Willebrord Snellius (born Willebrord Snel van Royen, also Willebrord van Roijen Snell (13 June 1580 – 30 October 1626), commonly known simply as Snellius and Snell, was a Dutch astronomer and mathematician.
Snell is best known for discovering the law of refraction of light, now known as Snell's law, his pioneering work in survey known as Snellius's triangulation, and the Snellius–Pothenot problem, a means in planar trigonometry of finding an unknown point from known ones.
Despite being commonly attributed to Snell, the law of refraction was first discovered by the Persian scientist Ibn Sahl around 984 AD.
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