A 1615 survey effort using triangulation to determine the Earth's circumference established Willebrord Snellius as a primary figure in 17th-century geodesy. By measuring distances between church spires across the Netherlands, he developed an innovative methodology for large-scale arc measurement, effectively acting as a modern successor to the ancient work of Eratosthenes in Egypt.
Academic Roots in Leiden
Born in Leiden in 1580, Willebrord Snel van Royen was the eldest child of Rudolph Snel van Royen, a mathematics professor at Leiden University. Although his father initially directed him toward legal studies, Snellius pursued mathematics throughout his youth. He eventually enrolled at Leiden University, where he refined his expertise under the influence of the mathematician Ludolph van Ceulen. Following his father’s death in 1613, Snellius assumed the position of professor of mathematics at the university, serving in that capacity until his death in 1626.
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In his 1617 publication, Eratosthenes Batavus, Snellius documented his use of triangulation to estimate the size of the planet. He established a network of fourteen observation points, primarily utilizing church steeples such as the Sint-Bavokerk in Haarlem and the Cathedral of Utrecht. By employing a large quadrant to measure angles, he calculated the length of one degree of latitude with significant precision, arriving at an estimate approximately 3.5% lower than the actual modern figure. This work also applied a trigonometric solution now identified as the Snellius–Pothenot problem.
Contributions to Optics and Geometry
Beyond his surveying accomplishments, Snellius conducted extensive research in optics and mathematics. In 1621, he identified the law of refraction, which describes how light bends when passing between different media. His mathematical output included the publication of Cyclometricus in 1621, which introduced an improved method for calculating the value of pi. His final major work on trigonometry, Doctrinae triangulorum canonicae libri quatuor, was prepared for publication shortly after his passing in 1626.
Fast facts
- Born: 1580, Leiden
- Died: 1626, Leiden
- Burial place: Pieterskerk
- Primary employer: Leiden University
- Notable law discovery: 1621
- Triangulation publication year: 1617
Questions readers ask
What is the Snellius–Pothenot problem?
It is a method in planar trigonometry used to determine an unknown point based on observations of known points.
Where is his measuring equipment kept?
The large quadrant used for his triangulation measurements is located at the Museum Boerhaave in Leiden.
Achievements
- Notable work: Snell's law
- Notable work: Snell's window
- Held posts at Leiden University
- Educated at Leiden University
- Fields of research: astronomy, mathematics and physics