Young, Thomas, an eminent man of science, was born at Milverton, England, in 1773. In 1801 he was appointed professor of natural philosophy in the Royal Institution. It was during his two years' occupancy of this chair that he published Outlines and Experiments Respecting Sound and Light, his most important memoir. In it he shows that two rays of light may be added together to produce darkness — the phenomenon of interference. Sir John Herschel asserted that, even if Young had made no other discovery, this alone would have made him immortal as a scientist. He died at London on May 10, 1829. Dr. Peacock has published an interesting Life of Young, and has edited his Miscellaneous Works. But all of Young's more important contributions are reprinted in his Lectures on Natural Philosophy, which exerted a powerful influence on physical science during half a century.