Cassius Dio's fragmentary Roman History 15 contains an account of Archimedes’ role in defending Syracuse during the Roman siege of 213–212 b.c., incorporating a legendary tale about a solar reflector Archimedes constructed to burn Roman warships, and including details of his death when the city fell. The textual basis of this famous episode depends on two derivative twelfth-century works: Zonaras’ Epitome of Histories (9.4–5) and Tzetzes’ Chiliades (2.35). After clarifying the present state of enquiry, this paper introduces two new witnesses, (...) overlooked by editors of Dio and extensive scholarship on Archimedes, and assesses their value for reconstructing Dio's text. Comparative analysis of corresponding Dio-derived material in Tzetzes’ Carmina Iliaca and Hypomnema in S. Luciam, especially verbal correspondences with Zonaras’ Epitome, demonstrates that they are independent and, sometimes, superior witnesses to Dio's wording and content, reflecting Tzetzes’ selective use of the Roman History in different verse and prose compositions over several decades. The study considers editorial implications for this section of Dio's work and general characteristics of Tzetzes’ writings as repositories of testimonia and fragments. (shrink)

In 1626, René Descartes and Claude Mydorge worked closely together on the problem of refraction, apparently discovering what is now known as the sine law of refraction. They constructed a plano-hyperbolic lens in order to test out the truth of this mathematical relationship. In 1637, Descartes finally published the sine method of determining refractions in his Dioptrique, which also demonstrated, on the basis of this relationship, that the hyperbola and ellipse were anaclastic lines (that is, that a lens with their (...) profile would refract rays perfectly to a single point) without mentioning Mydorge. Mydorge himself wrote a short manuscript on the subject of refraction and lenses, which is found in a copy among Mersenne’s papers. Scholars have usually assumed that this treatise was written as Mydorge and Descartes worked together in 1626. However, other evidence shows that only the first part of the treatise records the two men’s early collaboration. Subsequently, Mydorge and Descartes completed their arguments separately, Descartes with the help of Isaac Beeckman. (shrink)