ABSTRACT
In two articles in this journal the relationship has been studied between the Persian Zīj-i Muḥammad Shāhī, completed in Jaipur around 1735 under Sawā’ī Jai Singh, and the astronomical tables of Philippe de La Hire, printed in Paris in 1727. Mercier concluded that Jai Singh’s planetary tables were all taken directly from La Hire and do not depend on observations made in India. On the other hand, Sharma maintained that the planetary tables in theZīj-i Muḥammad Shāhī are independent from those of La Hire.
In this article, the methods by which Jai Singh’s tables for planetary mean motion were computed will be investigated in detail. First it will be shown that the initial mean positions in the Zīj-i Muḥammad Shāhī were calculated from La Hire’s mean motion tables by adding the entries for the appropriate numbers of years, months and days and applying a correction for a difference in geographical longitude between Paris and Delhi of 73°30′.
Next, the mean motion parameters underlying Jai Singh’s tables will be determined by means of recently introduced mathematical techniques and computer programs. It will be shown that the daily mean motions were calculated from particular values found in La Hire’s tables. Our recomputations of Jai Singh’s tables show only incidental differences of at most a couple of sexagesimal fourths of a degree. We conclude that the mean motion tables in the Zīj-i-Muḥammad Shāhī were in fact derived from the tables of La Hire, thus confirming Mercier’s result.
