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).
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