Foucault invented a type of pendulum, since named in his honor, which gives direct evidence of the rotation of the Earth. He also demonstrated the Earths rotation by means of a gyroscope.
Some of Foucaults most important work was in the study of light. He improved the method of measuring the speed of light devised by the French physicist A. H. L. Fizeau. By means of this method he found that the speed of light is inversely proportional to the index of refraction of the medium through which the light is passing. His other discoveries included a polarizer for light and an improved method of making telescope mirrors. Foucault also studied the eddy currents, sometimes called Foucault currents, produced when a copper disk rotates in a magnetic field.
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Reference: pagan-magic.blogspot.com
