§ 358. EASTING OF THE TKADE-WINDS, ETC. I57 



Mississippi, Tennessee, Missouri, Indiana, and Ohio ; and, subse- 

 quently, from Colonel W. A. Bird, Buffalo, New York, who says, 

 " The southwest winds are our fair-weather winds ; we seldom 

 have rain from the southwest." Buffalo may get much of its rain 

 from the Gulf Stream with easterly winds. But I speak of the 

 Mississippi Yalley ; all the respondents there, with the exception 

 of one in Missouri, said, "The southwest winds bring us our rains." 

 These winds certainly can not get their vapors from the Eocky 

 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 drv. These winds, that feed the 



7 »/ 7 



sources of the Mississippi with rain, like those between the same 

 parallels upon the ocean, are going from a higher to a lower tem- 

 perature ; and the winds in the Mississippi Yalley, 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 dep®sit. Therefore, though it may be 

 urged, inasmuch as the winds which brought the rains to Patago- 

 nia (§ 355) 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 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 Missis- 

 sippi Yalley, it was not perceived why the Patagonian rain winds 

 should not bring their moisture by a similar route. These last are 

 fi'om the northwest, from warmer to colder latitudes ; therefore, 

 being once charged with vapors, they must precipitate as they go, 

 and take up less moisture than they deposit. The circumstance 

 that the rainy season in the Mississippi Yalley (§ 355) alternates 

 with the dry season on the coast of California and Oregon, indi- 

 cates that the two regions derive vapor for their rains from the 

 same fountains. 



358. During the discussion of this subject, my friend Baron von 

 Ehrenberg and his Grcrolt, the Prussiau minister, had the kindness to 

 microscope. ^^^^^ ^^ ^^ ^^^^ Ehreubcrg's work, " Passat-Staub 



und Blut-Regen." Here I found another clew leading across the 

 calm places. That celebrated microscopist reports that he found 

 South American infusoria in the blood-rains and sea-dust of the 



