Playfair, John (1748-1819), Scotch mathematician, was the son of a clergyman, and was successively professor of mathematics and of natural philosophy in Edinburgh University, and became president of the Royal Society of Edinburgh. He published an edition of Euclid and other valuable works, which are still in use. and was known as an excellent geologist. There is a monument to his memory on Calton Hill, Edinburgh. His brother William (1759-1823) was an ingenious inventor.