The Astronomical Observatories of Jai Singh c8.29

c8.29

25. The Dhruva Bhrama Yantra or ‘Circumpolar instrument’ is another modern Hindu instrument of rather crude workmanship. It consists of a square plate, with a slit near to and parallel to one edge, and a freely revolving weighted index with four pointers. If the plate is held vertically in such a position that the Pole star and the star *Markati* (Kochab or *β* Ursae Minoris) are in line with the slit, then the pointer marked *Ghaṭī* will indicate sideral time in *ghaṭīs*.² The other pointers indicate the rising sign, the sign on the meridian, and the rising, and setting *nakshatras*.³ The back of the instrument is marked *Turīya Yantra* (quadrant instrument), and consists of a hinged rod, two sighting rings on the edge parallel to the slit, and a graduated quadrant consisting of eleven scales. When the sun shines through the sighting ring the index shows the altitude and the time. Also a list of the 28 *nakshatras* (initials only), starting with Aśvinī and proceeding in the usual order,³ is given, and to each asterism is attached a number varying from 12½ to 18½.