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Total Eclipse Tuesday, 24 August, 1999, 11:53 GMT 12:53 UK
Eclipse scientists in the swing
Nasa
Museums like the Smithsonian display a Foucault pendulum
The 11 August total eclipse of the Sun could settle a 45-year scientific riddle once and for all.

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Special report
11 August
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Researchers across the globe have been trying to repeat a baffling experiment first undertaken by the Nobel Laureate Maurice Allais.

In 1954, Allais observed odd deviations in the swing of a Foucault Pendulum. This device is simply a weight on a wire but, unlike the pendulum in a clock, is permitted to freely rotate as well as swing.

And once released, it appears to rotate at a steady rate. It is actually an illusion because, as we all learnt in our physics lessons at school, it is the Earth that is rotating, not the pendulum.

Giant pendulums of this kind are now routine exhibits at some of the major museums around the world including the Smithsonian in Washington and the Science Museum in London.

But the suggestion that a total eclipse of the Sun can somehow disrupt these swinging weights is highly controversial.

1954 eclipse

Maurice Allais started the fuss by conducting an experiment at his Paris laboratory in which he released a Foucault pendulum every 14 minutes - for 30 days and nights - recording the direction of rotation in degrees. It just so happened that the experiment coincided with the 1954 eclipse, and it was during the solar phenomenon that the pendulum took an unexpected turn, changing its angle of rotation by 13.5 degrees.

Eclipse
Could Wednesday's eclipse solve the riddle
Allais said the rotation of the pendulum was normal both before and after the eclipse. He later repeated the experiment and got similar results.

But the work has polarised scientific opinion. Some say there were flaws in the Frenchman's methods, whilst others claim to have witnessed the unusual effect as well.

Explanations have included the anisotropy of space - the condition of having different properties in different directions - gravitational waves and solar radiation.

The 1999 total eclipse will help to settle the arguments. Laboratories on four continents set up pendulums and gravity meters to test the effect. Their results will make interesting reading.



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BBC Science's Corinne Podger finds out how scientists will be using the eclipse
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17 Aug 99 | Eclipse99
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