The Ultra low temperature-differential (ltd) Stirling engine will actually run on the heat of your hand! Place this beautiful precision engine on any warm surface and within a few minutes it's chugging away. The engine runs any time the temperatures of the top and bottom plates differ by more than about 10° Celsius. Its upper black aluminum plate actually absorbs enough heat in direct sunshine to run on solar power. You may also try a cup of hot coffee, your computer monitor ... By placing the engine on some ice cubes, it is even possible to drive the engine by the heat of the surrounding air in the room. This is a great thermodynamic demonstration of air pressure change due to alternate heating and cooling.