The Astronomical Observatories of Jai Singh c9.s1.9

c9.s1.9

The construction of the instrument is seen in the plan and section shown in plate XVIII, and in figures 30, 32 and 33. Figure 38 shows a projection of a complete Jai Prakāś. The outer circle represents the horizon and is graduated in degrees. From the centre azimuth lines and altitude circles are drawn. (These are not all shown in the plate.) The pole P is at a point on the meridian line, BD, at a distance from the point B equal to the latitude of the place (in the plate 28°37′ approximately). The equator, AEC, and tropics, fff (Capricorn), ggg (Cancer), and intermediate diurnal circles (not shown) are drawn. The equator cuts the meridian at a point, E, at a distance from the centre point equal to the latitude of the place (28°37′), and the other circles cut the meridian at distances 23½°, 20°12′ and 11°30′ on either side of the equator. Through the pole, hour circles Pa¹ Pa², Pa³, etc., are drawn. The circles hh₁, ii₁, jj₁, kk are circles of the signs, and are such, that, when the shadow falls on any one of them, the corresponding sign is on the meridian. Two such circles cut each of the seven diurnal circles on the meridian, and cut the neighbouring diurnal circles at the proper intervals. At Jaipur a similar instrument (figure 31) called Kapāla (‘cup’ or ‘hemisphere’) is so constructed, as to show ‘rising signs.’ In this instrument the edge of the hemisphere corresponds, not to the horizon, but to the solstitial colure (i.e., the circle passing through the poles and the solstitial points), and, thus, is the Jai Prakāś turned through a right angle.²