The Astronomical Observatories of Jai Singh c16.3

c16.3

80. The bases of the designs of the particular instruments are always obvious, but Jai Singh showed very considerable ingenuity in the actual constructions. The Jai Prakāś is practically the hemisphere of Berosus, somewhat elaborated, and the Samrāṭ Yantra may also be considered as evolved from that instrument. This only means, however, that the dial of Berosus was of a very general nature. It consisted of a hemispherical bowl, placed with its rim horizontal, and in the centre and in the same plane as the horizontal edge, was fixed a bead, whose shadow on the concave surface of the hemisphere marked the trace of the sun's diurnal path. The resemblance to the Jai Prakāś is striking enough, but it is doubtful whether Jai Singh had any knowledge of the earlier instrument: he could only have learnt of it from the Muslim astronomers (e.g., al-Battānī, who refers to the principle of the instrument). The Jai Prakāś, however, is something more than the bowl of Berosus, for it is fully graduated, and appears to have been based upon the Muslim instrument known as al-Masāṭirah, descriptions of which are found in the works of the Muslim astronomers.¹