During the invasion of Egypt by the French, in 1798, General Desaix discovered some remarkable sculptures on the ceiling of an apartment in the great temple at Denderah (the ancient Tentyra), and MM. Jollois and Dovilliers almost immediately perceived among them figures nearly similar to those which arc traced on celestial globes at the prescut time. The whole of the astronomical figures are within the circumference of a circle above five feet in diameter; and the apartment in which they were found is in the upper part of the building : adjoining it is an apartment of equal size, which is open to the sky, the ascent to both lations, among which are those of the zodiac disposed in two lines, one near each extremity of the portico, and parallel to the longitudinal axis of the temple.
being by steps in the interior. Bas-reliefs, apparently of an astrono mical character, are found in several other apartments within the same temple ; and in the ceiling of its portico are figures resembling constel The zodiacal figures in the apartment first mentioned are disposed nearly within the breadth of an annulus formed by two circles, whose common centre is at some distance southward from the centre of the whole ; the figure which is conceived to represent Cancer is however within the space inclosed by the interior circumference of the annulus, and nearly opposite the interval between Gemini and Leo ; that interval being occupied by a human figure with a bird's head, above which are a bird and certain hieroglyphical symbols. The figure of Cancer is also surmounted by a hieroglyphical symbol, which, according to Visconti, seems to express a proper name. ' Except the zodiacal figures, scarcely any in the ceiling resemble those which are now assigned to the constellations ; and a great effort of the imagination is required to discover in what manner they may be con sidered as emblems of the latter. From the zodiacal figures only has it been possible to form opinions concerning the nature of the projec tion employed in the execution of the work, and the epoch to which the aspect of the heavens represented by it is to be referred.
The first discoverers of this ancient monument immediately per ceived that the horary or declination circles, if drawn upon it, would be represented by straight lines diverging from the centre : the latter is consequently the pole of the equator ; but we are indebted to M. Not (' Recherches sur l'Astronomie Egyptienne ') for the very probable idea that the space within the exterior circle represents a development of the whole surface of the celestial sphere, the radii of the circle being equal to half the circumferences of the hour circles, so that the exterior circle represents the south pole of the equator in the heavens. The figures of the constellations are supposed to be placed on the radii corresponding to the circumferences of the hour circles passing through the groups of stars to which the figures belong, and at distances from the centre of the planisphere equal to the angular distances of the figures from the north pole of the equator. The distortion produced
by such a development of a spherical surface is evidently very great near the margin ; but a spectator when duly instructed, on comparing the figures near the centre with the groups of stars about the north pole in the heavens, might distinguish those to which the figures were intended to refer ; and the apartment without a roof, adjoining that which contained the planisphere, is supposed to have been intended for the purpose of facilitating such comparison. One property of the species of projection or development just mentioned is, that in the direc tion of a line passing through the centre, or pole, the distance between two points corresponding to two which are diametrically opposite to one another in the heavens is equal to half the circumference of a great circle of the sphere; and M. Biot found that this condition is satisfied by the planisphere as nearly as can be expected in a representation which does not admit of great precision.
In order to ascertain, if possible, the epoch of the planisphere, M. Biot assumed as correct the positions of four stars upon it, which, being accompanied by figures of men and by hieroglyphical symbols, appeared to have been distinguished oh account of some particular interest attached to them ; and concluding from their positions with respect to the nearest zodiacal signs that they must represent Fomal haut, Antares, Arcturus, and 0 Pegasi, he first verified them by the near agreement of their measured distances from each other on the planisphere with the distances obtained by computation from their known angular distances in the heavens; then computing the angles of the triangle formed by two of the stars and the centre, or pole, of the planisphcre, and also the angles of the triangle in the heavens between the arcs joining the two stars and the pole of the ecliptic in 1750, he found, by comparison, the latitude and longitude of the centre of the planisphere with respect to the positions of the ecliptic and the equi noctial point for that year. The position of the centre, thus found, is that which the pole of the world must have occupied about the year 716 D.C.; and he thence concludes that the planisphere presents the state of the heavens at the latter epoch. M. Biot afterwards calcu lated for that epoch the places of the principal stars, and determined their situations on a plane by the rules of the projection supposed, as above mentioned, to have been used In constructing the Egyptian monument : on comparing the map so formed with an exact copy of the planisphere, he found the stars to fall upon or near the figures to which they were o belong. Thus the stars of Ursa Minor fall near the centre, precisely on the figure of an animal resembling a dog or wolf, probably the Cynosura of the Greeks ; and those of Orion on the figure of a man, apparently intended for Home, the son of Osiris, to whom, according to Plutarch (' De Iside et Osiride '), Orion was consecrated.