240 BOARD OF AGRICULTURE. 



clouds visiting this region have before been robbed of their mois- 

 ture. 



The portions of the earth where rainfall is frequent are those por- 

 tions over which the variable winds prevail, and hence embrace 

 the temperate regions. Upon this division of my subject I need 

 not dwell at length, for we are all acquainted with the character 

 of the rainfall in our own latitude. We know, moreover, that we 

 are largely dependent upon our southerly and northeasterly winds 

 for rain. Why is this ? These winds come to us charged with 

 moisture from the Atlantic ocean, and hence the rain that accom- 

 panies them. How is it with our westerly winds ? They come to 

 us after having blown over a large extent of land, and consequent- 

 ly they are dry winds. So we look for a storm when the wind is 

 from the northeast, east or south, but not when it is west. I was 

 told by a gentleman to-day, that in a region he visited in the 

 West, just a little east of the Rocky Mountains, a southerly wind 

 does not bring rain. He thought it very strange when he first 

 noticed the fact. He looked for a storm when the wind was 

 south, and the weather was quite as likely to be dry as wet. For 

 a very good reason, a southerly wind there must have blown over 

 a very large extent of land before reaching that locality. 



The rain of the southern part of the United States is due t« 

 moisture from the Gulf of Mexico, the southwest return trade 

 winds serving as carriers for the vapor-bearing clouds. 



The principal rainless region of the globe commences on the 

 western coast of Africa, and extends 1200 miles iu width, across 

 the northern part of Africa, over the Red Sea, over Arabia and 

 Persia, nearly to the Indies, and is continued north of the 

 Himalaya mountains, over the highlands of Thibet, the Desert of 

 Gobi, and part of Mongolia. On the western continent, the prin- 

 cipal desert region is that of Atacama, west of the Andes, and is 

 700 miles iu length. What is the reason that these regions are 

 desert ? The region north of the Himalaya is desert from the fact 

 that when the southwest monsoon prevails and brings vapor- 

 charged clouds to the mountains, those clouds are unable to pass 

 over and still retain their moisture, but ascending the slopes they 

 are chilled by the cold of elevation, and tlieir condensed vapor is 

 poured down the southern side. When the winds pass over, they 

 are consequent!}' dry winds, and of such a character they must 

 ever remain on the north side of the Himalayas. The same is 

 true of the desert region west of the Andes. The winds that come 



