The question "who invented the clock" is one that I get asked a lot in messages sent to me, but the clock as we know it was a gradually developed machine, not something that was invented in one day. Here's a brief rundown on the development of the measurement of time that eventually led to the clock.
Nobody actually knows the reason why the day was split into 12 hours and each hour split into 60 minutes and then each minute into 60 seconds. The best guess is that it was the Babylonians who worked out that there were 12 full moons in a year which gave them a 360 day year. They also knew the relationship between the radius of a circle and its circumference, which split the circle into six segments. Dividing this by two gave them 12 segments, which also fitted well with their religious beliefs that the number 12 had some kind of special significance.
Who Invented the Clock? - The Sun
Even though we are fairly sure that the Babylonians had some sort of sun dial it was the Egyptians that really took timekeeping to a new level with the invention of the obelisk. This was a tall slim structure with a pointed top that told the time by throwing a shadow that moved in a semi-circular rotation, allowing the Egyptians to segment a horizontal disk and thereby tell the time.
It was the Egyptians that discovered the Meridian Line, a line joining North and South, by observing that the shortest shadow cast by the obelisk would always point in the same direction, regardless of the season. It was about this point that the center of the dial was marked as midday. They also discovered the longest and shortest days, those where the shadow was either shortest (summer solstice) or longest (winter solstice) measured at midday.
As time passed and knowledge was gained the Egyptians created smaller sun dials, although it was soon learned that telling the time accurately with a small device was much harder due to the fact that even though the shadow cast was much sharper, it was much more difficult to accurately segment the disk.
The sun dial moved from Egypt into Greece and later Rome. The Romans improved the device further by developing the hemicycle, a sort of hollowed out sun dial in the shape of a half bowl that added further to the accuracy of timekeeping and also allowed much smaller devices to be made.
Who Invented the Clock? - Water Clocks (Clepsydra)
Although the Egyptians did use water clocks in around 1400BC, the advancement of mechanical theory by people like Archimedes (250BC) attracted more scientists and inventors to take these principles and apply them to the process of measuring time.
The principle was simple - fill a container with water and allow it to flow at a constant rate into another chamber that then operated some sort of float mechanism that moved a lever to show the hours. Various methods were used to maintain a constant water flow, the most common being the use of a constantly overflowing funnel, thereby ensuring that the same head of water was maintained at all times.
The only problem with these clocks was their poor accuracy. As time went by various methods were used to make the flow of water more accurate but it was the Chinese that appear to have made the most accurate water clocks around the 11th Century.
A Chinese monk by the name of Su Sung designed a huge clepsydra in the year 1092. Five stories high with numerous automata, the device was run by a very large water wheel that moved similarly to that of a modern clock escapement. Every quarter of an hour the wheel would turn, advancing all the other cogs and gears and opening and closing doors that released the automata.
It may be that this was the first mechanical clock as we know it today with its gears and pulleys, even though it still relied on water as its power source. Nevertheless, it is the first known use of a mechanical escapement and as such proved to be many hundreds of years of its time.
Who Invented the Clock? - Mechanical Clocks
The mechanical clock we know today was probably a result of a development of inventions and theories throughout the centuries, for we do not know precisely when the clock as we know it was first invented. In the 13th Century a clock was devised that used weights to drive a drum containing mercury. The mercury passed into each segment of the drum and slowly filtered through holes in the separating pieces, thereby controlling the rate at which the drum turned. This is of course a similar escapement to the one devised by Su Sung in 1092.
It is the escapement that clearly separates a water clock from a mechanical device. The first fully mechanical escapement was the verge and foliot, whereby a horizontal bar, or foliot, was impulsed by a vertical bar, or verge, with small pallets on a large wheel powered by a weight. The foliot had adjustable weights hanging off each end that gave it inertia and helped keep a constant timekeeping beat.
Most of these early clocks were 'clocks for the people; they were quite large, expensive and certainly were not clocks made for personal use. The advent of the clock for the home came with advances in escapements and a new power mechanism - the spring driven clock, the earliest known example dated at 1450, on display at the British Museum.
The spring driven clock was certainly a technological advance but timekeeping didn't improve as a result. As yet there was no method of keeping the power to the escapement constant. As the spring wound down so the clock would slow down. After it was wound up the clock would run faster. The solution was the fusee, a device that spread the force exerted by the unwinding spring in a more even manner.
It is thought that the fusee was invented by Jacob Zech of Prague, however others think that it was Leonardo DaVinci that first came up with the device. Da Vinci is credited with a drawing of such a mechanism in manuscripts dated around 1485.
It was Galileo Galilei that first studied the motion of the pendulum in 1602. His studies were followed later by Christiaan Huygens, who patented the first clock using the device.
Huygens' clock, using a short pendulum inside a wooden case proved to far more accurate than existing clocks and this led to the development of better and more accurate clocks. Later the pendulum's length was increased and accuracy increased again. The increased length of pendulum required a longer and larger wooden case and it was this development that gave birth to the longcase clock.
The pendulum has remained a popular method of keeping time for the past 300 years, and it has undergone improvements throughout that time, being made of differing materials to compensate against temperature differences and also the development of the 'free-pendulum' whereby as little friction as possible exists to slow the pendulum.
So as you can see, "who invented the clock" is not an easy question to answer!