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    Re: Sumner lines: was[NAV-L] Simple celestial navigation in 1897
    From: Frank Reed CT
    Date: 2006 Mar 14, 01:26 EST

    George H, you asked:
    "If there were a few  diehard old-school mariners clinging to older methods,
    then indeed position-line  navigation would not have become universal. Is that
    all that he is  implying?"
    No, nothing so wishy-washy! 
    As late as the  1930s, a substantial minority (maybe 25%??) of navigators
    were still using  straight, simple time sights and Noon Sun --no celestial lines
    of position. At  some earlier date, that proportion crossed the 50% "tipping
    point". I don't know  when that was (and it would be very tough to prove) but
    I'm looking at 1900-1905  right now. That's sixty years after Sumner published.
    I think there are plenty  of reasons for this including issues of plotting
    and charting, vessel speed,  mathematical complexity, bias regarding algebraic
    versus plotted solutions, and  also, perhaps, an intangible sense that a
    problem already solved did not need  solved again (thou shalt not re-invent the
    wheel --and yet we do).
    And  you wrote:
    "It seems to me that one of the conditions pushing mariners to  adopt Sumner
    techniques was the climate. Mariners returning to anywhere in  Northern Europe
    had to find one of the narrow approach channels around the  British Isles,
    after an ocean passage. Our climate is such that the Sun may be  only fleetingly
    visible for days at a time. If and when it appeared, the sextant  would be
    brought out, whether it was noon or not. The chance was too precious to  be
    missed. There might be weeks at a time when no noon sights were possible at  all."
    Yes, I agree with that. Climatic differences might well explain  variable
    rates of adoption of celestial lines of position in different parts of  the world.
    By the way, somewhere in W.E. May's navigation history, there  is a comment
    about pre-war navigators (meaning pre-1940s) in the merchant marine  dispensing
    with position lines and "reverting to" time sights and Noon Sun. I  don't
    have a copy handy, but I think I'm remembering the phrasing right. I don't  think
    he's specific, but I assume he was talking about *British*  navigators.
    42.0N 87.7W, or 41.4N  72.1W.

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