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rhythms: points where the mass and the spin of the planet resonate in some way.’

    But at that very point in time everything changed.
    At five o’ clock the following morning Chris was unable to sleep and decided to get up and make a cup of tea. It was then that a ‘library angel’ turned up. 7 Looking for something to read he pulled the delivery sleeve of a magazine that had arrived in the post the previous day and flicked it open. The main feature article in this edition of
New Scientist
was entitled: ‘Shadow over gravity’. It sounded interesting even early on a dark November morning.
    But he quickly realized it was far more important than merely ‘interesting’. The opening paragraph was incredibly similar to that which opens this book, carrying a description of how it feels to witness a total eclipse – and then it transpired that the thrust of the article was that solar eclipses have a profound effect on pendulums! A debate is presently raging as to why this should be the case, because the suggestion has been made that pendulums may well be the key to a significant hole in Einstein’s theory of relativity.
    The starting point concerns the work of Jean Bernard Leon Foucault who demonstrated a special quality of pendulums at the Great Exhibition, held in London in 1851. His pendulum, now always referred to as ‘Foucault’s pendulum’, is simply a very heavy weight fastened to a very long wire attached to a ceiling inside a very tall building, with a universal joint allowing it to rotate freely around a fixed point so that it will swing in a slow arc in any direction. 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.
    Once set in motion its direction of swing will appear to rotate at a rate of about twelve degrees an hour. But this is actually an illusion because it is the observer and the rest of the world that is moving whilst the pendulum is maintaining a fixed swing back and forth in relation to the Universe. This happens because the pendulum is independent of the movement of the Earth, which is rotating underneath the pendulum, making it appear that the pendulum is changing direction. The reason a pendulum swings is because the Earth’s gravity continually tugs down on it. According to Einstein’s general theory of relativity this relentless tugging is due to the fact that every mass bends the fabric of space-time around it causing other masses to slide down into the dimple it creates in space-time.
    The amount of rotation of a Foucault pendulum is dependent on latitude. At the North or South Pole the pendulum appears to rotate through an entire 360 degrees once every turn of the Earth (each sidereal day) because the planet rotates all the way round underneath it. In the northern hemisphere at the latitude of the British Isles the rate of rotation is reduced to around 280 degrees per day and the rate of rotation continues to fall the closer one gets to the equator, where a Foucault pendulum does not rotate at all.
    For over a hundred years everyone knew that a Foucault’s pendulum would swing in an entirely predictable manner at any specific location. Then in 1954 a French engineer, economist and would-be physicist by the name of Maurice Allais found that this was not always the case. He was conducting an experiment at the School of Mining in Paris to investigate a possible link between magnetism and gravitation, in which he released a Foucault pendulum every fourteen minutes for thirty days and nights, recording the direction of rotation in degrees. By chance, a total solar eclipse occurred on one of those days.
    Each day the pendulum moved with mechanical precision but on June 30 th 1954, when a partial eclipse occurred, one of Allais’ assistants realized that the pendulum had gone haywire. As the eclipse began, the swing plane of the pendulum suddenly started to rotate