286 WRITINGS OF JOSEPH HENRY. [1855- 



causes, which would bring the warm air of this stream to 

 our shores, it is cooled by crossing the cold current we have 

 mentioned, which reduces its temperature to the dew-point, 

 and produces the peculiar chilly effect so familiar to the 

 inhabitants of the Eastern States during the prevalence of a 

 northeast storm : while on the Pacific coast the west winds 

 from the ocean cross the comparatively cool current from 

 the north and impart their mild and uniform temperature 

 to the western slope of the Coast Range of mountains, giving 

 rise to the remarkable fact of the summer temperature being 

 the same for hundreds of miles in a north and south direc- 

 tion. 



Were the whole of North America — from the Atlantic to 

 the Pacific — a continuous plain, or were the surface diversi- 

 fied merely by eminences of comparatively small elevation, 

 the moisture from the Pacific would be carried into the in- 

 terior, and a much greater degree of fertilit}' in the western 

 portion of the Valley of the Mississippi would exist. In 

 the actual condition of the continent however, the westerly 

 wind which passes over the great mountain sj^stem extend- 

 ing from north to south along the western portion of the 

 continent, deposits its moisture principall}'^ on the western 

 slope of the Coast Range, and gives fertility and a mild 

 climate to California, Oregon, Washington, and particularly 

 to the regions farther north. The amount of rain which 

 falls at Sitka, Russian America, amounts in some years to 

 60 inches. The remaining moisture which this westerly 

 wind may contain is precipitated on the western slopes of 

 the high ridges farther east, and when the current has 

 passed over the whole Rocky Mountain sj'&tem, it is almost 

 entirely dessicated, and leaves the elevated plains east of the 

 Rocky Mountains an arid region, so deficient in moisture as 

 to be unfit for cultivation, unless by the aid of irrigation, 

 with the exception of occasional oases, and along the borders 

 of streams. 



We have seen that two great systems of wind prevail over 

 the United States, the upper from the northwest and the 

 lower from the southwest. The latter carries the moisture 



