458 ASTRONOMICAL OBSERVATORIES .
Longitude from Greenwich, 9 m 21.02 s E.
Latitude, 48° 50' 11.8" FT.
Directors : J. D. Cassini, 1671.
J. Cassini, 1712.
C. F. Cassini (de Thury), 1756.
J. D. Cassini (de Thury), 1784.
J. J. L. De La Lande, 1795.
P. Mechain, 1801.
A. Brunard, 1804.
D. F. J. Arago, 1811.
U. J. J. Le Yerrier, 1853.
C. E. Delaunay, 1871.
XJ. J. J. Le Yerrier, 1872.
E. Mouchez, 1878.
National Observatory (formerly royal, since imperial), built in 1667,under the auspices of the Academy of Sciences , according to plans ofC. Perrault. A vast central hall; two towers, east and west. In 1732a small room to accommodate a mural quadrant was added beyond theeastern tower, and in 1742 this was extended by a second inclosurefor a movable quadrant. In 1760 a turret, with a revolving roof, wasbuilt to the south of this addition. The main building, having becomedilapidated, was restored in 1786, completed 1793; since when it hasbeen detached and the south terrace built. In 1832 the small roomswhere observations are taken were repaired, and the amphitheater anda rotunda with a revolving roof built upon the principal terrace. Thedome intended for the shelter of the great equatorial was placed on thesummit of the building in 1850. The great telescope, with a mirror ofsilvered glass, 4 feet (1.2 m ) in diameter, was mounted in 1876, in a build-ing on the ground-floor level. John Dominic Cassini discovered fourof the satellites of Saturn at the Paris observatory, and also first inves-tigated the subject of the zodiacal light, and here, too, the great grand-son of this astronomer was the first to follow the variations of themagnetic needle with minute and persevering industry; and it was herethat Arago and Mathieu demonstrated the extrem'ely small parallaxof the stars.
A large number of astronomical manuscripts, containing matter ofgreat interest, are preserved at the Paris observatory.