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    Re: A key to the sketch map in "The geographical Lore..." of J.K. Wright (p. 245)
    From: John Huth
    Date: 2010 May 14, 06:39 -0400
    The typical uncertainty in those tables is about 1 degree in latitude and 6 degrees in longitude.

    If you do a fit to all place names that can be reliably identified in the Marseilles tables, the prime meridian is about 22 degrees W compared to Greenwich.   Baghdad also appears in the tables, along with Damascus and Mecca.  

    The "best fit" to the equator is about 0.25 +/- 0.27 degrees, consistent with the modern 0 and use of a shadow stick or equivalent.   The "best fit" to the prime meridian is 22 +/-1.6 degrees - consistent with??   Cape Verde?   In any case, I can post my fit to the tables so you can take a look and quibble, but I think there's only so much you can dig into them.   Wright himself concludes that multiple prime meridians were employed.   I'm not sure if that's the case, but everyone is free to draw their own conclusions.   

    In any case, I'm convinced it's not Baghdad, as Baghdad appears as a separate entry, and item 58 on his map is halfway between Baghdad and Damascus, which is where I would put "Aleufa" - sorry the light was low when I was reading my copy of the paper last night and I mistook the "e" for a "c", but I recall playing with Google earth for about an hour on this one and checking it against the relative positions of Baghdad, Damascus and Mecca.   

    The biggest problem is that longitude is very inexact at the time of the tables and was mostly based on dead reckoning.   There is some speculation that lunar eclipses were used perhaps for a few points, but during that period, lunar eclipses don't seem to be much better than dead reckoning.   The apparent longitude of Baghdad seems to be fairly far off in the tables, but if it's based on dead reckoning, I can see why - you either have to take a path across the desert or sail around the Arabian peninsula.  

    On Fri, May 14, 2010 at 2:39 AM, Vladimir Uvarov <v.a.uvarov@rambler.ru> wrote:

    Thank you for information.

    According to the map in "The geographical Lore..." (p. 245) the longitude of
    Alexandria is 51;20 and the longitude of Alcufa is 69;30. The difference is
    69;30-51;20=18;10.
    In his work related to geodesy Abu Rayhan Biruni gives the following longitude
    differences:
    Alexandria-Raqqa = 11;45,15
    Raqqa-Baghdad = 6;20,43
    The sum is 18;05,58 approx. 18;10.

    So, according to al-Biruni Alcufa is probably Baghdad

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