Hi Roger, Yes, Now that the concept finally comes fully in to mind, this is a great idea! As you say only about 4 degrees of rotation, a small width of incllined plane for the two sliding contacts, would do it for just EOT correction. Quite compactly too. To handle both Longitude and EOT just about anywhere it would be much larger. 3 hours in a time zone plus daylight saving time plus 4 degrees, What, 65 degrees or so??? total swing. We would need very strong bolts holding the sundial and maybe a mirror to view the dial? <G> I guess we could probably handle the 19 degrees or so of Daylight saving time and EOT with this inclined plane Poncet mount. Who knows when Daylight saving time will happen in your zone next time? Some of the more current designs that have the hour lines spaced evenly along a line or circular curve would allow us to just slide a straight or curved plate to correct for all three corrections. I think my future designs will tend in that direction.
Thanks for your persistance, sorry it took so long to soak in! Edley. > Chris, > > Concerning equatorial tables, people seem to be looking at recent > patents for ELABORATE designs (conical rollers and such). But the > original Poncet table is quite simple. I made my 1977 prototype out of > wood, with a piece of Formica for the inclined plane on which one end > of the table slides. My unit has no curved surfaces at all. > > I've used mine for astrophotography at latitudes other than 42 N (for > which it was constructed). Shoving a small rock under the north or > south end will tilt the whole unit appropriately. I made a couple of > small "alignment wedges" on which I can place a bubble level for > setting the proper base tilt when away from home. I took it to Turkey > for the 1999 eclipse (latitude 39 N) and to the Winter Star Party in > Florida (latitude 25 N) a few years later. The only restriction is > that it won't work too near the Earth's equator. > > I think there's definitely a sundial application here, and I hope to > make one in the coming weeks to show to the list. > > -- Roger > > ________________________________________ > From: [EMAIL PROTECTED] [EMAIL PROTECTED] On > Behalf Of Chris Lusby Taylor [EMAIL PROTECTED] Sent: > Tuesday, June 05, 2007 5:30 AM > > This has been an excellent discussion. As several of my designs > purport to be readable to a couple of minutes, I, too, had been > exploring ways to correct for the EoT. > > The Poncet platform rotates the entire sundial about a polar axis, but > has to be made for a specific latitude, so cannot be mass-produced. A > latitude-independent version is described in US patent 09874026 filed > just last year (see > http://www.patentstorm.us/patents/7035005-description.html) Patrick is > correct in saying that if the gnomon has two edges you must rotate it, > not just the dial, as the orientation of the edges would remain > correct, but their position in space would not. > > An alternative that I've investigated is to use two wedges, similar to > those Bill Gottesman uses for the latitude adjustment of his sundials > (also patented: see > http://www.precisionsundials.com/equant%20dial.htm). > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial >
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