Al-Kindi

Al-Kindi was the first significant philosopher to write in Arabic and the organising figure of the translation movement in ninth-century Baghdad, working under Abbasid patronage on the transmission of Greek philosophy and science into Arabic. Peter Adamson's study is the standard account. His range was enormous, metaphysics, optics, medicine, music, cryptanalysis, where he produced the earliest known description of frequency analysis.

His interest for this atlas is the treatise De radiis, On the Stellar Rays, which survives complete only in Latin. It argues that every object in the world emits rays that act upon everything else, that the stars are the most powerful emitters, and that the resulting web of influence explains astrology, the efficacy of words and images, and the operation of magic.

The crucial feature is that this is a naturalistic theory. It requires no spirits, no demons and no divine intervention; magical effect becomes a physical process obeying regular laws, in principle as investigable as optics, the model is deliberately optical, with rays radiating, weakening with distance, and reflecting. That move gave later Latin writers a defensible way to hold that magic could be natural rather than demonic, and the theory of correspondences and sympathies that runs through Ficino, Agrippa and everything downstream of them has a substantial debt to it. The book was condemned as it circulated in the West, which is a fair indication that its readers understood the implications.

Al-Kindi worked at the centre of the great ninth century effort, patronised by the Abbasid caliphs in Baghdad, to carry Greek science and philosophy into Arabic. He was not himself a translator; his role was to commission, correct and digest, standing at the head of a circle that produced Arabic versions of Aristotle, of Euclid and Ptolemy, and of the paraphrase of Plotinus that circulated, fatefully, as the Theology of Aristotle. On that foundation he wrote in his own voice across an astonishing range, and two threads matter most to his afterlife. The first is method: his treatise on deciphering encrypted messages describes counting the frequency of letters in a known language and matching the counts against a ciphertext, the earliest surviving statement of frequency analysis and the founding move of cryptanalysis. The second is the physics of influence.

In the work Latin readers knew as De radiis, everything in the world emits rays that act on everything else, and the rays of the stars shape events below; words, images and figures emit rays of their own, which is why, on this account, talismans and incantations can work. Medieval Europe read the book nervously and sometimes condemned it, precisely because it offered magic a natural mechanism rather than a demonic one. Astrologer, music theorist, optician and philosopher of the One, al-Kindi made the case that none of these was a separate pursuit.