English: Verge and foliot escapement mechanism from the De Vick (De Wyck) clock, built 1379 in Paris by Henri De Vick. An escapement is the mechanism in a mechanical clock that gives the balance wheel a push with each swing, to replace energy lost to friction and keep it moving, and releases the wheel train to move forward a fixed amount with each swing, moving the hands forward at a steady rate. The verge escapement (bottom) drives the foliot (top), a primitive timekeeper consisting of a horizontal bar with weights on each end, to oscillate back and forth. The rate of the clock can be adjusted by moving the weights in or out on the bar. The verge and foliot mechanism is important in the history of technology because it was the earliest escapement, and its invention in the late 13th century led the the first mechanical clocks. The De Vick clock is one of the first of these early clocks for which there exists detailed drawings of its mechanism. None of the actual mechanisms of the clocks of this era has survived unaltered to the present day.