I have wondered for a while if it was possible to make use of the two panes of glass in double glazed units to make a window sundial.
To try out the concept, I made a prototype dial using two panes of glass, clamped 44mm apart (I just happened to have some wood that thickness). The pane nearest to the sun carries a double arrow which acts as the gnomon nodus. The inner glass carries the dial face. The dial was designed for a site which declines 76 degrees West of South - the back of my house. I used Francois Blateyrons Shadow programme - Version 6.2.1 I have put a picture on my web page - follow the link to "Double Glazing Dial" - there is a link to Jim Tallman's single glazing dial there as well. The frosting was applied from a spray can, and the clear areas were simply masked off. For the lines, I used Magic tape - the type that doesn't show up on photocopiers, cut into thin strips using a straight edge and craft knife. The numbers were made by removing the frosting using a stencil and Dremel drill fitted with a flexible drive shaft. In this dial, I frosted both the "inside" faces, so there is no glass between the nodus and the dial face. Hence, no refraction problems. But in the real thing I would have to use the outside surfaces, and account would need to be taken of the refraction of two panes of glass. The effect would change throughout each day, and through the seasons. The dial would also be smaller, the gap between the panes in my units is only 20mm. A quick test (sticking OHP film on the windows) shows that errors of about 15 minutes at the extremities - I guess the varying error is related to the changing angle of incidence of the sunlight. My mathematics isnt up to the three dimensions involved - can anyone help? Mike Shaw mailto:[EMAIL PROTECTED] http://homepage.ntlworld.com/jmikeshaw/ N 53º 21' 24" W 03º 01' 47" Wirral, UK. -
