| Rasmus Bartholin | |
| Birth Date: | 13 August 1625 |
| Birth Place: | Roskilde |
| Death Date: | 4 November 1698 (aged 73) |
| Death Place: | Copenhagen |
| Nationality: | Danish |
| Field: | Physics |
| Known For: | Double refraction of a light ray |
Rasmus Bartholin (; Latinized: Erasmus Bartholinus; 13 August 1625 - 4 November 1698) was a Danish physician and grammarian.
Bartholin was born in Roskilde. He was the son of Caspar Bartholin the Elder (1585–1629) and Anna Fincke, daughter of the mathematician Thomas Fincke.[1]
As part of his studies, he travelled in Europe for ten years. He stayed in the Netherlands, England, France and Italy. In 1647, he took a Master's degree at the University of Copenhagen. In 1654, he received a Doctoral degree at the University of Padua.
He was a professor at the University of Copenhagen, first in Geometry, later in Medicine. He was also dean of the faculty of medicine, librarian, and rector.[2] He wrote, in Latin, the first grammar of the Danish language, the 1657 De studio lingvæ danicæ.
Rasmus Bartholin is remembered especially for his discovery (1669) of the double refraction of a light ray by Iceland spar (calcite).[3] He published an accurate description of the phenomenon, but since the physical nature of light was poorly understood at the time, he was unable to explain it.[4] It was only after Thomas Young proposed the wave theory of light, c. 1801 that an explanation became possible.
He was a younger brother of Thomas Bartholin (1616–1680).[5]