History of the time measurement

Measure the natural time
The sundial
The gnomon: the word comes from the Greek knowledge. It is the ancestor of the sundial. This is a rod fixed in the ground vertically, the length of the shadow can locate the time the sun.
The sundial oldest we know is Egyptian and dates back to 1500 BC. This system is known in all cultures, but it is unclear.
The sundial: this is a flat surface which is planted in a rod called style. The direction of the shadow indicates the time in the sun. the dial is divided into twelve hours from sunrise to sunset, but as the day length varies seasonally, the duration of hours varies. Gradually the scale of the dial is perfect, but it is always imperfect due to the vertical orientation of the style. In the fourteenth century, the Arabs, tilting rod dial according to the latitude of the place make it a reliable instrument.The sundial gives the local time when the sun is not warped.
below cons: sundial on a house Var. 
The clepsydra or water clock
The word comes from the Greek klepsydria robber water because it served to limit the speaking time of counsel at trial. It is an instrument that measures time by the passage of a certain amount of water from one container to another. It is believed that it was invented by the Egyptians in the sixteenth century BC. It is unreliable because the rate of flow varies with the temperature and pressure of the water, and difficult to be graduated. Egyptians compensate this disadvantage by using containers flared. But it is the Greek physician, Ctesibius Alexandria, which greatly improves the water clock by a float system that regulates the flow into a container attached. Complex enhancements improve reliability, but it must be set on the sundial.
Gradually the two techniques sundial and clepsydra associated in astronomical water clock developed from Greek antiquity.
The hourglass
Inexpensive and quiet, it must be sealed so that the sand is not wet. Progress made ​​glassware manufacturing its possible. Commonly used in the fourteenth century, it measures the time when the sky is overcast and sundials can no longer serve. It is used on boats where it is used to define the service on four hours a quarter.

Clock Incense
In China, the time is measured by a smoldering incense stick burning wire, this wire is connected to a ball that falls into a metal container marking a period of time.below against clock incense - Texts and Documents  
for the Classroom ", No. 746, 15-31 December 1997

Measure an artificial time: mechanical clocks

below cons: Hebrew clock, 
with hands turning in opposite directions, 
the former City Hall of Prague's Jewish Quarter.
What's new?
Time is measured by the discontinuous movement of gears which power is supplied by a falling weight. The technical and theoretical problem is how to stabilize the speed of the wheels while the weight loss accelerates. A regulatory mechanism is needed is the exhaust . It is to block the weight and therefore the rotation of the wheels during a short time and at regular intervals by means of a pendulum or pendulum. Thus measured an artificial time which depends on the correction of the effects of gravity. This is a time that is not continuous like the flow of water or the apparent motion of the sun, it is a time divisible into successive units.
First clocks foliot
In 1370 appears the true mechanical clock including a piece called foliot helps regulate the energy supplied by a weight to a wheel. The movement is then transmitted to the wheels that drive the needles. Regulation is imperfect because the drift can reach an hour a day. The first clocks do not show the time. Connected to a bell, ringing the hour and they are primarily intended for monks whose days were cut strictly by the rule of St. Benedict in seven periods of prayer, the middle of the night when you ring the first prayer, matins , until the last two, vespers and compline, at the end of the day.

From the fourteenth century, the cities of Europe to adopt the clock towers and belfries. They are very accurate and should be set to daily or sundials clepsydes.

below cons: astronomical clock, Belfry of the City Hall's Stare Mesto (Prague), fifteenth century. 

left, zodiac signs, numerals and human, to the right calendar
Then, in, 1657, the invention of the first clock pendulum revolutionizes watchmaking
It is the result of the work of Christiaan Huygens (1629-1695), mathematician, physicist and astronomer Dutch, whose father was a friend of Descartes and who had knowledge of the work of Pascal and Pierre de Fermat. From the discoveries of Galileo (1564-1642) on the properties of the oscillations of the pendulum, he had the idea of replacing the foliot by a pendulum is the clockmaker Salomon Coster who made ​​the first pendulum clock from indications of Huygens. Almost all existing clocks were then processed for modification allowed lower errors 6 to 1. There is therefore little more clock foliot.
This improvement in the measurement of time she could apply to the watch?
The invention of the spring setting , so spring by the same Huygens, allows the realization of the first spiral watch by Isaac Thuret, master watchmaker, in 1675. precision of the watch is multiplied by 5.At the end of the seventeenth century is developed indicating the hours and minutes with two concentric needles that go around in 12 hours and one hour, respectively. The great London watchmaker Daniel Quare (1649-1724) created our dial, which is later modified by the addition of the second hand.

Watch and industrial revolution

Watchmakers have played a key role in the development of the first machines for the textile industry. Thus, in 1768, John Dray, English watchmaker, designs the flying shuttle with another watchmaker Richard Arkwright, and built the first spinning machine using gears, wheels, springs ... adapted watchmaking. 
Denis Papin student of Huygens develops a piston steam in 1707, but it is still necessary for many years to James Watt, with the help of the watchmaker Wilkinson makes the steam engine.
below against the station clock Toulouse.
Watchmakers have also played a decisive role in the birth of the great industry. Thus, in 1770, Frédéric Japy, produced 100,000 watches per year at its plant in Beaucourt, near Montbéliard, where 300 employees work from local artisans and farmers. It is one of the first capitalists have consciously sought to monetize the huge capital invested in producing a maximum number of objects per unit time. The division of labor in watchmaking is so ahead of the rest of the industry.

Today, the quartz watch puts everyone on time
Quartz watch, the principle is known since 1920, operates through two key elements:
The stack with very low consumption of the order of a millionth of 10 watt / hours , is the energy source that replaces the spring.
The quartz is used for its stable oscillations, accurate and reproducible. What electronics called quartz, this is not the crystalline silica or synthetic form, it is the component that is derived which define the dimensions and cut a specific frequency.
Technology quartz watch is based on the piezo-electric phenomenon specific to certain types of crystals, such as quartz. It appears on the surface of the body when subjected to pressure or electrical charges. This provides electrical or mechanical vibrations stable. These properties have been demonstrated in Paris in 1880 by Pierre and Jacques Curie.

And we're all at the same time ...

In France, the law of 14 March 1891, the time fixed by law, which is the average time in Paris. 
international level, it is the law of 9 March 1911 which establishes the universal time (UT).
This decision was preceded by lengthy discussions on the choice of origin-meridian. In 1883, at the Rome Conference, the Greenwich meridian is adopted because it is the meridian which passes through the opposite side of the minimum land surface, which prevents a state cut in half for the date change. In addition, most sailors use English cards with Greenwich as the origin.
below against the clock tower of the Capitol in Toulouse.
... a few microseconds!
All years were not exactly the same length because the different movements of the earth rotation and revolution are not regular. They are disturbed by the presence of the moon and planets which generates large complex movements of the earth's axis called precession and nutation, which substantially alter the duration of the year a few microseconds. These variations interested scientists. Where was the development of International Atomic Time, TAI, whose use is mandatory for all date scientific events. The second is set in 1967, the General Conference of Weights and Measures, as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium atom 133" .

It is the Bureau International de l'Heure, located in the Paris observatory, which gives the time from TAI 230 best atomic clocks around the world. An atomic clock is a clock that cesium is a timepiece accurate to 10 ¯10 [10 ^ 10]. In 1958, by agreement, was to coincide TAI and UTC modified slightly, and then created the Coordinated Universal Time, a compromise between TAI and UTC modified. Thus, the planet moves to the rhythm of a time more homogeneous and more accurate.

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