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I repeat that using a pendulum of fixed length
is not a good standard of time.
Because the period depends on the amplitude.
This was already well-known in XVIII century.
Thus the US proposal (as explained in the following message)
was not
scientifically sound.

Alex.

On Tue, 19 Jul 2005, Gary J. LaPook wrote:

> 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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