The earliest measurements of time date back over 10,000 years. One of the key drivers of inventing methods of keeping track of time were the farmers needs to determine the best time to plant. Archaeologists have discovered bones with inscriptions that are believed to have been used to track lunar cycles.

The first real means of telling time with clocks appear to have been devised by the Egyptians. By 2100 BC, they had invented a means to divide the day into 24 hours. They used sundials or shadow clocks to measure the time of day. The Sundial indicates the time of day by the positioning of the shadow of some object on which the sun's rays fall. The shadow clock consists of a straight base with a raised crosspiece at one end. A scale with time divisions is inscribed on the base. The clock is set east-west and is reversed at midday.

Sundials were another early method for marking time. One of the first ancient people to use sundials were the Sumerians. They divided the day into 12 parts and each part was about 2 hours long. They measured the length of shadows to determine how much time had passed. No one is really sure why the Sumerians kept track of time; maybe it was for religious purposes. Sundials were dependent on the weather; it would be useless on a cloudy day and the winter and summer shadows would not correspond with the markings. In order for the sundial to work correctly, it had to be positioned correctly.

The Egyptians also divided the day into 12 parts as well. They used huge granite columns called Cleopatra Needles to keep track of time periods. They had 12 marks on the ground that equalled 12 parts of the day. When the sun touched the top, a shadow was created and the length and position of the shadow told the Egyptians how much daylight remained. They invented a portable piece called a sundial. It contains 3 parts: a circular dial, a needle and a style (gnomon) to keep the needle in place. Cleopatra's needles were inconvient and impractical for the average person.

The 'merkhet', the oldest known astronomical tool, was an Egyptian development of around 600�B.C. A pair of merkhets were used to establish a north-south line by lining them up with the Pole Star. They could then be used to mark off nighttime hours by determining when certain other stars crossed the meridian.

The Romans divided time into night and day. According to the writer Pliny, criers announced the rising/setting of the sun. In 30 B.C, they stole Cleopatra's needle but were unable to adapt. A man named Al-Battani knew something that the Romans didn't: the gnomon had to point towards the North Star and the length and size of the gnomon varied with the distance from the equator.

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 hemicycle, said to have been invented about 300�B.C., removed the useless half of the hemisphere to give an appearance of a half-bowl cut into the edge of a squared block. By 30�B.C., Vitruvius could describe 13 different sundial styles in use in Greece, Asia Minor, and Italy.

Discovery of an early historic clock dating to 6500 years

April 10, 2001- AP

The joint archaeological mission of the University of Dallas and the Polish Institute made huge discoveries in the area of Nabta 100 km west of Abou Simbel.

The discoveries are related to prehistoric times as the mission found a lot of tools, clay vessels, and skeletons.

The area of Nabta is one of the most important areas for archaeological excavation related to prehistoric times. It measures 5,000 square meters. It includes the remains of stores, wells and houses.

The mission also found tombs where in one of them there were 30 skeletons and some bracelets made of the teeth of animals and many clay vessels.

Also of the important discoveries is a clock thought to be the first historic one. It is shaped as a circle made of stones whose diameter is 4 meters. There are 6 stones near the center and arranged in two lines extending east and west.

Time is measured in this clock through the shade of the stones in the center which falls on the stones of the circle.

The archaeologists also found bulks of stones placed in correspondence with the positions of the stars in order to know the time of the different seasons especially the rainy ones.

They also found a tomb of a cow which indicates the beginning of cow-worship identified later with the cow-goddess Hathor.

These monuments should be studied thoroughly to give us a deeper understanding of the Pharaonic history.


Water clocks were among the earliest timekeepers that didn't depend on the observation of celestial bodies.

One of the oldest was found in the tomb of Amenhotep I, buried around 1500 B.C. Later named clepsydras ('water thief') by the Greeks,who began using them about 325 B.C. These were stone vessels with sloping sides thatallowed water to drip at a nearly constant rate from a small hole near the bottom.

Other clepsydras were cylindrical or bowl-shaped containers designed to slowly fill with water coming in at a constant rate. Markings on the inside surfaces measured the passage of "hours" as the water level reached them. These clocks were used to determine hours at night, but may have been used in daylight as well. Another version consisted of a metal bowl with a hole in the bottom; when placed in a container of water the bowl would fill and sink in a certain time. These were still in use in North Africa this century.

The need to track night hours lead to the invention of the water clock by 1500 BC, the Egyptians. This clock uses the steady dripping of water from a vessel to drive a mechanical device that tells the time.

It was basically a bucket of water with a hole in the bottom. A water clock showed the passage of time but it didn't keep exact hours in a day. Egyptians were the people most likely to have invented them but the Greeks had the most advanced ones.

In 250 B.C, Archimedes built a more elaborate water clock; he added gears and showed the planets and moon orbiting.

In order for a water clock to work properly, someone had to keep an eye on it; to make sure that no pebbles were in the bowl to increase talking time. These clocks were never exact; each clock had its own pace. And they couldn't be used in winter.

These clocks were used for nearly 3,000 years and grew more and more sophisticated. Water clocks were designed with ringing bells, moving puppets and mechanical singing birds.

More elaborate and impressive mechanized water clocks were developed between 100 B.C. and 500 A.D. by Greek and Roman horologists and astronomers. The added complexity was aimed at making the flow more constant by regulating the pressure, and at providing fancier displays of the passage of time. Some water clocks rang bells and gongs, others opened doors and windows to show little figures of people, or moved pointers, dials, and astrological models of the universe.

A Greek astronomer, Andronikos, supervised the construction of the Tower of the Winds in Athens in the 1st century B.C. This octagonal structure showed scholars and marketplace shoppers both sundials and mechanical hour indicators. It featured a 24-hour mechanized clepsydra and indicators for the eight winds from which the tower got its name, and it displayed the seasons of the year and astrological dates and periods. The Romans also developed mechanized clepsydras, though their complexity accomplished little improvement over simpler methods for determining the passage of time.


An hour glass is basically 2 bubbles of glass with a narrow middle; wood is used to close off the sand. The sand is measured and sealed and the hour glass is turned over and over. This type of clock was the first one to not be dependent on the weather. It's used for short periods of time such as speeches, sermons, watch duty, cooking, and at sea to calculate one's position.

To calculate the speed at sea, one would throw a piece of wood overboard tied with a knotted rope. When a knot ran through one's fingers in 1/2 a minute measured by the hour glass, it indicated that the vessel was going at the speed of 1 nautical mile an hour. The knots were very wide apart and one just counted the knots. Hence the phrase "knots an hour".

The center of the hour glass would get clogged. Course sand wore away at the center and made the opening wider. An hour glass had to be on a flat surface in order to work properly.


In the Far East, mechanized astronomical/astrological clock-making developed from 200 to 1300 A.D. Third-century Chinese clepsydras drove various mechanisms that illustrated astronomical phenomena. One of the most elaborate clock towers was built by Su Sung and his associates in 1088 A.D. Su Sung's mechanism incorporated a water-driven escapement invented about 725 A.D. The Su Sung clock tower, over 30 feet tall, possessed a bronze power-driven armillary sphere for observations, an automatically rotating celestial globe, and five front panels with doors that permitted the viewing of changing mannikins which rang bells or gongs, and held tablets indicating the hour or other special times of the day.


Modern clocks have three parts: a power source, a pace regulator and something that shows the time. The word 'clock' comes from the French word "cloche" meaning bell. The clock was developed 100-1300 A.D in Europe (although some say in China). The first clock used weights; gravity pulled weights which moved gears, which moved the gears which moved the hands. The problem with this device was someone had to constantly reset the weights.

The first major advance in clock construction occurred in Europe during the 14th century. It was found that the speed of a falling weight could be controlled by using a oscillating horizontal bar attached to a vertical spindle with two protrusions on it which acted like escapements, (cliff like ridges). When the protrusions meshed with a tooth of a gear driven by the weight, it momentarily stopped the revolving wheel and weight. These oldest type of mechanical clocks can still be seen in France and England.

The Strasbourg Cathedral was the first clock tower built (1352-54) and still works today. As Europe grew, each town had to find a way to tell time; there was an emphasis on productivity and work.

Near the end of the 15th century, the spring had begun to replace the weight in some clocks. This advancement allowed for clocks which could be carried. One problem with a spring clock is that the escapement mechanism must always be operated with a constant force. The problem was that as the spring unwound, it lost power. To solve this, the stackfreed was introduced. This is an extra spring that works against the motion when the watch is fully wound.

In 1504 the first protable time piece was invented in Nuremberg, Germany by Peter Henlein. Replacing the heavy drive weights permitted smaller (and portable) clocks and watches. Although they slowed down as the mainspring unwound, they were popular among wealthy individuals due to their size and the fact that they could be put on a shelf or table instead of hanging from the wall. These advances in design were precursors to truly accurate timekeeping.

In 1577 the minute hand was invented by Jost Burgi for Tycho Brahe; he was an astronomer who needed accurate clocks to track stars. By 1656, the pendulum was incorporated into clocks, which lead to better paced and more accurate clocks.

Although fairly accurate, clocks accuracy was dramatically improved by the introduction of the pendulum.


The pendulums swinging ensures that the protrusions move the gears wheels tooth by tooth while the motion of the protrusions keeps the pendulum moving. It was improved further by the Englishmen Robert Hooke who invented the anchor or recoil escapement.

During the 16th and 17th centuries the need for accurate clocks while sailing across the oceans arose. While springs made clocks portable, they were not accurate for long periods. Hooke realized that a spring would not be affected by the ship's motion as a pendulum would, but the available mainspring devices were not accurate enough for long periods of time until 1675, when the balance wheel, a very thin spiral hairspring (separate from the mainspring) whose inner end was secured to the spindle of a rotatable balance and whose outer end was fixed to the case of the timepiece. The spring stored or released energy during the rotation of the balance. John Harrison's chronometer no. 4, was in error by only 54 seconds after a sea voyage of 156 days.

The balance wheel, hairspring, and mainspring, together with the anchor escapement, or improved escapements, still make up the basics of even todays modern watches. Introduction of jewels as bearings have further improved on this basic system.

This improved the functioning of the gear train. Infact, this method is still used today. The greatest benefit of this method was that it allowed for very long pendulums with a swing of one second. The out growth of this invention was the walled pendulum clock where the weights and pendulum are completely enclosed in a case. Of course, most people are very familiar with these clocks with the most common being the 'Grandfather Clock'.

In 1656, Christiaan Huygens, a Dutch scientist, made the first pendulum clock, regulated by a mechanism with a "natural" period of oscillation. Although Galileo Galilei, sometimes credited with inventing the pendulum, studied its motion as early as 1582, Galileo's design for a clock was not built before his death. Huygens' pendulum clock had an error of less than 1 minute a day, the first time such accuracy had been achieved. His later refinements reduced his clock's errors to less than 10 seconds a day.

Around 1675 Huygens developed the balance wheel and spring assembly, still found in some of today's wrist watches. This improvement allowed 17th century watches to keep time to 10 minutes a day. And in London in 1671 William Clement began building clocks with the new "anchor" or "recoil" escapement, a substantial improvement over the verge because it interferes less with the motion of the pendulum.

In 1721 George Graham improved the pendulum clock's accuracy to 1 second a day by compensating for changes in the pendulum's length due to temperature variations. John Harrison, a carpenter and self-taught clock-maker, refined Graham's temperature compensation techniques and added new methods of reducing friction.

By 1761 he had built a marine chronometer with a spring and balance wheel escapement that won the British government's 1714 prize (of over $2,000,000 in today's currency) offered for a means of determining longitude to within one-half degree after a voyage to the West Indies. It kept time on board a rolling ship to about one-fifth of a second a day, nearly as well as a pendulum clock could do on land, and 10 times better than required.

Over the next century refinements led in 1889 to Siegmund Riefler's clock with a nearly free pendulum, which attained an accuracy of a hundredth of a second a day and became the standard in many astronomical observatories. A true free-pendulum principle was introduced by R. J. Rudd about 1898, stimulating development of several free-pendulum clocks. One of the most famous, the W. H. Shortt clock, was demonstrated in 1921. The Shortt clock almost immediately replaced Riefler's clock as a supreme timekeeper in many observatories. This clock consists of two pendulums, one a slave and the other a master. The slave pendulum gives the master pendulum the gentle pushes needed to maintain its motion, and also drives the clock's hands. This allows the master pendulum to remain free from mechanical tasks that would disturb its regularity.

Watches run by small batteries were introduced in the 1950s. The balance of such an electric watch is kept in motion electromagnetically by a coil that is energized by an electronic circuit.


The Shortt clock was replaced as the standard by quartz crystal clocks in the 1930s and 1940s, improving timekeeping performance far beyond that of pendulum and balance-wheel escapements.

The modern electronic watch is driven by a quartz crystal, which is made to vibrate at its natural frequency.

Quartz clock operation is based on the piezoelectric property of quartz crystals. If you apply an electric field to the crystal, it changes its shape, and if you squeeze it or bend it, it generates an electric field. When put in a suitable electronic circuit, this interaction between mechanical stress and electric field causes the crystal to vibrate and generate a constant frequency electric signal that can be used to operate an electronic clock display.

Quartz crystal clocks were better because they had no gears or escapements to disturb their regular frequency. Even so, they still relied on a mechanical vibration whose frequency depended critically on the crystal's size and shape. Thus, no two crystals can be precisely alike, with exactly the same frequency. Such quartz clocks continue to dominate the market in numbers because their performance is excellent and they are inexpensive. But the timekeeping performance of quartz clocks has been substantially surpassed by atomic clocks.

The latest digital quartz watches display time in numbers, using LEDs (light-emitting diodes) or an LCD (liquid-crystal display).


Scientists had long realized that atoms (and molecules) have resonances; each chemical element and compound absorbs and emits electromagnetic radiation at its own characteristic frequencies. These resonances are inherently stable over time and space. An atom of hydrogen or cesium here today is exactly like one a million years ago or in another galaxy. Here was a potential "pendulum" with a reproducible rate that could form the basis for more accurate clocks.

The development of radar and extremely high frequency radio communications in the 1930s and 1940s made possible the generation of the kind of electromagnetic waves (microwaves) needed to interact with the atoms. Research aimed at developing an atomic clock focused first on microwave resonances in the ammonia molecule. In 1949 NIST built the first atomic clock, which was based on ammonia. However, its performance wasn't much better than existing standards, and attention shifted almost immediately to more-promising, atomic-beam devices based on cesium.

In 1957 NIST completed its first cesium atomic beam device, and soon after a second NIST unit was built for comparison testing. By 1960 cesium standards had been refined enough to be incorporated into the official timekeeping system of NIST.

In 1967 the cesium atom's natural frequency was formally recognized as the new international unit of time: the second was defined as exactly 9,192,631,770 oscillations or cycles of the cesium atom's resonant frequency replacing the old second that was defined in terms of the earth's motions. The second quickly became the physical quantity most accurately measured by scientists. The best primary cesium standards now keep time to about one-millionth of a second per year.

Much of modern life has come to depend on precise time. The day is long past when we could get by with a timepiece accurate to the nearest quarter hour. Transportation, communication, manufacturing, electric power and many other technologies have become dependent on super-accurate clocks. Scientific research and the demands of modern technology continue to drive our search for ever more accurate clocks. The next generation of cesium time standards is presently under development at NIST's Boulder laboratory and other laboratories around the world.


The Candle was once used as an 'Alarm Clock'.

A nail was put into the wax, whenever the candle wax melted down to the nail then the nail would fall into a tin pan and make a noise.