How did the centrifugal governor control the speed of James Watt’s engine?

James Watt applied the centrifugal governor to his steam engine to provide automatic speed control. The device functions by utilizing two rotating masses (balls) attached to a vertical spindle driven by the engine.12

As the engine's speed increases—often due to a decrease in load—the centrifugal force causes these balls to move outward. This physical movement is transmitted to a valve mechanism that regulates the supply of steam to the engine. By reducing the amount of steam admitted when the engine runs too fast, the governor effectively lowers the engine's speed to maintain it within desired limits. Conversely, if the engine load increases and the speed drops, the balls move inward, allowing more steam to enter and increasing the engine's power. This mechanism ensured consistent operation, which was essential for the diverse industrial applications of Watt's rotative engine.23