We visited Green's Mill in Sneinton. The governor was invented by Christiaan Huygens for this purpose of ensuring the flour was evenly ground. The adjuster arm for the millstone separation has manual control on one end with the T-bar screw and the governor is the automatic control at the other end. As the mill spins faster, the heavy balls are dragged round faster. Their inertia causes increased tension in their angled supports. Since their weight mg=Tsin(theta), where theta is the angle to the horizintal, if T goes up, theta must go down. In other words, the balls tend to be nearer to the horizontal when they go faster. If you look, this would act to pull upwards on that adjuster bar.
