16 WRITINGS OF JOSEPH HENRY. [1855- 



In the North Pacific Ocean, on the western side of our 

 continent, the great circle of water passes up along the coast 

 of Japan, re-crosses the ocean in the region of the Aleutian 

 Islands, mingles with the fitful current outward through 

 Behring's Strait, and thence down along the northwest coast 

 of North America. In this long circuit the northeastern 

 portion of it is much more cooled than the similar portion 

 of the whirl of the Atlantic. It therefore modifies the tem- 

 perature of the northwestern coast and produces a remark- 

 able uniformity along its whole extent, from Sitka to the 

 soutRern extremity of California. It is an interesting fact, 

 which we have just derived from Captain John Rodgers, that 

 an offshoot from the great whirl in the Pacific, analogous to 

 that which impinges on the coast of Norway, enters along 

 the eastern side of Behring's Strait, while a cold current 

 passes out on the western side, thus producing almost as 

 marked a difference in the character of the vegetation on 

 the two shores of the strait as between that of Ireland and 

 Labrador. 



4. The effect of prevailing currents of air on the climate of 

 difierent portions of the earth is no less marked than that 

 of proximity to the sea. We have seen that on one side of a 

 line over which the sun passes, a current of air flows from 

 the northeast, and on the other from the southeast, giving 

 rise to the trade winds. These winds ascend obliquely, and 

 according to the views of Dove and others, rise to the upper 

 regions of the atmosphere, flow backward towards the poles, 

 and partaking of the rotary motion of the earth, gradually 

 turn to the eastward and approach its surface, producing a 

 series of whirls overlapping each other entirely around the 

 globe. Whatever may be the cause however of the phe- 

 nomena, Professor Coffin, in his admirable paper on the 

 winds of the northern hemisphere, has shown that from the 

 equator to the pole the whole space is occupied by three 

 great belts, or zones, of prevailing wind: the first extends 

 from the equator to an average latitude of 35° north, in 

 which the current is from the northeast, constantly growing 

 less intense as we approach the northern limit ; the second 



