escapement
An escapement is a mechanical linkage in mechanical watches and clocks that gives impulses to the timekeeping element and periodically releases the gear train to move forward, advancing the clock's hands. The impulse action transfers energy ...
, invented around 1637 by Italian scientist
Galileo Galilei
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He wa ...
(1564 - 1642). It was the earliest design of a
pendulum clock
A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element. The advantage of a pendulum for timekeeping is that it is a harmonic oscillator: It swings back and forth in a precise time interval dependent on i ...
. Since he was by then blind, Galileo described the device to his son Vincenzio, who drew a sketch of it. The son began construction of a prototype, but both he and Galileo died before it was completed.
Overview
Galileo was the first to investigate the timekeeping properties of
pendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward th ...
s, beginning around 1603. His interest was sparked by his discovery that, at least for small swings, the pendulum is
isochronous
A sequence of events is isochronous if the events occur regularly, or at equal time intervals. The term ''isochronous'' is used in several technical contexts, but usually refers to the primary subject maintaining a constant period or interval ( ...
; its
period
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
of swing is the same for different size swings. He realized that this property made the pendulum useful for timekeeping. He also discovered that the pendulum's period is dependent on its length, and independent of the mass of the pendulum bob. He used freeswinging pendulums as timers in scientific experiments and for keeping time for music.
In 1637, when he was 73, Galileo had the idea of a mechanism that would keep the pendulum swinging by giving it pushes, an
escapement
An escapement is a mechanical linkage in mechanical watches and clocks that gives impulses to the timekeeping element and periodically releases the gear train to move forward, advancing the clock's hands. The impulse action transfers energy ...
, thus allowing it to be applied to
clock
A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and t ...
s. Since he was by then totally blind, he described the mechanism to his son Vincenzio, who drew a picture from his description. Galileo's student and biographer,
Vincenzo Viviani
Vincenzo Viviani (April 5, 1622 – September 22, 1703) was an Italian mathematician and scientist. He was a pupil of Torricelli and a disciple of Galileo.
One day in 1641, while I was living with him at his villa in Arcetri, I remember that the idea occurred to him that the pendulum could be adapted to clocks with weights or springs, serving in place of the usual tempo, he hoping that the very even and natural motions of the pendulum would correct all the defects in the art of clocks. But because his being deprived of sight prevented his making drawings and models to the desired effect, and his son Vincenzio coming one day from Florence to Arcetri, Galileo told him his idea and several discussions followed. Finally they decided on the scheme shown in the accompanying drawing, to be put in practice to learn the fact of those difficulties in machines which are usually not foreseen in simple theorizing.
The existing clocks of the time which used the
verge escapement
The verge (or crown wheel) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks'. Its origin is unknown. V ...
with a crude
balance wheel
A balance wheel, or balance, is the timekeeping device used in mechanical watches and small clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a ...
were very inaccurate. The pendulum, due to its isochronism could be a much better timekeeper.
His son Vincenzio began building a clock, but both he and Galileo died before it was completed. The first pendulum clock was built in 1657 by Christiaan Huygens using a different design. The pendulum clock remained the world's most accurate timekeeper for 300 years, until the 1930s.
Since his time, various working models of Galileo's clock have been built ''(see picture at top)''.