3. By 1936, scientists had learned from the study of earthquake waves that the Earth has three layers, crust, mantle, and core. Denmark's Inge Lehmann was the first to demonstrate the existence of a change in compositon midway through the core, dividing it into an inner core and an outher core. This division is now known as the Lehmann discontinuity.
As a girl, at the turn of the century, Lehmann attended the first coeducational school in Denmark, which was founded and run by Hanna Adler. (Adler's nephew, Neils Bohr, was the first to describe the physical makeup of the atom). At that school, Lehmann wrote many years later, "No difference between the intellect of boys and girls was recognized--a fact that brought me dissapointment later in life when I found that this was not the general attitude."
Lehmann studied at Oxford, earned a master's degree in mathematics from the University of Copenhagen, and went to work as an actuary, calculating life expectancies and statistical risks for insurance companies. Beginning in 1925, however, she also served as a staff member of the Danish Geodetic Institute, helping to establish seismological stations in Greenland and in Copenhagen--a part of the world not noted for its seismicity. Seismology soon became her life work, and for 25 years, until just before her retirement, she was the only Danish seismologist.
As early as 1910 scientists had noticed a shadow zone in th Earth's interior, but seismographs had not been refined enough to explain this observation. In the course of the 1930s more and more sensitive seismographs were being developed. At the Copenhagen Seismological Observatory, Lehmann studied waves reflected through the core from earthquakes in Japan. In 1936, after 10 years of studying seismograms, she interpreted the newly revealed data to confirm the existence of a relatively small inner core in the center of the Earth. The paper in which she reported her findings has one of the shortest titles in the history of seismology, if not all science: It was called "P'."
Lehmann was among the founders of the Danish Geophysical Society in 1936, and served as its president from 1941 until 1944. She helped to formulate the constitution of the European Seismological Federation and was elected its first president in 1950. She found time to attend most of the meetings of the International Union of Geodesy and Geophysics, and served on the executive committee of the International Seismological Association from 1936 to 1944, from 1951-1954, and from 1957 to 1960. International cooperation in the sciences was one of her passions. She was active in national and international scientific organizations, and traveled in France, the Netherlands, Belgium, and Germany, where she worked with some of the leading seismologists of the day. In Canada, she worked at Ottowa's Dominion Observatory, and in the United States she conducted research at the Seismological Laboratory, California Institute of Technology; the University of California at Berkeley; and the Lamont-Doherty Geological Observatory, Columbia University, New York.
She loved hiking, skiing, and moutain climbing. Her favorite place indoors, aside from her own cottage in Denmark, was an art gallery. She love to visit galleries and look at paintings wherever she traveled, and she traveled widely, expecially after her retirement in 1953. She also loved music and gardening. Inge Lehman died in February, 1993, at the age of 105, leaving a worldwide network of friends.
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