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The History of Time-KeepingHome
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       The History of Time-Keeping

            In respect to human history, time keeping is a relatively recent 
            desire – probably 5000 to 6000 years old. It was most likely 
            initiated in the Middle East and North Africa.
            A clock is defined as a device that consists of two qualities:
              A regular, constant or repetitive process or action to mark off 
              equal increments of time. Early examples of such processes 
              included movement of the sun across the sky, candles marked in 
              increments, oil lamps with marked reservoirs, sand glasses 
              ("hourglasses"), and in the Orient, small stone or metal mazes 
              filled with incense that would burn at a certain pace.

              A means of keeping track of the increments of time and displaying 
              the result. 
            Relaying the history of time measurement has a degree of inaccuracy, 
            much like clocks themselves. What follows is, if not completely 
            accurate, as close as many researchers can ascertain. 
             

            Contents
            Keeping time with the Sun
            Keeping time with the Stars
            Keeping time with Water
            Mechanical Time
            Quartz Clocks
            Atomic Clocks

            Links to Horology Sites


            Using the Sun 
             
            The Egyptians are the first group of people that we can reasonably 
            prove that took time-keeping seriously as a culture. Many believe 
            that the Sumerians were thousands of years ahead of the game, but 
            proof of this is only speculative.  
            Around 3500 B.C. the Egyptians built “Obelisks” -- tall four-sided 
            tapered monuments -- and placed them in strategic locations to cast 
            shadows from the sun. Their moving shadows formed a kind of sundial, 
            enabling citizens to partition the day into two parts by indicating 
            noon. They also showed the year's longest and shortest days when the 
            shadow at noon was the shortest or longest of the year. Later, 
            markers added around the base of the monument would indicate further 
            time subdivisions. 
            Around 1500 B.C., the Egyptians took the next step forward with a 
            more accurate “shadow clock” or “sundial.” The sundial was divided 
            into 10 parts, with two “twilight” hours indicated. This sundial 
            only kept accurate time (in relative terms) for a half day. So at 
            midday, the device had to be turned 180 degrees to measure the 
            afternoon hours. 
            A sundial tracks the apparent movement of the sun around the earth's 
            celestial pole by casting a shadow (or point of light) onto a 
            surface that is marked by hour and minute lines. That is why the 
            shadow-casting object (the gnomon or style) must point towards the 
            north celestial pole, which is very near Polaris, the North Star. 
            The gnomon serves as an axis about which the sun appears to rotate.
            The sharper the shadow line is, the greater the accuracy. So, 
            generally speaking, the larger the sundial the greater the accuracy, 
            because the hour line can be divided into smaller portions of time. 
            But if a sundial gets too large, a point of diminishing returns is 
            reached because, due to the diffraction of light waves and the width 
            of the sun's face, the shadow spreads out and becomes fuzzy, making 
            the dial difficult to read.
            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, thought 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. 


            Obelisk

            Copper Sundial

            Using Stars  


            The Egyptians improved upon the sundial with a “merkhet,” the oldest 
            known astronomical tool. It was developed around 600 B.C. and uses a 
            string with a weight on the end to accurately measure a straight 
            vertical line (much like a carpenter uses a plumb bob today). 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 B.C., there were as many as 13 different types of sundials 
            used across Greece, Asia Minor and Italy. 

            Merkhet
            Using Water  

            “Clepsydras” or Water Clocks were among the first time-keeping 
            devices that didn’t use the sun or the passage of celestial bodies 
            to calculate time. One of the oldest was found in the tomb of 
            ancient Egyptian King Amenhotep I, buried around 1500 B.C.
            Around 325 B.C. the Greeks began using clepsydras (Greek for "water 
            thief") by the regular dripping of water through a narrow opening 
            and accumulating the water in a reservoir where a float carrying a 
            pointer rose and marked the hours. A slightly different water clock 
            released water at a regulated rate into a bowl until it sank. These 
            clocks were common across the Middle East, and were still being used 
            in parts of Africa during the early 20th century. They could not be 
            relied on to tell time more closely than a fairly large fraction of 
            an hour.  

            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. 
             
            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 mannequins which rang bells or gongs, and 
            held tablets indicating the hour or other special times of the day.  
             

            Su Sung's clock tower, ca. 1088 

            Water Clock


            Tower of the Winds, Athens, Greece 
            es·cape·ment (-skpmnt)
            n.A mechanism consisting in general of an escape wheel and an 
            anchor, used especially in timepieces to control movement of the 
            wheel and to provide periodic energy impulses to a pendulum or 
            balance. 
             
            Mechanical Clocks  

            The mechanical clock was probably invented in medieval Europe. 
            Clever arrangements of gears and wheels were devised that turned by 
            weights attached to them. As the weights were pulled downward by the 
            force of gravity, the wheels were forced to turn in a slow, regular 
            manner. A pointer, properly attached to the wheels, marked the 
            hours. 
            These clocks became common in churches and monasteries and could be 
            relied upon to tell when to toll the bells for regular prayers or 
            church attendance. (The very word "clock" is from the French cloche, 
            meaning "bell.") 
            Eventually, mechanical clocks were designed to strike the hour and 
            even to chime the quarter-hour. However, they had only an hour hand 
            and were not enclosed. Even the best such clocks would gain or lose 
            up to half an hour a day. 
            A technological advance came with the invention of the 
            “spring-powered clock” around 1500-1510, credited to Peter Henlein 
            of Nuremberg, Germany. Because these clocks could fit on a mantle or 
            shelf they became very popular among the rich. They did have some 
            time-keeping problems, though, as the clock slowed down as the 
            mainspring unwound. The development of the spring-powered clock was 
            the precursor to accurate time keeping. 
            In 1582, Italian scientist Galileo, then a teenager, had noticed the 
            swaying chandeliers in a cathedral. It seemed to him that the 
            movement back and forth was always the same whether the swing was a 
            large one or a small one. He timed the swaying with his pulse and 
            then began experimented with swinging weights. He found that the 
            "pendulum" was a way of marking off small intervals of time 
            accurately. 
            Once Galileo had made the discovery, the regular beat of the 
            pendulum became the most accurate source used to regulate the 
            movement of the wheels and gears of a clock. 
            It wasn't a perfect system, though, as a pendulum swings through the 
            arc of a circle, and when that is so, the time of the swing varies 
            slightly with its size. To make the pendulum keep truly accurate 
            time, it must be made to swing through a curve known as a "cycloid." 

            In 1656 Dutch astronomer Christian Huygens first devised a 
            successful pendulum clock. He used short pendulums that beat several 
            times a second, encased the works in wood, and hung the clock on the 
            wall. It had an error of less than one minute a day. This was a huge 
            improvement on earlier mechanical clocks, and subsequent refinements 
            reduced the margin of error to less than 10 seconds per day. 
            In 1670 English clockmaker William Clement made use of a pendulum 
            about a yard long that took a full second to move back and forth, 
            allowing greater accuracy than ever before. He encased the pendulum 
            and weights in wood in order to diminish the effect of air currents, 
            thus was born the "grandfather's clock." For the first time, it made 
            sense to add a minute hand to the dial, since it was now possible to 
            measure time to the nearest second. 
            In 1721George Graham improved the pendulum clock’s accuracy to 
            within a second a day by compensating for changes in the pendulum's 
            length caused by temperature variations. The mechanical clock 
            continued to develop until it achieved an accuracy of a 
            hundredth-of-a-second a day and it became the accepted standard in 
            most astronomical observatories. 

            Wall Clock from the 1870s


            early mechanical clock

                
            Galileo


            Christian Huygens

            George Graham

            Early Graham clock

            17th Century Pocket Watch
            Quartz Clocks  

            a quartz crystal
            chemical name: SiO2 , Silicon dioxide 
            The running of a Quartz clock is based on an electric property of 
            the quartz crystal. When an electric field is applied to a quartz 
            crystal, it changes the shape of the crystal itself. If you then 
            squeeze it or bend it, an electric field is generated. When placed 
            in an electronic circuit, the interaction between the mechanical 
            stress and the electrical field causes the crystal to vibrate, 
            generating a constant electric signal which can then be used to 
            measure time. 
            Quartz clocks continue to dominate the market because of the 
            accuracy and reliability of their performance and by their low cost 
            when produced in mass quantities. 
              
            A modern quartz digital watch that not only keeps accurate time, 
            but can check your heart rate, too.
             
              
            "The Black Watch", released in 1975 by the Sinclair Co., was one of 
            the first digital watches ever produced, and probably the worst.  If 
            you were unlucky enough to buy one of these lemons you could expect 
            various kinds of trouble: 
              The internal chip could be ruined by static from your nylon shirt, 
              nylon carpets or air-conditioned office. This problem also 
              affected the production facility, leading to a large number of 
              failures before the watches even left the factory. The result was 
              that the display would freeze on one very bright digit, causing 
              the batteries to overload (and occasionally explode). 
              The accuracy of the quartz timing crystal was highly 
              temperature-sensitive: the watch ran at different speeds in winter 
              and summer. 
              The batteries had a life of just ten days; this meant that 
              customers often received a Black Watch with dead batteries inside. 
              The design of the circuitry and case made them very difficult to 
              replace. 
              The control panels frequently malfunctioned, making it impossible 
              to turn the display on or off - which again led to exploding 
              batteries. 
              The watch came in a kit which was almost impossible for hobbyists 
              to construct. Practical Wireless magazine advised readers to use 
              two wooden clothes pegs, two drawing pins and a piece of insulated 
              wire to work the batteries into position. You then had to spend 
              another four days adjusting the trimmer to ensure that the watch 
              was running at the right speed. 
              The casing was impossible to keep in one piece. It was made from a 
              plastic which turned out to be unglueable, so the parts were 
              designed to clip together--which they didn't. 

              A very high percentage of Black Watches were returned, leading to 
              the legend that Sinclair actually had more returned than had been 
              manufactured. The backlog eventually reached such monstrous 
              proportions that it still hadn't been cleared two years later. 
             
             
            Atomic Clocks  

            Termed NIST F-1, the new cesium atomic clock at NIST, the National 
            Institute of Science and Technology, in Boulder, Colorado is the 
            nation's primary frequency standard that is used to define 
            Coordinated Universal Time (known as UTC), the official world time. 
            Because NIST F-1 shares the distinction of being the most accurate 
            clock in the world (with a similar device in Paris), it is making 
            UTC more accurate than ever before. NIST F-1 recently passed the 
            evaluation tests that demonstrated it is approximately three times 
            more accurate than the atomic clock it replaces, NIST-7, also 
            located at the Boulder facility. NIST-7 had been the primary atomic 
            time standard for the United States since 1993 and was among the 
            best time standards in the world. 
            NIST F-1 is referred to as a fountain clock because it uses a 
            fountain-like movement of atoms to obtain its improved reckoning of 
            time. First, a gas of cesium atoms is introduced into the clock's 
            vacuum chamber. Six infrared laser beams then are directed at right 
            angles to each other at the center of the chamber. The lasers gently 
            push the cesium atoms together into a ball. In the process of 
            creating this ball, the lasers slow down the movement of the atoms 
            and cool them to near absolute zero. 
            Two vertical lasers are used to gently toss the ball upward (the 
            "fountain" action), and then all of the lasers are turned off. This 
            little push is just enough to loft the ball about a meter high 
            through a microwave-filled cavity. Under the influence of gravity, 
            the ball then falls back down through the cavity.   

            The fountain action of the cesium clock.
            As the atoms interact with the microwave signal—depending on the 
            frequency of that signal—their atomic states may or may not be 
            altered. The entire round trip for the ball of atoms takes about a 
            second. At the finish point, another laser is directed at the cesium 
            atoms. Only those whose atomic states are altered by the microwave 
            cavity are induced to emit light (known as fluorescence). The 
            photons (tiny packets of light) emitted in fluorescence are measured 
            by a detector. 
            This procedure is repeated many times while the microwave energy in 
            the cavity is tuned to different frequencies. Eventually, a 
            microwave frequency is achieved that alters the states of most of 
            the cesium atoms and maximizes their fluorescence. This frequency is 
            the natural resonance frequency for the cesium atom—the 
            characteristic that defines the second and, in turn, makes ultra 
            precise timekeeping possible. 
            The 'Natural frequency' recognized currently as the measurement of 
            time used by all scientists, defines the period of one second as 
            exactly 9,192,631,770 oscillations or 9,192,631,770 cycles of the 
            Cesium Atom's Resonant Frequency. The cesium-clock at NIST is so 
            accurate that it will neither gain nor lose a second in 20 million 
            years! 

            The cesium atomic clock at the NIST. 
            This new standard is more accurate by a wide margin than any other 
            clock in the United States and assures the nation's industry, 
            science and business sectors continued access to the extremely 
            accurate timekeeping necessary for modern technology-based 
            operations. 
              
             
             
             
             
            ce·si·um (sz-m). n. 
            Symbol Cs
            A soft, silvery-white ductile metal, liquid at room temperature, the 
            most electropositive and alkaline of the elements, used in 
            photoelectric cells and to catalyze hydrogenation of some organic 
            compounds. Atomic number 55; atomic weight 132.905; melting point 
            28.5°C; boiling point 690°C; specific gravity 1.87; valence 1.

            Discovered by spectroscopy in 1860 by Robert Bunsen and Gustav 
            Kirchhoff. 
            One gram of cesium is an ample supply for a typical atomic clock to 
            run for one year.

            A gram of cesium could be found in about a cubic foot of ordinary 
            granite. Natural cesium is pure cesium-133 (55 protons and 78 
            neutrons in the nucleus, 55+78=133): it is non-radioactive.
               
             
             
            Links to Clock, Watch, Time and Horology Websites

            “Ultrasonic Ferroelectrics Frequency Control”
            http://www.ieee-uffc.org/fc 
            “Walsh Brothers Craftsmen Watchmakers & Jewelers”
            http://www.walshbrothers.co.uk/ 
            “Clockmakers Newsletter” 
            http://www.clockmakersnewsletter.com/ 
            “Clockstop.com” 
            http://www.clockstop.com/ 
            “Horology – The Hands of Time”   
            HTTP://horology.magnet.fsu.edu

            "All Clock-Wise"
            http://www.allclockwise.com