Willebrord Snellius
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Willebrord Snellius<ref>Willebrord Snellius at the Leiden Digital Family Tree.</ref><ref>Eerste Nederlandse Systematisch Ingerichte Encyclopaedie</ref> (born Willebrord Snel van Royen<ref>Encarta Winkler Prins, Grote Oosthoek, Eerste Nederlandse Systematisch Ingerichte Encyclopaedie</ref> (13 June 1580<ref>Sometimes mistakenly noted as 1590 or 1591; Cf. Template:Cite web.</ref>Template:Spnd30 October 1626), commonly known simply as Snellius and Snell, was a Dutch astronomer and mathematician.
Snell is best known for the law of refraction of light known as Snell's law, his pioneering work in survey known as Snellius's triangulation, and the Snellius–Pothenot problem, a means in planar trigonometry of finding an unknown point from known ones.
Despite being commonly attributed to Snell, the law of refraction was discovered by the Persian scientist Ibn Sahl around 984 AD.<ref>For a reconstruction of this discovery see Hentschel 2001. It is now known that this law was already known to Ibn Sahl in 984. The same law was also investigated by Ptolemy and in the Middle Ages by Witelo, but due to lack of adequate mathematical instruments (i.e. trigonometric functions) their results were saved as tables, not functions.</ref>
Early life
Willebrord Snellius was born in Leiden, Netherlands. In 1613 he succeeded his father, Rudolph Snel van Royen (1546–1613) as professor of mathematics at the University of Leiden.Template:Sfn
Surveying
In 1615, Snellius, became the first known surveyor since Eratosthenes in 3rd century BC Ptolemaic Egypt to use triangulation to make a large-scale arc measurement to determine the Earth's circumference.<ref>Haasbroek, N.D. (1968): Gemma Frisius, Tycho Brahe and Snellius and their triangulation. Publ. Netherl. Geod. Comm., Delft. [1] Template:Webarchive</ref><ref name="Torge Müller 2012 p. 5">Template:Cite book</ref>
In his work The terrae Ambitus vera quantitate (1617) under the author's name ("The Dutch Eratosthenes") Snellius describes achieving his result by calculating the distances between a number of high points in the plain west and southwest of the Netherlands using triangulation. By necessity Snellius's high points were nearly all church spires, virtually the only tall buildings at that time in the west of the Netherlands. More or less ordered from north to south and/or in successive order of measuring, Snellius used a network of fourteen measure points to make a total of 53 triangulation measurements.
These cities were: Alkmaar: St. Laurenskerk; Haarlem: Sint-Bavokerk; Leiden: a then new part (built in 1599) of the city walls;<ref>the tower of the Sint-Pieterskerk had collapsed in 1512</ref> The Hague: Sint-Jacobskerk; Amsterdam: Oude Kerk; Utrecht: Cathedral of Utrecht; Zaltbommel: Template:Ill; Gouda: Sint Janskerk; Oudewater: Template:Ill; Rotterdam: Sint-Laurenskerk; Dordrecht: Grote Kerk; Willemstad: Template:Ill; Bergen-op-Zoom: Gertrudiskerk; Breda: Grote Kerk.
Snellius was helped in measuring by two of his students, the Austrian barons Erasmus and Casparus Sterrenberg. In several cities he also received support of friends among the civic leaders (regenten).Template:Cn
In order to carry out these measurements accurately Snellius had a large quadrant built, with which he could accurately measure angles in tenths of degrees. This instrument can still be seen in the Museum Boerhaave in Leiden. In his calculations Snellius made use of a solution for what is now called the Snellius–Pothenot problem.
He came up with an estimate of 28,500 Rhineland rods – in modern units 107.37 km<ref>a Rhenish rod is in this calculation considered as 3.767358 meter</ref> for one degree of latitude. 360 times 107.37 then gives a circumference of the Earth of 38,653 km. The actual circumference is 40,075 kilometers, making Snellius' estimate 3.5% low.
Mathematics and physics
Snellius was also a distinguished mathematician, producing a new method for calculating π—the first such improvement since ancient times. He discovered the law of refraction in 1621.<ref>Template:Citation.</ref>
Other works
In addition to the Eratosthenes Batavus, he published Template:Lang (1621), and Tiphys Batavus (1624). He also edited Coeli et siderum in eo errantium observationes Hassiacae (1618), containing the astronomical observations of Landgrave William IV of Hesse. A work on trigonometry (Doctrina triangulorum) authored by Snellius was published a year after his death.Template:Sfn
Death
Snellius died in Leiden in October 1626, at the age of 46 from an illness diagnosed as colic.<ref>De Wreede, L. C. (2007). Willebrord Snellius (1580–1626): a humanist reshaping the mathematical sciences. Utrecht University</ref> His grave can be seen in the Pieterskerk, Leiden.
Legacy
Snellius Glacier in Antarctica is named after Willebrord Snellius.
The lunar crater Snellius is named after Willebrord Snellius.
The Royal Netherlands Navy has named three survey ships after Snellius, including a currently-serving vessel.
Works
See also
Notes
References
- Willebrord Snellius (1580-1626): a humanist reshaping the mathematical sciences, thesis of Liesbeth de Wreede, Dissertation Utrecht 2007
- N. Haasbroek: Gemma Frisius, Tycho Brahe and Snellius and their triangulations. Delft 1968.
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- Klaus Hentschel: Das Brechungsgesetz in der Fassung von Snellius. Rekonstruktion seines Entdeckungspfades und eine Übersetzung seines lateinischen Manuskriptes sowie ergänzender Dokumente. Archive for History of Exact Sciences 55,4 (2001), doi:10.1007/s004070000026.