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King of the swingers

David Hughes on why Foucault still matters

The Life and Science of Léon Foucault: The man who proved the Earth rotates By William Tobin, Cambridge University Press, £40/$60, ISBN 0521808553 Reviewed by David Hughes

A VERY long pendulum has kept Léon Foucault famous. But as William Tobin’s thorough, readable and beautifully illustrated biography reveals, there was much more to this self-taught French 19th-century experimental physicist.

Foucault (1819-1868) began his adult life as a happy amateur, with science as a Sunday recreation. After spending 10 years supporting himself as a science journalist, he passed his last 12 years as a government employee at the Paris Observatory. His acceptance by the Academy of Science was hindered by enmities engendered by the honest bluntness of his newspaper comments.

But the public were entranced by his pendulum. A 28-kilogram bob was suspended by a 67-metre wire from the dome of the Panthéon in Paris. The slow rotation of the swing plane proved what had for many years been merely assumed: that the Earth, not the sky, was spinning.

Foucault was also a pioneer photographer. He worked with Hippolyte Fizeau to measure the velocity of light to one part in 600, designed accurate gyroscopes, and single-handedly turned the art of polishing large glass telescope mirrors into a science.His mirror knife-edge test became a vital test for telescope optics, and is still an easy way to correct the shape of small telescope mirrors.

Foucault’s bachelor existence was plagued with worry that he had inherited his father’s madness, but multiple sclerosis brought about his untimely death. This unconventional experimenter springs back to life in the pages of this excellent book.

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