The laws of refraction
Although many scientists worked on the problem, the laws governing the refraction of light when it passes from one substance to another resisted discovery for centuries. It was not until 1621 that Willebrord Snell, Professor of Mathematics at Leyden University, discovered the exact relationship between the angles of incidence and refraction.
The laws of refraction are now stated as foJ1ows:
Law (1) The incident and refracted rays are on opposite sides of the normal at the point of incidence and all three are in the same plane.
Law (2) (Also known as Snell’s law.) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media.