"Frans W. MAES" wrote: > <snip> > > I do have a question about the #7. "Bifilaire zonnewijzer". One picture > > shows a curved chain and another shows a straight wire between two posts. > > In either case, I did not understand how it was "bifilar" in nature. > > You could not. The chain is easily vandalized, and has been > several times. My page shows several "repairs", which were not > always correct. > > The top picture shows the position of the chain at the official > opening, last March. The chain touches the pole style, and thus > there are no crossing lines, as you noted correctly. > > The correct position can be seen on the picture with the folks > gathering around the designer (Mr. Soler, at left, carrying the book): > the chain runs clearly BELOW the pole style. The next picture > (with the measuring tape) shows that it had regained its correct > height last July: the minimum is 70 mm above the dial plate. > > As a consequence of this arrangement, the date line for the > equinox is not straight, but slightly curved. > > Perhaps I'd better made the English version right away! Stimulated > by questions like yours, I have already expanded the English > summary slightly. > > Regards, Frans >
I, too, would appreciate an English translation, as I have no idea why a catenary has any special properties that commend its use in a bifilar sundial. I have to admit to being rather a purist (read 'pedant') in that it seems to me that the original bifilar sundial was invented to give the remarkable property that the elliptical dial of a 'normal' horizontal can be stretched into a perfect circle, with equally spaced hour lines and all the benefits that gives. (The way I visualise the bifilar sundial is that it handles the N-S and E-W scaling of the dial separately.) Many recent so-called bifilar sundials merely use the intersection of the shadows of two rather arbitrary lines/curves. These have no special properties other than novelty. I hope we (English speakers) will learn that the catenary/polar gnomon combination does indeed have some special property. Regards to all Chris Lusby Taylor Newbury, England 51.4N, 1.3W
