Willebrord Snellius

“Snellius” redirects here. For the lunar crater named Snellius, see Snellius (crater).

Willebrord Snellius^[1][2] (born Willebrord Snel van Royen^[3]) (1580 – 30 October 1626, Leiden) was a Dutch astronomer and mathematician. In the west, especially the English speaking countries, his name has been attached to the law of refraction of light for several centuries, but it is now known that this law was first discovered by 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 (trigonometric functions) their results were saved as tables, not functions.

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. In 1615 he planned and carried into practice a new method of finding the radius of the earth, by determining the distance of one point on its surface from the parallel of latitude of another, by means of triangulation. His work Eratosthenes Batavus ("The Dutch Eratosthenes"), published in 1617, describes the method and gives as the result of his operations between Alkmaar and Bergen op Zoom—two towns separated by one degree of the meridian—which he measured to be equal to 117,449 yards (107.395 km). The actual distance is approximately 111 km. 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. In addition to the Eratosthenes Batavus, he published Cyclometria sive de circuli dimensione (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 trigonometry (Doctrina triangulorum) authored by Snellius was published a year after his death.

The lunar crater Snellius is named after Willebrord Snellius.

See also

• Resection (orientation)
• Snellius–Pothenot problem

Notes

1. ^ Willebrord Snellius at the Leiden Digital Family Tree.
2. ^ Eerste Nederlandse Systematisch Ingerichte Encyclopaedie
3. ^ Encarta Winkler Prins, Grote Oosthoek, Eerste Nederlandse Systematisch Ingerichte Encyclopaedie

References

• N. Haasbroek: Gemma Frisius, Tycho Brahe and Snellius and their triangulations. Delft 1968.
• Struik, Dirk Jan (1970–80). "Snel, Willebrord". Dictionary of Scientific Biography. XII. New York: Charles Scribner's Sons. ISBN 0684101149. 
• "Snellius (Willebrord)". Nieuw Nederlandsch Biografisch Woordenboek. VII. 
• O'Connor, John J.; Robertson, Edmund F., "Willebrord van Royen Snell", MacTutor History of Mathematics archive, University of St Andrews, http://www-history.mcs.st-andrews.ac.uk/Biographies/Snell.html .
•  This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press. 

External links

• Willebord Snell in Archimedes to Hawking: Laws of Science and the Great Minds Behind Them (Clifford A. Pickover, 2008).
• Willebrord Snellius at the Mathematics Genealogy Project.
• Snell's Law Song