Erasmus Bartholin
1625-1698
Danish physician and mathematician remembered for discovering double refraction (1669).
Bartholin noticed that the transparent crystal Iceland spar (calcite) produced double images of objects viewed through it. He assumed light transmitted through the crystal was being refracted through different angles so as to produce two light rays. Christiaan Huygens explained certain aspects of double refraction with his wave theory of light but full understanding awaited the work of Etienne Malus, on polarization (1809), and Augustin Fresnel (1817).
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