Page:Popular Science Monthly Volume 24.djvu/624

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606
THE POPULAR SCIENCE MONTHLY.

peared to be volcanic hypersthene, pyroxene, magnetic iron, and volcanic glass. At Wageningen, every drop of the rain that fell upon the windows left, when it dried up, a slight sediment of grayish-colored matter which was compared with original volcanic ash from Krakatoa that had been sent to the Agricultural Laboratory for analysis. Both the sediment and the volcanic ash were found to contain in common—1. Small, transparent, glassy particles; 2. Brownish, half-transparent, somewhat filamentous little staves; and, 3. Jet-black, sharp-edged, small grains resembling augite. These observations, say Messrs. Beyerinck and Van Dam, who made the analyses, "fortify us in our supposition that the ashes of Krakatoa have come down in Holland." On the 17th of November a fall of layers of gray and black dust took place at Storlvdal, Norway, and a fall of discolored rain near Worcester, England. Grayish sediments were found deposited on windows at Gainsborough and York, England, after a heavy rain on the 12th of December.

Mr. E. Douglas Archibald has suggested in "Nature" that, whether the cause of the phenomena be meteoric dust or volcanic ashes, the reflection arises from a definite stratum, and not merely from an atmosphere filled throughout with such dust. Professor Roujon, of Clermont, France, has also observed that two of the twilights, one following the other one day apart, "were so different in intensity as to provoke the supposition that the substance which produced them, at a great height, was not uniformly diffused, but moved in vast masses." This would serve to account for the variations that all must have observed in the brilliancy of the glow.

Mr. Edmund Clark has offered a suggestion upon which the theory that invokes the agency of aqueous vapor and the one which refers the manifestations to volcanic or meteoric dust may be combined, viz., that the dust may act as a nucleus for the condensation of any vapor that may exist at such a high level. The height of the mass of the matter producing the glow has been fixed by Miss Ley, of England, at thirteen miles.

 
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THE ANCESTRY OF BIRDS.
By Professor GRANT ALLEN.

SEATED on the dry hill-side here, by the belted blue Mediterranean, I have picked up from the ground a bit of blanched and moldering bone, well cleaned to my hand by the unconscious friendliness of the busy ants; and looking closely at it I recognize it at once, with a sympathetic sigh, for the solid welded tail-piece of some departed British tourist swallow. He came here like ourselves, no doubt, to escape the terrors of an English winter: but among these pine-clad