1. The problem statement, all variables and given/known data This is less of a calculation and more of a observation problem: Our teacher shined a sodium light on top of two stacked pieces of translucent glass. We then had to bend down to get eye level with the stacked glass. When we did this you could see dark ( concentric?) rings reflecting off of the glass....sort of like contour lines on a map. When we pressed the two pieces together the lines straightened out until they were all parallel. What is going on here? 2. Relevant equations: It has something to do with thin film interference..... Maybe the equation 2T = (n + 1/2 )λ is involved 3. The attempt at a solution Im pretty lost here. Thanks in advance for any responses.