Hi John, I had to walk my room a number of times to know the answer but I think I do now.
The glass panes add an error in the reading of the dial. As long as you don't change the thickness of the panes the x,y shift of a certain point is constant in values. Increasing the distance between the panes enlarges the dimensions of the sundial pattern. So relative the x/y shift has less effect on the reading and the error decreases. The same happens if you enlarge the distance from the outside pane to the index on the gnomon. Then also the dials dimensions increase and the error decreases. This is also an answer to Karons question about changing the thicknes of the glass panes. Then the x/y shift increases in values and an extra error is aded. Best wishes, Fer. Fer J. de Vries De Zonnewijzerkring http://www.de-zonnewijzerkring.nl Molens http://www.collsemolen.dse.nl Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: John Carmichael To: [email protected] Sent: Thursday, August 04, 2011 4:13 PM Subject: RE: mock stained glass sundial Thanks for checking on that Fer, making a drawing, and for correction my assumption. You taught me not to assume anything! I have a question though- Does the refraction error increase if the distance between the two glass panes increases? From: fer de vries [mailto:[email protected]] Sent: Thursday, August 04, 2011 1:29 AM To: Mike Shaw; [email protected]; 'John Carmichael'; [email protected] Subject: Re: mock stained glass sundial Mike, Your question: ***** If you are going to allow your shadow to pass through two panes of glass, will refraction start to become important? ***** John Carmicael answered: ***** It's insignificant. ***** My answer is: It is significant. Your statement is: .... shadow to pass through two panes of glass .... This means that the gnomon is at the outside of the double glass and the sundials pattern is at the inside of the double glass. As an example I calculated such a vertical south facing dial for latitude 45 degrees with hourlines and datelines. The double glass has panes of 5 mm and the space between is 15 mm. Rather normal values. The glass has a refraction index of 1.4 For the index for the datelines I have chosen a distance from the glass of 20 mm. I assume the refraction index of the space between the panes is 1. (No refraction). The pattern of the sundial is attached and shows a significant shift, especially for the datelines. (It is only 16 kB and should pass.) Black lines are without refraction, blue lines with refraction. Best wishes, Fer. Fer J. de Vries De Zonnewijzerkring http://www.de-zonnewijzerkring.nl Molens http://www.collsemolen.dse.nl Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: Mike Shaw To: [email protected] ; 'John Carmichael' ; [email protected] Sent: Wednesday, August 03, 2011 5:28 PM Subject: Re: mock stained glass sundial If you are going to allow your shadow to pass through two panes of glass, will refraction start to become important? Mike Shaw 53º 22'N 03º02'W www.wiz.to/sundials ---------------------------------------------------------------------------- --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial ------------------------------------------------------------------------------ --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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