Kāshānī’s Equatorium: Employing Different Plates for Determining Planetary Longitudes (2019)
Ghīyāth al-Dīn Jamshīd ibn Mas‘ūd ibn Maḥmūd ibn Muḥammad Kāshānī (or al-Kāshī), the fifteenth-century Iranian astronomer and mathematician, is known nowadays for his precise calculation of π and Sin 1°, and for his con-tribution to Ulugh Beg’s observatory at Samarkand. In 818 H (1416 CE), most probably in his home town of Kāshān, he invented an equatorium,1 and wrote an Arabic treatise on its construction and use. The treatise had the title Nuzhat al-Ḥadāʾiq (Excursion to the Gardens) and the equatorium was called Ṭabaq al-Manāṭiq (Plate of the Deferents). In the Nuzha, he also described another instrument, named Lawḥ al-Ittiṣālāt (Plate of Conjunctions). The main pur-pose of both instruments was to reduce the amount of calculation astrologers needed to do. About ten years later, while Kāshānī was working at Samarkand Observatory, he wrote an Arabic supplementary tract to the Nuzha, in which he added a set of ten appendices. Most of them describe new methods of construction and give simple and more precise instructions for using the equatorium.During the reign of Sultan Bayezid II (from 1481 to 1512), most probably in Istanbul, an anonymous astronomer composed an untitled Persian treatise about Kāshānī’s equatorium, and dedicated it to the Sultan.2 Having found the only manuscript of this Persian treatise, the late Edward S. Kennedy surmised that the original work of Kāshānī was lost.3 He started his investigation of the equatorium using the Persian text and published two papers, one on the Plate of Conjunctions in 1947,4 and the other on the equatorium in 1950.5 In 1951 he discovered that a manuscript of Kāshānī’s Nuzha was preserved in the India Office Library in London, but he carried on his research without paying much attention to this original work of Kāshānī. The result was two more papers in the same year, 1951.6 It was only in his last paper in 1952 that he included some information about the original Arabic text.7 Eventually, in 1960 he published a book on the instrument entitled The Planetary Equatorium of Jamshīd Ghīyāth al-Dīn al-Kāshī,8 which included a facsimile of the Persian text, an English translation and a commentary. Kennedy also discussed briefly some of the appendices Kāshānī published in the supplementary tract.As nearly all of Kennedy’s contribution is based on the Persian treatise of the anonymous Ottoman astronomer, it is worth studying Kāshānī’s own text to learn more about his equatorium and his scientific career. In the present chapter I describe some of the features of the original text and explain how the three additional plates described in the Nuzha can be used to find the true lon-gitudes of the superior planets (Mars, Jupiter and Saturn) and of Venus. I also show how the equatorium can be used for different geographical longitudes.
...MoreBook Neil Brown (2019) Scientific Instruments between East and West.
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