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Elsasser, Walter Maurice

field magnetic earth’s theory

(1904–91) German–US theoretical physicist: developed theory of Earth’s magnetic field.

Elasser was born and educated in Germany; he left that country in 1933 and spent 3 years in Paris, where he worked on the theory of atomic nuclei. In 1936 he settled in the USA and began to specialize in geophysics. During the 1940s he developed the dynamo model of the Earth’s magnetic field, which attributes the field to the action of electric currents flowing in the Earth’s fluid metallic outer core. These currents are amplified through mechanical motions in the same way that currents are maintained in power station generators. The analysis of past magnetic fields, frozen in rocks, has since turned out a very powerful tool for the study of geological processes.

Elsasser’s theory of the origin of Earth’s magnetic field was confirmed in 2000 by groups in Germany, who used liquid sodium metal flowing at 15 m s –1 in a 25cm-wide pipe: a propeller recirculated the molten metal and also twisted its flow. A small electric field was used as a ‘seed’, and after its removal the system maintained the induced magnetic field.

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