Optics

Renaissance optical studies benefited from advances in geometry, from tables of refraction measuring starlight to geometric diagrams explaining retinal images. Although the properties of vision itself became better understood between 1400 and 1600, Renaissance eyeglasses were only concave lenses. Invented during the late 13 th century, eyeglasses were rare even in the 14th century. Evidence in art suggests that they had become something of a status symbol by the 16th century. The eyes, of course, were understood as the pathway of all visual knowledge. Renaissance scholars and artists realized that the eye was a receptor for images rather than a projector. The learned Frenchman Petrus Ramus (1515-72) collaborated with Friedrich Risner (d. 1580) to publish a work in 1572 that included scholarly editions of two important texts on optics. Entitled Opticae thesaurus (Thesaurus of optics), this publication influenced the study of optics for the next few decades. The work presented the work of Alhazen, a medieval Arabic scholar who had studied ancient Greek scientific treatises to create his own theory of vision, as well as the conclusions of Witelo, a student of Roger Bacon’s, written circa 1270. Not published until 1611, the work of a Benedictine monk, Francesco Maurolico (1494-1575) on optics would have been important if others had known about it. Maurolico explained the camera obscura in geometric terms, quantified the light reflected from mirrors of various shapes, and discussed refraction in the eye.

Anatomical discoveries included significant changes in assumptions about the eye and vision. Dissecting eyeballs, Leonardo realized that the external image received on the retina was inverted. He thus was able to compare the eye to the camera obscura, experimenting with variations in the pupil’s diameter. Although Renaissance researchers did not quite comprehend how the eye acts as a lens, they did locate the lens, which they called the crystalline humor. Experiments by Kepler, working on optics pertaining to astronomy, further distinguished various functions of vision. Giambattista Della Porta (c. 1535-1615) was a Neapolitan who studied what he called “natural magic.” The second edition of his book with this title, Magia naturalis, discussed his experiments with refraction of light. This topic very much appealed to Della Porta, who subsequently wrote a book focusing on refraction, De refractione (1593). His research with concave and convex lenses, and with the pupil of the eye, contributed to studies concerning distance vision and the invention of the telescope in the early 17 th century.