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    Re: Longitude by altitudes. was Re: How Many Chronometers?
    From: Marcel Tschudin
    Date: 2009 May 8, 15:28 +0300

    I din't seriously follow the thread on "How Many Chronometers?". After
    George did change its title it draw my attention.
    A few days ago I informed you under "Old map" on a book which I
    received as a present and that it requires some caution to appreciate
    its content. Since this book was published first in the mid 60s you
    may likely have read it a long time ago and probably also followed
    discussions on its pros and cons. Sorry that I'm sometimes late, but
    for me the content is new.
    Now, why do I mention this here? The main content of the book deals
    with the map of Piri Reis from 1513 which only was found in 1929. This
    map shows with an amazing accuracy also the east coast of the American
    continent. One presumes(?) that Columbus used a map from Piri Reis on
    his trip. The map which was found mentions apparently that it was made
    from even older maps. According to our "general" understanding it
    requires good means to measure the time (chronometers) for being able
    to determine the longitude and thus being able to draw an accurate
    map. However the chronometers were only invented in the middle of the
    17th century. If the date of the Piri Reis map is really correct,
    raises the question on how the longitude may have been determined
    before the time of chronometers we now of. It looks like there must
    have existed previously either accurate means of measuring the time OR
    an other mean of measuring longitude, like e.g. the one indicated by
    the new title of this thread "Longitude by altitude". That's the
    reason why the title of this thread draw my attention. However,
    reading George's comments shows the drawbacks of this method; as a
    consequence one may question whether this was really used.
    The members of NavList know that I'm a member without any navigational
    experience. I'm therefore interested to see how you, who have this
    experience, look at this.
    P.S: For those who don't know the map from Piri Reis; just Google for it.
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