If you've ever seen strange concentric ring patterns show up when two panes of glass are pushed together, you've seen Newton's rings. Most people see them as evidence of the wave nature of light. Newton, however, did not.

You've most likely made a set of Newton's rings by accident. Perhaps you've set down a lens from your glasses on a reflective surface. Maybe you've put two pieces of glass on top of each other and one was slightly curved. Whatever happened, you probably noticed the light and dark bulls-eye pattern formed by the two pieces of glass. Those are Newton's Rings.

Light rebounds from both the exterior and interior of a surface. We're used to the fact that when light moves from the air to a piece of glass, that transition reflects some of the light back. When light moves from the glass to the air, that transition also reflects back some light. Although different curves can form a ring pattern, to form Newton's Rings, you generally put a convex piece of glass face-down on a flat piece of glass. The light coming to your eye will come from two sources, the light bouncing back off the interior of the convex glass - off the "bottom of the bowl" - and the light bouncing back from the top of the flat piece of glass. Think of those two bits of light coming back as two waves.