Meteorological and Astronomical Notices. 171 



To microscopic analysis, however, the contents wore invariably 

 found to bo mainly organic, partly flint-shelled polygastric infusoria, 

 partly fragments of flint earth plants (JPhytolitharia)^ partly car- 

 bonaceous but uncarbonised fragments of other plants, and partly 

 chalk-shelled Polythalamia ; the Polygastrica and Phytolitharia evi- 

 dently giving the flint earth, the Gallionella the iron and probably 

 the manganese, and the Polythalamia the carbonic acid chalk earth. 



In nine specimens of dust gathered at very difi^erent places and 

 times, but of very similar constituents, there were found the follow- 

 ing number of species : — 



Polygastrica, 



Phytolitharia, 



Polythalamia, 



Particulse plantarum molles, 



Insectorum fragmenta, 



67 



46 



8 



7 



1 



119 



Evidently, then, this was not volcanic dust, and it had moreover 

 no symptoms of having been exposed to volcanic action. 



And again, it could not be fine sand from African deserts, for 

 there was so great a .preponderance of fresh-water forms ; and while 

 there were many of them which were common to many parts of the 

 world, there were none which were peculiar to Africa, but there was 

 a large proportion which were peculiar to South America. 



Of the above-mentioned 119 forms, 8 Polythalamia, 7 Polygastrica, 

 and 2 Phytolitharia, only, belong to sea-water, the rest appertaining 

 to fresh-water ; among which the following are forms indigenous and 

 peculiar to South America : — 



Arcella constricta. 

 Desmogonium Guayanense. 

 Eunotia Camelus. 



depressa. 



■ pileus. 



quaternaria. 



quinaria. 



Gomphonema Vibrio. 

 Himantidium papilio. 



Zygodon. 



Navicula undosa. 

 Stauroueis dilatata. 

 Suririella Peruana. 

 Synedra Entomon. 



From all these circumstances, Ehrenberg had been led to conclude, 

 altogether independently of Lieut. Maury, that there is some cur- 

 rent in the atmosphere, tending from tropical South America to 

 South-Western Europe, gathering dust and moistur*^ in the above- 

 mentioned regions, bringing them into the northern hemisphere, over 

 the NE. trades, and droppitig them on reaching the surface of the 

 earth in its course to the NE. Further, the sources of the Orinoco, 

 the " dned upland swamp regions,^' to which Ehrenberg was led for 

 the habitat of some of his infusoria, have been separately described 



