Cymatics is a study of visible sound and vibration. It is bothered with the study of modal phenomena and retitled Cymatics by Hans Jenny, a Swiss medical doctor and pioneer of this field.
Galileo Galilei, though, was an earlier one who observed a phenomenon like this:
As I was scraping a brass plate with a sharp iron chisel in order to remove some spots from it and was running the chisel rather rapidly over it, I once or twice, during many strokes, heard the plate emit a rather strong and clear whistling sound: on looking at the plate more carefully, I noticed a long row of fine streaks parallel and equidistant from one another. Scraping with the chisel over and over again, I noticed that it was only when the plate emitted this hissing noise that any marks were left upon it; when the scraping was not accompanied by this sibilant note there was not the least trace of such marks.
Cymatics, from the greek ‘kima’ (κύμα) which means wave, was explored by Hans Jenny in 1967 in his book Kymatik, which has to do with visual display of sound. He used standing waves, piezoelectric amplifiers an other methods and materials