Fill the jar or glass with water.
Place the mirror inside the water filled jar or glass.
Tilt the mirror slightly upward.
In a very dark room with white walls, shine the flashlight onto the mirror.
A rainbow will appear! (Note: If no rainbow appears at first, just change the angle of the light from the flashlight or change the angle of the mirror.)
The mirror reflects light that passes back through the water, traveling at an angle. The water bends, or refracts, the light. As the light bends, it separates into the colors of the rainbow...red, orange, yellow, green, blue, indigo and violet.