# Re: [MapHist] RE: Odd Numbers on an Old Wind Rose

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```You are all right. I also dear suggest a connection to the Taoleta de Marteloio
(see the link indicated by Joel), for the figures which appeared on each side
of the rose are (almost) exactly the same which are in the third column
(Ritorno) in Bianco's Taoleta (1436). The ratio then was 10, but if you put
17.5 you have the numbers of the wind rose (included the errors indicated by
Rob. it means that the figures reported in the Taoleta are better than the ones
in the wind rose!

The meaning (and the use) of the wind rose, as suggested by Wolfgang, is: how
leagues have I to sail in a given direction from the north (south) to reach one
degree north (south) from where I am? given the dimension of one degree be 17.5
leagues.

Il giorno 27/dic/2011, alle ore 19.22, Joaquim Alves Gaspar ha scritto:
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>
> I agree with Wolfgang that this is most probably from the sixteenth century
> (not before, for sure), when the module of 17 ½ leagues per degree started to
> be used. With a little patience maybe it is possible to recognize the style.
> It is very possible that the wind rose was drawn during Columbus life though
> not in the period when he lived in Porto Santo, still during the fifteenth
> century. Anyway, the length of the degree that he claimed when trying to
> convince the Spanish king that he could reach India by sailing west was much
> smaller than this one. That was, of course, a way of making the Earth smaller
> and the distance to India shorter!
>
> The best,
> 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 17:50
> Para: Discussion group for map history
> Assunto: Re: [MapHist] RE: Odd Numbers on an Old Wind Rose
>
> <image001.jpg>Thank you all so much for your answer to the mystery of the
> oddly labeled compass rose. I figured that it had to be a navigational aid,
> but never would have guessed 17.5 leagues had anything to do with it. Those
> old mariners were pretty clever!
>
> I checked the rules for posting and as long as I keep it under 50K, posting
> an image is OK. There are two original images (4.5 MB ea), which I'll send to
> anyone who wants them. Here's a  composite (because neither image shows the
> entire rose)
>
> BTW, if anyone recognizes the style, I'd be interested to know from what
> century this could have been used. It from Columbus' time or is it more
> recent?
>
> Regards,
> Bill Thoen
> GISnet - gisnet.com
>
>
> On 12/27/2011 5:08 AM, � wrote:
>
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>
> I think it is an illustration of the 16th century "rule to raise a degree",
> i.e. a means of calculation of a ship's position based on the assumption
> that there are 17 1/2 leagues to a degree:
>
> If you sail north or south you have to sail 17 1/2 leagues to arrive one
> degree to the north or south. And so on for every point of the compass
> (11,25 degrees).  And there can only be 8 numbers, because if you sail east
> or west your latitude doesn' t change at all.
>
> Diagrams of this sort can be found in manuals of navigation of the 16th and
> 17th century.
>
> Dr. Wolfgang K�berer
> Wolfsgangstr. 92
> D-60322 Frankfurt am Main
> Tel: + 49 69 95520851
> Fax: + 49 69 558400
>
>
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