Willebrord Snel van Royen

Willebrord Snel van Royen (Leiden, 1580 - October 30, 1626), also known as Snellius and misrepresented as Snell, He was a Dutch astronomer and mathematician famous for the law of refraction that bears his name. He introduced several important discoveries about the size of the Earth and made improvements to the applied method of calculation.

Biography

Despite beginning his law studies at the University of Leiden, he showed great interest in mathematics, a discipline that he was already teaching even while he was studying. In 1613 he replaced his father, Rudolph Snel (1546-1613), as professor of mathematics at the University of Leiden. In 1615 he planned and carried out a new method for measuring the radius of the Earth by determining the length of a meridian arc calculated by triangulation, work considered the foundation of geodesy; in his work Eratosthenes Batavus, sive de terræ ambitus vera quantitate, published in 1617, he describes the method used and the result obtained for the value in kilometers of a degree of meridian (107.395 km, compared to 111 current). In addition, Snel distinguished himself as a mathematician by improving the method for the calculation of π used by the ancient Greek sages; with a 96-sided polygon he obtained 7 correct figures, while with the classical methods only two had been obtained. In 1621 he enunciated the law of refraction of light, anticipating, according to Christiaan Huygens ( Dioptrika , 1703), Descartes, who was initially credited with the discovery when he published it in 1637.

In addition to his work on determining the size of the earth, he published Cyclometria sive de circuli dimensione (1621), and Tiphys Batavus, a treatise on navigation in which he studied the loxodromia (1624); Coeli et siderum in eo errantium observationes Hassiacae (1618), with the astronomical observations of landgrave William IV of Hesse, and Villebrordi Snelli doctrinæ triangulorum canoniæ libri quatuor (1627), treatise on trigonometry published posthumously.

Works

Cyclometricus, 1621

• Eratosthenes Batavus (in Latin). Lugduni Batavorum: Joost van Colster, Joris Abrahamsz van der Marsce. 1617.
• Coeli et siderum in eo erantium observationes Hassicae (in Latin). Lugduni Batauorum: Joost van Colster. 1618.
• Cyclometricus (in Latin). Lugduni Batavorum: Matthijs Elzevier, Bonaventura Elzevier. 1621.
• Doctrinae triangulorum canonicae libri quatuor (in Latin). Lugduni Batavorum: Joannes Maire. 1627.

Eponymy

• The Snell Law, which describes the refraction of light rays.
• The lunar crater Snellius carries this name in his memory.