Lehmann, Inge (1888–1993)

Danish geophysicist and mathematician who in 1936 discovered the existence of the inner core of the Earth. Born on May 13, 1888, at Osterbro by the Lakes in Copenhagen, Denmark; died in Copenhagen on February 21, 1993; daughter of Alfred Georg Ludvig Lehmann (a professor of psychology) and Ida Sophie (Torsleff) Lehmann; sister of Harriet Lehmann; University of Copenhagen, master's degree, 1920; also studied at Cambridge University and University of Hamburg; master of science degree in geodesy, 1928; honorary doctorates from the University of Copenhagen and Columbia University.

By studying the shock waves generated by earthquakes, was able to theorize that the Earth has a solid inner core, a finding that was substantiated by other scientists; was chief seismologist of the Royal Danish Geodetic Institute (1928–53); retired (1953).

In 1971, the Danish geophysicist Inge Lehmann 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." Lehmann, who had never earned a Ph.D., was one of the few women in her field for decades, and it took her determined nature to hold her own in a male, credentialed world where large egos were often the norm. "You should know how many incompetent men I had to compete with—in vain," she recalled. Lehmann nonetheless became one of the most innovative scientists of the 20th century. Born in the Victorian age, she lived to see both the birth and death of the Soviet Union, two World Wars, the coming of the Atomic Age, and the onset of a new world of computers and the Internet.

Lehmann was born in 1888 at Osterbro by the Lakes in Copenhagen, Denmark, the daughter of Alfred Lehmann and Ida Torsleff Lehmann . Inge's father was a professor of psychology at the University of Copenhagen and a pioneer in the study of experimental psychology in Denmark. She was sent to one of Denmark's most liberal and enlightened schools, the first coeducational institution in the country, which was founded and run by Hanna Adler , the aunt of Niels Bohr, a future Nobel Prize winner. From 1907 through 1910, Lehmann studied mathematics at the University of Copenhagen. During the 1911–12 academic year, she continued her mathematical studies at Cambridge University, returning to Denmark to begin work as an actuary. Her actuarial career lasted from 1912 through 1918, when she returned to the University of Copenhagen; two years later, she was awarded a master's degree. She took additional courses in mathematics at the University of Hamburg soon after.

In 1925, Lehmann began her career as a seismologist, working as a staff member of the Royal Danish Geodetic Institute. Decades later, she recalled being "thrilled by the idea that these instruments could help us explore the interior of the Earth, and I began to read about it." She helped install seismographs in her Copenhagen office and learned all she could about the nascent science from seismologists in Belgium, France, Germany, and the Netherlands. In 1928, after earning a master of science degree in geodesy (applied mathematics relating to the measurement of the Earth), Lehmann was promoted to the post of chief seismologist of the Royal Danish Geodetic Institute. One of the responsibilities in her heavy workload was the supervision of all aspects of Denmark's seismology program, which included writing the institute's bulletins and overseeing the operation of seismographic stations throughout Denmark and in Greenland. In addition, Lehmann continued independent research projects. From her first scientific essay (1926) to her last (1987), she published a total of 59 papers, many of which made significant contributions to her field.

A major earthquake in New Zealand in June 1929 produced sufficient data on European, including Danish, seismographs to be of great value for investigating the problem of whether the Earth had a liquid or solid inner core. The Danish seismographic network Lehmann was in charge of provided excellent data for such an investigation. In comparing a number of these recordings, she could clearly see onsets of various seismic waves through the Earth's core. This enabled her to make the necessary imaginative jump to conclude that the Earth had a tripartite structure, having a seismically distinct and solid inner core. This conclusion, which had taken Lehmann years of slow, painstaking effort, was published in her classic scientific paper of 1936, titled simply "P'." In 1938–39, her work was validated in papers published by seismologists Beno Gutenberg, Charles F. Richter, and Harold Jeffreys.

At the time of Lehmann's death in 1993, her aunt's grandson, Nils Groes, would remember Lehmann in her garden where she:

sat in the lawn with a big table filled with cardboard oatmeal boxes. In the boxes were cardboard cards with information on earthquakes and the times for these and the times for their registration all over the world. This was before computer processing was available, but the system was the same. With her cardboard cards and her oatmeal boxes, Inge registered the velocity of propagation of the earthquakes to all parts of the globe. By means of this information, she deduced new theories of the inner parts of the Earth.

After her retirement in 1953, Lehmann continued her scientific work and the writing and publication of papers. She visited research centers around the world, sharing decades of knowledge with scientists of her generation as well as the next. With a strong social conscience, she was concerned about the poor in Denmark and the conditions of refugees throughout Europe and the world. She also enjoyed attending art galleries in each country she visited. Among her favorites activities were hiking, skiing, and mountain climbing, particularly in the Alps. Having never received a Ph.D. degree, she was pleased to be awarded honorary doctorates both by her alma mater, the University of Copenhagen, as well as by New York's Columbia University. Other honors she received included being chosen as a foreign member of the prestigious British Royal Society in 1969. In her final years, Lehmann's research resulted in papers on the role of seismographic evidence in evaluating data generated by nuclear explosions, a subject of vital importance for the accurate monitoring of a comprehensive nuclear test-ban treaty. At the end of her life, while hospitalized, Lehmann told Nils Groes "that all day she had been thinking about her own life and she was content. It had been a long and rich life full of victories and good memories." She died in Copenhagen on February 21, 1993, three months shy of her 105th birthday.

sources:

Bolt, Bruce A. "Inge Lehmann," in Physics Today. Vol. 47, no. 1. January 1994, p. 61.

——. Inside the Earth: Evidence from Earthquakes. San Francisco, CA: W.H. Freeman, 1982.

—— and Erik Hjortenberg, "Inge Lehmann (1888–1993)," in Bulletin of the Seismological Society of America. Vol. 84, no. 1. February 1994, pp. 229–233.

Brush, Stephen G. "Discovery of the Earth's Core," in American Journal of Physics. Vol. 48, no. 9. September 1980, pp. 705–724.

Fowler, C.M.R. The Solid Earth: An Introduction to Global Geophysics. Cambridge, UK and NY: Cambridge University Press, 1990.

Jacobs, J.A. Deep Interior of the Earth. London: Chapman & Hall, 1992.

Jeffreys, Bertha Swirles. "Inge Lehmann: Reminiscences," in Quarterly Journal of the Royal Astronomical Society. Vol. 35, no. 2. June 1994, pp. 233–234.

Lehmann, Inge. "P'," in Bureau Central Seismoloque International, Ser. A, Travaux Scientifique. Vol. 14, 1936, pp. 87–115.

Runcorn, S.K. et al., eds. The Earth's Core: Its Structure, Evolution, and Magnetic Field: A Discussion. London: The Royal Society, 1982.

Schwarz, Joel. "Inge Lehmann, 1888–1993, Danish geophysicist," in Emily J. McMurray et al., eds., Notable Twentieth-Century Scientists. 4 vols. Detroit, MI: Gale Research, 1995, Vol. 3, pp. 1216–1217.

Williams, C.A., and J.A. Hudson, "Inge Lehmann (1888–1993)," in Quarterly Journal of the Royal Astronomical Society. Vol. 35, no. 2. June 1994, pp. 231–233.

Yount, Lisa. A to Z of Women in Science and Math. NY: Facts on File, 1999.

John Haag , Associate Professor of History, University of Georgia, Athens, Georgia