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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