Willebrord Snellius

Timeline

1. 1600–1613Leiden · LeidenSnellius was the son of Leiden mathematics professor Rudolph Snell. He traveled widely in Europe in his youth, and in 1600–1601 encountered Tycho Brahe's tradition of precise observation in Prague. After his father's death in 1613 he succeeded him as professor of mathematics at Leiden University, teaching geometry, astronomy and navigational calculation, and introduced the precision of Tycho-style instruments into scholarly measurement in the Netherlands.
2. 1615–1617Alkmaar–Bergen op Zoom survey line · Province of HollandIn 1615 Snellius adopted triangulation as proposed by Gemma Frisius and used by Tycho, linking church spires in western Holland into a triangulation network to measure the roughly 130-kilometer, nearly same-meridian distance between Alkmaar and Bergen op Zoom, thereby calculating the Earth's circumference. In 1617 he published the results as Eratosthenes Batavus; the arc-length accuracy surpassed older navigational figures and was hailed as the beginning of modern geodesy.
3. 1621Leiden · LeidenIn 1621 Snellius derived the law stating that the sines of the angle of incidence and the angle of refraction are proportional, later known as Snell's law, a fundamental relation of geometrical optics; it was not formally published in his lifetime and became widely known only after Huygens and others reported it in 1703. That same year he published Cyclometricus, improving the classical method of inscribing polygons to find π, and first printed the 35-digit value of pi computed by Van Ceulen.
4. 1624–1626Leiden · LeidenIn 1624 Snellius published Batava Typothetica, discussing rhumb lines and nautical charting. He also edited the astronomical observations of William IV, Landgrave of Hesse, and in a treatise on comets criticized blind adherence to Aristotle, though he himself still held to the geocentric system. He died in Leiden in 1626, and his trigonometrical manuscript was published the following year.