How A Pendulum Works to Keep Time

Up until about the 16th Century, time keeping was approximate at best. There were the beginnings of mechanical clocks that would sit in the homes of the wealthy or in the towers of churches, but they would start to slow in their time keeping -- up to one-half hour per day -- as the mechanical mechanisms would slowly wind down. It was at about this time that a young Galileo observed that the chandeliers of the church would sway in perfect rhythm moving from one spot to another quite methodically.
Galileo’s observations led him to start measuring the sway of the chandeliers against his own pulse. When he did this he saw that movement was consistent. He also observed that the relative timing remained the same even if the sway was large or small. Thus we have what many consider as being the first observations that a pendulum clock could accurately keep time.
It was discovered that there were variances in the timekeeping based on the pattern of the swinging, if not its distance. The swaying pendulum was then fashioned so that it could keep a swinging pattern with a curve that is called a cycloid.
In 1656 the first truly accurate pendulum clock was created by a Dutch astronomer, Christian Huygens. His clock used shorter pendulums that moved several times per second. Less than two decades later, William Clement, an English clockmaker, discovered that longer pendulums with weights took a full second to move back and forth and could measure that full unit of time more accurately.
Clock maker, George Graham was able to improve the pendulum’s accuracy in the early 1700s by controlling the pendulum length that was constantly fluctuating with temperature changes. He did this by enclosing the mechanism in a wooden box.
From there, the pendulum clock grew increasingly accurate. This was perfected at the beginning of the 20th century with the addition of the perfect amount of weight.
Up until this point, most clocks only had an hour hand. Chimes would sound on the quarter hour, but with the loss of so much time in a day, it was hard to measure the true time with this method. Clement’s pendulum clock, which came to be known as the Grandfather Clock, now had minute hands added that would move one spot after 60 complete swings of the pendulum. Now with the accuracy improved, most astronomical observatories of the day recognized the pendulum clock as the standard by which time would be measured.
Knowing gravity’s role in pulling the weighted pendulum and the rotation of the earth, scientists understood how the Foucault pendulum worked. This is a single weight at a specific length that swings in the cycloid pattern and appears to move around a large circle marked on the floor. Many science museums demonstrate the Foucault pendulum by having it knock over pegs with each hour that passes. Although it seems to be moving around the circle in order to reach each peg at the appointed hour, in reality it is the earth beneath it that is rotating to mark off the hours while the pendulum remains in its fixed pattern.
Grandfather and pendulums are still recognized as accurate ways of keeping time so long as the pendulums are properly weighted and climate can be controlled to keep the length consistent. Not only are they good at keeping time but pendulum clocks remain a decorative addition to many homes blending a timeless beauty with precision timekeeping.