Reflection and refraction in Robert Grosseteste's De Lineis, Angulis et Figuris

In his scientific treatise entitled De Lineis, Angulis et Figuris, seu Fractionibus et Reflexionibus Radiorum, Robert Grosseteste is discussing some qualitative geometric rules about reflection and refraction. However, he is also discussing about the power of reflected and refracted light. The reading of these discussions is quite interesting, and what Grosseteste is telling seems well-posed, when compared with the Fresnel reflectance.