Walter Elsasser

Born on 20 March 1904, Walter Elsasser was a German-born physicist who made a number of notable contributions to science, among them the development of the dynamo theory of Earth’s magnetic field. Elsasser earned his PhD in quantum mechanics at the University of Göttingen in 1927. He then spent the next decade working at various European universities with a number of noted physicists, among them Max Born, Paul Ehrenfest, Robert Oppenheimer, and Wolfgang Pauli. In 1936 he moved to the US and took a position at Caltech, where he developed an interest in meteorology and geophysics. In the early 1940s he performed pioneering research into Earth’s magnetic field. He showed that the field is generated by the kinetic energy of the motion of molten iron alloys in Earth’s core and sustained through a feedback process involving the field’s toroidal and poloidal components, terms which he coined. Elsasser’s career was decidedly peripatetic. After Caltech, he held positions at a number of universities, including Harvard, Princeton, Johns Hopkins, and Utah, where he developed an interest in theoretical biology. Elsasser was elected to the National Academy of Sciences in 1957 and was awarded the National Medal of Science in 1987. He died in 1991 at age 87. You can read his obituary in Physics Today. (Photo credit: AIP Emilio Segrè Visual Archives, Physics Today Collection)

Date in History: 20 March 1904