Page:Popular Science Monthly Volume 7.djvu/783

Rh of restoring their blighted vineyards. From a few rooted plants selected by Prof. Riley, and sent over four years ago to Gaston Bazille, then President of the Central Agricultural Society of Hérault, the demand increased each year, until in 1874 it reached many millions, and we have the curious spectacle of a large exportation of American vines to a country that has hitherto despised them as unworthy of culture. We see from some of the French papers that Prof. Riley has this summer revisited the south of France, and that he has found the American vines flourishing in the midst of the dying and dead French vines, and in the order of the varieties recommended four years ago. To testify their appreciation of his services, the Central Society of Agriculture of the department of Hérault held an extraordinary session at Montpellier, and gave a grand banquet at Palavas, in his honor.

Formation of Hail in the Spray of Yosemite Fall.—The American Journal of Science for September contains an interesting article, by Prof Brewer, on the formation of hail in the spray of the Upper Yosemite Fall, as observed by himself on the 14th of April last. This magnificent fall is 1,550 feet high, and at the time, the stream being swollen by rains and melting snow, leaped clear from the rocks into the air and was soon torn into spray. "It seemed," says the professor, "as mobile as smoke, and assumed new varieties of outlines each instant, so light and airy that it seemed as easily swayed by wind as lace, yet it struck with deafening thunder. The concussion was perceptible through the granite for some distance." The discharge of water was estimated at 250 to 300 cubic feet each second.

The water in winter falls behind a great cone of ice which forms from 100 to 200 feet in thickness, and emerging beneath the ice a grand arch is formed like that in the glacier at Mont Blanc, whence the Arveiron flows. Standing at the foot of this upper fall, a thousand feet above the bottom of the valley. Prof. Brewer and his companions felt, in the violent tempest of spray, ice-pellets or hail which stung their hands and faces like shot. They fell in considerable quantity, rapidly melting, for the sun shone full on the fall, and the rocks around reflected the heat. The diameter of some of the pellets was estimated at one-tenth of an inch.

Here we have the spray of the water-fall condensed and frozen into hail. The process by which this may occur is clearly stated by Prof Brewer.

The water, supplied from melting snow, plunges over the cliff at just about the temperature of freezing. "In the fall it appears to be 'atomized' for 1,200 or 1,400 feet of its descent. A great volume of air is drawn into this falling mass along its whole course, the sheet spreading as it descends. The quantity of air is so great that it pours outward on the bottom of the valley and is very perceptible as a cool current more than a mile distant from the base of the upper fall. The air as sucked into the fall is immediately cooled to 32° by the ice-cold water. As it passes in, it is very dry, and the rapid saturation within the sheet is sufficient to freeze a portion of the drops."

Distribution of Temperature on the Solar Disk.—From the researches of Prof Langley, referred to last month in the abstract of Secchi's observations on sun-spots, it appears that, though the nucleus of a spot is much cooler than the surface surrounding it, there is no great difference of temperature between it and the photosphere near the sun's limb, though the difference in brightness is so considerable. In fact, Mr. Langley has shown that the relatively black nucleus actually radiates more heat than the bright photosphere quite close to the limb. Following up this discovery, he has shown that the absorption of light, both in the case of a spot, and of the parts of the sun's surface near the limb, is not accompanied by a corresponding absorption of all the heat-rays (invisible as well as visible), so that, taking Sir W. Herschel's estimate of the brightness of the nucleus as $7/1000$ of that of the photosphere, Mr. Langley finds that we receive from a spot fifty times as much heat as light, and a similar conclusion is arrived at with reference to the surface near the limb. On comparing the equatorial and polar regions, no appreciable difference was observed in the heat received.