Chladni Plates

Invented by German physicist Ernst Chladni in the late 1700's to illustrate the patterns of two  dimensional sound waves.  They are created by stroking a bow against the edge of a steel plate that is covered with a thin layer of sand.  The plates' unique vibrations will cause the sand to move and settle in various nodal patterns; nodes are the points of absolutle zero vibrations.  The more complex the vibration is, the more elaborate the resulting pattern will be.  Chladni Plate techniques are commonly used to aide in the design of acoustic instruments such as violins, guitars, and cellos. 

I love that when I'm searching for something in Google Images, I often stumble upon something wholly unrelated yet amazing.  Chladni plates are one of these.  They have a couple videos online showing the technique in motion which are pretty cool.