An eminent Scottish natural philosopher, born at Jedburgh; edited the "Edinburgh Encyclopaedia," in the pages of which Carlyle served his apprenticeship; specially distinguished for his discoveries in light, his studies in optics, and for his optical inventions, such as the kaleidoscope and the stereoscope; connected with most scientific associations of his time; wrote largely on scientific and other subjects, e. g., a Life of Newton, as well as Lives of Euler, Kepler, and others of the class; Principal of the United Colleges of St. Andrews, and afterwards of Edinburgh, being succeeded at St. Andrews by James David Forbes, who years before defeated him as candidate for the Natural Philosophy chair in Edinburgh; bred originally for the Church, and for a time a probationer (1781-1868).