Willebrord Snel Biography

Valerie Korszen

DE Astronomy Period 1

Percival

15 October, 2010

Willebrord Snel (1580-1626)

            Born in 1580 in Leiden, Netherlands with the name Willebrord Snel van Royen, this Dutch mathematician, physicist, and astronomer later became known as Willebrord Snellius.  Snellius’ father was a mathematics professor at the University of Leiden until 1613, when he himself filled this position.  Snel made numerous contributions in the fields of science and mathematics, including the sine law, improvement of the method of using triangulation in measuring a distance, a proportion related to the refraction of light through a medium, and several more. 

In 1615, two years after he became professor of mathematics at the University of Leiden, Willebrord improved upon the method of determining using trigonometric triangulation, and used this method to calculate the dimensions of the Earth.  Gemma Frisius was responsible for the original idea upon which Willebrord based his own.  Eratosthenes Batavus was a major publication of Snel’s, which brought together his measurements and methods into a book that explains why and how these methods of triangulation were effective.  He successfully measured the distance of one degree of Earth’s meridian within a few hundred meters of today’s accepted values.  This is extraordinary when one considers the lack of advanced technology that he had compared to what we possess in the modern world.  He had no access to satellites that could transmit data down to Earth or accurate computer systems that can measure extremely small units, indiscernible by the human body.

One of Snel’s less significant, but still very important, contributions was his observations of the comet of 1618, and it is now named after him.  He measured the parallax of the comet, which indicated that it was above the Moon’s sphere.  Snel also used polygonal figures to more accurately calculate the value of pi, and in 1621, he published Cyclometria sive de circuli dimensione, which showed his work using Van Culen’s method of determining the value of pi to 34 deciaml places.

As a mathematician, Snel discovered the sine law.  Using this law, he also wrote a law of refraction in 1621, which was not published until after his death.  This law pertains to the angle at which a ray of light would refract through a medium and is now known as Snel’s Law.  Where Johannes Kepler and Ptolemy hit a brick wall, Snel was able to explain that the sines of the angles of incidence and refraction, relative to the normal line, remain constant.  This may be his most important and useful discovery, especially because it is still accepted by modern mathematicians.  Christiaan Huygens put his discoveries into a book called Dioptrica in 1703.

Snel died at Leiden on the October 30, 1626.  The list of contributions he made to astronomy, mathematics, and physics seems endless, which makes it very surprising that his name is not more well-known.  I use the sine law almost every day in multiple classes, but never knew that Snel had not only discovered it, but used it to make such accurate measurements of the dimensions of Earth.