First watch how awesome ferrofluid is, then stick around for the science.
And how cool is this?:
Ferrofluids are colloidal liquids made of nanoscale magnetic particles suspended in a carrier fluid (usually an organic solvent like kerosene or water). Each tiny particle is thoroughly coated with a surfactant to inhibit clumping.
When a ferrofluid fluid is subjected to a strong vertical magnetic field, such as the one produced by a small bar magnet when placed underneath the ferrofluid, the surface forms a regular pattern of peaks and valleys. This effect is known as the normal-field instability.
When you see the “spikes” that form in a ferrofluid, what you are seeing are the concentrations of the magnetic field in the fluid. Because the fluid is more easily magnetized than the surrounding air, the field concentrates in the spikes and, depending on the strength of the field, carries the spikes out into space as far as possible before transitioning to the air. The magnetic field lines are in this sense represent themselves in the fluid, making the invisible visible.
However, the spikes will only form after the magnetic field reaches a certain strength (although it is comparatively low) and even then the spikes have to fight against gravity and surface tension. The balance of all of these forces determines what the spikes will look like, and how big they get.
While all of the science is awesome, all I can think about when I see these videos is the recombination of that metal/mercury Terminator.
Go to PopSci to learn how to make your own ferrofluid on the cheap.
Here are more ferrofluid videos.