I Learned Some More About the Longcase Clock
Prior to 1670, pendulum clock movements used an older verge escapement mechanism, which required very wide pendulum swings of about 100 degrees.
(The verge (crown wheel) escapement is the earliest known type of mechanical escapement. It is the mechanism in a mechanical clock that controls its rate by moving forward the gear train at regular intervals or 'ticks'. The origin is unknown. At the heart of every clock are oscillating instruments for recording or keeping time. The invention of the verge escapement has an important role in the history of technology. It made the invention of all mechanical clocks possible. This moved the processes of time keeping from the flow of liquid in water clocks (continuous process) to pendulum clocks (oscillatory process). Time keeping became more accurate.)
Most clocks had short pendulums to be contained within a case. Long pendulums with such wide swings were used in open clocks usually outside. The anchor mechanism reduced the pendulum's swing to around 4° to 6°. This allowed clockmakers to use longer pendulums, which had slower "beats". These needed less power to keep going. They had less friction and wear in the movement, and were more accurate.
Most longcase clocks use a seconds pendulum ("Royal" pendulum). These are about 39 inches long.
(A seconds pendulum takes 2 seconds to make the full swing. In 1670 the seconds pendulum was employed by William Clement in his improved version of the original pendulum clock by Christian Huygens. An interesting factoid is that in Britain around 1855, the British ‘yard’ was defined as a specified fraction of the length of the seconds pendulum.)
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