Lénárd, Fülöp (Philip)

(Pozsony (Bratislava), June 7th, 1862 – Messelhausen, May 20th, 1947)

Lénárd, Fülöp

He was a Nobel-prize winner physicist, one of the outstanding personalities of the turn of the 19th – 20th century. Web link

From 1880, he attended the Technische Hochschule Web link in Vienna for one year and, then, he studied at the Budapest University of Science. Web link After a short break, he continued his studies in Heidelberg Web link and obtained his doctorate in 1886. He attended the lectures of Bunsen, Helmholtz, Königsberger and Quincke. Having graduated, he worked as an assistant of Quincke. Then, he also worked in Breslau and Aachen for short time and had the opportunity to get acquainted with the most important physicists of the then Germany.

He achieved his most significant results in Bonn as a colleague of Heinrich Hertz between 1892 and 1894. He was appointed to a professorship at the department of theoretical physics at Heidelberg University in 1896. From 1898, he was a professor at the Kiel University Web link and, from 1907 to his retirement, he taught as a professor at Heidelberg University.

It is in 1888 that he started the examination of cathode rays, which determined his further career. By examining the cathode ray, he demonstrated that the electrons in a cathode ray can be accelerated by means of an electric field and deflected by means of a magnetic field. He recognised that the cathode ray consists of particles of negative charge. These results offered J.J. Thomson the possibility of measuring the specific charge of electrons, which is considered as the discovery of electrons at present. By means of a window made of aluminium foil (Lénárd's window) and placing it on the wall of the cathode ray tube, Lénárd allowed the cathode ray to exit to the atmosphere. By measuring the permeability of the window, he arrived at the conclusion that atoms cannot consist of extensive solids; instead, they are essentially empty.

In 1902, he alone continued the work started with Hertz and recognised that the energy of electrons emerging from metals under the effect of light is proportional to the frequency of light while their number is proportional to the light intensity. He pointed out that, in order for the electrons to emerge, the frequency of light should exceed a specific limit value. His results were reassessed by Einstein, who recognised the quantum-nature of light and developed the photoelectric equation using Lénárd's results.

Late in his life, he actively supported German national socialism. He did not regard two fields of modern physics, namely the theory of relativity and quantum mechanics, as serious natural sciences, primarily due to the origin of the researchers.

Memberships: Associate member (1887) and ordinary member (1907) of the Hungarian Academy of Sciences; honorary doctor of the Universities of Christiania (1911), honorary doctor of Dresden University (1922); honorary doctor of Bratislava University (1942).

Honours: Vienna Academy Baumgartner-Prize of (1896), Royal Society Rumford-Prize (1896), Nobel Prize in physics (1905), Franklin Prize (1905).

References: Wolff, Stephan L., "Physicists in the 'Krieg der Geister': Wilhelm Wien's 'Proclamation'", Historical Studies in the Physical and Biological Sciences Vol. 33, No. 2 (2003): 337-368.