NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Navigational instruments at the Naval Museum in Lisbon
From: Jürgen Hoefeld
Date: 2010 Feb 25, 23:34 +0100
From: Jürgen Hoefeld
Date: 2010 Feb 25, 23:34 +0100
By the way, the Davis quadrant http://www.fer3.com/arc/imgx/IMGP5954.JPG labelled: 'Elton's quadrant replica' seems to be no Elton quadrant at all but an ordinary Davis quadrant. I can't see any bubble or levelling attachment.
This brings me to some more questions on diagonal scales on Davis quadrants:
Best regards,
Juergen Hoefeld
Aachen, Germany
This brings me to some more questions on diagonal scales on Davis quadrants:
- The sight vane on the 30° scale of a Davis quadrant has to be proper aligned with the horizon vane to get a meaningful reading on the transversal scale on the large arc. Otherwise the reading of minutes on the diagonal scale is meaningless.
- How did the manufacturers and/or users ensure this alignement?
- What is the oldest existing Davis quadrant? I only found examples which are not much older than the first octants from the 1730s, compared to Davis publication of 1595.
- Does anyone remember having seen in a museum or collection an existing Elton Quadrant like that by made by Sisson in the Phil. Trans. 1731-1732, vol. 37, 273-279, depicted in http://en.wikipedia.org/wiki/File:Elton-quadrant.jpg or on John Vanderbanks painting http://www.nmm.ac.uk/mag/pages/mnuExplore/PaintingDetail.cfm?ID=BHC3128 in the National Maritime Museum?
Best regards,
Juergen Hoefeld
Aachen, Germany
2010/2/25 Douglas Denny <douglas.denny@btopenworld.com>
Ah! but which came first the chicken or the egg?
Or, in this case: is 'Gunwhale Circle' a simple error by whoever wrote the label due to the fact a 'Borda Circle' (so called because of the inventor) has the same name in Portugese? It could be as simple as that.
I think your extrapolation needs further evidence of the use of a term like 'Gunwhale Circle' being in actual use by Portugese sailors contemporaneously with the use of the circle itself in the nineteenth century.
I have come across simple blunders in labelling in museums before where it is obvious the person who wrote the label did not 'know his onions'.
Douglas Denny.
Chichester. England.
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