Optics, Latin

Abstract

Medieval Latin optics had its sources in Greek and Arab thinkers, including Aristotle, Euclid, Ptolemy, Galen, al-Kindi, Avicenna, and Alhacen. Its prominent scholars had been Robert Grosseteste, Albert the Great, Roger Bacon, John Pecham, Witelo, and Theodoric of Freiburg. The medieval Latins discussed light’s ontological status and whether its mode of existence in the medium is spiritual or material. They adopted from Alhacen the model of radiation from individual point-sources and the idea of spherical propagation, thereby opening their account to radial analysis. Grosseteste identified light with the first corporeal form, which inserts dimensions onto matter, and Bacon developed the theory of multiplication of species, of which the activity of light was the observable instance. Light thus became the key to the workings of natural causality. The perspectivists formulated optical laws and applied them in explanations of natural phenomena such as the rainbow, pinhole images, and in their account of sight. They debated about the direction of the visual cone and subjected the eye to geometrical analysis. They explained sight as caused by the perpendicular species, since they are the shortest and therefore the strongest. Upon entering the eye, perpendicular rays pass through the cornea, refract at the rear surface of the crystalline lens, and project through the opening of the optic nerve. Sight perceives light and color directly, and twenty more visual qualities through complex processes of comparison, concept-formation, and reasoning. Attention was given to the various faculties of the brain – such as imagination and memory – and their role in processing visual information.