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    Re: Leap seconds at Big Ben.
    From: George Huxtable
    Date: 2009 Jan 4, 23:26 -0000

    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
    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
    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
    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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