Centrifugal governor

They are also found on stationary internal combustion engines and variously fueled turbines, and in some modern striking clocks.

The governor is connected to a throttle valve that regulates the flow of working fluid (steam) supplying the prime mover.

The rate of working-fluid entering the cylinder is thus reduced and the speed of the prime mover is controlled, preventing over-speeding.

Centrifugal governors were invented by Christiaan Huygens and used to regulate the distance and pressure between millstones in windmills in the 17th century.

They are also found on stationary internal combustion engines and variously fueled turbines, and in some modern striking clocks.

In 1868, James Clerk Maxwell wrote a famous paper "On Governors"[6] that is widely considered a classic in feedback control theory.

In his famous 1858 paper to the Linnean Society, which led Darwin to publish On the Origin of Species, Alfred Russel Wallace used governors as a metaphor for the evolutionary principle: The action of this principle is exactly like that of the centrifugal governor of the steam engine, which checks and corrects any irregularities almost before they become evident; and in like manner no unbalanced deficiency in the animal kingdom can ever reach any conspicuous magnitude, because it would make itself felt at the very first step, by rendering existence difficult and extinction almost sure soon to follow.