Janos Andras Segner

* Bratislava, October 9, 1704 – † Halle, October 5, 1777 / physician, mathematician, natural scientist, university professor ; ; He completed his primary school education in Bratislava and Győr. He began his higher education in 1724 at the Reformed College in Debrecen. His physics teacher was probably Sámuel Szilágyi. In 1725 he enrolled in the medical department in Jena, but also studied physics and mathematics. He completed his studies in 1729 and obtained his medical degree in 1730. In the same year, he began medical practice in Bratislava. In 1731, on the recommendation of Mátyás Bél, he became the city physician of Debrecen. But the following year, in 1732, he was invited to Jena as a private tutor148, and between 1733 and 1755 he was a professor of physics, mathematics and chemistry at the University of Göttingen, and also a member of the medical faculty. Between 1748 and 1754 he organized the university's astronomical observatory, and made observations himself, the results of which he published. From 1755 he was a physics and mathematics teacher in Halle, but also gave astronomical lectures. He is also considered the founder of mathematical meteorology. The most significant results of his versatile work were achieved in physics, within which in the field of rigid bodies and fluid mechanics. His study of the theory of the spinning top led to the formulation of Euler's equation of motion of a rotating rigid body. ; The history of science primarily records his work in the field of hydraulics – the investigation of the internal forces of liquids, the introduction of the concept of surface tension, and the Segner wheel named after him, the ancestor of reaction turbines. He first described the latter in his thesis Programa quo theoriam machinae cuiusdam hydraulicae praemittit, published in Göttingen in 1740. He built a mill whose driving mechanism was the Segner wheel (i.e. the water turbine). In addition, he was among the first to try to achieve the best efficiency based on calculations. His experimental results served as the basis for Leonhard Euler's (1707–1783) turbine equations, with which he laid the theoretical foundations for the development of turbines. With his textbooks and pedagogical work, he was a significant early representative of the educational reform demands of the 18th century. In addition to physics, he also dealt with mathematics and chemistry. He is well known for his proof of Descartes' rule of sign and his work on the approximate determination of the value of p. His mathematical books were among the best works of his time due to the thoroughness of their proofs. Several proofs are still used today in the way he gave them. He renewed the Cavalieri theorem for cubic calculations, after which it was mistakenly named after him for a while. He has interesting results regarding the graphical solutions of equations. He recommended sulfur dioxide for disinfecting grain seeds and wood dust for fertilizing. He also dealt with the technology of sugar, alcohol and gunpowder production. He was a member of the academies of St. Petersburg, London, Berlin and Göttingen. Segner and Euler were on good terms for many years, although the Bratislava scientist was noted for having a very difficult nature. Today, 159 letters from Segner to Euler are known, of which only 17 have survived. A crater on the Moon was named after him. ; ; His main works: ; De natura ac principiis medicinae (doctoral dissertation), 1730, ; Elementa arithmeticae et geometriae, 1739, ; Specimen Logicae, 1740, ; Einleitung in die Natur-Lehre, 1746, ; Specimen Theoriae Turbinum, 1755, ; Gründe der Perspective, 1799 (this was published by his son).