few hours. 
The winds of the greatest velocity in this region are from the north 
and northwest. The strongest wind that has ever occurred at Colorado 
Springs was from the northwest, in January, 1887. It began at about 8 
_o’clock in the morning, and gradually increasing in power, until at noon 
_its velocity was 72 miles per hour, it died away entirely by 4 o’clock 
in the afternoon. But these extreme winds only come two or three 
times a year, and a velocity exceeding 40 miles per hour is very rare. 
The destructive tornadoes of lower elevations are unknown, and this 
region is not subject to the continuons gales found elsewhere. This is 
demonstrated by the average yearly wind-velocity shown by the table, 
which is only 6.3 miles per hour. And this figure does not properly 









