RE: What's the inner scale on this photo for?
Hi Steve, The photo of the azimuth dial is hard to read. I don't know what screws you are talking about preventing the arm from turning. The arm is backwards at the moment since the pointed end should be on the scale of hour lines. I am not convinced that there is a flap on the square end of the arm for a vane. The sun at most angles would not fall far along the arm to reach the other end where the slot is. Rather, I suspect there was a vertical gnomon in the slot at the pointed end. Its shadow could have been aligned with the point so that the point was in line with the sun's azimuth. As for the round dial, it almost always shows minutes and is geared to the rotation of the arm. That's my best guess. Sara -Original Message- From: sundial On Behalf Of Steve Lelievre Sent: Monday, October 25, 2021 1:22 PM To: Sundial List Subject: What's the inner scale on this photo for? Hi, Today a website called Vermont Free Press published an appallingly confusing (to me) summary of types of sundials. If you can bear to look, it's at https://www.vermontpressbureau.com/types-of-sundials/ However, there was one thing about it that piqued my interest: the photo of an azimuth sundial ( https://www.vermontpressbureau.com/wp-content/uploads/2021/10/Azimuthal.jpg ). From what I can make out, there is a metal flap at the end of the alidade / sighting arm (the end at top in the photo). It must get turned up to make a shadow-caster. I guess the arm has to be rotated so that the shadow falls along it, and time is then read from where the right-hand edge of the arm crosses the net of hour and declination lines. But then, wouldn't the screws seen in the upper plate block the arm from being turned to the required orientation? Another bit I can't figure is the little circular scale just north of the centre of the dial, with the pointer. Perhaps just an Equation of Time scale? Or perhaps a cam connects it to the arm so that it can be used to set the arm's length? (The slot in the arm suggests it can be slid in and out to set the tip at the applicable declination circle, which is a nifty feature.) Cheers, Steve --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: What's the inner scale on this photo for?
I'm afraid I can't give you any answers , but the original is in the Science Museum, London. They don't give any clues either, but I guess you could contact them https://collection.sciencemuseumgroup.org.uk/objects/co143/azimuth-sun-dial-simple-azimuth-sundial Best wishes, Patrick Vyvyan On Mon, 25 Oct 2021 at 14:23, Steve Lelievre < steve.lelievre.can...@gmail.com> wrote: > Hi, > > Today a website called Vermont Free Press published an appallingly > confusing (to me) summary of types of sundials. If you can bear to look, > it's at https://www.vermontpressbureau.com/types-of-sundials/ > > However, there was one thing about it that piqued my interest: the photo > of an azimuth sundial ( > https://www.vermontpressbureau.com/wp-content/uploads/2021/10/Azimuthal.jpg > ). > > From what I can make out, there is a metal flap at the end of the > alidade / sighting arm (the end at top in the photo). It must get turned > up to make a shadow-caster. I guess the arm has to be rotated so that > the shadow falls along it, and time is then read from where the > right-hand edge of the arm crosses the net of hour and declination > lines. But then, wouldn't the screws seen in the upper plate block the > arm from being turned to the required orientation? > > Another bit I can't figure is the little circular scale just north of > the centre of the dial, with the pointer. Perhaps just an Equation of > Time scale? Or perhaps a cam connects it to the arm so that it can be > used to set the arm's length? (The slot in the arm suggests it can be > slid in and out to set the tip at the applicable declination circle, > which is a nifty feature.) > > Cheers, > > Steve > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
What's the inner scale on this photo for?
Hi, Today a website called Vermont Free Press published an appallingly confusing (to me) summary of types of sundials. If you can bear to look, it's at https://www.vermontpressbureau.com/types-of-sundials/ However, there was one thing about it that piqued my interest: the photo of an azimuth sundial ( https://www.vermontpressbureau.com/wp-content/uploads/2021/10/Azimuthal.jpg ). From what I can make out, there is a metal flap at the end of the alidade / sighting arm (the end at top in the photo). It must get turned up to make a shadow-caster. I guess the arm has to be rotated so that the shadow falls along it, and time is then read from where the right-hand edge of the arm crosses the net of hour and declination lines. But then, wouldn't the screws seen in the upper plate block the arm from being turned to the required orientation? Another bit I can't figure is the little circular scale just north of the centre of the dial, with the pointer. Perhaps just an Equation of Time scale? Or perhaps a cam connects it to the arm so that it can be used to set the arm's length? (The slot in the arm suggests it can be slid in and out to set the tip at the applicable declination circle, which is a nifty feature.) Cheers, Steve --- https://lists.uni-koeln.de/mailman/listinfo/sundial
