I. The push of steam

Boil water in a closed vessel and the steam presses outward on everything — including anything free to move. Give it a piston, and the pressing becomes pushing. The rule is simple bookkeeping: the force on the piston is the pressure times the piston's area. Twenty pounds on every square inch of a twenty-inch piston is three tons of push, from nothing but fire and water. Every engine in this museum, from 1712 to 1908, is a scheme for collecting that push over and over again.

One chapter of nine. Read the whole Primer, or work the engines themselves.