O'BRIEN 506 OCCULTATIONS Sonora. After he had obtained a scien- tific education he began his career as a successful farmer in 1902. In 1912 he recruited a force of Yaqui Indians and assisted Madero in gaining control of Mexico. His sympathy with the peons led him to espouse the cause of Carranza against Huerta in 1913, and again with Carranza against Villa in 1915. During these wars Obregon forged to the front as the ablest leader of the Constitution- alist armies, and due to his generalship Villa was defeated and forced into flight as an outlaw. After 1915 he co-operated with Carranza in his effort to pacify Mexico, and finally became a candidate for the Presidency of Mexico to succeed Carranza. Charging that the President was using unfair methods to defeat him in favor of his own candidate, Obregon revolted, and in May, 1920, drove Car- ranza from the capital. He was elected President of Mexico in October and in- augurated in December, 1920. O'BRIEN, FITZ-JAMES, an Irish- American author; born in Limerick, Ire- land, in 1828. His writings comprise "The Diamond Lens and Other Stories," and many poems. His collected works appeared in 1881. He died of wounds in the Civil War at Cumberland, Md., April 6, 1862. O'BRIEN, WILLIAM, Irish journalist and politician; born in 1852; educated at Cloyne College and Queen's College, Cork. In 1875 joined staff of "Freeman's Journal," and founded "United Ireland" 1880. Prosecuted nine times for political offenses, he spent over two years in prison. Nationals' parliamentary leader 1883-1895, retiring because of party dis- sensions. Toured the United States in 1890, collecting funds for Irish cause. Led Anti-Parnellites after leader's con- viction. 1898 organized an agrarian movement, United Irish League, and founded "The Irish People" as its organ. Member of Parliament for Cork, 1900- 1909. Has published "When We Were Boys" (1890) ; "Irish Idea" (1894) ; "A Queen of Men" (1897) ; "Recollections" (1906); "An Olive Branch" (1910). OBSERVATORY, a building devoted CO the observation of astronomical, mag- netic, meteorological, or other natural phenomena. The astronomical observa- tory is the one of most general interest. Astronomical observation began at an early date in China; the pyramids in Egypt seem in some way to have been associated with stellar observation; and the first historical observatory was founded in Alexandria 300 b. c. Its work Was begun by Aristillus, and continued by Timocharis, Hipparchus, Aristarchus, and others. The first European obser- vatory was built at Nuremberg by Ber- nard Walther in 1472, and this was fol- lowed in the 16th century by Tycho Brahe's famous observatory on the island of Hveen, near Copenhagen. These were followed by the construction of the Royal Observatory at Paris (1667), the Green- wich Royal Observatory (1675), the Tusculan Observatory near Copenhagen (1704), Berlin (1705; new observatory 1835), Vienna (1756), Dublin (1785), Konigsberg (1813), Sydney (1820), Cape of Good Hope (1820), Edinburgh (1825), Pulkowa near St. Petersburg (1839), Cambridge, Mass. (1839), Wash- ington, D. C. (1845), Melbourne (1853), Lick Observatory, California (1888), and the Yerkes Observatory at Lake Geneva, Wis. (1897). Dun Echt Observatory, the private ob- servatory of the Earl of Crawford, near Aberdeen, Scotland, has attracted con- siderable attention as a center of dis- tribution of astronomical telegraphic news, the Dun Echt circulars, in con- nection with the international code telegrams, being the medium of com- munication. The chief instrument used in the ob- servatory is the telescope, whether in the form of the equatorial or in the mural circle and transit instrument, to- gether with the sidereal and the solar clock. In 1919 the Carnegie Institute in- stalled a 100-inch reflector, largest in the world, in their Solar Observatory, Mt. Wilson, Pasadena, Cal. The observatory building must be constructed in a very stable manner, and as the instruments must be out of contact with the walls they are attached to stone pillars that rest on foundations separate from the rest of the building. OCANA, town in department of Santander, Colombia, 60 miles, N. W. of Pamplona. Region is rich in coffee, and is center of anise and hides trade car- ried on with Venezuela. Pop. about 18,000. OCCULTATIONS, eclipses, strictly, though the latter term is confined by usage to the obscuration of the sun by the moon, and of the moon by the earth's shadow, while the former is restricted to the eclipses of stars or planets by the moon. Occultations are phenomena of frequent occurrence; they are confined to a belt of the heavens about 10° 171/2' W., situated parallel to, and on both sides of, the equinoctial, and extending to equal distances N. and S. of it, being the belt within which the moon's orbit lies. These phenomena serve as data for the
