Willebrord Van Roijen Snell He was a Dutch mathematician who was born in 1591 and died in 1626. He was the son of a mathematics professor at Leiden University. In 1613, his father succeeded in this role. Four years later, he created a method for determining distances by trigonometric triangulation. This method is still used today to perform topographic mappings. (This is the basis even for satellite-aided ones.)
In the field of optics, Snell analyzed the deviation that a ray of light undergoes as it passes obliquely from a less dense to a denser medium (for example, from air to water). From the first century it was known that these two different angles, formed between the radius and the perpendicular to the boundary between the media, kept a proportionality that was maintained even when the position of the light source was changed.
Snell refined these observations and, through more accurate measurements, found that there was a constant relationship between the sines of these angles. Such a conclusion would only be published twelve years after his death by Descartes, who, however, did not cite its author.
Bibliography: Learning Physics, Publisher Scipione.