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Page:Popular Science Monthly Volume 24.djvu/623

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there seems little reason to doubt that the monsoon had carried the volcanic dust along with it, the dust obscuring the sun. The distance is nearly three thousand miles."

Dr. Budde, of Constantinople, was assured, when traveling in Southern Algeria in 1880, that the sun has a decidedly blue color when seen through the fine dust of a Sahara wind. Mr. Edward Whymper, remarking upon a metallic-green coloration of the moon, observed on some evenings in December, says that the peculiar hue recalled to him a similar appearance which he had witnessed in South America when the atmosphere was charged with volcanic dust; and he has described the colorings seen by his party under a cloud of ashes from Cotopaxi in language which would almost precisely apply to the diversified appearances that are the immediate subject of our discussion. Extremely brilliant colorations of the sky have been mentioned by several travelers as common spectacles in a particular tropical belt. Colonel Stuart Wortley, who spent the year 1862 in Southern Italy, in the study, by the aid of photography, of the formation of clouds, was struck with the unusual colors of the sunsets during and after the eruptions of Vesuvius with which that year was distinguished. Four years ago, while sailing in the Pacific, he was much impressed with the fact that "very frequently the whole vault of heaven was overspread with magnificent and glorious coloring, and that in the higher regions of the air colors were found that were never seen in the horizon or below a certain height." Inasmuch as this exceptional magnificence and peculiarity of coloring only occurs in certain latitudes and in well-defined belts, he suggests that, seen in the new light that is now cast on the subject, "the constant stream of volcanic matter thrown out by the great volcanoes in the mountain-ranges of South America, and possibly from elsewhere, form an almost permanent stratum of floating matter, carried in certain directions and kept in certain positions by alternating currents in the higher regions of the air, and that to this stratum of volcanic matter much of the exceptional coloring, found to be associated with sunrises and sunsets in portions of the Southern Pacific Ocean, is due." As an interesting coincidence in connection with this view may be noticed the extraordinary fact, to which Mr. Lockyer has called attention, that "before even the lower currents had time to carry the volcanic products to a region so near as India, an upper current from the east had taken them in a straight line via the Seychelles, Cape Coast Castle, Trinidad, and Panama, to Honolulu, in fact very nearly back again to the Straits of Sunda."

Very strong evidence in favor of the theory of the agency of volcanic dust has been derived from the examination of the sediment in freshly fallen snow at Madrid, Spain, on the 7th of December, and of the mineral matter deposited by a rain that fell at Wageningen, Holland, on the 13th of December. The sediment at Madrid, besides the ordinary atmospheric dust of the city, contained particles of what ap-