MAGNETISM AND CIRCULATION OF THE ATMOSPHERE. I17 
why the Patagonian rain wmds should not bring their moisture by 
a similar route. These last are from the northwest, from w^armer 
to colder latitudes ; therefore, being once charged with vapors, 
they must precipitate as they go, and take up less moisture than 
they deposit. 
216. This was circumstantial evidence. No fact had yet been 
elicited to prove that the course of atmospherical circulation sug- 
gested by my investigations is the actual course in nature. It is 
a case in which I could yet hope for nothing more direct than 
such conclusions as might legitimately flow from circumstances. 
My friend Lieutenant De Haven was about to sail in command 
of the American Arctic Expedition in search of Sir John Frank- 
lin. Infusoria are sometimes found in sea-dust, rain-drops, hail- 
stones, or snow-flakes ; and if by any chance it should so turn out 
that the locus of any of the microscopic infusoria which might be 
found descending with the precipitation of the Arctic regions should 
be identified as belonging to the regions of the southeast trade- 
winds, we should thus add somewhat to the strength of the many 
clews by which we have been seeking to enter into the chambers 
of the wind, and to " tell whence it cometh and whither it goeth." 
It is not for man to follow the "wind in his circuits ;" and all 
that could be hoped was, after a close examination of all the facts 
and circumstances which these researches upon the sea have 
placed within my reach, to point out that course which seemed to 
be most in accordance with them ; and then, having established a 
probability, or even a possibility, as to the true course of the at- 
mospheric circulation, to make it known, and leave it for future 
investigations to confirm or set aside. 
217. It was at this stage of the matter that my friend Baron 
von Gerolt, the Prussian minister, had the kindness to place in my 
hand Ehrenberg's work, " Passat-Staub und Blut-Regen." 
Here I found the clew which I hoped, almost against hope, De 
Haven would place in my hands 216). 
That celebrated microscopist reports that he found South Amer- 
ican infusoria in the blood-rains and sea-dust of the Cape Verd 
Islands— Lyons, Genoa, and other places (§ 158), 
Thus confirming, as far as such evidence can, the indications 
of our observations, and increasing the probability that the general 
course of atmospherical circulation is in conformity with the sug- 
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