It had always been supposed, that the dust which traversed the Mediterranean was borne from the Great Sahara; but in a quantity collected on board the ship Revenge, at Malta, an infusoria peculiar to Chili was met with, which, with other characteristics, proved the dust to be the same as that observed on the Atlantic.  Their colour, too, was identical; while the Sahara is a ‘dazzling white sand:’  hence the dust brought across the Mediterranean by the sirocco was not peculiar to Africa.  The conclusion here arrived at was still further verified by another sirocco-storm in May 1846, which extended to Genoa, and bore with it a dust that ’covered the roofs of the city in great abundance.’  This, as was clearly ascertained, contained formations identical with those which had been collected off the Cape de Verd; and it was shewn that the dust-showers of the Atlantic, and those of Malta and Genoa, were ’always of a yellow ochre-like colour—­not gray, like those of the kamsin, in North Africa.’  The peculiar colour of the dust was found to be caused by iron-oxide; and from one-sixth to one-third of the whole proved to consist ’of determinable organic parts.’  In the following year, 1847, Ehrenberg had another opportunity of testing his conclusions, in specimens of dust which had fallen in Italy and Sicily in 1802 and 1813; the same result came out on examination; ’several species peculiar to South America, and none peculiar to Africa.’

Thus, omitting the two last-mentioned instances, there had been five marked falls of dust between 1830 and 1846; how many others passed without notice, it would now be impossible to ascertain.  The showers sometimes occur at a distance of 800 miles from the coast of Africa, and this region lies between the parallels of 17 and 25 degrees north latitude, and whence, as we have seen, they extend to the northern shores of the Mediterranean.  In the dust collected from these various falls, there have been found altogether nineteen species of infusoria; of which eight were polythalamia, seven polygastrica, and two phytolitharia, these chiefly constituting the flint-earth portion of the dust.  The iron was composed of the gaillonilla, and ’the carbonic chalk earth corresponded tolerably well to the smaller number of polythalamia.’  The uniform character of the specimens obtained at intervals over so long a course of years is especially remarkable.

To turn, now, for a few moments to the second phenomenon indicated in our title.  In October 1846, a fearful and furious hurricane visited Lyon and the district between that city and Grenoble, during which occurred a fall of blood-rain.  A number of drops were caught and preserved, and when the moisture had evaporated, there was seen the same kind of dust—­of yellowish-brown or red colour—­as that which had fallen in a dry state on the occasions already referred to.  The strictest pains were taken to ascertain that it was not the common dust swept from