Two front surfaced mirrors apout 4 inches long and an inch and one-half high are mounted so as to rotate about the line of intersection of their planes. The gap between the intersection of the mirrors is less than 1/64th inch. The angle between the mirrors can be varied from slightly over 90° down to about 12°. A very small flashlight bulb is placed in the space between the mirrors. The students are asked to count the number of images that can be observed as a function of angle. If this small flashlight bulb is placed very close to the surface of one of the mirrors, it is possible to observe the way in which the number of images increases by two whenever the angle between the mirrors has become ever-so-slightly less than π over an integer.