Escapement An escapement in mechanical clocks and watches is a mechanism comprising an escape wheel and an anchor. It maintains the swing of the pendulum by giving it a small push for each swing, thus allowing the timepiece’s wheels to advance a fixed amount with each swing, moving the clock’s hands forwards. During this process, the escapement releases the tooth of a gear, therefore changing a ‘locked’ state to a ‘drive’ state until the opposite arm strikes another tooth on the gear, which locks the gear again. The clock’s audible ‘tick’ is the sound of the going train stopping as the escapement locks. Its push is driven by force from a coiled spring or a suspended weight, transmitted through the timepiece’s going train. The escapement also overcomes friction losses whether the oscillator is a pendulum or a spring balance wheel. Foliate and balance-wheel escapements are examples of pre-pendulum escapements in early clocks, such as the Gothic Iron Wall Clock made around 1500 and exhibited on Clocktime. These were inexact time regulators, as their early going trains did not have a true oscillator (such as a pendulum or spring-balance wheel) and instead relied on friction or inertia. Thus, the foliate and early balance-wheel timepieces had their pseudo periods increased or decreased with the increase or decrease in friction, temperature, air density, driving weight or spring force, hence their poor timekeeping. The pendulum was the first true oscillator with a natural period (although even a pendulum changes its period with amplitude). Pendulum escapements include the verge, anchor or recoil, the dead-beat, the grasshopper, the duplex and many more. The main watch escapements include the verge, the spring detent, the pivoted lever invented by Thomas Mudge, and the spring lever devised by Thomas Earnshaw and John Arnold (created independently of one another) as well as a plethora of variants.
