Willebrord Snellius (born Willebrord Snel van Royen) (13 June 158030 October 1626) was a Dutch

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either obse ...

and mathematician, Snell. His name is usually associated with the law of refraction of light known as Snell's law. 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.

Biography

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 Leiden University (abbreviated as ''LEI''; nl, Universiteit Leiden) is a public research university in Leiden, Netherlands. The university was founded as a Protestant university in 1575 by William, Prince of Orange, as a reward to the city of L ...

Snellius' triangulation

In 1615, Snellius, after the work of

Eratosthenes Eratosthenes of Cyrene (; grc-gre, Ἐρατοσθένης ; – ) was a Greek polymath: a mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandr ...

in Ptolemaic Egypt in the 3rd century BC, probably was the first to try to do a large-scale experiment to measure the

circumference of the earth Earth's circumference is the distance around Earth. Measured around the Equator, it is . Measured around the poles, the circumference is . Measurement of Earth's circumference has been important to navigation since ancient times. The first know ...

using

triangulation In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points. Applications In surveying Specifically in surveying, triangulation involves only angle me ...

. He was helped in his measurements by two of his students, the Austrian barons Erasmus and Casparus Sterrenberg. In several cities he also received support of friends among the city leaders ('' regenten''). In his work ''The terrae Ambitus vera quantitate'' (1617) under the author's name ("The Dutch Eratosthenes") Snellius describes the methods he used. He came up with an estimate of 28,500 Rhineland rods – in modern units 107.37 km for one degree of

latitude In geography, latitude is a coordinate that specifies the north–south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pole ...

. 360 times 107.37 then gives a

circumference of the Earth Earth's circumference is the distance around Earth. Measured around the Equator, it is . Measured around the poles, the circumference is . Measurement of Earth's circumference has been important to navigation since ancient times. The first know ...

of 38,653 km. The actual circumference is 40,075 kilometers, so Snellius underestimated the circumference of the earth by 3.5%. Snellius came to his result by calculating the distances between a number of high points in the plain west and southwest of the Netherlands using

. 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 quadrant can still be seen in the

Museum Boerhaave Rijksmuseum Boerhaave is a museum of the history of science and medicine, based in Leiden, Netherlands. The museum hosts a collection of historical scientific instruments from all disciplines, but mainly from medicine, physics, and astronomy. Th ...

in Leiden. In a network of fourteen cities a total of 53 triangulation measurements were made. In his calculations Snellius made use of a solution for what is now called the

Snellius–Pothenot problem The Snellius–Pothenot problem is a problem in planar surveying. Given three known points A, B and C, an observer at an unknown point P observes that the segment AC subtends an angle \alpha and the segment CB subtends an angle \beta; the problem ...

By necessity Snellius's high points were nearly all

church spire A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spires are ...

s. There were hardly any other 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:

Alkmaar Alkmaar () is a city and municipality in the Netherlands, located in the province of North Holland, about 30 km north of Amsterdam. Alkmaar is well known for its traditional cheese market. For tourists, it is a popular cultural destination. The ...

: St. Laurenskerk; Haarlem :

Sint-Bavokerk The Grote Kerk or St.-Bavokerk is a Reformed Protestant church and former Catholic cathedral located on the central market square ( Grote Markt) in the Dutch city of Haarlem. Another Haarlem church called the Cathedral of Saint Bavo now serves a ...

; Leiden : a then new part (built in 1599) of the

City wall A defensive wall is a fortification usually used to protect a city, town or other settlement from potential aggressors. The walls can range from simple palisades or earthworks to extensive military fortifications with towers, bastions and gates ...

s; The Hague : Sint-Jacobskerk; Amsterdam : Oude Kerk; Utrecht :

Cathedral of Utrecht St. Martin's Cathedral, Utrecht, or Dom Church ( nl, Domkerk), is a Gothic church dedicated to Saint Martin of Tours, which was the cathedral of the Diocese of Utrecht during the Middle Ages. It is the country's only pre-Reformation cathedral, ...

;

Zaltbommel Zaltbommel (), also known, historically and colloquially, as Bommel, is a municipality and a city in the Netherlands. History The city of Zaltbommel The town of Zaltbommel was first mentioned as "Bomela" in the year 850. Zaltbommel received ...

: Sint-Maartenskerk; Gouda :

Sint Janskerk The Sint Janskerk in Gouda, the Netherlands, is a large Gothic church, known especially for its stained glass windows, for which it has been placed on the list of the top 100 Dutch monuments. History The church is dedicated to John the Baptist ...

;

Oudewater Oudewater () is a municipality and a town in the Netherlands. History The origin of the town of Oudewater is obscure and no information has been found concerning the first settlement of citizens. It is also difficult to recover the name of Ou ...

: Sint-Michaelskerk; Rotterdam : Sint-Laurenskerk;

Dordrecht Dordrecht (), historically known in English as Dordt (still colloquially used in Dutch, ) or Dort, is a city and municipality in the Western Netherlands, located in the province of South Holland. It is the province's fifth-largest city after Ro ...

: Grote Kerk; Willemstad : Koepelkerk;

Bergen-op-Zoom Bergen op Zoom (; called ''Berrege'' in the local dialect) is a municipality and a city located in the south of the Netherlands. Etymology The city was built on a place where two types of soil meet: sandy soil and marine clay. The sandy soil ...

Gertrudiskerk The Gertrudiskerk is a church approachable from the large market in the center of Bergen op Zoom, Netherlands. The towers of the church are called "pepper plant towers". An old legend says Saint Gertrude of Nivelles, abbess of the abbey in Nivell ...

;

Breda Breda () is a city and municipality in the southern part of the Netherlands, located in the province of North Brabant. The name derived from ''brede Aa'' ('wide Aa' or 'broad Aa') and refers to the confluence of the rivers Mark and Aa. Breda has ...

: Grote Kerk The actual distance between the two church spires in

and

, two places nearly on the same

meridian Meridian or a meridian line (from Latin ''meridies'' via Old French ''meridiane'', meaning “midday”) may refer to Science * Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon * ...

, is 116.1 kilometers. The difference in latitude between Alkmaar (52° 37' 57" N) and Breda (51° 35' 20" N) is 1.0436 degree. Assuming Snellius corrected for this he must have calculated a distance of 107.37 * 1.0436 = 112.05 kilometers between the Sint-Laurenskerk in Alkmaar and the Grote Kerk in Breda. Plaquete huis Willebrord Snellius

Mathematics and physics

Snellius was also a distinguished mathematician, producing a new method for calculating π—the first such improvement since ancient times. He rediscovered the law of refraction in 1621.

Other works

In addition to the ''Eratosthenes Batavus'', he published (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 Trigonometry () is a branch of mathematics that studies relationships between side lengths and angles of triangles. The field emerged in the Hellenistic world during the 3rd century BC from applications of geometry to astronomical studies. ...

(''Doctrina triangulorum'') authored by Snellius was published a year after his death.

Death

Snellius died in Leiden in October 1626, at the age of 46 from an illness diagnosed as

colic Colic or cholic () is a form of pain that starts and stops abruptly. It occurs due to muscular contractions of a hollow tube (small and large intestine, gall bladder, ureter, etc.) in an attempt to relieve an obstruction by forcing content out. ...

.De Wreede, L. C. (2007). Willebrord Snellius (1580–1626): a humanist reshaping the mathematical sciences. Utrecht University His grave can be seen in the

Pieterskerk, Leiden The Pieterskerk is a late-Gothic Dutch Protestant church in Leiden dedicated to Saint Peter. It is known today as the church of the Pilgrim Fathers, where the pastor John Robinson was buried. It is also the burial place of the scientist Wil ...

Honours

Snellius Glacier in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

is named after Willebrord Snellius.

Works

* * * *

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. * * * * *

Klaus Hentschel Klaus Hentschel (born 4 April 1961) is a German physicist, historian of science and Professor and head of the History of Science and Technology section in the History Department of the University of Stuttgart. He is known for his contributions in ...

: ''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.

External links

* * * {{DEFAULTSORT:Snellius, Willebrord 17th-century Dutch mathematicians 1580 births 1626 deaths Astronomy in the Dutch Republic Burials at Pieterskerk, Leiden 17th-century Dutch astronomers Geodesists Leiden University faculty Mathematics educators