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    Re: Sumner's Line (Navigation question)
    From: Fred Hebard
    Date: 2006 Feb 3, 15:30 -0500

    On Feb 3, 2006, at 3:21 PM, George Huxtable wrote:
    
    > 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.
    
    
    George,
    
    Sumner may not have been the first to use the line of position
    method, but it appears he discovered it independently.  My comment
    was merely about the circumstances that might have prompted him to
    discover the method.
    
    Fred
    
    
    

       
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