A Look Back at the Department of Terrestrial Magnetism

Two years after the Carnegie Institution of Washington was formed in 1902, Louis Bauer, a scientist studying the Earth's magnetic field, was selected by the board of trustees to form the Department of Terrestrial Magnetism (DTM). Bauer was a man with big ambitions: he wanted to map the geomagnetic field of the entire Earth. Under his direction, "observers," as they were called, made worldwide expeditions to gather magnetic field data. They trekked through some of the remotest regions of the planet. The department also commissioned a ship, the Carnegie, fashioned primarily of nonmagnetic parts, to map the oceans' magnetic field. By 1929, DTM researchers had collected volumes of data that were used to correct navigational charts and quantify the mysterious temporal variations in the geomagnetic field. The work was completed, and the department turned its attention to other questions. 
In 1925 two DTM physicists, Gregory Breit and Merle Tuve, were already exploring new areas. They wanted to prove the existence of the ionosphere, the region of the upper atmosphere where the number of electrically charged particles, or ions, is large enough to affect the travel of radio waves. The collaborators directed pulsed radio waves into the atmosphere and, by observing the echoes, confirmed the existence of the ionosphere. The department managed a worldwide network of stations to monitor the condition of the ionosphere that allowed accurate prediction of the propagation of shortwave radio communications, an advance that was to become vitally important during World War II.
During the 1930s and 40s, studies in physics dominated research at the department, which was a world-class center for nuclear physics. DTM investigators made fundamental discoveries about atomic forces. Throughout World War II, department scientists - like scientists all over the country - became involved in the war effort. One project, the largest after the Manhattan Project and the MIT Radiation Laboratory, was directed by Tuve. Under his guidance, researchers engineered an invention called the proximity fuze into mass production. The device was a radio-controlled sensor installed in the nose of an artillery shell. It detected a radio-reflecting target and triggered a detonation when the shell was in close proximity to its mark. 
After the war, DTM physicists began some of the earliest work in biophysics using radioactive tracers. Later came ventures in seismology, astronomy, theoretical astrophysics, planetary formation and evolution, and radioisotope geochronology. Science at the department has evolved to reflect the growing multidisciplinary nature of the Earth, planetary, and astronomical sciences. However, the historic goal - to understand the physical Earth and its place in the universe - remains a compelling beacon.

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