a place destined for observing the heavenly bodies; being generally a building erected on some eminence, covered with a terrace for making astronomical observations.
The more celebrated observatories are, 1. The Greenwich observatory, built in 1676, by order of Charles II. at the solicitation of Sir Jonas Moore and Sir Christopher Wren; and furnished with the most accurate instruments; particularly a noble sextant of seven feet radius, with telescopic sights.
2. The Paris observatory, built by the order of Louis XIV. in the Fauxbourg St Jacques.
It is a very singular, but withal a very magnificent building, the design of Monsieur Perrault: it is 90 feet high; and at top is a terrace.
The difference in longitude between this and the Greenwich observatory is 2° 20'.
In it is a cave or cellar, of 170 feet descent, for experiments that are to be made far from the sun, &c., particularly such as relate to congelations, refrigerations, indurations, conservations, &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 furnished with instruments at his own expense, and called by him Uraniburg. Here he spent twenty years in observing the stars; the result is his catalogue.
4. Pekin observatory. Father Le Compte describes a very magnificent observatory, erected and furnished by the late emperor of China, in his capital, at the intercession of some Jesuit missionaries, principally Father Verbeift, whom he made his chief observer. The instruments are exceedingly large; but the division less accurate, and the contrivance in some respects less commodious, than that of the Europeans. The chief are, An armillary zodiacal sphere of six feet diameter; an equinoctial sphere of six feet diameter; an azimuthal horizon of six feet diameter; a large quadrant six feet radius; a sextant eight feet radius; and a celestial globe six feet diameter.
Observatories, as they are very useful, and indeed absolutely necessary for astronomers, so they have become far more common than they were. There is a very excellent one now at Oxford, built by the trustees of Dr Radcliffe, at the expense 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, because this great philosopher had used it; but it is gone to decay. It would well if the university would repair and preserve it in memory of that truly great man. In St John's, too, there is a small one. The late ingenious Mr Cotes had used to give lectures in Sir Isaac Newton's on experimental philosophy. There are several very good ones in the Scotch universities; and there is an excellent one lately erected at Dublin.
5. Bramins observatory at Benares. Of this Sir Robert Barker gives the following account, (Phil. Trans. Vol LXVII. p. 598.) "Benares in the East Indies, one of the principal seminaries of the Bramins or priests of the original Gentooos of Hindoitan, continues still to be the place of resort of that sect of people; and there are many public charities, hospitals, and pagodas, where some thousands of them now reside. 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 sun and moon, I made inquiry, when at that place in the year 1772, among the principal Bramins, to endeavour to get some information relative to the manner in which they were acquainted of an approaching eclipse. The most intelligent that I could meet with, however, gave me but little satisfaction. I was told, that these matters were confined to a few, who were in possession of certain books and records; some containing the mysteries..." teries of their religion; and others the tables of astronomical observations, written in the Sanscrit language, which few understood but themselves: that they would take me to a place which had been constructed for the purpose of making such observations as I was inquiring after, and from whence they supposed the learned Brahmins made theirs. I was then conducted to an ancient building of stone, the lower part of which, in its present situation, was converted into a stable for horses, and a receptacle for lumber; but, by the number of court yards and apartments, it appeared that it must once have been an edifice for the use of some public body of people. We entered this building, and went up a staircase to the top of a part of it, near to the river Ganges, that led to a large terrace, where, to my surprise and satisfaction, I saw a number of instruments yet remaining, in the greatest preservation, stupendously large, immovable from the spot, and built of stone, some of them being upwards of 20 feet in height; and although they are said to have been erected 200 years ago, the graduations and divisions on the several arcs appeared 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 exhibited a mathematical exactness in the fixing, bearing, fitting of the several parts, in the necessary and sufficient supports to the very large stones that composed them, and in the joining and fastening each into the other by means of lead and iron.
"The situation of the two large quadrants of the instrument marked A in the plate, whose 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 sight 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 artisans of Hindostan 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 twenty 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 afar; 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 Brahmins, without the assistance of optical glasses, OBY
glases, had nevertheless an advantage unexperienced by the observers of the more northern climates. The serenity and cleanness of the atmosphere in the nighttime in the East Indies, except at the seasons of changing the monsoons or periodical winds, 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."
Edinburgh Observatory. See Edinburgh.
OBSIDIANUS Lapis, in the natural history of the ancients, the name of a stone which they have also described under the name of the Chian marble. It is a very smooth and hard marble, extremely difficult to cut, but capable of a fine polish; and was used among the ancient Greeks for the purpose of making reflecting mirrors. The later writers have supposed the name obsidianus to be derived from somebody called Olpidius, who was the inventor of this use of it; but it seems only a false spelling of the word olpidius, ὀλπίδιος, from seeing the images of things in it.
See Gallinaceous Lapis.