The Travelers Guide on Drawing the Circle of Projection


This is a work on timekeeping and the determination of the direction of prayer (qibla), particularly intended for people who travel. The author, Abu al-‛Abbās Shihāb al-Dīn Ahmad b. Zayn al-Dīn Rajab b. Tubayghā al-Atābakī, known as al-Majdī or Ibn al-Majdī (1366-1447 [767-850 A.H.]), was descended from a powerful family with ties to Mamlūk rulers and was a renowned and prominent mathematician, geometrician, and astronomer. He served as the timekeeper of the Al-Azhar Mosque. This work is an abridgment of his other major book, Irshād al-ḥā’ir ilā ma‘rifat waḍ‘ khuṭūṭ faḍl al-dā’ir (Guide to the perplexed on drawing the circle of projection), but it also contains material not in the other book. The present manuscript, completed sometime before 1637-38 (1047 A.H.) by Ḥasan ibn abī al-Bajṭīṭī, once belonged to ‘Abd-Allāh al-Ṭūlūnī and then, from 1644 (1054 A.H.), to ‘Alī ibn Ḥājj Yūsuf al-Labūdī. The work is composed in three chapters: drawing the circle of projection (faḍl al-dā’ir) on a plane parallel to the horizon, which is called a simple plane (basīṭa); drawing it on a perpendicular place, known as a deviant plane (munḥarifa); and drawing it in parallel to other planes. The conclusion addresses issues such as locating the center of the circle, measurement of latitude, and other topics. The work contains extensive tables.

Last updated: March 8, 2016