The History of Refraction

al-Hitham's treatment of refraction in the book of optics takes a similar approach, combining a mathematical description with a physical explanation. He proposes that refractive materials allow light to propagate through them, but are partially resistant to light. In contrast, he proposes that materials which don't reflect light have pores, which trap the light and stop it from bouncing back. This was a reasonable explanation, which as it turns out, will have a long history. But there is an important feature of refracted light not equally felt in each direction. When light enters a denser medium, it will travel faster in the direction perpendicular to the surface compared to the direction parallel to the surface,. causing