a place deſigned for obferving the heavenly bodies; being generally a building erected on fome eminence, covered with a terrace for making astronomical obfervations.
The more celebrated observatories are, 1. The Greenwich observatory, built in 1676, by order of Charles II. at the folicitation of Sir Jonas Moore and Sir Chrifopher Wren; and furnifhed with the moft accurate instruments; particularly a noble fextant of feven feet radius, with telefopic sights.
2. The Paris observatory, built by the order of Louis XIV. in the faubourg St Jacques.
It is a very fingular, and a very magnificent building, the design of Monfieur Perault: it is 80 feet high; and has a terrace at the top.
The difference in longitude between this and the Greenwich observatory is 2° 20'.
In it is a cave or cellar, of 170 feet decent, for experiments that are to be made far from the fun, &c. particularly fuch as relate to congelations, refrigerations, indurations, confervations, &c.
3. Tycho Brahe's observatory, which was in the little island Ween, or Scarlet Island, between the coasts of Schonen and Zealand in the Baltic. It was erected and furnifhed with instruments at his own expence, and called by him Uraniburg. Here he fpent twenty years in obferving the stars; the reſult is his catalogue.
4. Pekin observatory. Father Le Compte defcribes a very magnificent observatory, erected and furnifhed by the late emperor of China, in his capital, at the interceffion of fome Jesuit miffionaries, principally Father Verbeift, whom he made his chief obferver. The instruments are exceedingly large; but the divifion lefs accurate, and the contrivance in fome reſpects lefs commodious, than that of the Europeans. The chief are, An armillary zodiacal fphere of fix feet diameter; an equinoctial fphere of fix feet diameter; an azimuthal horizon of fix feet diameter; a large quadrant fix feet radius; a fextant eight feet radius; and a celestial globe fix feet diameter.
Observatories, as they are very ufeful, and indeed abfolutely neceffary for astronomers, fo they have become far more common than they were. There is a very ex- cellent one now at Oxford, built by the trustees of Dr. Radcliffe, at the expence of nearly 30,000l. At Cambridge there is as yet no public observatory. Over the great gate of Trinity college, indeed, there is one which is called Sir Isaac Newton's, becaufe this great philofopher had ufed it; but it is gone to decay. It were well if the univerity would repair and preferve it in memory of that truly great man. In St John's, too, there is a small one. The late ingenious Mr Cotes had ufed to give lectures in Sir Isaac Newton's on experimental philofophy. In Scotland there is an observatory at Glasgow belonging to the univerity: there is one erected on the Calton hill at Edinburgh; but it is in very bad repair, (fee EDINBURGH); and there is an excellent one at Dublin.
5. Bramins observatory at Benares. Of this Sir Robert Barker gives the following account, (Phil. Tranf. vol. lxvii. p. 598.). "Benares in the Eaft Indies, one of the principal seminaries of the Bramins or priests of the original Gentoo of Hindoofan, continues till to be the place of refort of that fett of people; and there are many public charities, hospitals, and pagodas, where fome thousands of them now rehide. Having frequently heard that the ancient Bramins had a knowledge of astronomy, and being confirmed in this by their information of an approaching eclipse both of the fun and moon, I made inquiry, when at that place in the year 1772, among the principal Bramins, to endeavour to get fome information relative to the manner in which they were acquainted with an approaching eclipse. The moft intelligent that I could meet with, however, gave me but little satisfaction. I was told that thefe matters were confined to a few, who were in poſsession of certain books and records; fome containing the myftries of their religion; and others the tables of astronomical obfervations, written in the Shanfierit language, which few underfood but themfelves: that they would take me to a place which had been conftrufted for the purpoſe of making fuch obfervations as I was inquiring after, and from whence they fuppoſed the learned Bramins made theirs. I was then conducted to an ancient building of stone, the lower part of which, in its pre- fent situation, was converted into a fable for horses, and a recepacle for lumber; but by the number of court-yards and apartments, it appeared that it muft once have been an edifice for the ufe of fome public body of people. We entered this building, and went up a ftaicrafe to the top of a part of it, near to the river Ganges, that led to a large terrace, where, to my furi- priſe and fatisfaction, I faw a number of instruments yet remaining, in the greatest prefervation, fupendously large, immovable from the fpot, and built of stone, fome of them being upwards of 20 feet in height; and although they are faid to have been erected 200 years ago, the graduations and divisions on the feveral arcs appeared as well cut, and as accurately divided, as if they had been the performance of a modern artifit. The execution in the conftruftion of thefe instruments exhibited a mathematical exactness in the fixing, bearing, fitting of the feveral parts, in the neceffary and fufficient supports to the very large ftones that compofed them, and in the joining and fattening each into the other by means of lead and iron.
"The fitation of the two large quadrants of the instrument marked A in the plate, whole radius is nine feet two inches, by their being at right angles with a gnomon at twenty-five degrees elevation, are thrown into such an oblique situation as to render them the most difficult, not only to construct of such a magnitude, but to secure in their position for so long a period, and affords a striking instance of the ability of the architect in their construction: for by the shadow of the gnomon thrown on the quadrants, they do not appear to have altered in the least from their original position; and so true is the line of the gnomon, that, by applying the eye to a small iron ring of an inch diameter at one end, the light is carried through three others of the same dimension, to the extremity at the other end, distant 38 feet 8 inches, without obstruction; such is the firmness and art with which this instrument has been executed. This performance is the more wonderful and extraordinary, when compared with the works of the artificers of Hindoostan at this day, who are not under the immediate direction of an European mechanic; but arts appear to have declined equally with science in the east.
" Lieutenant Colonel Archibald Campbell, at that time chief engineer in the East India Company's service at Bengal, made a perspective drawing of the whole of the apparatus that could be brought within his eye at one view; but I lament he could not represent some very large quadrants, whose radii were about 20 feet, they being on the side from whence he took his drawing. Their description, however, is, that they are exact quarters of circles of different radii, the largest of which I judged to be 20 feet, constructed very exactly on the sides of stone walls, built perpendicular, and situated, I suppose, in the meridian of the place: a brass pin is fixed at the centre or angle of the quadrant, from whence, the Bramin informed me, they stretched a wire to the circumference when an observation was to be made; from which, it occurred to me, the observer must have moved his eye up or down the circumference, by means of a ladder or some such contrivance, to raise and lower himself, until he had discovered the altitude of any of the heavenly bodies in their passage over the meridian, so expressed on the arcs of these quadrants: these arcs were very exactly divided into nine large sections; each of which again into ten, making ninety lesser divisions or degrees; and those also into twenty, expressing three minutes each, of about two-tenths of an inch asunder; so that it is probable they had some method of dividing even these into more minute divisions at the time of observation.
"My time would only permit me to take down the particular dimensions of the most capital instrument, or the greater equinoctial sun-dial, represented by figure A, which appears to be an instrument to express solar time by the shadow of a gnomon upon two quadrants, one situated to the east, and the other to the west of it; and indeed the chief part of their instruments at this place appear to be constructed for the same purpose, except the quadrants, and a brass instrument that will be described hereafter.
"Figure B is another instrument for the purpose of determining the exact hour of the day by the shadow of a gnomon, which stands perpendicular to, and in the centre of, a flat circular stone, supported in an oblique situation by means of four upright stones and a cross piece; so that the shadow of the gnomon, which is a perpendicular iron rod, is thrown upon the division of the circle described on the face of the flat circular stone.
"Figure C is a brass circle, about two feet diameter, moving vertically upon two pivots between two stone pillars, having an index or hand turning round horizontally on the centre of this circle, which is divided into 360 parts; but there are no counter divisions on the index to subdivide those on the circle. This instrument appears to be made for taking the angle of a star at setting or rising, or for taking the azimuth or amplitude of the sun at rising or setting.
"The use of the instrument, figure D, I was at a loss to account for. It consists of two circular walls; the outer of which is about forty feet diameter, and eight feet high; the wall within about half that height, and appears intended for a place to stand on to observe the divisions on the upper circle of the outer wall, rather than for any other purpose; and yet both circles are divided into 360 degrees, each degree being subdivided into twenty lesser divisions, the same as the quadrants. There is a door-way to pass into the inner circle, and a pillar in the centre, of the same height with the lower circle, having a hole in it, being the centre of both circles, and seems to be a socket for an iron rod to be placed perpendicular into it. The divisions on these, as well as all the other instruments, will bear a nice examination with a pair of compasses.
"Figure E is a smaller equinoctial sun dial, constructed upon the same principle as the large one A.
"I cannot quit this subject without observing, that the Bramins, without the assistance of optical glasses, had nevertheless an advantage unexperienced by the observers of the more northern climates. The serenity and clearness of the atmosphere in the night-time in the East Indies, except at the seasons of the monsoons or periodical winds changing, is difficult to express to those who have not seen it, because we have nothing in comparison to form our ideas upon: it is clear to perfection, a total quietude subsists, scarcely a cloud to be seen, and the light of the heavens, by the numerous appearance of the stars, affords a prospect both of wonder and contemplation.
"This observatory at Benares is said to have been built by the order of the emperor Akbar: for as this wise prince endeavoured to improve the arts, so he wished also to recover the sciences of Hindoostan, and therefore directed that three such places should be erected; one at Delhi, another at Agra, and the third at Benares."