MAGNETISM AND CIRCULATION OF THE ATMOSPHERE. I39 



of vapor. The St. Lawrence River carries off the excess. 2d. 

 The mean climate of the lake country is colder than that of the 

 Mississippi Valley, and therefore, as a general rule, the tempera- 

 ture of the Mississippi Valley is unfavorable for condensing vapor 

 from that quarter. 



361. It can not come from the Atlantic, Ibecause the greater 

 part of the Mississippi Valley is to the windward of the Atlantic. 

 The winds that blow across this ocean go to Europe with their 

 vapors ; and in the Pacific, from the parallels of California down 

 to the equator, the direction of the wind at the surface is from, 

 not toward the basin of the Mississippi. Therefore it seemed to 

 be established with some degree of probability, or, if that expres- 

 sion be too strong, with something like apparent plausibility, that 

 the rain winds of the Mississippi Valley do not, as a general rule, 

 get their vapors from the North Atlantic Ocean, nor from the Gulf 

 of Mexico, nor from the great lakes, nor from that part of the Pa- 

 cific Ocean over which the northeast trade-winds prevail. 



362. The same process of reasoning which conducted us (§ 342) 

 into the trade-wind region of the northern hemisphere for the 

 sources of the Patagonian rains, now invites us into the trade-wind 

 regions of the South Pacific Ocean to look for the vapor springs 

 of the Mississippi. 



363. If the rain winds of the Mississippi Valley come from the 

 east, then we should have reason to suppose that tlieir vapors 

 were taken up from the Atlantic Ocean and Gulf Stream ; if the 

 rain winds come from the south, then the vapor springs might, 

 perhaps, be in the Gulf of Mexico ; if the rain winds come from 

 the north, then the great lakes might be supposed to feed the air 

 with moisture for the fountains of that river ; but if the rains come 

 from the west, where, short of the great Pacific Ocean, should we 

 look for the place of evaporation ? 



Wondering where, I addressed a circular letter to farmers and 

 planters of the Mississippi Valley, requesting to be informed as to 

 the direction of their rain winds. 



364. I received replies from Virginia, Mississippi, Tennessee, 

 Missouri, Indiana, and Ohio ; and, subsequently, from Col. W. A. 

 Bird, Buffalo, New York, who says, " The southwest winds are 



