Project icon: lavishly furnished initial letter with a painting of Ptolemy using an astrolab.

Ptolemaeus Arabus et Latinus

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Work A.6.2

Demonstrationes astrolabii (tr. Isaac Hebreus)


‘(Milan, BA, D. 114 inf.) Demonstrationes astrolabii a Ptholomeo editae, correctae et rectificatae per magistrum Hisaac Hebreum. Scripsit Ptholomeus ad Sirum: Postquam possibile est ut circuli secantes sphaeram appareant in superficie plana — (84v) non oportet dividere circulos per singulos gradus, sed sufficit divider eos per 30 gradus. Sequens capitulum non est Ptolomei sed est Abo Alcasis Mesulam filii Alchamad. Dixit Ptolomeus: Docuit in hoc tractatu quomodo debeamus describere orizontem et paralellos eius, qui dicuntur almucantarat — arcus eque divident horizontem et omnes eius paralellos. Finis.’


Ptolemy’s text, together with Maslama al-Majrīṭī’s additional material (see A.6.1), at least some of the notes (cf. ‘Aliter. Dico quod impossibile est ut he secet orizontem…’, f. 77r =Note 2; ‘Dixit Mesulam: Si huiusmodi circulus descriptus in astrolabio…’, f. 81v =Note 6; ‘Et nota, ut dixit Mesulam, quod distantia paralelli circulo signorum…’, f. 82v =Note 7; ‘Dixit Mesulam: Ptholomeus non demonstravit quod centra non sunt in eodem puncto…’, f. 83r =Note 8) and Maslama’s extra chapter at the end.


This previously unnoticed translation of the Planispherium is said to have been ‘edited, corrected and rectified’ by one master Isaac Hebreus (‘magister Hisaac Hebreus’), but it really is a distinct translation from Hermann of Carinthia’s (A.6.1). The text ultimately derives from the Arabic version, as shown by the presence of Maslama’s extra material, but it was perhaps translated from a Hebrew intermediary, for the only extant MS mixes both Latin and Hebrew scientific texts. The identity of this Isaac Hebreus is unclear. The only extant MS was copied in northern Italy c. 1500.