The Ikhwan al-Safa' (Brethren of Purity), the anonymous adepts of a tenth-century esoteric fraternity based in Basra and Baghdad, hold an eminent position in the history of science and philosophy in Islam due to the wide reception and assimilation of their monumental encyclopaedia, the Rasa 'il Ikhwan al-Safa' (Epistles of the Brethren of Purity). The fifty-two epistles offer synoptic accounts of the classical sciences of the age, treating themes...