The Introductory Epistle on Sinusoidal Operations


This manuscript is a copy of al-Risāla al-Fatḥīya fī al-a‘māl al-jaybīya (The introductory epistle on sinusoidal operations) by Muḥammad ibn Muḥammad ibn Aḥmad Abu ‘Abd Allāh, Badr al-Dīn (1423–1506), known as Sibṭ al-Māridīnī or the grandson of al-Māridīnī, in honor of his mother’s father, a famous astronomer. The manuscript consists of 16 pages of 14 lines each, and includes an introduction and 20 bābs (chapters or articles). They range in length from a few lines to a page, and cover such topics as determination of the cardinal directions and the qibla (direction of Mecca) using the sine quadrant. Sibt al-Māridīnī appears to have been born in Damascus but lived much of his life in Cairo, where he served as muwaqqit (timekeeper) at Al-Azhar Mosque. Like his grandfather, he was a prolific author and wrote on many topics, including fiqh (jurisprudence) and astronomy. Manuscript copies of many of his works have survived, and copies of this one exist in various European and Middle Eastern collections. The holdings of the National Library of Egypt, the Dār al-Kutub, alone include ten copies of this work, suggesting that it may have been one of the author's most popular writings. The cover of this manuscript shows the seal impression of the Egyptian Kurdish scholar and humanist Aḥmad Taymūr (1871–1930), indicating that it was bequeathed to the Dār al-Kutub by him. The cover also has an article in the same hand as the main text on the etymology of the word al-jayb (the sine function) and a short note at the top left on the magnitude of the sine function for several different angles. In his introduction, the author provides an alternate title for his work: Risāla fī al-‘amal bi al-rub‘ al-mujayyab (Epistle on the operation of the sine quadrant).

Last updated: April 3, 2018