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Philipp Lenard
Philipp Lenard in 1900
Born	June 7, 1862(1862-06-07) Pressburg, Hungary
Died	May 20, 1947 (aged 84) Messelhausen, Germany
Residence	Germany
Nationality	Hungarian (pre-1907) German (post-1907)
Field	Physicist
Institutions	University of Breslau University of Aachen University of Heidelberg University of Kiel
Alma mater	University of Heidelberg
Academic advisor	Robert Bunsen
Known for	Cathode rays (electron beams)
Notable prizes	Nobel Prize for Physics (1905)

Philipp Eduard Anton von Lénárd (June 7, 1862 in Pressburg (today's Bratislava), Austria-Hungary – May 20, 1947 in Messelhausen, Germany) was a Hungarian-German physicist and the winner of the Nobel Prize for Physics in 1905 for his research on cathode rays and the discovery of many of their properties. He was also an active proponent of Nazi ideology.

Contents 1 Biography 2 Photoelectric investigation 3 Meteorological contributions 4 Honours 5 Lenard and the "Deutsche Physik" 6 External links 7 Books by Philipp Lenard 8 Notes 9 References

Philipp Lenard was born in Pressburg (today's Bratislava, Slovakia), Austria-Hungary, on July 7, 1862. He studied under the illustrious Bunsen and Helmholtz, and obtained his doctoral degree in 1886 at the University of Heidelberg.^[1] After posts at Aachen, Bonn, Breslau, Heidelberg (1896-1898), and Kiel (1898-1907), he returned finally to the University of Heidelberg in 1907 as the head of the Philipp Lenard Institute.

Lenard retired from Heidelberg University as professor of theoretical physics in 1931. He achieved emeritus status there, but he was expelled from his post by Allied occupation forces in 1945 when he was 83. He died two years later in Messelhausen.

His early work included studies of phosphorescence and luminescence and the conductivity of flames. He also conducted studies on the size and shape distributions of raindrops and constructed a novel wind tunnel in which water droplets of various sizes could be held stationary for a few seconds. He was the first to recognize that large raindrops are not tear-shaped, but are rather shaped something like a hamburger bun.

As a physicist, Lenard's major contributions were in the study of cathode rays, which he began in 1888. Prior to his work, cathode rays were produced in primitive tubes which are partially evacuated glass tubes that have metallic electrodes in them, across which a high voltage can be placed. Cathode rays were difficult to study because they were inside sealed glass tubes, difficult to access, and because the rays were in the presence of air molecules (fully evacuated tubes didn't produce rays). Lenard overcame these problems by devising a method of making small metallic windows in the glass that were thick enough to be able to withstand the pressure differences, but thin enough to allow passage of the rays. These windows are also known as Lenard window. Having made a window for the rays, he could pass them out into the laboratory, or, alternatively, into another chamber that was completely evacuated. He was able to conveniently detect the rays and measure their intensity by means of paper sheets coated with phosphorescent materials.^[2]

Another observation that Lenard made was that the absorption of the rays was, to first order, proportional to the density of the material they were made to pass through. This appeared to contradict the idea that they were some sort of electromagnetic radiation. He also showed that the rays could pass through some inches of air of a normal density, and appeared to be scattered by it, implying that they must be particles that were even smaller than the molecules in air. He confirmed some of J.J. Thomson's work, which ultimately arrived at the understanding that cathode rays were streams of energetic electrons. In conjunction with his and other earlier experiments on the absorption of the rays in metals, the general realization that electrons were constituent parts of the atom enabled Lenard to claim correctly that for the most part atoms consist of empty space!

As a result of his Crookes tube investigations, he showed that the rays produced by radiating metals in a vacuum with ultraviolet light were similar in many respects to cathode rays. His most important observations were that the energy of the rays was independent of the light intensity, but was greater for shorter wavelengths of light.

These latter observations were explained by Albert Einstein as a quantum effect. This theory predicted that the plot of the cathode ray energy versus the frequency would be a straight line with a slope equal to Planck's constant, h. This was shown to be the case some years later. The photo-electric quantum theory was the work cited when Einstein was awarded the Nobel Prize in Physics. This much embittered Lenard, who became a prominent skeptic of relativity and of Einstein's theories generally.

Lenard was the first person to study what has been termed the Lenard effect in 1892. This is the separation of electric charges accompanying the aerodynamic breakup of water drops. It is also known as spray electrification or the waterfall effect.^[3]

• Together with Wilhelm Röntgen, he was awarded the Rumford Medal of the Royal Society in 1896.
• Also with Röntgen he received the Matteucci Medal of the Italian Society of Sciences in 1896.
• He was awarded the Franklin Medal of the Franklin Institute in 1905.

Lenard is remembered today as a strong German nationalist who despised English physics, which he considered as having stolen their ideas from Germany. He joined the National Socialist Party before it became politically necessary or popular to do so. During the Nazi regime, he was the outspoken proponent of the idea that Germany should rely on "Deutsche Physik" ("German physics") and ignore the (in his opinion) fallacious and perhaps deliberately misleading ideas of "Jewish physics", by which he meant chiefly the theories of Albert Einstein, including "the Jewish fraud" of relativity. An advisor to Adolf Hitler, Lenard became Chief of Aryan Physics under the Nazis. Austrian records show that Lenard was actually born a Jew.^[4]

• Nobel Foundation biography
• On Cathode Rays
• The Cathode Ray Tube site

• Ueber Kathodenstrahlen (1906)
• Ueber Aether und Materie (second edition 1911)
• Probleme komplexer Molekuele (1914)
• Quantitatives über Kathodenstrahlen (1918)
• Ueber das Relativitätsprinzip (1918)
• Aether und Uraether (1921)
• Grosse Naturforscher (second edition 1930)
• Deutsche Physik (1936-37, physics, 4 vols.)
• Great Men of Science (1950). Translated from the second German edition. G. Bell and sons, London. ISBN 0-8369-1614-X

• Beyerchen, Alan, Scientists under Hitler: Politics and the physics community in the Third Reich (New Haven, CT: Yale University Press, 1977).
• Hentschel, Klaus, ed. Physics and National Socialism: An anthology of primary sources (Basel: Birkhaeuser, 1996).
• Walker, Mark, Nazi science: Myth, truth, and the German atomic bomb (New York: Harper Collins, 1995).
• 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.

v • d • e Nobel Laureates in Physics
Wilhelm Röntgen (1901) • Hendrik Lorentz / Pieter Zeeman (1902) • Henri Becquerel / Pierre Curie / Marie Curie (1903) • Lord Rayleigh (1904) • Philipp Lenard (1905) • J. J. Thomson (1906) • Albert Michelson (1907) • Gabriel Lippmann (1908) • Guglielmo Marconi / Ferdinand Braun (1909) • Johannes van der Waals (1910) • Wilhelm Wien (1911) • Gustaf Dalén (1912) • Kamerlingh Onnes (1913) • Max von Laue (1914) • W. L. Bragg / W. H. Bragg (1915) • Charles Barkla (1917) • Max Planck (1918) • Johannes Stark (1919) • Charles Guillaume (1920) • Albert Einstein (1921) • Niels Bohr (1922) • Robert Millikan (1923) • Manne Siegbahn (1924) • James Franck / Gustav Hertz (1925)
Complete roster | (1901-1925) | (1926-1950) | (1951-1975) | (1976-2000) | (2001-2025)

Persondata
NAME	Lenard, Philipp
ALTERNATIVE NAMES
SHORT DESCRIPTION	Hungarian-German physicist
DATE OF BIRTH	June 7, 1862
PLACE OF BIRTH	Pressburg, Hungary
DATE OF DEATH	May 20, 1947
PLACE OF DEATH	Messelhausen, Germany