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    Re: Sumner's Line (Navigation question)
    From: George Huxtable
    Date: 2006 Feb 3, 20:21 -0000

    Here's another posting, that I sent at 11.20 GMT this morning, 9 hours ago, which hasn't yet been
    returned to me by Nav-L.
    
    Perhaps the mailings are being sent by reflection off a distant planet.
    
    So I will try sending it again. Apologies to those who have seen it before.
    
    Perhaps I should keep sending until I get a copy back
    
    George.
    
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
    
    |Fred Hebard, referring  to Chuck Taylor's posting, wrote-
    
     I would expect that strong pressure such as you describe would be
    | very helpful in spurring somebody to invent something like line-of-
    | position navigation.  It does seem though that there was no imminent
    | doom, just an impending delay in having to heave to or otherwise wait
    | while avoiding that lee shore.
    
    ============================
    
    Comment from George.
    
    I have no knowledge to base the following comment on; it's just a matter of opinion.
    
    I would be surprised, however, if Sumner was the first mariner ever to adopt such a strategy.
    
    This was the problem-
    
    In order for a mariner to deduce his longitude from a Sun sight, he needed to know his latitude. In
    order to deduce his latitude (other than at noon) he needed to know his longitude, to determine Sun
    LAT. Mariners could break that deadlock by taking a noon Sun observation.
    
    Without a recent noon Sun, a mariner had to make the best guess he could at his latitude, and work
    out the longitude accordingly. But was Sumner the first navigator to ask "what if...?", I wonder.
    Having made his guess, and deduced a longitude,  how many mariners before Sumner might have asked
    "but what if that latitude guess was wrong, and I was really at another latitude", and made a
    different guess accordingly. That was what Sumner did, and then extrapolated the resulting position
    line.
    
    Sumner was certainly the first to write that procedure down, and rationalise it in a convincing way
    that other mariners could follow,. He deserves all credit for doing so, in a profession that was so
    constrained by the traditional way of doing things, and was so resistant to any change. But at least
    some navigators were intelligent people, the equal of any of us in Nav-L, and were doing their
    business all day every day, so had a familiarity with the procedures that few of us can claim even
    to approach.
    
    The Sumner innovation was hardly "rocket-science". To me, it seems remarkable that after all the
    involvements of astronomers and mathematicians in the 18th century, in the longitude question,
    nobody had suggested, in print, such a procedure before, to break free from the constraints of
    considering lat and long to be such separate quantities. There were, of course, good reasons for
    thinking of them separately, in the days of lunars, when latitudes could be so precise, but there
    were such great errors in longitudes. Once good chronometers became common, lat and long were more
    on an equal footing, and perhaps it's no coincidence that the Sumner revolution came in as
    chronometers were becoming the standard way for ships to navigate.
    
    It's my opinion that before Sumner's time, there must have been many mariners quietly adopting his
    approach, without ever  thinking that they were introducing a "new navigation", or considering
    publication. But because they never did that, we will never know. It's a situation that must occur
    in many other aspects of life.
    
    None of that detracts in any way from Sumner's achievement.
    
    George.
    
    
    

       
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