111-427: Standard time is the synchronization of clocks within a geographical region to a single time standard, rather than a local mean time standard. Generally, standard time agrees with the local mean time at some meridian that passes through the region, often near the centre of the region. Historically, standard time was established during the 19th century to aid weather forecasting and train travel. Applied globally in
222-481: A master clock and slave clocks . Where an AC electrical supply of stable frequency is available, timekeeping can be maintained very reliably by using a synchronous motor , essentially counting the cycles. The supply current alternates with an accurate frequency of 50 hertz in many countries, and 60 hertz in others. While the frequency may vary slightly during the day as the load changes, generators are designed to maintain an accurate number of cycles over
333-528: A quartz crystal , or the vibration of electrons in atoms as they emit microwaves , the last of which is so precise that it serves as the definition of the second . Clocks have different ways of displaying the time. Analog clocks indicate time with a traditional clock face and moving hands. Digital clocks display a numeric representation of time. Two numbering systems are in use: 12-hour time notation and 24-hour notation. Most digital clocks use electronic mechanisms and LCD , LED , or VFD displays. For
444-400: A "particularly elaborate example" of a water clock. Pope Sylvester II introduced clocks to northern and western Europe around 1000 AD. The first known geared clock was invented by the great mathematician, physicist, and engineer Archimedes during the 3rd century BC. Archimedes created his astronomical clock, which was also a cuckoo clock with birds singing and moving every hour. It is
555-570: A 'great horloge'. Over the next 30 years, there were mentions of clocks at a number of ecclesiastical institutions in England, Italy, and France. In 1322, a new clock was installed in Norwich , an expensive replacement for an earlier clock installed in 1273. This had a large (2 metre) astronomical dial with automata and bells. The costs of the installation included the full-time employment of two clockkeepers for two years. An elaborate water clock,
666-478: A Scottish clockmaker, patented the electric clock in 1840. The electric clock's mainspring is wound either with an electric motor or with an electromagnet and armature. In 1841, he first patented the electromagnetic pendulum. By the end of the nineteenth century, the advent of the dry cell battery made it feasible to use electric power in clocks. Spring or weight driven clocks that use electricity, either alternating current (AC) or direct current (DC), to rewind
777-532: A chain that turns a gear in the mechanism. Another Greek clock probably constructed at the time of Alexander was in Gaza, as described by Procopius. The Gaza clock was probably a Meteoroskopeion, i.e., a building showing celestial phenomena and the time. It had a pointer for the time and some automations similar to the Archimedes clock. There were 12 doors opening one every hour, with Hercules performing his labors,
888-401: A day, so the clock may be a fraction of a second slow or fast at any time, but will be perfectly accurate over a long time. The rotor of the motor rotates at a speed that is related to the alternation frequency. Appropriate gearing converts this rotation speed to the correct ones for the hands of the analog clock. Time in these cases is measured in several ways, such as by counting the cycles of
999-464: A density of 111.04 inhabitants/sq mi (42.872/km ), compared to 93.844/sq mi (36.233/km ) for the nation as a whole. While conterminous U.S. has the precise meaning of contiguous U.S. (both adjectives meaning "sharing a common boundary"), other terms commonly used to describe the 48 contiguous states have a greater degree of ambiguity. Because Alaska is also a part of North America , the term continental United States also includes that state, so
1110-400: A few seconds over trillions of years. Atomic clocks were first theorized by Lord Kelvin in 1879. In the 1930s the development of magnetic resonance created practical method for doing this. A prototype ammonia maser device was built in 1949 at the U.S. National Bureau of Standards (NBS, now NIST ). Although it was less accurate than existing quartz clocks , it served to demonstrate
1221-416: A fire at the abbey of St Edmundsbury (now Bury St Edmunds ), the monks "ran to the clock" to fetch water, indicating that their water clock had a reservoir large enough to help extinguish the occasional fire. The word clock (via Medieval Latin clocca from Old Irish clocc , both meaning 'bell'), which gradually supersedes "horologe", suggests that it was the sound of bells that also characterized
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#17327753741831332-498: A kind of early clocktower . The Greek and Roman civilizations advanced water clock design with improved accuracy. These advances were passed on through Byzantine and Islamic times, eventually making their way back to Europe. Independently, the Chinese developed their own advanced water clocks ( 水鐘 ) by 725 AD, passing their ideas on to Korea and Japan. Some water clock designs were developed independently, and some knowledge
1443-401: A large astrolabe-type dial, showing the sun, the moon's age, phase, and node, a star map, and possibly the planets. In addition, it had a wheel of fortune and an indicator of the state of the tide at London Bridge . Bells rang every hour, the number of strokes indicating the time. Dondi's clock was a seven-sided construction, 1 metre high, with dials showing the time of day, including minutes,
1554-732: A meeting of the Royal Canadian Institute on February 8, 1879. Cleveland Abbe advocated standard time to better coordinate international weather observations and resultant weather forecasts , which had been coordinated using local solar time . In 1879 he recommended four time zones across the contiguous United States , based upon Greenwich Mean Time . The General Time Convention (renamed the American Railway Association in 1891), an organization of US railroads charged with coordinating schedules and operating standards, became increasingly concerned that if
1665-403: A more accurate clock: This has the dual function of keeping the oscillator running by giving it 'pushes' to replace the energy lost to friction , and converting its vibrations into a series of pulses that serve to measure the time. In mechanical clocks, the low Q of the balance wheel or pendulum oscillator made them very sensitive to the disturbing effect of the impulses of the escapement, so
1776-500: A nationwide standard time. A telegraph cable between New Zealand's two main islands became the instigating factor for the establishment of "New Zealand time". In 1868, the Telegraph Department adopted " Wellington time" as the standard time across all their offices so that opening and closing times could be synchronised. The Post Office, which usually shared the same building, followed suit. However, protests that time
1887-578: A new problem: how to keep the clock movement running at a constant rate as the spring ran down. This resulted in the invention of the stackfreed and the fusee in the 15th century, and many other innovations, down to the invention of the modern going barrel in 1760. Early clock dials did not indicate minutes and seconds. A clock with a dial indicating minutes was illustrated in a 1475 manuscript by Paulus Almanus, and some 15th-century clocks in Germany indicated minutes and seconds. An early record of
1998-554: A pendulum, which would be virtually useless on a rocking ship. In 1714, the British government offered large financial rewards to the value of 20,000 pounds for anyone who could determine longitude accurately. John Harrison , who dedicated his life to improving the accuracy of his clocks, later received considerable sums under the Longitude Act. In 1735, Harrison built his first chronometer, which he steadily improved on over
2109-488: A precisely constant frequency. The advantage of a harmonic oscillator over other forms of oscillator is that it employs resonance to vibrate at a precise natural resonant frequency or "beat" dependent only on its physical characteristics, and resists vibrating at other rates. The possible precision achievable by a harmonic oscillator is measured by a parameter called its Q , or quality factor, which increases (other things being equal) with its resonant frequency. This
2220-551: A provision for setting the clock by manually entering the correct time into the counter. Contiguous United States The contiguous United States (officially the conterminous United States ) consists of the 48 adjoining U.S. states and the District of Columbia of the United States in central North America . The term excludes the only two non- contiguous states, which are Alaska and Hawaii (they are also
2331-517: A seconds hand on a clock dates back to about 1560 on a clock now in the Fremersdorf collection. During the 15th and 16th centuries, clockmaking flourished, particularly in the metalworking towns of Nuremberg and Augsburg , and in Blois , France. Some of the more basic table clocks have only one time-keeping hand, with the dial between the hour markers being divided into four equal parts making
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#17327753741832442-471: A seven-sided brass or iron framework resting on 7 decorative paw-shaped feet. The lower section provided a 24-hour dial and a large calendar drum, showing the fixed feasts of the church, the movable feasts, and the position in the zodiac of the moon's ascending node. The upper section contained 7 dials, each about 30 cm in diameter, showing the positional data for the Primum Mobile , Venus, Mercury,
2553-441: A state, it was properly included within the continental U.S. due to being an incorporated territory . The term mainland United States is sometimes used synonymously with continental United States , but technically refers only to those parts of states connected to the landmass of North America, thereby excluding not only Hawaii and overseas insular areas , but also islands which are part of continental states but separated from
2664-579: A sundial. While never reaching the level of accuracy of a modern timepiece, the water clock was the most accurate and commonly used timekeeping device for millennia until it was replaced by the more accurate pendulum clock in 17th-century Europe. Islamic civilization is credited with further advancing the accuracy of clocks through elaborate engineering. In 797 (or possibly 801), the Abbasid caliph of Baghdad , Harun al-Rashid , presented Charlemagne with an Asian elephant named Abul-Abbas together with
2775-652: A way of mass-producing clocks by using interchangeable parts . Aaron Lufkin Dennison started a factory in 1851 in Massachusetts that also used interchangeable parts, and by 1861 was running a successful enterprise incorporated as the Waltham Watch Company . In 1815, the English scientist Francis Ronalds published the first electric clock powered by dry pile batteries. Alexander Bain ,
2886-421: A working model of the solar system. Simple clocks intended mainly for notification were installed in towers and did not always require faces or hands. They would have announced the canonical hours or intervals between set times of prayer. Canonical hours varied in length as the times of sunrise and sunset shifted. The more sophisticated astronomical clocks would have had moving dials or hands and would have shown
2997-469: Is actual land, composing 83.65 percent of the country's total land area, and is comparable in size to the area of Australia. Officially, 160,820.25 square miles (416,522.5 km ) of the contiguous United States is water area, composing 62.66 percent of the nation's total water area. The contiguous United States, if it were a country, would be fifth on the list of countries and dependencies by area , behind Russia , Canada , China , and Brazil . However,
3108-584: Is also derived from the Middle English clokke , Old North French cloque , or Middle Dutch clocke , all of which mean 'bell'. The apparent position of the Sun in the sky changes over the course of each day, reflecting the rotation of the Earth. Shadows cast by stationary objects move correspondingly, so their positions can be used to indicate the time of day. A sundial shows the time by displaying
3219-801: Is also on North America, but separated from the 48 states by British Columbia in Canada, but excludes Hawaii and all the insular areas in the Caribbean and the Pacific . The greatest distance (on a great-circle route) entirely within the contiguous U.S. is 2,802 miles (4,509 km), coast-to-coast between Florida and the State of Washington ; the greatest north–south line is 1,650 miles (2,660 km). The contiguous United States occupies an area of 3,119,884.69 square miles (8,080,464.3 km ). Of this area, 2,959,064.44 square miles (7,663,941.7 km )
3330-431: Is considered to be the world's oldest surviving mechanical clock that strikes the hours. Clockmakers developed their art in various ways. Building smaller clocks was a technical challenge, as was improving accuracy and reliability. Clocks could be impressive showpieces to demonstrate skilled craftsmanship, or less expensive, mass-produced items for domestic use. The escapement in particular was an important factor affecting
3441-402: Is one of the oldest human inventions , meeting the need to measure intervals of time shorter than the natural units such as the day , the lunar month , and the year . Devices operating on several physical processes have been used over the millennia . Some predecessors to the modern clock may be considered "clocks" that are based on movement in nature: A sundial shows the time by displaying
Standard time - Misplaced Pages Continue
3552-459: Is why there has been a long-term trend toward higher frequency oscillators in clocks. Balance wheels and pendulums always include a means of adjusting the rate of the timepiece. Quartz timepieces sometimes include a rate screw that adjusts a capacitor for that purpose. Atomic clocks are primary standards , and their rate cannot be adjusted. Some clocks rely for their accuracy on an external oscillator; that is, they are automatically synchronized to
3663-608: The Artuqid king of Diyar-Bakr, Nasir al-Din , made numerous clocks of all shapes and sizes. The most reputed clocks included the elephant , scribe, and castle clocks , some of which have been successfully reconstructed. As well as telling the time, these grand clocks were symbols of the status, grandeur, and wealth of the Urtuq State. Knowledge of these mercury escapements may have spread through Europe with translations of Arabic and Spanish texts. The word horologia (from
3774-564: The Colonial Time Service Observatory in Wellington, determined the correct time each morning. At 9 a.m. each day, it was transmitted by Morse code to post offices and railway stations around the country. In 1920, radio time signals began broadcasting, greatly increasing the accuracy of the time nationwide. Clock A clock or chronometer is a device that measures and displays time . The clock
3885-601: The Eastern Hemisphere and the Western Hemisphere , with one Prime Meridian replacing the various prime meridians that had previously been used. During the 19th century, scheduled steamships and trains required time standardisation in the industrialized world. A standardised time system was first used by British railways on 1 December 1847, when they switched from local mean time, which varied from place to place, to Greenwich Mean Time (GMT). It
3996-582: The Northwest Angle in Minnesota are three such places. Alburgh, Vermont , is not directly connected by land, but is accessible by road via bridges from within Vermont and from New York. By contrast, Hyder, Alaska , is physically part of contiguous Alaska and its easternmost town, but the only practical access is by road through Canada or by seaplane. The 48 contiguous states are: In addition,
4107-499: The Republic of China (Taiwan)'s National Museum of Natural Science , Taichung city. This full-scale, fully functional replica, approximately 12 meters (39 feet) in height, was constructed from Su Song's original descriptions and mechanical drawings. The Chinese escapement spread west and was the source for Western escapement technology. In the 12th century, Al-Jazari , an engineer from Mesopotamia (lived 1136–1206) who worked for
4218-628: The South Pacific Ocean in Polynesia , south of the equator — it is 2,200 miles (3,500 km) southwest of Hawaii . In American Samoa, the contiguous United States is called the "mainland United States" or "the states"; those not from American Samoa are called palagi (outsiders). Apart from off-shore U.S. islands , a few continental portions of the contiguous United States are accessible by road only by traveling through Canada. Point Roberts, Washington ; Elm Point, Minnesota ; and
4329-981: The University of Pittsburgh 's Allegheny Observatory (then known as the Western University of Pennsylvania , located in Pittsburgh, Pennsylvania ). Instituted in 1869, the Allegheny Observatory's service is believed to have been the first regular and systematic system of time distribution to railroads and cities as well as the origin of the modern standard time system. By 1870 the Allegheny Time service extended over 2,500 miles with 300 telegraph offices receiving time signals. However, almost all railroads out of New York ran on New York time, and railroads west from Chicago mostly used Chicago time, but between Chicago and Pittsburgh/Buffalo
4440-419: The anchor escapement , an improvement over Huygens' crown escapement. Clement also introduced the pendulum suspension spring in 1671. The concentric minute hand was added to the clock by Daniel Quare , a London clockmaker and others, and the second hand was first introduced. In 1675, Huygens and Robert Hooke invented the spiral balance spring , or the hairspring, designed to control the oscillating speed of
4551-415: The balance wheel . This crucial advance finally made accurate pocket watches possible. The great English clockmaker Thomas Tompion , was one of the first to use this mechanism successfully in his pocket watches , and he adopted the minute hand which, after a variety of designs were trialled, eventually stabilised into the modern-day configuration. The rack and snail striking mechanism for striking clocks ,
Standard time - Misplaced Pages Continue
4662-511: The "constant-level tank". The main driving shaft of iron, with its cylindrical necks supported on iron crescent-shaped bearings, ended in a pinion, which engaged a gear wheel at the lower end of the main vertical transmission shaft. This great astronomical hydromechanical clock tower was about ten metres high (about 30 feet), featured a clock escapement , and was indirectly powered by a rotating wheel either with falling water or liquid mercury . A full-sized working replica of Su Song's clock exists in
4773-459: The 'Cosmic Engine', was invented by Su Song , a Chinese polymath , designed and constructed in China in 1092. This great astronomical hydromechanical clock tower was about ten metres high (about 30 feet) and was indirectly powered by a rotating wheel with falling water and liquid mercury , which turned an armillary sphere capable of calculating complex astronomical problems. In Europe, there were
4884-575: The 17th and 18th centuries, but maintained a system of production that was geared towards high quality products for the elite. Although there was an attempt to modernise clock manufacture with mass-production techniques and the application of duplicating tools and machinery by the British Watch Company in 1843, it was in the United States that this system took off. In 1816, Eli Terry and some other Connecticut clockmakers developed
4995-400: The 1830s, when the use of the telegraph and trains standardized time and time zones between cities. Many devices can be used to mark the passage of time without respect to reference time (time of day, hours, minutes, etc.) and can be useful for measuring duration or intervals. Examples of such duration timers are candle clocks , incense clocks , and the hourglass . Both the candle clock and
5106-578: The 1883 west end of the railroad at Wallula Jct ; the Union Pacific Railway was at the other extreme, with only two time zones between Omaha and Ogden. In 1870, Charles F. Dowd proposed four time zones based on the meridian through Washington, DC for North American railroads. In 1872 he revised his proposal to base it on the Greenwich meridian . Sandford Fleming , a Scottish-born Canadian engineer, proposed worldwide Standard Time at
5217-405: The 20th century, the geographical regions became time zones . The standard time in each time zone has come to be defined as an offset from Universal Time . A further offset is applied for part of the year in regions with daylight saving time . The adoption of standard time, because of the inseparable correspondence between longitude and time , solidified the concept of halving the globe into
5328-674: The 49th state of the United States on January 3, 1959. Alaska is the northwest extremity of the North American continent, separated from the U.S. West Coast by the Canadian province of British Columbia . The term Lower 48 has, for many years, been a common Alaskan equivalent for "contiguous United States"; today, many Alaskans use the term "Outside" for those states, though some may use "Outside" to refer to any location not within Alaska. The territory of Hawaii , consisting of
5439-656: The 60th meridian west of Greenwich, instead adopting Eastern Time, so only four time zones were actually adopted by U.S./Canadian railroads in 1883. Major American observatories, including the Allegheny Observatory, the United States Naval Observatory , the Harvard College Observatory , and the Yale University Observatory , agreed to provide telegraphic time signals at noon Eastern Time. Standard time
5550-476: The AC supply, vibration of a tuning fork , the behaviour of quartz crystals, or the quantum vibrations of atoms. Electronic circuits divide these high-frequency oscillations to slower ones that drive the time display. The piezoelectric properties of crystalline quartz were discovered by Jacques and Pierre Curie in 1880. The first crystal oscillator was invented in 1917 by Alexander M. Nicholson , after which
5661-645: The District of Columbia who were born in, or can trace their family ancestry to, Puerto Rico. The U.S. Virgin Islands is a U.S. territory located directly to the east of Puerto Rico in the Caribbean Sea. The term "stateside" is used to refer to the mainland, in relation to the U.S. Virgin Islands (see Stateside Virgin Islands Americans ). American Samoa is a U.S. territory located in
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#17327753741835772-524: The Greek ὥρα —'hour', and λέγειν —'to tell') was used to describe early mechanical clocks, but the use of this word (still used in several Romance languages ) for all timekeepers conceals the true nature of the mechanisms. For example, there is a record that in 1176, Sens Cathedral in France installed an ' horologe ', but the mechanism used is unknown. According to Jocelyn de Brakelond , in 1198, during
5883-706: The Interior by the American military organizations of the time—the future states of Alaska and Hawaii , then each only organized incorporated territories of the Union, were respectively covered by the Eleventh Air Force and Seventh Air Force during the war. Residents of Alaska, Hawaii and off-shore U.S. territories have unique labels for the contiguous United States because of their own locations relative to them. The vast territory of Alaska became
5994-537: The Lion at one o'clock, etc., and at night a lamp becomes visible every hour, with 12 windows opening to show the time. The Tang dynasty Buddhist monk Yi Xing along with government official Liang Lingzan made the escapement in 723 (or 725) to the workings of a water-powered armillary sphere and clock drive , which was the world's first clockwork escapement. The Song dynasty polymath and genius Su Song (1020–1101) incorporated it into his monumental innovation of
6105-802: The US government adopted a standard time scheme it would be disadvantageous to its member railroads. William F. Allen, the Convention secretary, argued that North American railroads should adopt a five-zone standard, similar to the one in use today, to avoid government action. On October 11, 1883, the heads of the major railroads met in Chicago at the Grand Pacific Hotel and agreed to adopt Allen's proposed system. The members agreed that on Sunday, November 18, 1883, all United States and Canadian railroads would readjust their clocks and watches to reflect
6216-426: The astronomical clock tower of Kaifeng in 1088. His astronomical clock and rotating armillary sphere still relied on the use of either flowing water during the spring, summer, and autumn seasons or liquid mercury during the freezing temperatures of winter (i.e., hydraulics ). In Su Song's waterwheel linkwork device, the action of the escapement's arrest and release was achieved by gravity exerted periodically as
6327-573: The blind and for use over telephones, speaking clocks state the time audibly in words. There are also clocks for the blind that have displays that can be read by touch. The word clock derives from the medieval Latin word for 'bell'— clocca —and has cognates in many European languages. Clocks spread to England from the Low Countries , so the English word came from the Middle Low German and Middle Dutch Klocke . The word
6438-580: The clock's accuracy, so many different mechanisms were tried. Spring-driven clocks appeared during the 15th century, although they are often erroneously credited to Nuremberg watchmaker Peter Henlein (or Henle, or Hele) around 1511. The earliest existing spring driven clock is the chamber clock given to Phillip the Good, Duke of Burgundy, around 1430, now in the Germanisches Nationalmuseum . Spring power presented clockmakers with
6549-547: The clocks constructed by Richard of Wallingford in Albans by 1336, and by Giovanni de Dondi in Padua from 1348 to 1364. They no longer exist, but detailed descriptions of their design and construction survive, and modern reproductions have been made. They illustrate how quickly the theory of the mechanical clock had been translated into practical constructions, and also that one of the many impulses to their development had been
6660-565: The clocks readable to the nearest 15 minutes. Other clocks were exhibitions of craftsmanship and skill, incorporating astronomical indicators and musical movements. The cross-beat escapement was invented in 1584 by Jost Bürgi , who also developed the remontoire . Bürgi's clocks were a great improvement in accuracy as they were correct to within a minute a day. These clocks helped the 16th-century astronomer Tycho Brahe to observe astronomical events with much greater precision than before. The next development in accuracy occurred after 1656 with
6771-637: The concept. The first accurate atomic clock, a caesium standard based on a certain transition of the caesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK. Calibration of the caesium standard atomic clock was carried out by the use of the astronomical time scale ephemeris time (ET). As of 2013, the most stable atomic clocks are ytterbium clocks, which are stable to within less than two parts in 1 quintillion ( 2 × 10 ). The invention of
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#17327753741836882-404: The continental United States, and as the 48 contiguous states. The District of Columbia is not always specifically mentioned as being part of CONUS . OCONUS is derived from CONUS with O for outside added, thus referring to Outside of Continental United States. The term lower 48 is also used to refer to the conterminous United States. The National Geographic style guide recommends
6993-469: The continuous flow of liquid-filled containers of a limited size. In a single line of evolution, Su Song's clock therefore united the concepts of the clepsydra and the mechanical clock into one device run by mechanics and hydraulics. In his memorial, Su Song wrote about this concept: According to your servant's opinion there have been many systems and designs for astronomical instruments during past dynasties all differing from one another in minor respects. But
7104-471: The desire of astronomers to investigate celestial phenomena. The Astrarium of Giovanni Dondi dell'Orologio was a complex astronomical clock built between 1348 and 1364 in Padua , Italy, by the doctor and clock-maker Giovanni Dondi dell'Orologio . The Astrarium had seven faces and 107 moving gears; it showed the positions of the sun, the moon and the five planets then known, as well as religious feast days. The astrarium stood about 1 metre high, and consisted of
7215-399: The earlier armillary sphere created by Zhang Sixun (976 AD), who also employed the escapement mechanism and used liquid mercury instead of water in the waterwheel of his astronomical clock tower. The mechanical clockworks for Su Song's astronomical tower featured a great driving-wheel that was 11 feet in diameter, carrying 36 scoops, into each of which water was poured at a uniform rate from
7326-563: The earliest dates are less certain. Some authors, however, write about water clocks appearing as early as 4000 BC in these regions of the world. The Macedonian astronomer Andronicus of Cyrrhus supervised the construction of the Tower of the Winds in Athens in the 1st century BC, which housed a large clepsydra inside as well as multiple prominent sundials outside, allowing it to function as
7437-698: The east of the country, this was a few minutes earlier than in the west. After that, all parts of the country had the same local time—that of the Wester Tower in Amsterdam (Westertoren/4°53'01.95" E). This time was indicated as GMT +0h 19m 32.13s until 17 March 1937, after which it was simplified to GMT+0h20m. This time zone was also known as the Loenen time or Gorinchem time , as this was the exact time in both Loenen and Gorinchem . At noon in Amsterdam, it
7548-472: The energy it loses to friction , and converts its oscillations into a series of pulses. The pulses are then counted by some type of counter , and the number of counts is converted into convenient units, usually seconds, minutes, hours, etc. Finally some kind of indicator displays the result in human readable form. The timekeeping element in every modern clock is a harmonic oscillator , a physical object ( resonator ) that vibrates or oscillates repetitively at
7659-503: The entire Hawaiian Islands archipelago except for Midway Atoll , became the 50th state of the United States on August 21, 1959. It is the southernmost U.S. state, and the latest one to join the Union. Not part of any continent, Hawaii is located in the Pacific Ocean , about 2,200 miles (3,541 km) from North America and almost halfway between North America and Asia . In Hawaii and overseas American territories , for instance,
7770-421: The escapement had a great effect on the accuracy of the clock, and many escapement designs were tried. The higher Q of resonators in electronic clocks makes them relatively insensitive to the disturbing effects of the drive power, so the driving oscillator circuit is a much less critical component. This counts the pulses and adds them up to get traditional time units of seconds, minutes, hours, etc. It usually has
7881-459: The first carillon clock as it plays music simultaneously with a person blinking his eyes, surprised by the singing birds. The Archimedes clock works with a system of four weights, counterweights, and strings regulated by a system of floats in a water container with siphons that regulate the automatic continuation of the clock. The principles of this type of clock are described by the mathematician and physicist Hero, who says that some of them work with
7992-494: The first quartz crystal oscillator was built by Walter G. Cady in 1921. In 1927 the first quartz clock was built by Warren Marrison and J.W. Horton at Bell Telephone Laboratories in Canada. The following decades saw the development of quartz clocks as precision time measurement devices in laboratory settings—the bulky and delicate counting electronics, built with vacuum tubes at the time, limited their practical use elsewhere. The National Bureau of Standards (now NIST ) based
8103-404: The incense clock work on the same principle, wherein the consumption of resources is more or less constant, allowing reasonably precise and repeatable estimates of time passages. In the hourglass, fine sand pouring through a tiny hole at a constant rate indicates an arbitrary, predetermined passage of time. The resource is not consumed, but re-used. Water clocks, along with sundials, are possibly
8214-402: The invention of the pendulum clock by Christiaan Huygens . A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation. The mechanism of a timepiece with a series of gears driven by a spring or weights is referred to as clockwork ; the term is used by extension for a similar mechanism not used in a timepiece. The electric clock
8325-441: The invention of the pendulum clock . Galileo had the idea to use a swinging bob to regulate the motion of a time-telling device earlier in the 17th century. Christiaan Huygens , however, is usually credited as the inventor. He determined the mathematical formula that related pendulum length to time (about 99.4 cm or 39.1 inches for the one second movement) and had the first pendulum-driven clock made. The first model clock
8436-481: The last two states to be admitted to the Union ), and all other offshore insular areas , such as the U.S. territories of American Samoa , Guam , the Northern Mariana Islands , Puerto Rico , and the U.S. Virgin Islands . The colloquial term " Lower 48 " is also used, especially in relation to Alaska. The related but distinct term continental United States includes Alaska, which
8547-476: The liberation of the Netherlands in 1945, Summer time was abolished for over thirty years, so during those years, standard time was 40 minutes ahead of the original Amsterdam Time. As of 2017, the Netherlands is in line with Central European Time (GMT+1 in the winter, GMT+2 in the summer, which is significantly different from Amsterdam Time). In 1868, New Zealand was the first country in the world to establish
8658-596: The mainland, such as the Aleutian Islands ( Alaska ), San Juan Islands ( Washington ), the Channel Islands ( California ), the Keys ( Florida ), the barrier islands ( Gulf and East Coast states), and Long Island (New York). CONUS , a technical term used by the U.S. Department of Defense , General Services Administration , NOAA/National Weather Service , and others, has been defined both as
8769-404: The mechanical clock in the 13th century initiated a change in timekeeping methods from continuous processes, such as the motion of the gnomon 's shadow on a sundial or the flow of liquid in a water clock, to periodic oscillatory processes, such as the swing of a pendulum or the vibration of a quartz crystal , which had the potential for more accuracy. All modern clocks use oscillation. Although
8880-422: The mechanisms they use vary, all oscillating clocks, mechanical, electric, and atomic, work similarly and can be divided into analogous parts. They consist of an object that repeats the same motion over and over again, an oscillator , with a precisely constant time interval between each repetition, or 'beat'. Attached to the oscillator is a controller device, which sustains the oscillator's motion by replacing
8991-647: The meridians anchoring the Atlantic Time Zone and the Greenland Time Zone , voted in 1935 to create a half-hour offset time zone known as the Newfoundland Time Zone , at three and a half hours behind Greenwich time. In the Netherlands, introduction of the railways made it desirable to create a standard time. On 1 May 1909, Amsterdam Time or Dutch Time was introduced. Before that, time was measured in different cities; in
9102-456: The moon, Saturn, Jupiter, and Mars. Directly above the 24-hour dial is the dial of the Primum Mobile , so called because it reproduces the diurnal motion of the stars and the annual motion of the sun against the background of stars. Each of the 'planetary' dials used complex clockwork to produce reasonably accurate models of the planets' motion. These agreed reasonably well both with Ptolemaic theory and with observations. Wallingford's clock had
9213-497: The motions of all the known planets, an automatic calendar of fixed and movable feasts , and an eclipse prediction hand rotating once every 18 years. It is not known how accurate or reliable these clocks would have been. They were probably adjusted manually every day to compensate for errors caused by wear and imprecise manufacture. Water clocks are sometimes still used today, and can be examined in places such as ancient castles and museums. The Salisbury Cathedral clock , built in 1386,
9324-542: The new five-zone system on a telegraph signal from the Allegheny Observatory in Pittsburgh at exactly noon on the 90th meridian. Although most railroads adopted the new system as scheduled, some did so early on October 7 and others late on December 2. The Intercolonial Railway serving the Canadian maritime provinces of New Brunswick and Nova Scotia just east of Maine decided not to adopt Intercolonial Time based on
9435-482: The next thirty years before submitting it for examination. The clock had many innovations, including the use of bearings to reduce friction, weighted balances to compensate for the ship's pitch and roll in the sea and the use of two different metals to reduce the problem of expansion from heat. The chronometer was tested in 1761 by Harrison's son and by the end of 10 weeks the clock was in error by less than 5 seconds. The British had dominated watch manufacture for much of
9546-504: The norm was Columbus time, even on railroads such as the PFtW&;C and LS&MS , which did not run through Columbus. The Santa Fe Railroad used Jefferson City (Missouri) time all the way to its west end at Deming, New Mexico , as did the east–west lines across Texas; Central Pacific and Southern Pacific Railroads used San Francisco time all the way to El Paso . The Northern Pacific Railroad had seven time zones between St. Paul and
9657-501: The oldest time-measuring instruments, with the only exception being the day-counting tally stick . Given their great antiquity, where and when they first existed is not known and is perhaps unknowable. The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon and Egypt around the 16th century BC. Other regions of the world, including India and China, also have early evidence of water clocks, but
9768-421: The position of a shadow on a (usually) flat surface that has markings that correspond to the hours. Sundials can be horizontal, vertical, or in other orientations. Sundials were widely used in ancient times . With knowledge of latitude, a well-constructed sundial can measure local solar time with reasonable accuracy, within a minute or two. Sundials continued to be used to monitor the performance of clocks until
9879-539: The position of a shadow on a flat surface. There is a range of duration timers, a well-known example being the hourglass . Water clocks , along with sundials, are possibly the oldest time-measuring instruments. A major advance occurred with the invention of the verge escapement , which made possible the first mechanical clocks around 1300 in Europe, which kept time with oscillating timekeepers like balance wheels . Traditionally, in horology (the study of timekeeping),
9990-420: The principle of the use of water-power for the driving mechanism has always been the same. The heavens move without ceasing but so also does water flow (and fall). Thus if the water is made to pour with perfect evenness, then the comparison of the rotary movements (of the heavens and the machine) will show no discrepancy or contradiction; for the unresting follows the unceasing. Song was also strongly influenced by
10101-418: The prototype mechanical clocks that appeared during the 13th century in Europe. In Europe, between 1280 and 1320, there was an increase in the number of references to clocks and horologes in church records, and this probably indicates that a new type of clock mechanism had been devised. Existing clock mechanisms that used water power were being adapted to take their driving power from falling weights. This power
10212-698: The role of the Secretary of Commerce (effectively, the National Institute of Standards and Technology ) and the Secretary of the Navy (effectively, the U.S. Naval Observatory ) in interpreting standard time. In 1999, standard time was inducted into the North America Railway Hall of Fame in the category "National: Technical Innovations." The Dominion of Newfoundland , whose capital St. John's falls almost exactly midway between
10323-476: The spring or raise the weight of a mechanical clock would be classified as an electromechanical clock . This classification would also apply to clocks that employ an electrical impulse to propel the pendulum. In electromechanical clocks the electricity serves no time keeping function. These types of clocks were made as individual timepieces but more commonly used in synchronized time installations in schools, businesses, factories, railroads and government facilities as
10434-460: The term clock was used for a striking clock , while a clock that did not strike the hours audibly was called a timepiece . This distinction is not generally made any longer. Watches and other timepieces that can be carried on one's person are usually not referred to as clocks. Spring-driven clocks appeared during the 15th century. During the 15th and 16th centuries, clockmaking flourished. The next development in accuracy occurred after 1656 with
10545-683: The term is qualified with the explicit inclusion of Alaska to resolve any ambiguity. On May 14, 1959, the United States Board on Geographic Names issued the following definitions based partially on the reference in the Alaska Omnibus Bill, which defined the continental United States as "the 49 States on the North American Continent and the District of Columbia..." The Board reaffirmed these definitions on May 13, 1999. However, even before Alaska became
10656-648: The terms the Mainland or U.S. Mainland are often used to refer to the 49 states in North America. Puerto Rico is an unincorporated territory of the United States located in the northeast Caribbean Sea , approximately 1,000 miles (1,609 km) southeast of Miami , Florida . Puerto Ricans born in Puerto Rico are U.S. citizens and are free to move to the mainland United States. The term Stateside Puerto Rican refers to residents of any U.S. state or
10767-488: The time in various time systems, including Italian hours , canonical hours, and time as measured by astronomers at the time. Both styles of clocks started acquiring extravagant features, such as automata . In 1283, a large clock was installed at Dunstable Priory in Bedfordshire in southern England; its location above the rood screen suggests that it was not a water clock. In 1292, Canterbury Cathedral installed
10878-540: The time standard of the United States on quartz clocks from late 1929 until the 1960s, when it changed to atomic clocks. In 1969, Seiko produced the world's first quartz wristwatch , the Astron . Their inherent accuracy and low cost of production resulted in the subsequent proliferation of quartz clocks and watches. Currently, atomic clocks are the most accurate clocks in existence. They are considerably more accurate than quartz clocks as they can be accurate to within
10989-427: The timing of services and public events) and for modeling the solar system. The former purpose is administrative; the latter arises naturally given the scholarly interests in astronomy, science, and astrology and how these subjects integrated with the religious philosophy of the time. The astrolabe was used both by astronomers and astrologers, and it was natural to apply a clockwork drive to the rotating plate to produce
11100-411: The total area of the United States, including Alaska and Hawaii, ranks third or fourth. Brazil is 431,000 square kilometers (166,000 sq mi) larger than the contiguous United States, but smaller than the entire United States including Alaska, Hawaii and overseas territories. The 2020 U.S. census population of the area was 328,571,074, comprising 99.13 percent of the nation's total population, and
11211-587: The use of contiguous or conterminous United States instead of lower 48 when the 48 states are meant, unless used in the context of Alaska. Almost all of Hawaii is south of the southernmost point of the conterminous United States in Florida. During World War II , the first four numbered Air Forces of the United States Army Air Forces (USAAF) were said to be assigned to the Zone of
11322-599: Was 11:40 in London and 12:40 in Berlin . The shift to the current Central European Time zone took place on 16 May 1940. The German occupiers ordered the clock to be moved an hour and forty minutes forward. This time was kept in summer and winter throughout 1941 and 1942. It was only in November 1942 that a different Winter time was introduced, and the time was adjusted one hour backwards. This lasted for only three years; after
11433-432: Was also given the name railway time , reflecting the important role the railway companies played in bringing it about. The vast majority of Great Britain's public clocks were standardised to GMT by 1855. Until 1883, each United States railroad chose its own time standards. The Pennsylvania Railroad used the "Allegheny Time" system, an astronomical timekeeping service which had been developed by Samuel Pierpont Langley at
11544-512: Was being dictated by one government department, led to a resolution in parliament to establish a standard time for the whole country. The director of the Geological Survey, James Hector , selected New Zealand time to be at the meridian 172°30′E. This was very close to the country's mean longitude and exactly 11 + 1 ⁄ 2 hours in advance of Greenwich Mean Time. It came into effect on 2 November 1868. For over fifty years,
11655-470: Was built in 1657 in the Hague , but it was in England that the idea was taken up. The longcase clock (also known as the grandfather clock ) was created to house the pendulum and works by the English clockmaker William Clement in 1670 or 1671. It was also at this time that clock cases began to be made of wood and clock faces to use enamel as well as hand-painted ceramics. In 1670, William Clement created
11766-554: Was controlled by some form of oscillating mechanism, probably derived from existing bell-ringing or alarm devices. This controlled release of power – the escapement – marks the beginning of the true mechanical clock, which differed from the previously mentioned cogwheel clocks. The verge escapement mechanism appeared during the surge of true mechanical clock development, which did not need any kind of fluid power, like water or mercury, to work. These mechanical clocks were intended for two main purposes: for signalling and notification (e.g.,
11877-414: Was introduced during the 17th century and had distinct advantages over the 'countwheel' (or 'locking plate') mechanism. During the 20th century there was a common misconception that Edward Barlow invented rack and snail striking. In fact, his invention was connected with a repeating mechanism employing the rack and snail. The repeating clock , that chimes the number of hours (or even minutes) on demand
11988-446: Was invented by either Quare or Barlow in 1676. George Graham invented the deadbeat escapement for clocks in 1720. A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation. The position of a ship at sea could be determined with reasonable accuracy if a navigator could refer to a clock that lost or gained less than about 10 seconds per day. This clock could not contain
12099-425: Was not enacted into US law until the 1918 Standard Time Act established standard time in time zones; the law also instituted daylight saving time (DST). The daylight saving time portion of the law was repealed in 1919 over a presidential veto, but was re-established nationally during World War II. In 2007 the US enacted a federal law formalising the use of Coordinated Universal Time as the basis of standard time, and
12210-404: Was patented in 1840, and electronic clocks were introduced in the 20th century, becoming widespread with the development of small battery-powered semiconductor devices . The timekeeping element in every modern clock is a harmonic oscillator , a physical object ( resonator ) that vibrates or oscillates at a particular frequency. This object can be a pendulum , a balance wheel , a tuning fork ,
12321-420: Was transferred through the spread of trade. Pre-modern societies do not have the same precise timekeeping requirements that exist in modern industrial societies, where every hour of work or rest is monitored and work may start or finish at any time regardless of external conditions. Instead, water clocks in ancient societies were used mainly for astrological reasons. These early water clocks were calibrated with
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