622 FALLS OF DUST IN THE ATLANTIC. 



17^ 43' N., long. 25° 54' W., considerable quantities of Dust fell on his 

 vessel. The Dust which fell on the 7th, was preceded by a thick haze, and 

 it is coarser than that which fell on the succeeding days. It contains 

 numerous irregular, transparent, variously-coloured particles of stone about 

 1-lOOOth of an inch square, with some few a little larger, and much fine 

 matter. The fact of particles of this size having been brought at least 330 

 miles from the land is interesting, as bearing on the distribution of the 

 sporules of cryptogamic plants and the ovules of Infusoria. The Dust 

 which fell on the three succeeding days resembles in appearance, and in 

 its action under the blow-pipe, that collected by myself o£f St. Jago, and 

 is so excessively fine, that Lieut. James was obliged to collect it with a 

 sponge moistened with fresh water. As the wind continued nearly in the 

 same direction during the four days, and the distance from the land was 

 only a little increased after the first day, it would appear probable that the 

 coarser Dust was raised by a squall with which the breezes on this coast 

 so often begin blowing. 



With respect to the direction of the wind during the falls of Dust, in 

 every instance, where recorded, it has been between N.E. and S.E. ; 

 generally between N.E. and East. In the case, however, given by the 

 Rev. W. Clarke,* a hazy wind which had blown for some time from East 

 and S.E., first fell calm, and was succeeded for a few hours by a S.W. 

 wind, and then returned strongly to the East ; during this whole time Dust 

 fell. With respect to the time of year, the falls have always occurred in 

 the months of January, February, March, and April; but in the case of 

 the Frincess Louise, in 1840, as late as May 9th. In the year 1839, Dust 

 was recorded as having fallen in the Atlantic on January 14th and 15th, 

 and on February 2nd, 4th, 9th, 10th, 11th, 12th, and 13th. I may add, 

 that Baron Eoussin,f during his survey of the north-western African coast, 

 found that, whilst the wind keeps parallel to the shore, the haze and 

 Dust extend seaward only a short distance ; but when during the above 

 four specified months, the Harmattan blows from the N.E. and E.N.E.,. 

 accompanied by tornados, the Dust is blown far out, and is raised on high, 

 so that stars and all other objects within 30° of the horizon are hidden. 



Another account is given by Mr. George Peacock, as having occurred 

 on board H.M.S. Winchester, in February, 1829 : — " Shortly after leaving 

 Tenerife, when in about lat. 25° 30' N., and some 250 miles from the coast 

 of the Great Desert of Sahara, the weather became very hazy and sultry, 

 and one morning, at daylight, the lays of the lower rigging were obser\'ed 

 to be filled with fine, reddish-brown Dust, and the decks, whilst being 

 washed, were in as muddy a state as the pavement of a street after a 

 shower. This hazy unpleasant weather continued all day, and quite ob- 

 scured the horizon, rendering it difficult to observe even the crest of the 

 waves beyond a few cables' lengths, and the sun appeared as viewed 

 through the red shade-glass of a sextant. Towards evening it grew worse, 

 the wind became light, and the haze was almost as dense as a London 

 November fog, the air full of fine red Dust, which made it difficult to breathe. 



• Proceedings of the Eoyal Geographical Society, vol. iv., page 146. 

 t Nautical Magazine, 1838, page 824. 



