Mercury + Sound = Kooky Mad Science Party
Now let's watch what happens when you take a blob of mercury and subject it to different audio frequencies. Spoiler alert: the mercury forms geometric shapes and appears to dance. This is slow-motion footage (with music added, not the tones the mercury is reacting to -- we'll get to those original tones in a moment):
Okay, so what happened there?! I spoke to photographer Nick Moore about how this was filmed. (My suspicion was that he might be building a T-1000.) He wrote:
The mercury is sitting in a concave plastic lens from an old projection TV (it was convenient), the lens is stuck to a 12inch speaker using Silly Putty to stop it from rattling around or bouncing. The tone is a pure sine from an old signal generator (1960s) I believe it was between 10Hz and 120Hz. The higher the frequency the more nodes (bumps) appear on the mercury. They are actually 3 dimensional standing waves.
And here's the video in regular speed, with the original tones, so you can see how crazy this really is:
This phenomenon is part of a discipline called cymatics, the study of visible sound and vibration. According to Wikipedia, observations of these kinds of effects date back to Galileo and Hooke, among many others.
See also: Cymatics: Making Sound Visible, 600-Year-Old Music Found Encoded in Chapel Walls, and Burning Matches in Slo-Mo. I also recommend checking out Moore's YouTube channel for tons of great stuff like this.