Re: Strange analemmatic sundial - how does it work?

[Steve Lelievre]

Thank you to Joel, Fabio, and Bill.

Before I sent off my inquiry last night, I had got as far as deciding 
the dial must be some kind of Foster-Lambert similar to the Herstmonceux 
dial that Fabio mentioned, but I was still confused. I'm relieve to 
learn that it's not related to an analemmatic dial at all, and Wikipedia 
is simply wrong!


Steve


On 2019-05-31 5:14 a.m., Bill Gottesman wrote:

Hello Steve, I'll take a guess at this.
I think the dial is really a heliochronometer with an analemma, not an 
analemmatic dial.  I think the screws up top held a focusing lens or a 
pinhole aperture that projected a beam on to an analemma on to the 
lower plate.  The analemma is not visible in that picture.  The dial 
is turned to make the beam align, so the hours go counter-clockwise, 
and the time is read across from stationary indicator at the very top 
of the dial, hidden from view in this photo.
Similar to the upper left dial seen at 
https://equation-of-time.info/sundials-with-shaped-alidades . -Bill


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Re: Strange analemmatic sundial - how does it work?

[Bill Gottesman]

Hello Steve, I'll take a guess at this.
I think the dial is really a heliochronometer with an analemma, not an
analemmatic dial.  I think the screws up top held a focusing lens or a
pinhole aperture that projected a beam on to an analemma on to the lower
plate.  The analemma is not visible in that picture.  The dial is turned to
make the beam align, so the hours go counter-clockwise, and the time is
read across from stationary indicator at the very top of the dial, hidden
from view in this photo.
Similar to the upper left dial seen at
https://equation-of-time.info/sundials-with-shaped-alidades .  -Bill
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Re: Strange analemmatic sundial - how does it work?

[fabio.sav...@nonvedolora.it]

dear Steve,

I did a search.

At first I realize that the dial has equiangle hours, so it seems to me, 
if it is analemmatic sundial it means that the dial has the inclination 
to get this condition (e.g. UK744 www.sundialatlas.net/atlas.php?sun=UK744).
This condition allows to turn the dial to adapt it to the time of 
another longitude or to correct it for eot.


Than I thought that this condition is the same for an equinoctial dial 
and may be it is not an analemmatic sundial, but an equinctial dial 
adjustable for eot, so 'analemmatic' has this meaning.
The french page of wikepedia says the same of the english one: Cadran 
analemmatiqueE. Ducretet 
& L. Lejeune 
(Paris), fin du XIX^e siècle. L'analemme montre « l'équation de la 
fonction du temps » et permet la correction de ce que l'horloge lit.


I think something is lost, without the gnomon it is difficult to 
understand it.


I found a book on internet, Catalogue des instruments de précision, 
Lejuene, Ducretet (the two authors of the sundial and of others 
scientific instruments),  I found the book on sale on internet but also 
the possibility to consult it online 
(https://archive.org/details/cataloguedesins00parigoog). There is a 
section starting at page 222, Cosmographie, where there are:


n. 1898 Chronomètre solaire de Fléchet fig 500
n. 1809 Méridien universel sur pied fig 501

Unfortunately this figures are not present (not scanned)
So I search for 'Chronomètre solaire de Fléchet' and I found some pages like
http://www.mhs.ox.ac.uk/collections/imu-search-page/record-details/?thumbnails=on=2258=34749

http://www.tessier-sarrou.com/html/fiche.jsp?id=5754802=3=fr=20=2=1=

https://www.mhs.ox.ac.uk/collections/imu-search-page/record-details/?TitInventoryNo=42286=field==2257

and others. They are heliocronometers, that is equinoctial dial, with 
turnable dial and with a tilting lens to get the Sun beam on the analemma.


I think this misunderstanding of the definition on Wiki depends on the 
double meaning of 'analemmatic':

- with the analemma of eot
or
- azimuthal sundial with the gnomon adjustable for the declination of 
the Sun.


ciao Fabio



Il 31/05/2019 07:30, Steve Lelievre ha scritto:

Hello everyone,

The English language Wikipedia page on analemmatic sundials has a 
photo of a strange example at the National Polytechnic Museum, Sofia. 
See https://en.wikipedia.org/wiki/Analemmatic_sundial and scroll down 
to the last photo.


It's completely unlike any other analemmatic dial that I know of, so 
I'm struggling to understand it. Which part is the gnomon? Which part 
moves?  Why do the hours run counterclockwise (Sofia is northern 
hemisphere so presumably it was made for use there)?  Why is there a 
brace apparently welded to the dial face in front of the XII position? 
What angle is the dial face at?


So many questions!

In short, how does it work ... can anyone enlighten me?

Thanks,

Steve




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--
Fabio Savian
fabio.sav...@nonvedolora.it
www.nonvedolora.eu
Paderno Dugnano, Milano, Italy
45° 34' 9'' N, 9° 9' 54'' E, UTC +1 (DST +2)

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