James Watt's crucial improvements to the steam engine have rightly dominated biographical works about him, but this has generally been to the exclusion of most of his other inventions and discoveries. The invention for which he is best remembered is the addition of the separate condenser to the New- comen engine. Not only did this make a much more powerful and economical engine, but it led to his development of the steam engine from a machine that could only pump water into one that could turn rotating machinery directly.