Krakatoa by our knowledge of what has followed any other volcanic eruption; for the outburst at Krakatoa far exceeded in violence any event of the kind that is remembered in the history of man. Mr. W. J. Stillman, formerly United States consul in Crete, who has witnessed the explosions of two eruptions of the submarine volcano of Santorin, and has seen masses of rock weighing many tons thrown from a half a mile to a mile, and escaping gases expanding, after two seconds, into huge masses of cloud, at an elevation of from six to ten thousand feet, and then drifting away with the wind and dropping volcanic dust in its course, believes that on the enormously greater scale of the Krakatoa explosions the dust could have been thrown to the top of the atmosphere, there to drift over the whole earth; and he suggests that at such a height the distribution might be effected in twenty-four hours by a single revolution of the earth. Mr. Proctor's second difficulty is met by Messrs. Preece and William Crookes, who suggest that very finely divided particles of dust having an electrical charge of the same sign as that of the earth, may be kept suspended in the upper air for an indefinite period, by electrical repulsion; and Dr. Crookes adduces experiments showing how similar things have been done with electrified gold-leaf. Professor S. P. Langley contributes some interesting testimony on this point, which is based upon his observations on Mount Whitney, in 1881. On this mountain, from a height of twelve thousand feet, "we looked down," he says, "on what seemed a kind of level dust-ocean, invisible from below, but whose depth was six or seven thousand feet. . . . The color of the light reflected to us from this dust-ocean was clearly red, and it stretched as far as the eye could reach in every direction, although there was no special wind or local cause for it. It was evidently like the dust seen in mid-ocean from the Peak of Teneriffe—something present all the time, and a permanent ingredient in the earth's atmosphere. At our own great elevation the sky was of a remarkably deep violet, and it seemed at first as if no dust was present in this upper air, but in getting, just at noon, in the edge of the shadow of a range of cliffs which rose twelve hundred feet above us, the sky immediately took on a whitish hue. On scrutinizing this through the telescope, it was found to be due to myriads of the minutest dust-particles. . . . It is especially worth notice that, as far as such observations go, we have no doubt that the finer dust from the earth's surface is carried up to a surprising altitude. I speak here, not of the grosser dust-particles, but of those which are so fine as to be individually invisible, except under favorable circumstances, and which are so minute that they might be almost an unlimited time in settling to the ground, even if the atmosphere were to become perfectly quiet." Professor Langley thinks that the explosion of Krakatoa may have added millions of tons to the dust-envelope of the globe, and that the new contribution is not likely at once to fall to the surface again.
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GREEN SUNS AND BED SUNSETS.