VII. The governor

A mill's load changes by the minute, and nobody wants to stand at the throttle all day. Watt's answer: two spinning balls that rise as the engine speeds and, in rising, close the valve. This is feedback — the machine steering itself — a century before the word. Corliss's refinement was to let the governor set the cutoff instead of strangling the steam through a half-shut throttle: full pressure always, admitted for exactly as long as the load deserves. Drag the load about and watch the cutoff answer while the speed barely stirs.

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