166 PHYSICAL aEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



the calms of Cancer, and then as siu-face winds into the Mississippi 

 Valley, it was not perceived why the Patagonian rain winds 

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

 from the north-west, from warmer to colder latitudes ; therefore, 

 being once charged mth vapours, they must precipitate as they go, 

 and take up less moistm-e 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, indicates 

 that the two regions derive vapom- for their rains from the same 

 fountains. 



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

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

 microscope. placc in my hand Ehrenberg's work, " Passat-Staub 



und Blut-Eegen." Here I foimd 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 

 Cape Yerd Islands, Lyons, Genoa, and other places (§ 325) ; thus 

 confirming, as far as such evidence can, the indications of our 

 observations, and increasing the probability that the general com'so 

 of atmosjDherical chculation is in conformity with the suggestions 

 of the facts gathered from the sea as I had interpreted them, viz., 

 that the trade- winds of the southern hemisj)here, after arri-vdng at 

 the belt of equatorial calms, ascend and continue in then' course 

 towards the calms of Cancer as an upper cul'rent from the south- 

 west, and that after passing this zone of calms, they are felt on 

 the surface as the prevailing south-west wuids of the extra-tropical 

 parts of our hemisphere ; and that for the most part, they bring 

 their moistm-e with them from the trade-wind regions of the 

 opposite hemisphere. I have marked on Plate YII. the supposed 

 track of the " Passat-Staub," showing where it was taken up in 

 South America, as at P P, and where it was found, as at S S ; 

 the part of the Hne in dots denoting where it was in the upper 

 cm-rent, and the unbroken hne where it was wafted by a smface 

 cmTcnt ; also on the same plate is designated the part of the South 

 Pacific in which the vapour-springs for the Mississippi rains 

 are supposed to be. The hands ((m^) point out the dkection of 

 the wind. Where the shading is light the vapour is supposed to be 

 carried by an upper cmTent. Such is the character of the cu'cum- 

 stantial evidence which induced me to suspect that some agent,, 

 whose office in the grand system of atmospherical circulation is 

 neither understood nor recognized, was at work in these calm. 



