Lenard, Philipp Eduard Anton von (1862–1947)

Hungarian-born German physicist who was awarded the Nobel Prize for Physics in 1905 for his investigations into the photoelectric effect and cathode rays (the stream of electrons emitted from the cathode in a vacuum tube).

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 in 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 in 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.