The History of Time-Keeping

The Ancient Egyptians used the sun to get an idea of the time. They also constructed large, four-sided pillars that tapered towards the top that would act similarly to sun dials (see sundials). These structures were known as Obelisks. There is reasonable evidence to prove that the Egyptians were the first group of people to take timekeeping seriously although many people believed that the the Ancient Sumerians were thousands of years ahead of the Egyptians. However, there is no hard evidence of the theory that the Sumerians preceded the Ancient Egyptians. Despite this, we do know that the Ancient Sumerians did create the Sexagesimal system we use today to measure time that uses the number 60.

Around 1500 BC, the Ancient Egyptians took the next step in timekeeping and developed a more accurate 'shadow clock', also known as a sundial. Some variants of the sundials were divided into ten parts with two twilight stages and eight daytime stages. Others were divided into fourteen parts with ten daytime stages and four twilight stages (two in the early morning and two in the evening). There were no night stages as the sundials relied upon the sun to cast a shadow so at night, with no sun to cast a shadow, the devices were rendered useless as was the case on overcast days. The sundials often only represented half a day and had to be rotated 180 degrees to measure time after midday. In the quest for more year-round accuracy, sundials evolved from flat horizontal or vertical plates to more elaborate forms. One version was the hemispherical dial, a bowl-shaped depression cut into a block of stone, carrying a central vertical gnomon (pointer) and scribed with sets of hour lines for different seasons.

The Ancient Egyptians, once again, improved on their sundial with the merkhet (the oldest known astronomical tool). The merkhet uses a string with a weight on the end to accurately measure a straight vertical line. A pair of merkhets were used to establish a North-South line by lining them up with the Pole Star. This allowed for the measurement of nighttime hours as it measured when certain stars crossed a marked meridian on the sundial.

By 30 BC there were as many as 13 different types of sundials used across Greece, Asia Minor and Italy.

The oldest water clock was found in the tomb of Ancient Egyptian King, Amenhotep I who was buried around 1500 BC. Around 325 BC, the Greeks used the idea of a water clock and made their own. The Clepsydras worked by continuously dripping water down a through a narrow opening and accumulating the water in a reservoir where a float carrying a pointer rose and marked the hours. Another variant of the water clock regulated the flow of water into a bowl and it would eventually sink (at a specific time). Plato, the great Greek philosopher, created the first alarm clock. When the water gradually filled up in a jar, it triggered a whistle and woke him up. The water in Clepsydras was later replaced by mercury as water froze at 0 degrees celcius while Mercury would freeze at negative 38 degrees celcius, making it reliable on cold days.

In the tenth century AD, pocket sundials were being used but in the fourteenth century AD, a new type of clock appeared in large Italian cities. These clocks were invented in the 11th century by the Arab engineer Ibn Khalaf al-Muradi in Islamic Iberia; it was a water clock that employed a complex gear train mechanism. This inspired the use of a mechanism in a clock. Mechanical clocks began to appear, often on clock towers and were not driven by water or mercury but large weights that would forcefully turn a set of gears that would turn hands on a large clock-face. Although they were more accurate than water clocks, the workings of these clocks could still be hard to regulate.

In the early 1500s, a new type of clock was invented that was spring-powered rather than powered by heavy weights. The use of spring-powered mechanisms allowed clocks to be made smaller and easier to move. These springs were present in the early pocket watches. The drawback to these clocks was that they slowed as the spring unwound.The advancement of clock-making took a huge leap in the 1600s when the pendulum clock was invented. The earliest pendulum clocks were accurate within one minute of a day, and the later refinements were accurate within less than ten seconds a day.