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    Re: Leap seconds at Big Ben.
    From: Bruce Hamilton
    Date: 2009 Jan 04, 22:23 -0800

    But doesn't time get slower with increased height? :-)
    George Huxtable wrote:
    > Bill Morris (engineer@clear.net.nz) wrote, about adding fine-adjustment
    > weights to a precise pendulum clock-
    > "The regulating weight is usually half to two thirds of the way up the
    > pendulum. It has maximum effect at the half-way point, but it looks better a
    > little higher. Adding weights to the top of the pendulum bob does work, but
    > they have to be heavier. On the home-made regulator clock whose picture I
    > include as an attachment, I use increments of 100 milligrams and can achieve
    > a rate of two or three seconds a month, but as the brass-compensated Invar
    > pendulum rod is not (yet) correctly compensated, the rate changes with the
    > season."
    > ==========================
    > It isn't obvious to me whether adding an extra "regulating weight" to the
    > top of the bob would speed the clock up or slow it down. There will be two
    > effects, which work in opposite directions.
    > 1. If we can consider the rod as of negligible weight and inertia, compared
    > with the bob, then adding that exrea bit at the top will raise the centroid
    > of the bob and therefore effectively shorten the length and speed the clock
    > up.
    > 2. On the other hand, if the rod is not weightless, then adding extra weight
    > to the bob, at its centroid, would by increasing the weight of the bob,
    > reduce by a small proportion the relative effect of the rod, thus slowing
    > the pendulum down.
    > So in the real situation, with a rod that isn't weightless, and an extra
    > adjusting-weight that's above the centre of the bob, which of those effects
    > wins?
    > George.
    > contact George Huxtable, at  george@hux.me.uk
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    > >
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