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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,



De: [] 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


Image of a compass rose with odd numberingThank 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?

Bill Thoen
GISnet -

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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