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    Re: Sumner's Line (Navigation question)
    From: Bill B
    Date: 2006 Feb 15, 20:43 -0500

    George wrote:
    
    > I've been wondering what's behind the interesting discrepancy that Bill has
    > put his finger on, between the position of the Smalls lighthouse on Sumner's
    > plate III, and its modern position.
    
    I would have to credit George with unearthing the illustration
    discrepancies, or at very least providing the needed puzzle pieces and
    pointing out the path.
    
    Following is a summations of the data to date.  All measurements are
    approximate.
    
    SMALL'S
    
    Plate III
    51d 48' N
    5d 38' W
    
    Bowditch
    51d 43' N
    5d 40' W
    
    George's 1950 gazetteer
    51d 43' N
    5d 30 W
    
    Small's Rock: Collins (via George)
    51d 44' N
    
    TUSKER
    
    Plate III
    52d 13'
    6d 07' W
    
    Bowditch
    52d 12' N
    6d 13' W
    
    George's 1950 gazetteer
    52d 12' N
    6d 12'W
    
    I had been thinking along the same lines as George in that these are indeed
    illustrations to demonstrate a method, not actual charts, and also noticed
    the truncated longitude scale on the Plate III.  That said, the math should
    still work out drawings or not. For clarity, in PhotoShop I layered the
    Bowditch illustration over Plate III and scaled the Bowditch illustration to
    match the Sumner plate's longitude, as that is one place they do seem to
    closely match.  I also created a longitude scale for the Sumner plate.  I
    made two versions of this layered illustration.  The first matches up
    latitudes between the two, the second the LOP's and Small's within
    "tolerable" limits.
    
    If interested in obtaining these two JPEG's, let me know and I'll send them
    off list.  If there is enough interest, I'll be happy to upload them.
    
    I feel George has put his finger on it. Some form of poetic license is
    afoot.  To have Small's on an intended track of 22.5d from the ship you
    either have to move the lighthouse (as per Plate III) or move the ship's DR
    (as in Bowditch). Both Sumner and Bowditch seem to fudge or exclude just one
    little detail to make it work.  Bowditch omits then fudges the DR, Sumner
    appears to move the position of Small's.
    
    The Bowditch illustration seems to moves Small's up to the 1950 (and
    Collin's pre-1837) position George posted, but to make the LOP work the DR
    was dropped down to approx. 51d 32'.  The online version of Bowditch (Pub 9,
    1995) puts Small's at 5d 40' W rather than 5d 30' W, which is close to the
    Plate III, but 10' longitude off George's 1950 gazetteer.  Strange indeed.
    
    Tusker, on the other hand, seems to have used that fact that all eyes were
    on Small's to laterally migrate at will.  In Plate III it is about 44, not
    40 miles from the Sumner's DR.
    
    Past that, Ken's question as to why Sumner may have been a lot closer to
    impacting rocks than his DR would predict has been adequately answered.  But
    the devil is in the details.
    
    Its been my first history "hunt," so thank all of you for your patience.
    Now I appreciate why many of the list are interested in an accurate
    centuries-old almanac.
    
    Bill
    
    
    

       
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