#3c.     The Terrella

Gilbert's terrella

"Terrella" is Latin for "little Earth," the name given by William Gilbert to a magnetized sphere with which he demonstrated to Queen Elizabeth I his theory of the Earth's magnetism. By moving a small compass around the terrella and showing that it always pointed north-south, Gilbert argued that the same thing, on a vastly larger scale, was happening on Earth, and was the only reason why a compass pointed north-south.

Later scientists such as Birkeland used the name "terrella" for magnetized spheres used inside vacuum chambers, together with electron beams, to study the motion of fast charged particles near the Earth. A sophisticated terrella experiment in a vacuum chamber is currently operated by Dr. Hafez u-Rahman at the University of California at Riverside.

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Last updated March 13, 1999