Giambattista Della Porta’s Theory of Vision in the De refractione of 1593: Sources, Problems, Implications

Abstract

In both the Magiae Naturalis Libri XX of 1589 and the De Refractione of 1593, Giambattista Della Porta likens the eye to a camera obscura, the pupil serving as a narrow “window” through which images from outside are projected onto the screen of the crystalline lens. This, as Kepler recognized, was a major insight. Yet even a cursory look at Della Porta’s account of vision in the De Refractione shows that, far from being guided by this insight, he ignored it completely, the result being that his theory of sight conflicts with the idea that the eye acts like a camera obscura. It is my aim in this paper to explain precisely how the two conflict and, in the process, to suggest some possible sources and implications of that conflict. In the process, I will look at various aspects of his theory of sight with an eye toward explaining how they are at times both innovative and problematic.