PHILIPP LENARD

Philipp_Lenard

Philipp Lenard in 1905
Born	June 7, 1862 Pressburg, Hungary
Died	May 20, 1947 Messelhausen, Germany
Residence	Germany
Nationality	Hungarian before 1907, then German
Field	Physicist
Institution	University of Breslau, University of Aachen, University of Heidelberg, University of Kiel
Alma Mater	University of Heidelberg
Doctoral Advisor	Robert Bunsen
Doctoral Students	<please insert>
Known for	Cathode rays (electron beams)
Prizes	Matteucci Medal (1896), Nobel Prize for Physics (1905), Rumford Medal (1896)

Philipp Eduard Anton von Lenard, (Hungarian: Lénárd Fülöp) (June 7, 1862–May 20, 1947) was a 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.

Biography

Philipp Lenard was born in Bratislava (then as Pressburg part of the Austro-Hungarian Empire) on July 7, 1862, and he attended a Hungarian-language secondary school. He studied under the illustrious Bunsen and Helmholtz, and obtained his doctoral degree in 1886 at the University of Heidelberg. He was certainly a Hungarian citizen as of 1897 (when the Hungarian Academy of Sciences elected him to be a corresponding member) but he resigned his nationality probably before 1907. ([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.

As a physicist, Lenard's major contributions were in the study of cathode rays. 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.

Photoelectric investigation

The 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. 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.

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.

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.

These 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. Ironically, Einstein never really accepted quantum mechanics, and was its most prominent critic.

Later Years and Legacy

Lenard is most 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.

Lenard retired from Heidelberg Univerisity 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. He died two years later in Messelhausen.

Honors

• 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.

External links

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

Books by Philipp Lenard

• Ueber Aether und Materie (second edition 1911)
• Quantitatives über Kathodenstrahlen (1918)
• Ueber das Relativitätsprinzip (1918)
• Grosse Naturforscher (second edition 1930)
• Deutsche Physik (1936-37, physics, 4 vols.)
• Lenard, Philipp, Great Men of Science. Translated from the second German edition, G. Bell and sons, London (1950) ISBN 083691614X

References

• 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.