OBSERVATORY, a place destined for observing the heavenly bodies; it is a building usually in form of a tower, erect ed on an eminence, and covered with a terrace for making astronomical observa tions. Most nations have had observato ries, which have been noticed at large in La Lande's Astronomy : of these, the fol lowing may be mentioned : The Greenwich Observatory, or Royal Observatory of England. This was built and endowed in the year 1676, by order of King Charles the Second, at the in stance of Sir Jonas Moore, and Sir Chris topher Wren ; the former of these gen tlemen being Surveyor General of the Ordnance, the office of Astronomer Roy al was placed under that department, in which it has continued ever since.
This observatory was at first furnished with several very accurate instruments ; particularly a noble sextant of seven feet radius, with telescopic sights. And the first Astronomer Royal, or the person to whom the province of observing was first committed, was Mr. John Flamsteed ; a man who, as Dr. Halley expresses it, seem ed born for the employment. During fourteen years he watched the motions of the planets unwearied diligence, especially those of the moon, as was given him in charge ; that a new theory of that planet being found, shewing all her irre gularities, the longitude might thence be determined. In the year 1690, having provided himself with a mural arch of near seven feet radius, made by his as sistant, Mr. Abraham Sharp, and fixed in the plane of the meridian, he began to verify his catalogue of the fixed stars, which had hitherto depended altogether on the distances measured with the sex tant, after a new and very different man ner, viz. by taking the meridian altitudes, and the moments of culmination, or in other words, the right ascension and de clination. And he was so well pleased with this instrument, that he discontinued almost entirely the use of the sextant. Thtts, in the space of upwards of forty years, the Astronomer Royal collected an immense number of good observations ; i which may be found in his "llistoria Cce lestis Britannica," published in 1725 ; the principal part of which is the Britannic Catalogue of the fixed stars.
Mr. Flamsteed, on his death in 1719, was succeeded by Dr. Halley, and he by Dr. Bradley in 1742, and this last by Mr. Bliss in 1762 ; but none of the observa tions of these gentlemen have yet been given to the public.
On the demise of Mr. Bliss, in 1765, he was succeeded by Dr. Nevil Maskelyne, the present Astronomer Royal, whose va• luable observations have been published, from time to time, under the direction of the Royal Society, in several folio vo lumes.
The Greenwich Observatory is found, by very accurate observations, to lie in 51° 28'40" north latitude, as settled by Dr. Maskelyne, from many of his own observations, as well as those of Dr. Bradley.
The Paris Observatory was built by Louis the Fourteenth, in the Fauxbourg St. Jaques ; being begun in 1664, and finished in 1672. It is a singular but magnificent building, of eighty feet in height, with a terrace at top ; and here M. de la Hire, M. Cassini, &c. the King's Astronomers, have made their observa tions. Its latitude is 48° 50' 14" north, and its longitude 9' 20" east of Green wich Observatory.
In the Observatory of Paris is a cave, or pit, 170 feet deep, with subterraneous passages, for experiments that are to be made out of the reach of the sun, espe cially such as relate to congelations, re frigerations, &c. In this cave there is an old thermometer of M. de la Hire, which stands at all times at the same height ; thereby shewing that the temperature of the place remains always the same. From the top of the platform to the bottom of the cave is a perpendicular well or pit, used formerly for experiments on the fall of bodies ; being also a kind of long telescopical tube, through which the stars are seen at mid-day.
Tycho Brahe's Observatory was in the little island Weep, or the Scarlet Island, between the coasts of Schonen and Zea land, in the Baltic Sea. This observato ry was not well situated for some kinds of observations, particularly the risings and settings ; as it lay too low, and was land locked on all the points of the compass except three ; and the land horizon being very rugged and uneven.