Electromagnetic

Although he [Kindi, d. ca. 870] accepts that we perceive visible forms, he is always neutral about the mechanism by which we perceive them* [Footnote 19: Consider, for example, this passage from On First Philosophy: "our perception through the senses, upon direct contact (mubashara) of sense with its object is not in time" (AR 106.8). Here al-Kindi's statement is consistent with Aristotle, but emphasizes only the fact that sensation is through contact, which as previously mentioned is common to all ancient theories of vision. By the same token, al-Kindi does not try to bring together the Aristotelian doctrine of visible forms with his extramissionist mechanics]. Nowhere does al-Kindi imply that we must perceive forms through some sort of intromission view. In any case, al-Kindi may, like modern scholars, have been troubled by Aristotle’s own inconsistency on the question of the mechanism of vision. In the Meteorology and De Caelo he adopts an extramission theory like that of Plato, Euclid and al-Kindi* [Footnote 20: ... ]. Still, it is clear that [Kindi's] De Aspectibus considers and rejects an identifiably Aristotelian theory of vision.

Al-Kindi’s fidelity to Euclid is also less than complete. De Aspectibus diverges from the Optics on a number of points. This is done more in a spirit of charity than criticism: al-Kindi says in De Aspectibus, Prop. 11, II. 79-81, that we should not be eager to attribute error to a figure like Euclid, but instead “we should think well of him and shift what he says to the right path (convertamus eius sermonem ad semitam bonam).” In the rest of this section I want to present three such shifts:

(A) Euclid presents visual rays as one-dimensional lines emitted to form a cone. Al-Kindi argues that the rays must in fact be three-dimensional.

(B) Euclid also believed that as the lines emitted from the eye spread out, there will be gaps between them; this is why we do not see things clearly when they are far away. Al-Kindi denies this, and holds that the visual cone is continuous.

(C) Finally there is the aforementioned account of how light is propagated: along straight lines, but having an instantaneous effect over the whole extent of its path (in other words, light does not travel).

Adamson, Peter. “Vision, Light and Color in al-Kindi, Ptolemy and the Ancient Commentators” in Arabic Sciences and Philosophy. Vol. 16, No. 2, September 2006, pp. 213-14. Note: I have left out Adamson’s diacritics.