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Mike,

If you have 2 polaroid sheets and a quarter wave sheet, you might 
experiment with setting up the polaroid sheets crossed with the quarter 
wave sheet between then, then put some glass between them - it should be 
black when of uniform temperature.  Then, differentially heat the glass 
- even some sheet glass - and see if you can demonstrate stress lines in 
the glass.  I believe that it should work.

Good luck!  Peter Anderson

-- 
1449 Grant Street, Victoria  BC  V8R 1M4
T/F  250 592 3332
Cell 250 885 6724

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