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Hi Bill & all,


We have 32 points in a wind rose but you only refer to 9 in each direction.
It would also be nice to have an image even a small one (does the system
allow it to be attached?).




De: [] Em nome de
Bill Thoen
Enviada: terça-feira, 27 de Dezembro de 2011 02:32
Assunto: [MapHist] Odd Numbers on an Old Wind Rose


I recently was asked a question about a compass or wind rose that had some
odd numbers marking the 32 points. Instead of degrees or points it's marked
17 1/2 over the fleur de lis at north and then in both directions, every
11.25 degrees the markings go
31 1/2
0 at due west and due east.
The actual angles are 11.25 degrees per division, but if you plot these
numbers against the actual angles you get a very smooth curve that looks
exponential or maybe logarithmic. This graphic was seen in the Ch. Columbus
museum on Porto Santo, a small island of Madeira, Portugal.

The question is, what do these numbers mean? I've got a couple of images,
but they're too big to show you here. I thought I'd just ask if anyone knows
anything about this sort of numbering before I go to further lengths. For
all I know this could be an easy one. I just can't figure out if this is
some sort trigonometry calculator or what it was supposed to do for the
mariner of Columbus' time. (I don't have a date for it either; I'm assuming
it's 15th century.)

So is this a common numbering scheme or do you need to see the pictures?


Bill Thoen

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