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 by James Clerk Maxwell (1831–1879). He was born near Edinburgh, entered the University of Edinburgh, and became a pupil of Kelland and Forbes. In 1850 he went to Trinity College, Cambridge, and came out Second Wrangler, E. Routh being Senior Wrangler. Maxwell then became lecturer at Cambridge, in 1856 professor at Aberdeen, and in 1860 professor at King's College, London. In 1865 he retired to private life until 1871, when he became professor of physics at Cambridge. Maxwell not only translated into mathematical language the experimental results of Faraday, but established the electro-magnetic theory of light, since verified experimentally by Hertz. His first researches thereon were published in 1864. In 1871 appeared his great Treatise on Electricity and Magnetism. He constructed the electro-magnetic theory from general equations, which are established upon purely dynamical principles, and which determine the state of the electric field. It is a mathematical discussion of the stresses and strains in a dielectric medium subjected to electro-magnetic forces. The electro-magnetic theory has received developments from Lord Rayleigh, J. J. Thomson, H. A. Rowland, R. T. Glazebrook, H. Helmholtz, L. Boltzmann, O. Heaviside, J. H. Poynting, and others. Hermann von Helmholtz turned his attention to this part of the subject in 1871. He was born in 1821 at Potsdam, studied at the University of Berlin, and published in 1847 his pamphlet Ueber die Erhaltung der Kraft. He became teacher of anatomy in the Academy of Art in Berlin. He was elected professor of physiology at Königsberg in 1849, at Bonn in 1855, at Heidelberg in 1858. It was at Heidelberg that he produced his work on Tonempfindung. In 1871 he accepted the chair of physics at the University of Berlin. From this time on he has been engaged chiefly on inquiries in electricity and hydrodynamics. Helmholtz aimed to determine in what direction experiments should be made to