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    Re: Sumner's Line (Navigation question)
    From: George Huxtable
    Date: 2006 Feb 15, 17:59 -0000

    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 have a copy of Capt. Greenville Collins' collection of charts of the coast of Britain, in modern
    facsimile. The original edition dates from 1753, long before Sumner in 1837,  but Collins' survey
    work was done much earlier still, in the 1680s.
    
    Collins gives a chart of St George's Channel, which has a scale of latitude but not of longitude
    (which was common in those days). There was no lighthouse there then. He marks, on that chart,
    "Small's Rock", contrary to my bit of pedantry earlier, when I though fit to correct it to "the
    Smalls rock". Its latitude, by my measurement off his chart, is 51deg 44', close to the modern atlas
    position of 51deg 43', and several miles South of the position Sumner plots it on his plate III.
    
    Collins' text, in his sailing directions, reads- "The Smalls. The Smalls is a small rock always
    above the water, about the bigness of a long-boat, and lieth to the Westward of Gresholm two leages
    and a half, or three leagues: The WNW and NW end is foul and rocky a mile off, and is steep too. The
    tides run very strong amongst these islands and rocks."
    
    So it's looking as if Smalls rock, and presumably the lighthouse marking it, was several miles
    South, and several miles East, of the position that Sumner showed on his Plate III. What can we
    deduce from that?
    
    In that case, it was somethig like 6 miles away from the famous position-line that Sumner drew, and
    perhaps Sumner deliberately shifted the lighthouse on his plate III, to put it on that line, to
    illustrate the point he was trying to make. If the light was that far away, Sumner would have been
    unable to see it in such thick weather, yet his tale tells of it being seen only when "close
    aboard". Alternatively, if he really did see Smalls lighthouse when it was close aboard, he must
    have peen following a position line several miles South of the line he calculated.
    
    There's an important factor that Sumner says nothing about, but which a navigator in those waters
    neglects at his peril; the effect of the strong local tides around those rocks and headlands.
    
    Something gave Sumner cause to plot the lighthouse, not where it really is, but instead,
    conveniently on his position line. Was the whole event perhaps an invented story, designed as a
    homely illustration, to add force and interest to an otherwise-dull proposed new procedure? Did
    Sumner cook-up his observations, indeed?
    
    We really need to know what position Sumner's chart would have given him, for Smalls light. Can
    anyone suggest what an American captain, sailing out of Charleston, would have used for his source
    of charts of British waters, back in 1837? Would they have been the official British Admiralty
    charts, or commercial ones, such as the blue-back Imray charts, or were there American-published
    charts of European waters, perhaps as pirated versions? Investigation is called for.
    
    Bill has spotted another discrepancy. In his numerical calculation on page 15 of his pamphlet,
    Sumner calculates his position line between two latitudes, 1 degree apart, at 51 and 52 degrees. In
    his text on page 38, however, he refers to calculating longitudes from latitudes that correspond to
    his DR position, 10 minutes greater, and 20 minutes greater. Both alternatives are perfectly valid,
    of course.
    
    Anyone who looks at his Plate 3 with a critical eye can't fail to notice how crudely and
    inaccurately the Welsh and Irish shorelines have been drawn. No doubt Sumner would argue that they
    are quite irrelevant to his case; which they are. There's another, more subtle fault. He divides his
    longitude scale, between 7 and 8 degrees, to show minutes, with marks at 5-minute intervals.
    However, instead of 12 such divisions, as there should have been, Sumner (or perhaps more likely,
    his lithographer) has only shown 11. Which has clearly led to a problem in labelling them.
    
    Perhaps we are being unfair in examining Sumner's pamphlet too closely. Should it really be treated
    as no more than advocacy of a new technique, not as a historical account of a real event?
    
    There appears to be a case for for some real research work to be done, and perhaps Bill is keen
    enough to follow the matter up.
    
    George.
    
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
    

       
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