Transformation of Euclid’s Optics in Late Antiquity

Abstract

The tradition of Euclid’s Optics includes a number of versions and translations, whether in Greek, Arabic or Latin. They differ from each other to various extents with respect to their form, structure and content. Textual divergence concerns the very core of geometric optics, i.e. the opening definitions and first propositions. In these parts the variance of the different versions is most striking. Thus the tradition of the Euclidean text involved a transformation of the visual model that cannot be explained merely philologically or by incidental elements in the process of transmission. This paper aims to explain these textual transformations as an intentional process of updating and adapting geometric optics to the best of its understanding at a given time. For this purpose, the different versions of Euclid’s Optics are placed in the context of and compared with late antique and early medieval sources. From Ptolemy through al-Haytham, experience had been used as an argument either to refute or to defend the geometric model of vision. Indeed, the visual ray hypothesis turns out to be more or less or not at all compatible with experience in the various versions of Euclid’s Optics. Their divergence thus provides evidence of a lively tradition of Euclidean Optics whose core has been transformed by discussing and testing the visual model on empirical grounds.