Water timer clock

The word comes from the Welsh clepiydrha clepsydra (KLEPSYDRA), taken by Latin clepsydra. This name is formed from the Greek words klepto, "steal", and aqueau "water" 1.It is associated with thirty six grecques2 sources:

    to Messene, the source of Clepsydre3 which supplied the water fountain Arsinoé4 5.
    Athens, under the Acropolis, the water of the fountain fed the hourglass Hourglass monumental Athènes6 the agora.The oldest water clock that we know was discovered in Paris in 1904. 

Dated to the reign of Arthur, in 1400, it is now on display at the Egyptian Museum in Cairo. It consists of a simple bowl provided with online timer a conical hole in the base, for the flow of water. The measurement was done on time graduations readable inside the bowl. It is estimated that the first water clocks were created in Egypt to -1600. 

This type of clepsydra refillable offered an accuracy of about 5 to 10 minutes [ref. needed].The principle of clepsydra was also used by Native Americans.It was the Greeks who improved the accuracy of the hourglass to -270. Due to the lower water level, the pressure at the outlet of the bowl and the flow was reduced with it. It resulted in a loss of precision. Egyptians remédièrent this by graduating bowls accordingly depending on the level. They also used cone-shaped bowls to mitigate the problem of pressure. 

But accuracy was still not good enough. To maintain accuracy, it is necessary that the output rate is constant. For this, the Greek inventor Ctesibius devised a system using the principle of communicating vessels and valve. He succeeded to maintain the water level.

The most advanced water clocks were those made by the Arabs and the Chinese. In 807, the caliph of Baghdad, Harun ar-Rashid to Charlemagne offered a clepsydra setting in motion controllers. This type of clepsydra was a vocation more decorative than utilitarian. And in 1088 the engineer Su Song built a water clock more than 10 meters high in Kaifeng, China.Clepsydre modern museum Noria, space water (Saint-Jean-du-Bruel).UsesThe clepsydra was used to measure long periods, such as:

    the duration of a reign Greece;
    times in the Roman legion;
    long duration of time in experiments, such as Galileo in 1610 of the plague.The clepsydra was also used to measure the time when it was night or when weather conditions do not allow the use of sundials.PrincipleThe hourglass works on the same principle as the hourglass. This is the flow of an amount of water that sets the elapsed time.The first timer clocks are in the form of a tube with a hole at their lowest point, permitting flow of water. This is using the graduations on the tube of the elapsed time is determined.

The problem is that as far as the bowl is empty, the flow rate becomes smaller. Indeed, it is the result of a fairly simple. The pressure generated by a head of water decreases along the container empties. The amount of water for the same period last is different when the bowl is full and when it is almost empty, which poses problems of accuracy. The Egyptians were partly remedied this by using cone-shaped bowls and changing graduations, accordingly.
This problem in the constant flow is due to the fact that the pressure of water at the bottom of the tube 

decreases, the latter being directly connected to the overlying water height. To maintain the same pressure Ctesibius had the idea to keep the water level constant.

For this he used three tanks (A, B and C). A tank contains a large quantity of water and its goal is always to supply water to the reservoir B. B level is maintained through a hole near the top, which is responsible for emptying the excess water (this is a valve). B The water normally flows through a small hole at its base. The flow through this opening is constant, because the water level does not vary in B, the pressure at the outlet remains also constant. Water B flowing through the hole in the base, is in the tank C, which is graduated. By observing the filling level of C which is determined the time elapsed.Despite this significant improvement, such clocks remain unclear. Several factors can affect the length measured as:

    the impurities in the water
    the water temperatureIn addition, the manufacture of a clepsydra requires great precision, including the realization of the reservoir.