I. INTRODUCTION

Writing Implements, manual devices used to make alphanumeric marks on or in a surface. Peculiar to inscription is the removal of part of a surface to record such marks. The writing tool is usually controlled by movement of the fingers, hand, wrist, and arm of the writer. The development of writing implements in the West has been determined by the interplay of the demand and skills of the writer and the writing materials available

  II. ANCIENT IMPLEMENTS

The earliest form of Western writing was cuneiform, made by pressing an angular stick of three or four sides into soft clay that was then baked, making these wedge-shaped marks permanent. The next major developments in writing tools were the use of the brush and of the mallet and chisel by the Greeks. Writing found on ancient Greek pottery was done with a small round brush, and early Greek letters were incised on stone with a metal chisel driven by a mallet. Neither form of Greek writing shows any variation in the thickness of the lines of individual letters; the Romans, using broad-edged tools, introduced variations in the width of alphabetic marks

By the beginning of the 1st century ad, Roman writing implements varied according to both the purpose of the writing and the surface used. Ephemeral writing and school exercises were often done with pointed styluses made of metal or bone on small wax-coated wooden tablets. Letters were scratched on the waxed surface with the pointed end of the stylus and erasures were made with the other, blunt end of the same tool. Permanent writing was done on papyrus with a reed cut to a point and dipped in ink. The rough surface of papyrus was suited to this pointed tool, and the writing produced was similar to that found on waxed tablets. Flat brushes and reeds cut with a broad edge were used on smooth surfaces, such as specially prepared animal skins (vellum or parchment) and plaster or stone walls (see Graffito; Parchment and Vellum). Inscriptional writing was done with mallet and chisel, but the style of these inscribed letters, with their variations from thick to thin strokes, shows their origin in the use of a broad-edged tool

INTRODUCTION

Clocks and Watches, devices used to measure or indicate the passage of time. A clock, which is larger than a watch, is usually intended to be kept in one place; a watch is designed to be carried or worn. Both types of timepieces require a source of power and a means of transmitting and controlling it, as well as indicators to register the lapse of time units

  II. MECHANISMS

  
 Inside a Mechanical Clock 
   
 
 
   
 
 
 Inside a Mechanical Clock
Many mechanical clocks and watches are powered by a mainspring, which must be wound periodically to provide energy to drive the clock. The force from the wound mainspring drives the power wheel, which transmits motion through a series of pinion gears to the hour wheel and the minute wheel. The escapement wheel slows and regulates the motion of the power wheel. The motion of the escapement is regulated by the back and forth movement of the pivot. This motion also produces the familiar “tick-tock” of a clock and ensures that the hour and minute hands keep accurate time 
   
   
  
 

In a clock, the source of power may be produced by weight, a mainspring, or an electric current. Except in electric or electronic clocks, periodic adjustments, such as lifting the weight or tightening the spring, are needed. The motive force generated by the power source in a mechanical clock is transmitted by a gear train and regulated by a pendulum or a balance wheel. In such a clock, the time may be reported audibly by the striking of a gong or chime and is registered visually by the rotation of wheels bearing numerals or by the position of hands on a dial. In electric or electronic clocks, time may be shown by a display of numbers

       
  

 Weight-Driven Clock
Most grandfather clocks are weight-driven, which means they are powered by the pull of a hanging weight. A mechanism called the escapement regulates the incremental release of the weight’s energy via toothed gears, which set other wheels in motion. As the pendulum swings back and forth, the escapement “walks” along the escape gear, the clock ticks, and the weight moves gradually downward, until it eventually needs to be reset. In other clocks, a wound spring serves the purpose of the weight 
  
  
  
 
A mechanical watch uses a coiled spring as its power source. As in spring-powered clocks, the watch conserves energy by means of a gear train, with a balance wheel regulating the motive force. In self-winding watches, the mainspring is tightened automatically by means of a weight on a rotor that responds to the arm movements of the wearer

  III. ELECTRIC TIMEPIECES

In the electric clocks used in homes today, a small motor runs in unison with the power-station generator, which is regulated to deliver an alternating current of precisely 60 cycles per second. Electric currents may also be used to keep the movements of several “slave” clocks synchronized with the pendulum in a master clock

The quartz-crystal clock developed in 1929 for precision timekeeping employs a ring of quartz that is connected to an electrical circuit and made to oscillate between 10,000 and 100,000 hertz (cycles per second). The high-frequency oscillation is converted to an alternating current, reduced to a frequency more convenient for time measurement, and thus made to drive the motor of a synchronous clock or a digital display. The maximum error of the most accurate quartz-crystal clocks is plus or minus one second in ten years

The electric or electronic watch is powered by a small battery that functions for about one year without replacement. The battery may drive the balance wheel of an otherwise mechanical clock, or it may be used to drive the oscillations of either a small tuning fork or a quartz crystal

  IV. CHRONOMETERS

Carefully constructed mechanical timepieces known as chronometers are precision devices used by navigators in the determination of their longitude at sea and by astronomers and jewelers for calibrating measuring devices. The first successful chronometer was constructed in 1761 by English horologist John Harrison. These portable instruments are mounted on a box on gimbals so as to maintain the delicate movements in a level position. The modern wrist chronometer is a precision watch regulated in different positions and at various temperatures and certified by testing bureaus in Switzerland

Another precision timekeeper is the chronograph, which not only provides accurate time but also registers elapsed time in fractions of a second. Various forms of chronographs exist, including the telemeter, which measures the distance of an object from the observer; the tachometer, which measures speed of rotation; the pulsometer, which determines pulse rate; and the production counter, which indicates the number of products made in a given time. The timer, or stopwatch, a form of chronograph used in athletic contests, shows elapsed time without providing the time of day

  V. ATOMIC CLOCKS

  
 Atomic Clock  
    
  
Atomic Clock
On December 29, 1999, the United States National Institute of Standards and Technology unveiled the NIST F-1, the most accurate clock in the world (a distinction it shares with a similar device located in Paris, France). NIST F-1, an atomic cesium fountain clock, replaces the NIST-7, which served as the primary United States time standard from 1993 to the end of 1999. The new atomic timekeeper is so accurate that it could run for nearly 20 million years without gaining or losing a single second. The clock is called a fountain clock because it measures the light emitted by super-cooled cesium atoms as they fall through a microwave cavity

Courtesy of NIST Public Affairs
 
 
 
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The most precise timekeeping devices are atomic clocks. Their uses include measuring the rotation of the earth, which may vary by 4 to 5 milliseconds per day, and aiding navigational systems such as the global positioning system in computing distances. Atomic clocks are tuned to the frequency of the electromagnetic waves that are emitted or absorbed when certain atoms or molecules make the transition between two closely spaced, or hyperfine, energy states. Because the frequency of these waves is unaffected by external forces, the corresponding period of the waves can be used as a standard to define time intervals

The cesium-atom clock is used to define the second, the basic unit of time of the International System of Units. In this clock, cesium-133 atoms in one hyperfine energy state are subjected to microwave radiation that is near the resonant frequency of the transition to another hyperfine energy state. The microwave frequency is adjusted, and when the correct frequency is reached, many atoms make the transition to the new energy state. The frequency of the microwave radiation is then used to determine the period of the microwave, or the time interval between wave crests. The second is defined as the duration of 9,192,631,770 periods of radiation. The cesium-atom clock is very accurate and remains stable over long periods of time. The most stable cesium-atom clocks have an error of about plus or minus one second in one million years

The rubidium clock uses the transition of the rubidium-87 atom between two hyperfine energy states. It employs the same basic principle as the cesium-atom clock. The rubidium atoms, however, are first forced to change their hyperfine energy state and are then subjected to microwave radiation to return them to their original state. When many atoms return to their original state, the correct transition frequency has been reached and the period of the wave can be used to measure time. Rubidium clocks are not as stable or as accurate as cesium-atom clocks, but they are more compact and less expensive

The hydrogen clock and the ammonia clock rely on the maser principle. In a hydrogen clock, a

kashan

city in central Iran, located in Isfahan Province. The city dates from ancient times and

wasformerly important as a site along the caravan route from Kerman to Esfahan (Isfahan). Modern kashan is important as a transportation center for central Iran

Kashan has had a rich craft tradition since ancient times. The city was famed for its high-quality pottery during the Islamic period, which lasted from the 11th to the 13th century. Later, during the Safavid dynasty, Kashan was acclaimed for its exquisite porcelain tiles and its outstanding weaving workshop. Today, the city is noted for its tradition of producing fine carpets, woolen and silk goods, brass and copper work, jewelry, and ceramics. Blooms from nearby rose fields are used to create rose water, another well-known product of Kashan. Population 166,080 (1994 estimate)

Esfahan

Esfahn or Isfahan (ancient Aspadana), city in central Iran, capital of  Esfahan(Isfahan) Province, on the northern bank of the Zaindeh Rud. Farming is the chief occupation of the surrounding region in which cotton, grain, and tobacco are grown. The city is a major textile-milling center, and cotton, silk, and woolen goods are produced here; other manufactures include brocade, carpets, foodstuffs, and metalwork. The city also serves as the outlet for animal products of the province

 was renowned in former times for its architectural grandeur and the beauty of its public

 Esfahangardens. Most of the gardens and many of the edifices are now in ruins, but a number

 of imposing structures have been preserved or restored. In the central part of the city is a 17th-century royal mosque known as Masjid-i-Shah, which is faced with colored tile and regarded by

many as an outstanding example of Persian architecture. The mosque is located within a huge rectangular garden, now surrounded by bazaars. Nearby is the Masjid-i-Shaikh-Lutfullah, a

 mosque famous for its dome of blue tile. The Ali-Kapu gate leads to the former royal gardens, in which is found the throne room, Chihil Sutun, or Forty Pillars. Additional points of interest include the Shah Hussain madrasa, a magnificent building constructed in 1710 as a school for dervishes (see Dervish), and an arcaded bridge spanning the Zaindeh Rud

When it was known as Aspadana, the city formed part of the ancient Asian country of Media. In the middle of the 7th century the city was occupied by invading Arabs. The Seljuk Turks conquered Esfahan and made it the capital of their empire in 1051. Tamerlane, the Turkic conqueror, captured the city in 1387, during his invasion of Iran, and reputedly massacred 70,000 inhabitants

Esfahan golden age began in 1598 when Abbas I, shah of Iran, made it the national capital. Under his patronage the city attained the peak of its growth, commercial prosperity, and architectural splendor. According to an unofficial estimate the population then numbered at least 500,000. Invading Afghans captured Esfahan in 1722, and the seat of the Iranian government was removed to Shiraz. The Afghans were expelled in 1729, but the city never fully recovered from their occupation. Population (1996) 1,266,07