Willebrord van Roijen Snell (1580-1626) is proof that even training as a lawyer is not a bar to performing useful services to science. Although he studied law, Snell eventually succeeded his father as a professor of mathematics at the University of Leiden, in the Netherlands. He's best remembered as the discoverer of Snell's Law, which gives a formula for calculating the amount that a ray of light is bent when passing from one medium to another (such as from air to water).

During his lifetime Snell published many important works, including his Eratosthenes Batavus, which showed how to measure the earth using triangulation: the basis of modern surveying. He also developed a method of using nested polygons to calculate the approximate value of pi. Ironically, Snell's Law was not actually published until 1703, long after his death.

Snell was apparently rather precocious, perhaps from having a mathematician for a father. It's known that he was lecturing in university mathematics by the age of 20. Apparently mathematics paid well in those days, since he was able to travel to Switzerland, Wurtzburg, and Prague, among other European centers of learning of the day. Since Latin was in vogue in scientific circles, Snell was also sometimes known as Snellius, which probably didn't sound as silly then as it does now.

One way to express Snell's Law is as n1/n2 = sin(a1)/sin(a2)¹, where n1 and n2 are the indices of refraction of the two materials and a1 and a2 are the angles that the ray of light makes with the normal (perpendicular) to the boundary between the materials.