Relationship between the path taken by a ray of light as it moves from one medium to another and the refractive indices of the two media.
Discovered in 1621 by Willebrord Snell (1580–1626), the law went unpublished until its mention by n 1 and n 2 represent the indices of refraction of two media, and θ 1 and θ 2 are the angles of incidence and {{link=refraction">refraction that a ray of light makes with the line perpendicular to the boundary (the normal), Snell's law states that n 1 / n 2 = sin θ 2 /sin θ 1 . Because the ratio n 1 / n 2 is a constant for any given wavelength of light, the ratio of the two sines is also a constant for any angle.