Professor John Tyndall (1820-1893) was an Irish natural philosopher whose strong, picturesque mode of seizing and expressing things gave him an immense living influence both in speech and writing, and disseminated a popular knowledge of physical science such as had not previously existed. Tyndall was to a large extent a self-made man, but with indomitable earnestness devoted himself to study, to which he was stimulated by the writings of Carlyle. With much spirit and in face of many difficulties, he attended the University of Marburg (1848-1851), where he obtained his doctorate in two years. It was on the whole the personality, however, rather than the discoverer, that was greatest in Tyndall. In the pursuit of science for its own sake, undisturbed by sordid considerations, he shone as a beacon light to younger men. His investigations of the transparency and opacity of gases and vapours for radiant heat, which occupied him during many years are frequently considered his chief scientific work. His works include On Radiation (1865), Heat as a Mode of Motion (1863), Faraday as a Discoverer (1868) and Six Lectures on Light (1873).