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    Pendulous gyroscopes
    From: Peter Fogg
    Date: 2002 Sep 16, 10:13 +1000

    'Peter. I did my PhD on pendulous gyroscopes. Part of my field wok was
     at a station in latitude S80 degrees. I found the latitude of this
     from my gyroscope observations to within two minutes of arc. Of course
    nothing works at the pole. George.'
    This was in response to a query from Walter about whether polar
    explorers used pendulums (please excuse any inaccuracy here but I can't
    find this posting). Was interested enough to seek more information (over
    the phone) and this is my summary of what I found out:
    A pendulous gyroscope spins at about 20,000 rpm at the end of a fine
    thread.  As it is lowered it oscillates in a plane parallel to the
    direction of (true) north. It is accurate at low and medium latitudes,
    but at high latitudes the period of oscillation increases and it becomes
    progressively less accurate (which explains why it was a feat to find
    'the latitude of this station (S80 degrees) from my gyroscope
    observations to within two minutes of arc'. At the pole it doesn't work
    at all, 'just flops about'.
    It has practical uses in surveying, and my George has used it in
    surveying in underground mines where below ground workings can be
    correlated to above ground ones without any direct link between them.
    He also mentioned that while on the Antarctic mainland he developed
    tables for the observing of daylight stars through the telescope of a
    theodolite, which is feasible for the most bright stars. I asked whether
    in this case binoculars could be used for observing daylight stars, the
    problem is firstly 'you need to know where to look' and secondly, such
    observations are difficult because of the instability of the hand-held
    binoculars. This is why his instrument of choice for land based
    observations is the theodolite, rather than a hand-held sextant.
    Obviously these observations in Antartica were made in fine weather with
    full support, I don't mean to compare them with those of polar
    Any mistakes here are most likely to be mine.

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