(also W. K. Rontgen). Born Mar. 27, 1845, in Lennep, near Düsseldorf; died Feb. 10, 1923, in Munich. German physicist.

Roentgen studied at the Technische Hochschule in Zürich from 1865 to 1868. In 1868 he received his doctorate at the University of Zürich. He was an assistant to A. Kundt at the universities of Würzburg (from 1870) and Strasbourg (from 1872). Roentgen was a professor at the Agricultural Hochschule in Hohenheim from 1875, at the University of Strasbourg from 1876, at the University of Giessen from 1879, and at the University of Wrzburg from 1888. Beginning in 1894 he was rector of the University of Würzburg. From 1900 to 1920 he was a professor at the University of Munich, where A. F. Ioffe was his assistant from 1903 to 1906.

Roentgen was responsible for the classic investigations of the piezoelectric and pyroelectric properties of crystals, for the establishment of the interrelationship between electrical and optical phenomena in crystals, and for the investigations of magnetism that served as one of the bases for the electronic theory of H. A. Lorentz.

In 1895, Roentgen discovered radiation, which he called X-rays, and developed the first X-ray tube, whose design has basically been retained to the present day. In the period 1895–97 he published three works that contained a comprehensive analysis of certain properties of the newly discovered radiation. The discovery and study of X-radiation were important in the discovery of the structure of the atom and the structure of matter. X-radiation has been used in medicine, various fields of science, and technology. Roentgen was awarded a Nobel Prize in 1901.