Heinrich Rubens (30 March 1865, Wiesbaden, Nassau, Germany – 17 July 1922, Berlin, Germany) was a German physicist. He is known for his measurements of the energy of black-body radiation which led Max Planck to the discovery of his radiation law. This was the genesis of quantum theory.
After having attended realgymnasium Wöhlerschule in Frankfurt am Main, he started in 1884 to study electrical engineering at the technical universities in Darmstadt and Berlin. The following year he switched to physics at the University of Berlin which was more to his liking. After just one semester there he transferred to Strasbourg. There he benefited much from the lectures by August Kundt who in 1888 took over the vacant position of Hermann Helmholtz at the University of Berlin. Rubens followed after and got his doctors degree there the same year. In the period 1890–1896 he was employed as an assistant at the physics institute and made his habilitation in 1892. He was then a privatdozent and was allowed to teach. Already then he was praised for his experimental investigations of infrared radiation.
Rubens got a permanent position in 1896 as docent at the Technical University of Berlin in Berlin-Charlottenburg. He could continue his experimental research at the nearby Physikalisch-Technische Reichsanstalt. It was there he in 1900 did his important measurements of black-body radiation which made him world famous. He was promoted to professor the same year.