I have been thinking the same thing. That slate dial is strikingly beautiful and I like the idea of using a completely different type of hour that does have to offer any excuses for not being the same as what is on one's watch. Frank King's narrative write up answered one of my questions. I had assumed that Babylonian hours must be something from Babylon and therefore unequal hours but apparently they came into vogue along with "Italian hours" after the arrival of mechanical clocks. They are equal hours.
I was struck by the fact that the Italian and Babylonian hours coincide (cross each other) at the equinox line but not at the solstice lines. After staring at the two types of hours, which seem like they should be reciprocal, so to speak, for a while I was not able to come to any intuitive understanding of how they work and why they are not symmetrical. The only detailed instructions I have been able to find for construction of Italian hour dials is Mac Oglesby's paper on the dial he made for Moore's Field: http://www.mysundial.ca/files/H2SSManual040801.pdf. This method uses trigonometry and requires calculating the sun's azimuth among other things. I have no objection to using trig or computer software, but I wondered if there any geometry-based methods for laying out Italian/Babylonian hours? Were older dials with Italian and Babylonian hours always laid out using trigonometry? Also I wonder about combining a vertical sundial with a polar gnomon with a nodus for Italian/Babylonian hours. It might be too cluttered and complex to be worthwhile in practice but I wonder about the relationship if any between the two types of dial Jack -----Original Message----- From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Frank Evans Sent: Monday, March 29, 2010 6:47 AM To: Sundial Subject: how italian hours Greetings, fellow dialists, Following the pictures of the fine dial of Frank King in Selwyn College, Cambridge (congratulations) I began to wonder how it was laid out. Most of the commonly consulted books on dial construction (in English), Waugh, Mayall & Mayall, Cousins, etc. do no more than glance at Italian and Babylonian hours. Only Rohr has some account. His practical method appears to be to find the time and nodus point of sunrise and sunset at the solstices, count the hours back from them and join the winter and summer nodus points for each hour. This seems a pretty journeyman's procedure (nothing wrong with that) but I wonder if there is some more sophisticated method. Also, the assumption seems to be made that sunrise and sunset occurs when the altitude of the sun's centre is zero. This is far from sunset in any practical sense. Any comments, please? Frank 55N 1W --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
