FALLS OF DUST ON THE ATLANTIC.

Globe, Volume XX, Issue 1540, 24 January 1879, Page 3

FALLS OF DUST ON THE ATLANTIC.

[From the “Times.”]

About the latitude of the Capo Verde Islands on the Atlantic, it is a frequent experience of voyagers to observe fulls of red dust and a dry kind of mist. The material of the dust mass was examined microscopically many years ago by Ehrenberg, and his opinion was that small particles carried aloft from all countries here formed a transparent dust zone, from which they sometimes sank down, and in whirling movement came to the earth’s surface. The material of observation open to Ehrenberg was somewhat scanty. The phenomenon has, therefore, been late'y studied |anow, and in a more thorough way, by Herr Hellraann, who examined the logbooks of 1196 ships that had passed through the region in question during the years 1854 to 1871. He deals with the case chiefly from a meteorological point of view, and the following are some of the facts elicited. Most of the dust-falls occur in the zone of the Atlantic between 9deg. and 16deg. N, South of 6deg. N. they are extremely rare, and the furthest south hitherto was in 2.56 N., 26 W. The two farthest west were both in 38.4 W., both about 300 miles from Cape Verde. Dustfalls often occur simultaneously at very different points of the “ Dunkel Meer,” or Dark Sea (as Ehrenberg called it) ; in one case they were 150 miles apart. They also often last for several days, e.g., ten (April, 1850). Surfaces of very different size, up to 100,000 square miles, may receive dust-falls. There is a yearly period in the frequency of the falls. It seems that near the African coast most occur in winter; further west in the early spring. Tho direction of the wind during dust falls was from the east quadrant, and most frequently N.N.E. to N.E. The dust falls observed are very irregularly distributed over the years in question. Of 63, taken at random, there were eight falls of sand, three of sand or dust. Sometimes sand and dust fall simultaneously. The duet falls with great extent east and west are denser the nearer the African coast. In 40 out of 65 instances the color of the dust was red. Sometimes there is no colouration. The dry mist of tho Dark Sea is in casual connexion with the dust-falls. Herr Heilman concludes from the facts that the dust material comes principally from Africa and from tho Western Sahara. Tho possibility of occasional mixture of particles from South America is not excluded. The distribution of the dustfalls both in space and in time (they follow the movements of tho trade winds), supports the hypothesis, as also does tho fact that tho falling material is coarser in the east than in the west.