Nicol, William (1768–1851)

Scottish physicist and geologist who invented the first device for obtaining plane-polarized light – the Nicol prism – in 1828.

Nicol was born in Edinburgh and lectured at the university there. 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.

In 1815, Nicol developed a method of preparing extremely thin sections of crystals and rocks for microscopical study. His technique (which involved cementing the specimen to a glass slide and then carefully grinding until it was extremely thin) made it possible to view mineral samples by transmitted rather than reflected light and therefore enabled the minerals' internal structures to be seen.