Scientific Intelligence — Meteorology. 8TS 



3. Note on the Atmospheric Dust which fell at Genoa on 16tA 

 of May, 1846. (Extract of a Letter from M. Ehrenberg to M. F. 

 J. Pictet.) — We have given, in the 6th Number of the Archives (vol. 

 ii. p. 87) some details respecting an atmospheric dust which fell at 

 Genoa after a storm, on the 16th May 1846. I perceived in it 

 many carapaces of infusoria, and I therefore hastened to send a spe- 

 cimen to M. Ehrenberg, as the most competent observer of all that 

 relates to the history of microscopic animals. This expert mico- 

 grapher instantly examined it, and transmitted to me the following 

 details resulting from his investigation. F. J. P. 



•' Immediately after receiving the atmospheric dust, or powder of 

 Genoa, which you sent me, I examined it, and have found it very 

 interesting. My observations have not yet been very numerous, 

 but they have been made with care, and have enabled me to recog- 

 nise in the dust 46 species of minute organisms. It is ferruginous, 

 as the colour indicates ; the iron probably arises from the gaUionel- 

 les, which are very numerous in it. The form of this dust, its 

 colour and composition, render it in every respfect identical with that 

 which fell in the Atlantic Ocean, near Cape de Verd Islands, and 

 with that which was collected at Malta in 1834. But it is not only 

 the colour, form, and composition in general which are identical in 

 the dusts collected in these different times and places; the same 

 species which predominate in the one, likewise predominate in the 

 other. It appears natural to suppose that these sands come from 

 Africa ; however, they contain not only continental forms, but also 

 very distinct marine organisms. The Diploneis, for example, are 

 abundant in all these dusts, and in all seas, but have not been 

 hitherto found in any fresh water, properly so called. The dust of 

 Genoa, like the rest, contains many forms special to South America, 

 and wants, on the contrary, such as are peculiar to Africa, 



** It appears to me always more and more evident that the dust 

 of the Sirocco is a phenomenon more extensive and general than is 

 supposed, and deserves to be studied with great care- Does it come 

 from America % Has it its origin in Africa ? These are questions 

 which can be answered only after numerous observations. 



** Such, Sir, are the facts which I can at present communicate to 

 you respecting the dust you have sent me. By continuing my re- 

 searches, it is probable that I shall see the number of organic forms 

 increase still more. I wished to delay no longer in assuring you 

 that the present subject is one of great interest, and that it is very 

 important that the phenomena connected with it should be carefully 

 observed." 



Similar dust has been collected at Malta, Cape de Verd Islands, 

 and in the Atlantic Ocean, as far as 800 8ea miles from the west 

 coast of Africa. I have seen specimens collected in the years 1830, 

 1834, 1836, 1838, 1846. They are all so identical, that one would 

 believe they had been taken from the same packet. 



