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    Re: Timing Lunars with a Rock
    From: Gary LaPook
    Date: 2005 Jul 19, 08:22 -0700

    At one time, about 1790,  many, including Thomas Jefferson, wanted to
    the use the length of  a  one second pendulum as the standard meter, or
    standard unit of length, instead of the one proposed by the French
    Academy of one ten millionth of the meridian from the equator to the
    pole. The discussion broke down because the americans wanted to use a
    pendulum at 38? north (near the Monticello) and the french wanted to use
    one at 45? near Paris. The length of such a pendulum is 39.2 inches. The
    french eventually surveyed the meridian form Dunqerque to Barcelona and
    extrapolated it to the pole and defined the meter from it. An
    interesting book about the travails in accomplishing this survey, which
    took seven years and was conducted during the french revolution, is "The
    Measure Of All Things" by Ken Adler, $4.95 at Barnes and Noble. They
    came close. There are actually 10,002,290 meters in the arc.
    Gary LaPook
    george huxtable wrote:
    > 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.
    >> Bruce
    > 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!
    > George.
    > ===============================================================
    > 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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