Cataract (beam engine)

Okay kiddo, a cataract is a part of a big machine called a beam engine. The beam engine is like a really big see-saw that helps pump water out of mines or do other important work. The cataract is a special valve that helps control the flow of steam that makes the machine work. It's kind of like the knob on your bathtub that you turn to control how much water comes out. Without the cataract, the beam engine wouldn't work quite right and things could get pretty messy!