Inge Lehmann

Inge Lehmann
Lehmann in 1932
Born	(1888-05-13)13 May 1888 Copenhagen, Denmark
Died	21 February 1993(1993-02-21) (aged 104) Copenhagen, Denmark
Resting place	Hørsholm Cemetery 55°52′14.06″N 12°30′16.01″E
Alma mater	University of Copenhagen, University of Cambridge
Awards	William Bowie Medal (1971)
Scientific career
Fields	Seismology, geophysics
Institutions	Geodetical Institute of Denmark

Inge Lehmann ForMemRS (13 May 1888 – 21 February 1993) was a Danish seismologist and geophysicist who is known for her discovery in 1936 of the solid inner core that exists within the molten outer core of the Earth. The seismic discontinuity in the speed of seismic waves at depths between 190 and 250 km is named the Lehmann discontinuity after her. Lehmann is considered to be a pioneer among women and scientists in seismology research.

Early life and education

Inge Lehmann was born and grew up in Østerbro, a part of Copenhagen. She was very shy as a child, a behaviour that continued throughout her life. Her mother, Ida Sophie Tørsleff, was a housewife; her father was experimental psychologist Alfred Georg Ludvik Lehmann (1858–1921). The Lehmann family had its roots in Bohemia; the Danish branch included barristers, politicians and engineers. Inge Lehmann's paternal grandfather laid out the first Danish telegraph line (1854) and her great-grandfather was Governor of the National Bank. Her mother's father, Hans Jakob Torsleff, belonged to an old Danish family with a priest in every generation. Her mother's father, Hans Jakob Torsleff, belonged to an old Danish family with a priest in every generation. Members of the Tørsleff family were well-known public leaders and activists in the women's rights movement. Inge's cousins were the Minister of Trade, the chair of the Danish Women's Society, and the leader of the Danish Girl Scouts. Her younger sister Signe, who was a single mother, rose to popularity as a school superintendent.

Lehmann's parents enrolled both her and her sister at Fællesskolen in 1984, a remarkably progressive high school that taught women and men the same subjects together. This school was led by Hanna Adler, Niels Bohr's aunt. This was unusual seeing as most schools at the time had distinct academic avenues for males and females. The principles of gender isolation went much deeper for girls who were education-oriented. It was thought to be damaging to expose girls to mental exhaustion throughout puberty. Males were believed to be more biologically adapted for such activities and therefore, allowed to take the high school entrance exam and start upper-secondary education (high school) at 15 years old, where as females were not allowed to do so. This policy remained in effect. until 1903. According to Lehmann, her father and Adler were the most significant influences on her intellectual development.

At age 18, Lehmann achieved a first rank mark in the entrance exam for Copenhagen University. In 1907, she started her studies in mathematics, chemistry and physics at the University of Copenhagen. She continued her studies of mathematics in Cambridge from 1910 to 1911 at Newnham College. There, Lehmann faced gender-based adversities, not being allowed to fully participate in her studies, nor to achieve higher positions of education. As a result, Lehmann had a mental breakdown during her first year in 1911, and in 1912 returned to Denmark. She developed good computational skills in an actuary office she worked in for a few years until she resumed her studies at Copenhagen University in 1918. She completed the candidata magisterii degree in physical science and mathematics in two years, graduating in 1920. After a short period of time, studying mathematics at the University of Hamburg, in 1923 she accepted a position at Copenhagen University as an assistant to J.F. Steffensen, the professor of actuarial science.

Lehmann had a younger sister, Harriet, who became an actress. Inge Lehmann lived by herself all her adult life. She broke off an engagement in March 1917 and decided to remain unmarried, in order to pursue an academic career, which was not an unusual choice at the time.

Lehmann once complained to her nephew Niels Groes about the incompetence of her male colleagues, and wrote him: "You should know how many incompetent men I had to compete with—in vain."

Career

A modern understanding of the Lehmann discontinuity: velocity of seismic S-waves in the Earth near the surface in three tectonic provinces: TNA = Tectonic North America SNA = Shield North America and ATL = North Atlantic.

In 1925, Lehmann was assigned to be the assistant of seismologist Niels Erik Nørlund. She took an interest in his field, and she began studying it on her own. She was chosen as a delegate for Denmark to attend the International Union of Geodesy and Geophysics in 1927—a role she filled another eight times over the next forty years. By 1928, Lehmann obtained a magister scientiarum in seismology, and she was appointed head the Geodætisk Institut's seismological department the same year. In this position, she was responsible for overseeing the operation of three seismographic observatories, two of which were in Greenland. She personally operated the one in Copenhagen, producing reports based on its readings. Though it was not part of her job, Lehmann also engaged in research at the facility.

In 1929, Lehmann studied the Murchison earthquake which struck on the South Island of New Zealand. She analyzed the seismic data from the earthquake and noticed that there were waves of significant amplitude recorded in the Russian cities of Sverdlovsk and Irkutsk, both unexpected locations. They were unexpected locations due to the theory that S-waves and some P-waves are deflected by the core creating a shadow area in which waves are not able to pass through. The waves seemed to pass through that area to reach Russia. This led to her discovering that there is a spherical core of solid material at the Earth's centre.

Lehmann was the first to interpret P-wave arrivals as reflections from an inner core. She published her findings in a paper titled P′ (1936), The theory she developed was that the Earth consisted of 3 shells: the mantle, outer core and inner core. Lehmann inferred that the core wasn't homogeneous; rather, there is a smaller core that exists that is surrounded by the outer core. She deduced that waves travel faster in the smaller core, but the waves can be reflected off if it arrived tangentially. Her theory allows for another wave deflection at the extra boundary and this accounts for the direction and location in which the waves emerge. Other leading seismologists of the time, such as Beno Gutenberg, Charles Richter, and Harold Jeffreys, adopted this interpretation within two or three years, but it took until 1971 for the interpretation to be shown correct by computer calculations. She continued her work during World War II, though international collaboration was limited.

When American geologist Maurice Ewing visited her station in 1951, he invited Lehmann to work at the Lamont Geological Observatory that he ran at Columbia University, and she studied there for some of 1952.

She retired from her position as head of the Geodætisk Institut's seismological department in 1953, giving her more time to conduct research over the following decades. Throughout the 1950s and 1960s, Lehmann traveled to North America several times and visited different seismological observatories throughout the United States and Canada. She became a prominent member of the community at the University of California, Berkeley, one of her most frequent stops.

While in the United States, Lehmann collaborated with Maurice Ewing and Frank Press on investigations of the Earth's crust and upper mantle. During this work, she discovered another seismic discontinuity, which is a step-change increase in the speed of seismic waves at depths between 190 and 250 km. This discontinuity was named the Lehmann discontinuity after her. Francis Birch noted that the "Lehmann discontinuity was discovered through exacting scrutiny of seismic records by a master of a black art for which no amount of computerization is likely to be a complete substitute."

Lehmann was also involved in the creation of the International Seismological Centre from 1961 to 1967.

Awards, honours, and legacy

Memorial to Lehmann in Copenhagen (by Elisabeth Toubro)

Lehmann received many honours for her scientific achievements, among them the Harry Oscar Wood Award in 1960, the Emil Wiechert Medal in 1964, the Gold Medal of the Danish Royal Society of Science and Letters 1965, the Tagea Brandt Rejselegat in 1938 and 1967, her election as a Fellow of the Royal Society in 1969, the William Bowie Medal in 1971, and the Medal of the Seismological Society of America in 1977. She received the Medal of the Seismological Society of America. She was awarded honorary doctorates from Columbia University in 1964 and from the University of Copenhagen in 1968, as well as numerous honorific memberships.

Street art in Frederiksberg by Anne Bundgaard honouring Inge Lehmann

Because of her contribution to geological science, in 1996, the American Geophysical Union established the annual Inge Lehmann Medal to honour "outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth's mantle and core."

The asteroid 5632 Ingelehmann was named in Lehmann's honour. In 2015, a species of beetle was named after her on the hundredth anniversary of women's suffrage in Denmark:Globicornis (Hadrotoma) ingelehmannae. In the same year, on the 127th anniversary of her birth, Google dedicated its worldwide Google Doodle to Lehmann.

A memorial dedicated to Lehmann was installed on Frue Plads in Copenhagen in 2017, designed by Elisabeth Toubro.

Key publications

• Lehmann, Inge (1936). "P'". Publications du Bureau Central Séismologique International. A14 (3): 87–115.

See also

• Richard Dixon Oldham
• List of geophysicists
• Timeline of women in science

References

• Bolt, Bruce A. (1997). "Inge Lehmann. 13 May 1888-21 February 1993". Biographical Memoirs of Fellows of the Royal Society. 43: 287–301. doi:10.1098/rsbm.1997.0016. ISSN 0080-4606. JSTOR 770337. Archived from the original on 4 January 2001.

Further reading

• Hjortenberg, Erik (December 2009). "Inge Lehmann's work materials and seismological epistolary archive". Annals of Geophysics. 52 (6): 679–698. Retrieved 2 October 2017.
• Jacobsen, A. Lif Lund. "Inge Lehmann and the rise of international seismology 1925_1970". Carlsberg Foundation. Archived from the original on 4 January 2018. Retrieved 2 October 2017.
• Kousholt, Bjarne (2004). Inge Lehmann og Jordens kerne (in Danish). Polyteknisk. ISBN 9788750209577.
• Lehmann, Inge (1987). "Seismology in the Days of Old". EOS. 68 (3): 33–35. Bibcode:1987EOSTr..68...33L. doi:10.1029/EO068i003p00033-02. Archived from the original on 19 September 2013. Retrieved 16 May 2008.
• Swirles, Lady Jeffreys, Bertha (1994). "Inge Lehmann: Reminiscences". Quarterly Journal of the Royal Astronomical Society. 35 (2): 231. Bibcode:1994QJRAS..35..231W. Archived from the original on 6 July 2008.
• Swaby, Rachel (2015). "Inge Lehmann (1888-1993)". Headstrong: 52 women who changed science – and the world. New York: Broadway Books. pp. 161–164. ISBN 978-0-553-44679-1.

External links

• Inge Lehmann at CWP at UCLA
• Royal Society citation
• Inge Lehmann: Discoverer of Earth's Inner Core
• "WiP: Herstory: Spotlight Scientist: Inge Lehmann". Purdue University. Archived from the original on 26 March 2016. Retrieved 15 October 2013.{{cite web}}: CS1 maint: bot: original URL status unknown (link)