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Page:Popular Science Monthly Volume 19.djvu/861

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one-hundred-days men, mostly composed of the students of the college, who had volunteered at the call of Governor Tod, of Ohio, in 1862. The company was ordered to Vicksburg as escorts to a cartel of exchanged prisoners, and Professor Young's health received injuries during the expedition from which he has never entirely recovered.

He returned to his native town of Hanover in 1865, to take the professorship of Natural Philosophy and Astronomy in Dartmouth College, the same which had been held by his grandfather, and his father, who died in 1858. He was connected with this institution until 1877. During this time he was actively engaged on several astronomical expeditions. He was a member of the party which, under the charge of Professor J. H. C. Coffin, observed the eclipse of August 7, 1869, at Burlington, Iowa. Professor Young had devoted himself with great assiduity to spectroscopic investigations, and he had charge of the spectroscopic observations of the party. It was there that he discovered the green line of the corona spectrum, and identified it with the "1.474" line of the solar spectrum. It may be observed that Professor Harkness also discovered the same line on the same occasion, at Des Moines, though, on account of the inferior power of his instrument, he did not identify it correctly. In the winter of 1870-'71 Professor Young was a member of the Coast Survey party which, under the charge of Professor Winlock, observed the eclipse of December 22d at Jerez in Spain. It was on this occasion that Professor Young made his interesting discovery of what is called the "reversing layer" of the solar atmosphere, giving a bright-line spectrum correlative to that of the ordinary dark-line spectrum of sunlight. This remarkable effect is thus described by Professor Young, in his new work on the sun: "At a total eclipse of the sun, at the moment when the advancing moon has just covered the sun's disk, the solar atmosphere of course projects somewhat at the point where the last ray of sunlight has disappeared. If the spectroscope be then adjusted with its slit tangent to the sun's image at the point of contact, a most beautiful phenomenon is seen. As the moon advances, making narrower and narrower the remaining sickle of the solar disk, the dark lines of the spectrum for the most part remain sensibly unchanged, though becoming somewhat more intense. A few, however, begin to fade out, and some even turn palely bright a minute or two before the totality begins. But the moment the sun is hidden, through the whole length of the spectrum, in the red, the green, the violet, the bright lines flash out by hundreds and thousands, almost startlingly; as suddenly as stars from a bursting rocket-head, and as evanescent, for the whole thing is over within two or three seconds. The layer seems to be only something under a thousand miles in thickness, and the moon's motion covers it very quickly."

In August, 1872, Professor Young was stationed at Sherman, Wyoming Territory, the summit of the Pacific Railroad, to make solar