A pendulum clock is a clock that uses a pendulum, an oscillating weight, as a timekeeping element. From its invention in 1656 by Christiaan Huygens until the 1930s, the pendulum clock was the most accurate timekeeper in the world. Pendulum clocks had to be stationary and level (mounted perfectly straight) to work. Any movement or acceleration will affect the movement of the pendulum causing the pendulum to lose or gain speed and beat. Antique pendulum clocks are now mostly preserved for their decorative and antique value.
Galileo and his son came up with the idea of a pendulum clock in 1637, but neither lived to finish it. The introduction of the pendulum greatly increased the accuracy of clocks from about 15 minutes per day to 15 seconds per day, leading to their rapid spread, replacing older models.
Early pendulum clocks had wide pendulum swings of up to 100° due to their escapements on the edge. In his 1673 analysis of pendulums, Huygens showed that wide swings made the pendulum inaccurate. Watchmakers realized that only pendulums with small swings of a few degrees were isochronous, prompting the invention of the anchor escapement around 1670. This design reduced the swing of the pendulum to 4°-6°. In addition to increased accuracy, this allowed the watch case to accommodate longer, slower pendulums, which required less power and caused less wear and tear on the movement. The Seconds Pendulum (also called the Royal Pendulum) in which each swing lasts one second, which is about one meter (39.37 in) long, became widely used. The long, narrow clocks built around these pendulums, first made by William Clement around 1680, became known as tall case clocks and later, grandfather clocks. The increased accuracy resulting from these developments led to the addition of the minute hand to clock dials around 1690.
History of the pendulum clock
The deadbeat escapement invented in 1675 by Richard Towneley and popularized by George Graham around 1715 in his precision regulator clocks gradually replaced the anchor escapement and is still used in most modern pendulum clocks. The observation that pendulum clocks slowed down in the summer led to the realization that the thermal expansion and contraction of the pendulum rod with temperature changes was a large source of error. This was solved by the invention of temperature compensated pendulums. The mercury pendulum by George Graham in 1721 and the grid pendulum by John Harrison in 1726. Using vials of mercury on the base of the pendulum, the mercury would expand or contract to “compensate” for temperature differences, making the pendulum more accurate. By the mid-1700s, precision pendulum clocks achieved accuracy of a few seconds per week.
More accurate pendulum clocks, called regulators, were mostly installed in public areas and used to schedule work and set other clocks.
Pendulum clocks remained the world standard for accurate timekeeping for over 270 years and were used as the standard until the invention of the quartz clock in 1927.