Terrella

William Gilbert, the royal physician to Queen Elizabeth I, devoted much of his time, energy and resources to the study of the Earth's magnetism.

Earlier investigators (including Christopher Columbus) found that direction deviated somewhat from true north, and Robert Norman showed the force on the needle was not horizontal but slanted into the Earth.

Kristian Birkeland was a Norwegian physicist who, around 1895, tried to explain why the lights of the polar aurora appeared only in regions centered at the magnetic poles.

Neither he nor his associate Carl Størmer (who calculated such paths) could understand why the actual aurora avoided the area directly above the poles themselves.

Recently the terrella experiments have been further developed by a team of physicists at the Institute of Planetology and Astrophysics in Grenoble, France to create the "planeterrella" which uses two magnetised spheres which can be manipulated to recreate several different auroral phenomena.

Kristian Birkeland's magnetised terrella. In this experiment, he noted two spirals which he considered may be similar to that of spiral nebulae . ^{[

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