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4. -AM ACCOUNT OF THE FINE DUST WHICH OFTEN FALLS 

 ON VESSELS IN THE ATLANTIC OCEAN. 



By Charles Darwin, Esq., F.B.S., F.S.S. 



Many scattered accounts have appeared concerning the Dust which has 

 fallen in considerable quantities on vessels on the African side of the 

 Atlantic Ocean. It has appeared to me desirable to collect these accounts, 

 more especially since Professor Ehrenberg's remarkable discovery that the 

 dust consists, in considerable part, of Infusoria and Phytolitharia. I have 

 found fifteen distinct statements of Dust having fallen ; and several of 

 these refer to a period of more than one day, and some to a considerably 

 longer time. Other less distinct accounts have also appeared. I will here 

 only refer to the more striking ones, and make a few general remarks. 



The phenomenon has been most frequently observed in the neighbour- 

 hood of the Cape Verde Archipelago. The most southern point at which 

 Dust is recorded to have fallen is noticed by Captain Hay ward,* on whose 

 vessel it fell whilst sailing from lat. 10° N. to 2° 56' N. ; the distance from 

 the nearest of the Cape Verde Islands being between 450 and 850 miles. 

 Kespecting the northern limit, the water for a great distance on both sides 

 of Cape Noon (in lat. 38° 45') is discoloured, owing in part, according to 

 Lieut. Arlett,t to the quantities of falling Dust. Hence the phenomenon 

 has been observed over a space of at least 1,600 miles of latitude. This 

 Dust has several times fallen on vessels when between 300 and 600 miles 

 from the coast of Africa: it fell, in May, 1840, on the Princess Louise, ^ 

 (in lat. 14° 21' N., long. 35° 24' W.), when 1,030 miles from Cape Verde, 

 the nearest point of the continent, and therefore half-way between Cayenne 

 in South America and the dry country North of, the Senegal in Africa. 



On January 16th, 1833, when the Beagle was 10 miles off the N.W. end 

 of St. Jago, some very fine dust was found adhering to the under-side of 

 the horizontal wind-vane at the mast-head ; it appeared to have been 

 filtered by the gauze from the air, as the ship lay inclined to the wind. 

 The wind had been for twenty-four hours previously E.N.E., and hence 

 from the position of the ship, the Dust probably came from the coast of 

 Africa. The atmosphere was so hazy, that the visible horizon was only 

 1 mile distant. During our stay of three weeks at St. Jago (to February 

 8th), the wind was N.E., as is always the case during this time of the year; 

 the atmosphere was often hazy, and very fine Dust was almost constantly 

 falling, so that the astronomical instruments were roughened, and a little 

 injured. The Dust collected on the Beagle was excessively fine-grained, 

 and of a reddish-brown colour ; it does not effervesce with acids, and easily 

 fuses under the blow-pipe into a black or grey bead. 



In 1838, from the 7th to the 10th of March, whilst Lieut. James, in 

 H.M.S. Spey, was sailing, at the distance of from 330 to 380 miles from 

 the African continent, between lat. 21° 10' N., long. 22° 14' W., and lat. 



• Nautical Magacine, 1839, page 364. f Geographical Journal, vol. vi., page 296. 



t Ediiiburgh New Philosophical Journal, vol. xxxii., page 134. 



