Steam Engine Centrifugal Governor
This is a Jas. Barclay Automatic Governor Stop form Allis-Chalmers
A centrifugal governor is a specific type of governor that controls the speed of an engine by regulating the amount of fuel (or working fluid) admitted, so as to maintain a near constant speed whatever the load or fuel supply conditions. It uses the principle of proportional control.
Saw this old technology during a lunch stop in McCloud, California; on my way to Lake Tahoe