INGE LEHMANN (1888-1993)
(May 13, 1888 – February 21, 1993), Fellow of the Royal Society (London) 1969, was a Danish seismologist who, in 1936, argued that the Earth must not only have a molten interior, but a solid core at the center, which deflects P waves. She also wrote a book called P, which dealt with P waves and other aspects of seismography. She was awarded the Tagea Brandt Rejselegat twice, in 1938 and 1967.
Inge Lehmann grew up with the field of seismology, becoming a pioneer among women and scientists. Born in Denmark, on May 13, 1888, her early education came in Denmark at a coeducational school run by the aunt of Niels Bohr. It was a place where boys and girls studied the same subjects, where all played soccer and rugby and learned needlepoint.
In 1920 she earned her master's degree in mathematics after 12 years of undergraduate and graduate studies at the University of Copenhagen and University of Cambridge, studies that were interrupted by 6 years of full-time actuarial work. In later years, she would study in Germany, France, Belgium, and Netherlands; in 1928 she earned a second master's degree, in geodesy, from the University of Copenhagen.
Lehmann's career in seismology began in 1925 when she aided N. E. Norlund as he established seismic networks first in Denmark, then in Greenland. By 1928, Lehmann was named the first chief of the seismology department of the newly established Royal Danish Geodetic Institute, a position she held for 25 years. She recorded, analyzed, and cataloged seismograms from Denmark and Greenland, published seismic bulletins, and worked as the "only Danish seismologist," as she once described herself.
In 1936 she published the paper that sealed her place in the history of geophysics. Known simply as "P' (P-prime)," the paper suggested a new discontinuity in the seismic structure of the Earth, now known as the Lehmann discontinuity, a region that divides the core into inner and outer parts. Using ray theory and travel time curves to interpret seismograms, Lehmann discovered that the P' phase of seismic waves traveling through the inner Earth was not the result of diffraction, the commonly held interpretation at the time, but a clear indication of an inner core.
Later, Lehmann established herself as an authority on the structure of the upper mantle. Extended parts of her later years were spent as a visiting scientist at the Lamont-Doherty Earth Observatory, Dominion Observatory, the Seismological Laboratory at Caltech, and the University of California, at Berkeley. She also led her colleagues as a founder and president of the European Seismological Federation, president of the Danish Geophysical Society, and vice president of the International Association of Seismology and Physics of the Earth's Interior.
In 1971, Inge Lehmann was presented with the William Bowie Medal, the American Geophysical Union's highest honor, which is granted to a scientist who has made fundamental contributions to the study of geophysics and who has lived up to the AGU ideal of unselfish cooperation in research. Lehmann also was named an AGU Fellow and was awarded honorary doctorates from Columbia University and the University of Copenhagen.
American Geophysical Union
Lehmann, Inge (1888-1993), Danish geophysicist Trained as a mathematician and an actuary, Danish geophysicist Inge Lehmann used painstaking analyses, measurements and observations of shock waves generated by earthquakes to propose in 1936 that the earth had a solid inner core. Throughout her long career, which extended far beyond her official retirement in 1953, Lehmann conducted research in Europe and North America and was active in international scientific organizations including serving as the first president and a founder of the European Seismological Federation.
Lehmann was one of two daughters born to Alfred Georg Ludvig Lehmann, a University of Copenhagen professor of psychology, and Ida Sophie Torsleff. As a child, she attended and graduated from the first coeducational school in Denmark, an institution founded and run by Hanna Adler, the aunt of future Nobel Prize winning physicist Niels Bohr. She began her university education by studying mathematics at the University of Copenhagen from 1907 to 1910. She continued her mathematical studies the following year at Cambridge University in England before returning to Denmark, where she worked as an actuary from 1912 to 1918. She also continued her formal education. In 1920, Lehmann earned her masters degree in mathematics from the University of Copenhagen and later studied mathematics at the University of Hamburg. In 1925, Lehmann began her career in seismology as a member of the Royal Danish Geodetic Institute and helped install the first seismographs at her Copenhagen office. "I was thrilled by the idea that these instruments could help us to explore the interior of the earth, and I began to read about it," she was quoted in a 1982 article published in the Journal of Geological Education. Lehmann later helped establish seismograph stations in Denmark and Greenland.
After further study with seismologists in France, Germany, Belgium, and the Netherlands, and after earning a M.S. degree in geodesy from the University of Copenhagen in 1928, Lehmann was named chief of the Royal Danish Geodetic Institute. In that position, held until her retirement in 1953, Lehmann was Denmark's only seismologist for more than two decades. She was responsible for supervising the Denmark's seismology program, overseeing the operation of the seismograph stations in Denmark and Greenland, and preparing the institute's bulletins.
Despite this heavy workload, Lehmann still found time to explore scientific research. In 1936, she published her most significant finding, the discovery of the earth's inner core, under the simple title of "P." The letter P stood for three types of waves generated by Pacific earthquakes that Lehmann had been carefully observing through the planet for ten years. By studying the shock waves generated by earthquakes, recorded on seismographs as travel-time curves, she theorized that the earth has a smaller solid inner core. Within a few years, work by other scientists, including Harold Jeffreys and Beno Gutenberg, substantiated her findings.
Lehmann continued her research well after her retirement in 1953, exploring the nature of the planet's interior in Denmark, in Canada at the Dominion Observatory in Ottawa and in the United States at the University of California at Berkeley, the California Institute of Technology, and the Lamont Doherty Earth Observatory at Columbia University. She was a named a fellow of both the Royal Society of London and Edinburgh and was named to the Royal Danish Academy of Science and Letters and the Deutsche Geophysikalische Gesellschaft. In 1971, she was awarded the William Bowie Medal of the American Geophysical Union in recognition of her "outstanding contributions to fundamental geophysics and unselfish cooperation in research." She was also awarded honorary doctorates by the University of Copenhagen and Columbia University.
Lehmann remained single throughout her long and productive life. Her interests were not restricted to science. She was concerned with the poor in her native Denmark and the plight of European refugees. Travel in conjunction with her work also afforded her frequent opportunities to pursue two of her hobbies—visiting art galleries throughout Europe and the United States, and the outdoors. Lehmann enjoyed hiking, mountain climbing, and skiing. She died at the age of 105.
Some Important Contributions
Discovered 5121 km below the surface of the earth an inner core. This discovery was based on observations of the reflection and refraction of seismic waves generated by deep focus earthquakes. From Lehmann's discovery of the earth's inner core have come current ideas on th e origin of the earth's magnetic field described by Professor Leon Knopoff, UCLA.
"The inner core of the earth is now thought to be a solid precipitate of the molten iron/nickel outer core. One popular model has it that the condensation of the inner core is the heat source for driving convective motions in the outer core and hence is a mechanism for generating the earth's magnetic field." --- Leon Knopoff, 1996.
Discovered, at a depth of 220 km below the surface of the earth, the Lehmann discontinuity.
Some Important Publications
" P' ", Union Geodesique at Geophysique Internationale, Serie A, Travaux Scientifiques 14: 87 (1936).
"Velocities of Longitudinal Waves in the Upper Part of the Earth's Mantle", Annales de Geophysique 15: 93 (1959).
"The Travel Times of the Longitudinal Waves of the Logan and Blanca Atomic Explosions and Their Velocities in the Upper Mantle", Bulletin of the Seismological Society of America 52: 519 (1962).
A founder and chair (1941 and 1944) Danish Geophysical Society
First President of the European Seismological Commission
Associate, Royal Astronomical Society, London
Honorary Fellow, The Royal Society, Edinburgh
Foreign Member, The Royal Society, London
Honorary Member, European Geophysical Society
Member, Royal Danish Academy of Sciences and Letters
Wiechert Medal, Deutsche Geophysikalische Gesellschaft 1964
Doctor of Science, Columbia University, New York 1964
Gold Medal, Royal Danish Academy of Science 1965
Doctor of Philosophy, University of Copenhagen 1968
Bowie Medal, American Geophysical Union 1971
The Medal of the Seismological Society of America 1977
The Lehmann Medal, instituted by the American Geophysical Union in 1997, is to be awarded in recognition of outstanding research on the structure, composition, and dynamics of the Earth's mantle and core. This medal is the first AGU honor to be named for a woman, and the first to be named for a scientist who worked outside the United States.
1925 Royal Danish Geodetic Institute
1928-53 Chief of the Seismological Department of the Royal Danish Geodetic Institute
Attended the first co-educational school in Denmark founded by Hanna Adler, aunt of Niels Bohr.
University of Copenhagen 1907-10
M.S. (mathematics) University of Copenhagen 1920
M.S. (geodesy) University of Copenhagen 1928Recommended Reading
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