Roget studied medicine at the University of Edinburgh and later helped found the medical school at Manchester. In 1814 he invented a “log-log” slide rule for calculating the roots and powers of numbers. From 1808 to 1840 he practiced in London. The first edition of the Thesaurus, which was begun in his 61st year and finished in his 73rd, was a product of his retirement from active medical practice, although it was based on a system of verbal classification he had begun in 1805. Roget was a fellow (from 1815) and secretary (from 1827) of the Royal Society.