WILLEBRORD

SNELL (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 3oth of October 1626 . In addition to the Eratosthenes Batavus he published Cyclometria sive de circuli dimen,.ione (1621), and Tiphys Batavus s . Histiodromice, 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 (Doctrine triangulorum,) by him was published a year after his death .