Sterling Engines are often called external combustion engines. The heat source is external to the engine, unlike an internal combustion engine, where the heat source is inside the cylinders. In this case, heat was delivered via the hot water sitting in the mug that the Sterling Engine was placed upon. I walked up the shutter speed from my initial guess until I could see the blurred spokes of the flywheel, and adjusted aperture for the light as I went.
