Loránd Eötvös

Loránd Eötvös (1848 to 1919), known in German-language literature as Baron Roland von Eötvös, was a Hungarian physicist and politician who spent almost half a century at the University of Budapest. Born in the year of the Hungarian revolution to a baron who was a poet, writer and liberal minister, he began by studying law, then turned to physics and studied at Heidelberg and Königsberg before taking his doctorate and returning to a Budapest professorship. He first became known for his work on capillarity and surface tension, then for refined experimental methods and field studies of gravity. His torsion pendulum, often called the Eötvös balance, measures not only the direction of gravity but its change across the horizontal plane, and it was used to probe the density of rock beneath the surface and to find oil and ores. With it he tested, to high accuracy, that gravitational and inertial mass are equivalent, the weak equivalence principle that Einstein cited in his 1916 paper on general relativity. The CGS unit of gravitational gradient, the eotvos, carries his name, as do a university, a geophysical institute, a lunar crater and a mineral.