http://en.wikipedia.org/wiki/Newton_rings
I found a wikipedia article about newton rings.
The picture shows the phenomenon that I thought of as Newton rings prior to my recent experiment. I have seen them on scans when I scanned a negative in direct contact with the scanner glass. My rings didn't really look like the picture. But they looked exactly as the article describes them:
<x-tad-bigger> When viewed with a </x-tad-bigger><x-tad-bigger>monochromatic light</x-tad-bigger><x-tad-bigger> it appears as a series of concentric, alternating light and dark rings centered at the point of contact between the two surfaces.
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