Philipp Lenard

Infobox_Scientist
name = Philipp Lenard


image_width = 200px
caption = Philipp Lenard in 1900
birth_date = birth date|1862|6|7|mf=y
birth_place = Bratislava, Austria-Hungary
death_date = death date and age|1947|5|20|1862|6|7
death_place = Messelhausen, Germany
nationality = Germany
field = Physics
work_institution = University of Breslau
University of Aachen
University of Heidelberg
University of Kiel
alma_mater = University of Heidelberg
doctoral_advisor = Robert Bunsen
doctoral_students =
known_for = Cathode rays
prizes = Nobel Prize for Physics (1905)
footnotes =

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

Early life and work

Philipp Lenard was born in Pressburg (today's Bratislava, Slovakia), Austria-Hungary, on July 7, 1862. He studied under the illustrious Robert Bunsen and Hermann von Helmholtz, and obtained his doctoral degree in 1886 at the University of Heidelberg. [ [http://www.mek.iif.hu/porta/szint/tarsad/tudtan/nobel/html/lenard/lenard.htm Lénárd Fülöp ] ] 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.

His early work included studies of phosphorescence and luminescence and the conductivity of flames.

Contributions to physics

Photoelectric investigation

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. 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. [cite journal | author=Philipp Lenard | title=Ueber Kathodenstrahlen in Gasen von atmosphärischem Druck und im äussersten Vacuum | journal=Annalen der Physik | volume=287 | issue=2 | pages=225–267 | year=1894 | doi=10.1002/andp.18942870202] These windows have come to be known as "Lenard windows".

Lenard observed 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.

Meteorological contributions

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". [ [http://amsglossary.allenpress.com/glossary/search?id=lenard-effect1 American Meteorological Society Glossary] ]

He 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. [ [http://hypertextbook.com/facts/2001/IgorVolynets.shtml Diameter of a Raindrop - the Physics Handbook] ]

"Deutsche Physik" and anti-semitism

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" and ignore what he considered the fallacious and 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 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 in 1947 in Messelhausen.

Honours and awards

* Royal Society Rumford Medal, 1896
* Italian Society of Sciences Matteucci Medal, 1896
* Franklin Institute Franklin Medal, 1905

Bibliography

*cite book | last=Lenard | first=Philipp | title=Über Kathodenstrahlen (On Cathode Rays) | language=German | location= | publisher= | year=1906 | isbn=
*cite book | last=Lenard | first=Philipp | title=Über Aether und Materie (On Aether and Matter) | language=German | location= | publisher= | year= | isbn=
*cite book | last=Lenard | first=Philipp | title=Probleme komplexer Moleküle (Problems of complex molecules) | language=German | location= | publisher= | year=1914 | isbn=
*cite book | last=Lenard | first=Philipp | title=Quantitatives über Kathodenstrahlen | language=German | location= | publisher= | year=1918 | isbn=
*cite book | last=Lenard | first=Philipp | title=Über das Relativitätsprinzip (On the Principle of Relativity)| language=German | location= | publisher= | year=1918 | isbn=
*cite book | last=Lenard | first=Philipp | title=Aether und Uraether | language=German | location= | publisher= | year=1921 | isbn=
*cite book | last=Lenard | first=Philipp | title=Grosse Naturforscher | language=German | location= | publisher= | year=1930 | isbn=
*cite book | last=Lenard | first=Philipp | title=Great Men of Science | location=London | publisher=G. Bell and sons | year=1933 | oclc=1156317
*cite book | last=Lenard | first=Philipp | title=Deutsche physik in vier bänden | language=German | location=| publisher=J.F. Lehmann | year=1936 | oclc=13814543

References

*Beyerchen, Alan, "Scientists under Hitler: Politics and the physics community in the Third Reich" (New Haven, CT: Yale University Press, 1977).
*Cornwell, John, "Hitler's Scientist: Science, War and the Devil's Pact" (Penguin Books, 2003), ISBN 0-14-200480-4.
*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.

External links

* [http://nobelprize.org/physics/laureates/1905/lenard-bio.html Nobel Foundation biography]
* [http://nobelprize.org/physics/laureates/1905/lenard-lecture.html On Cathode Rays]
* [http://members.chello.nl/~h.dijkstra19/page7.html The Cathode Ray Tube site]

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