170 



Professor C. Piazzi Smvth's 



which M. Constant Prevost has pointed out. I only con- 

 clude as I began, by maintaining, that the existing causes 

 amply suffice, without its being necessary to have recourse 

 to a glacial era or period, to explain the fact generally ad- 

 mitted by geologists, namely, the successive appearance and 

 disappearance of the ancient glaciers. 



Meteorological and Astronomical Notices for December 1851. 

 By Professor C. PlAZZl Smyth, Astronomer- Royal for 

 Scotland. 



The Appendix to the second volume of the Observations of the 

 National Observatory at Washington has recently been received 

 here, and contains further interesting and important particulars with 

 reference to Lieutenant Maury's important generalization on the 

 motions of the atmosphere. 



The most crucial and convincing proof of the truth of the Lieu- 

 tenant's idea, that the trade-winds cross over into opposite hemi- 

 spheres at the pole, instead of returning to their own poles, was 

 mentioned in our last Notices, as being the fact of Ehrenberg having 

 ascertained that in rain falling on the west coast of North Africa, 

 and in Spain, certain dust had been dropped, which consisted mainly 

 of infusorial animalcules of South American origin ; this being pre- 

 cisely the direction which the trade- winds of the southern hemisphere, 

 after getting up exhalations of all kinds in their passage over South 

 America, should take on passing to the north of the equator. 



It now appears that Ehrenberg had had sent to him specimens of 

 this dust which had fallen at various periods between 1803 and 

 1849, and over various parts of NW, Africa, Spain, Portugal, 

 France, and Italy, with the adjacent seas. The dust was almost 

 always sent with the statement, that it was volcanic dust, or that it 

 was the fine sand of the African deserts ; while mere chemical ana- 

 lysis gave the following comparatively uninteresting and uninstruc- 

 tive table of contents : — 



10000 



