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Edley,
You can see one of these conical gnomon sundials in
the web page of the city of Gent in Belgium.
This is a clever and elegant design, and very
easy to put into practice.
Another of its virtues is that these dials are
more robust, ie., VANDALS-PROOF, than ordinary ones.
This is a property which, at least here in Spain, is an
essential one (!). I know there are more dials with
that kind of 'robusness' (for instance, several
polyhedrons laid so that one casts its shadow over the other),
but does anybody know about some more dials like
these?
Anselmo
----- Original Message -----
Sent: Sunday, January 13, 2002 9:57
AM
Subject: Re: Acadian domestic
sundials
Hi Steve, Fer, Warren, Dialists
all,
I'm remembering more and more regarding notch dials that tell the
number of hours til sunset.
With what I've been reading lately of all
the richness in the NASS repository CD, much of what I was told, but didn't
understand at the time is making a great deal more sense.
I'll explain
the basic procedure of what I've been told as the main ideas and then expand
on them.
I was told in other terms, but it seems to be easier to relate
to an article written in 1998 by Javier
Moreno Bores in the NASS Compendium of June of that year called "A NEW FAMILY OF SUNDIALS WITH CONICAL
GNOMON". In that article he covers a number of dials giving Italian and
Babylonian hours using cones as the gnomons. The particular dial of interest
is the horizontal dial.
As he explains this:
1. First create a
standard horizontal dial for the latitude with half hour lines.
2. Create a
cone with an included angle of twice the latitude.
3. Place the cone in
place of the gnomon on the horizontal dial with the point of the cone pointing
due south touching the point all the lines come together and the cone axis
then parallel with the earth's axis and in contact with the substyle
area.
4. Each half hour line extending to the west of the cone is where the
cone's shadow will mark the hours before sunset starting from close to the
cone and moving outward.
Now, take a flat thin blade and place it in
contact with the cone and the sharp edge in contact with the line of a given
hour before sunset and apply pressure along the plane of the knife forcing it
into the surface some considerable distance and rock it slightly to open a
kerf or deep narrow notch which now, when the sun's light fills it fully
indicates that hour before sunset. If the surface was of limited depth the
knife could be forced all the way through leaving a thin slit. If all the
hours were so made into slits then if this board were lifted up a bit the
light would shine all the way through and make a lines of light on a surface
below which would indicate, again, the hours before sunset. This board could
be used as a template to mark the lines on another surface.
Now,
starting with a fresh surface, If one slowly brought the knife to the proper
angles for say each of the six hours before sunset as it was drawn along the
cone we would have a long curving line with the angle of the kerf varying as
the angle on the surface changed. If this were done slowly enough the one line
would be able to tell all the times in the interval from 6 hours before sunset
to sunset. If one were a master wood carver then one could even remember that
cut and be able to make it whenever and wherever we wanted. With skill the
hours could be made to be linearly spaced along this curve and so
marked.
An exact mirror curve could be cut on the other side of the
cone and thus mark all the Babylonian hours or hours after
sunrise.
This sounds like a pretty nice sundial, I'll try making it
myself.
Apparently this approach will work well only in the middle
latitudes from say 20 to 66 degrees.
I hope this sounds like as much
fun as it does to me ( after a mostly sleepless night thinking about it.
)
Good luck in your search, I hope this is what you are looking
for.
Edley
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