Sundial were simple and reliable indicator of the time, but suffered from some serious drawbacks: their work is dependent on the weather and was restricted to the time between sunrise and sunset. There is no doubt that because of this, scientists began to explore other ways to measure time, not related to the observation of celestial bodies. Also, it is understandable that the new instruments of measurement of time must have been fundamentally different from the sundial.

The unit of time for the sun clock output from the rotation of the Earth and its motion around the Sun, for the star – from the apparent motion of stars. New hronometricheskie apparatus (liquid, sand, air, fire, etc.) have an artificial standard unit of time in the form of the interval required for the outflow, inflow, or burning a certain amount of substance. Like a solar clock, this group is the simplest clock has come a long way of development, with the discovery of interesting action principles and structural elements. Indeed, the measurement of time using the clock «inflow» or «profluvium» was quite difficult: they must have had a lot of scales, or special devices for the management of revenue, or the expiry of the water. Some, such as gears, rollers, chain pendants, and weights, were used in the subsequent era of timekeeping – the era of mechanical watches. Water taken hours after the sun second largest number and most important in this group of elementary hours.

The literature often refers to them as «klepsidrah». This name comes from combining two Greek words klepto – and take idor – water. Many people, judging by the Greek name, mistakenly believe that it is in Greece, they were coined. But this is not the case: in the primitive form of water clocks were already known to the Egyptians, who preserved in all likelihood, the oldest water clock in the world. They were discovered in 1940 in the temple of Amon in the Eastern Febah, and now kept in a museum in Cairo. The inner surface of alabaster shell nakolkami designated 12-hour scale for measuring time in the respective months. Remember that a solar clock give me a different length of hours in different months? This was reflected in the Egyptian water clock. The vessel is filled to the brim with water, which then escape through a small hole bottom. But there is a riddle. The point is that the most significant problem in creating such a clock – practice this form of the receptacle, which would lapse with the uniform lowering of water levels. These Egyptian clock already provide quite a uniform lower level, albeit with some errors. This suggests that they are indeed ancient, but still not the first.

In ancient Greece, water clocks used to regulate the time to be allowed during the trials. Those hours were, in fact, large amphoras, the internal surface of which had the shape formed by rotating a parabola or ellipsoid. Amphora height of about 1 m and a width of slightly more than 40 cm contains approximately 100 liters of water. When the diameter of the end of 1.4 mm was required almost 10 hours to complete emptying of the receptacle. The water was attached to a float with a long rod, above the edge of the receptacle. At the rod was engraved scale. Since the beginning of the end of the water, indicated at this scale. Float fallen in Amphora evenly, since the slowing down of the end offset by decreasing the internal diameter of the vessel.

What klepsidra not dependent on the light of the sun, made of a water clock device, suitable for continuous measurement of time of day and night. Besides, is it possible to develop some mechanical elements. The competition designers witty in the invention of hydraulic and pneumatic mechanisms: to sound the alarm about the time for the light hours of the night, such elements can be found in a variety of water hours of Arabic origin. In the hands of imaginative works of prominent artists have emerged, distinguished by high artistic value and unique features.

Truly a legendary figure among the masters for the production of is considered a well-known Greek engineer Ktesiby Alexandria, who lived about 150 BC Roman Vitruvy even called him the inventor of the water clock.