Debating vision and refraction in Galileo's time: Marcantonio De Dominis and Cesare Cremonini

This article provides a reading of Marcantonio De Dominis' De radiis visus et lucis (1611) in light of the discovery of its substantial dependence on Cesare Cremonini's manuscript De iride. The relationship between the two works is examined by comparing their structure and diagrams. Placing De radiis into context with the long-standing perspectivist tradition and the sixteenth-century development in optics, this article analyses how De Dominis' argumentative strategy was carried out, with particular reference to the alternative between extramission and intromission and the use of the concept of refraction. It is argued that De Dominis addressed issues advanced, among others, by Giambattista Della Porta, to build a coherent optical theory based on Aristotelian-oriented concepts and notions. Moreover, the article analyses how the general purpose of De Dominis' De radiis provides context to his way of rethinking the theoretical novelty of the telescope, announced in Galileo Galilei's Sidereus nuncius.