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    Double Altitudes: Prelude to Sumner's line?
    From: Jim Thompson
    Date: 2005 Feb 28, 07:34 -0400

    > -----Original Message-----
    > > on 2/11/05 7:22 AM, Jim Thompson at jim2@JIMTHOMPSON.NET wrote:
    > > Sumner opens his Introduction with this glorious single-sentence
    paragraph:
    > > "It is not so much the object of this work to present the navigator with
    a new method of 'Double Latitudes', as to afford him an accurate method of
    finding, by one Altitude of the Sun taken at any hour of the day, with the
    Chronometer time, the True Bearing of the Land, the Latitude, &c., being,
    from any cause, uncertain; and to place him on his guard, when near a
    dangerous coast..."
    
    On re-reading this paragraph, I think that I need to understand the
    significance of his phrase, "Double Latitudes".  If calculating a second
    solution for a sight based on an assumed latitude was well known practice by
    1837 for other purposes, then that would have been the building block that
    allowed Sumner to creatively apply the technique to his problem, and thus
    allow him to stumble on the celestial line of position concept when he found
    himself off Small's Light.  I do not understand the concept of "Double
    Latitudes", however, so I might have that all wrong.  I tried a google
    search, but turned up nothing on that technique.  I found lots on "double
    altitude", but not "double latitude".  Does anyone wish to explain the
    concept?
    
    Jim Thompson
    
    
    

       
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