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    Re: Sextant Accuracy and anomalous dip
    From: Bruce Stark
    Date: 2003 Mar 19, 14:20 EST

    Even if a boat could be made as steady as a lighthouse foundation, altitudes
    taken from it would not be as reliable as those taken from a ship. Or so it
    seems to me. I believe that the nearer the navigator's eye is to the water,
    the more anomalous refraction will displace the horizon.
    
    To simplify the logic behind this idea, forget about normal refraction.
    Suppose that under normal conditions light would come to your eye from the
    horizon in a straight line. To simplify things further, suppose anomalous
    refraction occurs at a particular point along the line, making an angle at
    that point. So the navigator will see the horizon at that point, rather than
    at its true place.
    
    Air near the water is the main breeding ground of anomalous refraction in the
    dip. A navigator on the bridge of a ship will be a long way from the point
    where anomalous refraction has bent the line. The angle at his eye, between
    the true horizon and the point where he sees it, will be small.
    
    A navigator on a small boat, on the other hand, will be close to that point.
    Consequently the angle at his eye, between the true horizon and the point
    where he sees it, will be larger.
    
    I hope List members will overlook the simplistic way this is presented and
    examine the question in their own minds, as well as in the light of
    experience.
    
    Bruce
    
    
    

       
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