Hi Chris, Really Cool Chris! So all those houswives have been correct enough all this time! Thanks!
Edley. > 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 usetwo wedges, similar to > those Bill Gottesman uses for the latitude adjustment of his sundials > (also patented: see > http://www.precisionsundials.com/equant%20dial.htm). The wedge angle > can be vey small -just 2 degrees. But having to set three alignments > seems an unacceptable burden. > > My latest approach is to take the "Housewife's Trick" from AP Herbert: > just turn the whole horizontal sundial about a vertical axis, so the > dial plate remains horizontal but the gnomon and the 12 o'clock line > are no longer North-South. This is very much easier to do than any of > the other suggestions. But, is it accurate? > > Of course not - an article in The Compendium a few years ago analysed > it and rejected it. But The Compendium is written with a USA > perspective. AP Herbert was English. The housewives to whom he > referred were at 51 or more degrees North. Does this make a > difference? > > Yes, it does. By rotating the sundial appropriately, the maximum time > error can be made to be less than one minute except in July when it > may be as much as 90 seconds. Well, for my money that's a pretty good > result. I'm sorry it doesn't work as well in the USA because you're > too near the equator. For us in northern Europe I suggest it is quite > good enough. The further north you are, the less the error. Should I > patent it, or at leastthe calculation of the "appropriate" angle? I > think I'm too late. It appears that it's common knowledge amongst > housewives in this country. > > Chris Lusby Taylor > 51.4N 1.3W > > ----- Original Message ----- > From: Edley McKnight > To: Roger Sinnott ; [email protected] > Sent: Tuesday, June 05, 2007 6:59 AM > Subject: RE: Equation of Time > Hi Folks, just a short note on hinging in latitude/EOT > corrections. > > I tend to think of the hinge as one side of a parallelogram with > the gnomon as the opposite side. The parallelogram extending down > through the dial plate and base. When any set of parallel lines is > rotated around one of them, they still stay parallel, further, if > only a subset of these lines is rotated, all of them are still > parallel. So, really, the hinge could be just below an edge of the > dial plate if the dial plate is allowed to swing to positive and > negative angles. So long as the hinge is parallel to the gnomon. A > half circle with a screw clamp or any number of other ways could > be used to set the angle/time. I hope this makes sense. It is all > equivalent to translating the dial in Longitude( rotating around > the earth's axis as a hinge). > > Enjoy the Light! > > Edley. > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > >
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