This very short work by Ibn al-Ṣalāḥ (for whom see C.1.15) deals with Ptolemy’s account of the retrogradations of the planets in Almagest XII.2–6. All manuscript witnesses of this work also contain various paraphrases and abridgements composed in the Maragha circle, for example of Ibn al- Haytham’s Ḥall shukūk (C.1.10) and of Naṣīr al-Dīn al-Ṭūsī’s Multaqaṭāt min Kitāb al-Majisṭī (C.1.19). This can be seen most clearly from the extant version of Ibn al-Ṣālāḥ’s treatise on Ptolemy’s star table (C.1.24), whose colophon states explicitly that it is an abridgement by Quṭb al-Dīn al-Shīrāzī. Therefore, it is theoretically possible that also the present work by Ibn al-Ṣālāḥ was originally more extensive, although there is no explicit indication of this in any of the manuscript witnesses. The anonymous Muqaddima fī taʿyīn nuqṭatay al-wuqūf (C.1.31), which follows this text immediately in MS Istanbul, Topkapı, Hazine 455 and also deals with retrogradations, may be part of the same work, although it appears at different places in the other witnesses.

Text: [Istanbul, Topkapı, Ahmet III 3455]

(82r) كلّ عددين مسطّحين متشابهين معلومين أحدهما مجهول الأضلاع والآخر معلومها قإذ أضربنا جذر الخارج من قسمته مجهول الأضلاع على الآخر — فإذا أخذنا جذره وهو ط كان معلومًا وإذا ضربنا المعلوم في ه ز المعلومين خرج ج د معلومين وهذا مراد.

Bibl.: KrauseMax Krause, ‘Stambuler Handschriften islamischer Mathematiker’, Quellen und Studien zur Geschichte der Mathematik, Astronomie und Physik, Abteilung B: Studien 3 (1936), pp. 437–532, p. 486; GAS VIFuat Sezgin, Geschichte des arabischen Schrifttums, Vol. VI: Astronomie bis ca. 430 H., Leiden: Brill, 1978, pp. 92–93; MAOSICBoris A. Rosenfeld and Ekmeleddin İhsanoğlu, Mathematicians, Astronomers, and other Scholars of Islamic Civilization and their Works (7th–19th c.), Istanbul: Research Centre for Islamic History, Art and Culture (IRCICA), 2003, pp. 177–178 (no. 458, A4); Paul Hullmeine, ‘Correcting Ptolemy and Aristotle. Ibn al-Ṣalāḥ on Mistakes in the Almagest, On the Heavens, and Posterior Analytics’, Arabic Sciences and Philosophy 32 (2022), pp. 201–246, here pp. 213–214.

Ed.: None.