Friends,
There is some contradiction in the answers about the equation of time on a
sundial.
1 At first there is the proof of the existence of the EoT by Huygens, de
Fouchy or Flamsteed.
As I think it was Huygens.
2 Second there are tables and graphs on or with a sundial to correct for EoT
in an indirect way.
3 Third there are sundials with curved hourlines to correct in a direct way
for the EoT.
The discussion on the sundial list now is like mentioned in point 3.
Hagen published in the bulletin of De Zonnewijzerkring in the following way:
The dial by Coster with EoT curves around each hourline is thought to be
from 1730( or earlier).
But Coster and/or Cruquius made a graph earlier around 1719.
BTW: the EoT curves on Coster's dial are only drawn for half a year, the
summer part.
The armillary with EoT correction is found on a painting by Verkolje and
the painting is dated 1740.
I don't know anything about Vogler's dial.
So far for an EoT curve on a dial, to read directly the clock time, we are
still around 1730.
Best wishes, Fer.
Fer J. de Vries
De Zonnewijzerkring
mailto:[EMAIL PROTECTED]
http://www.de-zonnewijzerkring.nl
Eindhoven, Netherlands
lat. 51:30 N long. 5:30 E
----- Original Message -----
From: "Patrick Powers" <[EMAIL PROTECTED]>
To: "SundialList" <[email protected]>
Sent: Monday, October 17, 2005 5:21 PM
Subject: Re: equation of time
Message text written by "Frans W. Maes"
Much older is a very elaborate copper horizontal dial, engraved around
1730
by David Coster, now in the Rijksmuseum (Amsterdam-4 in the book, with
picture). It has analemmas for all hours from 8 to 16.<
Hi Frans, this gets more and more interesting! Thanks for that. Just
whilst you must have been sending your reply to the list I was looking at
the web site of
La Commission des Cadrans solaires du Québec
(URL: http://cadrans_solaires.scg.ulaval.ca/cadransolaire/toronto.html)
which has even more references....
La CCSQ has the following text:
"Our French tradition, by its numerous authors of Gnomonics (Deparcieux
(1741); Rivard (1742); Delambre (1819); Gotteland and Camus (1993)), has
established that the analemma was invented in 1730, by the French
astronomer Grandjean de Fouchy . Is it the final argument? I doubt it very
much... And I am not alone for doing so!
Ms. Gotteland continues her researches on that topic, and she revealed, in
1993, that there was no evidence that Grandjean de Fouchy has ever
published a paper about his "invention". More, Mr Hagen, from the Dutch
Sundial Society, told her that he found three portable sundials, with an
analemma, and all of them were made before 1730:
- one armillary sphere on a painting from the Fine Arts Museum of
Amsterdam;
- one table sundial, in the Greenwich Maritime Museum; let's recall that
its sundialist is Mr. Vogler, who deceased in 1725;
- and one horizontal sundial, kept in the Rijksmuseum of Amsterdam, with
analemmas on each line of the hours. That sundial was carved in 1719 by
David Coster...(eleven years before the supposed invention of 1730)
According to Ms. Gotteland, de Fouchy would have been the first one, in
France, to use the analemma on his sundials, but he did not invent it!"
I wonder if there are any other references?
Patrick
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