(Buda, July 27th, 1848 – Budapest, April 8th, 1919)
Loránd Eötvös (Baron) was the son of the well-known Hungarian writer, political scientist and politician, József Eötvös. He began his studies in the Piarist Grammar School in Pest then he studied mathematics and physics at the University of Heidelberg. During his university years his masters were Ányos Jedlik in Pest, and among others Gustav Kirchhoff, Robert Bunsen and Hermann Helmholtz in Heidelberg. He also took his Ph. D. degree there in 1870 with a thesis which studied problems of Fizeau on the relative motion of a light source, which was one of the first steps towards relativity theory..
His interests turned to the phenomenon of capillarity in the field of experimental physics, and within a short time he determined the relationship, later named after him as the Eötvös rule, between the surface tension, the molecular volume of fluids and temperature.
Following this he began to carry out methodological research in the phenomenon of gravity. He constructed a new instrument, the torsion balance (or Eötvös pendelum) for gravitional investigations which met the requirements of the measurement procedures he had developed to the highest degree. The first version of the device was completed in 1891 and was a human-sized measuring device.
He started to study the geographical micro structure (changes at different locations) of the gravitational field of the earth with the use of his torsion balance. A method in field work was developed, by means of which the visible and invisible distribution of material - unevenness of distribution according to the density of surrounding masses - could be mapped, which made the Eötvös balance an effective means of raw material exploration. This procedure arrived for applied geophysics at just the right time, because at that time interest in crude oil and natural gas had increased tremendously.
The Eötvös balance became more and more significant in basic research. By use of the balance it was successfully proved that the so-called heavy mass featuring the gravitational nature of a material and the so-called inertial mass featuring the inertia of a material are generally proportional (independently of the chemical composition of bodies), i.e. the two masses are equal in a proper measuring system. By means of his balance Eötvös proved this equivalence with record accuracy (he measured that the ratio of the deviation of the two masses and the mass, so the relative deviation, was less than 1/2,000,000). This result was 3 to 4 times more accurate than earlier measurements. This is called the equality independent of the chemical composition of heavy and inertial mass.
At the beginning Einstein did not know Eötvös' result, though the Hungarian scientist was just on the top with his work when Albert Einstein developed his general theory of relativity.
In 1906 the international geodetical society, the Internationale Erdmessung, held its XV. congress in Budapest. Eötvös presented his measurements on gravity and also demonstrated in field application of his balance. The success of his presentation resulted in a grant of annually 60,000 crowns of the Hungarian government from 1907 onwards for his gravitational and geomagnetic research. By this decision the first applied geophysical institute in the world was established under Eötvös's direction. The institute later was named after him.
In the meantime, between 1910 and 1918, Eötvös continued his investigations in gravity and earth magnetism. He proved that the weight of the bodies moving on the surface of the Earth (the resultant of the gravitational effect and the centrifugal force resulting from the rotation of the Earth) is not constant but in case of objects moving towards the west, it increases and in case of objects moving towards the east, it decreases as compared to those standing on the Earth (Eötvös effect).
After the death of Eötvös, his former assistant, Dezső Pekár carried on the torsion balance measurements.
From 1873 he was correspondent member of the Hungarian Academy of Sciences. In 1983 full member and in 1889, he was elected President and he performed this duty in several terms till 1905.
From 1871 he lectured theoretical physics at the Budapest University of Sciences, in the next year professor and in1891-92 he became its rector. During this interval he organized the Mathematical and Physical Society. From 1878 he led the Institute of Experimental Physics.
In 1894 and 1895 he filled a governmental post as Minister of Religion and Education. In 1895 he established the Eötvös College in memory of his father.
Representatives of the international scientific world regard him even today as the master of classical physics. In 1909 he received the Benecke prize in Göttinga for his gravity measurements. Two years later the Royal Prussian Academy of Science, the Jagello University of Krakow and the Norwegian Royal University conferred the title of honorary doctor upon him.
- Eötvös,L.: Über den Zusammenhang der Oberflächenspannung der Flüssigkeiten mit ihrem Molekularvolumen. Annalen der Physik und Chemie, 1886. pp. 448 – 459.
- Eötvös,L.: Über die Anziehung der Erde auf verschiedene Substanzen. Matematische und Naturwissenschaftliche Berichte aus Ungarn, 1890. pp. 65-68.
- Eötvös,L.: Messung von langen Schwingungsdauern. Matematische und Naturwissenschaftliche Berichte aus Ungarn, 1891. pp. 450-451.
- Eötvös,L.: Untersuchungen über Gravitation und Erdmagnetismus. Annalen der Physik und Chemie, 1896. pp. 354-400.
- Eötvös,L.: Étude sur les surfaces de niveau et la variation de la pesanteur et de la force magnétique. Rapports présentés au Congrès International de Physique réuni à Paris en 1900. Tome III. 6. pp. 371-393.
- Eötvös,L.: Programme des recherches gravimétriques dans les régions vésuviennes. Comptes rendus des séances de la première réunion de la commission permanente de l' Association International de Sismologie réuni à Rome. 1906. pp. 177-179.
- Eötvös,L.: Bestimmung der Gradienten der Schwerkraft und ihrer Niveauflächen mit Hilfe der Drehwage. Leiden: Brile, 1907.t. 1. p. 59.
- Eötvös,L.: Sur les travaux géodétiques exécutés en Hongrie, spécialement à l' aide de la balance de torsion. Budapest: Imp. Hornyánszky, p. 40., 1 carte
- Eötvös,L.: Über Arbeiten mit der Drehwage. Berichte an die XVII. Allgemeine Konferenz der Internationalen Erdmessung, Budapest: Druck Hornyánszky, 1912. p. 1., 1 Karte
- Eötvös,L.: Bericht über Arbeiten mit der Drehwage ausgeführt im Auftrage der kön. ung. Regierung in den Jahren 1909-1911. Verhandl. D. XVII. allg. Konferenz der internat. Erdmessung in Hamburg, 1912. I. pp. 427-438.
- Eötvös,L.: Experimenteller Nachweis der Schwereänderung die ein auf normal geformter Erdoberfläche in östlicher oder westlicher Richtung bewegter Körper durch diese Bewegung erleidet. Annalen der Physik, 1919. pp. 743-752.
- Eötvös,L.: Beiträge zum Gesetze der Proportionalität von Trägheit und Gravität. (Mit Dezső Pekár und Jenő Fekete). Annalen der Physik, 1922. pp. 11-66.
- Eötvös,L.: Gesammelte Arbeiten. Hrsg. (und Vorwort) von Pál Selényi, Budapest: Akadémiai Kiadó, 1953.