James Watt’s flyball governor is where automatic control was born. Two weighted balls spin on a steam engine’s shaft; spin too fast and centrifugal force flings them outward, which closes the throttle, which slows the engine — a machine that reins in its OWN speed. Load it heavier and it settles a touch slower but holds near its setpoint. It gave us the word ‘cybernetics.’ Slide the load and watch it self-regulate.
Watt’s centrifugal governor (1788) is a mechanical feedback loop: flyweights on the rotating shaft rise with speed (centrifugal force ∝ ω²), and their rise mechanically CLOSES the steam throttle, reducing torque and hence speed — negative feedback that holds engine speed near a setpoint despite changing load. Add load and the speed dips slightly, the flyballs drop, the throttle opens, and it recovers to a new steady speed just below setpoint (the small residual droop is the P-controller offset again). Maxwell’s 1868 analysis ‘On Governors’ founded control theory; Wiener named the field cybernetics (Greek kybernetes, the steersman). A fail-loud self-check throws unless the regulated speed stays near the setpoint across a range of loads. ◆ real control theory, node-verified.
A lumped negative-feedback model of the governor (the exact speed-regulation and load-droop behaviour); the real device can hunt/oscillate if under-damped (Maxwell’s actual concern) — the machine-reins-in-its-own-speed mechanism is exact.