The Astronomical Observatories of Jai Singh c10.6

c10.6

37. The Samrāṭ Yantra is the central building of the observatory. It is the largest and most imposing, although a considerable portion of it is below the surface of the earth. It is, indeed, built into a quadrangular excavation some 15 feet deep, 125 feet from east to west, and 120 feet from north to south. The structure is 68 feet high, of which 60·3 feet is above the earth’s surface; 125 feet from east to west, and 113·5 feet from north to south. The details are exhibited in the plans and photographs (plate XV and figures 40, etc.). The essential parts are the inclined edges of the huge gnomon and the quadrants attached to it.³ The edges of the gnomon point to the celestial north pole, that is, they make an angle (28°37') with the horizon, equal (approximately) to the latitude of Delhi, and are parallel to the earth's axis. The quadrants (M K G E D, figure 35) are at right angles to the gnomon, and, therefore, the circles, of which they form part, are parallel to the plane of the equator. These quadrants have each a radius of 49·5 feet, and are graduated on each edge in hours, degrees and minutes,¹ the scales on the northern edges being marked in English and those on the southern edges in Indian symbols. The edges of the gnomon are marked with scales of tangents, as already explained (page 36, see figures 34 and 35). The shadow of the edge of the gnomon on the quadrants gives the local time. In figure 40 the time is about ten minutes to four in the afternoon. The sun's declination is found by observing which part of the gnomon's edge casts its shadow on one of the edges of the corresponding quadrant (see page 36).