Ibn Sahl Refraction

Discovered by: Ibn Sahl around 984.

What is it? A formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air.

Why is it important? Used in optics to predict how lenses will affect light rays. [Image - Ibn Sahl, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3303465]