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    Re: Fortunate Islands question
    From: John Huth
    Date: 2009 Nov 17, 16:34 -0500
    I rechecked J.K. Wright's article.   He suggests that the PM was moved 10 degrees west from the Canary Islands arbitrarily.   Perhaps this was because of locations like Gana, which are close to the same longitude.  

    This still doesn't square with my other source of Yaqut who seems to have a location more consistent with Cape Verde Islands.

    On Tue, Nov 17, 2009 at 4:24 PM, Apache Runner <apacherunner@gmail.com> wrote:

    Sorry to pester y'all with these details.   When I did a fit to the Marseilles tables, I got a value of 23 degrees W for the "best fit" prime meridian, with an uncertainty of about 1.5 degrees.  The standard deviation is about 7 degrees.

    Now, I'd assumed that the PM was represented by the westernmost "known" land - either on the coast of Africa or the Canary islands.  But, the Canary Islands are 15 degrees W, which is too far east given the data. 

    A much better "fit" would be the Cape Verde Islands, at roughly 23 degrees W.  

    In reading this treatise on geography in the medieval Arab world, the commentator, Yaqut, says that the PM is calculated from either the westernmost point of land in the land of the Maghrib (Berbers = N. Africa), or from the Fortunate Islands, which lie 200 farsakhs from the coast.   A farsakh is 3 or 4 miles long, depending on the source.  So, for 600 miles from the coast, it's a good fit for Cape Verde and a poor fit for the Canaries.

    Now, my history books tell me that the Cape Verde Islands weren't discovered until the mid/late 1400's by the Portuguese, but the statement about the Fortunate Islands being 200 farsakhs to the west of the coast of land of the Maghribs, and the best fit of 23 degrees W sure fits Cape Verde better than the Canary Islands.

    What am I doing wrong?   Is it possible that the Arab geographers knew about the Cape Verde Islands?

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