Abstract

At the end of the Renaissance, the complete understanding of the experiment of the camera obscura required dealing with the physical problem of the relationship between light and images. According to Kepler, this experiment demonstrated that the geometry and the physics of light were one and the same thing and that there was no need for the luminous rays to transport any form or species. The Jesuits Franciscus Aguilonius and Christoph Scheiner were conscious of the superiority of Kepler's analysis of the camera obscura, but remained attached to the old theory of species. Scheiner's attitude was particularly significant. Although he had almost entirely assimilated the new Keplerian method of demonstration, he retained the traditional conception of realism. He still believed that the mediation of species was indispensable for making certain that what was seen was a real object.