Page:The American Cyclopædia (1879) Volume XVI.djvu/240

 220 URANUS is quadrivalent, as uranous oxide, U0 a (oxygen being bivalent), and uranous chloride, tCU; and the uranio, in which it is sexvalent, as ura- nic oxide, UO 3, and uranic oxychloride, UOaCli. Prof. Roscoe in 1875 described a pentachloride, UC1 5. There is also a uranoso-uranic oxide, UOj, 2UO-3, or U 3 O 8. Uranic oxide unites with basic metallic oxides, forming uranates ; and there are salts of the metal uranium with iodine, bromine, and fluorine. The compounds of ura- nium are employed chiefly in giving yellowish hues to glass and porcelain. The peculiar yel- low tint with greenish or opaline reflections seen in Bohemian glass is derived from them. Uranium glass is remarkable for exhibiting with great distinctness the phenomenon of fluorescence, and this property, together with the absorption spectra afforded by uranium salts, has been recently thoroughly investigated by President Morton of the Stevens institute, Hoboken, and Dr. H. Carrington Bolton of Co- lumbia college, New York. (See " The Ameri- can Chemist," 1873.) Uranium compounds are of great value in porcelain painting, mineral pitchblende being used to a considerable extent at Joachimsthal in Bohemia, whore it is con- verted into uranate of soda for this purpose. It produces an orange color in the enamelling fire, and a fine black in the furnace in which the porcelain is baked. The uranate of soda is of tine orange color, and has been proposed as a paint. Uranium is found accompanying various ores of silver and lead in several of the mining districts of Bohemia, Hungary, and Saxony. It also occurs as a sulphate and carbonate. Torbernite, occurring in beautiful green crystals, is a phosphate of uranium and copper; autunite, found in yellow scales, con- tains phosphate of uranium and lime. Uranic arsenates of similar composition have been re- cently discovered. Fine specimens of uranium minerals are found near Itedruth in Cornwall, and in various localities in Bohemia and Sax- ony. See "Index to the Literature of Ura- nium," by II. Carrington Bolton, in the "An- nals of the Lyceum of Natural History," New York, 1870. URANUS, or Cains (Gr. and Lat., heaven), in classical mythology, sometimes the son and sometimes the husband of Gtea or Terra. Ho preceded Saturn and Jupiter on the throne of heaven. By Gaea he was the father of Oceanus, Saturn, Tethys, Themis, Mnemosyne, the Cy- clops, and others. He hated his children, and immediately after their birth confined them in Tartarus ; but one of them, Saturn, at the in- stigation of Gsea, mutilated and dethroned him. From the drops of his blood sprang the Gi- gantes, and from the foam gathering around him in the sea, according to some accounts, Aphrodite or Venus. URANUS, the seventh planet in order of dis- tance from the sun, and the outermost but one of all the known members of the planetary system. Uranus travels at a mean distance of 1,753,869,000 m. from the sun, his greatest dis- tance being 1,835,561,000 m., his least 1,672,- 177,000 m. Hence it will be perceived that the eccentricity of his orbit is considerable, the greatest exceeding the least distance by 163,- 384,000 m., or by a greater distance than that which separates Venus from the earth when these two planets are furthest from each other. The eccentricity of Uranus's orbit is in fact 0-046578. As a consequence of this eccen- tricity, his apparent brightness in different op- positions varies considerably. It is not merely that his distance from the earth varies, but his distance from the sun varies also, and con- sequently the amount of light ho receives from it. When at opposition near to the perihelion of his orbit his distance from the earth amounts to 1,581,700,000 m., and when in opposition near aphelion it amounts to 1,744,100,000 m. As his apparent size varies inversely as the square of the distance from the earth, while his apparent intrinsic brightness varies as the square of the distance from the sun, it follows that his apparent absolute brightness is greater when he is at opposition near perihelion than when he is at opposition near aphelion in the proportion of (17,441)" x (1,885,561) 9 to (15,- 8 1 7)" x (1,672, 177)", or as 14,651 to 10,000; that is, nearly as 3 to 2. His orbit is only inclined 46i' to the ecliptic. His mean diam- eter is about 33,000 m., the compression of his globe unknown. In volume he exceeds ] the earth about 74 times ; but his density be- ing barely -^ of hers, his mass exceeds the earth's only about 12$ times. Some astron- omers assert that marks can be recognized on the surface of Uranus, and that by noting these his rotation period can be determined ; but very little reliance can be placed on the assigned period of 9J hours. The sidereal revolution of Uranus is accomplished in 84 years 6 days, or 30,686-8208 days; his mean synodical pe- a tropical year. Uranus was discovered by Sir W. Herschel on March 18, 1781, when he was examining the constellation Gemini (near rj) for double stars. Observing that a star in the telescopic field looked larger than the rest, ho suspected it to be a comet. Using higher powers, he found the disk enlarged, which would not happen with a star. He thereupon announced the discovery of a comet. But after a short time it was found that the sup- posed comet was travelling on a nearly cir- cular orbit around the sun ; and Jt was pres- ently recognized as a member of the sun's fam- ily of planets. Herschel called it the Geor- gium Sidus, and foreign astronomers called it Herschel ; but the name Uranus, assigned to it by Bode of Berlin, is now always used. In 1787 Herschel discovered two satellites attend- ing on Uranus, and ho afterward supposed he had discovered four others ; but there is every reason to believe that he had mistaken in most cases small stars for satellites. It appears probable, however, from an inquiry recently instituted by Prof. Holden of "Washington, that
 * riod is 369'5 days, or only 4^ days more than