Euclid's Extramission Theory

Of all the means through which humans perceive the world, sight is perhaps the most important. It is our primary means of understanding the physical nature of our surroundings, both immediate and distant. It is only natural that the great thinkers of antiquity were curious about the nature of vision, and inseparably, that of light itself. In the manner characteristic of ancient science, many common ideas about optics were “hit or miss”, so to speak. Certain Greek thinkers had hypotheses about optics which are more or less in line with modern principles, but many held firmly to ideas which are at odds with the current understanding of reality. I discuss extramission theory (a hallmark of Greek optical science), the work of the atomists Democritus and Leucippus who rejected it and presented compelling (but flawed) alternative frameworks, the contrasting views of pivotal (and ubiquitous) philosophers Plato and Aristotle, Euclid’s highly mathematical and geometric treatment of optics, and Ptolemy’s …show more content…
Plato himself was an extramissionist. Unlike Empedocles, his theory had a clearer logic behind the mixing of internal and external light: as Nightingale writes, the two kinds of light were believed to share a kinship, and “because of this kinship, the light coming from the eye is able to coalesce with the light of the sun to form … a single beam of light,” which is the ultimate light of vision through which objects are perceived. Finally, the image is distributed out of the physical world to the soul of the observer by this light. Plato’s theory is at its core much the same as Empedocles’s, and shares its deepest flaws (mainly, a lack of evidence or reason to believe that there is such an internal light or, if it does exist, that it plays a part in the process of vision). That being said, it has some appealing nuance that might lend a modern reader to view it more favorably than that of his predecessor