A perpetual motion machine would use kinetic energy and potential energy to replenish itself and keep moving. An example would be a highly efficient pendulum. However, the air resistence eventually slows it down. The perfect perpetual motion machine has never been found.
Reading the comments from
The Dome Did Not Work
http://www.dailykos.com/...
there is a lot of methane on the ocean floor which is released into the atmosphere naturally in various ways, sometimes in giant methane bubbles that kill people.
At low temperatures and high pressures, it turns into a solid. When it changes from solid to gas (melts) it increases in volume.
Can the force released by this change in volume be used to drive a generator? Obviously, the methane could not be released into the atmosphere.
Since the frozen methane is a form of potential energy, you could generate electricity just by warming it to surface temperatures, which is abundant and seems an efficient trade. This might be a truly perpetual motion machine.
It would be mechanical, not chemical. The methane hydrate would be drawn into a piston, warmed and cause a force during the expansion, like in a car engine. The released methane would be captured and gravity would carry it back down to the ocean floor where it would refreeze.
Here is a link to the wiki page:
http://en.wikipedia.org/...