This very short work by Ibn al-Ṣalāḥ deals with Ptolemy’s account of the retrogradations of the planets in Almagest XII.2–6. Complete title: al-Maʿnā dhakara-hu Baṭlamyūs fī l-bāb al-thānī min al-maqāla al-thāniya ʿashara fī maʿrifat miqdār rujūʿ Zuḥal wa-fī l-abwāb al-arbaʿa allatī baʿda-hu li-rujūʿ bāqī l-kawākib (“The Meaning of What Ptolemy Says in Chapter 2 of Book XII [of the Almagest] on Knowing the Amount of the Retrogradation of Saturn and in the Following Four Chapters on the Retrogradation of the Remaining Planets”).

Origin: All manuscript witnesses of this work also contain various paraphrases and abridgements composed within the Marāgha school (e.g., of Ibn al- Haytham’s Ḥall shukūk (C.1.10) and the Multaqaṭāt min Kitāb al-Majisṭī (C.1.19)). This can be seen most clearly from Ibn al-Ṣālāḥ’s treatise on Ptolemy’s star table (C.1.24), whose colophon explicitly states 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 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]

[Incipit] (f. 82r) كلّ عددين مسطّحين متشابهين معلومين أحدهما مجهول الأضلاع والآخر معلومها قإذ أضربنا جذر الخارج من قسمته مجهول الأضلاع على الآخر. — [Explicit] (f. 82r) 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.