Cet article a pour objet la réinterprétation, dans le sillage de la rénovation keplérienne de l’optique, de la fonction de l’image rétinienne pour la vision par Gassendi et Descartes. Une comparaison de leurs approches montre qu’elles reposent sur une interprétation différente du modèle iconique de la perception. S’ils attribuent un rôle crucial à l’imagination pour la perception visuelle, leurs positions philosophiques font jouer un rôle différent à l’image dans la perception visuelle et les amènent à concevoir de façon divergente l’imagination (...) et son rapport aux autres pouvoirs de l’esprit. (shrink)

According to the received view, the first spyglass was assembled without any theory of how the instrument magnifies. Galileo, who was the first to use the device as a scientific instrument, improved the power of magnification up to 30 times. How did he accomplish this feat? Galileo does not tell us what he did. We hold that such improvement of magnification is too intricate a problem to be solved by trial and error, accidentally stumbling upon a complex procedure. We construct (...) a plausibility argument and submit that Galileo had a theory of the telescope. He could develop it by analogical reasoning based on the phenomenon of reflection in mirrors—as it was put to use in surveying instruments—and applied to refraction in sets of lenses. Galileo could appeal to this analogy and assume Della Porta’s theory of refraction. He could thus turn the spyglass into a revolutionary scientific instrument—the telescope. (shrink)

En el artículo se ofrece un análisis de los argumentos que condujeron a Kepler a la defensa y demostración del teorema fundamental de la óptica. Según este teorema, un haz homocéntrico de luz que se ve obligado a atravesar una esfera transparente, siempre que la amplitud del haz no sea mayor, se concentra de nuevo en un punto al otro lado de la esfera. La demostración de Kepler se compara con la ofrecida por Malebranche años más tarde. Este teorema fue (...) determinante para la consolidación de la óptica moderna. (shrink)

“Although up to now the [visual] image has been [understood as] a construct of reason,” Kepler observes in the fifth chapter of his Ad Vitellionem Paralipomena, “henceforth the [visible] representations of objects should be considered as paintings [ picturae ] that are actual[ly projected] on paper or some other screen.” While not intended as a historical generalization, this claim nonetheless reflects historical reality. Virtually all visual theorists before Kepler did, in fact, conceive of optical images as subjective, not objective constructs (...) – or, to put it in modern terms, as virtual rather than real entities. By current lights, of course, the distinction between virtual and real images is both obvious and common-place: whereas the latter can be physically projected upon a screen, the former cannot. (shrink)

This paper argues that Kepler considered his work in optics as part of natural philosophy and that, consequently, he aimed at change within natural philosophy. Back-to-back with John Schuster’s claim that Descartes’ optics should be considered as a natural philosophical appropriation of innovative results in the tradition of practical and mixed mathematics the central claim of my paper is that Kepler’s theory of optical imagery, developed in his Paralipomena ad Vitellionem (1604), was the result of a move similar to Descartes’ (...) by Kepler. My argument consists of three parts. First, Kepler borrowed a geometrical model and experiment of optical imagery from the mélange of mixed and practical mathematics provided in the works of the sixteenth-century mathematicians Ettore Ausonio and Giovanni Battista Della Porta. Second, Kepler criticized the Aristotelian theory of light and he developed his own alternative metaphysics. Third, Kepler used his natural philosophical assumptions about the nature of light to re-interpret the model of image formation taken from Della Porta’s work. Taken together, I portray Kepler’s theory of optical imagery as a natural philosophical appropriation of an innovative model of image formation developed in a sixteenth-century practical and mixed mathematical tradition which was not interested in questioning philosophical assumptions on the nature of light. (shrink)