Hendrik Antoon Lorentz (18.07.1853-4.02.1928) was a Dutch theoretical physicist, the creator of the classical electron theory and a member of the Royal Netherlands Academy of Arts and Sciences. He was born in Arnhem. He studied at the University of Leiden, and in 1875 he defended his doctoral dissertation “On the theory of the reflection and refraction of light”. In 1878—1913 he was professor at the University of Leiden and head of the department of theoretical physics. From 1913 he was director of the physics cabinet of the Teyler Museum in Haarlem.
His research was in the field of electrodynamics, thermodynamics, statistical mechanics, optics, the theory of radiation, the theory of metals and atomic physics. Starting from the electromagnetic theory of Maxwell and Hertz, and bringing atomism into the study of electricity, he created (1880 — 1909) the classical electron theory as a theory of the electrical, magnetic and optical properties of matter and of the electromagnetic phenomena that rest on an analysis of the motions of discrete electric charges (the Lorentz — Maxwell equations). On the basis of the electron theory he explained a whole series of physical facts and phenomena and predicted new ones.
He derived a formula relating the permittivity to the density of a dielectric, and the dependence of the refractive index of a substance on its density (the Lorenz — Lorentz formula); he gave an expression for the force acting on a moving charge in an electromagnetic field (the Lorentz force); he explained the dependence of the electrical conductivity of a substance on its thermal conductivity; and he developed the theory of the dispersion of light. He predicted the splitting of spectral lines in a strong magnetic field, and when it was discovered by P. Zeeman in 1896 he worked out (1897) its theory (Nobel Prize, 1902).
To explain the Michelson — Morley experiment he put forward (1892), independently of G. FitzGerald, the hypothesis that the dimensions of bodies contract in the direction of their motion (the Lorentz — FitzGerald contraction), and introduced (1895) the concept of local time, which passes differently in moving bodies from the way it passes in bodies at rest. He developed the electrodynamics of moving bodies. In 1904 he derived the formulae relating the spatial coordinates and the instants of time of one and the same event in two different inertial frames of reference (the Lorentz transformations). All the kinematic effects of special relativity are obtained from the Lorentz transformations. In 1904 he obtained the formula for the dependence of the mass of an electron on velocity. He prepared the way for the transition to relativity and quantum mechanics, and did particularly much to further the creation of relativity.
Lorentz's research also concerned the kinetic theory of gases, the kinetics of solids and the electron theory of metals, which he created in 1904. He had a considerable influence on the young generation of physicists. In his world outlook he was a materialist, and he actively fought against manifestations of idealism in physics.
A member of many academies of sciences and scientific societies, and in particular a foreign member of the USSR Academy of Sciences (1925). The organiser and chairman (1911 — 27) of the Solvay Congresses of physicists.