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    Re: Sumner's Line (Navigation question)
    From: Fred Hebard
    Date: 2006 Feb 11, 10:18 -0500

    George has added another important component to the invention of the
    Sumner line, the fact that Sumner's first line happened to pass right
    through his destination.  Here we have a captain sailing into port
    making nice time with a favorable, strong wind but lousy visibility.
    He can make port this evening or stand off to possibly struggle up
    the channel to his destination with an unfavorable wind or no wind
    whatsoever.  He's 10-20 miles from some rocks and making 5-12 knots.
    So the time has come to make the decision and every minute counts.
    The sun peaks out and he gets a sight.  Plots his longitude, knows it
    doesn't help him, so tries another assumed latitude.  Puts him right
    on Small's light.  That's it, time to go on deck, find the light and
    spend the rest of the passage guiding the vessel into port, probably
    not to write in the log much, just the traverse board or whatever,
    until reaching port.  He won't have time to ponder his invention
    until he goes to write up his log after anchoring.
    
    The big question being asked is, "Why didn't somebody think of this
    before Sumner?"  First, I can assure you that, compared to sitting in
    the office, my brain works much more efficiently when the chips are
    down, such as being on a broad reach with the chute set coming up to
    the mark.  That's the same straights Sumner finds himself in after
    plotting his first longitude, probably knowing before undertaking the
    calculation that he will still be in a pickle, but sensing there's
    something he's missing, knowing his latitude is not accurate.  The
    results of the second calculation are enough to tip the balance and
    enable him to go on deck and make for port with that wonderful gale
    from a favorable quarter speeding his passage.
    
    Just like many other inventions, everybody slaps their forehead
    afterward and says, 'why didn't I think of that.'  We're sitting here
    more than 150 years later wondering the same thing.  Eliminate the
    benefit of hindsight and it's not so obvious.  Sumner also wrote up
    his invention and tried to profit from it with his book.  There may
    also be some academics among us who assume that the folks back on dry
    land working on this problem, such as Newton and Maskelyne, were a
    lot smarter than those captains, so should have thought of this
    first.  I doubt that.
    
    Fred
    
    On Feb 10, 2006, at 7:03 AM, George Huxtable wrote:
    
    > In one respect, Sumner was lucky, and took advantage of that luck.
    > The point he needed to aim for, and aim for very precisely, was the
    > Smalls lighthouse. If he had missed it, and sailed past into those
    > rocks, he would have been in serious trouble. And his position
    > line, taken from the Sun observation, happened to pass exactly
    > through that spot. So then, all he had to do was so sail along the
    > appropriate line. It didn't matter how far away from the Smalls he
    > was, along that line; all he had to do was to stick to it (tide
    > permitting) and he would arrive there some time.
    
    
    Fred Hebard wrote:
    
    > Well yes, he was courting disaster had he kept his course up to the
    > moment of spotting Small's light, lacking the LOP.  But lacking the
    > LOP, I expect that he would have stood off or similar, and lost time.
    
    
    

       
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