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 ca^e 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 winds 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 
