Chladni patterns are visual representations of the nodes of vibrations setup in the a surface while it is subject to a specific frequency.  This and more on modern acoustics is found in Chapter 5 of Erik Jansson’s publication “Acoustics for Violin and Guitar Makers” here.  A good overall description of Chladni patterns can be found on the New South Whales University website here.

Ernst Florens Friedrich Chladni has been around a while and published a book on the patterns seen in vibrating plates in 1787.  His original publication is on Google Books here, however, a knowledge of old German and a Ph.D. in physics are prerequisite.  It’s reported that his interests in the patterns were inspired by George Christoph Lichtengberg’s earlier experiments on electrical figures[1].  Interest in this visual representation of sound waves was such that Chladni demonstrated it for Nepolean in 1809[2].  A plate of the image of Chladni is seen below [2].