Lenard, Philipp Eduard Anton (1862-1947)

Hungarian-born German physicist who investigated the photoelectric effect and cathode rays (the stream of electrons emitted from the cathode in a vacuum tube). Nobel prize 1905. Lenard was born in Pozsony, Hungary (now Bratislava, Slovak Republic), and studied at Heidelberg and Berlin. In 1898 he became professor of experimental physics at Kiel, and held the same post at Heidelberg 1907-31. In 1924 Lenard became a Nazi. Obsessed with the idea of producing a purely 'Aryan' physics, he spent his later years reviling Albert Einstein and other Jewish physicists. Lenard's work on cathode rays began 1892, and led him to the conclusion that an atom is mostly empty space. He also suggested that the part of the atom where the mass was concentrated consisted of neutral doublets or 'dynamids' of negative and positive electricity. This preceded by ten years the classic model of the atom proposed by Ernest Rutherford 1911. Lenard devised the grid in the thermionic valve that controls electron flow. He showed that an electron must have a certain minimum energy before it can produce ionization in a gas. He also studied luminescent compounds and, from 1902 onwards, discovered several fundamental effects in photoelectricity.