Physics: 1905

Lenard, Philipp Eduard Anton von pronounced LAY nahrt, (1862-1947), a Hungarian-born German physicist, studied the properties of streams of electrons called cathode rays. For his discoveries, Lenard was awarded the Nobel Prize for physics in 1905.

Lenard performed many important experiments, though his theories and opinions were controversial. He made many public attacks on other physicists, particularly foreigners and those associated with what he thought of as "Jewish" science. Lenard was a supporter of Nazism and served as a scientific advisor to the Nazi Party.

Lenard's early work centred on how light is given off by the process of phosphorescence and luminescence. He discovered that phosphorescent minerals, such as calcium sulphide, can glow in the dark after being illuminated only if traces of heavy metals, such as copper and bismuth, are present. Lenard also disproved the theory that cathode rays were similar to ultraviolet light, by attempting to pass cathode rays through a quartz window in a discharge tube. Unlike ultraviolet light, the cathode rays would not pass through the quartz.

In 1898, Lenard constructed a cathode-ray tube with a thin sheet of aluminum serving as a window to keep the vacuum contained but to let cathode rays out. With this Lenard window, he showed that the rays decreased in number as the distance from the tube increased. He also demonstrated that the density of materials affects their ability to absorb cathode rays.

Working with German physicist Hienrich Hertz, Lenard also demonstrated how light striking a metal surface could create a cathode ray, a phenomenon that became known as the photoelectric effect. The number of electrons given off by this process, Lenard proved, was proportional to the energy carried by the light, whereas the electrons' speed was independent of this energy.

These facts conflicted with the theories of the time. Only in 1905 did the German physicist Albert Einstein explain the photoelectric effect by showing that light consists of particles of energy called photons. Lenard, however, never forgave Einstein for discovering and giving his name to the theory of light quanta, the law that explained Lenard's results.

Lenard's later work covered such areas as the energy needed by an electron to produce ionization in a gas; a model of the atom as an assemblage of particles that he called dynamides; and the nature and origin of the lines of the spectrum.

Lenard was born in Pressburg, Hungary (now Bratislava, Slovakia). He studied physics at Heidelberg University, Gemany. He taught at the universities of Breslau, Aachen, Heidelberg, and Kiel.