EÖTVÖS, Lóránd

E. comes from a noble family. His father Joseph was a liberal politician and minister of culture of the first democratically elected government (1848/49), as well as the second after the equivalence of the Austrian and Hungarian part of the country (1867-1871). He was also an important writer. His son attended grammar school in Budapest and then studied in Heidelberg. E. completed his studies in 1871 and the same year began his science career in the Department of Theoretical Physics at the University of Budapest. In 1872 he received an invitation to the Department of Experimental Physics, where he worked until his death. Hungarian Academy of Sciences elected him a corresponding member in 1873 and a full member in 1893. From 1899 to 1903 he held the post of President of the Academy of Sciences and was the Minister of Culture and Education for half a year (1894/95). In 1891 he founded Hungarian Society for Mathematics and Physics.
In his first scientific works he was concerned with the capillarity. He developed a new method for measuring surface tension. He discovered the connection between an arbitrary liquid pure substances at all temperatures and the molecular weight (E.’s rule). In the 1880s he became interested in gravity. For measuring the spatial change of gravity, he designed the torsion balance, with which he became internationally famous.
First measurements with torsion balance were carried out by him in the university building and in the garden of his villa in Pestlőrinc, a former suburb of Budapest. In the winters of 1901/02 and 1902/03, he carried out the measurements on the lake Balaton ice cover in order to eliminate any disruption of gravity. By then E. was already thinking about the use of his measurement techniques for investigating underground geological masses. He disclosed his instrument to the public in 1906 at the Budapest Congress of the International Earth measurements. The Congress put together a council which observed earth measurements performed by E. in the vicinity of Arad.
The first successful measurements in practice were carried out in 1915 while searching for oil around Egbell. These measurements marked the beginning of geophysics application in searching for earth materials. In the following two decades, E.'s torsion balance was the most important tool in such research ventures. It was used in the search for oil fields in Texas, Venezuela and the Middle East. With the help of the torsion balance and in cooperation with Dezső Pekár and Jenő Fekete, E. was in 1908 able to demonstrate that the gravity with an accuracy of 2x10-8 is independent of the material mass structure. This evidence of the equivalence of gravitational and inertial mass played a prominent role in relativity theory. E. drew attention to the importance of Coriolis force that occurs in moving bodies, and thus contributed further evidence that the earth revolves. He also measured the earth magnetic field and designed a measuring device - magnetic translatometer - which was used in archeomagnetic research.
E. was enthusiastic traveler and photographer of nature. Some several hundred of his mountain photos, especially of Visoke Tatre, is owned by the Hungarian Technical Museum. E. was also the founder and first president of the Carpathian Tourist Association.