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whose effect on temperature and evaporation, as already noticed, is 

 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 Foehn wind of Switzerland, and similar currents are found on the 

 leeward sides of all extensive mountain ranges. Starting, it may be, 

 from the surface of the Pacific, or in the warm valleys of the western 

 slope, this aerial current is cooled and more or less completely deprived 

 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 arrives at 

 the foot even warmer than it started. The direct effect of this higher 

 temperature 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 w^arm, the change in temperature on 

 their account is not appreciable. Their effect on climate is to make the 

 region they i'requent of higher average winter temperature than in the 

 center of the continent, as may be seen by the isothermal lines of any 

 climatic 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 sloi)es of the Eocky Mountains, 

 as compared with the western, is caused partly by the blasting, scorch- 

 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, 

 no 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, cut 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 continuous 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 



