William Nicol (geologist)

William Nicol FRSE (18 April 1770 – 2 September 1851) was a Scottish geologist and physicist who invented the Nicol prism, the first device for obtaining plane-polarized light, in 1828.

He was born in Humbie (East Lothian) in 1770 the son of Walter Nicol and Marion Fowler. He was baptised on 18 Apr 1770 this being recorded in the parish register. Some sources (including his gravestone) give his date of birth as 1766.

He started out as aide to his uncle, Henry Moyes, an itinerent lecturer in Natural Philosophy whose blindness necessitated assistance for his chemistry and optics demonstrations. Nicol, having himself become a popular lecturer on that subject at the University of Edinburgh, settled in Edinburgh to live a very retired life. He conducted extensive studies of fluid inclusions in crystals and the microscopic structure of fossil wood. He did not publish any of his research findings until 1826.

Nicol made his prism by bisecting a parallelepiped of Iceland spar (a naturally occurring, transparent crystalline form of calcium carbonate) along its shortest diagonal, then cementing the two halves together with Canada balsam. Light entering the prism is refracted into two rays, one of which emerges as plane-polarized light. Nicol prisms greatly facilitated the study of refraction and polarization, and were later used to investigate molecular structures and optical activity of organic compounds.

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