On the Ewing Model of Magnetism

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137

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6

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6

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1

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0.01

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0.9

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7900.

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0.1

J

1.

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0.

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2.

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10

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-4.

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As the Scottish physicist James A. Ewing wrote near the end of the nineteenth century [1, p. 348]: "It is extremely helpful… to experiment with a model consisting of a number of short steel magnets pivoted like compass needles on fixed centers and placed near enough to one another to allow their mutual control to be felt." This Demonstration is a mathematical model of Ewing's device (for Ewing, a model was something that came out of a workshop). The main action is to activate the run box. Hover the pointer over the control labels to see tooltips with explanations.