Inbāṭ al-Miyāh al-Khafīya: An Early Work on Hydrology

Hailed as “one of the greatest mathematicians of his time” and “one of the greatest Muslim mathematicians,” Abū Bakr Muḥammad ibn al-Ḥasan al-Karajī (fl. at the end of the tenth and beginning of the eleventh centuries CE) has been recognized for his contributions to various branches of mathematics. Of these the most important, perhaps, were Karajī’s formulation of the algebra of polynomials, and his extension of the algebraic formulations of his predecessors to include irrational solutions; innovations that had a major influence on the subsequent development of algebra. That Karajī was not only interested in mathematical theory can be seen in the contents of his surviving engineering book Inbāṭ al-Miyāh al-Khafīya (Extraction of Hidden Waters). The main topic of Inbāṭ al-Miyāh al-Khafīya is the construction and maintenance of the qanāt aqueducts, upon which agriculture on the Iranian plateau has depended on since pre-Islamic times. In this work, Karajī begins his presentation with theoretical knowledge regarding geology and hydrology, and continues with discussions regarding the legal and practical aspects of the qanāt. Karajī’s discussion of the theoretical aspects of hydrology draws on Aristotle’s Meteorologica and the tradition of al-āthār al-’ulwīya, which was based on Aristotle’s work. A comparative reading of this section of Karajī’s Inbāṭ al-Miyāh al-Khafīya and of related works in the al-āthār al-’ulwīya tradition helps locate the theoretical portion of Karajī’s masterpiece of engineering in the context of the prevalent geological theories of his era.