6. SHABNUMA-ROZNUMA BY NASIR AL-DIN HASAN (1218/ 1803)

                     In the early part of the fifteenth century, Padmanabha invented an instrument called Dhruvabhrama-yantra. It consists of an oblong metal plate. On one side is a horary quadrant with which time can be measured in the day time. On the reverse is a nocturnal which measures the sidereal time at night on the basis of the apparent rotation of the stars around the pole star.

            The present instrument can be called an Islamic version of the Dhruvabhrama-yantra, and is therefore important for studying the history of the exchange of scientific knowledge between the Sanskritic and Islamic traditions in India. We do not yet know if Nasir al-Din Hasan was the first one to make such instrument or there were others before him.

            The inscription states that it was made on the orders of Munshi Sahib Walashan Lalah Pyare Lal in 1218 AH (1803 AD) at Bareilly. It is calibrated for the latitude of 28⁰ N, which is approximately the latitude of Bareilly (modern values are 28; 22⁰ N and 79; 27⁰ E).

            It is an oblong copper plate measuring 178 x 174 mm. On the Shabnuma side, there are seven circular scales engraved around the centre. Two indices are pivoted to the centre. With these one can measure for any moment of the night, the time in ghatis, and determine the ascendant and the culmination.

            The reverse side, designated as Roznuma, is actually a sine quadrant (rub’ al-mujayyab). There is 176 mm long graduated index with which time in ghatis or the solar altitude in degrees can be measured in the daytime.