This is an attractive table-top model of the fascinating Stirling Engine. The Stirling engine is a heat engine and is much more efficient than an internal-combustion engine that is often used in cars. The engine uses a system called the Stirling Cycle. The Stirling Cycle uses an external heat source, in our case it is a small alcohol lamp, but it can be almost anything that produces heat. The engine operates without an exhaust system and without combustion taking place. Thus, it is quiet and efficient. The gas sealed inside the engine (in our case test tubes) never leaves the system. By changing the temperature of the gas inside the engine, the pressure is changed, and that pressure is used to do all the engine’s work.