Joseph John Thomson (18.12.1856-30.08.1940) was an English physicist and a Fellow of the Royal Society (1884), its president in 1916-20. He was born in Cheetham Hill. He studied at Owens College, Manchester, and graduated from the University of Cambridge (1880). In 1884-1919 he was a professor at the University of Cambridge and director of the Cavendish Laboratory, and in 1905-18 he was also a professor at the Royal Institution. From 1918 he was Master of Trinity College, Cambridge.
His research concerned the passage of electric current through rarefied gases, cathode rays and X-rays, and atomic physics. In 1897, studying the deflection of cathode rays in magnetic and electric fields, he showed that they are a stream of negatively charged particles, measured the specific charge of these particles and found that their mass is approximately 1837 times smaller than the mass of the hydrogen atom. This was the direct and reliable discovery of the electron (Nobel Prize, 1906). In the same year he put forward the hypothesis that atoms are composed of electrons (intra-atomic electrons). In 1899 he detected electrons in the photocurrent and the effect of thermionic emission. He developed the theory of the motion of an electron in magnetic and electric fields. He studied many features of electric discharge in gases. He explained the origin of the continuous spectrum of X-rays.
In 1903 he proposed one of the first atomic models, according to which the atom was a positively charged sphere with electrons embedded in it, whose total negative charge equals the positive charge of the sphere (the Thomson model of the atom). In 1904 he introduced the idea that the electrons in an atom divide into groups, forming various configurations that account for the periodicity of the chemical elements. In 1907 he proposed the principle of operation of the mass spectrometer. In 1911 he developed the parabola method for determining the relative masses of the particles in ion beams (the ions of various gases), which was of great importance for the study of isotopes; in 1912 he obtained the first experimental data on the existence of isotopes, detecting neon atoms with masses of 20 and 22. In the classical theory of scattering he gave the expression for the cross section for the scattering of light by free electrons (the Thomson formula). He was one of the founders of the classical electron theory of metals (1900).
He was a member of many academies of sciences, among them the USSR Academy of Sciences (1925). He created a large international school of experimental physicists (F. Aston, C. Barkla, C. Wilson, E. Rutherford, O. Richardson, G. P. Thomson, P. Langevin, J. Townsend, H. Callendar, J. McLennan, T. Lyman, W. Natanson, J. Taylor, E. Appleton, J. McClelland, W. Nicholson, R. Strutt, J. Searle and others).
Medals: B. Franklin (1923), M. Faraday (1938), D. Hughes (1902), Copley (1914) and others.