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    Re: Leap seconds at Big Ben.
    From: Bill Morris
    Date: 2009 Jan 6, 00:30 -0800

    I think I knew the answer in advance, but was thrown by George's learned use 
    of the word "centroid" which is, informally, what I call centre of mass. It 
    would need an exceptionally weighty pendulum rod to bring the centre of mass 
    above the top of the bob (let's not go into Captain Kater's pendulum). 
    I added 50 grams to the top of my regulator's pendulum and it gained over a 
    period of 12 hours. As Matthys' book points out, you can hang a small 
    adjusting nut below the bob to raise or lower the centre of mass of the 
    pendulum. Lowering the nut slows the clock, but you have to stop it to make 
    the adjustment, whereas adding weights to a pan 2/3rds up the pendulum is 
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