The law of refraction is also called Snell's law. Who was Snell?

1. The law of refraction is named after the Dutch mathematician Willebrord Snell, who discovered it in 1621. 2. His experiments showed that a characteristic index of refraction could be assigned to a given medium. 3. Snell was not aware that the speed of light varied in different media, yet his measured angles still gave the right indices. 4. The Danish astronomer of the late 17th century is Ole Roemer, who timed light rather than measuring refraction angles. _Source: OpenStax College Physics (CC BY 4.0), Ch 25 "Geometric Optics", section 25.3 The Law of Refraction_