A small addition If we have a horizontal sundial we cannot use the method that I have described yesterday.
In this case, however, the point where the Modern hour line HMOD and the Italic hour line HIT=2 HMOD cross the " horizon line" becomes a “point to infinity” (I hope that this is the mathematical term in English :-) ) , that is a direction. Therefore the modern hour line HMOD is parallel to the Italic hour line HIT = 2 HMOD and to the Babylonian one HBAB=24-2HMOD Gianni Ferrari P.S. I am completely in agreement with Frank on the difficulties that the method (simple) can introduce: as often happens, the things theoretically simple become difficult in the practice . ---------------------------- 2010/3/30 Frank King <frank.k...@cl.cam.ac.uk> > Dear Gianni, > > I like your explanation and I like the > extra comments too. > > You have: > > P1 on the equinoctial line and > > P2 on the horizon line > > This is good in theory but not so > good in practice. For example, my > line for Bab = 11 does not run > as far as the equinoctial line or > the horizon line!! > > Several other lines do not reach > one or other of the equinoctial > line and the horizon line. > > Another practical problem is that P1 > and P2 can be quite close together > and a small error in either will make > for a large error in the extension > towards the summer solstice curve! > > I very much agree with this: > > 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... > > My practical problem here is that it has > taken me 20 years to find a client who > agrees with this suggestion :-)) > > Now, when I look at the finished sundial, > people keep coming up to me to ask, "How > do I tell the time, the REAL time?" > > I explain that Babylonian hours and > Italian hours ARE real times but this > is not the answer they want. > > "OK," I have to say, "take the average of > Babylonian and Italian hours and you will > find the time on an ordinary sundial!" > > It is VERY nice to have an Italian Hours > sundial so close to home!! > > Cordiali saluti > > Frank > > -- Mail to : gfme...@gmail.com Lat. 44;38,18.5N Long. 10;56,05.3E
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