The hourglass timer

The hourglass and a device for time measuring the passage of time based on a steady stream of water in output from a container.

The name derives from the greek κλεψύδρα (Klepsydra), which literally means "water-stealing."

In Italian the generic term is also used to indicate the devices consisting of two glass bulbs connected through a narrow hole, inside which is placed very fine sand, more correctly called clepsamie.

Hydraulic clock of the Pincio in Rome

Because the flow of water is not easily controllable and dependent on several variables, this watch is neither very exact nor very accurate. However, it was the first instrument for measuring time independent of astronomical observations. One of the oldest specimens was found in the tomb of Pharaoh Amenhotep I, dating from the fifteenth century BC

In Greece, the use of the hourglass was introduced in 325 BC, in the form of containers in stone truncated cone shape that made water come out from a hole on the bottom, at a steady pace.
Other hourglasses had a cylindrical shape or cup and venivLOLLLano slowly filled by a constant flow of water. Some signs on the inner surface of the container indicating the passing of time to rise the level of the liquid.
Another version was made up of a metal container drilled on the bottom that, place to float in a larger container, sank in a certain time. This system remained in use until the twentieth century in North Africa. These watches were generally used during the night, but not during the day, when they were available the most accurate sundials.

In the first half of the third century BC Ctesibus turned the hourglass in more complex water clock. He and others were introduced various mechanisms to increase the accuracy of adjusting the pressure and keeping the flow of water, but also to provide a better display. The specimens could play more advanced bells or gongs, open windows to display images, or had mobile indicators, dials or representations of celestial bodies. Among the designers of online stopwatches of this type there were Archimedes and Heron of Alexandria.

The Macedonian astronomer Andronicus of Cirrus, was responsible for the construction dell'Horologion, now known as the Tower of the Winds in Athens market in the first half of the first century BC It is an octagonal tower with representations of students and people at the market, and carries a sundial that is an indication of mechanical timer.


Contains a mechanism hourglass able to show all the 24 hours, the season of the year and astrological dates and periods. It also indicates the main direction of the wind, hence the current name.
Reconstruction from original fragments, an hourglass to Greek Stoa of Attalos, the Museum of the Ancient Agora of Athens

Water clocks were also used in the imperial era.

In the Far East were made mechanical watches astronomical between 200 and 1300. One of the most elaborate is the ten meter high clock tower probably built by Su Song (苏颂) in 1088.
The mechanism incorporates a water escapement invented in 725 and has an armillary sphere move automatically, a celestial globe, and five panels that open showing characters who play gong show and tablets on which it is given the time and other special times of the day. The hourglass at that time was important.