  Despite the anti-empiricist character of al-Kindi’s epistemology noted above, he devoted enormous energy to various branches of the physical sciences. Particularly well represented in the extant corpus are his work on optics and medicine, especially the compounding of drugs (for optics see Rashed 1997; for medicine see Gauthier 1939, Klein-Franke 1975, Celentano 1979; for these aspects of al-Kindi’s thought generally see Adamson 2007, ch.7). What is characteristic about al-Kindi’s approach to such topics is the use of mathematics. It has been persuasively argued that mathematics was fundamental to al-Kindi’s own philosophical method (Gutas 2004, cf. Endress 2003); a good example is his mathematical approach to Aristotle’s categories, which makes quantity and quality fundamental for Aristotelian logic (Ighbariah 2012). Certainly he missed no opportunity to apply mathematical techniques to what we would now think of as “scientific” topics. In addition, he wrote numerous works on music (edited in Zakariyya’ 1962), which for the ancients and al-Kindi himself was a branch of the mathematical sciences. He also wrote extensively on more recognizably mathematical topics, as is attested by the Fihrist, though again much of this material is lost.