An Unexpected Heat Engine

It's common knowledge that light can produce chemical and electronic changes (photography is based on those effects); however, many people consider light to have no mechanical effect. Some are familiar with the novelty of a radiometer that spins when placed in the light. Fewer are aware that a cymbal will vibrate audibly if hit by the light from a camera flash.1 It came to our attention that the bubble in an ultra-sensitive level would move toward a flashlight beamed at the level from one end. Our investigations of this phenomenon show that it is thermal in nature and the effect large enough to be demonstrated in a classroom. With the addition of a small heating wire, the bubble level can be converted into a small heat engine.