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    Re: Refraction
    From: Robert Eno
    Date: 2005 Aug 6, 13:17 -0400

    George wrote:
    
    > Refraction works in the opposite direction to geometrical dip, reducing it
    > by about 8% when seen from a boat. It can be roughly predicted, for
    > standardised atmospheric conditions. However, the lower few feet of the
    > air, being strongly influenced by the temperature of the sea surface just
    > below it, can suffer from unpredictable temperature gradients, which can
    > upset the predicted dip by several arc-minutes, on a bad day. This can be
    > the biggest source of error in marine sextant observations.
    
    Robert responds:
    
    Again, this gets back to a handful of questions I earlier asked but to which
    no one replied, so I will ask you directly George:
    
    In your experience, are there certain weather conditions and/or other
    observable factors during which these unpredictable errors are likely to
    occur?
    
    
    Robert
    
    
    

       
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