-1859] WRITINGS OF JOSEPH HENRY. 17 



is that from 35° to about 60°, the current from the west be- 

 ing more intense in the middle of the belt, and gradually- 

 diminishing on either side almost into a calm; third, from 

 60° to the pole, or rather to a point of greatest cold in the 

 Arctic regions, the wind is in a northeasterly direction. 



The first of these belts would constitute what is called the 

 trade winds, produced as we have said, by the combined ef- 

 fects of the heat of the sun and the rotation of the earth ; 

 the second is the return trade, and the third the current 

 which would be produced by an opposite eflfect to that of the 

 rarefaction of the air by the sun at the equator, namely, the 

 condensation of the air by the cold portion of the earth. 

 The air should flow out in every direction from the coldest 

 point, and combining its motion towards the south with 

 the rotation of the earth, it should take a direction from 

 the east to the west or become a northeasterly wind. 



The effects which these currents must have upon the 

 climate of the United States will be made clear by a little 

 reflection. The trade winds within the tropics, charged with 

 vapor, in their course towards the west impinging upon the 

 mountainous parts of South America, will deposit their 

 moisture on the eastern slope and produce a rainless district 

 on the western side. Again, a lower portion of the Atlantic 

 and Gulf trade wind will be deflected from these mountains 

 along the eastern coast of the United States and through 

 the valley of the Mississippi as a surface wind, and thus 

 give rise to our moist and warm summer breezes from the 

 south, while the principal or upper portion of the trade 

 wind (or the return westerly current) sweeping over the Pa- 

 cific Ocean, and consequently charged with moisture, will 

 impinge on the Coast Range of mountains of Oregon and Cal- 

 ifornia, and in ascending its slopes deposit moisture on the 

 western declivity, giving fertility and a healthful climate to 

 a narrow strip of country bordering on the ocean and steril- 

 ity to the eastern slope. All the moisture however will not 

 be deposited in the passage over the first range, but a por- 

 tion will be precipitated on the western side of the next, 

 until it reaches the eastern elevated ridge of the Rocky 

 2-2 



