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"Another form is called the polyangular kaleidoscope. The only essential difference in it is that the mirrors are so arranged that the angle between them can be varied at pleasure. This, being very useful for illustrating the theory of the instrument, is the form usually found in collections of philosophical apparatus." —The Encyclopedia Britannica, 1910

Polyangular Kaleidoscope

"Another form is called the polyangular kaleidoscope. The only essential difference in it is that the…