A verge and foliot is a clock reduced to its simplest elements. A suspended mass M provides a torque that drives the verge and foliot escapement (at top) alternately in one direction and then the other.
The verge and foliot escapement mechanism permits a mathematically simple illustration of a dynamical system exhibiting a limit cycle and stability. Similar to the previous exercise in the construction of the astrolabe and Alberti’s map of Rome, the Verge and Foliot Escapement follows a mathematical logic. One can determine time by the dial’s position or the mass’s location above the ground.
The beauty lies in the physical connection to the surrounding world. The clock is gravity-driven and one could sense this connection as the mass drops. Like how the astrolabe relate to the heavenly bodies, the Verge and Foliot relate to the earthly body.
The suspended weight causes the gear wheel to rotate. This rotation brings a peg into contract with one of the pallets. The rotation brings a peg into contact with one of the pallets, causing the verge and foliot escapement to rotate. By the time that the escapement rotation has reached angle P, the right gear wheel has disengaged the right pallet, and now the left gear wheel engages the left pallet, causing the escapement to rotate in the opposite sense. Because of the inertia provided by the foliot masses, the gear wheels’ rotation is interrupted. The result is a regular oscillation of the escapement and a slow rotation of the gear wheels.