Hi Mac and Others,, As a contribution to the discussion about the polar dial I made a drawing of the construction of such a dial.
In this picture I try to explain what I did. At the left from top to bottom you find a series of gnomons for each hour starting at noon with the appropriate hourline with date points for the solstices and equnioxes. The lengths of the gnomons are as Bits formula ( graphic 11, bottom) gn = g . cos t Now all the hourlines with datepoints are equal, only the place and length of the gnomons is different. In the middle top figure these gnomons and hourlines are placed on a north-south line, using the formula an = g . sin t . tan alpha. with alpha = 45. The distance between the footpoints of the gnomons aren't equal. In that case we get the pattern as by Oyen. The shape of the line through all the endpoints of the hourgnomons is a semi-circle. The second half of the pattern is added in the figure middle bottom. The difference with the figure by Bits is that he had all the gnomons equidistant as may be seen at the left in graphic 8. Now shift the gnomons and hourlines with datepoints according the formula by Bits for delta-x and delta-y and the result is in the figure right bottom. The footpoints of the hourgnomons are drawn in red. The footpoints for 6 and 18 are arbitrary because the gnomonlength is 0. Now it's easy to draw a side vieuw of the wire. We know the distance of the footpoints from the center point and the lengths of the hourgnomons. The figure at top right shows roughly the result in blue Reading the time before about 7 am and after 5 pm is difficult because the length of the hourgnomon is small. If I didn't make a mistake I conclude that the principle by Bits is all right but his drawings are some misleading. Best wishes, Fer. Fer J. de Vries mailto:[EMAIL PROTECTED] http://www.iae.nl/users/ferdv/ Eindhoven, Netherlands lat. 51:30 N long. 5:30 E Attachment converted: Macintosh HD:polar.gif 1 (GIFf/JVWR) (0006792E)
