NATIONAL OBSERVATORY, THE, a Government institution, Division of the Navigation Bureau of the Navy Depart ment, Washington, D. C. Here the posi. tion of the sun, moon, planets, and stars is determined for "The American Ephem erics and Nautical Almanac," and standard time is issued by radio and tele graph at noon and 10 p. m. for naviga tion, and the general public. The insti tution also purchases, tests, and repairs instruments used in the navy, and con ducts investigations of scientific and gen eral interest. The observatory developed from the Chart and Instrument Depot of the Navy Department of 1838. Lieuten ant Wilkes at his own expense built an observatory on Capitol Hill in this year, and the Secretary of the Navy directed the purchase of necessary instruments for observations in meteorology, and as tronomy. The results accomplished at the observatory were published in 1846, the first American work of its kind. Con
gress authorized the erection of a Na tional observatory in 1842, and under Lieutenant M. F. Maury a special study was made of ocean currents, and hydrog raphy.
Recording observations by electricity was begun in 1849. Professor Asaph Hall in 1877 discovered satellites of Mars through Alvan Clark's 26-inch lens tele scope, the largest made up to that time. In 1893 the observatory was moved to Georgetown Heights. Since 1893 the ob servatory has co-operated with other na tions in astronomical work. In 1913 1914 the 'observatory, acting with the French, made the first direct determina tion of the difference of longitude be tween Washington and Europe by ex change of radio signs from Arlington and the Eiffel Tower station, Paris. The National Observatory has published 50 volumes descriptive of its work.