Page:Popular Science Monthly Volume 10.djvu/94

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astronomical discovery, which has since been ascribed to Janssen, who, later (though independently and by another method), effected it. Prof. Cooke made a series of observations on those bands in the solar spectrum which are due to our own atmosphere, with the object of ascertaining whether they are due to the constant constituents of the air, Or to the aqueous vapor which is present in the air in variable quantity. Combining hygrometric with spectroscopic observations, he found that when the air is moist these bands are more clearly seen than when the air is dry, and by systematic observations so definitely ascertained this relation as to prove beyond all manner of doubt that the bands are due to aqueous vapor. Unfortunately, though his results were published in America, they were not published in such a way as to attract notice in Europe, and accordingly European astronomers remained ignorant of the most important fact discovered by Cooke until they had rediscovered it for themselves.

The observatory at Ann Arbor, Michigan, was erected in 1854, chiefly through the exertions of Chancellor Tappan, of the Michigan University. Dr. Brünnow, our present Astronomer Royal for Ireland, was for a long time director of this observatory. It is at present under the able control of Prof. Watson, who has added nearly a score of planetoids to the known members of the solar family.

The observatory of Dartmouth College, Hanover, New Hampshire, illustrates in a remarkable way the energy and zeal with which college observatories are managed in America. It would be difficult to name any observatory in this country where observations of greater interest, as respects the physics of astronomy, have been made than those effected by Prof. Young with the nine-inch telescope constructed by Alvan Clark for the Dartmouth College; or than the supplementary observations made by Young with a powerful telescope conveyed to an elevated pass in the Rocky Mountains. Among his results may be specially mentioned—first, the observations of the most remarkable solar outburst yet witnessed, an outburst during which the glowing hydrogen of the prominences was driven to a height of at least 200,000 miles from the surface of the sun; and, secondly, the identification of more than 250 lines in the spectrum of the solar sierra.

And as the most interesting and characteristic observations yet made upon solar prominences are due to Prof. Young, of Dartmouth Observatory, so the most accurate and detailed drawings yet made of sun-spots are those by Prof. S. Langley, of the Alleghany Observatory, near Pittsburg.

At Chicago, a very fine telescope, eighteen inches in aperture, by Alvan Clark, has been erected; but, owing to pecuniary difficulties consequent on the great fire (followed by the commercial depression which has recently affected the United States), that observatory has suffered considerably from the want of a properly remunerated director. The Astronomical Society of Chicago has done its best to set