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Willebrord Snellius 2, photo by R. Koot.

Top 10 Amazing Facts about Willebrord Snellius

Willebrord Snell was a 17thcentury Dutch astronomer and mathematician best known for the law of refraction, a basis of modern geometric optics and Snell’s law. His father was Rudolph Snell, the professor of mathematics at Leiden University, and his mother was Machteld Cornelisdochter.

Willebrord was the eldest of his parents’ three children. His two younger brothers were Jacob who died in 1599 aged 16 and Hendrik who died in childhood. There are different biographies of Snell each with different dates of birth.

Some state that he was between 1580 or 1581 but claim that his date of birth is unknown. He was a well known mathematician and has the lunar crater Snellius and The Royal Netherlands Navy’s ships named after him.

During his lifetime he dedicated his time to helping his father and pursuing his love for astronomy and mathematics. Here are top 10 amazing facts about Willebrord Snellius.

1.The controversy over his date of birth

There are different biographies of Snell each with different dates of birth. Most of them state that he was born in 1591 but this is simply an error copied from an already existing old biography. Some state that he was between 1580 or 1581 but claim that his date of birth is unknown.

The fact still remains that there is completely no record of his birth; however, some have concluded that his date of birth can be deduced with a fair degree of certainty from a letter his father wrote on his son’s birthday.

2.He succeeded his father as a professor of mathematics    

Snell had begun teaching at the university as a way of assisting his father due to his deteriorating health. The two taught mathematics together at the University of Leiden for several years.

Gradually, Snell was offered an official position and was assigned to teach at 8 o’clock every Saturday morning in the year 1609. In 1613 he officially succeeded his father, Rudolph Snell, as professor of mathematics in the University of Leiden and was receiving additional payment for his work.

When his father retired, Snell took the opportunity and went ahead to publish translations, commentaries and editions of several works.

3.He improved the classical version of calculating the approximate value of ‘Pi’

Being a mathematical genius he developed a new method to calculate the mathematical function, Pi. He explained the theory in polygons which he published in 1621, named Cyclometricus. Using this method, 96 sided polygons branched to 7 theorems in pi, whereas the classical method yielded only 2 theorems.

The new method brought about a notable development in the field of mathematics and was widely accepted by his successors. This theory appeared in Snell’s publication for the first time.

4.He discovered Snell’s law

Snell’s law explains the relationship between the path taken by a ray of light in crossing the boundary or surface of separation between two contacting substances and the refractive index of each.

In 1621 Willebrord Snell discovered this law and credited for having discovered the law of refraction in 1621, which was published in 1703 in ‘Dioptrica’. A manuscript with a treatise on the study of optics was also included in these works which helped him come up with Snell’s Law.

5.Snell rediscovered the law of refraction

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He made several theories on the law of refraction, on the basis of the work which he rediscovered in 1621. The law of refraction denotes when light rays pass obliquely from a rarer to denser medium such as air to water, they are bent toward the vertical.

Scientists from Ptolemy had searched in vain for a law to explain this phenomenon. It was discovered that the law was actually formulated by Ibn Sahl and that Snell had only rediscovered it.

6.He travelled extensively all around Europe to study and discuss astronomy

As his career reached its peak, Snell travelled extensively all around Europe to study and discuss astronomy. As he travelled, he worked with some of the best minds in the field of astronomy, such as Johannes Kepler and Tycho Brahe.

7.Snell’s Astronomical Interests

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Snell had shown interest in the field of astronomy and published several works on the same. One of Snell’s astronomical works was Observationes Hassiacae (1618), written based on the observations recorded by Tycho Brahe and Joost Burgi. He came up with Descriptio Cometae in 1619, which were his own observations that studied the movements of comets.

8.Although he had originally studied law, he was a mathematical genius

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Snell studied law in university but he was always interested in astronomy and mathematics. He was a mathematical genius and made countless contributions to the field such as developing a new method of calculating Pi. The new method brought about a major revolution which led to tremendous development in the field of mathematics.

9.He attempted to measure the circumference of the earth

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Snell tried to do a large-scale experiment to measure the circumference of the earth using triangulation with the help of some of his students and friends. Snell describes the method he used for the measurements in his work the terrae Ambitus vera quantitate (1617) under the author’s name The Dutch Eratosthenes.

His method involved determining the distance of one point on the earth’s surface and the latitude of another point, by the means of triangulation. He concluded that the circumference of the Earth to be 38,653 km. The actual circumference is 40,075 kilometers, so Snellius underestimated the circumference of the earth by 3.5%.

10.When he died his students carried his coffin

Plaquete huis Willebrord Snellius, Leiden, photo by Michiel1972.

Snellius died in Leiden in October 1626, at the age of 46 from an illness diagnosed as colic which caused a fever and paralysis of his arms and legs. His illness lasted two weeks and in the evening of 30 October, the doctors went to visit him to monitor the side effects of the new medicine, but his condition did not improve.

He was unable to walk and his servants had to lift him up when he wanted to move from one place to another. He was buried on 4 November in the Pieterskerk in Leiden where approximately twenty students carried his coffin.

Willebrord Snellius was indeed among the most successful and influential mathematician. He developed methods that are still applicable today to the field of mathematics. By 1615, Snell was intrigued about the geometry and the dimensions of the earth and thus, decided to carry out a new method of finding out the radius of the planet.