Humankind has always recognized the passing of time and has tried to measure and record that passing. The simple alarm clock at your bedside table owes its existence to more than 6,000 years of thinking about time and tinkering with devices to accurately mark its passage.
A general knowledge of time division was relevant to the earliest of farmers, who sectioned quadrants of time into broad periods of seasons for planting, growing and harvesting. In those days however, the actual hour of any particular day was not important.
As early civilizations grew and became more complex in their needs for order and governance a more precise measure of time was required. The early Egyptians originated the division of each day into two measurable parts, using the position of an obelisks shadow to mark high noon. Other early and more precise timekeeping devices also include the hourglass, indexed candles that burned at a fixed rate, and water powered devices.
The history of clocks is very long, and there have been many different types of clocks over the centuries. Not all historians agree on the history of the clock. The word clock was first used in the 14th century (about 700 years ago). It comes from the word for bell in Latin ("clocca").
At best, historians know that 5000 - 6000 years ago, great civilisations in the Middle East and North Africa started to examine forms of clock-making instead of working with only the monthly and annual calendar. Little is known on exactly how these forms worked or indeed the actual deconstruction of the time, but it has been suggested that the intention was to maximise time available to achieve more as the size of the population grew. Perhaps such future periods of time were intented to benefit the community by allotting specific lengths of time to tasks. Was this the beginning of the working week?
Using the Sun
The first way that people could tell the time was by looking at the sun as it crossed the sky. When the sun was directly overhead in the sky, it was the middle of the day, or noon. When the sun was close to the horizon, it was either early morning (sunrise) or early evening (sunset). Telling the time was not very accurate.
With the disappearance of any ancient civilisation, such as the Sumerian culture, knowledge is also lost. Whilst we can but hypothesise on the reasons of why the equivalent to the modern wristwatch was never completed, we know that the ancient Egyptians were next to layout a system of dividing the day into parts, similar to hours.
'Obelisks' (tall four-sided tapered monuments) were carefully constructed and even purposefully geographically located we believe around 3500 BC. A shadow was cast as the Sun moved across the sky by the obelisk, which it appears was then marked out in sections,
allowing people to clearly see the two halves of the day. Some of the sections have also been found to indicate the 'year's longest and shortest days', which it is thought were developments added later to allow identification of other important time subdivisions.
Another ancient Egyptian 'shadow clock' or 'sundial' has been discovered to have been in use around 1500 BC, which allowed the measuring of the passage of 'hours'. The sections were divided into ten parts, with two 'twilight hours' indicated, occurring in the morning and the evening. For it to work successfully then at midday or noon, the device had to be turned 180 degrees to measure the afternoon hours.
The Egyptians also used the 'Merkhet', the oldest known astronomical tool, which is believed to have been developed around 600 BC. Two merkhets were used to establish a north-south line which was achieved by lining them up with the 'Pole Star'. This enabled the measurement of night-time hours, when certain stars crossed the marked meridian. By 30 BC, 'Vitruvius' describes thirteen different sundial styles being used across Greece, Asia Minor, and Italy, inherently demonstrating how the development must have grown to be more complex.
Around 1400 B.C. (about 3,400 years ago), water clocks were invented in Egypt. The name for a water clock is clepsydra (pronounced KLEP-suh-druh).
A water clock was made of two containers of water, one higher than the other. Water traveled from the higher container to the lower container through a tube connecting the containers. The containers had marks showing the water level, and the marks told the time.
Look at the picture right. Water drips from the higher container to the lower container. As the water level rises in the lower container, it raises the float on the surface of the water. The float is connected to a stick with notches, and as the stick rises, the notches turn a gear, which moves the hand that points to the time.
'Water clocks' were among the earliest time keeping devices that didn't use the observation of the celestial bodies to calculate the passage of time. The ancient Greeks, it is believed, began using water clocks around 325 BC. Most of these clocks were used to determine the hours of the night, but may have also been used during daylight. An inherent problem with the water clock was that they were not totally accurate, as the system of measurement was based on the flow of water either into, or out of, a container which had markers around the sides. Another very similar form was that of a bowl that sank during a period as it was filled of water from a regulated flow. It is known that water clocks were common across the Middle East, and that these were still being used in North Africa during the early part of the twentieth-century.
In the Far East, mechanised 'astronomical' and 'astrological' clock-making is known to have developed between 200-1300 AD. In 1088 AD, 'Su Sung' and his colleagues designed and constructed a highly complex mechanism that incorporated a water-driven escapement, invented about 725 AD. It was over seven metres in height and had all manor of mechanisms running simultaneously. During each hour an observer could view the movement of a power-driven armillary sphere, constructed of bronze rings, an automatically rotating celestial globe, together with five doors that allowed an enticing glimpse of seeing individual statues, all of which rang bells, banged gongs or held inscribed tablets showing the hour or a special time of the day. The appearance and actions would have appeared similar to the automaton we know so well today.
Dividing the Year into Months and Days
The Greeks divided the year into twelve parts that are called months. They divided each month into thirty parts that are called days. Their year had a total of 360 days, or 12 times 30 (12 x 30 = 360). Since the Earth goes around the Sun in one year and follows an almost circular path, the Greeks decided to divide the circle into 360 degrees.
Dividing the Day into Hours, Minutes, and Seconds
The Egyptians and Babylonians decided to divide the day from sunrise to sunset into twelve parts that are called hours. They also divided the night, the time from sunset to sunrise, into twelve hours. But the day and the night are not the same length, and the length of the day and night also changes through the year. This system of measuring the time was not very accurate because the length of an hour changed depending on the time of year. This meant that water clocks had to be adjusted every day.
Somebody finally figured out that by dividing the whole day into 24 hours of equal length (12 hours of the day plus 12 hours of the night), the time could be measured much more accurately.
Why was the day and night divided into 12 parts? Twelve is about the number of moon cycles in a year, so it is a special number in many cultures.
The hour is divided into 60 minutes, and each minute is divided into 60 seconds. The idea of dividing the hour and minute into 60 parts comes from the Sumerian sexagesimal system, which is based on the number 60. This system was developed about 4,000 years ago.
Early Mechanical Clocks
In medieval times, the regulation of monastic calls to prayer was accomplished by means of mechanical tower clocks. This revolutionary device soon synchronized the rhythms of entire cities. World views of entire cultures were influenced by the type of clocks they used. The development of atomic clocks, accurate to a billionth of a second, seem to reflect modern society's near-obsession with youth, age and the passage of time.
The very first early mechanical clocks, which didn’t have pendulums, were developed in the last half of the thirteenth century, probably by monks from central Europe, and were placed within the church. They did not have
dials or hands and only struck bells on the hour. These mechanical devices were probably placed in the church belfry in order to make use of the existing church bell. It was over 100 years before visible dials and hands were added. These early clocks were very large and were made of heavy iron frames and gears forged by the local blacksmiths.
In 1580 or so, the Astronomer Galileo observed a swinging lamp suspended by a long chain from a cathedral ceiling. He studied its swing and discovered that each swing was equal and had a natural rate of motion. He later found this rate of motion depended upon the length of the chain or pendulum. Galileo Galilei is credited, in most historical books, for inventing the pendulum. Many years later in 1640 he designed a clock mechanism incorporating the swing of a pendulum, but he died before building his clock design. Later in 1656 Christian Huygens added a pendulum to a clock mechanism of his own design and found it kept excellent time. Regulating the speed of the movement was done, as it is today, by simply raising or lowering the pendulum bob-up to speed-up the clock, down to slow-down the clock-thus the terms “speed-up;’ “slow-down.” Note: the length of a pendulum is usually considered to be the length from the center of the shaft that holds the hands to the center of the pendulum bob (some-times it is from the center of the shaft that holds the hands to the bottom tip of the pendulum bob).
Huygens invention allowed clocks to be accurate to as little as three minutes loss or gain per day instead of the previous quarter to half an hour per day variance. The introduction of minute hands resulted from this increased accuracy.
Meanwhile, in London, England (UK) in 1671, 'William Clement' began building clocks with an 'anchor' or 'recoil' escapement, which interfered even less with the perpetual motion of the pendulum system of clock.
By the first part of the fifteenth century, small domestic clocks started to appear. They were probably made by the local gunsmiths or locksmiths. After1630, a weight-driven lantern clock became popular for the home use of the very wealthy. When the swinging pendulum was added in 1656, clocks became more accurate. Very early clock movements were mounted high above the floor because they required long pendulums and large cast-iron descending weights. In reality, they were nothing more than simple mechanical works with a face and hands. They were referred to as “wags-on-the-wall” The long-case, or grandfather clock actually evolved from these early wags-on-the-wall prototypes. Wooden cases were used only to hide the unsightly weights and cast-iron pendulum.
Although the Dutchman Hyugens’ innovative pendulum design brought a great leap forward in clockmaking, it was English clockmakers who reigned supreme in Europe from about 1660 to the early 19th century.
'George Graham', in 1721, invented a design with the degree of accuracy to 'one second a day' by compensating for changes in the pendulum's length caused by temperature variations. The mechanical clock continued to develop until they achieved an accuracy of 'a hundredth-of-a-second a day', when the pendulum clock became the accepted standard in most astronomical observatories
Before pendulum clocks were invented, Peter Henlein of Germany invented a spring-powered clock around 1510. It was not very precise. The first clock with a minute hand was invented by Jost Burgi in 1577. It also had problems. The first practical clock was driven by a pendulum. It was developed by Christian Huygens around 1656. By 1600, the pendulum clock also had a minute hand.
The pendulum swings left and right, and as it swings, it turns a wheel with teeth (see the picture to the right). The turning wheel turns the hour and minute hands on the clock. On the first pendulum clocks, the pendulum used to swing a lot (about 50 degrees). As pendulum clocks were improved, the pendulum swung a lot less (about 10 to 15 degrees). One problem with pendulum clocks is that they stopped running after a while and had to be restarted. The first pendulum clock with external batteries was developed around 1840. By 1906, the batteries were inside the clock.
As you already learned, a clock only shows 12 hours at a time, and the hour hand must go around the clock twice to measure 24 hours, or a complete day. To tell the first 12 hours of the day (from midnight to noon) apart from the second 12 hours of the day (from noon to midnight), we use these terms:
A.M.--Ante meridiem, from the Latin for "before noon"
P.M.-- Post meridiem, from the Latin for "after noon"
Quartz Crystal Clocks
Quartz is a type of crystal that looks like glass. When you apply voltage, or electricity, and pressure, the quartz crystal vibrates or oscillates at a very constant frequency or rate. The vibration moves the clock's hands very precisely. Quartz crystal clocks were invented in 1920.
During the period of 500-1500 AD, the development of time measuring devices in Europe is known not to have improved in any great way technologically, relying mainly on the use of the sundial and principles of measurement used in ancient Egypt.
These dials were placed above doorways and indicated the midday and four 'tides' or times of the sunlit day. In the tenth-century, one English (UK) model showed the marking of the tides compensated for including seasonal changes caused by the Sun's altitude.
In Italy, during the early-to-mid fourteenth-century, large mechanical clocks housed in towers began to appear in several of the large cities. These clocks appear to have been plagued by the same problem as that of the 'water clock', that of regulating the mechanisms and maintaining the accurate time. This appears to have been due to the oscillation period of the escapement depending on a driving force which had sufficient friction in the drive mechanism.
A technological advance came with the invention of the 'Spring-powered' clock, around 1500-1510, credited to 'Peter Henlein' of Nuremberg (Germany). These were instantly popular although the spring-powered clock did have one problem, that of slowing down when the mainspring unwound. In the sixteenth-century, and even through until the nineteenth-century, these clocks were mainly the reserve of the wealthy, when the reduced size meant it could now be put on a mantle shelf or table. The development of the spring-powered clock was the precursor to accurate time keeping
Because the Earth turns, it is daytime in part of the world when it is nighttime on the other side of the world. In 1884, delegates from 25 countries met and agreed to divide the world into time zones. If you draw a line around the middle of the Earth, it is a circle (equator). The delegates divided the 360 degrees of the circle into 24 zones, each 15 degrees (24 x 15 = 360). They decided to start counting from Greenwich, England, which is 0 degrees longitude.
So To Recap..................................
In the beginning of civilization, knowing what time it is had stayed elusive and hap hazard at best, till the 14th century. With the advent of mechanical clock movements and rapid technical advancement civilization has progressed to accurate time keeping to a second off every 20 million years.
Estimate at Best
The earliest people used the position of the sun in the sky to tell morning and evening with the horizon. During the day was a complete estimate except midday. This didn't work at all during the night, season changes and cloudy days.
Around 3500 B.C., the Egyptians began to use huge obelisks as sun dials. They would cast shadows on the ground which changed position during the day as the sun travelled across the sky. This along with smaller sun dials by 1500 B.C. was a slight improvement. The problem of nights and cloudy days still existed.
Shadow Clock (Sun Dial)
Another Egyptian sundial or shadow clock, possibly the first portable timepiece, came into use around 1500 B.C. This device divided a sunlit day into 10 parts in the morning and evening. When the long stem with 5 variably spaced marks was oriented east and west in the morning, an elevated crossbar on the east end cast a moving shadow over the marks. At noon, the device was turned in the opposite direction to measure the afternoon "hours".
Water Hour Glass
Hour glasses came on the scene about 3400 B.C. which were very primitive and fraught with problem. These hour glasses consisted of a bowl with a hole in the bottom that water dripped through. Consistency couldn't be maintained because of the pressure of the water travelling through the hole. All though it did take care of the problem of night time and cloudiness temperature change and freezing was also a big problem.
Sand Hour Glass
Sand hour glasses came about around 700 A.D. This hour glass used sand being poured through a small hole into a glass tube. This was much improved over the water hour glass. The problem with this time keeping device was it only measured small amounts of time and was affected by humidity.
A huge leap occurred in the 14th century when mechanical clocks appeared. The first clock during this period had no face, hour or minute hands. They struck a bell every hour. More improvements brought about faces and hands on the clocks. These early mechanical clock movements worked by having a lever that pivoted and mashed with a toothed wheel (gear) at certain intervals. The speed of the clock movements was powered by weights or springs.
Keywind Clock Movement
In the 15th century, Coiled springs unwinding could be used to drive the movement of the hand of the clock was discovered This clock movement was in addition to weight or springs that made smaller clocks and later watches possible. This is the same dependable movement used in our grandfather clocks, wall clocks, and table / mantel clocks.
Pendulum Clock Movement
In 1656, Christian Huygens invented the pendulum clock. Whether using coil springs being wound (keywind) or weighted chain drive the pendulum made the clocks accurate with in a minute or two per day compared to 15 minutes a day of earlier clocks. This is the same movement used today in grandfather clocks, cuckoo clocks, and wall clocks.
The need for accurate time keeping at sea was so crucial that in 1714 the British Parliament offered a cash reward to invent one. To know the exact location at sea through latatude and longatude, an accurate and small time piece was needed. Large pendulum clocks were impractical on ships. After 4 attempts in 1761,John Harrison succeeded in inventing a small enough clock to be used for navigation at sea. The tiny pocket watch lost only 5 seconds in 6 1/2 weeks. This was the fore runner of wrist watches.
In the early 19th century the most important event not only in clock making, but in history took place. The introduction of mass production and interchangeable parts. This was fuelled by the industrial revolution. Before this time grandfather clocks or any other clocks were only available to the wealthy. Eli Terry was the main driver in the clock industry at the time receiving the first patent issued by the Patent Office in 1801.
During the mid to late 19th century the need for uniform time standards brought about worldwide time zones. In 1852, England implemented a telegraph network that transmitted "Greenwich Means Time", so the whole country was on the same time. In 1884, 4 time zones were created in the United States. In 1884, worldwide time zones were adopted by 25 countries.
At the beginning of the 20th century, only women wore wrist watches. Wide spread use by men happened after the First World War Wearing watches by men was not seen as manly. The military implemented wide spread use of wrist watches because it was much more efficient during battle as apposed to a pocket watches. By the 1950's digital watches came about which used electrical currents running through quartz crystals to cause vibrations to operate the movements. This is the type movement used in ourgrandfather clock, cuckoo clocks, wall clocks, and table /mantel clock.
The latest leap in time keeping was achieved in 1967, when atomic clocks were invented using oscillations of cesium-133 atoms to tell time. This clock has an error ratio of 1 second for every 1.4 million years. In 1999 with the development of the caesium fountain atomic clock the error rate dropped to only one second every 20 million years. This is the most accurate clock in the world.
Rapid advancements in technology will keep scientists striving to create the perfect clock in the future. 100% accuracy may not be attainable but we have come a very close. Remarkable improvements of already discovered time keeping devices are destined to continue.