Chladni plate, Science Teaching Collection

„This instrument was used in an Ohio high school and probably dates from the late 19th or early 20th centuries. The replication of classic experiments was a common way to teach science at this time, and Chladni’s figures were considered to be both instructive and beautiful. 

To “play” this instrument, first sprinkle a thin layer of sand (or salt) on it and then activate the plate by bowing the middle of one edge with a well-rosined bow. A pattern will quickly form because, as the plate vibrates, the sand on the moving areas bounces off and accumulates on the places that aren’t moving (the “nodes”). With a little practice it becomes easy to produce the plate’s “fundamental” tone and this forms the sand into a large “X” that covers the entire plate. Bowing harder and faster on the same place produces a much higher tone and creates a more detailed pattern that has more nodes and smaller open spaces.“

Source: Steven Turner; Curator, Physical Sciences, National Museum of American History, Smithsonian Institution. 

Picture: Steven Turner

http://americanhistory.si.edu/science/