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
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