Snellius Willebrord was born 1580 in Leiden, where his father Rudolphus Snellius, was professor of mathematics for thirty years.
Although he studied law at the University of Leiden, he was most interested in mathematics and at age nineteen he received permission to lecture on mathematics and astronomy. Later he succeeded his father as professor of at the university.
Snellius is famous for having explained the refraction of light, discovering the sine law, and improving the method for calculating approximate values for π.
Based in research begun in 1615, he published in 1617 his Eratostheses Batavus, a work advancing his method for measuring the size of the earth through the use of triangulation, concept first proposed by the sixteenth-century scientist Tycho Brahe.