*HOW TRACE THE ITALIC HOUR LINES (in not horizontal sundials)*
*The sundial with Modern hours (Local Solar Time) must have been already drawn. * For each point of the Equinoctial line pass one hour line with Modern , one with Italic and one with Babylonian hours. The values of the different hours are HIT = HMOD + 6, HBAB=HMOD-6 and HIT-HBAB=12 For example: HMOD=11, HIT=17, HBAB=5 --------------------------- Also for each point of the line of horizon (on the sundial) pass one hour line with Modern , one with Italic and one with Babylonian hours. Now the values are : HIT = 2 HMOD , HBAB = 24 - 2 HMOD , HIT=24 - HBAB For example: HMOD=11, HIT=22, HBAB=2 I remember that the horizontal line on the sundial is the line where the plane of the sundial is cut by the horizontal plane through the nodus (or the end of the style) --------------------------- Then to draw the hour line with the Italic hour HIT we have to find: - the point P1 of intersection with the Equinoctial line of the line with modern hour HMOD = HIT - 6 - the point P2 of intersection with the line of horizon of the line with modern hour HMOD = HIT / 2 The straight line through P1 and P2 is the Italic hour line that we are looking for. Example: if we want HIT = 22: - P1 where Equnoctial meets Modern hour line HMOD = 22 - 6 = 16 - P2 where Modern hour line HMOD = 22/2 = 11 meets the horizon line. --------------------------- When a friend asks me a suggestion to draw a sundial, I always recommend him a sundial that marks the hours to sunset , that is a sundial with italic hours.. This because when a person sees a sundial, immediately looks at his wristwatch to check if it works correctly: almost always immediately he affirms that the sundial is wrong L, because he don’t know that the sundial says the time of the Sun and not our mean and artificial time . With a sundial with hours to sunset this cannot happen and the observer can never realize if I have made an error, obviously unless he is one of the readers of this list J These sundials are enough used in places where it is important to know how many hours of light remain, as fields for games, small airports, sea places, wide parks, etc. Best wishes Gianni Ferrari 2010/3/30 Jack Aubert <jaub...@cpcug.org> > 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 > > -- Mail to : gfme...@gmail.com Lat. 44;38,18.5N Long. 10;56,05.3E
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