116 THE PHYSICAL GEOGRAPHY OF THE SEA. 



The same process of reasoning which conducted us (^ 203) 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. 



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

 east, then we should have reason to suppose that their 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. 



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

 Missouri, Indiana, and Ohio ; and they all, with the exception of 

 one person in Missouri, said, " The southwest winds bring us our 

 rains." 



215. These winds certainly can not get their vapors from the 

 Rocky Mountains, nor from the Salt Lake, for they rain quite as 

 much upon that basin as they evaporate from it again ; if they did 

 not, they would, in the process of time, have evaporated all the 

 water there, and the lake would now be dry. 



These winds, that feed the sources of the Mississippi with rain, 

 like those between the same parallels upon the ocean, are going 

 from a higher to a lower temperature ; and these winds in the 

 Mississippi Valley, not being in contact with the ocean, or with 

 any other evaporating surface to supply them with moisture, must 

 bring with them from some sea or another that which they deposit. 



Therefore, though it may be urged, inasmuch as the winds 

 which brought the rains to Patagonia came direct from the sea, 

 that they therefore took up their vapors as they came along, yet 

 it can not be so urged in this case ; and if these wdnds could pass 

 with their vapors from the equatorial calms through the upper 

 regions of the atmosphere to the calms of Cancer, and then as 

 surface winds into the Mississippi Valley, it was not perceived 



