Who really discovered Snell's law?

Abstract

Open any physics textbook and you'll soon come across what English-speaking physicists refer to as "Snell's law". The principle of refraction – familiar to anyone who has dabbled in optics – is named after the Dutch scientist Willebrørd Snell (1591–1626), who first stated the law in a manuscript in 1621. In French, however, the same law is often called "la loi de Descartes" because it was René Descartes (1596–1650) who first put the law into widespread circulation in his Discourse on Method, published in 1637.