Pekin Observatory. Father Le Compte describes a very magnificent observatory, erected and furnished by the late Empe ror of China, in his capital, at the inter cession of some Jesuit missionaries, chief ly Father Verbest, whom he appointed his chief observer. The instruments here are exceedingly large ; but the divisions are less accurate ; and, in some respects, the contrivance is less commodious than in those of the Europeans. The chief are, an armillary zodiacal sphere of six Paris feet diameter, an azimuthal horizon six feet diameter, a large quadrant six feet radius, a sextant eight feet radius, and a celestial globe six diameter.
Bramin's Observatory at Benares, in the East Indies, which is still one of the prin cipal seminaries of the Bramins, or priests of the original Gentoos of Hindostan. This observatory at Benares, it is said, was built about 200 years since, by order of the Emperor Ackbar ; for as this wise prince endeavoured to improve the arts, so he wished also to recover the sciences of Hindostan, and therefore ordered that three such places should be erected ; one at Delhi, another at Agra, and the third at Benares.
Wanting the use of optical glasses, to magnify very distant, or very small ob jects, these people directed their atten tion to the increasing the size of their in struments, for obtaining the greater ac curacy and number of the divisions and subdivisions in their instruments. Ac cordingly, the observatory contains seve ral huge instruments of stone, very nice ly erected and divided, consisting of cir cles, columns, gnomons, dials, quadrants, &c. some of ;hem of 20 feet radius, the circle divided first into 360 equal parts, and sometimes each of these into 20 other equal parts, each answering to 3', and of about two tenths of an inch in extent. And although these wonderful instru ments have been built upwards of 200 years, the graduations and divisions on the several arcs appear as well cut, and as accurately divided, as if they had been the performance of a modern artist. The execution, in the construction of these instruments, exhibits an extraordinary mathematical exactness in the fixing, bearing, fitting of the several parts, in the necessary and sufficient supports to the very large stones that compose them, and in the jomingand fastening them into each other by means of lead and iron.
We have referred to this article from the EMTATORIAL, for some account of practical astronomy, and the instruments used in this branch of science.
By practical astronomy is implied the knowledge of observing the celestial bo dies, with respect to their position and time of the year, and of deducing from those observations certain conclusions, useful in calculating the time when any proposed position of these bodies shall happen. For this purpose, it is neces sary to have a room or place convenient ly satiated, suitably contrived, and fur nished with proper astronomical instru ments. It should have an uninterrupted view from the zenith down to, or even below, the horizon, at least towards the cardinal points ; and for this purpose, that part of the roof which lies in the direc tion of the meridian, in particular, should have moveable covers, which may easily be moved, by which means an instrument may be directed to any point of the hea vens between the horizon and the 'ze nith, as well to the northward as south ward. This place, called an observatory, should contain the following instru ments: I. .4 Pendulum Clock, for showing equal time. This should show time in hours, minutes, and seconds : the observ er, by hearing the beats of the pendu lum, may Count them by his ear, while his eye is employed on the motion of the celestial object he is observing. Just be fore the object arrives at the position de scribed, the observer should look on the clock and remark the time, suppose it 9 hours, 15 minutes, 25 seconds ; then saying, 25, 26, 27, 28, &c. responsive to the beat of the pendulum, till he sees through the instrument the object arriv ed at the position expected ; which sup pose to happen when he says thirty-eight, he then writes down 9h 15' 38" for the time of observation, annexing the parti cular day. If two persons are concerned in making the observation, one may read the time audibly while the other observes through the instrument, the observer re peating the last second read when the de sired position happens.
IL .471 Achromatic Refracting Telescope, or a reflecting one of two feet at least in length, for observing particular pheno mena. See TELESCOPE.
HI. A Micrometer for measuring small angular distances. See MICROMETER.