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    Re: Timing Lunars with a Rock
    From: George Huxtable
    Date: 2005 Jul 19, 09:44 +0100

    Come on, Bruce, your memory is as bad as Jared's, when you write-
    >The old navigation manuals suggested checking the log line and half minute
    >glass occasionally. One way to check the glass was by pendulum. As I
    >recall, the length of the pendulum, to the center of the musket ball that
    >formed the weight, was sometimes given as 29 and 1/4 inches, and sometimes
    >as 29 and 1/8. Count a second each time the pendulum passed the bottom. I
    >suppose you had to give the pendulum a few moments to settle the length of
    >its swing.
    It's not 29 and-a-bit, but 39 and-a-bit inches, which I have just confirmed
    by working it out from the expression for a period of 2 seconds as 2 x pi x
    sguare-root-of( length / gravity acceleration ). And to be doubly sure,
    I've just checked it against the pendulum of my old grandfather clock in
    the hall. 39 and-a-bit it is.
    What a mess listmembers would make of estimating time at an African lake,
    if that's the best they can do between them!
    Contact George at george@huxtable.u-net.com ,or by phone +44 1865 820222,
    or from within UK 01865 820222.
    Or by post- George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13
    5HX, UK.

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