It seems that scientists at the University of Oregon have discovered a way to make liquid droplets walk on their own.
In the phenomenon called the Leidenfrost effect, or film boiling, liquid droplets on a surface heated above their boiling point form an underlayer of vapor, which suspends them above the surface like a hovercraft. Normally, the droplets would move about erratically. However, Professor Heiner Linke and his colleagues have discovered that if “placed on asymmetrically structured surfaces, such as a piece of brass with periodic, saw-tooth shaped ridges” they would self-propel themselves in one direction. And quite literally using their own steam power.
You can see their movies for yourself.
Professor Heiner Linke is not yet certain where the propulsive forces come from, but he has already speculated on how it can be applied: “This method uses heat to pump liquid, and could therefore be used in pumps for coolants, for instance to cool microprocessors. Such a pump would need no additional power (it's run by the heat that needs to be removed anyway), it would have no moving parts, and it wouldn't require a thermostat.”
Of course, I'd like to know if you can construct a landscape feature exploiting this phenomenon. Parks criscrossed by racheted channels heated simply by the Earth or the parking garage underneath, and on these channels, giant film-boiling droplets race past by, indifferent to gravity.
If you turn on the heat, will the Chicago River re-reverses to its original course? Probably not, but I'd like that to see that happen as an annual event.