Willebrord Snellius

Biography

Willebrord Snellius (Latinized name Snellius) was born in Leiden, the son of a mathematician. He studied law and mathematics at Leiden University, then traveled through Europe, communicating with scientists. Upon returning, he became professor of mathematics at Leiden University. He worked on geodesy, introducing the method of triangulation for measuring the arc of the meridian. He experimentally discovered the law of refraction in 1621, but did not publish it; the law was publicized by Descartes in 1637. He died at the age of 46.

Key discoveries

• Snell's law: the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media and equals the relative refractive index (n1 sin θ1 = n2 sin θ2).
• Development of the triangulation method for precise distance measurement on the ground, which allowed refining the length of a degree of the meridian.
• Astronomical and navigational calculations, improvement of tables for marine navigation.