Re: What's the inner scale on this photo for?
Or the slot near one end of the adelaide is just to guide the adelaide as it slides back and forth in the internal geared mechanism. Clearly a vertical gnomon had to be present on some part of the adelaide. I think Steve is on the right track. In terms of the screws or pins blocking movement of the adelaide, I think the whole center section (curcular brass plates) pivots along with the adelaide, so that is moot. -Bill again. On Fri, Oct 29, 2021 at 9:24 PM Bill Gottesman wrote: > My two cents: > I have a different guess about the round dial with the indicator. My > guess is that it is a calendar of months, and that turning the indicator to > the correct month adjusts the length of the adelaide to the correct > distance for reading time on the azimuth dial. I do not know what casts > the shadow, but I will guess that Sara is correct, that the slot holds a > vertical vane. > > Being an azimuth dial, the correct declination scale must be used. I see > the circular declination lines, but they are not named. So I think the > pointer of the adelaide is set to the correct circle radius (correct > length) by turning the indicator. > > -Bill > > On Fri, Oct 29, 2021 at 6:04 PM Steve Lelievre < > steve.lelievre.can...@gmail.com> wrote: > >> Thank you, Sara and Patrick for your replies to my question. >> >> I shall try to get to the Science Museum sometime to have a look at the >> dial, if that can be arranged. >> >> I’ve been trying to figure out how the cam that Sara mentioned might work. >> >> I’ve never studied the working of cams and this case isn’t obvious to me >> as there are two inputs, azimuth and declination, that must drive the >> minutes shown. >> >> If anyone can send me an explanation or drawing, it would me much >> appreciated. >> >> Steve >> >> On Mon, Oct 25, 2021 at 19:19, Schechner, Sara >> wrote: >> >>> 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 >>> >>> -- >> Cell +1 778 837 5771 >> --- >> 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?
My two cents: I have a different guess about the round dial with the indicator. My guess is that it is a calendar of months, and that turning the indicator to the correct month adjusts the length of the adelaide to the correct distance for reading time on the azimuth dial. I do not know what casts the shadow, but I will guess that Sara is correct, that the slot holds a vertical vane. Being an azimuth dial, the correct declination scale must be used. I see the circular declination lines, but they are not named. So I think the pointer of the adelaide is set to the correct circle radius (correct length) by turning the indicator. -Bill On Fri, Oct 29, 2021 at 6:04 PM Steve Lelievre < steve.lelievre.can...@gmail.com> wrote: > Thank you, Sara and Patrick for your replies to my question. > > I shall try to get to the Science Museum sometime to have a look at the > dial, if that can be arranged. > > I’ve been trying to figure out how the cam that Sara mentioned might work. > > I’ve never studied the working of cams and this case isn’t obvious to me > as there are two inputs, azimuth and declination, that must drive the > minutes shown. > > If anyone can send me an explanation or drawing, it would me much > appreciated. > > Steve > > On Mon, Oct 25, 2021 at 19:19, Schechner, Sara > wrote: > >> 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 >> >> -- > Cell +1 778 837 5771 > --- > 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?
Thank you, Sara and Patrick for your replies to my question. I shall try to get to the Science Museum sometime to have a look at the dial, if that can be arranged. I’ve been trying to figure out how the cam that Sara mentioned might work. I’ve never studied the working of cams and this case isn’t obvious to me as there are two inputs, azimuth and declination, that must drive the minutes shown. If anyone can send me an explanation or drawing, it would me much appreciated. Steve On Mon, Oct 25, 2021 at 19:19, Schechner, Sara wrote: > 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 > > -- Cell +1 778 837 5771 --- https://lists.uni-koeln.de/mailman/listinfo/sundial
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
