Prisms, known as Nicol prisms

Prisms of this type are known as Nicol prisms, after their inventor, Edinburgh geologist William Nicol (1768-1851). These two examples were made in England in the early 19th century. They are unsigned, but may have been made by Watkins of London.

The Nicol prism is an optical filter for polarising light. Used in pairs as polariser and analyser, the prism enables minerals to be identified through optical characteristics which derive from their crystal structures.

Both of these prisms were used by William Henry Fox Talbot (1800-77), inventor of positive/negative photography and man of science, with interests ranging from optics to Egyptian hieroglyphics.

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