Snell's law

Etymology
For Willebrord van Roijen Snell, Dutch mathematician.

Noun

 * 1)  the law that, for a ray incident on the interface of two media, the sine of the angle of incidence times the index of the refraction of the first medium is equal to the sine of the angle of refraction times the index of refraction of the second medium

Translations

 * French: loi de Snell-Descartes de la réfraction
 * Polish: prawo Snelliusa, prawo Snella