Inge Lehmann

KEYWORDS: Inge Lehmann, Denmark, 20th century, Seismology, Seismic Waves, Lehmann Discontinuity, Structure of the Earth, Earth’s core, P wave

SHE THOUGHT IT

Inge Lehmann discovered the Earth’s inner core in 1936 by using seismic wave data¹. In her studies, she also identified the low velocity layer located 220 kilometres beneath the Earth’s surface. This layer is now called the “Lehmann discontinuity.” Another Lehmann discontinuity is to be found between the inner and outer core of the Earth at approximately a depth of 5,100km ¹.

SHORT BIOGRAPHY

Inge Lehmann

Inge Lehmann was born in Copenhagen, Denmark in 1888 to an intellectual family² (p.287). She received her early education at Hannah Adler’s progressive high school, which promoted equal treatment of boys and girls² (p.287). Early on, her mathematics teacher noticed her talent for the subject and encouraged her to take on extra tasks² (p. 287). After passing the university entrance exam at the top of her class, she went on to study mathematics at the University of Copenhagen in 1907. In the autumn of 1910, she moved to England to study at Newnham College, Cambridge, for a year. At Newnham, she was confronted with the hardships of sexism and a prevailing bias against women in science which stood in sharp contrast to her experiences at school² (p. 288). In December 1911, she returned to Copenhagen and went on hiatus from her studies for a while² (p. 288). During that time, she worked at an actuary’s office for several years, where she improved her computational skills, until she returned to university in 1918. Two years later, she graduated with a Candidate’s Magisterial Degree in Mathematics and Physical Science³. In 1923, she was offered a position as an assistant to a professor of actuarial science at Copenhagen University¹. During her long and studious life⁴, she made significant contributions to the world of science, especially in the field of geoscience and seismology, became the founder and longstanding president of the European Seismological Federation, and the American Geophysical society recognises extraordinary contributions to geosciences with the Inge Lehmann Medal. She died at the age of 104 in Copenhagen¹.

SCIENTIFIC COLLABORATION AND RECOGNITION

Inge Lehmann first came in contact with seismology in 1925 when she was appointed to a position as a research assistant by Niels Erik Nørlund. The young scientist helped Nørlund establish seismological stations in Denmark and Greenland. During her travels, the time she spent in Darmstadt with Professor Beno Gutenberg was especially path-breaking for her future career. Gutenberg had published on measuring the distance between the Earth’s surface and its core using seismographic waves² (p. 288). Being an avid learner² (p.287), Lehmann took to the field quickly and went on to obtain a Magister Scientiarum Degree in Geodesy in 1928 at the University of Copenhagen⁵. In the same year, she was appointed head of the Department of Seismology at the Royal Danish Geodetic Institute. She vacated that position only in 1953, when she retired² (p. 288). While she was at the Department’s Observatory, she was primarily responsible for taking measurements and overseeing the instruments, with research not being one of her assigned tasks. Nevertheless, she took the initiative and started her own research on what she thought were unreliable measurements of earthquakes² (p. 289).

In 1929, a great earthquake occurred near New Zealand. While analysing the seismographic data collection after the earthquake, she noticed that the fluidity of the outer core results in a characteristic distortion of seismic waves which are coming through the solid mantle¹. Lehmann theorised that these waves must have travelled some distance into the core and then were deflected by some kind of boundary. She then concluded that the Earth’s core has to consist of two parts: a solid inner core surrounded by a liquid outer core, separated from each other by a boundary later known as the “Lehmann Discontinuity”¹. Even though parts of the scientific community supported her ideas from an early stage, it was not until 1970 that they confirmed her theory with precise measurements⁵. For her discoveries and outstanding scholarship, she received the honorary degree of Doctor of Science from Columbia University and a Doctor of Philosophy from the University of Copenhagen⁵.

Inge Lehmann remained involved in the scientific community even after her retirement (p. 293-94)². Retirement for her just meant a retirement from administrative work, which allowed her to take time off for her passion, the scientific research she carried out mostly in the USA and Canada² (p.293-94).

SHE SAID IT

I was the only Danish seismologist for 25 years. I began to work on travel times and I was fortunate in that Harold Jeffreys, who at that time was doing his important work on travel time tables could use some of my research. For several years we had quite a correspondence, this was, of course a great encouragement to me.

Cited by Erik Hjortenberg (2009), “Inge Lehmann’s work materials and seismological epistolary archive”, Annals of Geophysics, vol. 52, no. 6, 679-98.

You should know how many incompetent men I had to compete with – in vain.

Cited by Dana Hunter (2015), “Inge Lehmann: ‘A Small Solid Core in the Innermost Part of the Earth’”, Scientific American, Nature American, Inc.

THEY SAID IT

Inge had great energy, both mental and physical. She loved mountains, particularly in Switzerland. In the citation for the Bowie medal in 1971 Francis Birch […] provided what could be a fitting epitaph, describing her as “the master of a black art [seismology calculations] for which no amount of computerizing is likely to be a complete substitute.

Bertha Swirles (1994), “Inge Lehmann: Reminiscences”, Quarterly Journal of the Royal Astronomical Society, 35(2), 231.

Inge Lehmann had an enormous fund of knowledge and experience about seismology from its early days in this century; in retrospect, it is a great shame that more effort was not made to persuade her to write up her reminiscences in more detail.

Bruce Bolt cited by Erik Hjortenberg  (2009), “Inge Lehmann’s work materials and seismological epistolary archive”, Annals of Geophysics, 52(6), 679-98.

PRIZES, DISTINCTIONS, HONORS
1936-1948: Member of the Executive Committee of the International Seismological Association
1938: Tagea Brandt Award
1951-1954: Member of the Executive Committee of the International Association of Seismology
1957-1960: Physics of the Earth’s Interior (IASPEI)
1957: Associate Royal Astronomical Society, London
1959: Honorary Fellow Royal Society, Edinburgh
1960: The Harry Oscar Wood Award in Seismology
1963-1967: Vice President of the Executive Committee of the International Association of Seismology and Physics of the Earth’s Interior
1964: Doctor of Science (Sc.D.) h.c. Columbia University in the city of New York
1964: Deutsche Geophysikalische Gesellschaft, Emil-Wiechert Medal
1965: Kgl. Danske Videnskabernes Selskab (Royal Danish Academy of Sciences and Letters) Gold Medal
1967: Tagea Brandt Award
1968: Doctor of Philosophy (Dr. Phil.) h.c. University of Copenhagen
1971: American Geophysical Union, Bowie Medal given for outstanding contributions to fundamental geophysics and unselfish cooperation in research
1973: Honorary membership of European Geophysical Society
1977: Medal of the Seismological Society of America

INTERTEXTUAL MATERIALS

Google Doodlers (2015), Inge Lehmann’s 127th birthday, digital.

WORKS BY INGE LEHMANN

The following is a selection of Inge Lehmann’s most relevant works. These works are the ones most commonly referred to in articles about her and her scientific contributions.

“P’ as read from the records of the earthquake of June 16th 1929” (1930), Gerlands Beiträge zur Geophysik, 26, 402-412.

“P'” (1936), Bureau Central Séismologique International Strasbourg, Publications du Bureau Central Scientifiques, 14, 87-115.

“Velocities of Longitudinal Waves in the Upper Part of the Earth’s Mantle” (1959), Annales de Geophysique, 15, 93.

“The Travel Times of the Longitudinal Waves of the Logan and Blanca Atomic Explosions and Their Velocities in the Upper Mantle” (1962), Bulletin of the Seismological Society of America 52, 519.

FURTHER READING

“Inge Lehmann: Discoverer of the Earth’s Inner Core”, AMNH, American Museum of Natural History, <http://www.amnh.org/explore/resource-collections/earth-inside-and-out/inge-lehmann-discoverer-of-the-earth-s-inner-core/> (last accessed 7 Mar. 2017).

Bolt, Bruce A. (1997), “Biographical Memoirs. Inge Lehmann”, Royal Society Publishing, The Royal Society, <http://rsbm.royalsocietypublishing.org/content/43/287> (last accessed 7 Mar. 2017).

Hjortenberg, Erik (2009), “Inge Lehmann’s work materials and seismological epistolary archive”, Annals of Geophysics, vol. 52, no. 6, 679-98, <http://www.annalsofgeophysics.eu/index.php/annals/article/viewFile/4625/4693> (last accessed 7 Mar. 2017).

Rafferty, John P. (2015), “Inge Lehmann”, Encyclopedia Britannica Online, Encyclopedia Britannica, <https://www.britannica.com/biography/Inge-Lehmann> (last accessed 7 Mar. 2017).

Richardson, Eliza, “Inge Lehmann. Discoverer of Earth’s Inner Core”, E-Education, PSU, John A. Dutton E-Education Institute, The Pennsylvania State University, <https://www.e-education.psu.edu/earth520/content/l2_p23.html> (last accessed 7 Mar. 2017).

WORKS CITED

1. Richardson, Eliza, “Inge Lehmann. Discoverer of Earth’s Inner Core”, E-Education, PSU, John A. Dutton E-Education Institute, The Pennsylvania State University, <https://www.e-education.psu.edu/earth520/content/l2_p23.html> (last accessed 7 Mar. 2017).
2. Bolt, Bruce A. (1997), “Biographical Memoirs. Inge Lehmann”, Royal Society Publishing, The Royal Society, <http://rsbm.royalsocietypublishing.org/content/43/287> (last accessed 7 Mar. 2017).
3. “Lehmann, Inge.” Encyclopedia. Complete Dictionary of Scientific Biography. , www.encyclopedia.com/people/science-and-technology/geology-and-oceanography-biographies/inge-lehmann, (last accessed 7 Mar. 2017).
4. Hjortenberg, Erik (2009), “Inge Lehmann’s work materials and seismological epistolary archive”, Annals of Geophysics, 52 (6), 679-98, http://www.annalsofgeophysics.eu/index.php/annals/article/viewFile/4625/4693, (last accessed 7 Mar. 2017).
5. Carlowicz, Michael, “Inge Lehmann (1888-1993)”, American Geophyscial Union, American Geophysical Union, <https://honors.agu.org/inge-lehmann-1888%E2%80%931993/> (last accessed 7 Mar. 2017).