GREEN SUNS AND BED SUNSETS. 603 



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 wit- 

 nessed 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 vol- 

 canic 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 atmos- 

 phere. 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-par- 

 ticles, 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 Lang- 

 ley 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. 



