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Hello David,
The principle of the design of the your dial,
showed at your page, indeed isn't new, the final shape may be, of
course.
Any hollow thing, cut by the horizontal plane, and
with an indactor in the same horizontal plane, can act as a sundial that will
show the time all day, all year.
The hemispherium is the most common, however a
cone, a cylinder, a shalow bowl, may be used and they can be placed in any
position, as long as cut off at the top by the horizontal plane.
The indicator then always will give a shadow or
spot of light inside as soon as the sun is above the horizon.
As such you may find many existing examples and I
have seen some cylindrical as well.
Your example could be named a cylindrical dial or
polar cylindrical dial if you refer to its shape and position.
Or "point-sundial" because the dial uses a point of
shadow or light to read the dial.
I don't know how this sounds in English, it is a
direct translation of a word in our language where it sounds well. (
punt-zonnewijzer )
Best wishes, Fer.
----- Original Message -----
Sent: Saturday, October 06, 2001 3:57
PM
Subject: RE: Projection Sundials
Dear
Fer,
Which covers the
usage that you are referring to. Didn't find the entry earlier. In
anycase, it would seem that I have misnamed this sundial.
Suggestions for
a more appropriate name? Perhaps "Equatorial Analemmic" would be
more appropriate?
("Double
Barrelled Overhead Gnomon Oblique Cylinder" does not need to be
suggested.)
One interesting feature of this sundial design
is that (mean time) of the solar transit and sunrise/sunset times may be
read off the dial face for the whole year. With appropriate markings,
the azimuth of sunrise/sunset could also be read
off.
While I
'discovered' this sundial design independently, I suspect that it has a
history. Can anyone point to earlier presentations of this
design?
Thanks
David
-----Original
Message-----
From: fer j. de vries
[mailto:[EMAIL PROTECTED]
Sent: Friday, 5 October 2001 1:10
AM
To: [EMAIL PROTECTED]; Sundial
Subject: Re: Projection
Sundials
Hello David,
The term Projection Sundial also is used by
J.A.F. de Rijk, Netherlands, in an article
(1986, 97, 1 Journal British astronomical Association. Equator
projection sundials) that is also pubished on my Website.
Use the link Projection dials from my homepage.
Address below.
As such it is the projection of a universal
equatorial ring sundial onto any plane and into any direction.
You then get all kind of analemmatic and
Foster's sundials.
Best wishes, Fer.
----- Original Message -----
Sent: Thursday, October 04, 2001 5:38
PM
Subject: Projection Sundials
Dear
All,
Could
someone help me with a definition of a 'Projection Sundial'.
- Couldn't
find it in the BSS Glossary.
- Folkard
& Ward 1996 "Sundials Australia" have included in their section on
Projection Sundials - The chapel sundial (Merton College, Oxford), a Sun
Compass, a direct sunlight through a hole onto analemmas on the horizontal
ground, Monash University Union Building- Melbourne Australia (wall
mounted rod tipped by a disk making shadows on analemmas on a wall),
the Augustus Sundial from 9BC, Ulugh Bek's Observatory, mirror sundials
shining on analemmas on a roof, various noon marks and a Scottish
polyhedral 'lectern' sundial.
The common
factor seems to be that the shadow (or light ray) approximates a
point rather than a segment.
Is
Projection Sundial a recognised term?
What is the
characteristic that Projection Sundials have that other sundials
don't?
David
Pratten
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