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Willebrord Snellius | |
|---|---|
 Willebrord Snel van Royen (1580–1626) | |
| Born | 13 June 1580 |
| Died | 30 October 1626(1626-10-30) (aged 46) |
| Alma mater | University of Leiden |
| Known for | Snell's law,Snellius's triangulation,Snellius–Pothenot problem |
| Scientific career | |
| Fields | Astronomy andmathematics |
| Institutions | University of Leiden |
| Academic advisors | Ludolph van Ceulen Rudolph Snellius |
| Notable students | Jacobus Golius |
Willebrord Snellius[1][2] (bornWillebrord Snel van Royen[3] (13 June 1580[4] – 30 October 1626), commonly known simply asSnellius andSnell, was a Dutchastronomer andmathematician.
Snell is best known for the law ofrefraction of light known asSnell's law, his pioneering work in survey known asSnellius's triangulation, and theSnellius–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 scientistIbn Sahl around 984 AD.[5]
Willebrord Snellius was born inLeiden,Netherlands. In 1613 he succeeded his father,Rudolph Snel van Royen (1546–1613) as professor ofmathematics at theUniversity of Leiden.[6]
In 1615, Snellius, became the first known surveyor sinceEratosthenes in 3rd century BCPtolemaic Egypt to usetriangulation to make a large-scalearc measurement to determine theEarth's circumference.[7][8]
In his workThe 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 usingtriangulation. By necessity Snellius's high points were nearly allchurch 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 thecity walls;[9]The Hague:Sint-Jacobskerk;Amsterdam:Oude Kerk;Utrecht:Cathedral of Utrecht;Zaltbommel:Sint-Maartenskerk [nl;de];Gouda:Sint Janskerk;Oudewater:Sint-Michaelskerk [nl];Rotterdam:Sint-Laurenskerk;Dordrecht:Grote Kerk;Willemstad:Koepelkerk [nl;de];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).[citation needed]
In order to carry out these measurements accurately Snellius had a largequadrant built, with which he could accurately measure angles in tenths of degrees. This instrument can still be seen in theMuseum Boerhaave in Leiden. In his calculations Snellius made use of a solution for what is now called theSnellius–Pothenot problem.
He came up with an estimate of 28,500 Rhinelandrods – in modern units 107.37km[10] for one degree oflatitude. 360 times 107.37 then gives acircumference of the Earth of 38,653 km. The actual circumference is 40,075 kilometers, making Snellius' estimate 3.5% low.
Snellius was also a distinguished mathematician, producing a new method for calculatingπ—the first such improvement since ancient times. He discovered thelaw of refraction in 1621.[11]
In addition to theEratosthenes Batavus, he publishedCyclometricus, de circuli dimensione (1621), andTiphys Batavus (1624). He also editedCoeli et siderum in eo errantium observationes Hassiacae (1618), containing the astronomical observations of LandgraveWilliam IV of Hesse. A work ontrigonometry (Doctrina triangulorum) authored by Snellius was published a year after his death.[6]
Snellius died in Leiden in October 1626, at the age of 46 from an illness diagnosed ascolic.[12] His grave can be seen in thePieterskerk, Leiden.
Snellius Glacier inAntarctica is named after Willebrord Snellius.
Thelunar craterSnellius is named after Willebrord Snellius.
The Royal Netherlands Navy has named three survey ships after Snellius, including acurrently-serving vessel.
This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Snell, Willebrord".Encyclopædia Britannica. Vol. 25 (11th ed.). Cambridge University Press. p. 293.
(in Latin)