The presence in these seeds of a large quantity of fatty matters and sugar, and especially of albuminoid matters (very nutritive), largely justifies the use made of them as a food. The innate instinct of the savage peoples of Africa has thus anticipated the data of science.—La Nature.
THE HEIGHT OF SUMMER CLOUDS.
A knowledge of the heights and movements of the clouds is of much interest to science, and of especial importance in the prediction of weather. The subject has therefore received much attention during recent years from meteorologists, chiefly in this country and in Sweden. In the last published report of the Meteorological Council for 1885-86 will be found an account of the steps taken by that body to obtain cloud photographs; and in the Meteorologische Zeitschrift for March last, M.M. Ekholm and Hagstrom have published an interesting summary of the results of observations made at Upsala during the summers of 1884-85. They determined the parallax of the clouds by angular measurements made from two stations at the extremities of a base of convenient length and having telephonic connection. The instruments used were altazimuths, constructed under the direction of Prof. Mohn, specially for measuring the parallax of the aurora borealis. A full description of these instruments and of the calculations will be found in the Acta Reg Soc. Sc. Ups., 1884. The results now in question are based upon nearly 1,500 measurements of heights; the motions will form the subject of a future paper. It was found that clouds are formed at all levels, but that they occur most frequently at certain elevations or stages. The following are, approximately, the mean heights, in feet, of the principal forms: Stratus, 2,000; nimbus, 5,000; cumulus (base) 4,500, (summit) 6,000; cumulo-stratus (base), 4,600; "false-cirrus" (a form which often accompanies the cumulo-stratus), 12,800; cirro cumulus, 21,000; cirrus, 29,000 (the highest being 41,000). The maximum of cloud frequency was found to be at levels of 2,300 and 5,500 feet.
Generally speaking, all the forms of cloud have a tendency to rise during the course of the day; the change, excepting for the cumulus form, amounting to nearly 6,500 feet. In the morning, when the cirrus clouds are at their lowest level, the frequency of their lowest forms—the cirro-cumulus—is greatest; and in the evening, when the height of the cirrus is greatest, the frequency of its highest forms—the cirro-stratus—is also greatest. With regard to the connection between the character of the weather and the height of the clouds, the heights of the bases of the cumulus are nearly constant in all conditions. The summits, however, are lowest in the vicinity of a barometric maximum. They increase in the region of a depression, and attain their greatest height in thunderstorms, the thickness of the cumulo stratus stretching sometimes for several miles. The highest forms of clouds appear to float at their lowest levels in the region of a depression. The forms of clouds are identical in all parts of the world, as has been shown in papers lately read by the Hon. R. Abercromby before the English and Scottish Meteorological Societies.—Nature.
ON THE CAUSE OF IRIDESCENCE IN CLOUDS.
By G. JOHNSTONE STONEY.
When the sky is occupied by light cirro-cumulus cloud, an optical phenomenon of the most delicate beauty sometimes presents itself, in which the borders of the clouds and their lighter portions are suffused with soft shades of color like those of mother-of-pearl, among which lovely pinks and greens are the most conspicuous. Usually these colors are distributed in irregular patches, just as in mother-of-pearl; but occasionally they are seen to form round the denser patches of cloud a regular colored fringe, in which the several tints are arranged in stripes following the sinuosities of the outline of the cloud.
I cannot find in any of the books an explanation of this beautiful spectacle, all the more pleasing because it generally presents itself in delightful summer weather. It is not mentioned in the part of Moigno's great Repertoire d'Optique which treats of meteorological optics, nor in any other work which I have consulted. It seems desirable, therefore, to make an attempt to search out what appears to be its explanation.