SNELL, WILLEBRORD (1591-1626), commonly known as SNELLIUS, Dutch astronomer and mathematician, was born at Leiden in 1591. In 1613 he succeeded his father Rudolph Snell (1546-1613) as professor of mathematics in the university of Leiden. In 1615 he planned and carried into practice a new method of finding the dimensions of the earth, by determining the distance of one point on its surface from the parallel of another, by means of a triangulation. His work Eratosthenes Batavus, published in 1617, describes the method and gives, as the result of his operations between Alkmaar and Bergen- opZoom a degree of the meridian equal to 55,100 toises= 117,449 yds. (A later recalculation gave 57,033 toises =121,569 yds., after the application of some corrections to the measures indicated by himself.) Snell also distinguished himself as a mathematician, and discovered the law of refraction, in 1621 (see LIGHT). He died at Leiden on the 30th of October 1626.
In addition to the Eratosthenes Batavus he published Cydometria sive de circuit dimen f ione (1621), and Tiphys Batavus s. Histiodrpmice, de navium cursibus et re navali (1624). He also edited Coeli el sideruni in eo errantium observations Hassiacae (1618), containing the astronomical observations of Landgrave William IV. of Hesse. A trigonometry (Doctrina triangulorum,) by him was published a year after his death.