Jābir Ibn Aflaḥ
Almost nothing is known of Jābir’s life, but remarks by Maimonides (d. 1204), e.g., that he knew Jābir’s son, place Jābir probably in the first half of the twelfth century, and the name “al-Ishbīlī” establishes a connection with Seville. Indeed, legend associates his name (wrongly) with the building of the Torre del Oro and of the tower now belonging to the cathedral in Seville. Jābirs’ principal work was a commentary (or correction, iṣlāḥ) on Ptolemy’s Almagest, the standard textbook on mathematical astronomy, which he had seen in two translations from the Greek. In this treatise he not only simplified the mathematics and separated theory from calculation (there are no tables in the book), but also indulged in violent criticisms of Ptolemy. The introduction to the commentary contains a list of Ptolemy’s “errors”, which are considered in detail in the body of the book. His best known astronomical claim of this kind was his assertion, against Ptolemy, that Venus and Mercury must lie...
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