roads during a gale of wind; and when placed under the microscope, it exhibited a greater proportion of fresh-water and marine formations than the former instances.  Phytolitharia were numerous, as also ‘neatly-lobed vegetable scales;’ which, as Ehrenberg observes, is sufficient to disprove the assertion, that the substance is formed in the atmosphere itself, and is not of European origin.  For the first time, a living organism was met with—­the ’Eunotia amphyoxis, with its ovaries green, and therefore capable of life.’  Here was a solution of the mystery:  the dust, mingling with the drops of water falling from the clouds, produced the red rain.  Its appearance is that of reddened water, and it cannot be called blood-like without exaggeration.

Again, in March 1847, a coloured snow fell in the Tyrol, presenting a most singular appearance, and, when dried, leaving behind a brick-coloured dust.  Most of the organised forms therein contained were European and American, with a few African; and again the microscope shewed it to be similar to the dust before examined, leaving no room to suppose it of local origin.  ’The predominating forms, numerically, of one kind of dust, are also the predominating forms in all the rest,’ as Ehrenberg observes; and says further:  ’Impossible as it is to conceive of all the storms now compared from 1830 to 1847, as having a continuous genetic connection, it is equally impossible also to imagine the masses of dust transported by them, with such a degree of similarity, not to have a genetic connection....  The great geographic extent of the phenomenon of a reddish dust nearly filling the atmosphere, and itself filled with organisms so similar, many of which are characteristic of South America, not only admits of, but demands a more earnest attention to the probable cyclical relations in the upper and lower atmosphere, whereby very great masses of fixed terrestrial matter, earths and metals, and especially flint-earths, chalk, iron, and coal, apparently heterogeneous, and yet related by certain peculiarities, are held swimming in the atmosphere, now like clouds thinly spread by whirlwinds or electricity over a broad space, and now condensed, and, like the dust of the fir-blossoms, falling in showers in every direction.’

Ehrenberg, then, states his views as to the cause of the phenomenon.  ’Although far from attaching undue weight to a hypothesis, I cannot but consider it a matter of duty to seek for a connection in the facts, and feel myself constrained—­on account of the above-mentioned particulars, and in so far as they justify a conclusion—­to suppose an atmospheric current, connecting America and Africa with the region of the trade-winds, and sometimes, particularly about the 15th and 16th of May, turning towards Europe, and bringing with it this very peculiar, and apparently not African dust, in countless measure.  If instead of attacking hypothesis by hypothesis, we strive with united effort to multiply scientific observations, we may then hope for a progressive explanation of these mysterious relations, so especially worthy of study.’