The Astronomical Observatories of Jai Singh c15.s2.t1.17

c15.s2.t1.17

The astrolabe,⁵ the theory of which was due to Ptolemy, was improved by the Muslims, almost to perfection, and many of these instruments were so beautifully made, as to become valuable works of art, as well as efficient calculating machines, and useful instruments of observation. As a portable instrument of observation it was only superseded about A.D. 1731 by Hadley's quadrant; for purposes of astrological calculations the astrolabe is still in use in the East. The flat astrolabe has already been described in some detail, as also has al-Zarqālī's modification of it, and al-Bīrūnī's invention has also been referred to (p. 37). There is also the linear astrolabe, or *‘aṣā ’l Ṭūsī* (the rod of al-Ṭūsī),¹ called *yaṣhṭi* by the Hindus. Great ingenuity was exercised in devising improvements and variations of the astrolabe, and there are numerous Arabic and Persian works describing the theory and construction of the instrument. The term al-Aṣṭurlābī, as a name suffix, was not at all uncommon.²