[Bleep]

This site is good, it has animates of the various steam engines:

http://www.makingthemodernworld.org.uk/ ... /03.ST.02/

I like how much refinement went into the Trevithick engine over the Watt engine. The Watt engine was based on sound principles but the way they were carried out was just absurd. The cord with the two levers that have four valves between them were replaced by one little rotary valve that accomplished the same purpose.