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    Re: Longitude by altitudes. was Re: How Many Chronometers?
    From: Marcel Tschudin
    Date: 2009 May 13, 18:36 +0300

    Frank, without having gone into details my thoughts went in a
    direction as outlined below. For this I assume certain knowledges
    which I presume that they should have been known from long periods of
    observations. I just tried to find a way how it might have been
    possible to obtain the longitude without the means which were in use
    Based on the assumptions, that
    - one possibly could produce predictions of sunrise/sunset for a
    reference place.
    - one possibly could also produce predictions for the position of the
    moon relative to the sun at the moment of sunrise/sunset for a
    reference place.
    - one possibly could measure the latitude from the sun's position and
    - one possibly could also calculate the differences resulting from
    changing the latitude such as changed sun-moon position due to changed
    moments of sunrise/sunset.
    At this stage one would then be able to calculate a new reference
    value corresponding to the longitude of their reference location
    corrected for their current latitude which might be different to the
    reference location.
    - It would remain now to measure the difference between the sun and
    moon positions at the moment of sunrise/sunset at their actual
    location and the calculated (corrected) one of the reference place.
    It's here where I thought that the water-glass might become useful for
    measuring the time difference between the two moments one being the
    actual sunrise/sunset and the other one being the moment when sun and
    moon have the angular position of the reference place.
    I guess that their are still various snags in this "virtual"
    procedure. In addition I have no idea on the attainable accuracy.
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