In 1816, Scottish inventor Robert Stirling patented an alternative to the steam engine. His closed-cycle engine runs on pressure created by air moving back and forth between heat exchangers. An external heat source warms one exchanger, causing the air inside it to expand into the cold heat exchanger, pushing a piston. The air then cools and contracts, pulling back the piston, which pushes the air back into the warm heat exchanger, restarting the cycle.
Though Stirling's engine was more efficient and ran at lower pressure than early steam engines (which exploded occasionally), it proved impractical for industrial use and was supplanted as steam engines improved. There is now resurging interest in Stirling's invention, since it runs on any heat source, including alternative energy such as solar or geothermal. This kit is not just a technical marvel; almost a form of moving sculpture it is satisfying to build and mesmerizing in action.
Though it works on the same principle as any Stirling engine, this modern adaptation requires only a low energy input. It can run on top of a mug of hot liquid or a bowl of ice, from the heat of a desk lamp or in warm sunshine. It exploits the temperature difference between the top and bottom discs, which function as heat exchangers. Manufactured in England from brass, aluminum and acrylic, the parts are carefully finished and fit to exacting tolerances.
The kit is easily assembled in under an hour with only #0 Phillips and 1/8" slot screwdrivers. Finished engine stands about 5 1/4" high.