The Astronomical Observatories of Jai Singh c10.31

c10.31

38. The Jai Prakāś consists of two complementary concave hemispheres, situated immediately south of the Samrāṭ Yantra. Their structure is best seen in plates XVIII and figures 41 and 42. Theoretically, only a single hemisphere is necessary, but, to facilitate observation, pathways are cut into the surface; and the second Jai Prakāś is so constructed that the two instruments together show the complete surface. Cross wires were, originally, stretched across the hemispheres north to south and east to west, and the shadow of the intersection of these wires on the concave surface of the hemisphere indicated the position of the sun. The surface of the hemisphere is marked with altitude and azimuth circles, the tropics and intermediate circles (declination parallels), etc., so that the position of the sun can be directly read off. Also there are ‘circles of the signs of the zodiac,’ by which the particular sign on the meridian is indicated by the position of the sun's shadow.¹ In the Delhi instruments the cross wires have been discarded, although the pins to which they should be fastened are still there; and iron rods (2 inch galvanized piping) have been fixed at the centre of each Jai Prakāś. The pipes should be removed and the cross-wires replaced.