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    Timing Lunars with a Rock
    From: Frank Reed CT
    Date: 2005 Jul 17, 21:23 EDT

    Here's a nice trick. A rock on a string and an assistant with a bag of
    pebbles will make do for a clock for timing the separate sights involved in  a
    lunar observation.
    The details:
    "  Pendulum.--A Traveller, when the last of his watches breaks down,  has no
    need to be disheartened from going on with his longitudinal  observations,
    especially if he observes occulations and eclipses. The object  of a watch
    is to tell the number of seconds that elapse between the instant  of
    occulation, eclipse, etc., and the instant, a minute or two later,  when
    the sextant observation for time is made. All that a watch actually  does
    is to beat seconds, and to record the number of beats. Now, a string  and
    stone, swung as a pendulum, will beat time; and a native who is taught  to
    throw a pebble into a bag at each beat, will record it; and,  for
    operations that do not occupy much time, he will be as good as a  watch.
    The rate of the pendulum may be determined by taking two sets  of
    observations, with three or four minutes' interval between them; and,  if
    the distance from the point of suspension to the centre of the stone  be
    thirty-nine inches, and if the string be thin and the stone very  heavy,
    it will beat seconds very nearly indeed. The observations upon which  the
    longitude of the East African lakes depended, after Captain Speke's  first
    journey to them, were lunars, timed with a string and a stone, in  default
    of a watch."
    --From "The Art of Travel: Shifts and Contrivances Available in Wild
    Countries" by Francis Galton, London, 1872. (google it if you want to read it.  lots
    of other interesting suggestions)
    42.0N 87.7W, or 41.4N  72.1W.

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