How sharp is the point of the cone, wouldn't it be dangerous. I would hate some kid to climb on it and hurt themselves.
Roderick Wall. ----- Original Message ----- From: John Carmichael To: sund...@rrz.uni-koeln.de ; 'Colby Lamb' ; hend...@analemma.nl Sent: Sunday, August 30, 2009 6:40 AM Subject: Inclining Cone Gnomons I have been thinking a lot about Colby Lamb's inclining cone gnomons that he uses on his horizontal sundials, because I love conical gnomons since they have wide pointed easily read and highly visible shadows that look like the pointed hands of a clock. I also just like the look of them. These are what some people call 'point-in-space' gnomons or nodi. Others call them 'nodus based' sundials. You use the shadow of the tip of a gnomon (located on the polar axis) to tell the time and/or solar declination. But unlike most nodus based sundials which are usually rods or spheres on rods, these are pointed cones. See photos of Colby's cone gnomon here: http://www.flickr.com/photos/jlcarmichael/3868639918/ and http://www.flickr.com/photos/jlcarmichael/3860044836/ There is no law that says that point-in-space gnomons need to be placed perpendicularly (vertically) on the face. Colby realized this and he places his at an angle. When I asked him why he did this, he said he did it for purely artistic reasons. (Hendick Hollander also uses inclining cone gnomons on his unique award winning Standard Time dials, but he does it because his design requires it for specific gnomonic reasons which I won't get into here). I also asked Colby if the inclining cone angle was some special angle, but if I understood him correctly, he said that he just picked an angle that looked good. So here is my question. But I'm thinking that there just might be a good gnomonic reason to tilt a cone gnomon on a dial's like Colby's because the shadow produced from an inclining cone gnomon might be a better more uniform shadow than that cast by a perpendicular cone, especially if it were angled to the North in line with the polar axis. I did not measure the angle of tilt of Colby's cone, but it seemed to be smaller than the latitude polar axis angle for Portland. If the cone was angled to match the polar axis, then during the day, the sun would revolve around it in a more uniform way- much more uniform than if the cone were perpendicular to the face (vertical). Does this make sense? John p.s. I've discussed with Colby the advantage of blunting the sharp point on cone gnomons because blunting the sharp point increases the time and date readings when the shadow is long. But angling the cone might make them even better! John L. Carmichael Sundial Sculptures 925 E. Foothills Dr. Tucson AZ 85718-4716 USA Tel: 520-6961709 Email: jlcarmich...@comcast.net My Websites: (business) Sundial Sculptures: http://www.sundialsculptures.com (educational) Chinook Trail Sundial: http://advanceassociates.com/Sundials/COSprings/ (educational) Earth & Sky Equatorial Sundial: http://advanceassociates.com/Sundials/Earth-Sky_Dial/ (educational) My Painted Wall Sundial: http://www.advanceassociates.com/WallDial (educational) Painted Wall Sundials: http://advanceassociates.com/WallDial/PWS_Home.html (educational) Stained Glass Sundials: http://www.stainedglasssundials.com (educational) Sundial Cupolas, Towers & Chimneys: http://StainedGlassSundials.com/CupolaSundial/index.html ------------------------------------------------------------------------------ --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.71/2333 - Release Date: 08/29/09 06:39:00
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