Stewart, BALFOUR, LL.D., F.R.S.

Stewart, BALFOUR, LL.D., F.R.S., physicist, was born at Edinburgh, November 1, 1828. He studied at both St Andrews and Edinburgh universities, but in 1846 entered on a commercial career. Seven years later he forsook business, returned from Australia to Edinburgh, and became assistant to Professor Forbes. In 1859 he was appointed director of the Kew Observatory, and in 1870 professor of Physics at Owens College, Manchester. He died, December 19, 1887, near Drogheda, Ireland. He made his first reputation by his work on Radiant Heat (1858), by which he established the equality of the emissive and absorptive powers of bodies. He is rightly regarded as one of the founders of the method of spectrum-analysis, of which the complete theory was given by Kirchhoff a little later (see HEAT and SPECTRUM). In connection with his work on radiant heat the experiments (in conjunction with Professor Tait) on the heating of a rotating disc in vacuo (1865-78) should be mentioned, as should also his remarks on the effect of relative motion on radiation. His other labours were chiefly meteorological, his name being specially associated with such subjects as the relation between sun-spots and temperature and magnetic changes, terrestrial magnetism, and the daily ranges of the meteorological elements. Particularly valuable are his numerous papers on terrestrial magnetism. As a writer of text-books on physics he earned a high reputation, the Treatise on Heat (1866; 5th ed. 1888), the Elements of Physics (1870; 4th ed. 1891), and the Conservation of Energy (1873; 7th ed. 1887) being all excellent works, especially the first. Very concise in statement and suggestive in treatment is his contribution on terrestrial magnetism to the Encyclopaedia Britannica (article 'Meteorology'). With Professor Tait he published in 1875 The Unseen Universe, or Physical Speculations on a Future State, a book which had a phenomenal reception and passed rapidly through several editions (17th ed. 1890).