The Astronomical Observatories of Jai Singh c5.55

c5.55

But finding that brass instruments did not come up to the ideas which he had formed of accuracy, because of the smallness of their size,¹ the want of division into minutes, the shaking and wearing of their axes, the displacement of the centres of the circles, and the shifting of the planes of the instruments, he concluded that the reason why the determinations of the ancients, such as HIPPARCHUS and PTOLEMY, proved inaccurate, must have been of this kind. Therefore he constructed in Dār al-Khilāfat Shāh Jahānābād,² which is the seat of empire and prosperity, instruments of his own invention, such as *Jai Prakas* and *Rām Yantra* and *Samrāt Yantra*,³ the semi-diameter of which is of eighteen cubits and one minute on it is a barley corn and a half⁴—of stone and lime of perfect stability, with attention to the rules of geometry and adjustment to the meridian and to the latitude of the place, and with care in the measuring and fixing of them, so that the inaccuracies from the shaking of the circles and the wearing of their axes and displacement of their centres and the inequality of the minutes might be corrected. Thus an accurate method of constructing an observatory was established and the difference which had existed between the computed and observed places of the fixed stars and planets by means of observing their mean motions and observations was removed.