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Good point, Rob! Then, the numbers represent the distances sailed in each 
course for each degree of latitude (tables with this kind of information were 
common at the time). 17 1/2 Castilian leagues was the length of the degree of 
latitude most often adopted by the Portuguese and Spanish 
navigators/cartographers from the begining of the sixteenth century on.

Joaquim Gaspar


-----Mensagem original-----
De: maphist-boun...@geo.uu.nl em nome de Gent, R.H. van (Rob)
Enviada: ter 27-12-2011 10:47
Para: 'Discussion group for map history'
Assunto: RE: [MapHist] Odd Numbers on an Old Wind Rose
 
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The numbers seem to obey the relation 17.5 / cos D, with D representing the 
compass direction (measured from the north).

However, the last two numbers (88 and 0) should then read 90 (rounded from 
89.7) and infinity. 

Rob van Gent


-----Original Message-----
From: maphist-boun...@geo.uu.nl [mailto:maphist-boun...@geo.uu.nl] On Behalf Of 
Vladimiro Valerio
Sent: dinsdag 27 december 2011 11:21
To: Discussion group for map history
Subject: Re: [MapHist] Odd Numbers on an Old Wind Rose

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Me too, I will be interested in receiving an image. You may sent at my address 
also a big one (up to 10 MB).
vladimiro

vladi...@iuav.it



Il giorno 27/dic/2011, alle ore 10.41, Joaquim Alves Gaspar ha scritto:

> This is a MapHist list message.
> News: If you don't get messages anymore, go to http://www.maphist.nl 
> for news about the new MapHist Forum o + o + o + o + o + o + o + o + o 
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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?).
>  
> Joaquim
>  
> De: maphist-boun...@geo.uu.nl [mailto:maphist-boun...@geo.uu.nl] Em 
> nome de Bill Thoen
> Enviada: terça-feira, 27 de Dezembro de 2011 02:32
> Para: maphist@geo.uu.nl
> 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
> 18
> 19
> 21
> 25
> 31 1/2
> 46
> 88
> 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?
> 
> Regards,
> 
> Bill Thoen
> GISnet
> http://gisnet.com
> 303-786-9961
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