# 1911 Encyclopædia Britannica/Snell, Willebrord

**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-op-Zoom
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 90th of October 1626.

In addition to the *Eratosthenes Batavus* he published *Cyclometria*
*sive de circuli dimensione* (1621), and *Tiphys Batavus s. Histfiodromice,*
*de navium cursibus et re navali* (1624). He also edited *Coeli et siderum*
*in eo errantium observationes 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.