1.2 Navigation

Accurate navigationThis article concerns navigation in the sense of determination of position and direction on the surface of the Earth. See Navigation (disambiguation) for other meanings. There are several traditions of navigation . Polynesian navigation The Polynesian nav by ships beyond the sight of land depends on the ability to measure latitudeLatitude denoted φ, gives the location of a place on Earth north or south of the Equator. Latitude is an angular measurement ranging from 0° at the Equator to 90° at the poles. Usually, the difference in latitude largely affects the climate and/or wea and longitudeMap of Earth showing vertical lines of longitude Longitude sometimes denoted λ, describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. Longitude is given as an angular measurement ranging from 0° at. Latitude is fairly easy to determine through celestial navigationCelestial navigation is a position fixing technique that was the first system devised to help sailors locate themselves on a featureless ocean. Celestial navigation uses angular measurements (sights) between the horizon and a common celestial object., but the measurement of longitude requires accurate measurement of time. This need was a major motivation for the development of accurate mechanical clocks. John Harrison created the first, highly accurate marine chronometers in the mid-18th century. The Noon gun in Cape Town still fires an accurate signal to allow ships to check their chronometers.

2 Displays

A clock face is the part of an analog clock that tells time through the use of a fixed numbered dial or dials and moving hand or hands. It usually has a circular scale of 12 hours, which also serves as a scale of 60 minutes, and often also as a scale of 60 seconds. A digital clock expresses a numerical hour range of 1-12 (or 0-23), with an indication am/pm.

3 History

The history of the time telling device can be traced to Antiquity. Vitruvius reports that the ancient Egyptians used clepsydras, a time mechanism run by flowing water. By the 9th century AD a mechanical timekeeper had been developed that lacked only an escapement mechanism. There is a record that in 1176 Sens Cathedral installed a “horologe” – the word still used in French for large clocks. It is derived from the Greek hora meaning hour and legein meaning to tell. This word has led scholars to believe that these earliest timekeepers did not employ hands or dials, but “told” the time with audible signals.

The earliest reasonably accurate clocks are the 13th century tower clocks probably developed for (and perhaps by) monks in Northern Italy. These were used to announce the canonical hours or intervals between set times of prayer. Canonical hours differ in length, and varied as the times of sunrise and sunset shifted.

The earliest clocks that survive in any quantity are mid- 16th century table clocks from the metalworking towns of Nuremberg and Augsburg. These clocks have only one hand. The dial between the hour markers is divided into four equal parts making the clocks accurate only to within 15 minutes.

The next major development in accuracy occurred in 1657 with the invention of the pendulum clock. Galileo had the idea to use a swinging bob to propel 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 (99.38 cm/39 in. for the one second movement) and had the first pendulum driven clock executed. In 1670, the English clockmaker William Clement created the anchor escapement, an improvement over Huygens' crown escapement .

The excitement over the pendulum clock attracted the attention of artisans and designers resulting in a proliferation of clock forms. Notably, the longcase clock (aka grandfather clock) was created to house the pendulum and works. The English clockmaker William Clement , inventor of the anchor escapement, is credited developing this form in 1670. It was also at this time that clock cases began to be made of wood and clock faces to employ enamel.

Modern clocks define constant units of time: an hour is always sixty minutes, of sixty seconds each.

4 Notable clocks

a clock in the Salisbury Cathedral, reportedly the oldest working clock in the world

• Tower Clock (see Big Ben, its largest bell) at the Palace of Westminster, London
• Prague Orloj, a 15th century astronomical clock at the Town Hall, Prague, Czech Republic
• Peace Tower clock at the Centre Block of the Parliament of Canada, Ottawa
• 10,000-year Clock of the Long Now
• Harrison H4, John Harrison clock that won the Longitude prize
• Doomsday clock shows the symbolic minutes to midnight where midnight represents destruction by nuclear war (not a clock in the traditional sense)
• The Allen-Bradley Clock , the world's largest four sided clock, located in Wisconsin.

Probably the most comprehensive online resource guide on clocks can be found at http://www.clock-finder.com which links to many thousands of clock related sites.

5 Types of clock

• alarm clock
• analog clock with digital display
• astronomical clock
• atomic clock
• binary clock
• bracket clock
• cartel clock
• chronometer
• doll's head clock
• Railroad chronometers
• countdown clock
• cuckoo clock
• game clock
• grandfather clock
• hourglass
• longcase clock
• mantel clock
• pedestal clock
• swinging pendulum clock
• torsion pendulum clock
• projection clock
• quartz clock
• religieuse clock
• radio clock
• skeleton clock
• stopwatch
• sundial
• time clock
• timer
• watch
• water clock
• watchclock

6 See also

• Allan variance
• biological clocks
• clock face
• Clock signal (digital circuits)
• clock tower
• Horology
• Metrology
• Timeline of time measurement technology
• Time standard

7 External Links

• 24 hour analog clocks

8 Miscellaneous

The British band Coldplay also has a popular song called "Clocks".

9 References

• Bruton, Eric. The History of Clocks and Watches. London: Black Cat, 1993.

• Edey, Winthrop. French Clocks. New York: Walker & Co., 1967.

• Lloyd, Alan H. “Mechanical Timekeepers.” In A History of Technology. Vol. III. Edited by Charles Joseph Singer, et. al. Oxford: Clarendon Press, 1957, pp. 648-675.

• Robinson, Tom. The Longcase Clock. Suffolk, England: Antique Collector’s Club, 1981.

• Smith, Alan. The International Dictionary of Clocks. London: Chancellor Press, 1996.

• Tardy. French Clocks the World Over. Part One and Two. Translated with the assistance of Alexander Ballantyne. Paris: Tardy, 1981.

• Yoder, Joella Gerstmeyer. Unrolling Time: Christiaan Huygens and the mathematization of nature. New York: Cambridge University Press, 1988.

Clocks

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