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Earnshaw (1805–1888) and passive magnetic levitation. (English) Zbl 1197.78013

Summary: S. Earnshaw, a mathematical physicist born in England two centuries ago, was the author of studies on the transmission of sound and light. His theory on the transmission of light by “detached particles” has also influenced some studies on the stability of bodies in potential fields, particularly studies on the levitation of permanent magnets, i.e., on passive magnetic levitation. This theorem was so well known that even Maxwell mentioned it, and is today cited almost as an axiom in the ambit of passive magnetization. However, what is less well known is that the theory actually only relates to magnetostatics.
In this paper, the mathematical model of the theory that refers to stability is outlined, along with some works that refer to it, in particular, those on passive magnetic levitation. It is then pointed out that spaces of low instability exist in magnetostatics, and that stability may exist in the magneto-stationary and in magneto-dynamic ambit.

MSC:

78A30 Electro- and magnetostatics
78A25 Electromagnetic theory (general)
01A70 Biographies, obituaries, personalia, bibliographies

Biographic References:

Earnshaw, S.
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