This exhibit consists of four different sets of images. Each image is printed twice, once on clear plastic and once on white paper. The matching images are to be used together. If a pair of matching images are overlaid perfectly, one copy of the image is seen. If they are even slightly offset relative to each other, then the result is not a clear image but a combination of the two. And if one of the matching images is moved relative to the other, then a moving interference pattern is observed.
Two different sets of images are hung with a small gap between the two copies of each image. This small gap means that as one walks past the offset between the two images changes, creating the moving interference pattern.
One possible use of Moire patterns is to "see" what is normally invisible. For example, x-rays travel as a wave pattern with a crest and a trough, just like a wave on the ocean. A scientist studying x-ray emissions from a distant star would expect the intensity of the x-ray to rise and fall regularly like a wave. The Moire pattern of many thin circles could represent such x-ray emissions - the solid black line could represent the x-ray maximum (wave crest) and the white or clear area between black lines could represent the x-ray minimum (wave trough). But what should be expected if there are two stars close together, both emitting x-rays. The interference pattern resulting from the combination of these two sources can be represented by slightly offsetting the two Moire images. Moire patterns are an important consideration for color printing. Color printing requires taking a separate picture of the original for each of the colors black, magenta, yellow and cyan. In order to prevent creation of a Moire pattern in the printed result, the original must be rotated before each of these pictures is taken.
When machinists are working metal, they often must remove a very small amount of material, perhaps a few thousands of an inch. The metal being worked might be attached to the machine bed, and the tooling head then is moved the necessary amount. Using the naked eye and scale, one cannot see a movement on a ruler of just a few thousands of an inch. Instead, a Moire pattern was used to make an accurate movement. A metal plate with very fine lines was attached to the bed of the machine, and a glass plate with the same pattern of very fine lines was overlaid on the metal plate. This glass plate was twisted ever so slightly, and was attached to the tooling head. As the head was moved, interference lines ran across the overlapping plates and indicated the amount of movement.