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Portrait of the Dutch mathematician and physicist Willebrord Snell (1580-1646). Snell studied law and mathematics, and in 1613 succeeded his father as professor of mathematics at Leiden University. He published translations of mathematical works, and also became interested in geodesy (the science of mapping the Earth's surface and correlating geological, gravitational and magnetic measurement). He developed the basic law of the refraction of light known as Snell's law, in 1621. This states that for light passing from one medium into another, the ratio between the sines of the angle of incidence and of the angle of refraction is a constant. The law was published by Descartes in 1637.
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