I was watching a movie from the 1930's yesterday, and it showed a steam engine pulling a train out of the station. I noticed that the smoke coming out of the smokestack was in synchrony with the steam coming out of the cylinders that drive the wheels. There was definitely a "puff" "puff" coming out of the smokestack. Since this movie was from the 1930's, I assume that it was an authentic movie of a real steam train, and not some special effect. Forgive me, but I always thought that train smoke stacks were more analogous to ocean liner smoke stacks, where the smoke coming out is *not* under pressure. I can only speculate that some steam engines might have a *fan* (or equivalent) that forced cool air through the burning coal. Since early steam engines didn't have electricity, these "fans" would have to be something more akin to the old-style *belt-driven* engine fans on automobiles. Or perhaps there is some sort of reciprocating *air pump* attached to the steam engine that pumps air through the coals in synchrony with the main steam cylinders?