A short note on Ptolemy’s motivation for the introduction of the equant in Almagest X based on his planetary observations. This is part of section II.8 of al-Shīrāzī’s Nihāyat al-idrāk fī dirāyat al-aflāk, but in the three manuscripts listed below it is found as an independent work, in two cases appended to al-Ṭūsī’s Taḥrīr al-Majisṭī (C.1.18).

Note Al-Shīrāzī finished his Nihāyat al-idrāk in Sivas in Shaʿbān 680/No­vember-December 1281 (Niazi). However, MS Oxford, Bodleian, Thurston 3 is dated 660/1262, with some parts copied in 675/1277. It was written by al-Shīrāzī’s disciple or close collaborator Suhrāb b. Amīr al-Ḥājj, the same scribe who also copied MS Leiden, UB, Or. 203 , a copy of the Nihāyat al-idrāk dated 682/1283. In MS Thurston 3, as well as in MS Mashhad, Āstān-i Quds, 5452, the method presented in this treatise is ascribed to Thābit b. Qurra (for which, however, there seems to be no evidence in the extant works by Thābit, see Gamini & Masoumi Hamedani, p. 61). Assuming that Suhrāb was well informed about the works of al-Shīrāzī, it seems most plausible that al-Shīrāzī first wrote a short treatise on Ptolemy’s equant following a method already employed by Thābit b. Qurra and later inserted it into his Nihāyat al-idrāk.

Text: [MS Oxford, Bodleian, Thurston 3]

(101v–102r) الطريق فيه أنّ بطلميوس أخذ بالرصد في سنين متوالية مقدار الرجوع أعني الدرج التي يرجع فيها الكوكب من فلك البروج من الوقوف الأوّل إلى الوقوف الثاني — ولأنّه استخرج الحركات والنسبة المذكورة من جداول القدماء قبل التصحيح قال في كتابه إنّه وجد هذا الخطّ ضعف هذا الخطّ بالتقريب. وهو أعلم بالسرائر إنّه هو العليم الحكيم.

Bibl.: SuterHeinrich Suter, Die Mathematiker und Astronomen der Araber und ihre Werke, Leipzig: Teubner, 1900, pp. 158–159 (no. 387); GAS VIFuat Sezgin, Geschichte des arabischen Schrifttums, vol. VI: Astronomie bis ca. 430 H., Leiden: Brill, 1978, pp. 90 (no. 5c) and 168; F. Jamil Ragep, ‘Shīrāzī’s Nihāyat al-Idrāk: Introduction and Conclusion’, Tarikh-e Elm 11/2 (2013), pp. 41–57; Amir Mohammad Gamini and Hossein Masoumi Hamedani, ‘Al-Shīrāzī and the Empirical Origin of Ptolemy’s Equant in His Model of the Superior Planets’, Arabic Sciences and Philosophy 23 (2013), pp. 47–67; Kaveh Niazi, Quṭb al-Dīn Shīrāzī and the Configuration of the Heavens. A Comparison of Texts and Models, Dordrecht: Springer, 2014, esp. p. 85; Fateme Savadi, The Historical and Cosmographical Context of Hayʾat al-arḍ with a Focus on Quṭb al-Dīn Shīrāzī’s Nihāyat al-Idrāk, PhD dissertation, McGill University, 2018, esp. pp. 21–44 and 107–108.

Ed.: Critical edition, based on the Mashhad manuscript and two manuscripts of the Nihāyat al-idrāk, in Gamini & Masoumi Hamedani, pp. 64–67, with an English translation on pp. 61–64.