The pendulum clock did not immediately come to Galileo’s mind when he noticed, in his late teens, that regardless the size of the arc a lamp hanging from the ceiling of an Italian cathedral makes when it swings, the time it takes to make that arc is always the same. Always.
Galileo would utilize this observation in his astronomical work which dominated his life. It was only in his old age that it occurred to him to apply it to mechanical construction and the keeping of time.
The First Pendulum Clock Design
The first pendulum clock of any practical import wasn’t invented until the mid-seventeenth century when Dutchman Christiaan Huygens patented a design in which he used a pendulum in conjunction with a verge escapement. (An escapement is the mechanism in a clock movement that controls the rate at which the clock ticks. The verge escapement is also known as the crown-wheel escapement.)
The accuracy of a clock is, ironically, determined by the amount of time that it loses over a period of time. With Huygens’s design, so begins the pursuit to perfect the design and construction of clocks that lost fewer and fewer minutes and then seconds a day. When his design was actually constructed, humanity saw a shift in timekeeping devices that lost anywhere from five to twenty minutes a day to timekeepers that maybe now lost only two to three minutes a week.
Further study of the principle which Galileo discovered, known as isochronous, discovered that the steepness of a pendulum’s arc was directly related to the amount of time a clock lost. Perfecting, then, not only the escapement’s rate, the pendulum’s length, and a clock’s weight, one also had to factor in the pendulum’s arc of oscillation when in search of appreciably accurate timekeeping.
Huygens’ patented his design in The Netherlands in 1656. Within a few decades, publications about pendulum clocks and the mechanics behind them were already being written. This, keep in mind, at a time when publications in any mass form were themselves new to humanity. Horological Disquisitions, for example, by John Smith, writes that by 1694, the “curious kind of long pendulum . . . is at this day so universally in use among us.”
Source: Roberts, Derek. Precision Pendulum Clocks: The Quest for Accurate Time Keeping. Schiffer Publishing Ltd., 2003. Print.