"fer j. de vries" <[EMAIL PROTECTED]> writes: > Back to the bifilar dial : A bifilar dial can be constructed in such > a way that the hourlines ( for local suntime ) are equi-angular > spaced. Than it is also possible to correct for EoT and/or > longitude by rotating the hourscale. So we have at least 2 > possibilities to correct for EoT with bifilar sundials.
Is there a resource on the Web with the theory of bifilar sundials, or at least a picture or some info on constructing them? I spent many idle hour trying to come up with a sundial that would allow an easy mechanical correction for the equation of time. The best I could devise was using a gnomon tilted halfway between the Earth's axis and either the vertical or the meridian. This allows the hour marks to be placed evenly around the circumference of a circle, so that the dial can easily be set forward or back by rotating the circle. The catch is that the center of the circle has to be moved to match the declination. (I assume that also this invention of mine is old hat and has a name that someone will kindly tell me about.) It sounds like the bifilar dial is the solution I was not clever enough to find myself. Given time, I would be able to work out the theory on my own, but I'm also willing to forgo some of the fun on this one and just read about it. Art
