William Oughtred (1575-1660), English mathematician, holding a book. Oughtred was educated at Eton College and later at Cambridge University, England. He was ordained as a priest in 1603. His clerical post gave him time to work on mathematics. In 1631 he published the Clavis mathematicae (the key to mathematics). Oughtred also introduced a number of mathematical symbols, such as the 'x' for multiplication and the sin and cos notation for trigonometry. He also invented the circular slide rule and the rectilinear slide rule.