WILLIAM (?(? NICOL 1768-18511, Scottish physicist, was born about 1768, and died Edinburgh on the 2nd of September 1851. Nothing is known of his early history beyond the fact that, after amassing a small competence as a popular lecturer on natural philosophy, he settled in Edinburgh to live a very retired life in the society of his apparatus alone. Besides the invention of the prism known by his name ("A method of increasing the divergence of the two rays in calcareous spar, so as to produce a single image," New Edin. Journ., 1828), he devoted himself chiefly to the examination of fluid-filled cavities in crystals, and of the microscopic structure of various kinds of fossil wood. His skill as a working lapidary was very great; and he prepared a number of lenses of garnet and other precious stones, which he preferred to the achromatic microscopes of the time.