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I will begin this article with phenomena visible on an ordinary triangular prism. Consider the following experiment: in a room, in which direct sunlight enters, we hold the prism with the refracting angle downwards. With the other hand we hold a white sheet of paper behind the prism. When the sheet is very close to it, we see only a regular bright rectangle without any colors. As we move the sheet away from the prism, then a violet-cyan band appears on the upper edge of the rectangle, while a yellow-red band on the bottom edge (image below). We see that the yel