Both the Earth and the Sky: al-Misaha of al-Muhammadiyya

Al-Risālat al-Muḥammadiyya fi ʿilm al-ḥisāb, the only known comprehensive Arabic mathematics book written by ʿAlī al-Qūshjī, was dedicated and gifted to Sultan Mehmed II by the author himself. According to the available copies, the work was reproduced over the course of two centuries, and its deficiencies and mistakes were corrected during reproduction. This means that it was read and taught by experts in the field. Given its circulation, existing research on this book is quite insufficient. Considering this deficiency together with the knowledge that the author was a polymath, research in each field in which he wrote becomes more important in order to understand the work as a whole. In view of this, the subject of this article is the chapter on al-misāḥa of al-Muḥammadiyya, the content of which points to both the author’s astronomical and linguistic orientations. In order to determine the position of the chapter on al-misāḥa, it is first necessary to see its place in the whole book, after which the position of the chapter on al-misāḥa is compared to other chapters and its internal classification is discussed. Following a detailed presentation of the chapter’s contents and the features of this content that differ from the al-misāḥa chap- ters of earlier mathematical books, the main purpose of the article is realised by drawing attention to al-Muḥam- madiyya’s possible relation to astronomy and language studies. The article argues that ʿAlī al-Qūshjī took a different position from his predecessors and contemporaries in terms of (i) the classification of general mathematical books, (ii) the place where he positioned al-misāḥa, (iii) the points of emphasis in the content of al-misāḥa, (iv) the defi- nitions of the concepts of al-misāḥa, and (v) the fields related to al-misāḥa.