Dear Frank, Maes and other friends, The question about the introduction of use of the polar gnomon is old. Actually, are very few the informations about this. Rohr wrote in his book that the polar gnomon was introduced in Europe with the Crusaders returning from the arabian country. I also think that the polar gnomon was re-invented in Europe from the Arabian astronomical science.
Sure the mechanical tower clock with the equal hours was a good reason for the use of polar gnomon in the equal hours sundials, but I have some dubt about the importance of this "only one" reason. It is true that the first mechanical clocks was on the towers around the begin of the 1300. And the first vertical sundials with the polar gnomon was done arond the first half of 1300. The interesting articles of Curt Roslund in the BSS Bulletin, september 2005, pag. 116-119, show the vertical sundial of Braunschweig Cathedral of 1346 with the equal hour lines and a polar gnomon. A have find recently a important gnomonical manuscript attribuited to the end of 1300 with drawings of horizontal and vertical (also east and west plane) sundials with the equal hours line. But this is a new topic for a my next articles. Hence, we have the sources that the equal hours line on the horizontal and vertical sundials with an probable polar gnomon was used in the Europe at the end of 1300. Thanks for attention and the best wishes to all Nicola Severino --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
