Your message and especially the attached draw recalls to mind that in my site:
http://web.tiscali.it/partena/index.htm
I have published a short note (alas in italian!) on the theoretical problem of inserting a cylindrical polar gnomon into a wall.
As the lecture of the hour is made with reference to the center of the gnomon shadow, the axis of the cylindrical polar gnomon should coincide with the center of the sundial, that is the point where meet all the hour lines.
The intersection of a cylinder (the cylindrical polar gnomon) with a plane (the wall) generates an ellipse. The center of the sundial should coincide with the center of the ellipse. Once you have fixed the gnomon to the wall that coincidence point is hidden.
I was interested in calculating the distances of the orizzontal and vertical tangents from that point, in order to use them in the program for calculating the coordinates of the points of the hour lines with reference to a system using those orizzontal and vertical tangents as xy axis.
In the same note I pointed out (and this might have some reference to the content of your message) that in the case that the sundial shows also the solar declination curves, it should be taken into account that the material length of the the cylindrical polar gnomon is longer than the theoretical one by:
d/(tan lat * cos decl)
where d is the radius of the cylindrical gnomon.
Ciao
Angelo
At 08.11 01/08/03 -0700, you wrote:
Hello All:
Because of the importance of rod gnomon attachment on stained glass sundials and the interest in the subject, I thought I'd make a Delta Cad scale drawing for the website showing a sideview of the hardware used to attach it to a pane of glass, using the bolting method.
Before I made the drawing I already suspected I see one very interesting detail. This may come as a surprise to most of you, but the drawing clearly shows that the center of the sundial, where the hour lines converge, IS NOT where you drill the hole in the glass! This is true for all those bent rod gnomons that are not perpendicular to the dial face. And it applies to all sundials with bent rod gnomons, not just stained glass ones.
In my drawing, I used 1/8" (3mm) thick glass, 1/4" (6mm) thick rod gnomon, 1/2" padded and flat washers, and 1/4" nuts. You can see that the glass hole is .371 inches (9mm) below the dial's center.
This is an important design consideration that the designer must consider in his plans.
John
John L. Carmichael Jr.
925 E. Foothills Dr.
Tucson Arizona, USA
Tel: 520-696-1709
Email: [EMAIL PROTECTED]
Sundial Sculptures Website: http://www.sundialsculptures.com
Stained Glass Sundials Website: http://advanceassociates.com/Sundials/Stained_Glass
Angelo Brazzi
mailto:[EMAIL PROTECTED]
http://web.tiscali.it/partena/index.htm
