Proximate Causes of certain Winds and Storms. 291 



1. The wind itself descends in part from the higher regions of the 

 atmosphere, and in part pours, with a temperature below 32°, over 

 the Rocky Mountains. 



i&. It is therefore extremely dry, and creates a brisk evaporation, 

 with a depression of temperature, through the absorption of latent 

 heat, by the vapor that is produced wherever it meets with water in 

 its passage. 



3. For the same reason — its extreme dryness — it brings no clouds 

 with it, nor except when it first bursts down upon the air, previously 

 resting upon the country east of the mountains, does it create any. 

 It is part of the great circulation, and has not, therefore, that vertigin- 

 ous motion, on a comparatively small scale, upon which the forma- 

 tion of clouds depends. The sky becomes of a deep blue, and the 

 radiation is immense. Is it wonderful, that under these circum- 

 stances, the mercury in the thermometer should suffer a great de- 

 pression — that the country west of Hudson's Bay, should be in win- 

 ter, perhaps, the coldest part of the world ? 



The west winds of summer are, like those of winter, originally 

 cold, and frequently continue so till they reach the Atlantic States ; 

 but when their velocity is small, passing over tracts of land intensely 

 heated by the sun's rays, they sometimes acquire the burning tempe- 

 rature of the torrid zone. 



The sudden changes, complained of in the climate of North Ame- 

 'ica, are almost exclusively changes from heat to cold. We have a 

 warm day ; the wind comes round to the north-west at night, and by 

 the next morning the earth, which was a mass of soft mortar in the 

 roads, has acquired the solidity of a rock. The reason of the dif- 

 ference that obtains between this country and Europe, in regard to 

 the suddenness and frequency of changes of temperature is, that 

 no where, except on the eastern coasts of America and Asia, can 

 powerful causes, such as those mentioned above, as concurring 

 to produce our coldest winter weather, be brought to exert their com- 

 bined action as suddenly and as frequently. The cold— bringing 

 north-west winds, are the natural winds of the country, which, after 

 vibrating through other quarters of the compass, show a constant ten- 

 dency to settle on that point. Here, as before, all depends upon 



our position and predominant winds. 



If the views taken in this paper are correct, and its arguments 

 sound, the peculiarities of our climate depend upon three things 

 the prevalence of westerly winds between the latitudes of 30° and 



i 



