Dear Karlheinz Thank you for sending us this information...
> only in 1985 there were placed a polar > gnomon on the dial from "1346"... > > If the date of 1346 is correct nobody > knows. I think you said 1346 is the date of the buttress into which the sundial is cut. This is clearly a poor basis for dating a sundial! > See also my article that you may find on > my web page > > www.antike-sonnenuhren.de/artikel.htm I imagine this is the article with the title: Vertical Sundials of the 5-15th Centuries I had a little trouble navigating to this but it is an excellent article and gives a splendid summary of this thread. In this article you refer to the Brunswick dial of circ. 1350. This might be where Nicola and Gianni got that date from. You say that... in Roman times it seemed as a matter of course that only the tip of the gnomon shadow gave the hour. This must be a problem when trying to decide whether or not a missing gnomon was polar-oriented... For example, the winter side of the Oropos dial (which you date between 350 and 320 BC) seems to have hour lines that are almost perfectly set out for an equal-hours dial with a polar-oriented gnomon. You elegantly explain that the gnomon was in fact *horizontal* but the shadow of its tip, used as a nodus, would have indicated equal hours. I don't think such a gnomon is polar oriented (because it was horizontal) but others may say that such a gnomon has been described as polar-oriented sufficiently often in the literature that we must accept that usage. What do you think? Also, you say that: with an angle of 90 degrees minus half of the latitude, between the wall and south-facing pointer results in the sundial giving quite a reasonable approximation for equal hours. I haven't investigated this claim. For a proper polar-oriented gnomon, the angle is 90 degrees minus the latitude (not half the latitude). Can you tell us a little more about how this half-angle rule works? May I say just how much I have enjoyed reading your articles? Best wishes Frank --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
