The following link has some interesting history on the developement of the steam engine; for those of us who enjoy reading about the history of steam power and its contribution to economic growth. This article is written by William Rosen author of THE MOST POWERFUL IDEA IN THE WORLD: A STORY OF STEAM, INDUSTRY AND INVENTION.
http://www.bloomberg.com/news/2012-09-11/how-matthew-murray-s-sliding-d-valve-made-us-prosper.html