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 OBSERVATORY OBSIDIAN AND PUMICE 567 other European observatories justly famous, including those of Abo, Altona, Athens, Bonn, Bremen, Breslau, Brussels, Buda, Florence, Gottingen, Hamburg, Leipsic, Munich, Rome, Santiago, Gotha, Upsal, and Vienna. The English have also observatories at Madras, at Sydney (formerly at Paramatta) and at Mel- bourne. Numerous private observatories in various parts of the British empire have en- riched science with many brilliant discoveries. Thus, Lord Rosse erected at Parsonstown, county Louth, Ireland, the most stupendous instrument known. Lassell, with his beauti- ful reflector established at Liverpool, was the first to detect a satellite of Neptune, and con- tests with the Bonds at Cambridge, Mass., the honor of the discovery of Hyperion, the seventh in order of the satellites of Saturn. At the private observatory of George Bishop, in Regent's park, London (1836), J. R. Hind has labored since 1844 with great success. To these may be added Admiral Smyth's obser- vatory at Bedford, now dismantled ; Sir John Herschel's late establishment at Feldhuysen, Cape of Good Hope ; and those of Messrs. Car- rington, Dawes, Cooper, and others. A tele- scope of 25 in. aperture (by Cook), finished in 1868, is destined for the island of Madeira. A new observatory, under Prof. "Winnecke, was established in 1874 at the university of Stras- burg. An observatory especially for observa- tions of the sun is constructing at Potsdam. A new observatory nearly finished (1875) is to replace the old in Vienna. The first telescope used in the United States for astronomical purposes was set up in 1830 at Yale college. The first observatory building was erected in 1836 at Williams college, Mass., by Prof. Hop- kins. Two years later the Hudson observatory was organized in connection with the Western Reserve college, Ohio, under Prof. Loomis as director. About the same time the high school observatory at Philadelphia was established, which introduced a class of instruments supe- rior to any before employed. The West Point observatory, under Prof. Bartlett, and the naval observatory at Washington, under Capt. Gilliss, soon followed. The latter is now (1875) under the superintendence of Rear Admiral Davis. In 1874 it was supplied with a refractor (by Alvan Clark) having an object glass 26 in. in aperture, and being probably the most pow- erful refracting telescope in the world. At Georgetown, D. 0., an observatory was erected in 1844, and about the same time that at Cin- cinnati began operations under Prof. Mitchel, with instruments of admirable performance. The telescope and property of this observatory have been transferred to the university, and a site of four acres for a new observatory has been selected at Mount Lookout, near Lin- wood, 6 m. from the city. The observatory at Cambridge, established a year or two later, is furnished with one of the best equatorials in the world. By means of it Messrs. William C. and George P. Bond added to astronomical knowledge a new satellite of Saturn ; the fact of the semi-transparency of the inmost zone of the ring of the same planet ; the conjecture, established by Prof. Peirce's demonstration, of the non-continuous nature of the ring ; im- proved accounts of the nebulae ; and observa- tions of new planets, and of the satellites of Saturn, Uranus, and Neptune. It is now under Prof. Winlock. The Allegheny (Pa.) observa- tory, under Prof. S. P. Langley, is mainly de- voted to physical astronomy, especially to the study of solar physics. At Ann Arbor, Mich., an observatory was established in 1854 on a very liberal scale. Prof. Watson is its director. A more recent establishment is the Dudley ob- servatory at Albany (now a branch of Union university, Schenectady), the gifts to which since its foundation exceed $200,000. In ad- dition to the foregoing, celestial telescopes have been set up at Nantucket, Mass., where Miss Maria Mitchell won a European fame; one at Vassar college, Poughkeepsie, where Miss Mitchell is at present professor of astron- omy ; near Darby, a few miles from Philadel- phia, by the late John Jackson ; at Tuscaloosa, Ala. ; at Charleston, S. C., by Prof. Lewis R. Gibbes ; at New York city by Mr. Rutherfurd, and another by Mr. Campbell ; at Hastings, N. Y., by Dr. Henry Draper ; at Newark, N. J., by Mr. Van Arsdale; at Philadelphia, by the Friends; at Amherst college; at Dartmouth college, due chiefly to the munificence of George C. Shattuck of Boston, and supplied in 1871 with a new (Clark) telescope of 9-4 in. aperture; and at Hamilton college. The last has been liberally endowed by Edwin C. Litch- field of Brooklyn, N. Y., and is now known as the Litchfield observatory. The observatory at Chicago, where there is a fine telescope 18 in. in aperture (by Alvan Clark), is under the management of Prof. Safford. The observa- tory of the Sheffield scientific school, Yale col- lege, occupies two towers recently added to Sheffield hall, in one of which is mounted an equatorial telescope of 9 in. aperture (by Clark), and in the other a meridian circle with a side- real clock, both instruments given by Mr. Shef- field. In 1874 James Lick of San Francisco gave $700,000 for a telescope and other appa- ratus for an observatory. The observatory of the Argentine Republic was organized at Cor- dova in 1870, under Prof. B. A. Gould, for- merly director of the Dudley observatory. An observatory was established at Quito in 1874, Father Menten director. OBSIDIAN AND PUMICE, two modifications of feldspathic or trachytic lava, obsidian being glassy, while pumice is a porous, fibrous, or tumefied mass. The different conditions to which the lava is subjected are the cause of the difference in the two minerals; obsidian is produced by the action of heat principally, while pumice is the effect of various external agencies, principally aqueous vapor and a cer- tain temperature while the lava is fluid. Many obsidians when ignited swell into a mass of