The extreme dimensions (i. e. including the verandahs) are seventy-eight feet in length, east and west, and thirty-eight feet in breadth, north and south; these, although small compared with most other public Observatories, will, it is hoped, prove amply sufficient for all useful purposes.
The hill on which the observatory is erected is a solid mass of laterite, in which granite is largely disseminated, and is so hard as to be penetrated with great difficulty; but little depth was therefore required for the foundations, which are accordingly only sunk one foot below the surface, on which the granite bases for the instruments are erected—this surface is by excavation three feet below the general level of the soil outside, and three and a half feet below the floor of the observing rooms. On it is erected, nearly to the height of the floor, but without contact with it, or With the surrounding walls, a solid mass of granite masonry for each instrument, consisting of large pieces of stone clamped together; that in the transit room (a) is ten feet long, by four feet broad; that in the circle room (c) ten feet square, and that in the centre room (b) six feet square. The walls are two feet in thickness, built of squared stones of laterite, and afford a clear height in the observing rooms of seventeen feet. The meridional openings are three in number, each two feet wide, and extend across the building to within three feet of the ground on each side—they are well secured and conveniently laid open by shutters covered with canvas, and painted, and having slips of copper over the abutments. The roof is flat, and on the centre of it is erected a wooden circular building, of nine feet diameter, with a revolving dome which covers a solid pillar of granite, coming up through the centre room without contact with floor, roof, or any part of the building, and terminating about three feet above the flat roof. This pillar is two feet in diameter at the top, and four feet at bottom, and is erected on the granite base of six feet square—the pillar consists of five pieces in the form of a frustrum of a cone. Two other revolving domes of the same size are placed over the circular rooms at the southern corners of the Observatory, which are square turrets of solid masonry. The roof or terrace is conveniently approached by two stair-cases outside the building, and winding round the turrets. The verandahs are divided into small rooms as sleeping apartments, computing offices, library, &c.
| The clear dimensions (inside) of the transit room (a) are | 14 ft. by 12. |
| Do. of the circle room (c) | 14 ft. by 12. |
| Do. of the centre room (b) | 20 ft. by 12. |
The breadth of the verandah is eleven feet.
