OBSERVATORY ( from Lat. obserrar( , to observe, from oh, before + serrare, to keep; con nected with Ski. Av. to protect). An institution supplied with instruments for the regular observation of astronomical, meteorologi cal, or magnetic phenomena. lm some observa tories all three classes of observation are carried 011, hilt in 010'4 cases special attention is paid to astronomy alone, and only such meteorological observations are taken as are required for the calculation of the effect of atmospheric refrac tion on the position of a heavenly body; there are, however, a few observatories which are de voted solely to meteorological or magnetical ob servations.
While observation of the heavenly bodies dates from prehistoric times and individuals at inter vals made their crme observations of the heavens, the first observatory, in onr modern sense of the word, was that of Alexandria, founded about B.C. 300. It continued in activity till A.m. 200: and it was here that Ilipparchus dis covered the precession of the equinoxes and fixed the positions of the sun, moon, and planets by means of armillary spheres (q.v.) and astro labes, having graduated circles on which celestial latitudes and longitudes could be read off, when a pair of sights was pointed to the heavenly body. Ptolemy used a quadrant, with which he measured zenith distances on the meridian. In the ninth and tenth centuries the Arabs founded observatories at Bagdad, Damascus, and Alokat tam, near Cairo. In the latter place the Ilakimite tables were constructed. In the thirteenth century the splendid I )bservatory at Meragha, Persia, and in the fifteenth century that I )f Sa markand were founded by Aloilool Khans. Here planetary tables and star catalogues were con structed. The first observatory in Europe was that of Nuremberg, erected in 1472, and the re vival of astronomical observations in Europe dates from its foundation. In 1576 Tycho Brahe began the erection of his famous observatory on liven. an island in the Sound. He con verted] the quadrant used by Ptolemy into all altazimuth by mounting it on a vertical axis in connection with a horizontal or azimuth circle. It was not till the middle of the eighteenth tUry that the improvement of tilne measurement with pendulum clocks enabled astronomers to rely for the determination of right ascensions on the times of passage across the meridian. instead of measurements with a graduated circle. The quadrant was then fixed in the meridian, and be Mg attached to a massive wall, its dimensions were increased, and greater accuracy thereby secured in the determination of meridian zenith distances. Neither the quadrant nor the mural circle (q.v.) which succeeded it. however. could be relied upon for acenrate motion in the plane of the meridian. but Rihner remedied this defect
by inventing the transit instrument (q.v.), which enabled astronomers to the times of meridian passage or transit with great acen rney. and thus to determine the right ascension of the heavenly bodies by means of the apparent diurnal movement. \\ ith the transit and quad rant climmeneed that series of tions of the positions of the snit, moon. planets. and stars, which have continued ever since at Greenwich, and on Ivhich, in combination with less extensive series at Paris, Kimigsberg. and elsewhere, all our tables of the motions of the heavenly bodies are founded. In modern observa tories the transit and mural circle have been combined into one in-Outman. the meridian cir cle (q.v.). which determines both right ascen sions and declensions at a single observation.
In planning observatories a very usual mistake is an over-supply of instruments and too few astronomers. A large telescope really needs six persons to keep it busy: two astronomers, two assistants, and two eomputers. Moreover. the 'life' of a telescope is very short. Every few year- new instruments are invented. and unless these are supplied to the observatory its astron omers will work at a disadvantage. and its astro nomical output will be diminished in quantity and vainly, 'Flue great observatories of the world may be divided into several classes. In the first place, we have the great Government institutions occu pied with continuous observations such as are needed to strengthen our knowledge of the fund:i nternal parts Of astronomy. The Royal Observa tory at Greenwich. England. is perhaps the most important of this class. It was founded by Charles II. Similar institutions are established at Paris. Benin. Pulkova (q.v.). near Saint Pe tersburg. and Washington. At the last-named place the observatory is called the United States Naval Observatory (see NAVAL )IISERVATORY) and the astronomers arc pnifessors of mathe matics in the United States Navy. Another class of observatories are maintained by universities and other educational institutions. These are in tended to combine instruction with research, and in them an effort is usually made to extend the science of special rather than by long continued routine observation. In the Unit ed States the principal observatories of this class are the Harvard y Observatory, the Lid; observatory (q.v.) of the l'niversity of California. and the Yerkes observatory (q.v.), belonging to Chicago University. Finally. we have the very important class of astrophysical observatories, which are occupied with a study of the physics of the heavenly bodies. Probably the most important of these is at Potsdam. Germany. Much astrophysical work is also done at the uni versity observatories of Ilarvard and Chicago.