Baron Loránd von Eötvös (Hungarian Vásárosnaményi Báró Eötvös Loránd or Loránd Eötvös, pronounced [ˈloraːnd ˈøtvøʃ]; July 27, 1848 - April 8, 1947), more commonly called Baron Roland von Eötvös in the English literature, was a Hungarian physicist. Born in 1848, the year of the Hungarian revolution, he was the son of József Eötvös, a well-known poet, writer, and liberal politician, who was cabinet minister at the time, and played an important part in 19th century Hungarian intellectual and political life.
Loránd Eötvös first studied law, but soon switched over to physics and went abroad to study in Heidelberg and Königsberg. After his doctorate he became a university professor in Budapest and played a leading part in Hungarian science for almost half a century. He gained international recognition first by his innovative work on capillarity, then by his refined experimental methods and extensive field studies in gravity. He died in 1947, but his last and probably most important paper, written together with his colleagues D. Pekár and J. Fekete, was published only in 1950.
Eötvös is remembered today for his experimental work on gravity, in particular his study of the equivalence of gravitational and inertial mass (the so-called weak equivalence principle) and his study of the gravitational gradient on the Earth's surface.
The weak equivalence principle plays a prominent role in relativity theory and the Eötvös experiment was cited by Albert Einstein in his 1916 paper The Foundation of the General Theory of Relativity.
Measurements of the gravitational gradient are important in applied geophysics, such as the location of petroleum deposits. The CGS unit for gravitational gradient is named the eotvos in his honor.
From 1886 until his death, Loránd Eötvös researched and taught in the University of Budapest, which in 1950 was renamed after him (Eötvös Loránd University).