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Bullard, Sir Edward (Crisp)

field magnetic theory earth’s

(1907–80) British geo-physicist: made first measurement of geothermal heat flow through the oceanic crust, and proposed dynamo theory for the Earth’s magnetic field.

Bullard served in naval research during the Second World War, afterwards working in Cambridge and North America before becoming director of the National Physical Laboratory, England. In 1964 he was appointed director of the Department of Geodesy and Geophysics at Cambridge. Bullard made the first successful measurements of geo-thermal heat flow through the oceanic crust, establishing that it is similar in magnitude to that of continental crust, and not lower as had been thought.

After the start of the Second World War in 1939 he devised a protection for ships against magnetic mines by ‘degaussing’ ships with an applied external current.

In the late 1940s and 1950s, independently of , he proposed the dynamo theory for the origin of the Earth’s magnetic field, in which the field is generated by the motion of the Earth’s liquid iron core undergoing convection. Providing that there is a small magnetic field to start with, the movement of the molten iron will set up electric currents which will in turn generate the observed magnetic field. In 1965 Bullard was also the first to use computer modelling techniques to study continental drift, finding an excellent fit between Africa and South America at the 500-fathom (close to 1000 m) contour: a valuable contribution to what became the theory of plate tectonics.

Bullock, Chick (Charles) [next] [back] Bull, Ole (Bomemann)

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