HERTZ, HEINRICH RUDOLF (18S7-94), German phys icist, was born at Hamburg on Feb. 22, 1857. On leaving school he studied engineering, but abandoned it in favour of physics. Hertz went to Berlin, where he studied under Helmholtz (q.v.). In 1883 he went to Kiel, becoming Privatdozent, and there he began the studies in Maxwell's electromagnetic theory which a few years later resulted in the discoveries that rendered his name famous. These were actually made between 1885 and 1889, when he was professor of physics in the Carlsruhe Polytechnic. Helm holtz drew Hertz's attention to a prize offered by the Berlin Academy of Sciences for the experimental establishment of a relation between electromagnetic actions and the polarization of a dielectric, and promised him the assistance of the Institute if he decided to work on the subject. Hertz did not take it up seriously at that time, because he could not think of any procedure likely to prove effective. Later he was able to discover the pro gressive propagation of electromagnetic action through space, to measure the length and velocity of electromagnetic waves, and to show that in the transverse nature of their vibration and their susceptibility to reflection, refraction and polarization they are in complete correspondence with the waves of light and heat. The result was to establish beyond doubt the electromagnetic nature of light. In 1889 Hertz was appointed to succeed R. J. E. Clausius as ordinary professor of physics in the university of Bonn. There he continued his researches on the discharge of electricity in rarefied gases, only just missing the discovery of the X-rays de scribed by W. C. Röntgen a few years later, and produced his treatise on the Principles of Mechanics. This was his last work, for after a long illness he died at Bonn on Jan. 1, 1894. By his premature death science lost one of her most promising disciples.
Hertz's scientific papers were translated into English by D. E. Jones, and published in three volumes: Electric Waves Miscellaneous Papers (1896), and Principles of Mechanics 0899). The preface contributed to the first of these by Lord Kelvin, and the introductions to the second and third by P. E. A. Lenard and Helmholtz, contain many biographical details.